Cosmos Explains: What are carbon sinks?

Each year, humans burning fossil fuels emit about 10 billion tonnes of carbon, mostly in the form of carbon dioxide (CO₂). But not all of this greenhouse gas ends up in our atmosphere, thanks to carbon sinks. Carbon sinks are natural systems that absorb more CO₂ than they emit.

The world’s forests absorb approximately 3.5 billion tonnes of carbon per year. Plants take in CO₂ during photosynthesis, storing carbon in their biomass and the soil. This makes large, forested areas, like the Amazon Rainforest, vital in the fight against climate change. However, deforestation poses a significant threat, converting these carbon sinks into carbon sources as the plants break down. 

Oceans absorb almost 30% of human CO₂ emissions—that’s about 3 billion tonnes of  a year. CO₂ dissolves in surface water. Some of it is photosynthesised by marine plants, and some is consumed by chemical reactions in the water. However, these chemical reactions lead to ocean acidification, jeopardizing marine ecosystems.

Peat bogs are another noteworthy carbon sink. They cover only 3% of the Earth’s land surface yet store around 600 billion tonnes of carbon. That’s twice the carbon content stored in all forests. These wetlands have been incredibly efficient at trapping carbon for thousands of years. But draining and land-use changes could turn them into major carbon sources.

Carbon sinks play a critical role in the Earth’s carbon cycle. Their sensitivity to human activity underscores the urgency of preserving and restoring these ecosystems.

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