To an untrained eye, the crystal waters of the Clinch River, which meanders southwest across the Virginia-Tennessee border, look clean and healthy. But Jordan Richard can spot the dead bodies within seconds. On a crisp fall morning on Sycamore Island, just before the Clinch crosses into Tennessee, Richard bends over to pluck a palm-size brown…

In the thick of a Greenland summer of field work in 2015, Benjamin Hmiel and his team drilled into the massive ice sheet’s frozen innards, periodically hauling up a motorcycle-engine-sized chunk of crystalline ice. The ice held part of the answer to a question that had vexed scientists for years: How much of the methane…