4x4s whip up a worldwide dust storm

Dust storms emanating from the Sahara have increased tenfold in 50 years, contributing to climate change as well as threatening human health and destroying coral reefs thousands of kilometres away.

And one major cause is the replacement of the camel by four-wheel drive vehicles as the desert vehicle of choice.

Andrew Goudie, professor of geography at Oxford University, blames the process of Toyotarisation -- a coinage reflecting the near-ubiquitous desert use of Toyota Land Cruisers -- for destroying a thin crust of lichen and stones that has protected vast areas of the Sahara from the wind for centuries.

Four-wheel drive use, along with overgrazing and deforestation, were the major causes of the world's growing dust storm problem, the scale of which was much bigger than previously realised, Goudie, master of St Cross College, told the International Geographical Congress in Glasgow on Thursday.

"I am quite serious, you should look at deserts from the air, scarred all over by wheel tracks, people driving indiscriminately over the surface breaking it up. Toyotarisation is a major cause of dust storms. If I had my way I would ban them from driving off-road."

The problem has become so serious that an estimated 2-3-billion tons of dust is carried away on the wind each year. Storms in the Sahara transport dust high into the atmosphere and deposit it as far away as Greenland and the United States.

Britain was seeing increasing levels of "blood rain" in spring that came direct from the Sahara, Goudie said. From an aircraft over the Alps in summer it was possible to see the telltale colour of red dust on the mountains.

Although the storms are mainly particles of quartz, smaller than grains of sand, they also contain salt and quantities of pesticide and herbicide which can cause serious health problems. Microbe-laden dust from storms is also credited with carrying cattle diseases such as foot and mouth.

The world's largest single dust source is the Bodélé depression in Chad, between an ever-shrinking Lake Chad (now a twentieth of its size in the 1960s) and the Sahara. The depression releases 1 270-million tons of dust a year, 10 times more than when measurements began in 1947, according to Goudie's research.

Taking the whole Sahara, and the Sahel to the south, dust volumes had increased four to sixfold since the 1960s. Countries worst affected were Niger, Chad, northern Nigeria, Burkina Faso, and Mauritania, the research found.

Smothering of coral reefs

But the effects went far beyond. In the Caribbean, scientists had directly linked the death of coral reefs to smothering by dust which had travelled 4 800km.

African dust had also found its way to Greenland, Goudie said. While white ice reflected sunlight and remains frozen, the dark dust on top absorbed the sun's heat, causing the ice to melt and accelerating the raising of sea levels.

Goudie said it was as yet uncertain what other effects the dust was having on the climate. The airborne dust both reflected sunlight back into space and blanketed the earth holding the heat in. When it dropped in the sea it fertilised the plankton which absorbed carbon dioxide and cooled the ocean surface, creating fewer clouds and less rain -- a vicious circle which made the dust problem worse.

Where the dust source was the dried-up bed of a salt lake or sea, salt deposited from the storms could ruin agricultural land, leading to more deserts and more dust. There might be more serious consequences for human health emerging elsewhere in the world.

The Aral Sea in central Asia had almost dried up, according to the research. Its inflowing rivers were used for irrigating cotton, causing the seabed to be contaminated by pesticide toxins which were now being blown about in the dust. People who have breathed in the dust have serious allergic reactions.

Goudie also warned that climate change might cause dust problems to return to the US prairies. While improved agricultural practices, wind breaks and higher rainfall had cured the Dust Bowl of the 1930s (immortalised in John Steinbeck's novel the Grapes of Wrath), the conditions were once again similar. Dust storms were now common in the US and could lead to a disease, Valley Fever, an allergic reaction to pesticides in the dust which caused inflammation of the nose and throat, killing several people a year.

In China, extensive efforts had been made to plant trees to hold back the dust, and increases in rainfall had also helped, the study found. However, large dust storms were still emanating from the vast deserts in the north, which included the Lopnor nuclear test site -- raising fears that storms could interfere with the 2008 Olympics in Beijing and might contain radioactive particles. The Chinese have said they were confident this would not happen.

Choking storms hit far and wide

Dust storms are typically 200km wide and carry 20 to 30-million tons of dust. Some carry up to 100-million tonnes Worldwide dust in the atmosphere is predicted to be 2-billion-3-billion tons this year
Florida receives more than 50% of the African dust that hits the US, causing increased respiratory problems

Mauritania, which had two dust storms a year in the early 1960s, now has 80 a year

The worst dust storm to reach Britain was in 1903 when an estimated 10-million tons landed from the Sahara

- Guardian Unlimited © Guardian Newspapers Limited 2004