A new study has some reassuring news about how fast Greenland\'s glaciers are melting away. Greenland\'s glaciers hold enough water to raise sea level by 20 feet, and they are melting as the planet warms, so there\'s a lot at stake. A few years ago, the Jakobshavn glacier in Greenland really caught people\'s attention. In short order, this slow-moving stream of ice suddenly doubled its speed. It started dumping a whole lot more ice into the Atlantic. Other glaciers also sped up. \"Some people feared if they could double their speed over two or three years, they could keep doubling and doubling and doubling and reach very fast speeds,\" says Ian Joughin of the University of Washington\'s Polar Ice Center. If the world\'s big glaciers were on their way to a 10-fold speedup, that could lead to a staggering 6 feet of sea level rise by the end of this century. So Joughin and colleagues have been trying to see if that acceleration is under way. They pored over radar images of 200 Greenland glaciers gathered over the past decade. Graduate student Twila Moon says some of Greenland\'s glaciers picked up the pace and started surging forward more than 5 miles in a year.