Blowing In The Wind

Every year, the United States and the Caribbean get a dusting from Asian and African deserts. The results are not pretty and may be getting worse.

Health & Fitness

June 24, 2005|By Dennis O'Brien | Dennis O'Brien,Sun Staff

It's a world traveler that affects climate and may have wiped out the dinosaurs.

Dust, scientists say, is more than something vacuumed from under our beds.

This time each year, dust from Africa hitches a ride on trade winds across the Atlantic Ocean to Florida, where it strengthens thunderstorms, pollutes the air and may be damaging sea corals. Dust storms in China routinely affect Pacific Ocean chemistry. This spring, they clouded the skies over Colorado.

But despite decades of research, scientists say, there is still much to learn about dust and its effect on our lives.

"Dust, with regard to climate, is just not as simple as you might expect," said Steven M. Babin, a researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel.

Dust particles that travel the globe are different from the dust in your home. Household dust consists of fibers from clothing, carpets and upholstery, as well as particles of skin, hair, pollens, mold, wood and paint. Dust that crosses the oceans is made up mostly of tiny sand and soils.

"It can have the consistency of finely milled flour," said Ben Barnum, another Hopkins APL researcher who has developed dust forecasting systems for the military.

But the world's dust problem may be getting worse. As parts of the globe become drier, millions of acres of productive land in Africa and Asia are lost each year, raising more dust as deserts expand, forests disappear and soils erode, according to a United Nations panel.

A U.N. report released last week ranks desert growth and land degradation as one of the world's top environmental problems. Experts say that droughts, population growth and global warming are making things worse, drying up areas and producing more dust.

"While warming might increase rainfall in some parts of the world, areas that are dry lands are getting drier," said Zafar Adeel, an author of the report.

Whether dust speeds up, slows down or even contributes to climate change is still unresolved -- in part because dust is being blown all over the world and comes in different sizes.

Large dust particles reflect sunlight and cool things down. But smaller particles absorb sunlight and radiate it, boosting temperatures, experts say. And dust's effect on the oceans may be different from its effect on various terrestrial environments.

"You can't just say dust causes cooling or dust causes warming. It kind of does both," says Babin. "When you're trying to determine the net effect on climate, I don't think it's been conclusively demonstrated at this point.

Weeklong journey

What is certain is that millions of tons of dust are lofted each year from Africa's Sahara and China's Gobi deserts, rising 20,000 feet on thermal winds. Once airborne, the dust takes about a week to make its way to the United States.

Some scientists blame dust raised by an asteroid strike with blocking out the sun and causing climactic changes that wiped out the dinosaurs 65 million years ago.

Dust has been migrating around the globe for centuries. Much of the Caribbean's soil is, in fact, dust blown from Africa, researchers say.

"A major source for soils in the Bahamas, the Florida Keys and the Caribbean islands is dust from Africa," said Joseph M. Prospero, a researcher at the University of Miami who has been studying African dust transport for 30 years. He said small amounts of African dust contribute to air pollution in Miami every summer and traces of it have been found as far north as New England.

Dust can be tracked by satellite imagery and traced to its origin by its chemical composition. Dust from Africa has less calcium than dust native to the United States, said Kevin Perry, a researcher at the University of Utah.

"We know that in terms of the dust from Africa, it's not coming from the entire continent, but from some very localized sources. Some dry lake beds and basins," Perry said.

Satellites show that 230 million tons of dust leaves Africa each year. About half of that ends up in the Atlantic. But about 50 million pounds of it winds up clouding the skies each summer over the Caribbean and Florida, said Yoram Kaufman, a physicist and atmospheric scientist at the NASA Goddard Space Flight Center. His findings were recently published in the Journal of Geophysical Research.

Some researchers argue that while dust feeds phytoplankton -- tiny marine organisms that help offset the effects of climate change -- dust from Africa could be killing Caribbean sea corals.

Dust increases the number of updrafts of warm, moist air created just before a thunderstorm. Updrafts which are considered a basic ingredient in a storm's formation. The dust also increases the strength of the updrafts, researchers reported this year.

"The dust essentially invigorates the storm," said Paul DeMott, an atmospheric scientist at Colorado State University.

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