Glossary of road map assessment parameters Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in, soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region; however, research and deployment has happened within Arctic nations.

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in, soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region; however, research and deployment has happened within Arctic nations.

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in, soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km ² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region; however, research and deployment has happened within Arctic nations.

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in , soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km ² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region; however, research and deployment has happened within Arctic nations.

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in , soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km ² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region, however research and deployment has happened within Arctic nations.

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in , soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km ² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region, however research and deployment has happened within Arctic nations

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

Description of approach

• Anthropogenic activities removing carbon dioxide (CO₂) from the atmosphere and durably storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical sinks and direct air capture and storage but excludes natural CO₂ uptake not directly caused by human activities (IPCC 2018). Biological (e.g., photosynthesis) or chemical/geochemical (e.g., direct air capture, rock weathering) processes are used to capture and store carbon dioxide, resulting in a net removal of carbon dioxide from the atmosphere. Proposed approaches can occur on land (e.g., direct air capture) or in the ocean (e.g., ocean alkalinity enhancement). Currently, global carbon dioxide removal (not including indirect effects) totals 2 Gt CO₂/year, with only 0.002 Gt CO₂/year resulting from novel methods intended to provide durable carbon dioxide removal (novel methods include bioenergy with carbon capture and storage (BECCS), biochar, other CDR approaches beyond conventional methods that capture and store carbon in the land reservoir) (Smith et al. 2023).

Description of what it does mechanistically

• All methods of CDR aim to remove and store atmospheric carbon dioxide, resulting in lower temperatures due to the sensitivity of Earth’s climate to greenhouse gases. Note that lower temperatures will only occur when net negative emissions is met, which for all practical purposes will require both deep decarbonization and CDR.
  • Carbon dioxide can be captured from the atmosphere via photosynthesis (trees, grasses, agricultural crops, wetlands, macroalgae, microalgae), biogeochemistry (rock weathering and mineralization), and engineered chemical processes (direct air capture, electrodialysis). The captured carbon dioxide can then be stored in , soils/sediments, minerals, deep geologic reservoirs, or long-lived products.

Spatial extent (size)

• Rock CDR: Deploying 1 Gt CO₂/year of rock CDR would require 1-5 Gt of rock to be crushed and spread each year (RMI 2023). Deployment of 3 Gt of alkaline material would require distribution over 3 million km² (RMI 2023).
• Land CDR: Deploying 1 Gt CO₂/year of land CDR through afforestation would require a dedicated land area equivalent to several southern US states (RMI 2023). Reforestation at scale could use more than 8.1 million km ² (RMI 2023).
• Ocean CDR: Sequestering 1 Gt CO₂/year through large-scale seaweed farming would require an ocean area equivalent to ¼ of the Gulf of Mexico (RMI 2023). Removal of 100 Mt CO₂e/year is estimated to require 73,000 km² of ocean surface (RMI 2023).
• Air CDR: Deploying 1 Gt CO₂/year of air CDR would require filtering a volume of air equivalent to the whole atmosphere above 150,000 km² (RMI 2023). Facilities can require between 10-10,000 km²/GtCO₂ (RMI 2023).

Where applied – vertically

• Methods either happen on land at the surface (afforestation, biochar, etc), in the ocean (ocean fertilization, growing and sinking macroalgae), or in the lower atmosphere (direct air capture (DAC)). For ocean-based approaches, most activities would take place on the surface, however some approaches include sequestration in the deep ocean.

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Global potential: The atmosphere is well mixed on timescales over a year such that effects of CDR anywhere will be globally distributed within approximately one year.
  • On land: Depending on the approach, applied to existing forests, agricultural lands, or abandoned mines. To date, applied locally and regionally. Not targeting the Arctic.
  • In the ocean: Methods may be applied to the coast or open ocean and may also take advantage of existing coastal infrastructure such as desalination plants. To date, applied locally in field/pilot studies.
  • Application would not be specifically targeting the Arctic region, however research and deployment has happened within Arctic nations

When effective (summer, winter, all year)

• Most proposed CDR approaches would be effective year-round. Some biologically based CDR approaches may be more effective in spring or summer.

    This is when captured CO₂ is turned into products - happening with algae. @Sarah Mastroni do you want to add some clarifying language?         @Sarah Mastroni or @David Koweek any chance we can come up with size estimates? If so then also update the synthesis table.   From p. 168 of the cited document:   “Deployment rates stabilize at ~3 Gt of alkaline material deployed globally each year. This mass is about half the size of the current coal industry, the largest currently mined commodity on earth, extracting ~8 Gt per year.1 This scale provides around 600 MtCO₂/y of removals and would require distribution4 over a land area of 3 million km2 every year. This is equivalent to the land mass of India.”     Yes.   I changed to ‘has happened’. @David Koweek or @Sarah Mastroni do you know of any other Arctic efforts?       Great thanks   Change ‘local’ to ‘Arctic’ here? @Kerry  Nickols   When you wrote this were you meaning spring and summer of the area where CDR occurred? If so, I think local is fine

Impact on

Albedo

• Methods may have different effects on albedo, e.g. afforestation/reforestation may decrease albedo (NASEM 2019) and phytoplankton growth may increase albedo indirectly (Oeste et al. 2017).

