Potential feedback of thawing permafrost to the global climate system through methaneemission

Abstract

Large amounts of soil carbon deposited in permafrost may be released due to deeperseasonal thawing under the climatic conditions projected for the future. An increase in thevolume of the available organic material together with the higher ground temperatures maylead to enhanced emission of greenhouse gasses. Particular concerns are associated withmethane, which has a much stronger greenhouse effect than an equal amount ofCO2. Production of methane is favored in the wetlands, which occupy up to0.7 million km2 in Russian permafrost regions and have accumulated about 50 Gt of carbon (Gt C). We usedthe permafrost model and several climatic scenarios to construct projections of the soiltemperature and the depth of seasonal thawing. To evaluate the effect of such changes onthe volume of the seasonally thawing organic material, we overlaid the permafrostprojections on the digitized geographically referenced contours of 59 846 wetlands in theRussian Arctic. Results for the mid-21st century climate indicated up to 50% increase inthe volume of organic substrate in the northernmost locations along the Arctic coast and inEast Siberia, where wetlands are sparse, and a relatively small increase by 10%–15% inWest Siberia, where wetlands occupy 50%–80% of the land. We developed a soil carbonmodel and used it to estimate the changes in the methane fluxes due to highersoil temperature and increased substrate availability. According to our results,by mid-21st century the annual net flux of methane from Russian permafrostregions may increase by 6–8 Mt, depending on climatic scenario. If other sinks andsources of methane remain unchanged, this may increase the overall content ofmethane in the atmosphere by approximately 100 Mt, or 0.04 ppm, and lead to0.012 °C global temperature rise.