Geoscience Reference
In-Depth Information
water and power for 30 million people in Los Angeles, Phoenix, Tucson, and
Las Vegas.
human-caused or natural climate change?
Climate researcher Tim Barnett and his colleagues have analyzed the cli-
mate and hydrology of the American West over the past sixty years, particu-
larly river l ow data from the Columbia River, Colorado River, Sacramento
R iver, and San Joaquin R iver, draining watersheds in the Cascades, northern
Rockies, and Sierra Nevada across nine western states. At er the research
team demonstrated that their global climate model could realistically portray
the natural climate in the West, they then ran climate simulations of the
West to predict changes in snowpack and river l ows.
Using these data and some very long (greater than 800-year) simulations
of natural variations (without the human-caused greenhouse gas additions)
of climate and river l ows from the models, Barnett and his team showed
that changes in temperature and snowpack over the last half of the twentieth
century were not simply the result of the natural, long-term climatic shit s
of the Pacii c Decadal Oscillation (PDO). Although the PDO moved to a
warmer phase in 1976-77, which was consistent with warmer temperatures
and earlier spring snowmelt in the West, it then swung back to a cool phase
starting in 1999. Yet this phase shit did not reverse the trends of increasing
temperatures and earlier snowmelt. h e researchers also showed that volcanic
eruptions and solar activity occurring over the past several decades could
not have been responsible for changes in snowpack and temperature—in
fact, such events would have caused an opposite response: a decrease in
temperature and an increase in snowpack. h eir conclusion was that only
anthropogenic increases in greenhouse gases—that is, human causes—could
account for the rising temperature and diminishing snowpack trends they
were seeing.
h e days of water “on demand” will surely end in the West, replaced by des-
perate ef orts to capture and control what water is let . h e Southwest will
become a region of extremes as the early spring brings massive l ooding and
the relentless summer bakes the region dry. While climate scientists have
presented the potential risks facing our society, environmental scientists and
