San Diego, California
February 1, 2008
Computer model analyses trace
hydrological trends to human causes with unprecedented
robustness
A new analysis led by researchers at
Scripps Institution of
Oceanography at UC San Diego
shows that climate change from human activity is already
disrupting water supplies in the western United States.
Trends in snowpack, river runoff and air temperatures - three
fundamental indicators of the status of the West's hydrological
cycle - point to a decline in the region's most valuable natural
resource, water, as population and demand grows in the West.
Details of the analysis appear in "Human-induced changes in the
hydrology of the western United States" in today's issue of
Science Express, the online edition of the journal
Science.
The study focused on the western United States because of its
large and growing population in a generally dry region where
battles over water are becoming increasingly common. The
researchers report that the declines in snowpack, warming air
temperatures and earlier spring river runoff that are already
seen in the region are well explained by climate impacts
expected from greenhouse gas and aerosol emissions from human
activities.
The team also notes that the demonstrated accuracy of the
computer models used in this analysis of the current situation
bolsters the credibility of their predictions of future climate
trends. These results show climate change is already affecting
water supplies, a limited natural resource in the western U.S.,
and the region is facing a looming climate crisis.
The team, which included researchers from Scripps Oceanography,
Lawrence Livermore National Laboratory, University of
Washington, the National Institute for Environmental Studies in
Japan and the San Diego Supercomputer Center (SDSC), relied on
multiple computer models and intensive data analysis. The
scientists found that observed hydroclimatic changes differ in
length and strength from trends that would be expected from
natural variability, changes in solar activity or large-scale
precipitation changes.
The observed changes, however, do correspond to those expected
from the impacts of human activity on the climate system.
Lead researcher Tim Barnett, a research marine physicist at
Scripps, said the analysis is unprecedented in its
sophistication and novelty of approach.
"We couldn't shake the results," he said. "We got the same
answer no matter what analysis techniques or datasets we used."
Team members said that the specific focus of the analysis on the
real-life issues affecting one region is also new. The climate
models were chosen based on their realistic portrayals of
observed global climate and of region-specific climate phenomena
such as the Pacific Decadal Oscillation, an oceanic pattern that
has a strong bearing on the climate of the western United
States. Several of the member institutions took part in the
analysis while SDSC team members helped manage the more than 20
terabytes of data incorporated by the climate models.
The accuracy of the representation of past climate trends and
their cause suggests that the same models are a reliable
predictor of future conditions in the West. These models have
forecast a serious water supply problem for those dependent on
the Colorado River drainage and substantial alterations to the
hydrology of the Sacramento River delta, home to many sensitive
ecosystems and economically important wildlife.
The models "portend a crisis," said Barnett. "After the
performance on the last 50 years of observations, we can put
high confidence in their general predictions for the next 20
years, at least in the western United States. |
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