Windblown: huge clouds packed with desert dust churn across earth's skies. Are these gritty clouds dangerous?

DID YOU KNOW?

* In 1988, residents of the Caribbean islands were surprised to see African locusts dropping from the sky. Scientists believe that thousands of the insects were sent airborne during a dust storm. The strong winds carried them across the Atlantic. But none of the locusts survived the 10-day-lang trip.

* Pink snow sometimes falls from the sky in countries as far north as Norway. The snow is tinted by Saharan sand carried by winds blowing across Era-ape. The sand contains reddish iron oxide.

CRITICAL THINKING:

* Because of global wind systems, pollution and dust that is produced in one country can be carried to another country. What are some issues that might result from this?

CROSS-CURRICULAR CONNECTIONS:

LANGUAGE ARTS: In the 1930s, the United States experienced The Dust Bowl--a severe drought which caused huge dust storms that devastated the country's plains for nearly a decade. Research this time period and write a short stow about the life of someone living in the plains during the dust storms.

RESOURCES

* "Blown Away," by Karen Wright, Discover, March 2005.

* See satellite images of dust storms at: www.esa.int/ esaKIDSen/SEMQ4P5TI8E_Earth_0.html

When howling winds whip up in Earth's largest deserts, it's time to head for cover. Billowing gusts kick up sand, forming walls of fast-moving dust that can block the sun. "You can't see anything that's more than a few meters away," says Joseph Prospero, an atmospheric chemist at Florida's University of Miami, who studies dust storms.

Grains of sand pelt against your skin like thousands of piercing needles, and musty-smelling grit coats your mouth and nostrils. "The amount of dust that gets in the air feels suffocating," says Prospero.

For people who live in and around the deserts along Earth's midsection--such as Central Asia's Gobi Desert and Africa's Sahara Desert--dust storms frequently disrupt daily routines. "When a storm kicks up, you just have to go inside and wait it out," says Prospero. But scientists have discovered that the effects of dust storms extend much farther than the deserts' sandy borders.

Global winds lift dust from Asia and Africa and carry it to other continents thousands of miles away, including North America. Now, many scientists are concerned that the grimy visitor may be putting people and other organisms in danger. Hoping to learn more about the storms' potential health risks, researchers are following the dust trails.

WORLD TOUR

Since the 1990s, scientists have used satellites to spy on wandering dust. Images snapped by these satellites show that high-altitude wind systems (see Nuts & Bolts, p. 20) can carry the dust fast and far.

During the Asian dust storm season--from March through May--winds frequently blow dust clouds eastward across the Pacific Ocean. In just a week, the dust can complete a journey from Asia, over the Pacific, and across the entire United States.

As Asia's storms settle, windstorms begin kicking up dust in Africa's deserts. Between May and October, African dust drifts westward across the Atlantic Ocean, making its way toward the south-eastern coast of the U.S. and islands in the Caribbean Sea.

FOUL CLDUDS

The billows of traveling dust disrupt air quality--creating hazy skies along their routes. Eventually, the winds slow and can no longer keep sandy particles airborne. The dust drops from the sky, depositing a gritty film on every exposed surface.

Studies have shown that this falling desert dust is actually an important nutrient for plants. "Researchers think that rain forests in the northern Hawaiian Islands are nurtured by Asian dust events," says Dale Griffin, a microbiologist with the U.S. Geological Survey.

But the same falling dust that is welcomed by plants can cause health problems for humans and other animals that inhale it. The fine grains can get lodged in people's lungs, as well as cause respiratory problems, such as asthma.

HITCHHIKERS

Many scientists are now concerned that dust storms are also carrying harmful chemical pollutants. In many areas around deserts, farmers sprinkle artificial herbicides and pesticides onto the soil. When that soil blows skyward, these dangerous chemicals hitch a ride too.

By examining Asian dust that has been dumped on the U.S., scientists have also discovered that soot and other air pollutants can latch on to the particles. In New England, scientists analyzed the material left behind after dust from a Gobi Desert storm passed by in 2001. They discovered that the airborne particles contained the toxic gas carbon monoxide--probably emitted by a power plant in Asia. "As a dust storm generated in Asia passes over urban areas, polluted air gets mixed with the dust, and it all gets transported at the same time," explains Robert Talbot, an atmospheric chemist at the University of New Hampshire.

