California Drought Is Made Worse by Global Warming, Scientists Say
Global warming caused by human emissions has most likely intensified the drought in California by 15 to 20 percent, scientists said on Thursday, warning that future dry spells in the state are almost certain to be worse than this one as the world continues to heat up.
Even though the findings suggest that the drought is primarily a consequence of natural climate variability, the scientists added that the likelihood of any drought becoming acute is rising because of climate change. The odds of California suffering droughts at the far end of the scale, like the current one that began in 2012, have roughly doubled over the past century, they said.
“This would be a drought no matter what,” said A. Park Williams, a climate scientist at the Lamont-Doherty Earth Observatory of Columbia University and the lead author of apaper published by the journal Geophysical Research Letters. “It would be a fairly bad drought no matter what. But it’s definitely made worse by global warming.”
The National Oceanic and Atmospheric Administration alsoreported Thursday that global temperatures in July had been the hottest for any month since record-keeping began in 1880, and that the first seven months of 2015 had also been the hottest such period ever. Heat waves on several continents this summer have killed thousands of people.
The paper on the California drought echoes a growing body of research that has cited the effects of human emissions, but scientists not involved in the work described it as more thorough than any previous effort because it analyzed nearly every possible combination of data on temperature, rainfall, wind speed and other factors that could be influencing the severity of the drought. The research, said David B. Lobell, a Stanford University climate scientist, is “probably the best I’ve seen on this question.”
The paper provides new scientific support for political leaders, including President Obama and Gov. Jerry Brown of California, who have cited human emissions and the resulting global warming as a factor in the drought. As he races around his battered state, from massive forest fires to parched farms, Mr. Brown has been trying to cajole the Republican presidential candidates into explaining what they would do about climate change.
“To say you’re going to ignore that there’s a huge risk here, the way we’re filling the atmosphere with heat-trapping gases, is folly, ignorance and totally irresponsible,” Mr. Brown said Thursday in a telephone interview. “And virtually the entire Republican Party in Congress is saying exactly that. It’s inexplicable.”
Several Republican presidential candidates, including Senator Lindsey Graham of South Carolina and Gov. John R. Kasich of Ohio, do acknowledge that climate change poses risks, but they are skeptical of the way Mr. Obama has gone about trying to limit emissions, with aplan expected to force the shutdown of many coal-fired power plants.
Chris Schrimpf, a spokesman for Mr. Kasich, said Thursday that political leaders confronting questions about climate change “can’t stick their heads in the sand and pretend it isn’t happening. Instead we need to be about the business of taking action, but action that doesn’t throw the economy and jobs out the window at the same time.”
However, many of the leading Republican candidates are openly skeptical of climate science and play down the risks. In response to aletter from Mr. Brown asking about their plans, several of the candidates retorted last week that California should be building more dams to store water for future droughts. Senator Ted Cruz of Texas said that “alarmists” about global warming were trying to gain “more power over the economy and our lives.”
A report this week by researchers at the University of California, Davis, projected that the drought would cost the California economy some $2.7 billion this year. Much of that pain is being felt in the state’s huge farming industry, which has been forced to idle a half-million acres and has seen valuable crops like almond trees and grape vines die.
As climate scientists analyze the origins of the drought, they have been tackling two related questions: What caused the dearth of rain and snow that began in 2012? And, regardless of the cause, how have the effects been influenced by global warming?
The immediate reason for the drought is clear enough: For more than three years, a persistent ridge of high pressure in the western Pacific Ocean has blocked storms from reaching California in the winter, when the state typically gets most of its moisture. That pattern closely resembles past California droughts.
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