Warming frees microbes to convert organic carbon from ancient plants into carbon dioxide. But the study, by U.S. Geological Survey researchers, reveals that much of this carbon is in complex forms that microbes consume only slowly. And permafrost often thaws into waterlogged mud that lacks the oxygen microbes need to process the carbon.
Even so, up to 100 billion tons of carbon could still escape by 2100. That’s equal to 20 percent of all the carbon released from burning fossil fuels in the past 200 years.