What are the world’s biggest natural carbon sinks?

Natural climate solutions have a key role to play in the race to net zero. It’s estimated that natural carbon sinks – environments which capture and store carbon – already absorb half of the human-produced carbon emissions which are driving the climate emergency.

As the World Economic Forum’s 2023 report on the Voluntary Carbon Market pointed out, oceans, forests and other natural carbon sinks are “some of the few solutions that are ready today for carbon removal”.

Put simply, a carbon sink is anything that absorbs more carbon than it produces, especially if it can store captured carbon indefinitely. They are no substitute for reducing our emissions, but they can offset some climate risks.

Carbon sinks come in a surprising variety of forms. But they all need to be protected if they are to continue to fulfil this vital function because, if they are damaged – as in the case of rainforests – their destruction releases their stored carbon back into the atmosphere.

Let’s take a look at some of the world’s biggest carbon sinks.

The United Nations describes the oceans as “not just ‘the lungs of the planet’ but also its largest carbon sink” providing a vital buffer against the impacts of climate change. As well as generating half the world’s oxygen, oceans also absorb 25% of all carbon emissions.

As temperatures rise, oceans also absorb 90% of the excess heat in the atmosphere which, combined with rising levels of CO2, is acidifying seawater, damaging sea life and ultimately reducing the role they can play in stabilizing the climate.

Trees take in and store carbon, but the amount of woodland on the Earth’s surface has declined since the start of this millennium. Data compiled by Global Forest Watch shows global tree cover shrank by an eighth between 2000 and 2022, releasing 195 billion tonnes of CO2.

NASA satellite data shows the world’s forests absorb 15.6 billion tonnes of CO2 a year, although wildfires and deforestation release almost half as much (8.1 billion tonnes) back into the atmosphere, highlighting the need to protect woodlands everywhere.

Scientists estimate Earth’s soils contain 2,500 billion tonnes of carbon – three times as much as the atmosphere and four times as much as plants and animals. Sustainable farming methods like crop rotation could boost that total by 1.85 billion tonnes each year.

Rocks, too, have a role to play. Carbon is naturally absorbed by certain types of rocks in a process known as carbon mineralization. Now scientists are working on ways to speed it up with the potential to remove 10 billion tonnes of atmospheric carbon a year by 2050.

Beneath our feet there’s a secret world of microscopic fungi whose role in fighting the climate crisis may have been seriously overlooked. Filament-like mycorrhizas live on plant roots extending their reach and extracting nutrients from the soil which they share with their hosts.

Scientists now believe they capture and store over a third of global carbon emissions every year. But the fungi need protection from modern farming methods. Experts say that phosphorus-based fertilizers stop them working, undermining their vital climate role.

Large mammals tend to be more associated with disrupting the plant kingdom than protecting it. But now scientists believe that even the largest play an important role in helping to fight the climate crisis by speeding up natural carbon capture.

Elephants, for example, not only inhibit wildfires by eating flammable vegetation, but by trampling plants underfoot they also help accelerate the process by which carbon in foliage is forced into the soil where it is much less likely to be released back into the atmosphere.