Dust Bowl No Fluke

The Dust Bowl of the 1930s still resonates in our cultural memory as a tragic, traumatic event. Each dry summer brings the dread of a return of the near-apocalyptic landscape of dust-covered, wind-blasted farmlands.

Scientific detective work by Jim Clark, H.L. Blomquist Professor of biology at the Nicholas School of the Environment and Earth Sciences, and his colleagues has revealed that cycles of drought were regular events in the Great Plains in ancient times, persisting for decades or longer. The scientists analyzed sediments for evidence of erosion, charcoal (an indication of prairie fires), and pollen, which reveals the kinds of grasses that grew in the time and places studied. Their analysis covered a period 5,000 to 8,000 years ago in the Dakotas, Montana, and Western Minnesota. The scientists postulated that fires were evidence that grasslands existed, and erosion marked periods of a landscape denuded by drought.

When the data were analyzed, "the patterns just jumped right out at us," Clark says. "We were seeing these very coherent drought cycles" in which grass would disappear and erosion would take over for decades or longer.

The regularity of these droughts makes the more recent droughts of the 1890s and 1930s appear "unremarkable," says Clark. While the study did not address the effects of the anticipated climate change from global warming, "what we can say is that these sorts of drought cycles are common, and most of the climate models predict increased aridity in continental interiors in the future," he says. "One could speculate that the droughts could be all that much worse when you realize that it's not only climate change from changing CO2 content in the atmosphere, but also this natural variability out there that we don't fully understand."

The researchers reported their findings at last summer's meeting of the Ecological Society of America.