• In this strategy hollow glass microspheres (HGMs) made of silicon dioxide would be spread across surfaces to increase albedo. HGMs are commercially made and range in size from 10-200 μm (Farkas et al. 2023). They are manufactured for incorporation in polymers for density reduction as well as for thermal insulation and other properties (see 3M website). There are multiple kinds of HGMs that vary in size, density, and other properties. The HGMs that have received the most attention are the K1 and P5P45 microspheres. Proposed delivery of HGMs is via aircraft (drones or other) or ships with blowers (Field et al. 2018). Arctic Ice Project (formerly Ice911 Research) is the primary organization working on this approach in the Arctic.

• Expected physical changes (global)
  • Likely none
• Expected physical changes (Arctic region)
  • Increase surface albedo of sea ice surfaces, decrease heat absorption (dependent on absorption properties of HGMs), decrease temperature, delay sea ice melt

• Variable
  • Originally proposed for sea ice area in Arctic Ocean.
  • Recent modeling work (Ivanova et al. in prep.) examines the Beaufort Gyre region – 15% of the Arctic Ocean area.

• Sea ice surface

• Defined areas of the Arctic Ocean where efficacy is predicted
  • Some studies modeled application to all sea ice area in the Arctic Ocean. A recent study, Ivanov et al. (in preparation) looked at application covering 1,500,000 km² in the Beaufort Gyre region (approximately 11% of the Arctic Ocean).

• Summer, but deployed in early Spring
  • Webster and Warren 2022 state maximum benefit achieved by distribution during the month of May (if non-absorbing HGMs developed).
  • Johnson et al. (2022) provides experimental evidence that HGM application prior to ice melt results in extended ice preservation beyond control ice, suggesting that HGM application in early spring should be most effective in preserving ice into summer months.

• In this strategy hollow glass microspheres (HGMs) made of silicon dioxide would be spread across surfaces to increase albedo. HGMs are commercially made and range in size from 10-200 μm (Farkas et al. 2023). They are manufactured for incorporation in polymers for density reduction as well as for thermal insulation and other properties (see 3M website). There are multiple kinds of HGMs that vary in size, density, and other properties. The HGMs that have received the most attention are the K1 and P5P45 microspheres. Proposed delivery of HGMs is via aircraft (drones or other) or ships with blowers (Field et al. 2018). Arctic Ice Project (formerly Ice911 Research) is the primary organization working on this approach in the Arctic.

• Expected physical changes (global)
  • Likely none
• Expected physical changes (Arctic region)
  • Increase surface albedo of sea ice surfaces, decrease heat absorption (dependent on absorption properties of HGMs), decrease temperature, delay sea ice melt

• Variable
  • Originally proposed for sea ice area in Arctic Ocean.
  • Recent modeling work (Ivanova et al. in prep.) examines the Beaufort Gyre region – 15% of the Arctic Ocean area.

• Sea ice surface

• Defined areas of the Arctic Ocean where efficacy is predicted
  • Some studies modeled application to all sea ice area in the Arctic Ocean. A recent study, Ivanov et al. (in preparation) looked at application covering 1,500,000 km² in the Beaufort Gyre region (approximately 11% of the Arctic Ocean).

• Summer, but deployed in early Spring
  • Webster and Warren 2022 state maximum benefit achieved by distribution during the month of May (if non-absorbing HGMs developed).
  • Johnson et al. (2022) provides experimental evidence that HGM application prior to ice melt results in extended ice preservation beyond control ice, suggesting that HGM application in early spring should be most effective in preserving ice into summer months.

• In this strategy hollow glass microspheres (HGMs) made of silicon dioxide would be spread across surfaces to increase albedo. HGMs are commercially made and range in size from 10-200 μm (Farkas et al. 2023). They are manufactured for incorporation in polymers for density reduction as well as for thermal insulation and other properties (see 3M website). There are multiple kinds of HGMs that vary in size, density, and other properties. The HGMs that have received the most attention are the K1 and P5P45 microspheres. Proposed delivery of HGMs is via aircraft (drones or other) or ships with blowers (Field et al. 2018). Arctic Ice Project (formerly Ice911 Research) is the primary organization working on this approach in the Arctic.

• Expected physical changes (global)
  • Likely none
• Expected physical changes (Arctic region)
  • Increase surface albedo of sea ice surfaces, decrease heat absorption (dependent on absorption properties of HGMs), decrease temperature, delay sea ice melt

• Variable
  • Originally proposed for sea ice area in Arctic Ocean
  • Recent modeling work (Ivanova et al. in prep.) examines the Beaufort Gyre region – 15% of the Arctic Ocean area.

• Sea ice surface

• Defined areas of the Arctic Ocean where efficacy is predicted
  • Some studies modeled application to all sea ice area in the Arctic Ocean. A recent study, Ivanov et al. (in preparation) looked at application covering 1,500,000 km² in the Beaufort Gyre region (approximately 11% of the Arctic Ocean).

• Summer, but deployed in early Spring
  • Webster and Warren 2022 state maximum benefit achieved by distribution during the month of May (if non-absorbing HGMs developed)
  • Johnson et al. (2022) provides experimental evidence that HGM application prior to ice melt results in extended ice preservation beyond control ice, suggesting that HGM application in early spring should be most effective in preserving ice into summer months.

• In this strategy hollow glass microspheres (HGMs) made of silicon dioxide would be spread across surfaces to increase albedo. HGMs are commercially made and range in size from 10-200 μm (Farkas et al. 2023). They are manufactured for incorporation in polymers for density reduction as well as for thermal insulation and other properties (see 3M website). There are multiple kinds of HGMs that vary in size, density, and other properties. The HGMs that have received the most attention are the K1 and P5P45 microspheres. Proposed delivery of HGMs is via aircraft (drones or other) or ships with blowers (Field et al. 2018). Arctic Ice Project (formerly Ice911 Research) is the primary organization working on this approach in the Arctic.

