Global Warming Deepening Drought -- And Without Climate Action, It'll Get Worse

Human-caused global warming has exacerbated California's extreme four-year drought by as much as 25 percent, according to a new study that is just the latest to link the abnormally dry conditions with man-made climate change.

The study by Columbia University's Lamont-Doherty Earth Observatory, published Thursday in the journal Geophysical Research Letters, suggests that within a few decades, continually increasing temperatures and resulting moisture losses will push California into even more persistent aridity.

The current drought--dubbed by scientists to be the worst on record, sparking wildfires and devastating the state's agricultural sector--has been primarily caused by natural weather variations, experts say.

But the Columbia researchers say rising temperatures, which have crept up "in step with building fossil-fuel emissions," are making things worse by driving moisture from plants and soil into the air.

"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. "But warming changes the baseline amount of water that's available to us, because it sends water back into the sky."

He explained further to Al Jazeera America: "Rising temperatures mean we have to get more rain just to break even. Each raindrop and each snowflake is a little less valuable."

Moreover, while rain is expected to resume as early as this winter, "as time goes on, precipitation will be less able to make up for the intensified warmth," Williams added. "People will have to adapt to a new normal."

The paper adds to growing a body of evidence, though scientists say it is the most specific look at the question yet. A study issued in March by Stanford University concluded that human-driven global warming had intensified Calfornia's drought and would likely lead to increased droughts in the future; while a paper by scientists from Lamont-Doherty and Cornell University, published this February, warned that climate change will push much of the central and western United States into its driest period for at least 1,000 years.

Furthermore, writes the New York Times, the Columbia study "provides fresh 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 substantial factor in the drought. They have been attacked for that stance by Republicans who question the science of climate change."

Speaking to the paper's significance, 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."

And, he added, "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."