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May 1, 2008
Columbia Scientists Warn of Modern-Day
Dust Bowls in Vulnerable Regions
Farming transformed a natural drought into
an extreme disaster—and may do so again
Climate scientists using computer models to simulate the 1930s Dust Bowl that devastated the U.S. Great Plains region have found that dust caused by farming activities probably amplified a natural drop in rainfall, turning a normal drying cycle into a widespread agricultural collapse. The Columbia University researchers state that the findings raise concerns that ongoing pressures on farmland from population growth and climate change could worsen the current global food crises by leading to similar extreme events in other vulnerable regions.
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Farmer Arthur Coble and sons, Cimmaron County Oklahoma, April 1936
Photo credit: Arthur Rothstein/Library of Congress
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Recent studies indicate that periodic droughts in the Western United States are controlled by naturally occurring periods of cool sea-surface water temperatures over the eastern tropical Pacific—so-called La Niña phases. Via long-distance winds, these phases indirectly affect faraway rain patterns. In addition to the 1930s, such patterns have occurred in the 1850-60s, 1870s, 1890s, 1950s, and 1999 to present.
The La Niña of 1930s was different—and so extreme—because it was coupled with the arrival of farmers into the Great Plains, where they replaced drought-resistant wild prairie grasses with fragile wheat, neglected to plant cover crops in unused fields, and allowed livestock to overgraze pastures, leading to increased levels of dust.
According to this new study, the dust caused by these unsustainable farming activities fed the disaster, doubling the drop in rainfall, and moving the drought itself northward into major farming regions. When the 1932-1939 drought struck, plants shriveled and more bare soil was exposed. The land was quickly eroded by gigantic dust storms, leading to widespread collapse of the U.S. agricultural system. Skies were chronically darkened by dust. In some years, an estimated 770 million metric tons of topsoil were lost, and over the entire period, 3.5 million people were displaced. The 1930s Dust Bowl was one of the 20th century’s worst environmental disasters.
The researchers, based at Lamont-Doherty Earth Observatory and NASA Goddard Institute for Space Studies, both part of Columbia University’s Earth Institute, used a computer model to simulate a 1930s drought driven only by La Niña. This showed a 5 percent drop in rainfall, centered over northern Mexico and the U.S. Southwest. This would have affected the Great Plains too, but probably would have not brought disaster. Then the modelers added in the effects of dust, using data from the ‘30s representing dust sources, and allowing the computer to create dust storms. This yielded a simulated event much like the Dust Bowl of the ‘30s with a full 10 percent drop in rain—to just 18 inches a year—centered over the prairie farm regions of Northern Texas, Oklahoma, Missouri, Kansas, Nebraska and Iowa.
Lead author Benjamin Cook, a National Oceanic and Atmospheric Administration postdoctoral researcher affiliated with both Lamont-Doherty and the Goddard Institute, said the effect occurred because dust particles suspended in air reflect solar radiation. Studies by other researchers show that this causes a drop in temperatures at or near the soil surface, lessening evaporation of moisture into the air, and thus decreasing precipitation even further. Dust on the Great Plains, therefore, helped draw the drought northward like a siphon, said Cook. “This is what made the Dust Bowl the Dust Bowl,” he said. “It was a process that fed on itself.”
The U.S. Southwest is currently suffering from a serious long-term drought that threatens agriculture and population growth. Cook said it is unlikely that this by itself will cause another Dust Bowl in the United States. One reason for this is due to the Soil Conservation Service (now known as the U.S. Natural Resources Conservation Service), founded in response to the ‘30s crisis, which has shifted farmers into more sustainable practices. Cook, however, points out that many scientists believe hard-pressed farmers and herders in places like China and Africa’s Sahel region may be repeating the history of the U.S., ruining marginal lands in order to have food in the short term.
“This highlights the fact that humans can alter natural events and make them worse,” said coauthor Richard Seager, a modeler at Lamont-Doherty. Seager says that scientists studying global climate change predict many subtropical regions will dry in coming years. “That, in combination with the pressure from rising population and demand for food, could lead to a similar cycle of drought, dust storms and more drought,” he said. “The lesson of the Dust Bowl is there to be learned.”
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