Carbon Dioxide Removal

Carbon dioxide removal (CDR) means taking carbon dioxide already present in the atmosphere and storing it in vegetation, soils, geological formations or other reservoirs. It produces net-negative emissions when the quantity removed and retained exceeds the greenhouse gas emissions caused by the removal process over its life cycle.

How removal and storage are achieved

Every CDR method needs both atmospheric carbon uptake and storage. Capturing carbon alone is insufficient if it is soon released again.

• Afforestation, reforestation and improved soil management use photosynthesis to transfer atmospheric carbon into vegetation and soils; the climate benefit depends on maintaining these stocks.
• Bioenergy with carbon capture and storage (BECCS) uses biomass that absorbed atmospheric carbon while growing, captures carbon dioxide released during energy production, and stores it underground.
• Direct air carbon capture and storage (DACCS) chemically captures carbon dioxide from ambient air and stores it, usually in geological formations.
• Enhanced weathering accelerates reactions between carbon dioxide and suitable minerals, storing carbon in dissolved bicarbonates or solid carbonates.

When removal becomes net-negative

The relevant measure is net removal, not simply the amount captured. Life-cycle accounting must include emissions from energy use, materials, cultivation where relevant, transport, processing and storage.

• A method is net-negative only when durably stored atmospheric carbon dioxide exceeds associated emissions, with different greenhouse gases compared on a consistent carbon dioxide-equivalent basis.
• An energy-intensive process can deliver little net removal if its electricity and heat cause substantial emissions; low-emission energy improves its carbon balance.
• Monitoring, reporting and verification must establish the quantity removed and track storage losses, so credited removals reflect actual climate benefits.
• Capturing carbon dioxide from fossil-fuel combustion prevents some new emissions but does not itself remove atmospheric carbon; fossil-source carbon capture and storage is therefore not CDR.

Why durability and emission cuts remain essential

At the economy-wide or global level, net-negative carbon dioxide emissions occur only when total removals exceed total human-caused carbon dioxide emissions. A net-negative project does not automatically make the entire economy net-negative.

• Storage durability varies: forests and soils can lose carbon through fire, disturbance or land-use change, while well-managed geological storage can retain it much longer.
• Land-based methods face constraints involving land, water, food production and biodiversity; biological carbon stocks also cannot increase indefinitely.
• CDR can counterbalance residual emissions that are difficult to eliminate, but it complements rather than replaces deep emission reductions.