A report issued on Monday by the National Oceanic and Atmospheric Administration said natural variations – mostly a La Niña weather oscillation – were the primary drivers behind the drought that has now stretched to three years.
The study’s lead author, Richard Seager of Columbia University, said the paper has not yet been published in a peer-reviewed scientific journal. He and NOAA’s Martin Hoerling said 160 runs of computer models show heat-trapping gases should slightly increase winter rain in parts of California, not decrease.
“The conditions of the last three winters are not the conditions that climate change models say would happen,” Hoerling said. But he said La Niña, which is the cooler flip side of the warming of the central Pacific ocean, can only be blamed for about one-third of the drought. The rest of the causes can be from just random variation, he said.
Some outside climate scientists criticised the report, saying it did not take into effect how record warmth worsened the drought. California is having its hottest year on record, based on the first 11 months of the year and is 4.1 degrees warmer than the 20th-century average, according to the National Climatic Data Center.
http://www.theguardian.com/us-news/2014/dec/08/california-drought-not-caused-by-global-warming-official-study-finds
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