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FRESNO, Calif. -- Global warming from carbon dioxide
emissions may not be to blame for rising nighttime temperatures in
the San Joaquin Valley, according to a study funded by the National
John Christy, director of the Earth System Science Center at the
University of Alabama in Huntsville, said rising valley temperatures
may be caused by an overabundance of irrigated land that increases
humidity in the air.
Nighttime temperatures in the study's six-county region -- Fresno,
Kings, Madera, Mariposa, Merced and Tulare -- have risen more than
four degrees Fahrenheit over seven decades, said Christy, who is
leading the three-year study.
``One of the big issues right now is human-induced climate change
from carbon dioxide,'' Christy said. ``Actually, it appears
temperature change in the valley could be due to a different human
factor, and that is irrigation.''
California has more than eight million irrigated acres, some two
million of which are in the study's five-county region.
Christy's preliminary data conflicts with global warming theories
suggesting carbon dioxide is the cause of rising temperatures. His
data suggests increased humidity in the valley is preventing
nighttime air from cooling.
``The evidence shows that if this were a large scale climate
change caused by carbon dioxide, it would affect the valley, the
foothills and the mountains. But we have not seen these changes in
the higher elevations,'' Christy said.
Dave Kranz, a California Farm Bureau spokesman, questioned
``Is it irrigation that's adding to warming temperatures or is it
sunlight reflecting off all the paved roads that come with
urbanization?'' Kranz said.
He said Christy's theories seem somewhat flawed.
``The crops that are grown on irrigated land actually help clean
the air,'' Kranz said. ``For example, it's estimated that each acre
of rice in California scrubs about 23,000 pounds of carbon dioxide
from the atmosphere.''
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