• Expected physical changes (global)
  • Likely none
• Expected physical changes (Arctic region)
  • Increase surface albedo of sea ice surfaces, decrease heat absorption (dependent on absorption properties of HGMs), decrease temperature, delay sea ice melt

• Variable
  • Originally proposed for sea ice area in Arctic Ocean
  • Recent modeling work (Ivanova et al. in prep.) examines the Beaufort Gyre region – 15% of the Arctic Ocean area.

• Sea ice surface

• Defined areas of the Arctic Ocean where efficacy is predicted
  • Some studies modeled application to all sea ice area in the Arctic Ocean. A recent study, Ivanov et al. (in preparation) looked at application covering 1,500,000 km² in the Beaufort Gyre region (approximately 11% of the Arctic Ocean).

• Summer, but deployed in early Spring
  • Webster and Warren 2022 state maximum benefit achieved by distribution during the month of May (if non-absorbing HGMs developed)
  • Johnson et al. (2022) provides experimental evidence that HGM application prior to ice melt results in extended ice preservation beyond control ice, suggesting that HGM application in early spring should be most effective in preserving ice into summer months.

• In this strategy hollow glass microspheres (HGMs) made of silicon dioxide would be spread across surfaces to increase albedo. HGMs are commercially made and range in size from 10-200 μm (Farkas et al. 2023). They are manufactured for incorporation in polymers for density reduction as well as for thermal insulation and other properties (see 3M website). There are multiple kinds of HGMs that vary in size, density, and other properties. The HGMs that have received the most attention are the K1 and P5P45 microspheres. Proposed delivery of HGMs is via aircraft (drones or other) or ships with blowers (Field et al. 2018). Arctic Ice Project (formerly Ice911 Research) is the primary organization working on this approach in the Arctic.

• Expected physical changes (global)
  • Likely none
• Expected physical changes (Arctic region)
  • Increase surface albedo of sea ice surfaces, decrease heat absorption (dependent on absorption properties of HGMs), decrease temperature, delay sea ice melt

• Variable
  • Originally proposed for sea ice area in Arctic Ocean
  • Recent modeling work (Ivanova et al. in prep.) examines the Beaufort Gyre region – 15% of the Arctic Ocean area.

• Sea ice surface

• Defined areas of the Arctic Ocean where efficacy is predicted
  • Some studies modeled application to all sea ice area in the Arctic Ocean. A recent study, Ivanov et al. (in preparation) looked at application covering 1,500,000 km² in the Beaufort Gyre region (approximately 11% of the Arctic Ocean).

• Summer, but deployed in early Spring
  • Webster and Warren 2022 state maximum benefit achieved by distribution during the month of May (if non-absorbing HGMs developed)
  • Johnson et al. (2022) provides experimental evidence that HGM application prior to ice melt results in extended ice preservation beyond control ice, suggesting that HGM application in early spring should be most effective in preserving ice into summer months.

• In this strategy hollow glass microspheres (HGMs) made of silicon dioxide would be spread across surfaces to increase albedo. HGMs are commercially made and range in size from 10-200 μm (Farkas et al. 2023). They are manufactured for incorporation in polymers for density reduction as well as for thermal insulation and other properties (see 3M website). There are multiple kinds of HGMs that vary in size, density, and other properties. The HGMs that have received the most attention are the K1 and P5P45 microspheres. Proposed delivery of HGMs is via aircraft (drones or other) or ships with blowers (Field et al. 2018). Arctic Ice Project (formerly Ice911 Research) is the primary organization working on this approach in the Arctic.

• Expected physical changes (global)
  • Likely none
• Expected physical changes (Arctic region)
  • Increase surface albedo of sea ice surfaces, decrease heat absorption (dependent on absorption properties of HGMs), decrease temperature, delay sea ice melt

• Variable
  • Originally proposed for sea ice area in Arctic Ocean
  • Recent modeling work (Ivanova et al. in prep.) examines the Beaufort Gyre region – 15% of the Arctic Ocean area.

• Sea ice surface

• Defined areas of the Arctic Ocean where efficacy is predicted
  • Some studies modeled application to all sea ice area in the Arctic Ocean. A recent study, Ivanov et al. (in preparation) looked at application covering 1,500,000 km² in the Beaufort Gyre region (approximately 11% of the Arctic Ocean).

• Summer, but deployed in early Spring
  • Webster and Warren 2022 state maximum benefit achieved by distribution during the month of May (if non-absorbing HGMs developed)
  • Johnson et al. (2022) provides experimental evidence that HGM application prior to ice melt results in extended ice preservation beyond control ice, suggesting that HGM application in early spring should be most effective in preserving ice into summer months.

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al. in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023).
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models.
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023).
• Arctic region
  • Disagreement amongst studies; decrease of 3 W/m² to increase of 3.5 W/m² annually, depending on sea ice surface and HGM properties.
    • Modeling study said maximum benefit achieved is decrease of 3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023).

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Largest deployment for research study to date was 0.00418 km² (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT (for non-absorbing HGMs, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT (for non-absorbing HGMs, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown

• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1-5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al. in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models.
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023).
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties.
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023).

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Largest deployment for research study to date was 0.00418km² (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown

• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1-5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Largest deployment for research study to date was 0.00418km² (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown

• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1-5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Largest deployment for research study to date was 0.00418km² (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown

• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1-5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Largest deployment for research study to date was 0.00418km² (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown

• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1 -5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Largest deployment for research study to date was 0.00418km² (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown

• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1 -5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Largest deployment to date was 4,180m² (Field et al. 2018)
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT¹ (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT¹ (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown
• Timeline to Arctic region impact (has to be within 20 yr)
• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1 -5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

Impact on

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

Scalability

• Unknown
  • Largest deployment to date was 4,180m² (Field et al. 2018)
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT¹ (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT¹ (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown
• Timeline to Arctic region impact (has to be within 20 yr)
• Large field tests estimated to be 4-5 years away.

