Greenwire: Dust storms accelerated by a warming climate have covered the Rocky Mountains with dirt whose heat-trapping properties have caused snowpacks to melt weeks earlier than normal, worrying officials in Colorado about drastic water shortages by late summer. Snowpacks from the San Juan Mountains to the Front Range have either completely melted or will be gone within the next two weeks, said Tom Painter, director of the Snow Optics Laboratory at the University of Utah and a leading expert on …