california<u+2019>s drought was spawned by<u+00a0>natural weather variations<u+00a0>that<u+00a0>have bedeviled the west throughout recorded history.









but a new study released thursday says human-caused global warming is worsening the natural phenomenon. the study by columbia university<u+2019>s earth institute isn<u+2019>t the first to<u+00a0>say warming has played a key role in fueling california<u+2019>s dry conditions, <u+00a0>but it<u+2019>s the first to measure its impact, calculating that<u+00a0>it increased the problem by<u+00a0>as much as 25 percent.









natural weather patterns that push away atmospheric<u+00a0>moisture that carries rain are normal for the state. but warming adds to the resulting dryness and heat. a small amount of moisture stored in plants and the soil evaporates into the drier atmosphere.









<u+201c>a lot of people think that the amount of rain that falls out the sky is the only thing that matters,<u+201d> said park williams, a bio-climatologist at columbia university<u+2019>s lamont-doherty earth observatory who was the study<u+2019>s lead author. <u+201c>but warming changes the baseline amount of water that<u+2019>s available to us, because it sends water back into the sky.<u+201d>









[as water runs dry, californians brace for a new way of life]









lightning strikes on parched earth are igniting wildfires all over the state. there are so many blazes that firefighters from across the world are rushing<u+00a0>to help put them out.









in the central valley, the land is so dry that <u+00a0>farmers are drilling deep into the soil to extract groundwater to irrigate crops. the drilling and pumping are drawing down aquifers that serve as a sort of liquid bank that the state can rely on when rivers and reservoirs aren<u+2019>t replenished by rain and snow because of drought.









farmers have been the targets of critics who say they take too much water, but irrigation<u+00a0>actually has environmental benefits, williams said. it provides moisture that cools the air, offsetting rising heat. but there<u+2019>s a drawback. when too much is drained, the state loses its artificial moisture, making the air even hotter.









the current drought is the most severe on record, state officials say, and 2014 was the hottest year in state history.<u+00a0>snowpack levels that recharged aquifers was near zero in the sierra-nevada and there<u+2019>s little rainfall.<u+00a0>as the water supply in dozens of metropolitan reservoirs drops to historic lows, californians are hoping that a giant el ni<u+00f1>o weather pattern forming in the pacific ocean will deluge the state with rain next winter.









but even a large seasonal gusher would only delay the inevitable <u+2014> a future of longer and more frequent droughts in california, numerous researchers have said.









in february, researchers at nasa and cornell and columbia universities predicted that california and the southwest would slip into a 30-year megadrought by 2050 if greenhouse gas emissions are not curtailed.









a month later, researchers at stanford university said californians by then will be well accustomed to drought. they used historical data to predict that average temperature increases would continue, quickly evaporating average precipitation that will remain steady and increasing the likelihood of prolonged dryness.









scientists have been reluctant to link the state<u+2019>s drought to global warming, saying there was not enough data to support such a conclusion.<u+00a0>but the current study is part of a growing body of evidence that<u+2019>s changing the minds of researchers.









[a megadrought will grip the southwest in coming decades, scientists say]









williams said his team read all the studies and sought to answer whether or not global warming was having an immediate impact. <u+201c>we didn<u+2019>t look at the future at all. this is a study about now,<u+201d> he said.









they analyzed month-to-month climate data between 1901 and 2014 to find fluctuations in precipitation, wind, temperature and humidity. the study, published in the journal geophysical research letters, said average temperatures in california have increased by 2.5 degrees fahrenheit over 113 years. and, starting in the 1960s, heat increased with the introduction of more greenhouse gases from automobiles and other sources.









richard seager, a climate scientist at columbia<u+2019>s earth observatory; john t. abatzoglou, an associate professor at the university of idaho; and benjamin i. cook,<u+00a0>a research scientist for nasa<u+2019>s goddard institute for space studies, were co-authors of the study.









<u+201c>when greenhouse gases accumulate, it<u+2019>s like a bully showing up at your door to demand that you give it more and more every year,<u+201d> williams said. in california, that meant more moisture, evaporating from rain and ground water sprayed on crops in farming regions such as the central valley.









after a century, the effects of warming are becoming more noticeable in the current drought.<u+00a0><u+201c>the current drought would be bad without the bully,<u+201d> williams said, referring to global warming. with it, the problem can become catastrophic.









williams said the state, which only loosely regulates the withdrawal of groundwater by farms and other sources of agriculture, should act more aggressively in policing its use, attaching higher fees for removing it, and fines for overdoing it. state officials who<u+2019>ve been diligent on capping greenhouse gas emissions might consider tougher regulations to avoid more severe drought.









noah diffenbaugh, author of the stanford study, called the earth institute study <u+201c>a step forward,<u+201d> saying it was based on firm data showing <u+201c>that temperature makes it harder for drought to break, and increases the long-term risk.<u+201d>









amir aghakouchak, a hydrology professor at the university of california at irvine who said in june that science did not support connecting the drought to warming, said the report<u+2019>s results show that human influences are having an effect.









with a stunning 7 million acres burned so far, the u.s. wildfire situation is looking dire









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global warming worsened the california drought, scientists say
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