Churchville, VA—Does the modern warming doom the western U.S. to drought? Two climate experts have just noted that the region now has “the worst drought since measurements began,” and they predict a future of soaring temperatures and declining snow-packs.
“The climate changes in western North America, particularly in the Southwest, have outstripped change elsewhere on the continent, save perhaps in the Arctic,” say Jonathon Overpeck of the University of Arizona, and Bradley Udall, of the University of Colorado. “In the past decade, many locations, notably in the headwaters region of the Colorado River, have been more than 1 degree C warmer than the 20th-centuiry average.”
Funny they should mention the Arctic, which the back copies of the New York Times testify was as warm in the 1920s as it is today. The Russians confirm a 70-year cycle in Arctic temperatures and sea ice.
Could today’s warming and drought in the American Southwest be cyclical too?
Even as the Overpeck/Bradley study was released, the University of Miami published a countervailing study strongly suggesting that the sun is a far more powerful climate force than human-emitted greenhouse gasses. The Miami researchers used fossil coral from a Central Pacific island to measure sea surface temperatures between 1320 and 1462 AD, the era in which Columbus discovered America.
Robert Burgman, the lead Miami author, says Pacific sea temperatures dropped only one-tenth of a degree C in that long-ago period—but that was enough to trigger whole decades of drought in what’s now the southwestern U.S. The severe dryness collapsed the Anasazi Indians’ rain-fed agriculture in southern Colorado and northern New Mexico. Warfare broke out over food, so the Anasazi built their dramatic cliff-side fortresses. But even these were eventually plundered. The Anasazi refugees then walked to the Colorado Plateau, but the drought there turned out to be even worse. A few survivors finally settled in the lower reaches of the Colorado River.
In Europe, say the coral researchers, farmers suffered three years of torrential rains, which led to the Great Famine from 1315 to 1320, and marked the transition from the Medieval Warming to the Little Ice Age. Extremely cold and unstable weather then bedeviled Europe with crop failures and famines through the rest of the 14th century.
Burgman says the “marriage” of complex climate models and paleoclimate evidence is helping us understand the workings of the long, moderate Dansgaard-Oeschger Climate cycle which brought us the Roman Warming, the Dark Ages, the Medieval Warming and quite recently the Little Ice Age.
Burgman finds the earth has had much more severe droughts during its natural cycles than we’ve seen recently—including two century-long droughts in California between 900 and 1200 AD.
Will $8-a-gallon gasoline and quintupled electric bills stave off the droughts and crop failures? Probably not. The correlation between our thermometer record and CO2 is weak—only 22 percent. The correlation with the sunspot index is a powerful 79 percent. That says giving up fossil fuels will do no more to change the climate than did the Aztecs sacrificing thousands of human victims on the alters of their weather gods. This time, the human sacrifice might be in the millions.
We’ll have to adapt. Fortunately, we can do this far better then the hapless Anasazi and the hunger-stricken French peasantry 600 years ago. We can move livestock, grow crops in far-flung regions where the rain does fall, and desalinate drinking water for San Diego. We can even evacuate a whole region, without the huge death toll suffered by the Anasazi and the European peasants of the Little Ice Age.
Remember earth’s history, be grateful, and stay flexible.
Jonathon Overpeck and Bradley Udall, “Dry Times Ahead,” Science, vol. 328, p. 1642; June 25, 2010.
Robert Burgman, et al., “Role of tropical Pacific SST’s in global medieval hydroclimate: A modeling study,” Geophysical Research Letters, vol. 37, 2010.