The Greenland Ice Sheet saw a sharp spike in the rate and extent of melting last week, with 18 billion tons of water running into the North Atlantic in just three days. Satellite photos reveal melt ponds dotting the ice cover, particularly near the coasts.
Why it matters: Greenland's melting ice is the top annual contributor to global sea level rise. How much of and how quickly the ice sheet is lost will determine the fate of coastal cities from Hong Kong to Miami.
