Scientists say warming is making matters worse, but they dispute Obama's contention that it's to blame.
Regional water agency declares 'drought alert'
Brown, task force to attack climate change
BY JUSTIN GILLIS / The New York Times
In delivering aid to drought-stricken California last week, President Barack Obama and his aides cited the state as an example of what could be in store for much of the rest of the country as human-caused climate change intensifies.
In doing so, however, they were pushing at the boundaries of scientific knowledge about the relationship between climate change and drought. While a trend of increasing drought that may be linked to global warming has been documented in some regions, including parts of the Mediterranean and the American Southwest, there is no scientific consensus that it is a worldwide phenomenon. Nor is there definitive evidence it is causing California's problems.
In fact, the most recent computer projections suggest that, as the world warms, California should become wetter, not drier, in winter, when the state receives the bulk of its precipitation. That has prompted some leading experts to suggest climate change most likely had little role in causing the drought.
“I'm pretty sure the severity of this thing is due to natural variability,” said Richard Seager, a climate scientist who studies water issues at the Lamont-Doherty Earth Observatory of Columbia University.
To be sure, 2013 was the driest year in 119 years of record-keeping in California. But extreme droughts have happened previously, and experts say this one bears a notable resemblance to some of those, including a crippling drought in 1976 and 1977.
Overall, drought seems to be decreasing in the central United States and certain other parts of the world, though that is entirely consistent with the longstanding prediction that wet areas of the world will be wetter in a warming climate, even as dry ones become drier.
What may be different about this drought is that, whatever the cause, the effects appear to have been made worse by climatic warming. In making that case last week, scientists said, the administration was on solid ground.
California has been warming along with most regions of the United States, and temperatures in recent months have been markedly higher than during the 1976-77 drought. In fact, for some of the state's most important agricultural regions, summer lasted practically into January, with high temperatures of 10 or 15 degrees above normal on some days.
The consequence, scientists say, has been that any moisture that falls on the state evaporates more rapidly, intensifying the effects of the drought on agriculture in particular. “We are going through a pattern we've seen before, but we're doing it in a warmer environment,” said Michael Anderson, the California state climatologist.
The drought eased a bit with heavy rains in Northern California this month, but many major reservoirs have only half the water expected for this time of year. “I think the situation is still pretty severe,” said professor Alex Hall, who studies climate at UCLA.
Columbia's Seager noted that much of the West Coast had been in a drought of fluctuating severity for 15 years. In some areas, moreover, the warmer climate is causing winter precipitation to fall as rain rather than snow, meaning less melting snowpack to help parched states through hotter summers.
“It all adds up across the Southwest to an increasingly stressed water system,” he said. “That's what they might as well get ready for.”
Source: http://www.ocregister.com/articles/drought-602096-climate-california.html--
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