Carbon Sink
A carbon sink is any reservoir that absorbs more carbon than it releases. Oceans, forests, and soils are the main natural sinks, and together they remove a little over half of the CO₂ that human activity emits each year.
The ocean absorbs CO₂ at the surface and stores it as dissolved carbon, which also makes seawater more acidic. Land sinks store carbon in wood, roots, and soil organic matter. Both can flip: a forest that burns or is cleared becomes a source, and warmer soils release carbon faster than they accumulate it.
A sink is not the same as a carbon offset. A sink is a physical store. An offset is a tradable claim that a specific tonne was removed or avoided, which requires that the removal is additional, measured, and held long enough to matter.
The distinction decides how a company reports. Under the GHG Protocol, removals are reported separately from gross emissions rather than netted against them, and land sector removals follow the FLAG guidance with its own rules on permanence and reversal. A target that relies on sinks has to state the storage duration and what happens if the carbon comes back.
Frequently asked questions
What is a carbon sink? +
A carbon sink is a reservoir that absorbs more carbon than it releases. The main natural sinks are the oceans, forests, and soils, which together take up more than half of annual human CO₂ emissions.
What is the difference between a carbon sink and a carbon offset? +
A carbon sink is a physical store of carbon. A carbon offset is a tradable claim to a specific tonne removed or avoided, which must be additional, measured, and durably stored to be credible.
How are carbon sinks reported in a GHG inventory? +
Removals are reported separately from gross emissions rather than subtracted from them. Land sector removals follow the GHG Protocol FLAG guidance, which sets rules for permanence and reversal.
Related terms
Carbon Sequestration
Carbon sequestration is the long-term storage of carbon dioxide so that it stays out of the atmosphere. It happens biologically, in trees and soils, and geologically, by injecting captured CO₂ into deep rock formations.
Carbon Cycle
The carbon cycle is the continuous movement of carbon between the atmosphere, oceans, soil, rock, and living things. Burning fossil fuels releases carbon that was locked underground for millions of years, and it enters the atmosphere far faster than natural processes remove it.
Carbon Offsets
Carbon offsets are verified emission reduction or removal credits purchased by an organization to compensate for its own greenhouse gas emissions. One carbon offset represents one tonne of CO₂e reduced or removed from the atmosphere through a project elsewhere, such as reforestation, renewable energy deployment, or methane capture.
FLAG (Forest, Land, and Agriculture)
FLAG is the SBTi sector guidance for companies with significant emissions from forestry, land use, and agriculture. It provides target-setting methods for land-related emissions and removals.
Net Zero
Net zero means reducing greenhouse gas emissions as close to zero as possible, with any remaining residual emissions balanced by an equivalent amount of carbon removal from the atmosphere. The SBTi Corporate Net-Zero Standard requires at least 90–95% absolute emission reductions before carbon removals can be used.