Climate Central: On a clear day, anyone flying over Greenland on the route between North America and Europe can look down and see the bright blue patches of melted water atop the flat, blindingly white expanse of the ice sheet that covers the island, the second largest chunk of ice on Earth.
Scientists have long known this meltwater flows in streams along the ice sheet's surface before disappearing down chutes that take it tumbling to the bottom of the ice sheet, where the ice scrapes against bedrock.
It was...