In the far north, buried soil known as "permafrost" used to stay frozen year round. But in the past few decades, the Arctic has been warming more quickly than the rest of the planet. Scientists are working to explain why the thaw is outpacing even their worst-case predictions.

The mystery is urgent—melting permafrost releases carbon dioxide and methane, gases that accelerate the pace of global warming. U-M researchers track the movement of heat energy from the Sun to air, water, and soil, and note the northward creep of the tree line.