Cost

• Estimated total cost $1 -5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

• Increases of 0.2 across field studies; modeling studies report decreased or increased albedo depending on albedo of initial surface and properties of HGMs.
  • Small-scale field study in Minnesota showed increase in albedo from 0.17 to 0.36 (Johnson et al. 2022).
  • Previous study at same site reported increase in albedo around 0.2 between site treated with HGMs and untreated (size of area 2,807m²; Field et al. 2018).
  • Limits on albedo impact will depend on the albedo of the HGMs and that of the sea ice surface.
    • Some of the studies report different properties of the same microsphere used in the studies (e.g., different albedo values of the K1 microsphere) or used different microspheres (K1 vs 25P45).
    • Field et al. 2018 reported results based on use of the K1 microsphere and reported its albedo as 0.45 (Field et al. 2018). Webster and Warren (2022) report that the K1 microsphere has absorbance of 10% and therefore would darken any surfaces with albedo >0.61 (Webster and Warren 2022), such as sea ice covered in snow that is prevalent during spring. Sea ice covered in snow has an albedo of around 0.85 (Perovich and Polashenski 2012). Albedo decreases below 0.61 after snow melt creates melt ponds (Perovich and Polashenski 2012).
    • Strawa et al. (in preparation) provide more recent data reporting absorbance of the K1 microsphere of 1%, leading to different conclusions than Webster and Warren (2022).
    • A study of a different microsphere, 25P45, reports albedo up to 0.92 (Springstein et al., in preparation).
• The largest benefit for HGMs may potentially be on melt ponds, which have a lower albedo than ice or snow-covered ice, but here wind will cause HGMs to accumulate along the edge of melt ponds.

• Global
  • Variable predictions
    • Review of interventions reported this approach unlikely to have an effect (Duffey et al. 2023)
    • Recent unpublished modeling study found some potential for global cooling that simulated annual application of HGMs in the Beaufort Gyre in an area covering 1,500,000 km² (Ivanova et al. in preparation).
• Arctic region
  • 0-3.0°C temperature reduction estimated in models
    • Recent unpublished modeling study reports decreases in Arctic mean temperatures up to 3°C with application in the Beaufort Gyre covering 1,500,000 km² (11% of the Arctic Ocean area; Ivanova et al. in preparation).
    • Previous modelling study reported 1.5°C temperature reduction in the Arctic region with up to 3°C in some areas (Barents and Kara Seas; Field et al 2018). However, Webster and Warren (2022) point out that the model in Field et al. 2018 is based on a uniform increase of sea ice albedo, which is unrealistic given the difference in ice types, assumptions about the HGM properties, and response to HGM coverage and could result in warming in some areas.

• Global
  • Unlikely to have effect (Duffey et al. 2023)
• Arctic region
  • Disagreement amongst studies; -3 W/m² to +3.5 W/m² annually, depending on sea ice surface and HGM properties
    • Modeling study said maximum benefit achieved -3 W/m² with 360 megatons spread annually over all sea ice in May (but only if HGMs are non-absorbent; Webster and Warren 2022). With K1 microspheres and considering sea surface albedos, HGMs could lead to warming with an annual average of 3.3-3.5 W/m² (Webster and Warren 2022). This study may need to be repeated with updated values of HGM albedo.
    • Field study in pond in Minnesota reported 29% reduction in net radiative energy where microspheres were applied (Johnson et al. 2022).
    • Order of magnitude too small to stop loss of Arctic sea ice under high emissions (Tilmes et al. 2014 in Duffey et al. 2023)

• Direct or indirect impact on sea ice?
  • Applied directly on sea ice surfaces to slow melt
• New or old ice?
  • Existing ice
    • Most effective on new (young) ice, and less effective on old ice (S. Zornetzer pers. comm.). New and multiyear ice have similar albedo when covered with snow, but as the snow melts, multiyear ice has higher albedo than new ice and also forms fewer melt ponds than younger, seasonal ice (Perovich and Polashenski 2012).
• Impact on sea ice
  • Varies depending on properties of microspheres and sea ice; some studies report increased sea ice thickness and reduced melt, while increased melt also possible
    • Field study in pond in Minnesota reported 33% reduction in ice melt in area where microspheres were applied (Johnson et al. 2022).
    • Recent modeling work by Ivanova et al. (in prep.) shows multi-year HGM intervention in the Beaufort Gyre region (15% of the Arctic Ocean area) yields a 56% increase in sea ice area and a 91% increase in sea ice volume for the Arctic Ocean, compared to the reference case without a treatment. This study also reports increased thickness over one meter that persists into late summer (Ivanova et al. in prep.).
    • Modeling study considering the absorbance properties of microspheres and the time-varying properties of Arctic surfaces not accounted for in earlier studies reports increased sea ice melt (Webster and Warren et al. 2022).

• Unknown
  • Largest deployment to date was 4,180m² (Field et al. 2018)
  • Deployment of 25,000 km² recommended in Field et al. 2018, which would require 300,000 t of microspheres (Field et al. 2018).
  • Spatial scalability will depend on further testing of the properties, toxicity, and fate of HGMs, development of methods for deployment, and increased manufacturing and shipping of HGMs.

• Unknown
  • Global annual radiative forcing efficiency -0.18 W/m²GT¹ (for non-absorbing HGMS, Webster and Warren et al. 2022)
    • Global efficiency for SAI is a factor of 1,000–4,000 larger than the HGM efficiency (Webster and Warren et al. 2022).
  • Regional (within the Arctic Ocean) annual radiative forcing efficiency -8.26 W/m²GT¹ (for non-absorbing HGMS, Webster and Warren et al. 2022).
  • This technique will become increasingly inefficient as sea ice extent declines. Conversely, if sea ice loss is reversed and sea ice extent increases, the technique will become increasingly efficient.

• Unknown, will require:
  • Continued studies on the properties, toxicity, and fate of HGMs
  • Development of methods for deployment
  • Increased manufacturing and shipping of HGMs

• Unknown
• Timeline to Arctic region impact (has to be within 20 yr)
• Large field tests estimated to be 4-5 years away.

