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The Turn-of-the-20th-Century North American Drought
Seager, R. 2007. The turn of the century North American drought: Global context, dynamics, and past analogs. Journal of Climate 20: 5527-5552.

Whenever a major drought occurs somewhere in the world, climate alarmists use it as an opportunity to decry what they describe as CO2-induced global warming, which they say is responsible for it. Over the past several years, this has been the mantra of many who have promoted global warming as the cause of the North American drought that began in 1998 and has been especially severe throughout the western United States. But does this contention hold up under the strict scrutiny of science?

What was done
The author studied the global context of the drought that affected nearly the entire United States, northern Mexico and the Canadian Prairies -- but most particularly the American West -- between 1998 and 2004, based on atmospheric reanalysis data and ensembles of climate model simulations forced by global or tropical Pacific sea surface temperatures over the period January 1856 to April 2005, comparing the climatic circumstances of the recent drought with those of the five prior great droughts of North America: (1) the Civil War drought of 1856-65, (2) the 1870s drought, (3) the 1890s drought, (4) the great Dust Bowl drought, and (5) the 1950s drought.

What was learned
Seager says that the 1998-2002 period of the recent drought "was most likely caused by multiyear variability of the tropical Pacific Ocean," noting that the recent drought "was the latest in a series of six persistent global hydroclimate regimes, involving a persistent La Niņa-like state in the tropical Pacific and dry conditions across the midlatitudes of each hemisphere."

What it means
There is no aspect of this study that implicates global warming, either CO2-induced or otherwise, as a cause of -- or contributor to -- the great turn-of-the-20th-century drought that affected large portions of North America. Seager notes, for example, that "although the Indian Ocean has steadily warmed over the last half century, this is not implicated as a cause of the turn of the century North American drought because the five prior droughts were associated with cool Indian Ocean sea surface temperatures [our italics]." In addition, the five earlier great droughts occurred during periods when the mean global temperature was also significantly cooler than what it was during the last great drought.

Reviewed 19 March 2008