Temperature

• Global
  • Best estimate of impacts of CDR while net overall emissions are still positive is approximately 0.45°C per 1000 gigaton of carbon dioxide removal (1.65°C per 1000 Pg C). Unknown whether this transient climate response to emissions holds when net emissions become negative (Canadell et al. 2021).
  • Best available estimate of global temperature impact by 2050 is a decrease of 0.08-0.12°C. According to the State of CDR 2024 Report (Smith et al. 2024), between 170 and 260 gigatons of CDR are needed by around 2050 to stabilize temperatures in alignment with the goals of the Paris Agreement. The amount of CDR needed varies depending on assumptions about rates of emissions reductions, as well as the target temperature. Using the transient climate response to cumulative emissions of carbon dioxide (TCRE) from Canadell et al. (2021), CDR would result in temperature decreases of 0.08-0.12°C by 2050 compared to what would have otherwise happened if everything else was held constant (i.e., emissions reductions continued as planned in scenarios without CDR).
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of CDR is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice
  • Indirect via decreases in global mean surface temperature
• New or old ice
  • Unknown
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• On land: Many approaches will be limited by competition for space, nutrients, water, places to sequester the carbon captured in biomass.
• Direct air capture: Direct air capture (DAC) plants are limited by access to low-carbon energy and nearby sequestration availability.
• In the ocean:
  • Macroalgae: availability of space for infrastructure, proper nutrients, light, temperature, suitable area to sink and sequester biomass or harvest for storage.
  • Microalgae: nutrient-limited (e.g. iron, nitrate, phosphate) water, proper nutrients, light, salinity, temperature.
  • Alkalinity enhancement (electrochemical): space for facilities, access to low-carbon power, markets for byproducts, space competition with other human activities.
  • Alkalinity enhancement (mineral): access to minerals, space competition with other human activities.
  • Blue carbon: limited by habitats that can be restored (ecosystem specific), competition for space with other coastal ecosystems and human developments.

Efficiency

• Unknown

Timeline to scalability

• Scalability is path dependent. It is also dependent on the results of field trials and pilot testing. Large financial investment is needed to support innovation and drive down costs to support project development. The gap between estimated investment and what is estimated to be needed by 2030 to put CDR on track to meet the 2050 targets of the Paris Agreement is between $400 billion and $1.6 trillion (Mannion et al. 2023) RMI (2023) calculates an optimistic scenario for technical viability and deployment of CDR (in addition to emissions reductions) is 2.2 Gt CO₂/year in 2040, 13.7 Gt CO₂/year in 2050, and 35 Gt CO₂/year in 2100.

Timeline to global impact (has to be within 20 yr)

• Likely >20 years to reach global impact at climate relevant scales (RMI 2023).

Timeline to Arctic region impact (has to be within 20 yr)

• Due to atmospheric mixing, there won’t be a large difference between global and Arctic impact.

Cost

Economic cost (Jones et al. 2024)

• Improved forest management < $150/t CO₂
• Afforestation/reforestation < $150/t CO₂
• Coastal blue carbon < $150/t CO₂
• Soil carbon sequestration < $150/t CO₂
• Peatland/wetland restoration < $150/t CO₂
• Ocean fertilization < $600/t CO₂
• Macroalgae < $600/t CO₂
• Artificial upwelling and downwelling < $150/t CO₂
• Biomass burial < $150/t CO₂
• Biochar < $600/t CO₂
• Ocean alkalinity enhancement < $600/t CO₂
• Bio-oil injection $150-600/t CO₂
• Bioenergy with carbon capture and storage (BECCS) < $600/t CO₂
• Surficial mineralization/enhanced weathering < $600/t CO₂
• Ex-situ mineralization < $600/t CO₂
• In-situ mineralization < $600/t CO₂
• Direct ocean capture $150-600/t CO₂
• Electrochemical Direct Air Capture (DAC) > $600/t CO₂
• Solid solvent/mineralization DAC > $600/t CO₂
• Solid sorbent DAC > $150/t CO₂
• Liquid solvent DAC > $150/t CO₂

CO₂ footprint

• Depends on the method but many approaches have high energy costs and transportation or processing needs. Full life cycle analyses are needed for each approach to understand net impact on carbon removal.

Impact on

Albedo

• Methods may have different effects on albedo, e.g. afforestation/reforestation may decrease albedo (NASEM 2019) and phytoplankton growth may increase albedo indirectly (Oeste et al. 2017).

Temperature

• Global
  • Best estimate of impacts of CDR while net overall emissions are still positive is approximately 0.45°C per 1000 gigaton of carbon dioxide removal (1.65°C per 1000 Pg C). Unknown whether this transient climate response to emissions holds when net emissions become negative (Canadell et al. 2021).
  • Best available estimate of global temperature impact by 2050 is a decrease of 0.08-0.12°C. According to the State of CDR 2024 Report (Smith et al. 2024), between 170 and 260 gigatons of CDR are needed by around 2050 to stabilize temperatures in alignment with the goals of the Paris Agreement. The amount of CDR needed varies depending on assumptions about rates of emissions reductions, as well as the target temperature. Using the transient climate response to cumulative emissions of carbon dioxide (TCRE) from Canadell et al. (2021), CDR would result in temperature decreases of 0.08-0.12°C by 2050 compared to what would have otherwise happened if everything else was held constant (i.e., emissions reductions continued as planned in scenarios without CDR).
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of CDR is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice
  • Indirect via decreases in global mean surface temperature
• New or old ice
  • Unknown
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• On land: Many approaches will be limited by competition for space, nutrients, water, places to sequester the carbon captured in biomass.
• Direct air capture: Direct air capture (DAC) plants are limited by access to low-carbon energy and nearby sequestration availability.
• In the ocean:
  • Macroalgae: availability of space for infrastructure, proper nutrients, light, temperature, suitable area to sink and sequester biomass or harvest for storage.
  • Microalgae: nutrient-limited (e.g. iron, nitrate, phosphate) water, proper nutrients, light, salinity, temperature
  • Alkalinity enhancement (electrochemical): space for facilities, access to low-carbon power, markets for byproducts, space competition with other human activities
  • Alkalinity enhancement (mineral): access to minerals, space competition with other human activities
  • Blue carbon: limited by habitats that can be restored (ecosystem specific), competition for space with other coastal ecosystems and human developments

