New research led by the University of Exeter and Stockholm University has found that global warming is reducing the capacity of soil to store carbon. This causes more carbon to be released into the atmosphere, further accelerating climate change.
By studying data on over 9,000 soil samples from around the globe, collected in the World Soil Information database, the scientists found that carbon storage declines strongly as average temperatures increase: for every 10°C of increase in temperature, average carbon storage across all soils fell by over 25 percent.
“Because there is more carbon stored in soils than there is in the atmosphere and all the trees on the planet combined, releasing even a small percentage could have a significant impact on our climate,” said study lead author Iain Hartley, a professor of Terrestrial Ecosystem Science at the University of Exeter.
“Even bleak forecasts do not anticipate this level of warming, but we used this scale to give us confidence that the effects we observed were caused by temperature rather than other variables.”
Professor Hartley and his colleagues also discovered that the amount of carbon that could be released depends on the soil type, with coarse-textured, low-clay soils losing three times more carbon than fine-textured, clay-rich soils.
“Our analysis identified the carbon stores in coarse-textured soils at high-latitudes (far from the Equator) as likely to be the most vulnerable to climate change,” explained Professor Hartley. “Such stores, therefore, may require particular attention given the high rates of warming taking place in cooler regions. In contrast, we found carbon stores in fine-textured soils in tropical areas to be less vulnerable to climate warming.”
According to the researchers, this happens because finer soils offer more mineral surface area for carbon-based organic material to bond to, and thus reduces the ability of microorganisms to access and decompose it.
These findings will help identifying vulnerable carbon stocks and provide opportunities to improve Earth System Models that predict future climate change. “There is an opportunity to use the patterns we have observed to improve how models represent soils, and further reduce uncertainty in their projections,” Professor Hartley concluded.
The study is published in the journal Nature Communications.