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When I was in Chersky, Zimov took me out to the lake. We walked through shrubs and felt the crunch of bright-red cloudberries under our feet. At the water’s edge, Zimov asked, “You see the bubbles?” Once I knew to look for them, they were impossible to miss. It was as if the lake were a giant cauldron on the brink of a very slow, barely perceptible boil, with a pop of air here and there. Methane.
Zimov explained that, even during Chersky’s frigid winters, temperatures under the lake’s surface remain above freezing. Unfrozen water allows microbes to keep digesting organic matter long after the surrounding landscape is covered in snow. Water also has a powerful erosion effect. “The bank is slowly thawing and collapsing, taking with it fresh pieces of permafrost into the lake,” Zimov said—more fuel for the release of methane. As Walter Anthony, who is now a professor at the University of Alaska Fairbanks, put it to me, “Once permafrost thaws to the point where it creates depressions filled with water, the thaw starts to go deep and fast and expands laterally—you can’t really stop it.”
The mean annual temperature in Chersky has risen by three degrees Celsius in the past fifty years. An equally pressing problem is snow cover. “Snow is like a warm blanket—it doesn’t allow the wintertime cold to penetrate all the way into soil,” Zimov said. One of the effects of climate change is more precipitation in the Arctic ecosystem around Chersky. Yearly snowfall has increased by as much as twenty centimetres since the early eighties, adding two more degrees of warming effect. As a result, Zimov explained, permafrost that used to be minus seven degrees Celsius is now on the verge of thawing, if it hasn’t already.
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