Efficiency

• Unknown

Timeline to scalability

• Scalability is path dependent. It is also dependent on the results of field trials and pilot testing. Large financial investment is needed to support innovation and drive down costs to support project development. The gap between estimated investment and what is estimated to be needed by 2030 to put CDR on track to meet the 2050 targets of the Paris Agreement is between $400 billion and $1.6 trillion (Mannion et al. 2023) RMI (2023) calculates an optimistic scenario for technical viability and deployment of CDR (in addition to emissions reductions) is 2.2 Gt CO₂/year in 2040, 13.7 Gt CO₂/year in 2050, and 35 Gt CO₂/year in 2100.

Timeline to global impact (has to be within 20 yr)

• Likely >20 years to reach global impact at climate relevant scales (RMI 2023)

Timeline to Arctic region impact (has to be within 20 yr)

• Due to atmospheric mixing, there won’t be a large difference between global and Arctic impact.

Cost

Economic cost (Jones et al. 2024)

• Improved forest management < $150/t CO₂
• Afforestation/reforestation < $150/t CO₂
• Coastal blue carbon < $150/t CO₂
• Soil carbon sequestration < $150/t CO₂
• Peatland/wetland restoration < $150/t CO₂
• Ocean fertilization < $600/t CO₂
• Macroalgae < $600/t CO₂
• Artificial upwelling and downwelling < $150/t CO₂
• Biomass burial < $150/t CO₂
• Biochar < $600/t CO₂
• Ocean alkalinity enhancement < $600/t CO₂
• Bio-oil injection $150-600/t CO₂
• Bioenergy with carbon capture and storage (BECCS) < $600/t CO₂
• Surficial mineralization/enhanced weathering < $600/t CO₂
• Ex-situ mineralization < $600/t CO₂
• In-situ mineralization < $600/t CO₂
• Direct ocean capture $150-600/t CO₂
• Electrochemical Direct Air Capture (DAC) > $600/t CO₂
• Solid solvent/mineralization DAC > $600/t CO₂
• Solid sorbent DAC > $150/t CO₂
• Liquid solvent DAC > $150/t CO₂

CO₂ footprint

• Depends on the method but many approaches have high energy costs and transportation or processing needs. Full life cycle analyses are needed for each approach to understand net impact on carbon removal.

Impact on

Albedo

• Methods may have different effects on albedo, e.g. afforestation/reforestation may decrease albedo (NASEM 2019) and phytoplankton growth may increase albedo indirectly (Oeste et al. 2017).

Temperature

• Global
  • Best estimate of impacts of CDR while net overall emissions are still positive is approximately 0.45°C per 1000 gigaton of carbon dioxide removal (1.65°C per 1000 Pg C). Unknown whether this transient climate response to emissions holds when net emissions become negative (Canadell et al. 2021).
  • Best available estimate of global temperature impact by 2050 is a decrease of 0.08-0.12°C. According to the State of CDR 2024 Report (Smith et al. 2024), between 170 and 260 gigatons of CDR are needed by around 2050 to stabilize temperatures in alignment with the goals of the Paris Agreement. The amount of CDR needed varies depending on assumptions about rates of emissions reductions, as well as the target temperature. Using the transient climate response to cumulative emissions of carbon dioxide (TCRE) from Canadell et al. (2021), CDR would result in temperature decreases of 0.08-0.12°C by 2050 compared to what would have otherwise happened if everything else was held constant (i.e., emissions reductions continued as planned in scenarios without CDR).
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of CDR is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice
  • Indirect via decreases in global mean surface temperature
• New or old ice
  • Unknown
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• On land: Many approaches will be limited by competition for space, nutrients, water, places to sequester the carbon captured in biomass.
• Direct air capture: Direct air capture (DAC) plants are limited by access to low-carbon energy and nearby sequestration availability.
• In the ocean:
  • Macroalgae: availability of space for infrastructure, proper nutrients, light, temperature, suitable area to sink and sequester biomass or harvest for storage.
  • Microalgae: nutrient-limited (e.g. iron, nitrate, phosphate) water, proper nutrients, light, salinity, temperature
  • Alkalinity enhancement (electrochemical): space for facilities, access to low-carbon power, markets for byproducts, space competition with other human activities
  • Alkalinity enhancement (mineral): access to minerals, space competition with other human activities
  • Blue carbon: limited by habitats that can be restored (ecosystem specific), competition for space with other coastal ecosystems and human developments

Efficiency

• Unknown

Timeline to scalability

• Scalability is path dependent. It is also dependent on the results of field trials and pilot testing. Large financial investment is needed to support innovation and drive down costs to support project development. The gap between estimated investment and what is estimated to be needed by 2030 to put CDR on track to meet the 2050 targets of the Paris Agreement is between $400 billion and $1.6 trillion (Mannion et al. 2023) RMI (2023) calculates an optimistic scenario for technical viability and deployment of CDR (in addition to emissions reductions) is 2.2 Gt CO₂/year in 2040, 13.7 Gt CO₂/year in 2050, and 35 Gt CO₂/year in 2100.

