Oceans, forests and other ecosystems continue to soak up 50% of the carbon emitted by human activities, despite those emissions increasing, according to new research.
The new study, published in Nature, analysed 50 years of global carbon dioxide.
“Earth is taking up twice as much CO2 today as it was 50 years ago,” said Ashley Ballantyne, lead author of the report from Colorado University.
Scientists try to better understand how the earth's forests, oceans and ecosystems absorb carbon emitted by human activities
The researchers found that the processes by which the planet’s ecosystems and oceans absorb greenhouse gases are not yet at capacity, despite recent studies predicting the earth’s ‘natural sinks’ were no longer keeping pace with the rate of emissions.
“Globally these carbon sinks have roughly kept pace with emissions from human activities, continuing to draw about half of the emitted CO2 back out of the atmosphere,” said Pieter Tans, co-author of the study from the National Oceanic and Atmospheric Administration.
“However we do not expect this to continue indefinitely,” he added.
Carbon dioxide is released into the atmosphere mainly by fossil fuel combustion but also forest fires and some other natural processes.
Some of this is then pulled back out of atmosphere into the tissues of growing plants or absorbed in ocean waters.
If these ecosystems were unable to keep up with the amount of carbon being released by human activity and more were to remain in the atmosphere the faster-than-expected rise could see climate change accelerate.
The researchers say this new study highlights how much there is still to know about how the process of carbon absorption takes place.
A recent study, for example, predicted that as much as 40% of emissions absorbed into the oceans could happen in the Southern Ocean. Similar disparities could potentially be found amongst different tree species growing in different regions of the world.
“Since we do not know why or where this process is happening, we cannot count on it,” Tans said. “We need to identify what’s going on here, so that we can improve our projections of future CO2 levels and how climate change will progress in the future.”
In the oceans, for example, Tans says scientists predict that rising acidity levels – a negative impact of their role absorbing carbon – will make it increasingly difficult for them to absorb more CO2.
“The uptake of carbon dioxide by the oceans and by ecosystems is expected to slow down gradually,” he says. “We just don’t see a let-up, globally, yet.”