The unexpectedly rapid collapse of ice-rich permafrost in the Arctic could pump billions of additional tons of methane and carbon dioxide into the atmosphere every year—a threat that has yet to be fully accounted for in climate models.  Scientists are discovering destabilized landscapes where permafrost that once thawed a few inches a year can now abruptly thaw up to 10 feet within days or weeks, creating wetlands in once frozen regions and accelerating emissions from up to 1,600 gigatons of carbon still locked underground.  – National Geographic, September 2019.