Reuters: A meltdown of West Antarctica’s ice sheet would raise sea levels by half as much as previously expected, but the impact would still be catastrophic, especially for U.S. coastal cities, a study showed. A collapse of the ice sheet, viewed by scientists as more vulnerable than Greenland or East Antarctica because of global warming, would push up world sea levels by 3.3 meters (11 ft) over hundreds of years rather than 5-6 as long estimated. “The long-term impact of West Antarctica …