Earlier this month, a storm front swept across the Great Plains of the United States, plowing up a wall of dust that could be seen from space, stretching from eastern Colorado into Nebraska and Kansas. It was a scene straight from the Dust Bowl of the 1930s, when farmers regularly saw soil stripped from their fields and whipped up into choking blizzards of dust.
Better get used to it. According to a new study, dust storms on the Great Plains have become more common and more intense in the past 20 years, because of more frequent droughts in the region and an expansion of croplands. “Our results suggest a tipping point is approaching, where the conditions of the 1930s could return,” says Gannet Haller, an atmospheric scientist at the University of Utah who led the study.
The dust storms not only threaten to remove soil nutrients and decrease agricultural productivity, but also present a health hazard, says Andy Lambert, a co-author on the study and a meteorologist at the U.S. Naval Research Laboratory in Monterey, California. The dust contains ultrafine particles that can penetrate cells in the lungs and cause lung and heart disease.
Lambert came across the trend unexpectedly, while reviewing data from NASA satellites that remotely measure atmospheric haze due to smoke and dust. No matter how far back he went in the data, the trend remained. Using a network of dust sensors in the region, Lambert and his colleagues were able to corroborate the satellite data and push the trend back more than 20 years.
The findings, reported on 12 October in Geophysical Research Letters, show that across large parts of the Great Plains, levels of wind-blown dust have doubled over the past 20 years. One clue that agriculture is responsible is that the dust levels tend to peak during spring and fall—planting and harvesting seasons, Hallar notes.
Experts have blamed the original Dust Bowl events on a combination of climate and agricultural drivers. Beginning in the 1920s, croplands across the Great Plains expanded massively—thanks in large part to mechanized farming and easy plowing. That was followed by an extended drought during the ’30s that included record-breaking heat waves in 1934 and 1936.
But recent studies are showing how climate change is drying out the region. Greenhouse gases are making heat waves like those in the 1930s far more likely, according to a study published in May in Nature Climate Change. And in an April study in Science, researchers suggested much of the western United States is on the brink of a prolonged megadrought that could outrank anything in more than 1000 years. “We really are at the point where droughts could again be as bad as in the 1930s,” says Kasey Bolles, an expert on the Dust Bowl at Columbia University’s Lamont-Doherty Earth Observatory and a co-author on the Science study.
Renewed agricultural expansion is adding to the problem. Grasslands are being plowed up to plant corn near refineries that turn corn into biofuels—spurred by U.S. policies that encourage renewable fuels. Soil is left exposed at critical times of the year. “Much of the expansion has been on less suitable land,” Lambert says. “It’s particularly ironic that the biofuel commitments were meant to help the environment.” Underlining the connection, Haller says the new study identifies a strong correlation between new croplands and the downwind areas where dust levels are growing the fastest.
What worries Lambert is a potential repeat of the 1930s feedbacks, where the wind-borne dust carried away vital nutrients from the soil, leading to crop losses and the need to plow up more terrain—thereby removing stabilizing ground cover and adding to the supply of dust.
Bolles has another concern. Recent research, she says, shows the worst of the dust in the 1930s came not from the fields themselves, but from marginal grasslands scattered around the plains, which perished in the deep droughts and exposed the soil to the wind. With global warming altering regional climate patterns, she once again fears for those grasslands—and is bracing for the Dust Bowl’s second coming.