Manmade climate change could be intensifying California’s drought, according to a new Columbia University study. Scientists generally agree that natural weather variations have caused a lack of rain, but an emerging school of thought theorizes that rising temperatures may be making things worse by driving moisture from plants and soil into the air.

This new study is the first to estimate just how much worse rising temperatures make things: by as much as a quarter.

The findings suggest that within a few decades, constantly increasing temperatures and the resulting moisture losses will push California into even more stubborn aridity. Lead author A. Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory, says:

“A lot of people think that the amount of rain that falls out the sky is the only thing that matters. But warming changes the baseline amount of water that’s available to us, because it sends water back into the sky."

Because the data is so complex, the scientists could put only a range, not a definite 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–probably 15 to 20 percent–is most likely.

[caption id=“attachment_78957” align=“alignright” width=“400”]Horseshoe Lake This image shows an abnormally low lake level at Horseshoe Lake in the high-elevation Mammoth Lakes Basin, Sierra Nevada Mountains, This photo was taken June 2015. Credit: Jennifer Bernstein[/caption]

The study adds more evidence that already, climate change is bringing extreme weather to some parts of the world. California is the world’s eighth-largest economy, ahead of most countries, but many scientists think that the pleasant weather it is famous for may now be in the process of going away.

California’s record-breaking drought is now in its fourth year. It is drying up wells, affecting major produce growers and feeding wildfires now sweeping over vast areas.

Many researchers believe that rain will resume as early as this winter.

“When this happens, the danger is that it will lull people into thinking that everything is now OK, back to normal,” said 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."

Williams, A. P., R. Seager, J. T. Abatzoglou, B. I. Cook, J. E. Smerdon, and E. R. Cook (2015) Contribution of anthropogenic warming to California drought during 2012–2014 Geophys. Res. Lett., , doi:10.1002/2015GL064924

Photo: Dry grassland and oak landscape of the Coastal Mountain Range are among the parts of California most affected by the current drought. This photo was taken in August 2015. / Credit: Dominick McPeake

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