To determine how these processes affect the balance of carbon dioxide and methane in high-latitude soils, the scientists ran four simulations from 1860 to 2100, each with a different assortment of processes. They added in a middle-of-the-road climate change scenario that caused high-latitude surface soil to rise 8 degrees Celsius by 2100, which is much greater than the global average.
The simulations revealed a climate-induced loss of between 25 and 85 petagrams of carbon, depending on the processes included. The best estimate is from a simulation that includes all of the permafrost soil processes. It found that 62 petagrams of soil carbon will be released into the atmosphere by 2100, or about 68 billion U.S. tons. This release of carbon is equivalent to an additional 7.5 years of global anthropogenic emissions at today’s rate.
The simulation also found only a slight increase in methane release, which is contrary to previous predictions.
“People have this idea that permafrost thaw will release methane,” says Koven. “But whether carbon comes out as carbon dioxide or methane is dependent on hydrology and other fine-scale processes that models have a poor ability to resolve. It’s possible that warming at high latitudes leads to drying in many regions, and thus less methane emissions, and in fact this is what we found.”
Koven adds that there are large uncertainties in the model that need to be addressed, such as the role of nitrogen feedbacks, which affect plant growth. And he says that more research is needed to better understand the processes that cause carbon to be released in permanently frozen, seasonally frozen, and thawed soil layers. Researchers in Berkeley Lab’s Earth Sciences Division are focusing on improving global climate model representations of these processes under two Department of Energy-funded projects.
The research was supported by the Department of Energy’s Office of Science and project Impact-Boreal, which is funded by France’s Agence Nationale pour la Recherche and the European Union project COMBINE.
Details of the Study:
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The Lawrence Berkeley National Laboratory (Berkeley Lab) addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 12 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.
Source: Lawrence Berkeley National Laboratory (Berkeley Lab).