DRIED OUT

Scientists believe that local sources of air pollution outweigh the input from foreign dust storms. But the amount of dust traveling across oceans--and the pollutants it carries--is growing. Today, an estimated 3 billion metric tons of dust blow around Earth each year. And, according to the United Nations Environmental Programme, dust storms in Northeast Asia have increased five fold in the last 50 years. Africa's storms have also intensified over the last 30 years.

What's to blame for the increase? Africa has been experiencing a drought, or period of time when there is unusually low rainfall. With less moisture weighing down the sand, it's easier for strong winds to kick it up. And in some areas, humans may be partly to blame for the growing intensity of the dust storms. Overuse of water has drained lakes--leaving behind dusty holes. Plus, farmers sometimes cut down forests to plant crops, or they allow livestock to overgraze grasslands. "In areas where agriculture strips the protective vegetation from the surface of the soil, you can get a lot more dust moving," says Prospero.

CLEAN UP

Better farming practices may keep more soil packed close to the ground. But, Griffin says, "You are never going to stop the dust storms. They have been occurring for billions of years."

Still, scientists hope that by reducing worldwide pollution from sources like power plants and cars, the most negative impacts of the storms can be lessened. "There's not much that humans can do to control the emissions [of dust] from a desert," says Talbot. "But you can do something to reduce the emissions [of pollutants] in industrial areas."

Nuts & Bolts

Two major global wind belts blow dust around Earth. Along the planet's midsection, trade winds (examples shown below), blow from east to west while moving toward the equator. These winds model dust from Africa across the Atlantic Ocean. At mid-latitudes, prevailing westerlies (examples shown below), travel from west to east while blowing toward Earth's poles, Dust from Asia that gets caught in this wind pattern journeys to the U.S.

It's Your Choice:

1 The Gobi Desert is located in--.

(A) Africa

(B) the Caribbean Sea

(C) Asia

(D) North America

2 Which of the following would NOT increase dust storms?

(A) drought

(B) overgrazing 

(C) cutting down forests

(D) increased rainfall

3 Earth's trade winds

(A) blow toward the poles.

(B) travel from east to west.

(C) are located at northern latitudes.

(D) often blow dust from Asia to North America.

ANSWERS

1. c 2. d 3. b

CHECK FOR UNDERSTANDING

DIRECTIONS: On a separate sheet of paper, answer the following in complete sentences:

1. How do the two major global wind belts blow desert dust around Earth?

2. Name two ways in which traveling desert dust disrupts the environment.

3. How are the dust storms beneficial?

4. Why have dust storms intensified over the years?

5. Although dust storms can't be stopped, what are two ways to decrease their negative impact?

ANSWERS

1. Along the planet's midsection, trade winds blow from east to west while moving toward the equator. These winds propel dust from Africa across the Atlantic Ocean At mid-latitudes, prevailing westerlies travel from west to east while blowing toward Earth's poles. Dust from Asia that gets caught in this wind pattern journeys to the U.S.

2. Traveling desert dust creates hazy skies along its route. And when winds slow and can no longer keep sandy particles airborne, the dust drops from the sky, leaving behind a gritty film. This falling dust can cause problems for humans and other animals that inhale it. The fine grains can get lodged in people's lungs, as well as cause respiratory problems such as asthma Many scientists are concerned that harmful chemical pollutants--such as artificial herbicides and pesticides--and industrial pollutants, including soot and carbon monoxide, are also being delivered by dust storms.

3. Studies have shown that falling desert dust is actually an important nutrient for plants. Researchers think that rain forests in the northern Hawaiian Islands are nurtured by Asian dust events.

4. Africa has been experiencing a drought. With less moisture weighing down the sand, it's easier for strong winds to kick it up. In some areas, humans may be partly to blame Overuse of water has drained lakes leaving behind dusty holes. Plus, farmers sometimes cut down forests to plant crops, or they allow livestock to overgraze grasslands In areas where agriculture strips the protective vegetation from the surface of the soil, you can get a lot more dust moving.

5. Better farming practices may keep more soil packed close to the ground, reducing the amount of dust that gets whipped into the air. Decreasing the amount of pollution that's emitted worldwide by sources like power plants and cars can help reduce the amount of pollutants delivered by the dust storms