The thick layer of permafrostunderneath the Alaska Highway is thawing, and with it goes the highway’s integrity. “It is really, really bumpy,” says Tanis Davey of the Yukon Research Center, where scientists study the effects of rising annual temperatures on permafrost. Permafrost is a layer of frozen soil or rock that sits under an estimated 20 percent of the world’s total land area. That includes stretches of the Alaska Highway—the only land route from Alaska to the continental U.S.— where the layer can be up to 65 feet thick. Geoscientists from the center have collected samples of permafrost (right) along the 1,390-mile-long highway for the past three summers to record how global warming is changing the ground and to predict where future damage may appear. Roadways with recurring damage from thawing permafrost cost about 10 times more than average roads to maintain, according to scientist Fabrice Calmels, who submitted this photograph to Scientific American.