Newspaper article MinnPost.com

California's Drought, and Recent Trends, May Pale beside Our Probable Future

Newspaper article MinnPost.com

California's Drought, and Recent Trends, May Pale beside Our Probable Future

Article excerpt

Minnesota has had its brushes with drought in recent years, but nothing like the experience of the American Southwest, where 11 years out of the last 14 have been marked by seriously deep, dry spells across large parts of Arizona, Nevada, New Mexico, Oklahoma and Texas.

Not to mention California, now in its fourth year of a drought that could go into the record books right now as the worst in more than a thousand years.

Such a comparison is possible - and verifiable - because of tree- ring data assembled into the North American Drought Atlas, which came out in 2009 and presents a record stretching back roughly 2,000 years.

Two millennia is an unusually long timeframe for climate data, and last week the atlas enabled this striking conclusion from climate scientists at NASA, Columbia and Cornell:

Under any reasonable outlook for global warming over the rest of this century, both the American Southwest and the central Great Plains - including much of Minnesota - are likely to experience drought on a level "unprecedented" since the year 1000, and significantly more severe than a pattern known to have occurred early in the last millennium.

I put the quotes around "unprecedented" not to qualify it, nor to quibble with it, but because it is precisely (and I think remarkably) the term used in the title of the paper, which was unveiled late last week at the American Association for the Advancement of Science's annual conference in San Francisco, and published simultaneously in AAAS's new online journal, called Science Advances.

(Because it's an open-access journal, you can read Unprecedented 21st century drought risk in the American Southwest and Central Plains for yourself without fee and at your convenience.)

The paper's point is not that the coming drought regimes lack for serious though less severe predecessors. In medieval times, the paper says, both the Southwest and the Central Plains experienced "megadroughts" -- periods of seriously depressed soil moisture much worse than anything in the so-called historical period of 1850- 2005.

Disappearance of the Anasazi

For one example, there's the prolonged drought about 1,300 years ago that is thought to have wiped out the Anasazi Indians and the pueblo culture they had developed on the Colorado Plateau, in today's Four Corners region.

And as shown in the graph below, from an earlier paper on megadroughts as recorded in tree rings, the current patterns are approaching the intensity of some earlier extremes.

But megadroughts of the future, according to the new publication, will be worse, because of global warming and other climate shifts driven by our loading of the atmosphere with greenhouse gases.

From the announcement issued by Columbia:

Many studies have already predicted that the Southwest could dry due to global warming, but this is the first to say that such drying could exceed the worst conditions of the distant past. The impacts today would be devastating, given the region's much larger population and use of resources.

"We are the first to do this kind of quantitative comparison between the projections and the distant past, and the story is a bit bleak," said Jason E. Smerdon, a co-author and climate scientist at the Lamont-Doherty Earth Observatory, part of the Earth Institute at Columbia University. "Even when selecting for the worst megadrought- dominated period, the 21st century projections make the megadroughts seem like quaint walks through the Garden of Eden. …

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