Record dust clouds cause continental rifts

May 23, 2001
Web posted at: 4:32 p.m. EDT (2032 GMT)

Monster dust cloud from China drifts over North Korea and Japan as it embarks on a world tour in April

By Richard Stenger
CNN

(CNN) -- A new report suggests that alarming increases in desert dust are the cause of droughts rather than the result, a surprising find that comes on the heels of record levels of stifling particulate matter in China and Africa.

Scientists had previously theorized that wind-borne desert dust actually enhanced rainfall, presuming that large airborne particles formed larger cloud droplets.

But detailed observations of parched regions in central Africa demonstrated the contrary, according to the study, which focused on the African Sahel, a grassy savanna bordering the Sahara desert that once provided natural pastureland for livestock.

Increasing population pressure has turned much of the semi-arid expanse into desert, leading to higher levels of airborne dust during the rainy season. And the dust and other particles in the air actually produce smaller water droplets in clouds, which means hard times for Sahel farmers and herders.

"The effect of dust on cloud properties is to inhibit precipitation," said author Daniel Rosenfeld and colleagues in the May 15 Proceedings of the National Academy of Sciences.

Dust begets more dust

Using satellite and aircraft observations, the team found that clouds forming within desert dust contain small droplets bearing little liquefied fruit. Moreover, the increased dust and drought can beget still more dust and drought.

"The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation," said Rosenfeld, an Earth sciences professor at Hebrew University in Israel.

The authors note that manmade substances are more to blame for killing the rain over dry lands, such as particulate matter from smoke and pollution.

No matter the cause, dust storms that swirl beyond borders have increasingly blanketed countries sometimes oceans away from their source.

The streets of Baichen in the Jilin Province of northern China on April 7 during the peak of the dust storms that gave birth to the dust cloud

Winds have pushed dust from the Sahara across the Atlantic, where the minute grains settle into a reddish haze over much of the East Coast.

And last month, a sprawling Asian dirt storm blew across the Pacific and sprinkled millions of tons of the Gobi and Takla Makan deserts as far east as Florida, making one of the largest North American dust clouds ever recorded.

"You couldn't miss it," said Duane Hilton of Bishop, California. "We usually have 50 miles visibility, but at one point you could see dust in the air looking at objects just 8 to 10 feet away."

Much of Asia soiled again

Such episodes have comparatively little effect on air quality in the United States. But the periodic plumes cause major headaches in cities hundreds of miles downwind like Beijing, blotting out the sun, slowing traffic and closing airports.

The eastward winds have long spurred protests from residents of Korea and Japan, who have faced similar, if milder, dust epidemics from China. The three nations have organized a committee to find a strategy to combat the dust, according to the Earth Policy Institute, an environmental advocacy group.

Overplowing, overgrazing and ill-advised government policies have exacerbated the drought conditions, according to institute president Lester Brown.

"Accelerating wind erosion of soil and the resulting land abandonment are forcing people to migrate eastward, not unlike the U.S. westward migration from the southern Great Plains to California during the Dust Bowl years," he said Wednesday.