Global warming worsened the California drought: study confirms

Human-caused global warming has measurably worsened California's crippling drought and has "substantially increased" the chances of future extreme droughts in the state, a new study released Thursday said.

The study by Columbia University's Earth Institute isn't the first to say warming has played a key role in fueling California's dry conditions, but it's the first to estimate how much worse: as much as a quarter.

The findings suggest that within a few decades, continually increasing temperatures and resulting moisture losses will push California into even more persistent aridity.

"A lot of people think that the amount of rain that falls out the sky is the only thing that matters," said lead author A. Park Williams, a bioclimatologist at Columbia University's Lamont-Doherty Earth Observatory. "But warming changes the baseline amount of water that's available to us, because it sends water back into the sky."

While scientists largely agree that natural weather variations have caused a lack of rain, an emerging consensus says that rising temperatures may be making things worse by driving moisture from plants and soil into the air.

The study adds to growing evidence that climate change is already bringing extreme weather to some regions. Due to the complexity of the data, the scientists could put only a range, not a single number, on the proportion of the drought caused by global warming. The paper estimates 8 to 27 percent, but Williams said that somewhere in the middle.

California is the world's eighth-largest economy, ahead of most countries, but many scientists think that the nice weather it is famous for may now be in the process of going away.

The current drought is now in its fourth year, state officials say, and 2014 was the hottest year in state history. The record-breaking drought is drying up wells, affecting major produce growers and feeding wildfires now sweeping over vast areas. Snowpack levels that recharged aquifers was near zero in the Sierra-Nevada and there's little rainfall.

Contributions of individual climate variables to recent drought are also examined, including the temperature component associated with anthropogenic warming.

Jonathan Overpeck, co-director of the Institute of the Environment at the University of Arizona, said, "It's important to have quantitative estimates of how much human-caused warming is already making droughts more severe." But, he said, "it's troubling to know that human influence will continue to make droughts more severe until greenhouse gas emissions are cut back in a big way." Enditem