There’s an Arctic lake in northern Alaska that bubbles and hisses and never freezes. Scientist Katey Walter Anthony has discovered the reason for the lake’s weird behavior: methane. Rising temperatures are thawing the permafrost and making holes in the bottom of the lake. Methane comes up through the holes. Scientists worry that this will start a feedback loop. The melting permafrost is releasing carbon dioxide into the air. Add large quantities of methane, another powerful greenhouse gas, and temperatures will climb even higher. This will lead to more thawing and more greenhouse gases.