Washington — IN the 1930s, the Midwestern United States suffered the hottest and driest weather on record and crops failed.
Cattle had been allowed to graze freely across the plains, even in dry months, eating what little cover there was and leaving the soil exposed.
Tractors were a new invention, and huge areas of grassland had been ploughed. When the wind came, it lifted tons of sand, then dropped it from the sky.
That was 90 years ago and the author John Steinbeck won a Nobel Prize for his writing about the "dust bowl": sandstorms that saw the ruin of farms and wiped entire settlements off the map.
And the problem is back. In October 2020, NASA used a satellite camera to film a moving mountain of soil 300 kilometres wide and swirling 1 200 metres high, as it covered roads and buildings, silted dams and damaged crops.
On that day, Christi Stulp and her husband were at their farm in Colorado.
"It was Sunday afternoon and my husband was finishing planting wheat," Mrs Stulp told the BBC (British Broadcasting Corporation).
"He said I should go inside, make sure the kids were safe, batten down the hatches and wait for it to go by. It was moving the pastures, moving everything that day," Mrs Stulp added.
According to the BBC Radio 4 programme, Inside Science, the cause is man-made.
NASA has also logged an increase in sandstorms across Africa. On a continent where an estimated 600 million people lack electricity, firewood is used for cooking and to heat homes, and the loss of trees has seen a rapid spread of desert.
Along the edge of the Sahara, winds of up to 90 kilometres per hour move the dunes in such volume they can strip paint from cars and buildings.
Forbes magazine warned that sand from the Sahara was moving fast and high enough to cross the Atlantic and reach North America.
On its website, NASA blames the African dust storms on 'cutting of trees and overgrazing', adding that 'without vegetation to anchor the soil in place, wind erosion scours away the topsoil'.
In countries like Malawi, loosening the protective crust of the earth has had a different but equally serious effect: the silting of dams.
Crops grown illegally along river banks are washed away in a flood, with tons of soil churning in the flow until it reaches a dam where it fills the basin with mud. According to the World Wide Fund for Nature (WWF), more than 200m hectares in Africa -- an area four times the size of Botswana -- could be earmarked for biofuel projects.
The African savanna, like the prairies, sustains a complex ecosystem that if disturbed could lead to the same problem seen in the US. Large parts of Zimbabwe, Mozambique, Kenya and Tanzania have never been farmed intensively, with locals grazing cattle and growing market crops on a scale compatible with the land.
In West Africa, there has been conflict over fields taken from traditional owners for palm-oil plantations. Academic papers have noted the danger of land-wars if large areas are earmarked for biofuel, and rising food prices if current maize production is diverted to ethanol.
The new US dust-bowl has shown how quickly the over-use of land can bring disaster. Namibia and the west coast of South Africa have been hit in recent years by clouds of dust.
"Grasslands with year-round cover have been ploughed up to make way for seasonal crops: echoes of what happened when tractors first arrived on the Great Plains," presenter Roland Pease told listeners.
As in the 1930s, the affected area covers North and South Dakota, Kansas, Nebraska, Iowa, western Minnesota and part of Colorado.
'The irony is that, in much of the Mid-West, expansion of maize production has been encouraged by biofuel incentives, intended to offset global warming," Mr Pease said.
In London, Dr Benny Peiser, director of the Global Warming Policy Foundation (GWPF) has called for a commission of inquiry into the biofuel industry, which, he says, is largely unregulated.
'The threat of a new dust bowl is the direct yet unintended consequence of ill-conceived climate policies," Dr Peiser said.
"While biofuel may attract investment from companies trying to go green, we must learn from history. Or the road to hell will be paved with good, green intentions."
THREAT TO AFRICA
In September 2019, the airport at Alexander Bay north of Cape Town had to be closed because pilots were unable to see the runway.
NASA says it will continue to monitor the aerial movement of sand in both Africa and the Americas.