Timeline to global impact (has to be within 20 yr)

• Likely >20 years to reach global impact at climate relevant scales (RMI 2023)

Timeline to Arctic region impact (has to be within 20 yr)

• Due to atmospheric mixing, there won’t be a large difference between global and Arctic impact.

Cost

Economic cost (Jones et al. 2024)

• Improved forest management < $150/t CO₂
• Afforestation/reforestation < $150/t CO₂
• Coastal blue carbon < $150/t CO₂
• Soil carbon sequestration < $150/t CO₂
• Peatland/wetland restoration < $150/t CO₂
• Ocean fertilization < $600/t CO₂
• Macroalgae < $600/t CO₂
• Artificial upwelling and downwelling < $150/t CO₂
• Biomass burial < $150/t CO₂
• Biochar < $600/t CO₂
• Ocean alkalinity enhancement < $600/t CO₂
• Bio-oil injection $150-600/t CO₂
• Bioenergy with carbon capture and storage (BECCS) < $600/t CO₂
• Surficial mineralization/enhanced weathering < $600/t CO₂
• Ex-situ mineralization < $600/t CO₂
• In-situ mineralization < $600/t CO₂
• Direct ocean capture $150-600/t CO₂
• Electrochemical Direct Air Capture (DAC) > $600/t CO₂
• Solid solvent/mineralization DAC > $600/t CO₂
• Solid sorbent DAC > $150/t CO₂
• Liquid solvent DAC > $150/t CO₂

CO₂ footprint

• Depends on the method but many approaches have high energy costs and transportation or processing needs. Full life cycle analyses are needed for each approach to understand net impact on carbon removal.

Impact on

Albedo

• Methods may have different effects on albedo, e.g. afforestation/reforestation may decrease albedo (NASEM 2019) and phytoplankton growth may increase albedo indirectly (Oeste et al. 2017).

Temperature

• Global
  • Best estimate of impacts of CDR while net overall emissions are still positive is approximately 0.45°C per 1000 gigaton of carbon dioxide removal (1.65°C per 1000 Pg C). Unknown whether this transient climate response to emissions holds when net emissions become negative (Canadell et al. 2021).
  • Best available estimate of global temperature impact by 2050 is a decrease of 0.08-0.12°C. According to the State of CDR 2024 Report (Smith et al. 2024), between 170 and 260 gigatons of CDR are needed by around 2050 to stabilize temperatures in alignment with the goals of the Paris Agreement. The amount of CDR needed varies depending on assumptions about rates of emissions reductions, as well as the target temperature. Using the transient climate response to cumulative emissions of carbon dioxide (TCRE) from Canadell et al. (2021),CDR would result in temperature decreases of 0.08-0.12°C by 2050 compared to what would have otherwise happened if everything else was held constant (i.e., emissions reductions continued as planned in scenarios without CDR).
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of CDR is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice
  • Indirect via decreases in global mean surface temperature
• New or old ice
  • Unknown
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• On land: Many approaches will be limited by competition for space, nutrients, water, places to sequester the carbon captured in biomass.
• Direct air capture: Direct air capture (DAC) plants are limited by access to low-carbon energy and nearby sequestration availability.
• In the ocean:
  • Macroalgae: availability of space for infrastructure, proper nutrients, light, temperature, suitable area to sink and sequester biomass or harvest for storage.
  • Microalgae: nutrient-limited (e.g. iron, nitrate, phosphate) water, proper nutrients, light, salinity, temperature
  • Alkalinity enhancement (electrochemical): space for facilities, access to low-carbon power, markets for byproducts, space competition with other human activities
  • Alkalinity enhancement (mineral): access to minerals, space competition with other human activities
  • Blue carbon: limited by habitats that can be restored (ecosystem specific), competition for space with other coastal ecosystems and human developments

Efficiency

• Unknown

Timeline to scalability

• Scalability is path dependent. It is also dependent on the results of field trials and pilot testing. Large financial investment is needed to support innovation and drive down costs to support project development. The gap between estimated investment and what is estimated to be needed by 2030 to put CDR on track to meet the 2050 targets of the Paris Agreement is between $400 billion and $1.6 trillion (Mannion et al. 2023) RMI (2023) calculates an optimistic scenario for technical viability and deployment of CDR (in addition to emissions reductions) is 2.2 Gt CO₂/year in 2040, 13.7 Gt CO₂/year in 2050, and 35 Gt CO₂/year in 2100.

Timeline to global impact (has to be within 20 yr)

• Likely >20 years to reach global impact at climate relevant scales (RMI 2023)

Timeline to Arctic region impact (has to be within 20 yr)

• Due to atmospheric mixing, there won’t be a large difference between global and Arctic impact.

Cost

Economic cost (Jones et al. 2024)

• Improved forest management < $150/t CO₂
• Afforestation/reforestation < $150/t CO₂
• Coastal blue carbon < $150/t CO₂
• Soil carbon sequestration < $150/t CO₂
• Peatland/wetland restoration < $150/t CO₂
• Ocean fertilization < $600/t CO₂
• Macroalgae < $600/t CO₂
• Artificial upwelling and downwelling < $150/t CO₂
• Biomass burial < $150/t CO₂
• Biochar < $600/t CO₂
• Ocean alkalinity enhancement < $600/t CO₂
• Bio-oil injection $150-600/t CO₂
• Bioenergy with carbon capture and storage (BECCS) < $600/t CO₂
• Surficial mineralization/enhanced weathering < $600/t CO₂
• Ex-situ mineralization < $600/t CO₂
• In-situ mineralization < $600/t CO₂
• Direct ocean capture $150-600/t CO₂
• Electrochemical Direct Air Capture (DAC) > $600/t CO₂
• Solid solvent/mineralization DAC > $600/t CO₂
• Solid sorbent DAC > $150/t CO₂
• Liquid solvent DAC > $150/t CO₂

CO₂ footprint

• Depends on the method but many approaches have high energy costs and transportation or processing needs. Full life cycle analyses are needed for each approach to understand net impact on carbon removal.

