Sustainability Language

Climate & Greenhouse Gas Emissions

Carbon sink

Any process or reservoir that removes more carbon from the atmosphere than it releases — forests, oceans and soils being the great natural sinks.

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Definition

Per the UNFCCC, any process, activity or mechanism that removes a greenhouse gas from the atmosphere; the IPCC glossary defines it as a reservoir — natural or human, in soil, ocean and plants — that stores carbon. A sink must absorb more carbon than it releases; reservoirs that release more than they absorb are sources.

References

Greenly

~50% of anthropogenic CO₂ absorbed by sinks; forests, oceans, soils as principal natural sinks; sink-decline trend.

Overview

What it means

Natural sinks perform the largest free climate service on Earth: oceans and land ecosystems together absorb roughly half of human-caused CO₂ emissions each year, slowing atmospheric accumulation.

But sink strength is not guaranteed — deforestation flips forests from sink to source, droughts and wildfires weaken land uptake (the 2023 land sink dropped to historic lows in research syntheses), and ocean uptake comes at the cost of acidification. Artificial sinks (geological CCS storage, durable products) are engineered complements, still tiny by comparison.

How it is used

The sink/source vocabulary structures national GHG inventories (LULUCF accounting), REDD+ and nature-based carbon crediting, and the global carbon budget; policy tracks sink saturation and reversal risks as systemic climate risks.

Why it matters

Every climate pathway assumes sinks keep working; protecting and restoring natural sinks — and honestly accounting for their fragility — is as load-bearing as cutting emissions.

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