Scientists sometimes refer to the effect a hotter world will have on this
country’s fresh water as the other water problem, because global warming more
commonly evokes the specter of rising oceans submerging our great coastal
cities. By comparison, the steady decrease in mountain snowpack — the loss of
the deep accumulation of high-altitude winter snow that melts each spring to
provide the American West with most of its water — seems to be a more modest
worry. But not all researchers agree with this ranking of dangers. Last May, for
instance, Steven Chu, a Nobel laureate and the director of the Lawrence Berkeley
National Laboratory, one of the United States government’s pre-eminent research
facilities, remarked that diminished supplies of fresh water might prove a far
more serious problem than slowly rising seas. When I met with Chu last summer in
Berkeley, the snowpack in the Sierra Nevada, which provides most of the water
for Northern California, was at its lowest level in 20 years. Chu noted that
even the most optimistic climate models for the second half of this century
suggest that 30 to 70 percent of the snowpack will disappear. “There’s a
two-thirds chance there will be a disaster,” Chu ...