• Estimated total cost $1 -5 billion/year (Arctic Ice Project (formerly Ice911 Research) quoted by the Guardian, Wired, and BBC).
  • Field et al. (2018) provides estimates for costs of increased production of HGMs and shipping.

• Unknown
  • CO₂ footprint will be determined by manufacturing processes, shipping, and deployment strategies (ship or air-based).

• 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
• Summary of existing literature and studies:
  • Conceptual paper by Walter 2011
  • Small-scale field trials
    • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018).
  • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation).
  • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by SINTEF.
  • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.

• This may be possible.
  • Large field tests and studies are estimated to be 4-5 years away (Zornetzer quoted in 2023).

• 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
• Summary of existing literature and studies:
  • Conceptual paper by Walter 2011
  • Small-scale field trials
    • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
  • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation).
  • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by SINTEF.
  • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.

• This may be possible.
  • Large field tests and studies are estimated to be 4-5 years away (Zornetzer quoted in 2023).

• • 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation).
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by SINTEF.
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.

• • This may be possible.
    • Large field tests and studies are estimated to be 4-5 years away (Zornetzer quoted in 2023).

• • 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation).
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by SINTEF.
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.

• • This may be possible.
    • Large field tests and studies are estimated to be 4-5 years away ( Zornetzer quoted in 2023).

• • 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation)
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by SINTEF.
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.

• • This may be possible.
    • Large field tests and studies are estimated to be 4-5 years away ( Zornetzer quoted in 2023).

• • 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation)
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by .
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.

• • This may be possible.
    • Large field tests and studies are estimated to be 4-5 years away ( Zornetzer quoted in 2023).

• TRL
  • 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation)
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by .
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.
• Technical feasibility within 10 yrs
  • This may be possible.
    • Large field tests and studies are estimated to be 4-5 years away ( Zornetzer quoted in 2023).

• TRL – 4
  • Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation)
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by .
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.
• Technical feasibility within 10 yrs
  • This may be possible.
    • Large field tests and studies are estimated to be 4-5 years away ( Zornetzer quoted in 2023).

• TRL
  • 4 – Modeling studies, proof of concept field study, field study in experimental setting, engineering and toxicity studies on HGMs.
  • Summary of existing literature and studies:
    • Conceptual paper by Walter 2011
    • Small-scale field trials
      • Proof of concept studies in Minnesota and Alaska (Field et al. 2018, Johnson et al. 2022), deployment technique tested (Field et al. 2018)
    • Some modeling studies have been published (Field et al. 2018, Webster and Warren 2022) with others unpublished (Bhattacharyya et al. 2019, Ivanova et al. 2020, Ivanova et al. 2023, Ivanova et al. in preparation)
    • Some toxicity studies previously conducted with fish, avians, and mice showed no to minor indication of toxicity from ingestion (Field et al. 2018, L. Field pers. comm.). Additional toxicity studies examining a variety of benthic and pelagic species native to the Arctic Ocean are being conducted by .
    • Engineering tests on commercial particles done in Farkas et al. 2023, concluded that material 25P45 is most stable in conditions related to Arctic and had least biofouling. This was the material used in Johnson et al. 2022.
  • Technical feasibility within 10 yrs
    • This may be possible.
      • Large field tests and studies are estimated to be 4-5 years away ( Zornetzer quoted in 2023).

Physical and chemical changes

• Co-benefits
  • A layer of HGMs on sea ice could decrease gas and aerosol fluxes to the atmosphere from sea ice (Miller et al. 2020). Decreases in aerosols generally lead to cooler temperatures. However, depending on the gases and aerosols involved, the consequences are difficult to predict (Miller et al. 2020).
• Risks
  • When ice melts, HGMs float on water and are blown around (Field et al. 2018) with unknown fates. If applied in areas with high wind and currents, HGMs are likely to be quickly redistributed and concentrated in gyres and on shorelines.
  • HGMs leach aluminum (Al), silicon (Si), iron (Fe), and barium (Ba) with unknown consequences; the most stable HGM recommended in Farkas et al. 2023, 25P45, also leached zinc (Zn).
  • Aerosols from ships or other infrastructure needed for this technology could impact the local climate (Miller et al. 2020).
  • Depending on the fate of the HGMs, they might contribute to aerosol production if they break up into powder.
  • Potential breakage of HGMs would increase their surface area, decrease particle size, and change radiative properties.

Impacts on species

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
• Risks
  • Toxicity studies are being conducted by SINTEF, still unpublished.
  • HGMs are similar in size to phytoplankton (diatoms) and are likely ingested by zooplankton (copepods). Even if not toxic, HGMs could have other impacts if organisms’ guts become full, as has been shown with microplastics (Cole et al. 2013, Egbeocha et al. 2018).
  • Unknown impacts of HGMs on mammals rearing young on ice and feeding. There are 8 species of phocid seals, walruses, and polar bears that breed and feed on sea ice.

Impacts on ecosystems

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
  • Prevention of loss of sea ice habitats and their ecosystem services.
• Risks
  • Sea ice covered with HGMs and a high albedo could decrease light availability to ice algae and algae below the ice (Miller et al. 2020). Altering phytoplankton blooms could disturb Arctic ecosystems and alter carbon fluxes.
  • HGMs could serve as a source of silica fertilizer to phytoplankton populations which could alter phytoplankton bloom dynamics.
  • If HGMs sink, there may be direct effects on benthic communities as it would change sedimentary properties and sedimentation rates over longer timescales.

Impacts on society

• Co-benefits
  • Slowing the loss of Arctic sea ice could benefit culturally important species.
  • Maintenance of sea ice could protect Arctic coastal communities from erosion.
• Risks
  • HGMs might enter food and water supplies with unknown consequences.
  • If HGMs can break due to shearing, they might enter a respirable size range. This would be particularly important if deployed close to communities.

Ease of reversibility

• Medium
  • Ceasing application of HGMs would return sea ice to previous albedo conditions over time. HGMs have unknown fates in the environment and are very small. The likelihood of retrieving them after deployment is small.

