Whipping up a worldwide dust storm
By Paul Brown
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 miles 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.
Major causes
Four-wheel drive use, along with overgrazing and deforestation, were the major causes of the world's growing dust storm problem, Prof Goudie, master of St Cross College, told the International Geographical Congress in Glasgow, Scotland.
"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. ''
The problem has become so serious that an estimated 2-3 billion tonnes 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 U.S. Britain was seeing increasing levels of `blood rain' in spring that came direct from the Sahara, Prof Goudie said.
Not just quartz
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 Bodele depression in Chad, between an ever-shrinking Lake Chad (now a twentieth of its size in the1960s) and the Sahara. The depression releases 1,270m tonnes of dust a year, 10 times more than when measurements began in 1947, according to Prof Goudie's research.
Taking the whole Sahara, and the Sahel to the south, dust volumes had increased four to six-fold since the 1960s. Countries worst affected were Niger, Chad, northern Nigeria, Burkina Faso, and Mauritania, the research found.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 3,000 miles. African dust had also found its way to Greenland, Prof Goudie said.
While white ice reflected sunlight and remained frozen, the dark dust on top absorbed the sun's heat, causing the ice to melt and accelerating the raising of sea levels. Prof 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 fertilized the plankton, which absorbed carbon dioxide and cooled the ocean surface, creating fewer clouds and less rain — a vicious circle that made the dust problem worse.
Health hazards
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.
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.
Prof Goudie also warned that climate change might cause dust problems to return to the U.S. prairies. While improved agricultural practices, windbreaks and higher rainfall had cured the Dust Bowl of the 1930s, the conditions were once again similar.
Dust storms were now common in the U.S. 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. — Guardian Newspapers Limited 2004
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