Rising temperatures could release more carbon from soil than previously thought

Canadian Arctic Tundra

The rates of CO2 loss from soils as global temperatures rise may be greater than has been predicted, according to research involving scientists from Heriot-Watt University.

Because soils store more than twice as much carbon as is in the atmosphere, changes in rates of decomposition and CO2 release are very important. In a paper published in Nature, and based on research at sites ranging from the Arctic to Peru, via Scotland, the authors argue that the response of soil microbial communities to changes in temperature increases the potential for more carbon dioxide (CO2) to be released from the world's soils to the atmosphere as global temperatures rise.

It is well known that the rate of loss of carbon from soils increases as soil becomes warmer, but until now it has been argued that this increase may be kept in check by internal biochemical systems in the soil microorganisms responsible for decomposition. The researchers found that, contrary to this expectation, the decomposers in most cases do not control their respiration rates as temperature increases.

..if not counterbalanced by other processes in the Earth System, (this) could have far-reaching consequences; it's a classic form of 'positive feedback' to further change.

Philip Wookey, Professor of Ecosystem Science at Heriot-Watt University

The findings suggest that warming will increase the activity of soil microbes to a greater extent than was previously expected, which could have implications for future rates of climate change. The study included many soils from around the world from different ecosystems and land uses and the only major exception to the findings was intensively-managed agricultural soils. These were the only soils in which the microbial responses were 'checked' as temperatures increased. On the other hand, the greatest stimulating effects of temperature were observed in the soils with the greatest carbon contents and from the regions of the world which are warming most rapidly; boreal and arctic ecosystems. This indicates that the responses we observed could increase the vulnerability of some of the world's most important soil carbon stocks to climate change.

Philip Wookey, Professor of Ecosystem Science at Heriot-Watt University and a co-author of the paper, warned, "The responsiveness of cold, carbon-rich soils, to warming is a particular concern: although this study did not extend to the permafrost regions of the world, in these soils alone there are carbon stocks equivalent to nearly 250 years' worth of current annual emissions of CO2 to the atmosphere from fossil fuel combustion. Any warming-induced conversion of soil carbon into carbon dioxide or methane in the atmosphere, if not counterbalanced by other processes in the Earth System, could have far-reaching consequences; it's a classic form of 'positive feedback' to further change."

The research was led at the University of Exeter, with collaborators at Heriot-Watt, the University of Aberdeen, the University of Edinburgh, University of Stirling, Rothamsted Research and collaborators in continental Europe, Australia and South America. The research was supported primarily by the UK Natural Environment Research Council.