Doyle Rice has an invaluable piece in USA Today placing California’s persistent and exceptional* drought in the broader context of a very dry West — and the even broader context of the last 1,000 years or so.

Here’s the core point in Rice’s story:

The dryness in California is only part of a longer-term, 15-year drought across most of the Western USA, one that bioclimatologist Park Williams said is notable because “more area in the West has persistently been in drought during the past 15 years than in any other 15-year period since the 1150s and 1160s” — that’s more than 850 years ago.

“When considering the West as a whole, we are currently in the midst of a historically relevant megadrought,” said Williams, a professor at the Lamont-Doherty Earth Observatory of Columbia University in New York.

Megadroughts are what Cornell University scientist Toby Ault calls the “great white sharks of climate: powerful, dangerous and hard to detect before it’s too late. They have happened in the past, and they are still out there, lurking in what is possible for the future, even without climate change.”

Please read the rest and pass to folks out west.

There are promising signs that politicians, farmers and other water users in the West are getting the message that a long verdant spell was the exception, not the rule. Hopefully, more focus on the science that reveals this will help prevent backsliding if rains briefly return.

The piece goes on to describe the anomalously equable nature of climate in the region in much of the period when the West was “won” (despite some severe droughts, including the 1930s dry spell shown in the music video above).

For more on that disturbing reality read these illuminating papers:

“A 1,200-year perspective of 21st century drought in southwestern North America,” by Connie A. Woodhouse of the University of Arizona and four other researchers (Proceedings of the National Academy of Sciences, Dec. 14, 2010). Here’s the takeaway line:

The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future.

“North American Drought: Reconstructions, Causes, and Consequences,” a long fascinating monograph by Edward R. Cook (cited in Rice’s article), Richard Seagar and Mark A. Cane of Collumbia University’s Lamont-Doherty Earth Observatory and David Stahle of the University of Arkansas (Earth-Science Reviews, 2007).

The paper has a particularly interesting section on “The Garden Myth of the Great Plains,” a combination of propaganda and climatological chance that sped western settlement and development.

Here’s the kicker:

It may well be that the West will luck out as rising greenhouse gases induce an equatorial warming, or an El Niño-like response, and the resulting circulation changes increase precipitation across the mid-latitudes. But we have the nagging reality that a previous time of high positive radiative forcing – the Medieval period – was associated with both colder tropical Pacific SSTs [sea surface temperatures] and epic drought across the West. Were the climate system to revert to that severity of drought, conflict, at least on a political level, would return to the West as cities, with relatively modest claims on available water but huge and growing populations, and water-hungry agribusiness, with great political clout, do battle over diminishing resources. The ancient Pueblo migrations may be an unfair analogy, but modern Western society, highly dependent on hydraulic engineering, is yet to be tested by the dreadful droughts we know can occur.