Vast quantities of carbon—twice the size of the current amount in the atmosphere—are stored in frozen permafrost soils in Arctic regions. The Arctic climate is warming much more rapidly than the global average, leaving these carbon pools highly vulnerable to release into the atmosphere as carbon dioxide and methane as soils thaw and decompose, leading to a feedback cycle of further warming and increasing carbon release. The potential for these carbon stocks to increase global-warming rates, and the rapid changes already observed in the permafrost region, have captured the attention of scientists and policymakers. Scientists funded by several USGCRP agencies are working to quantify emissions from permafrost carbon, using observations and modeling to reduce uncertainties surrounding future carbon release. The Permafrost Carbon Network (PCN), with participation from USGCRP agencies and multiple countries, is working to evaluate the state of models that represent permafrost-carbon dynamics, and identify common approaches for improving model skill.
Underlying many of the uncertainties surrounding permafrost carbon release is the need to better integrate observations into models. By synthesizing observational data and model outputs from multiple sources, recent PCN activities have found that permafrost-carbon feedbacks to global warming are likely to be strong but relatively slow, operating on timescales of about a century or longer, and that carbon stocks are unlikely to be released abruptly. Permafrost carbon release is likely to be roughly linear with warming, with a feedback magnitude of about one third of the total estimated global carbon-climate feedback. However, uncertainty surrounding key processes that control the feedback from permafrost is high, particularly with regard to changes in the water cycle and soil moisture conditions. Further critical uncertainties include the decomposition dynamics of thawed permafrost soils, and how vegetation response to changing soil conditions affects the stability of carbon stocks.
Across USGCRP agencies, many activities focus on translating understanding derived from observations into climate models. Together, the DOE-led Next-Generation Ecosystem Experiments in the Arctic (Highlight 26), NASA’s Arctic-Boreal Vulnerability Experiment (Appendix III. Observations to Support Global-Change Research), and complementary activities from other agencies are helping advance understanding of permafrost response to warming, and its implications for regional and global climate change.