Impact on

Albedo

• Methods may have different effects on albedo, e.g. afforestation/reforestation may decrease albedo (NASEM 2019) and phytoplankton growth may increase albedo indirectly (Oeste et al. 2017).

Temperature

• Global
  • Best estimate of impacts of CDR while net overall emissions are still positive is approximately 0.45°C per 1000 gigaton of carbon dioxide removal (1.65°C per 1000 Pg C). Unknown whether this transient climate response to emissions holds when net emissions become negative (Canadell et al. 2021).
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of CDR is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice
  • Indirect via decreases in global mean surface temperature
• New or old ice
  • Unknown
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• On land: Many approaches will be limited by competition for space, nutrients, water, places to sequester the carbon captured in biomass.
• Direct air capture: Direct air capture (DAC) plants are limited by access to low-carbon energy and nearby sequestration availability.
• In the ocean:
  • Macroalgae: availability of space for infrastructure, proper nutrients, light, temperature, suitable area to sink and sequester biomass or harvest for storage.
  • Microalgae: nutrient-limited (e.g. iron, nitrate, phosphate) water, proper nutrients, light, salinity, temperature
  • Alkalinity enhancement (electrochemical): space for facilities, access to low-carbon power, markets for byproducts, space competition with other human activities
  • Alkalinity enhancement (mineral): access to minerals, space competition with other human activities
  • Blue carbon: limited by habitats that can be restored (ecosystem specific), competition for space with other coastal ecosystems and human developments

Efficiency

• Unknown

Timeline to scalability

• Scalability is path dependent. It is also dependent on the results of field trials and pilot testing. Large financial investment is needed to support innovation and drive down costs to support project development. The gap between estimated investment and what is estimated to be needed by 2030 to put CDR on track to meet the 2050 targets of the Paris Agreement is between $400 billion and $1.6 trillion (Mannion et al. 2023) RMI (2023) calculates an optimistic scenario for technical viability and deployment of CDR (in addition to emissions reductions) is 2.2 Gt CO₂/year in 2040, 13.7 Gt CO₂/year in 2050, and 35 Gt CO₂/year in 2100.

Timeline to global impact (has to be within 20 yr)

• Likely >20 years to reach global impact at climate relevant scales (RMI 2023)

Timeline to Arctic region impact (has to be within 20 yr)

• Due to atmospheric mixing, there won’t be a large difference between global and Arctic impact.

Cost

Economic cost (Jones et al. 2024)

• Improved forest management < $150/t CO₂
• Afforestation/reforestation < $150/t CO₂
• Coastal blue carbon < $150/t CO₂
• Soil carbon sequestration < $150/t CO₂
• Peatland/wetland restoration < $150/t CO₂
• Ocean fertilization < $600/t CO₂
• Macroalgae < $600/t CO₂
• Artificial upwelling and downwelling < $150/t CO₂
• Biomass burial < $150/t CO₂
• Biochar < $600/t CO₂
• Ocean alkalinity enhancement < $600/t CO₂
• Bio-oil injection $150-600/t CO₂
• Bioenergy with carbon capture and storage (BECCS) < $600/t CO₂
• Surficial mineralization/enhanced weathering < $600/t CO₂
• Ex-situ mineralization < $600/t CO₂
• In-situ mineralization < $600/t CO₂
• Direct ocean capture $150-600/t CO₂
• Electrochemical Direct Air Capture (DAC) > $600/t CO₂
• Solid solvent/mineralization DAC > $600/t CO₂
• Solid sorbent DAC > $150/t CO₂
• Liquid solvent DAC > $150/t CO₂

CO₂ footprint

• Depends on the method but many approaches have high energy costs and transportation or processing needs. Full life cycle analyses are needed for each approach to understand net impact on carbon removal.

Impact on

Albedo

• Methods may have different effects on albedo, e.g. afforestation/reforestation may decrease albedo (NASEM 2019) and phytoplankton growth may increase albedo indirectly (Oeste et al. 2017).

Temperature

• Global
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of CDR is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice
  • Indirect via decreases in global mean surface temperature
• New or old ice
  • Unknown
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• On land: Many approaches will be limited by competition for space, nutrients, water, places to sequester the carbon captured in biomass.
• Direct air capture: Direct air capture (DAC) plants are limited by access to low-carbon energy and nearby sequestration availability.
• In the ocean:
  • Macroalgae: availability of space for infrastructure, proper nutrients, light, temperature, suitable area to sink and sequester biomass or harvest for storage.
  • Microalgae: nutrient-limited (e.g. iron, nitrate, phosphate) water, proper nutrients, light, salinity, temperature
  • Alkalinity enhancement (electrochemical): space for facilities, access to low-carbon power, markets for byproducts, space competition with other human activities
  • Alkalinity enhancement (mineral): access to minerals, space competition with other human activities
  • Blue carbon: limited by habitats that can be restored (ecosystem specific), competition for space with other coastal ecosystems and human developments

Efficiency

• Unknown

Timeline to scalability

• Scalability is path dependent. It is also dependent on the results of field trials and pilot testing. Large financial investment is needed to support innovation and drive down costs to support project development. The gap between estimated investment and what is estimated to be needed by 2030 to put CDR on track to meet the 2050 targets of the Paris Agreement is between $400 billion and $1.6 trillion (Mannion et al. 2023) RMI (2023) calculates an optimistic scenario for technical viability and deployment of CDR (in addition to emissions reductions) is 2.2 Gt CO₂/year in 2040, 13.7 Gt CO₂/year in 2050, and 35 Gt CO₂/year in 2100.

