New research shows the fingerprints of global warming in worsening the California drought and suggests a future of more dryness for the suffering state.
A major new study released Thursday adds to the growing scientific consensus that rising temperatures linked to the burning of fossil fuels are intensifying the crisis, although climate scientists believe natural weather variations are responsible for the lack of rainfall that created the drought.
The study in the journal Geophysical Research Letters estimates that global warming has worsened California’s drought by 15 percent to 20 percent, the first time a figure has been placed on the phenomenon.
“The current drought in California would still be occurring just based on pure natural climate variability,” the lead author of the study, Columbia University climate scientist A. Park Williams, said in an interview. “But over the last 120 to 130 years, as the greenhouse gases have been accumulating in the atmosphere, there has been this extra thing going on.”
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What’s happening is the warming atmosphere robs moisture from plants and soil on the surface, he said.
“A lot of people think that the amount of rain that falls out the sky is the only thing that matters,” Williams said. “But warming changes the baseline amount of water that’s available to us, because it sends water back into the sky.”
The study adds to earlier research from scientists like Noah Diffenbaugh, a climatologist at Stanford University.
“We’re seeing more and more the role of temperature in intensifying the drought and prolonging the drought,” Diffenbaugh said in an interview.
His research shows drought is far more likely to happen at higher temperatures and that California’s warming trend is increasing the chances for more droughts in the state’s future.
It’s very clear the warming of California has increased the probability of conditions that create drought. It’s also very clear from our work that the warming of California would not have occurred without the human emission of greenhouse gases.
Stanford University climate scientist Noah Diffenbaugh
Scientists said it could be just a temporary reprieve when California’s rains resume, which might happen this winter.
“When this happens, the danger is that it will lull people into thinking that everything is now OK, back to normal,” said Columbia University climate scientist Williams. “But as time goes on, precipitation will be less able to make up for the intensified warmth. People will have to adapt to a new normal.”
California is in the fourth year of the drought, with more than 70 percent of the state classified as in “exceptional” or “extreme” drought. Wildfires are accelerating, reservoirs are drained, cropland is out of production and farm worker unemployment is growing. The University of California, Davis, estimates the state’s agricultural economy will lose about $1.84 billion this year.
California Gov. Jerry Brown has declared that his drought-stricken state proves “climate change is not a hoax.” President Barack Obama has linked the drought to global warming as well, warning of increasing environmental disasters tied to human emissions. But Republican leaders are not convinced.
“California and the West are being stifled by a natural drought that has been exacerbated by man-made, radical environmental policies that divert water from communities that badly need it,” Republican Rep. Rob Bishop of Utah, chairman of the House Committee on Natural Resources, charged Thursday.
The Senate earlier this year voted to reject the scientific consensus that humans are causing climate change. The chairman of the Senate’s Environment Committee, Sen. James Inhofe, R-Okla., calls the link between human activities and climate the “biggest hoax perpetrated against mankind.”
NASA declared 2014 the hottest year ever recorded on Earth, and it was also California’s hottest. The state’s snowpack, which is crucial for the state’s water supply, diminished to virtually nothing.
The real driver of the drought of course has been the drop in precipitation.
Columbia University climate scientist Richard Seager
Global warming did not cause the drought, said Columbia University climate scientist Richard Seager, lead author of a National Oceanic and Atmospheric Administration report last year. That study blamed a high-pressure ridge off the West Coast that’s blocked storms from reaching California in the winter, when the state receives the majority of its rain and snow.
“The real driver of the drought of course has been the drop in precipitation,” Seager said in an interview.
But the new study, which Seager co-authored, says that global warming can be blamed for between 8 percent and 27 percent of the severity of the drought through the removal of moisture from the soils, trees and crops. The scientists said the most likely range is about 15 percent to 20 percent.
Other research bolsters the case for a connection between warming and the intensity of the drought. A study published in June compared California’s record-breaking temperatures last year to the temperatures since 1916, and examined the impact on snowfall and evaporation.
“We found if the temperature were like any other year in the past, there was about an 86 percent probability that the drought in 2014 would not have been as severe,” said Shrad Shukla, a researcher in the climate hazard group at the University of California, Santa Barbara.
Alex Hall, a climate expert at the University of California, Los Angeles, said the water evaporation has combined with the state’s lack of precipitation to create extraordinary conditions.
“You do get something at the surface that really is unprecedented,” Hall said. “There’s evidence going back to the Paleo record that you really don’t find anything comparable to this over the past thousand years.”