The storage potential of one of the Earth’s biggest carbon sinks – soils – may have been overestimated, research shows. This could mean ecosystems on land soaking up less of humanity’s emissions than expected, and more rapid global heating.
Soils and the plants that grow in them absorb about a third of the carbon emissions that drive the climate crisis, partly limiting the impact of fossil-fuel burning. Rising carbon dioxide levels in the atmosphere can increase plant growth and, until now, it was assumed carbon storage in soils would increase too.
But the study, based on over 100 experiments, found the opposite. When plant growth increases, soil carbon does not. The finding is significant because the amount of organic carbon stored in soils is about three times that in living plants and double that in the atmosphere. Soils can also store carbon for centuries, whereas plants and trees rot quickly after they die.
It is not yet known how big the effect of lower carbon storage in soils might be on the speed of climate change, and experts cautioned that other impacts of the climate emergency such as drought would also affect how well plants and soils store carbon.
“We found that when rising CO2 increases plant growth, there is a decrease in soil carbon storage. That’s a very important conclusion,” said Cesar Terrer, who led the research while at Stanford University in the US. He said that if soils do absorb less in future, “the speed of global warming could be higher”.
Terrier said soils, plants and trees were important for carbon levels, but that ending the burning of fossil fuels remains essential. “If we really want to stop global warming, we need to stop emissions, because ecosystems only take up a fraction of all the CO2 emissions,” he said.