Timeline to global impact (has to be within 20 yr)

• Likely >20 years to reach global impact at climate relevant scales (RMI 2023)

Timeline to Arctic region impact (has to be within 20 yr)

• Due to atmospheric mixing, there won’t be a large difference between global and Arctic impact.

Cost

Economic cost (Jones et al. 2024)

• Improved forest management < $150/t CO₂
• Afforestation/reforestation < $150/t CO₂
• Coastal blue carbon < $150/t CO₂
• Soil carbon sequestration < $150/t CO₂
• Peatland/wetland restoration < $150/t CO₂
• Ocean fertilization < $600/t CO₂
• Macroalgae < $600/t CO₂
• Artificial upwelling and downwelling < $150/t CO₂
• Biomass burial < $150/t CO₂
• Biochar < $600/t CO₂
• Ocean alkalinity enhancement < $600/t CO₂
• Bio-oil injection $150-600/t CO₂
• Bioenergy with carbon capture and storage (BECCS) < $600/t CO₂
• Surficial mineralization/enhanced weathering < $600/t CO₂
• Ex-situ mineralization < $600/t CO₂
• In-situ mineralization < $600/t CO₂
• Direct ocean capture $150-600/t CO₂
• Electrochemical Direct Air Capture (DAC) > $600/t CO₂
• Solid solvent/mineralization DAC > $600/t CO₂
• Solid sorbent DAC > $150/t CO₂
• Liquid solvent DAC > $150/t CO₂

CO₂ footprint

• Depends on the method but many approaches have high energy costs and transportation or processing needs. Full life cycle analyses are needed for each approach to understand net impact on carbon removal.

TRL

• 1-9 – Varies widely across approaches. Theoretical, laboratory, and pilot studies have been done, depending on approach. In some cases, deployment is already occurring.
  • See The Applied Innovation Roadmap for CDR (RMI 2023) for a comprehensive description of approaches across land and marine locations.
  • See the Ocean Visions mCDR Road Maps for detailed descriptions of marine-specific approaches.
• Summary of existing literature and studies
  • Conventional CDR makes up over 99.9% of all current CDR and represents approaches with the highest TRLs.
  • Biochar, soil carbon sequestration, and afforestation/reforestation continue to dominate research publications on CDR (Smith et al. 2024).
  • There has been rapid growth in the number and capacity of direct air capture plants. The US has funded a 1 million ton per year of direct air carbon capture and storage demonstration plant with another in negotiations (Smith et al. 2024).
  • Growth in novel CDR startups has surpassed growth in conventional CDR startups (Smith et al. 2024).

Technology feasibility within 10 years

• Approaches that currently have TRLs of 6+ may be feasible within the next 10 years.
  • Some CDR approaches are already being deployed, but novel CDR methods will be needed to meet climate goals. The next decade is crucial for the growth and development of novel CDR. Recent assessments show that few countries have actionable national plans to develop CDR, particularly for novel methods (Smith et al. 2023).

TRL

• 1-9 – Varies widely across approaches. Theoretical, laboratory, and pilot studies have been done, depending on approach. In some cases, deployment is already occurring.
  • See The Applied Innovation Roadmap for CDR (RMI 2023) for a comprehensive description of approaches across land and marine
  • See the Ocean Visions mCDR Road Maps for detailed descriptions of marine specific approaches
• Summary of existing literature and studies
  • Conventional CDR makes up over 99.9% of all current CDR and represents approaches with the highest TRLs.
  • Biochar, soil carbon sequestration, and afforestation/reforestation continue to dominate research publications on CDR (Smith et al. 2024).
  • There has been rapid growth in the number and capacity of direct air capture plants. The US has funded a 1 million ton per year of direct air carbon capture and storage demonstration plant with another in negotiations (Smith et al. 2024).
  • Growth in novel CDR startups has surpassed growth in conventional CDR startups (Smith et al. 2024).

Technology feasibility within 10 years

• Approaches that currently have TRLs of 6+ may be feasible within the next 10 years.
  • Some CDR approaches are already being deployed, but novel CDR methods will be needed to meet climate goals. The next decade is crucial for the growth and development of novel CDR. Recent assessments show that few countries have actionable national plans to develop CDR, particularly for novel methods (Smith et al. 2023).

TRL

• 1-9 – Varies widely across approaches. Theoretical, laboratory, and pilot studies have been done, depending on approach. In some cases, deployment is already occurring.
  • See RMI The Applied Innovation Roadmap for CDR, 2023 for a comprehensive description of approaches across land and marine
  • See the Ocean Visions mCDR Road Maps for detailed descriptions of marine specific approaches
• Summary of existing literature and studies
  • Conventional CDR makes up over 99.9% of all current CDR and represents approaches with the highest TRLs.
  • Biochar, soil carbon sequestration, and afforestation/reforestation continue to dominate research publications on CDR (Smith et al. 2024).
  • There has been rapid growth in the number and capacity of direct air capture plants. The US has funded a 1 million ton per year of direct air carbon capture and storage demonstration plant with another in negotiations (Smith et al. 2024).
  • Growth in novel CDR startups has surpassed growth in conventional CDR startups (Smith et al. 2024).

