The drought parching the U.S. state of California is one of the worst on record. And although researchers say greenhouse gases likely made heat waves worse in Asia, Australia and Europe last year, climate change is probably not behind California’s troubles.
The last three years have been among the warmest and driest on record in the West Coast state, costing an estimated $2.2 billion in crop and livestock losses so far.
A ridge of high pressure has blocked Pacific storms from coming ashore for the last three winters.
“The atmosphere, through its own internal weather variability, is quite capable of creating ridges like that,” said study lead author Richard Seager at Columbia University’s Lamont Doherty Earth Observatory. “But what we found in this report was that the particular configuration of the ocean in these past three winters favored that ridge and dry conditions in California.”
Cold temperatures in some parts of the Pacific Ocean and warm spots in others can affect how air circulates in the atmosphere. In the new report, researchers found that over the past three years, the cold and warm spots have lined up in a way that makes that rain-blocking ridge likely.
Plus, Seager says, computer models predict that drought is not the impact that climate change will have on California.
“The models are actually projecting not overall drier conditions as a result of rising greenhouse gases but a shorter, sharper rainy season,” he said.
But Kevin Trenberth at the National Center for Atmospheric Research says, at this point, climate change is not likely to have had much effect on global circulation patterns, “so, looking for a change in circulation with climate change is largely an irrelevant thing to do.”
“There is absolutely nothing in this study that deals with one of the main effects of climate change, which is increased heating, high temperatures, increased drying, increased evaporation,” he added.
The study authors acknowledge that ocean temperatures only explain part of the severity of the current drought.
“In particular, why was the last year of the drought the most severe, even though the ocean conditions were perhaps the weakest during the three-year period?” asked study co-author Martin Hoerling at the National Oceanic and Atmospheric Administration. “It’s a bit of a puzzle to us.”