In a warmer world, many researchers are concerned that soils will become a “carbon bomb,” accelerating climate change. While previous research suggests the richest soils would be most easily triggered, a new, global compilation of climate change studies suggests the soil’s future relationship with climate is more complex.
Carbon in the atmosphere, mostly in the form of carbon dioxide, traps heat and warms the Earth. Compared to the atmosphere, soils hold a vast reservoir of carbon; about four times as much. If soils lose this carbon to the atmosphere in the form of carbon dioxide or methane, another heat-trapping gas, then the pace of climate change will quicken.
Scientists around the globe have studied the fate of soil carbon in a warming world by heating up soils in field experiments and using mathematical equations to describe what happens to the carbon. Recently, a highly publicized study analyzed data from experiments warming soils in many locations around the world and concluded the soils that contain the most carbon also lose their carbon most easily when they become warmer.
However, a more exhaustive study, published today (Feb. 22) in the scientific journal Nature, shows the answer is not that simple.
“We had access to a larger data set than was used in the original paper, and we were concerned the original paper’s conclusions relied heavily on just a few experiments that had carbon-rich soils,” said Natasja van Gestel, lead author of the study and a research assistant professor in the Texas Tech University Climate Science Center and Department of Biological Sciences. “We had access to more data points from a wide range of soils, so we could do a more powerful and balanced analysis. For a global analysis like this, having more data is always better.”
With the larger data set, scientists concluded soil carbon responses were not easily predicted, either from soil carbon stocks or from other variables that were examined.
“Our study doesn’t change the fact that some soils lose carbon in warmer conditions,” van Gestel said. “However, our larger data set showed that the relationship between soil carbon and warming is complicated – it varies from place to place and is likely dependent on not one, but several variables.”
Scientists from both the original paper and the new analysis agree this relationship will be better understood once information is available from parts of the world that currently have no warming experiments and from deeper soil layers, such as the permafrost layers in the arctic. Both studies focused only on the upper soil layers, but there is a lot of soil carbon at lower depths that has not been examined.
The researchers leading the two projects are now banding together to address remaining unknowns.
“I hope by pointing out these important, unsolved problems, our work will inspire other researchers to get together to work on this,” van Gestel said. “It is important that we find out what makes the carbon in soil sensitive to warming, because if certain conditions are ripe for a carbon ‘bomb’ situation, we want to know what these conditions are.”