http://www.eurekalert.org/pub_releases/2002-06/uoc--ncs060302.php
Contact: Tim Stephens
[log in to unmask]
831-459-4352
University of California - Santa Cruz

New climate study shows California's vulnerability to global warming
SANTA CRUZ, CA--Researchers at the University of California, Santa Cruz,
have produced a detailed picture of how California's climate is likely
to change within the next 50 to 100 years as a result of global warming.
Their study, complete with temperature and precipitation data for
different parts of the state, goes far beyond the usual speculation
about the potential impacts of climate change on the state.
Despite uncertainties in the climate models used to generate these
scenarios, they are valuable tools for planning, said Lisa Sloan, an
associate professor of Earth sciences at UCSC. The findings of Sloan and
her coauthors will be published online on June 7 by the journal
Geophysical Research Letters.

The study supports what many have already guessed--global warming will
mean warmer temperatures and smaller snowpacks in California, with
serious adverse effects on the state's water supply. But the study also
reveals more subtle details, and offers regional specificity and precise
numbers backed by a statistical analysis.

"Everybody has guessed at the effects on water resources, but now we
have numbers and locations. It's a lot different from the standard
arm-waving," Sloan said. "Our hope is that this kind of study will give
state and regional officials a more reliable basis for planning how to
cope with climate change."

Sloan's research group used a sophisticated computer model of the
regional climate system to look at the response of California's climate
to changing concentrations of carbon dioxide, the heat-trapping
"greenhouse gas" released by burning of fossil fuels. Sloan worked with
graduate students Mark Snyder, who is first author of the paper, and
Jason Bell, now a computer programmer in the Earth Sciences Department,
to develop a regional climate model centered over California. The
regional model offers much finer spatial resolution than larger models
used to study the global climate. Since the regional climate is driven
by global processes, the regional model was coupled with a global
climate model.

The researchers looked at the effects of doubling the amount of carbon
dioxide in the atmosphere compared to the preindustrial level. The
latest projections of carbon dioxide emissions indicate that the
atmospheric concentration will be twice the preindustrial level well
before the end of this century and possibly as soon as 2050.

With atmospheric carbon dioxide doubled, the California regional climate
model showed higher average temperatures every month of the year in
every part of the state. The extent of the warming varied, however, with
the greatest increases in temperature occurring at high elevations in
the Sierra Nevada and the Cascade Range. For example, the average
temperature in June in the Sierra Nevada increased by 11 degrees
Fahrenheit.

The model also showed rainfall increasing in northern California but
staying largely the same in southern California, while snow accumulation
in the mountains decreased dramatically. In March, for example, it
showed an additional 8 inches of rain falling in the central Sierra,
while the height of the snowpack at the end of March dropped by 13 feet.
By the end of April, the snowpack was almost completely gone.

"With less precipitation falling as snow and more as rain, plus higher
temperatures creating increased demand for water, the impacts on our
water storage system will be enormous," Sloan said.

Snyder said this report is only the first step in an ongoing effort to
understand the implications of climate change for California. The
results represent an "average" year, based on 15 years worth of data
generated by the model for each carbon dioxide concentration. Additional
studies will try to capture the natural variability of the climate and
how that variability may change in the future, he said.

"This opens the door for a lot more studies to look at regional climate
change in more detail, and to understand the variability that is likely
to occur," Snyder said. "It's important to consider not only the average
conditions but also what the extremes will be."

The researchers are also exploring refinements in the model that would
yield even higher spatial resolution. Already, the model provides more
detail than any previous study, showing how climate change is likely to
affect different parts of the state, such as the Coast Ranges, the
Central Valley, the Mojave Desert, and the Sierra Nevada.

All of the major features of the results were statistically significant,
Sloan said. She added, however, that the results are not predictions.

"The model gives us scenarios of what the future may look like," Sloan
said. "There are only two ways to tell how good the model is: One is to
wait for 50 years and see what happens, and the other is to model the
present day. We've done the latter quite rigorously and have satisfied
ourselves that the model does a good job of representing the present
climate. So our confidence in these scenarios is pretty good."


###
In addition to Sloan, Snyder, and Bell, the paper's authors include
Philip Duffy and Bala Govindasamy, both climate researchers at Lawrence
Livermore National Laboratory. Sloan's research is supported in part by
a fellowship from the David and Lucile Packard Foundation