California Drought Linked to Climate Change, Greenhouse Gases: Stanford

The dry earth, the raging wildfires and the other symptoms of California's drought are "very likely" linked to human-caused climate change because of the abundance of greenhouse gases created by burning fossil fuels and cutting down forests, according to a new study by Stanford University scientists.

"Our research finds that extreme atmospheric high pressure in this region – which is strongly linked to unusually low precipitation in California – is much more likely to occur today than prior to the human emission of greenhouse gases that began during the Industrial Revolution in the 1800s," Noah Diffenbaugh, an associate professor of environmental Earth system science at Stanford and a senior fellow at the Stanford Woods Institute for the Environment, said in a statement.

Other scientists have warned that global warming will increase the risk of drought. But this study, published Monday, is one of the most comprehensive studies to connect the current drought, one of the worst in the state's history, to more general climate trends. Diffenbaugh led the team and used computer simulations and statistical techniques to come up with his theory.

Combined with unusually warm temperatures and stagnant air conditions, the lack of rain has triggered a dangerous increase in wildfires and incidents of air pollution across the state, the study noted.

Scientists agree that the immediate cause of the drought is a particularly stubborn "blocking ridge" over the northeastern Pacific – popularly known as the Ridiculously Resilient Ridge, or "Triple R" – that prevented winter storms from reaching California during the 2013 and 2014 rainy seasons.

Scientists compared it to a large boulder that has tumbled into a narrow stream. The "Triple R," they said, diverted the flow of high-speed air currents known as the jet stream far to the north, causing Pacific storms to bypass not only California but also Oregon and Washington. As a result, rain and snow that would normally fall on the West Coast was instead re-routed to Alaska and as far north as the Arctic Circle, the researchers found.

Blocking ridges are regions of high atmospheric pressure that disrupt typical wind patterns in the atmosphere. "Winds respond to the spatial distribution of atmospheric pressure," said Daniel Swain, a graduate student in Diffenbaugh's lab and lead author of the study. "We have seen this amazingly persistent region of high pressure over the northeastern Pacific for many months now, which has substantially altered atmospheric flow and kept California largely dry."

A recent report estimated that the water shortage would result in direct and indirect agricultural losses of at least $2.2 billion and lead to the loss of more than 17,000 seasonal and part-time jobs in 2014 alone.

The research was published as a supplement to the Bulletin of the American Meteorological Society.

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