Excerpts from Books and Wikipedia
"A 2011 U.S. Geological Survey study found that global warming was driving a snowpack loss in the Rocky Mountains unrivaled in 800 years, which in turn was threatening the region’s water supply. That study noted, 'Runoff from winter snowpack—layers of snow that accumulate at high altitude—accounts for 60 to 80% of the annual water supply for more than 70 million people living in the western United States.' A 2013 U.S. Geological Survey study found that 'Warmer spring temperatures since 1980 are causing an estimated 20% loss of snow cover across the Rocky Mountains of western North America.'” [Romm, p. 46]