Even into early winter, when typically the ground was frozen 40 years ago, microbes in the permafrost are now continuing to release heat-trapping greenhouse gases. Carbon dioxide emissions are now outpacing the uptake of CO2 during the spring and summer growing season, the study suggests.
The researchers from Harvard, the National Oceanic and Atmospheric Administration, and other institutions measured atmospheric CO2 in Alaska and found that emissions from October through December have increased by 73 percent since 1975 and that the increase correlates with rising summer temperatures.
The findings suggest that global climate models are underestimating how much heat-trapping greenhouse gas pollution will be unleashed as the Arctic continues to warm at twice the global average rate, said lead author Roisin Commane of the Harvard School of Engineering and Applied Sciences.
The Arctic climate feedback loop is stronger than scientists estimated, Commane said. Global warming thaws permafrost, releasing more greenhouse gases, which causes yet more warming.
"It's consistent with the effects of a warming Arctic," she said. "We're seeing very large emissions in the early winter. When I looked at the models used by the IPCC [Intergovernmental Panel on Climate Change], none of them looked at the fall respiration. They didn't realize how important that is."
The study, published May 8 in the Proceedings of the National Academy of Sciences, adds critical emissions data for the autumn season, from October through December, after Arctic vegetation stops growing but before the ground freezes solid and locks up the carbon again.
Read more at Thawing Alaska Permafrost Sends Autumn CO2 Emissions Surging
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