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Some apocalyptic news out of UCLA today: today’s increasing greenhouse gas levels could lock the Golden State into centuries of drought.
The study, published today in the journal Scientific Reports, looked at the history of California's dry periods over the past 10,000 years. The researchers, led by UCLA professor Glen MacDonald, tracked California's historic and prehistoric climate by examining a sediment core in the Sierra Nevada mountains. They found that there were a number of natural, climactic factors (sun spots, a slight change in the earth's orbit, decreased volcanic activity) that intermittently warmed the region through a process called radiative forcing.
“Radiative forcing in the past appears to have had catastrophic effects in extending droughts,” MacDonald, an international authority on drought and climate change, said in a news release. “When you have arid periods that persist for 60 years, as we did in the 12th century, or for millennia, as we did from 6,000 to 1,000 B.C., that’s not really a ‘drought.’ That aridity is the new normal.”
Now, it seems there is a new source of radiative forcing on the horizon, one that could "extend drought-like conditions more or less indefinitely," according to MacDonald. Enter greenhouse gases.
Essentially, the drought lasts as long as whatever is causing the radiative forcing is present. In the past, when that forcing was caused by natural phenomena, those factors always eventually diminished as nature took its course. Sure, their devastation could last hundreds of years at a time, but it was never permanent. What makes this time different is that greenhouse gases levels are only expected to increase. The last three years were the hottest and driest in California since 1895, and there is no end in sight.
And there is even more cause for alarm when you consider how closely these processes are linked to prolonged changes in Pacific Ocean surface temperatures:
Changes in ocean temperatures are linked to El Niño and La Niña conditions, which increase and decrease precipitation in California. Until now, no one had the long, detailed record of California’s dry periods needed to show that that aridity went hand-in-hand with changes in the prehistoric climate records of the Pacific Ocean, MacDonald said.
“In a century or so, we might see a retreat of forest lands, and an expansion of sagebrush, grasslands and deserts,” MacDonald said. “We would expect temperatures to get higher, and rainfall and snowfall would decrease. Fire activity could increase, and lakes would get shallower, with some becoming marshy or drying up.”
