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September 30, 2014

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Global warming will strike us first

As the world gets hotter, no region in the continental United States will feel it as much as the Southwest, a scientist said Friday at an international meeting on climate change.

Jonathan Overpeck, director of the University of Arizona's Institute for the Study of Planet Earth, said the evidence is overwhelming that the Earth is becoming hotter because of the increase in human-generated greenhouse gases. The change will have profound impacts throughout the world - and particularly in the desert Southwest, he said.

"We have confidence in these projections that is greater than we have had in the future and that is reflected in a number of statements," Overpeck said. "The term we now use is 'unequivocal.' "

Overpeck was among thousands of scientists in Paris participating in efforts by the United Nation's Intergovernmental Panel on Climate Change to produce a comprehensive report on global warming.

Overpeck said 113 governments unanimously agreed to the final summary, on which scientists worked until the early-morning hours throughout the past week. The much-anticipated report is likely to serve as the basis for policy decisions worldwide despite criticism from conservatives who dismiss climate change as a hoax perpetuated by scientists.

Global average temperatures, which have risen a little more than 1 degree over the previous century, will rise another 3 to 8 degrees in the coming century; sea levels will rise from 7 to 23 inches and potentially more; hurricanes and typhoons will become stronger; heat waves, hot weather and heavy rainfalls will be more frequent, the report says.

The Southwest United States will get hit harder and sooner than other parts of the country, Overpeck said, summarizing research by a number of scientists. "There is broad agreement among the models that we will see a drying out across the Southwest," he said. "It's a swath that cuts from about San Francisco southeast to New Orleans and the southern tip of Florida. The models are agreeing because there is a clear mechanism that seems to be represented the jet stream in winter and the average position of storms, that's moving northward."

Overpeck said the six years of drought that have afflicted the Southwest can't necessarily be attributed to global warming, but it is consistent with the models. Those changes will only persist and increase in the future, he said.

Overpeck said the biggest impacts could be felt in the winter, when snowfall in the Rocky Mountains provides the critically important reservoir for water used by cities, including Las Vegas, Los Angeles and Phoenix, and millions of acres of farmland. Warmer winters and earlier springs mean less snow and less water for the urban and agricultural users.

Hotter temperatures in the summer also will mean greater demand for water, stressing water sources such as the Colorado River that have already been hit hard by drought and demand.

Overpeck's colleague at the University of Arizona, biologist Travis Huxman, said the implications for the Southwest are significant.

"The projected warming and reductions in precipitation will compromise water delivery to our communities," Huxman said from Tucson. "Colorado River flows are expected to decline, and local water resources are predicted to be less sustainable. At the same time, we still have continued growth of human populations on the landscape. This all puts our cities at risk. Considering the increased demand on water resources, costs of delivery may increase, and there may be greater conflict between human consumption and other uses."

The natural world also will suffer, he said, because of less plant production at the bottom of the food web.

Scientists also predict a seemingly ironic increase in summer rain storms and flooding despite an overall drop in precipitation, Huxman said.

Kelly Redmond, regional climatologist with the Desert Research Institute's Western Regional Climate Center in Reno, said the conclusions reached in Paris mirror what scientists have been finding for years. There are still questions about the ultimate impact of climate change, but no real debate that it is happening, he said.

"There is a long process by which this stuff is vetted and passed around," he said. "It would be surprising if there were surprises coming out of this process."

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