Carbon dioxide removal

Carbon dioxide removal (CDR) is the deliberate removal of carbon dioxide from the atmosphere and its durable storage in geological, biological, or material reservoirs.

Direct air capture: Technology that uses chemical or physical processes to capture carbon dioxide directly from ambient air. It separates carbon dioxide from air before the gas is stored or used.
Afforestation: The establishment of forest on land that has not recently been forested. New forests can remove atmospheric carbon as trees and soils accumulate biomass.
Net zero emissions: A state in which human-caused greenhouse-gas emissions are balanced by removals over a specified period. Most net-zero pathways require removals to balance residual emissions.
Carbon dioxide equivalent: A unit that expresses the warming effect of different greenhouse gases as an equivalent amount of carbon dioxide. CDR removes carbon dioxide itself, while climate accounting may combine its effect with other gases.
Carbon removal verification: Methods for measuring and confirming the amount of atmospheric carbon dioxide removed and durably stored. Reliable verification is needed to distinguish net removals from estimates or temporary storage.
Enhanced rock weathering: The accelerated reaction of finely ground silicate rocks with carbon dioxide and water, producing dissolved bicarbonate and carbonate minerals. It draws carbon dioxide into chemical forms that can persist in soils, waters, and minerals.
Reforestation: The re-establishment of forest on land where forest has been lost or degraded. Restored forests can rebuild carbon stocks, though storage can be reversed by disturbance.
Carbon budget: The cumulative amount of carbon dioxide emissions compatible with limiting warming to a specified temperature threshold. Large-scale future removals affect how some pathways allocate the remaining emissions budget.
Emission reduction: A decrease in greenhouse gases released into the atmosphere compared with a defined baseline. Reducing a source prevents emissions; CDR removes carbon dioxide already in the atmosphere.
Carbon dioxide removal scale-up: The expansion of carbon removal capacity from current levels to the quantities proposed in climate pathways. Projections often require deployment at scales that remain unproven.

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