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Sunday, January 04, 2009
Drier Climate on the Way for Southwest
By John Fleck
Journal Staff Writer
Climate change is increasing the chances of severe and persistent drought in the Southwest, according to a new report from a panel of federal scientists.
"It's going to get drier," said Richard Seager, a climate researcher at Columbia University in New York.
That means diminished water supplies, Seager said.
It is possible that greenhouse-induced drying may have already begun, though the evidence is unclear, according to Seager, one of the report's authors. "We can't tell yet," Seager said in a telephone interview.
The report, from the U.S. Geological Survey, is one in a series produced by the U.S. Climate Change Science Program. The program brings together teams of scientists to give government decision-makers their assessment of the latest science related to the way Earth's climate is changing.
There is broad scientific agreement that human emissions of carbon dioxide from burning coal and oil are changing Earth's climate. While an overall planetary warming, often called "global warming," is the most notable effect, scientists say regional effects — such as drought in the Southwest — are likely to have the greatest effect on society.
In addition to the problems of drought in the Southwest, according to the report, other problems faced by the United States could include:
• Increased emissions of methane in the arctic. The methane, created as organic matter decomposes, is trapped in the frozen soil and is released as the soil warms. Methane is a powerful greenhouse gas, and growth in emissions could create a feedback effect, speeding up global warming, according to the report.
• Rising sea levels.
• "Rapid and sustained" loss of arctic sea ice.
In New Mexico, the data on long term warming is clear. The last 15 years have been warmer than the long-term average for the state, according to data from the Western Regional Climate Center in Reno, Nev., with nine of the 15 warmest years on record in the state falling during that span.
But the question of whether climate change is already drying us out is less clear. After an extremely wet period, beginning in the 1970s, our climate began drying out in the late 1990s. Scientists are trying to determine whether the drying trend is the result of global warming or natural variability, Seager said.
Even without the effects of climate change, the Southwest is subject to "megadroughts" far more severe than anything experienced in the past century, including the Dust Bowl and the devastating drought that swept across New Mexico and Arizona in the 1950s, according to the new report.
Scientists who use tree rings to study ancient droughts have seen evidence for repeated decadeslong droughts, which are possible even without the effects of climate change, noted Balaji Rajagopalan, a climate researcher at the University of Colorado who did not work on the new federal study.
Rajagopalan noted that, while there is uncertainty about how large the effect of climate change will be here, the collision of a rapidly growing population and inevitable drought in the region is a problem no matter what global warming dishes out.