Carbon sink

A carbon sink is anything that absorbs more carbon than it releases, removing carbon dioxide from the atmosphere and storing it. The IPCC defines a sink as any process, activity or mechanism that removes a greenhouse gas from the atmosphere. The world's two most important natural sinks are vegetation — above all forests — and the oceans, while soils are a major sink as well. This function is vital in the fight against climate change.

How carbon sinks work

A sink is essentially the oceans and plant life in a growing phase, such as when plankton and trees grow and bind carbon. Soil is a natural carbon sink too, which is why ploughing farmland releases carbon dioxide. The opposite of a carbon sink is a carbon source, which produces and releases more carbon than it stores. A forest can be both, but is most often associated with being a sink, because its long growing life binds a great deal of carbon.

Carbon sinks and the UN (LULUCF)

In climate negotiations, carbon sinks are discussed in relation to LULUCF — Land Use, Land-Use Change and Forestry. Each year, countries submit reports on changes in their so-called carbon stock to the UN climate convention. Parts of these reports cover LULUCF by giving a picture of the annual net uptake of greenhouse gases, accounting for both the sector's emissions and its removals — the latter being the carbon bound up in a country's natural environment.

Artificial carbon sinks

There are also various initiatives to capture carbon dioxide or other greenhouse gases artificially. One example is BECCS — bioenergy with carbon capture and storage — which captures the CO₂ that would otherwise be emitted at, say, a power plant, with the aim of storing it underground. The technology is expensive but is being tested in several places around the world, and IPCC scenarios count on carbon sinks in some future pathways for limiting warming. In the end, the future will likely need more carbon sinks, made up of a combination of natural and artificial measures.

Sources: UNFCCC — Land Use, Land-Use Change and Forestry (LULUCF)