Technology feasibility within 10 years

• Approaches that currently have TRLs of 6+ may be feasible within the next 10 years.
  • Some CDR approaches are already being deployed, but novel CDR methods will be needed to meet climate goals. The next decade is crucial for the growth and development of novel CDR. Recent assessments show that few countries have actionable national plans to develop CDR, particularly for novel methods (Smith et al. 2023).

TRL

• • 1-9 – Varies widely across approaches. Theoretical, laboratory, and pilot studies have been done, depending on approach. In some cases, deployment is already occurring.
    • See RMI The Applied Innovation Roadmap for CDR, 2023 for a comprehensive description of approaches across land and marine
    • See the Ocean Visions mCDR Road Maps for detailed descriptions of marine specific approaches
  • Summary of existing literature and studies
    • Conventional CDR makes up over 99.9% of all current CDR and represents approaches with the highest TRLs.
    • Biochar, soil carbon sequestration, and afforestation/reforestation continue to dominate research publications on CDR (Smith et al. 2024).
    • There has been rapid growth in the number and capacity of direct air capture plants. The US has funded a 1 million ton per year of direct air carbon capture and storage demonstration plant with another in negotiations (Smith et al. 2024).
    • Growth in novel CDR startups has surpassed growth in conventional CDR startups (Smith et al. 2024).

Technology feasibility within 10 years

• • Approaches that currently have TRLs of 6+ may be feasible within the next 10 years.
    • Some CDR approaches are already being deployed, but novel CDR methods will be needed to meet climate goals. The next decade is crucial for the growth and development of novel CDR. Recent assessments show that few countries have actionable national plans to develop CDR, particularly for novel methods (Smith et al. 2023).

TRL

• • TRL -- 1-9
    • Varies widely across approaches
      • See RMI The Applied Innovation Roadmap for CDR, 2023 for a comprehensive description of approaches across land and marine
      • See the Ocean Visions mCDR Road Maps for detailed descriptions of marine specific approaches
    • Theoretical, laboratory, and pilot studies have been done, depending on approach. In some cases, deployment is already occurring.
  • Summary of existing literature and studies
    • Conventional CDR makes up over 99.9% of all current CDR and represents approaches with the highest TRLs.
    • Biochar, soil carbon sequestration, and afforestation/reforestation continue to dominate research publications on CDR (Smith et al. 2024).
    • There has been rapid growth in the number and capacity of direct air capture plants. The US has funded a 1 million ton per year of direct air carbon capture and storage demonstration plant with another in negotiations (Smith et al. 2024).
    • Growth in novel CDR startups has surpassed growth in conventional CDR startups (Smith et al. 2024).

Technology feasibility within 10 years

• • Approaches that currently have TRLs of 6+ may be feasible within the next 10 years.
    • Some CDR approaches are already being deployed, but novel CDR methods will be needed to meet climate goals. The next decade is crucial for the growth and development of novel CDR. Recent assessments show that few countries have actionable national plans to develop CDR, particularly for novel methods (Smith et al. 2023).

• TRL
  • TRL -- 1-9
    • Varies widely across approaches
      • See RMI The Applied Innovation Roadmap for CDR, 2023 for a comprehensive description of approaches across land and marine
      • See the Ocean Visions mCDR Road Maps for detailed descriptions of marine specific approaches
    • Theoretical, laboratory, and pilot studies have been done, depending on approach. In some cases, deployment is already occurring.
  • Summary of existing literature and studies
    • Conventional CDR makes up over 99.9% of all current CDR and represents approaches with the highest TRLs.
    • Biochar, soil carbon sequestration, and afforestation/reforestation continue to dominate research publications on CDR (Smith et al. 2024).
    • There has been rapid growth in the number and capacity of direct air capture plants. The US has funded a 1 million ton per year of direct air carbon capture and storage demonstration plant with another in negotiations (Smith et al. 2024).
    • Growth in novel CDR startups has surpassed growth in conventional CDR startups (Smith et al. 2024).

• Technology feasibility within 10 years
  • Approaches that currently have TRLs of 6+ may be feasible within the next 10 years.
    • Some CDR approaches are already being deployed, but novel CDR methods will be needed to meet climate goals. The next decade is crucial for the growth and development of novel CDR. Recent assessments show that few countries have actionable national plans to develop CDR, particularly for novel methods (Smith et al. 2023).

For detailed information on the socio-ecological co-benefits and risks of the wide array of CDR approaches, explore synthesis publications by NASEM 2022 (marine based CDR), NASEM 2019 (negative emissions tech), and RMI (2023), as well as the 2024 paper on co-benefits and challenges of CDR.

Ease of reversibility

• Easy
  • Easily reversible, although significant infrastructure will be required for carbon dioxide removal.

Risk of termination shock

• No risk

For detailed information on the socio-ecological co-benefits and risks of the wide array of CDR approaches, explore synthesis publications by NASEM 2022 (marine based CDR), NASEM 2019 (negative emissions tech),  and RMI, as well as the 2024 paper on co-benefits and challenges of CDR.

Ease of reversibility

• Easy
  • Easily reversible, although significant infrastructure will be required for carbon dioxide removal.

Risk of termination shock

• No risk

For detailed information on the socio-ecological co-benefits and risks of the wide array of CDR approaches, explore synthesis publications by NASEM 2022 (marine based CDR), NASEM 2019 (negative emissions tech),  and RMI, as well as the 2024 paper on co-benefits and challenges of CDR.

