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March 28, 2007
GOLDEN STATE HEATING UP, NEW NASA/UNIVERSITY STUDY FINDS
Average temperatures
in California rose
almost one degree Celsius
(nearly two degrees Fahrenheit) during the second half of the 20th
century,
with urban areas blazing the way to warmer conditions, according to a
new study
by scientists at NASA and California
State University,
Los
Angeles.
Bill Patzert of NASA's Jet Propulsion Laboratory, Pasadena,
Calif., teamed with
Steve LaDochy of California
State
University,
Los Angeles, and
Richard Medina, now a doctoral candidate at the University of Utah,
Salt Lake City, to
investigate California
air temperature patterns from
1950 to 2000. They analyzed data from more than 330 state weather
stations,
looking for patterns of climate warming and cooling in each of the
state's
seven major climatic subregions. Their objective was to shed new
insights into
the relative roles humans and natural climate events play in affecting California
regional
temperatures.
The scientists found great variations in temperature patterns
throughout the
state. Average temperatures increased significantly in nearly 54
percent of the
stations studied, with human-produced changes in land use seen as the
most
likely cause. The largest temperature increases were seen in the
state's urban
areas, led by Southern California and the San Francisco Bay
area, particularly for minimum temperatures. Minimum temperatures at
some
agricultural sites showed increases comparable to some urban areas.
Rural,
non-agricultural regions warmed the least. The Central
Valley warmed slowest, while coastal areas warmed
faster, and the
southeast desert warmed fastest.
The only area to cool was a narrow band of the state's mainly rural
northeast
interior. While few stations overall showed decreases in average and
minimum
temperatures, 13 percent of the stations for which sufficient maximum
temperature data were available showed a significant drop in average
maximum
temperatures, including some urban sites.
Across most of the state, minimum (nighttime) temperatures increased
more than
average and more than maximum (daytime) temperatures did. Fifty-five
percent of
the weather stations tested for minimum average temperatures saw
significant
warming, while only six percent saw significant cooling. For example,
minimum temperatures
at the Los
Angeles Civic
Center
have increased by about five degrees Celsius (9 degrees Fahrenheit)
since 1878.
During that same time, maximum temperatures increased by only about 2
degrees
Celsius (3.6 degrees Fahrenheit).
Patzert said the increased rate of minimum temperatures has led to
narrower
daily temperature ranges throughout the state. "California
nights are heating up, giving us
a jump start on hotter days," said Patzert. "This is primarily due to
increased urbanization, not increases in cloudiness or precipitation.
Rainfall
and snowfall didn't increase significantly for most California
stations during the study period."
"California's
complex topography and
large latitude range give it some of the most diverse microclimates in North America," said LaDochy.
"Climate change
models and assessments often assume global warming's influence here
would be
uniform. That is not the case. If we assume global warming affects all
regions
of the state, then the small increases our study found in rural
stations can be
an estimate of this general warming over land. Larger increases would
therefore
be due to local or regional changes in land surface use due to human
activities."
The researchers cited numerous factors contributing to California's
temperature trends, including urbanization, population, Pacific Ocean conditions and
elevation. They found a strong correlation
between air temperatures and Pacific coastal sea surface temperatures.
The
Pacific temperatures warmed 0.09 degrees Celsius (0.16 degrees
Fahrenheit) per
decade during the study, about half the amount the state warmed overall
during
that time.
Patzert said air temperatures were significantly influenced by
fluctuations in
the Pacific Decadal Oscillation, a basin-wide oceanic pattern similar
to El
Niño and La Niña but much larger, lasting many
decades rather than just a few
months. "During the positive, warm phase of the oscillation, from about
1977 to 1997, average air temperatures were higher," he said. "During
the negative, cold phase, from 1950 to 1976, they were lower." Patzert
and
other scientists track Pacific Ocean
patterns
using NASA's Jason satellite altimeter.
Results of the study appeared in the journal Climate Research.
For
more information and images,
visit:
http://www.jpl.nasa.gov/news/news.cfm?release=2007-035
Jason
satellite:
http://sealevel.jpl.nasa.gov/
##
Contact:
Alan Buis
NASA Jet Propulsion Laboratory
818-354-0474
This text is
derived from:
http://www.jpl.nasa.gov/news/news.cfm?release=2007-035
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