Risk of termination shock

• Medium
  • If deployment of HGMs were halted, sea ice and surrounding areas would return to their natural albedo, likely in the following season.

Physical and chemical changes

• Co-benefits
  • A layer of HGMs on sea ice could decrease gas and aerosol fluxes to the atmosphere from sea ice (Miller et al. 2020). Decreases in aerosols generally lead to cooler temperatures. However, depending on the gases and aerosols involved, the consequences are difficult to predict (Miller et al. 2020).
• Risks
  • When ice melts, HGMs float on water and are blown around (Field et al. 2018) with unknown fates. If applied in areas with high wind and currents, HGMs are likely to be quickly redistributed and concentrated in gyres and on shorelines.
  • HGMs leach aluminum (Al), silicon (Si), iron (Fe), and barium (Ba) with unknown consequences; the most stable HGM recommended in Farkas et al. 2023 25P45 also leached zinc (Zn).
  • Aerosols from ships or other infrastructure needed for this technology could impact the local climate (Miller et al. 2020).
  • Depending on the fate of the HGMs, they might contribute to aerosol production if they break up into powder.
  • Potential breakage of HGMs would increase their surface area, decrease particle size, and change radiative properties.

Impacts on species

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
• Risks
  • Toxicity studies are being conducted by SINTEF, still unpublished.
  • HGMs are similar in size to phytoplankton (diatoms) and are likely ingested by zooplankton (copepods). Even if not toxic, HGMs could have other impacts if organisms’ guts become full, as has been shown with microplastics (Cole et al. 2013, Egbeocha et al. 2018).
  • Unknown impacts of HGMs on mammals rearing young on ice and feeding. There are 8 species of phocid seals, walruses, and polar bears that breed and feed on sea ice.

Impacts on ecosystems

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
  • Prevention of loss of sea ice habitats and their ecosystem services.
• Risks
  • Sea ice covered with HGMs and a high albedo could decrease light availability to ice algae and algae below the ice (Miller et al. 2020). Altering phytoplankton blooms could disturb Arctic ecosystems and alter carbon fluxes.
  • HGMs could serve as a source of silica fertilizer to phytoplankton populations which could alter phytoplankton bloom dynamics.
  • If HGMs sink, there may be direct effects on benthic communities as it would change sedimentary properties and sedimentation rates over longer timescales.

Impacts on society

• Co-benefits
  • Slowing the loss of Arctic sea ice could benefit culturally important species.
  • Maintenance of sea ice could protect Arctic coastal communities from erosion.
• Risks
  • HGMs might enter food and water supplies with unknown consequences.
  • If HGMs can break due to shearing, they might enter a respirable size range. This would be particularly important if deployed close to communities.

Ease of reversibility

• Medium
  • Ceasing application of HGMs would return sea ice to previous albedo conditions over time. HGMs have unknown fates in the environment and are very small. The likelihood of retrieving them after deployment is small.

Risk of termination shock

• Medium
  • If deployment of HGMs were halted, sea ice and surrounding areas would return to their natural albedo, likely in the following season.

Physical and chemical changes

• Co-benefits
  • A layer of HGMs on sea ice could decrease gas and aerosol fluxes to the atmosphere from sea ice (Miller et al. 2020). Decreases in aerosols generally lead to cooler temperatures. However, depending on the gases and aerosols involved, the consequences are difficult to predict (Miller et al. 2020).
• Risks
  • When ice melts, HGMs float on water and are blown around (Field et al. 2018) with unknown fates. If applied in areas with high wind and currents, HGMs are likely to be quickly redistributed and concentrated in gyres and on shorelines.
  • HGMs leach aluminum (Al), silicon (Si), iron (Fe), and barium (Ba) with unknown consequences; the most stable HGM recommended in Farkas et al. 2023 25P45 also leached zinc (Zn).
  • Aerosols from ships or other infrastructure needed for this technology could impact the local climate (Miller et al. 2020).
  • Depending on the fate of the HGMs, they might contribute to aerosol production if they break up into powder.
  • Potential breakage of HGMs would increase their surface area, decrease particle size, and change radiative properties.

Impacts on species

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
• Risks
  • Toxicity studies are being conducted by SINTEF, still unpublished.
  • HGMs are similar in size to phytoplankton (diatoms) and are likely ingested by zooplankton (copepods). Even if not toxic, HGMs could have other impacts if organisms’ guts become full, as has been shown with microplastics (Cole et al. 2013, Egbeocha et al. 2018).
  • Unknown impacts of HGMs on mammals rearing young on ice and feeding. There are 8 species of phocid seals, walruses, and polar bears that breed and feed on sea ice.

Impacts on ecosystems

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
  • Prevention of loss of sea ice habitats and their ecosystem services.
• Risks
  • Sea ice covered with HGMs and a high albedo could decrease light availability to ice algae and algae below the ice (Miller et al. 2020). Altering phytoplankton blooms could disturb Arctic ecosystems and alter carbon fluxes.
  • HGMs could serve as a source of silica fertilizer to phytoplankton populations which could alter phytoplankton bloom dynamics.
  • If HGMs sink, there may be direct effects on benthic communities as it would change sedimentary properties and sedimentation rates over longer timescales.

Impacts on society

• Co-benefits
  • Slowing the loss of Arctic sea ice could benefit culturally important species.
  • Maintenance of sea ice could protect Arctic coastal communities from erosion.
• Risks
  • HGMs might enter food and water supplies with unknown consequences.
  • If HGMs can break due to shearing, they might enter a respirable size range. This would be particularly important if deployed close to communities.

Ease of reversibility

• Ceasing application of HGMs would return sea ice to previous albedo conditions over time. HGMs have unknown fates in the environment and are very small. The likelihood of retrieving them after deployment is small.

Risk of termination shock

• If deployment of HGMs were halted, sea ice and surrounding areas would return to their natural albedo, likely in the following season.

