Some scientists have said they believe climate change is at least partly to blame for California's ongoing crippling drought, and a new study bears that out, its authors say.
If human-caused greenhouse gas emissions were not trapping heat, leading to climate change, the state's drought could be up to 27 percent less severe than it is, the study researchers say.
Writing in the journal Geophysical Research Letters, the study authors say human activity — anthropogenic warming — has made the drought between eight and 27 percent worse than natural climate variation would create.
That suggests any drought caused by natural climate variability has a greater chance of becoming severe and even acute in the future with climate change, they explain.
"This would be a drought no matter what," study lead author A. Park Williams, a climate scientist at Columbia University, says of the current situation in California. "It would be a fairly bad drought no matter what. But it's definitely made worse by global warming."
Climate change will contribute to an ever-growing portion of drought effects, while natural variation continues "to do its thing," Williams points out.
The researchers evaluated annual variations in drought and weather conditions for 23,955 locations in California, analyzing temperature, precipitation, humidity, wind and solar radiation at each spot for each month over the last 120 years.
Feeding that data into computer models yielded a calculation of a minimum of eight percent of drought being due to climate change, with an upper limit of 27 percent.
The study should clear up some confusion in the public mind about the causes of the current drought, Williams says.
"Some people believe it's entirely natural variability, and others [who] think it's entirely global warming," he points out. "Both of those perspectives are dangerous for California's future."
The current drought could mean a loss for the state's economy of around $2.7 billion this year alone, according to a study by researchers at the University of California, Davis.
The main cause of the current drought, underlying the added effect of climate change, is a persistent ridge of high pressure in the western Pacific Ocean that for three years has blocked winter storms that bring California much of its water supply from reaching the state.
That's a pattern historically seen in California droughts of the past, researchers say.
