Geoscience Reference
In-Depth Information
figu r e 32 . Annual mean atmospheric temperature (in degrees Fahrenheit) in the west-
ern United States from 1895 to 2010. (Figure courtesy of Kelly Redmond, Desert Research
Institute, Nevada.)
evaporation, placing more water as vapor in the atmosphere. Eventually, this
additional vapor condenses, resulting in increased precipitation. However,
the relationship between warmer temperatures and precipitation is not
straightforward. Climate models predict that some areas will experience net
losses in moisture because of increased evaporation whereas other areas may
experience net gains. Scientists are predicting that the already dry regions,
like the American West, will become even drier and that wet regions farther
north will become even wetter.
h ese predictions are increasingly supported by observation. For
example, climate models indicate that warming will cause a northward
shit of the Aleutian Low and the North Pacii c Storm Track, which will
intensify precipitation over the Pacii c Northwest, leaving the southerly
regions, including much of the American West, drier. Researchers at the
University of Arizona have observed that, since 1978, the storm track dur-
ing wintertime (February to April) has been shit ing northward, meaning
that fewer rain-bearing storms are reaching the southwestern states—that
is, Southern California, Arizona, Nevada, Utah, western Colorado, and
western New Mexico. h ese researchers believe the trend will continue
into the future if warming continues. Such shit s in the regional water
regime may seem subtle in and of themselves, but the impacts are anything
but subtle.
