DATE: May 8, 2017
Over a large area, we’re seeing a substantial increase in the amount of CO2 that’s coming out in the fall. We all knew this was coming, but I’m surprised that we can even see it now.
— Roisin Commane, Harvard atmospheric scientist, lead author of the study
A new study, published in the Proceedings of the National Academy of Sciences, suggests that frozen northern soils — often called permafrost — are unleashing an increasing amount of carbon dioxide into the air as they thaw in summer or subsequently fail to refreeze as they once did, particularly in late fall and early winter.
The study, based on aircraft measurements of carbon dioxide and methane and tower measurements from Barrow, Alaska, found that from 2012 through 2014, the state emitted the equivalent of 220 million tons of carbon dioxide gas into the atmosphere from biological sources (the figure excludes fossil fuel burning and wildfires). That’s an amount comparable to all the emissions from the U.S. commercial sector in a single year.
The chief reason for the greater CO2 release was that as Alaska has warmed up, emissions from once frozen tundra in winter are increasing — presumably because the ground is not refreezing as quickly.
The new study is “the first to show that a large region of the Arctic is a carbon source and that this change is driven by increased carbon emissions during the winter,” said Sue Natali, a permafrost researcher with the Woods Hole Research Center, who was not involved in the study. “Because the models aren’t capturing these cold-season processes, we’re very likely underestimating carbon losses from the Arctic under current and future climate scenarios.”
The fears about permafrost carbon losses are based on some simple chemistry. Unlike at warmer latitudes, where microorganisms in the soil constantly break down plant matter and return the carbon it contains to the atmosphere, Arctic soils have been cold enough to preserve the frozen remains of ancient plant life. But as the planet warms, soil microbes become able to break down more and more of this carbon, sending it back into the atmosphere and worsening global warming in a troubling feedback loop.
Some scientists, however, held out hope that there would be a key offsetting process: As the Arctic warms, it might also stow away more carbon as it becomes greener and supports the additional plant life, particularly in tundra regions. This “Arctic greening” is indeed occurring, but the new research suggests that the permafrost losses in early winter are more than enough to offset that.