• Co-benefits
  • A layer of HGMs on sea ice could decrease gas and aerosol fluxes to the atmosphere from sea ice (Miller et al. 2020). Decreases in aerosols generally lead to cooler temperatures. However, depending on the gases and aerosols involved, the consequences are difficult to predict (Miller et al. 2020).
• Risks
  • When ice melts, HGMs float on water and are blown around (Field et al. 2018) with unknown fates. If applied in areas with high wind and currents, HGMs are likely to be quickly redistributed and concentrated in gyres and on shorelines.
  • HGMs leach aluminum (Al), silicon (Si), iron (Fe), and barium (Ba) with unknown consequences; the most stable HGM recommended in Farkas et al. 2023 25P45 also leached zinc (Zn).
  • Aerosols from ships or other infrastructure needed for this technology could impact the local climate (Miller et al. 2020).
  • Depending on the fate of the HGMs, they might contribute to aerosol production if they break up into powder.
  • Potential breakage of HGMs would increase their surface area, decrease particle size, and change radiative properties.

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
• Risks
  • Toxicity studies are being conducted by SINTEF, still unpublished.
  • HGMs are similar in size to phytoplankton (diatoms) and are likely ingested by zooplankton (copepods). Even if not toxic, HGMs could have other impacts if organisms’ guts become full, as has been shown with microplastics (Cole et al. 2013, Egbeocha et al. 2018).
  • Unknown impacts of HGMs on mammals rearing young on ice and feeding. There are 8 species of phocid seals, walruses, and polar bears that breed and feed on sea ice.

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
  • Prevention of loss of sea ice habitats and their ecosystem services.
• Risks
  • Sea ice covered with HGMs and a high albedo could decrease light availability to ice algae and algae below the ice (Miller et al. 2020). Altering phytoplankton blooms could disturb Arctic ecosystems and alter carbon fluxes.
  • HGMs could serve as a source of silica fertilizer to phytoplankton populations which could alter phytoplankton bloom dynamics.
  • If HGMs sink, there may be direct effects on benthic communities as it would change sedimentary properties and sedimentation rates over longer timescales.

• Co-benefits
  • Slowing the loss of Arctic sea ice could benefit culturally important species.
  • Maintenance of sea ice could protect Arctic coastal communities from erosion.
• Risks
  • HGMs might enter food and water supplies with unknown consequences.
  • If HGMs can break due to shearing, they might enter a respirable size range. This would be particularly important if deployed close to communities.

• Ceasing application of HGMs would return sea ice to previous albedo conditions over time. HGMs have unknown fates in the environment and are very small. The likelihood of retrieving them after deployment is small.

• If deployment of HGMs were halted, sea ice and surrounding areas would return to their natural albedo, likely in the following season.

• Co-benefits
  • A layer of HGMs on sea ice could decrease gas and aerosol fluxes to the atmosphere from sea ice (Miller et al. 2020). Decreases in aerosols generally lead to cooler temperatures. However, depending on the gases and aerosols involved, the consequences are difficult to predict (Miller et al. 2020).
• Risks
  • When ice melts, HGMs float on water and are blown around (Field et al. 2018) with unknown fates. If applied in areas with high wind and currents, HGMs are likely to be quickly redistributed and concentrated in gyres and on shorelines.
  • HGMs leach aluminum (Al), silicon (Si), iron (Fe), and barium (Ba) with unknown consequences; the most stable HGM recommended in Farkas et al. 2023 25P45 also leached zinc (Zn).
  • Aerosols from ships or other infrastructure needed for this technology could impact the local climate (Miller et al. 2020).
  • Depending on the fate of the HGMs, they might contribute to aerosol production if they break up into powder.
  • Potential breakage of HGMs would increase their surface area, decrease particle size, and change radiative properties.

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
• Risks
  • Toxicity studies are being conducted by SINTEF, still unpublished
  • HGMs are similar in size to phytoplankton (diatoms) and are likely ingested by zooplankton (copepods). Even if not toxic, HGMs could have other impacts if organisms’ guts become full, as has been shown with microplastics (Cole et al. 2013, Egbeocha et al. 2018).
  • Unknown impacts of HGMs on mammals rearing young on ice and feeding. There are 8 species of phocid seals, walruses, and polar bears that breed and feed on sea ice.

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
  • Prevention of loss of sea ice habitats and their ecosystem services.
• Risks
  • Sea ice covered with HGMs and a high albedo could decrease light availability to ice algae and algae below the ice (Miller et al. 2020). Altering phytoplankton blooms could disturb Arctic ecosystems and alter carbon fluxes.
  • HGMs could serve as a source of silica fertilizer to phytoplankton populations which could alter phytoplankton bloom dynamics.
  • If HGMs sink, there may be direct effects on benthic communities as it would change sedimentary properties and sedimentation rates over longer timescales.

• Co-benefits
  • Slowing the loss of Arctic sea ice could benefit culturally important species
  • Maintenance of sea ice could protect Arctic coastal communities from erosion
• Risks
  • HGMs might enter food and water supplies with unknown consequences.
  • If HGMs can break due to shearing, they might enter a respirable size range. This would be particularly important if deployed close to communities.

• Ceasing application of HGMs would return sea ice to previous albedo conditions over time. HGMs have unknown fates in the environment and are very small. The likelihood of retrieving them after deployment is small.

• If deployment of HGMs were halted, sea ice and surrounding areas would return to their natural albedo, likely in the following season.

• Co-benefits
  • A layer of HGMs on sea ice could decrease gas and aerosol fluxes to the atmosphere from sea ice (Miller et al. 2020). Decreases in aerosols generally lead to cooler temperatures. However, depending on the gases and aerosols involved, the consequences are difficult to predict (Miller et al. 2020).
• Risks
  • When ice melts, HGMs float on water and are blown around (Field et al. 2018) with unknown fates. If applied in areas with high wind and currents, HGMs are likely to be quickly redistributed and concentrated in gyres and on shorelines.
  • HGMs leach aluminum (Al), silicon (Si), iron (Fe), and barium (Ba) with unknown consequences; the most stable HGM recommended in Farkas et al. 2023 25P45 also leached zinc (Zn).
  • Aerosols from ships or other infrastructure needed for this technology could impact the local climate (Miller et al. 2020).
  • Depending on the fate of the HGMs, they might contribute to aerosol production if they break up into powder.
  • Potential breakage of HGMs would increase their surface area, decrease particle size, and change radiative properties.

• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
• Risks
  • Toxicity studies are being conducted by SINTEF, still unpublished
  • HGMs are similar in size to phytoplankton (diatoms) and are likely ingested by zooplankton (copepods). Even if not toxic, HGMs could have other impacts if organisms’ guts become full, as has been shown with microplastics (Cole et al. 2013, Egbeocha et al. 2018).
  • Unknown impacts of HGMs on mammals rearing young on ice and feeding. There are 8 species of phocid seals, walruses, and polar bears that breed and feed on sea ice.
• Impacts on ecosystems
• Co-benefits
  • Cooling and maintenance of sea ice could prevent alteration of food webs and poleward migration of non-Arctic species.
  • Prevention of loss of sea ice habitats and their ecosystem services.
• Risks
  • Sea ice covered with HGMs and a high albedo could decrease light availability to ice algae and algae below the ice (Miller et al. 2020). Altering phytoplankton blooms could disturb Arctic ecosystems and alter carbon fluxes.
  • HGMs could serve as a source of silica fertilizer to phytoplankton populations which could alter phytoplankton bloom dynamics.
  • If HGMs sink, there may be direct effects on benthic communities as it would change sedimentary properties and sedimentation rates over longer timescales.

• Co-benefits
  • Slowing the loss of Arctic sea ice could benefit culturally important species
  • Maintenance of sea ice could protect Arctic coastal communities from erosion
• Risks
  • HGMs might enter food and water supplies with unknown consequences.
  • If HGMs can break due to shearing, they might enter a respirable size range. This would be particularly important if deployed close to communities.

• Ceasing application of HGMs would return sea ice to previous albedo conditions over time. HGMs have unknown fates in the environment and are very small. The likelihood of retrieving them after deployment is small.

• If deployment of HGMs were halted, sea ice and surrounding areas would return to their natural albedo, likely in the following season.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership, and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska, and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Here we define justice related to approaches to slow the loss of Arctic sea ice through distributive justice, procedural justice, and restorative justice. Following COMEST (2023), we consider questions of ethics through a justice lens. Note that this is not an exhaustive list of justice dimensions and as the field advances, so will the related considerations and dimensions.
• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
• Procedural justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
    • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
  • Specific to Hollow Glass Microspheres:
    • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
• Restorative justice
  • Applicable to all approaches within Surface Albedo Modification:
    • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
  • Specific to Hollow Glass Microspheres:
    • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
    • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment, and people creating further disruption (compared to microplastics) to human, plant, and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Here we define justice related to approaches to slow the loss of Arctic sea ice through distributive justice, procedural justice, and restorative justice. Following COMEST (2023), we consider questions of ethics through a justice lens. Note that this is not an exhaustive list of justice dimensions and as the field advances, so will the related considerations and dimensions.
• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
• Procedural justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
    • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
  • Specific to Hollow Glass Microspheres:
    • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
• Restorative justice
  • Applicable to all approaches within Surface Albedo Modification:
    • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
  • Specific to Hollow Glass Microspheres:
    • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Here we define justice related to approaches to slow the loss of Arctic sea ice through distributive justice, procedural justice, and restorative justice. Following COMEST (2023), we consider questions of ethics through a justice lens. Note that this is not an exhaustive list of justice dimensions and as the field advances, so will the related considerations and dimensions.
• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
• Procedural justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
    • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
  • Specific to Hollow Glass Microspheres:
    • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
• Restorative justice
  • Applicable to all approaches within Surface Albedo Modification:
    • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
  • Specific to Hollow Glass Microspheres:
    • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Here we define justice related to approaches to slow the loss of Arctic sea ice through distributive justice, procedural justice, and restorative justice. Following COMEST (2023), we consider questions of ethics through a justice lens. Note that this is not an exhaustive list of justice dimensions and as the field advances, so will the related considerations and dimensions.
• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
• Procedural justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
    • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
  • Specific to Hollow Glass Microspheres:
    • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
• Restorative justice
  • Applicable to all approaches within Surface Albedo Modification:
    • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
  • Specific to Hollow Glass Microspheres:
    • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
• Procedural justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
    • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
  • Specific to Hollow Glass Microspheres:
    • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
• Restorative justice
  • Applicable to all approaches within Surface Albedo Modification:
    • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
  • Specific to Hollow Glass Microspheres:
    • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
  • Procedural justice
    • Applicable to all approaches within Surface Albedo Modification:
      • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
      • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
    • Specific to Hollow Glass Microspheres:
      • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
  • Restorative justice
    • Applicable to all approaches within Surface Albedo Modification:
      • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
    • Specific to Hollow Glass Microspheres:
      • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
  • Procedural justice
    • Applicable to all approaches within Surface Albedo Modification:
      • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
      • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
    • Specific to Hollow Glass Microspheres:
      • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
  • Restorative justice
    • Applicable to all approaches within Surface Albedo Modification:
      • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
    • Specific to Hollow Glass Microspheres:
      • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability - Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
  • Procedural justice
    • Applicable to all approaches within Surface Albedo Modification:
      • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
      • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
    • Specific to Hollow Glass Microspheres:
      • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
  • Restorative justice
    • Applicable to all approaches within Surface Albedo Modification:
      • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
    • Specific to Hollow Glass Microspheres:
      • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability - Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.

• Applicable to all approaches within Surface Albedo Modification:
  • Application of any approach in national waters (within territorial waters or a state’s exclusive economic zone (EEZ)) would be governed by those states. Small-scale field studies would likely be within national jurisdiction. However, even if applied with national jurisdiction there may be potential for transboundary effects due to dispersal of materials. Any application on the high seas would be within international jurisdiction. See “Existing governance” for other available information on relevant governance structures.
• Specific to Hollow Glass Microspheres:
  • No additional information.

