The ‘Dust Bowl’ of the 1930s saw high winds and choking dust snarl their way across the Great Plains of the USA. The disaster was a result of both manmade and natural causes. As farmers sought to grow their way out of the economic hardship of the Great Depression, they used newly mechanised equipment to convert soil-stabilising grasses to crops. Convinced by land developers that ‘rain follows the plough’, they left the land defenceless against the wind.
A similar pattern has been developing today. Writing in Geophysical Research Letters, a group of climatologists from the University of Utah has shown that since 2000, dust cover in the Great Plains has been increasing by five per cent per year.
Once again, the increase is related to farming. Between 2006 and 2011, 530,000 hectares of grassland across North and South Dakota, Nebraska, Minnesota and Iowa were replaced by new crops. Cropland surface coverage on the Great Plains has increased by five to ten per cent annually since 2000.
A chief contributor to this rise is the 2005 Corn Ethanol Mandate, created to help supplement the nation’s dwindling gas reserves with renewable biofuels. Tracts of native grasslands in the Great Plains have been converted to corn – a biofuel feedstock. ‘On the one hand, the biofuel transition lowers carbon emissions, but a side effect is the rising dust levels,’ says Andy Lambert, one of the study’s authors.
‘I’ve heard reports of 40 per cent corn acreage increases in the state of Iowa due to this policy,’ adds Scott Denning, professor of atmospheric science at Colorado State University. He largely agrees with Lambert: ‘Agricultural intensification in North America has consequences; environmental and human health consequences that arise from increased dust.’
Anna Gannet-Haller, the study’s lead author, says that farmers are actively encouraged to cultivate marginal lands. ‘Across the USA, farmers buy crop insurance, which allows them to receive payments back from cultivated lands. They’re in a scenario where they’re not losing money by farming more land.’ As a result, she says, insurance policies have a hand in thickening the dust cover. She is quick to divert blame from farmers themselves, however. ‘Farmers care deeply for their land, and they want to preserve it for the next generation,’ she says. ‘It’s not that farmers aren’t deserving of government help. There are just better ways to incentivise farming without encouraging expansion into marginal lands.’
One approach is to improve existing policies aimed at preserving soil quality. ‘Some do exist already,’ says Lambert. The ‘Sod saver’ provision of the 2014 US Farm Bill disincentivises grassland–cropland conversion by reducing crop insurance subsidies. However, enforcement is limited to just 36 per cent of the region where grassland is being converted.
Any policy change will need to be steered carefully. The biofuel boom saw power plants emerge across the ‘grain belt’ of the Great Plains, creating new labour opportunities for rural economies. The Renewable Fuels Association estimates that 49,937 jobs were created by Iowa’s ethanol industry alone. ‘Farmers are dependent on their livelihoods here. We can’t just rapidly change that,’ says Lambert.
However, without intervention, the dust is only likely to worsen. The Great Plains are once again in severe drought. Tree-ring reconstructions of summer soil moisture for 2000–2018 show that the period was the driest since 800 CE. The plains’ inhabitants will bear the health burden. Current models show that, between 2076 and 2095, dust thickening in the southwest of the Great Plains will increase annual hospitalisations from cardiovascular and respiratory illnesses by 300 per cent.
Gannet-Haller and Lambert say that the time to act is now. ‘The question we’re asking is: “How do we make policy changes that can help us to avoid the situations that climate models predict?”’