A new Yale University-led study suggests that climate warming will drive the loss of at least 55 trillion kilograms of carbon from the soil by mid-century, adding a further 17% to the projected emissions due to human-related activities during that period. That would be roughly the equivalent of adding to the planet another industrialized country the size of the United States.

Significantly, the researchers found that carbon losses will be greatest in the world’s colder places, at high latitudes, locations that have largely been missing from previous research on this issue. In those regions, massive carbon stocks have built up over thousands of years, and slow microbial activity has kept them relatively secure.

Carbon stores are greatest in places where the soil is cold and often frozen. Image credit: Pixabay.According to the researchers, most prior research has been conducted in the world’s temperate regions, where there are smaller carbon stocks. Studies that focused only on these regions would have missed the vast proportion of potential carbon losses, says lead author Thomas Crowther, who carried out his research while a postdoctoral fellow at the Yale School of Forestry and Environmental Studies and at the Netherlands Institute of Ecology.

“Carbon stores are greatest in places like the Arctic and the sub-Arctic, where the soil is cold and often frozen. In those conditions, microbes are less active and so carbon has been allowed to build up over many centuries," Crowther says. "But as you start to warm, the activities of those microbes increase, and that’s when the losses start to happen. The scary thing is, these cold regions are the places that are expected to warm the most under climate change.”

The study's conclusions are based on an analysis of raw data on stored soil carbon from dozens of studies conducted over the past 20 years in different regions of the world. It predicts that for one degree of warming, about 30 petagrams of soil carbon will be released into the atmosphere, or about twice as much as is emitted annually due to human-related activities (a petagram is equal to 1 trillion kilograms). This is particularly concerning, Crowther says, because previous climate studies predicted that the planet is likely to warm by 2 degrees Celsius by mid-century.

The study considered only soil carbon losses in response to warming. There are several other biological processes—such as accelerated plant growth as a result of carbon dioxide increases—that could dampen or enhance the effect of this soil carbon feedback. Understanding these interacting processes at a global scale is critical to understanding climate change, according to the researchers.