Missing information in this section does not indicate the absence of risks or co-benefits; it simply reflects that sufficient information is not yet available. For detailed information on the socio-ecological co-benefits and risks of the wide array of CDR approaches, explore synthesis publications by NASEM 2022 (marine based CDR), NASEM 2019 (negative emissions tech),  and RMI, as well as the 2024 paper on co-benefits and challenges of CDR.

International vs national jurisdiction

• Land based CDR activities fall under national jurisdiction and vary greatly accordingly. The World Resources Institute published a paper on the international governance of technological carbon removal in 2023. Many marine based CDR approaches would take place in the open ocean and thus fall under international law. Marine CDR approaches that take place in coastal waters or have elements that are land-based (e.g., electrochemical processes) may fall under national jurisdiction.

Existing governance

• There are no international or national laws or regulations designed specifically for CDR. Instead, existing laws and policies are often used but are not fit-for-purpose and can cause issues.
• At this point in time, The London Protocol is the dominant international regulation that is applied to marine CDR.
• In the ocean: The Sabin Center for Climate Change Law released a framework for legislation for marine CDR field trials. For an in-depth summary of marine CDR governance, see Webb 2024.
• The Aspen Institute released a Code of Conduct for Marine Carbon Dioxide Removal Research and the American Geophysical Union has proposed an Ethical Framework for Climate Intervention (includes CDR). These have yet to be put into practice or widely adopted.

Justice

• 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
  • Largely unexplored
    • 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.
• Procedural justice
  • Largely unexplored
    • 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.
• Restorative justice
  • Largely unexplored
    • If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.

Public engagement and perception

• While CDR is becoming more of a public talking point, awareness and engagement remain low, especially relative to other aspects of climate change (Smith et al. 2023).
• Generally, CDR approaches seen as “natural” (e.g., reforestation, blue carbon restoration) are favored by the public over approaches that are seen as tampering with nature or labeled as “geoengineering” (Bertram & Merk 2020, Corner & Pidgeon 2015, Wolske et al. 2019).

Engagement with Indigenous communities

• Largely lacking

International vs national jurisdiction

• Land based CDR activities fall under national jurisdiction and vary greatly accordingly. The World Resources Institute published a paper on the international governance of technological carbon removal in 2023. Many marine based CDR approaches would take place in the open ocean and thus fall under international law. Marine CDR approaches that take place in coastal waters or have elements that are land-based (e.g., electrochemical processes) may fall under national jurisdiction.

Existing governance

• There are no international or national laws or regulations designed specifically for CDR. Instead, existing laws and policies are often used but are not fit-for-purpose and can cause issues.
• At this point in time, The London Protocol is the dominant international regulation that is applied to marine CDR.
• In the ocean: The Sabin Center for Climate Change Law released a framework for legislation for marine CDR field trials. For an in-depth summary of marine CDR governance, see Webb 2024.
• The Aspen Institute released a Code of Conduct for Marine Carbon Dioxide Removal Research and the American Geophysical Union has proposed an Ethical Framework for Climate Intervention (includes CDR). These have yet to be put into practice or widely adopted.

Justice

• 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
  • Largely unexplored
    • 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.
• Procedural justice
  • Largely unexplored
    • 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.
• Restorative justice
  • Largely unexplored
    • If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.

Public engagement and perception

• While CDR is becoming more of a public talking point, awareness and engagement remain low, especially relative to other aspects of climate change (Smith et al. 2023).
• Generally, CDR approaches seen as “natural” (e.g., reforestation, blue carbon restoration) are favored by the public over approaches that are seen as tampering with nature or labeled as “geoengineering” (Bertram & Merk 2020, Corner & Pidgeon 2015, Wolske et al. 2019).

Engagement with Indigenous communities

• Largely lacking

International vs national jurisdiction

• Land based CDR activities fall under national jurisdiction and vary greatly accordingly. The World Resources Institute published a paper on the international governance of technological carbon removal in 2023. Many marine based CDR approaches would take place in the open ocean and thus fall under international law. Marine CDR approaches that take place in coastal waters or have elements that are land-based (e.g., electrochemical processes) may fall under national jurisdiction.

Existing governance

• There are no international or national laws or regulations designed specifically for CDR. Instead, existing laws and policies are often used but are not fit-for-purpose and can cause issues.
• At this point in time, The London Protocol is the dominant international regulation that is applied to marine CDR.
• In the ocean: The Sabin Center for Climate Change Law released a framework for legislation for marine CDR field trials. For an in-depth summary of marine CDR governance, see Webb 2024.
• The Aspen Institute released a Code of Conduct for Marine Carbon Dioxide Removal Research and the American Geophysical Union has proposed an Ethical Framework for Climate Intervention (includes CDR). These have yet to be put into practice or widely adopted.

Justice 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
  • Largely unexplored
    • 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.
• Procedural justice
  • Largely unexplored
    • 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.
• Restorative justice
  • Largely unexplored
    • If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.

Public engagement and perception

• While CDR is becoming more of a public talking point, awareness and engagement remain low, especially relative to other aspects of climate change (Smith et al. 2023).
• Generally, CDR approaches seen as “natural” (e.g., reforestation, blue carbon restoration) are favored by the public over approaches that are seen as tampering with nature or labeled as “geoengineering” (Bertram & Merk 2020, Corner & Pidgeon 2015, Wolske et al. 2019).

Engagement with Indigenous communities

• Largely lacking