• Applicable to all approaches within Surface Albedo Modification:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • These approaches may be subject to regulation by the London Protocol as a type of solar radiation modification (C2G 2021 Evidence Brief CAT Arctic). Article 6 prohibits the placement of matter into the sea for marine geoengineering activities and to date has been used to regulate ocean iron fertilization.  The London Protocol only applies to the currently 55 parties to the Protocol, which includes Arctic coastal states except the United States and Russia.
  • The Arctic Council has been called upon as a venue for providing oversight on approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
• Specific to Hollow Glass Microspheres:
  • There is currently not an adequate governance framework for ice in general. For a detailed review of governance and legal frameworks related to ice and ice interventions, see Argüello and Johansson 2022, Wood-Donnelly 2022, and Chuffart et al. 2023.
  • While the legal status of sea ice is unclear according to international law, there are principles within international customary law that are relevant: 1) the no harm principle (placing an obligation on the acting state to take reasonable measures to minimize transboundary harm), and 2) the precautionary principle (calling for caution in the absence of appropriate knowledge to understand what measures could be taken to minimize harm) (Chuffart et al. 2023).
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples. FPIC is meant to be a collaborative process, not a top-down, unilateral approach. FPIC needs to start early, continue as a long-term partnership and begin and end with consent. No universal model for Indigenous FPIC exists due to diversity of Indigenous Peoples and their structures around the world. With many Indigenous Peoples, silence however does not mean agreement or yes.
    • Chuffart et al. (2023) mentions that the right of Indigenous Peoples to FPIC is seldom implemented in a domestic context, let alone in more complex transboundary scenarios.
  • To date this approach has been explored using small scale studies domestically on shallow lakes on private land and at an observatory operated by the US National Oceanic and Atmospheric Administration (NOAA) and reported to have occurred with approval from local regulatory bodies (Ice911, Field et al. 2018). However, the field site at NOAA’s Barrow Atmospheric Baseline Observatory is located on Indigenous Inupiat territories near Utqiagvik, Alaska and although the Ukpeaġvik Iñupiat Corporation provided permission, Utqiagvik residents were not consulted and there was a lack of free, prior, and informed consent (FPIC) (Indigenous Environmental Network 2022).
  • The Arctic Ice Project suggests localized field studies of less than 10 km² be conducted to demonstrate safety and efficacy. Larger deployments will be up to nation states or international collaborations.
  • Bodansky and Hunt (2020) argue that localized interventions in the Arctic are more like mitigation and adaptation rather than climate intervention; although the scale of HGM application for a climate effect might be more regional than localized.

• Distributive justice
  • Applicable to all approaches within Surface Albedo Modification:
    • If distributive justice is considered, the objective would be that benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
  • Specific to Hollow Glass Microspheres:
    • Impacts will be focused on communities in the Arctic (Bennett et al. 2022) – likely both the benefits and the risks. While climate change also poses many specific risks for Arctic communities, approaches like the application of HGMs must consider the potential for disproportionate impacts to avoid exacerbating disparities (Bennett et al. 2022).
    • Importantly, different communities and governance authorities will have varied perspectives regarding acceptable levels of risk associated with potential impacts, underscoring the importance of inclusion of local communities who will be impacted by the approach (Bennett et al. 2022), also speaking to procedural justice.
  • Procedural justice
    • Applicable to all approaches within Surface Albedo Modification:
      • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed.
      • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk.  Within the development of such a framework there is an opportunity to prioritize Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
    • Specific to Hollow Glass Microspheres:
      • A previous small-scale experiment of HGM application in Alaska by Ice-911 was criticized for not including local perspectives and for violating the Indigenous right to free, prior, and informed consent.
  • Restorative justice
    • Applicable to all approaches within Surface Albedo Modification:
      • It is unknown if there have been restorative justice actions for any Surface Albedo Modification approaches. If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.
    • Specific to Hollow Glass Microspheres:
      • As of the writing of this version, we are not aware of any plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored. There is argument that some localized approaches such as the application of HGMs would restore sea ice (Desch et al. 2017), which would potentially make this technique a method for restorative justice to communities suffering from sea ice loss. However, there are still many questions surrounding the potential negative consequences for species, ecosystems, and society and there is not enough knowledge about this approach to know about its potential for restoration efficacy.

• This particular approach has received media attention (e.g., Elliott 2023, Riederer 2023). Other public engagement efforts are unknown.
• Acceptance among sea ice scientists is currently low due to conflicting results of studies that depend on the properties of the hollow glass microspheres and the condition of sea ice.

• Applicable to all approaches within Surface Albedo Modification:
  • The principle of free, prior and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability - Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2019) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
• Specific to Hollow Glass Microspheres:
  • In 2022 the Indigenous Environmental Network (IEN) organized a delegation of Alaska native leaders and stakeholders to protest outside a fundraising dinner for the Arctic Ice Project (AIP) and to deliver a group letter to the AIP leaders citing concerns on the lack of consultation and FPIC (Indigenous Environmental Network 2022). The reasons for opposition included:
  • Lack of free, prior and informed consent from local communities (and especially with those that rely on subsistence hunting, gathering and fishing) is considered not only unethical, but also dangerous.
    • Lack of tribal government consultation.
    • Not enough assessment on the environmental impacts of these synthetic beads upon regional ecosystems.
    • Concern over cumulative and future impacts of a scaled-up version of the tested technology on the ocean and ocean-dependent communities.
    • Claims of the project operating without permits from regulating bodies such as the EPA, Fish and Wildlife, or the US Wildlife Enforcement agency [could not be verified].
    • Concern over clean-up of the project and the synthetic microspheres being ingested and carried through marine life, birds, winds, testing equipment and people creating further disruption (compared to microplastics) to human, plant and animal health in the oceans and on land.
  • IEN is leading a petition called Organizational Sign-On: Alaska Native Orgs Demand Stop to Microbeads Research Project that offers concrete guidance to the project being opposed.