Professor's Research Shows Irrigation Hides Global Warming Effects

MERCED, CA— The prevalence of irrigation throughout California — especially in the Central Valley — could mask the effects of global warming, a new research paper indicates.

Professor Lara Kueppers, with the School of Natural Sciences at UC Merced, said she and two colleagues from UC Santa Cruz began looking at how irrigation's natural cooling can affect mean temperatures in certain areas.

What they found is that irrigation causes the mean temperature in summer months to drop, even as greenhouse gas emissions drive temperatures upward.

"It gives a false sense of security," Kueppers said, "because the irrigation makes it really difficult to assess the effects of greenhouse gases."

Kueppers and her colleagues used a computer model to look at California, which essentially became a look at the Central Valley, the state's largest irrigated area.

Their model indicates that August's mean temperature in irrigated areas has dropped by about 6.5 degrees Fahrenheit, while greenhouse gas emissions are expected to warm the Earth about the same amount.

Kueppers' paper has a major implication: activities related to agriculture, forestry and development do matter to the climate, she said.

"If we don't consider what we're doing to the area by urbanizing, which removes farmland that has a cooling effect, we could very well end up with a much hotter Central Valley," she said.

She and co-authors Mark A. Snyder and Lisa C. Sloan, of the Climate Change and Impacts Laboratory, Department of Earth and Planetary Sciences at UC Santa Cruz, said more research looking at absolute temperatures — not using computer models — is already under way at Lawrence Livermore National Laboratory.

"From what I've seen, their work is coming to similar conclusions as ours," Kueppers said.

The abstract of Kueppers' paper can be viewed for free online. Geophysical Research Letters, published by The American Geophysical Union, presents short research letters that offer scientific advances likely to have immediate influence other investigators' research. It has been published since 1974.

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