Of the 37.4 billion tonnes of carbon dioxide we emitted into the atmosphere in 2024 from burning fossil fuels, about half was sequestered by the planet’s oceans, soils, forests and other natural processes. But evidence is suggesting a weakening of this service, some of which is related to heat—and 2024, was the hottest year ever recorded since we were a Homo species inhabiting Earth. Among other factors, photosynthesis—the process that plants use to convert atmospheric carbon dioxide into sugars and an oxygen byproduct—begins to slow when temperatures rise too high, until it stops at 45°C. Consequently, certain areas of the planet sequestered absolutely no CO2 in 2023.
“We’re seeing cracks in the resilience of Earth’s systems. We’re seeing massive cracks on land—terrestrial ecosystems are losing their carbon store and uptake capacity, but the oceans are also showing signs of instability,” says Johan Rockström, director of the Potsdam Institute for Climate Impact Research (“Are Earth’s Carbon Sinks Collapsing?” by Patrick Greenfield, The Guardian Weekly, October 25, 2024). “Nature has so far balanced our abuse. This is coming to an end.” Should this happen, we will be unable to meet any of our climate goals.
Climate models suggested that the rise in atmospheric CO2 would actually increase plant growth and aid carbon sequestration. This was the theory for a while, but this benefit is now being undone by the consequences of higher temperatures. Because of deforestation and agriculture, some southern portions of the Amazon have now become net emitters of carbon dioxide, and an unprecedented drought has slowed plant growth and impaired sequestration in its soils. Meanwhile, the expansion of agriculture in Southeast Asia has altered it from being a net store of carbon to a net emitter. This leaves the Congo basin as the major tropical area sequestering CO2.
The sequestration of carbon dioxide in soils, once the second highest store for carbon after the oceans, is being handicapped by heat and dehydration. Some soils are now net emitters. This is expected to increase by 40% by the end of the century as microbes break down soils more quickly.
And the boreal forests, stretching across Scandinavia, Russia, Canada and Alaska, are the location of almost a third of all the carbon sequestered on stored land. But they have lost about one-third of their absorbing capacity due to fire, beetle infestations and logging. Indeed, in 2022, the boreal fires in Canada emitted about as much carbon dioxide as six months of emissions from the United States. Russia’s forest fires made a similar contribution to global emissions. And Finland, which carefully monitors both its emissions and sequestration, discovered that its 43% reduction in anthropogenic carbon dioxide production was completely negated by the losses in its land sequestration.
The oceans have been the largest single absorbers of atmospheric carbon dioxide, but as they warm and acidify, they are also losing this sequestering capacity—not that we want acetic oceans. And, as ice sheets melt and ocean temperatures rise, we are impairing the migration of phytoplankton to the surface to feed on algae, so this transfer of millions of tonnes of carbon from the air to storage at the bottom of the ocean is now slowing.
Meanwhile, as carbon sequestration is being threatened, anthropogenic CO2 emissions continue to rise. Emissions were 36.3 billion tonnes in 2021, 36.8 billion tonnes in 2022, 37.15 billion tonnes in 2023 and, as previously noted, 37.4 billion tonnes in 2024. Past decades of attempted emission reductions have been futile. And the objective of keeping the rise in global temperature to below 1.5°C is now, by most scientific accounts, in “tatters”.
This alone is worrying enough, without the prospect of losing any of the natural carbon sinks that have been compensating for our failed efforts to keep down the level of atmospheric carbon dioxide. It is now at 426.91 parts per million as of February 28, 2025, compared to the 180 parts per million that we once had for climate stability.
Except for the few who are in a state of denial, the sobering reality is that most people know about the unfolding environmental disaster and have a sense of its seriousness, but are too immersed in the comfort of the moment to change their behaviour.
Ray Grigg for Sierra Quadra
Top image credit: Signs of drought in Morocco – Photo by Houssain tork (own work) via Wikimedia (CC BY-SA 4.0)
