But as he spoke, Brown hit a darker note. Last week, amid the driest year for the state since record-keeping began in the 1840s, Brown declared a drought emergency for California, and in his speech he warned of harder times ahead:
Among all our uncertainties, weather is one of the most basic. We can’t control it. We can only live with it, and now we have to live with a very serious drought of uncertain duration…We do not know how much our current problem derives from the build-up of heat-trapping gasses, but we can take this drought as a stark warning of things to come.(MORE: Can GM Crops Bust the Drought?)
Californians need to be ready, because if some scientists are right, this drought could be worse than anything the state has experienced in centuries. B. Lynn Ingram, a paleoclimatologist at the University of California, Berkeley, has looked at rings of old trees in the state, which helps scientists gauge precipitation levels going back hundreds of years. (Wide tree rings indicate years of substantial growth and therefore healthy rainfall, while narrow rings indicate years of little growth and very dry weather.) She believes that California hasn’t been this dry since 1580, around the time the English privateer Sir Francis Drake first visited the state’s coast:
If you go back thousands of years, you see that droughts can go on for years if not decades, and there were some dry periods that lasted over a century, like during the Medieval period and the middle Holocene [the current geological epoch, which began about 11,000 years ago]. The 20th century was unusually mild here, in the sense that the droughts weren’t as severe as in the past. It was a wetter century, and a lot of our development has been based on that.Ingram is referring to paleoclimatic evidence that California, and much of the American Southwest, has a history of mega-droughts that could last for decades and even centuries. Scientists like Richard Seager of Columbia University’s Lamont-Dohery Earth Observatory have used tree-ring data to show that the Plains and the Southwest experienced multi-decadal droughts between 800 A.D. and 1500 A.D. Today dead tree stumps—carbon-dated to the Medieval period—can be seen in river valley bottoms in the Sierra Nevada mountains, and underwater in places like California’s Mono Lake, signs that these bodies of water were once completely dry. Other researchers have looked at the remains of bison bones found in archaeological sites, and have deduced that a millennium ago, the bison were far less numerous than they were several centuries later, when they blanketed the Plains—another sign of how arid the West once was. The indigenous Anasazi people of the Southwest built great cliff cities that can still be seen in places like Mesa Verde—yet their civilization collapsed, quite possibly because they couldn’t endure the mega-droughts.