In the 1930′s, a decade-long drought, high winds, and lack of soil conservation combined to strip the topsoil from hundreds of millions of acres of Great Plains farmland. The loosened soil blew east across Oklahoma, Kansas, and the Texas Panhandle in thick black clouds that turned day into night. This disaster displaced millions of people and came to be known as the Dust Bowl.

The dust storms persisted for ten years, the concentration of flying dirt so thick at times that people couldn’t see more than a few feet ahead. Frequently the strong winds would carry the black blizzards east to Chicago, New York, Philadelphia, and other eastern U.S. cities, obscuring the sun and increasing the incidence of respiratory illness. Eventually, millions of tons of prime Great Plains topsoil sank to the bottom of the Atlantic Ocean.

Conditions made family farming in the Dust Bowl nearly impossible. Between 1935 and 1940, 2.5 million people gave up their farms and businesses in Oklahoma, Texas, Kansas, Colorado, and New Mexico, and migrated west, many of them ending up as migrant workers in California fruit orchards and vegetable fields.

Now, 75 years later, the southwestern U.S., including some of the original Dust Bowl territory, finds itself in the grip of another long-term drought. Texas, Arizona, New Mexico, and parts of Oklahoma have had little or no rain for over a year. Weather forecasts indicate no sign of the drought letting up anytime soon.

On July 5, 2011, high-energy downdrafts triggered by thunderstorms south of Phoenix, Arizona, created 60 mph (96kph) winds that scooped up tons of drought-dry soil and formed into a gigantic dust storm 100 miles (160k) wide and 5,000 ft. (1,524m) high.  Minutes later, this menacing black front roared through Phoenix, coating everything with fine dirt, knocking out power, disrupting travel, and creating health problems.

According to research conducted by USGS, as global warming raises temperatures, dust storms in the American southwest will become more frequent. Average temperature in the region has risen by 1.5°F (approx. 1°C) since 1950, and is projected to increase another 4° to 10°F by the end of the century. Higher temperatures will not only spawn more dust storms, but will also reduce plant density, weakening roots that hold the soil together. Human activities such as farming on arid or semi-arid land, overgrazing, and use of off-road vehicles break the soil crust. This exposes the land to wind erosion and dust storm formation.

Even though long-term drought and adverse weather conditions may bring an increased number of dust storms to the southwest, a Dust Bowl disaster is not a likely outcome, mainly due to improved farming and soil conservation practices in use in the U.S. over the last 70 years. Dust storms will happen but will be localized, and probably not develop on the massive, region-wide scale of the 1930s. However, dust storms of Dust Bowl magnitude are occurring with increased frequency in Saharan Africa, the Middle East, and northwestern China. Although these dust storms appear to be confined to local regions, wind currents carry their dust in suspension to many other parts of the world.

West Africa. There has been a 10-fold increase in dust storms in Saharan Africa since 1950. The increase has been even more dramatic in specific areas, increasing in Mauritania from 2 dust storms in 1960, to 80 last year. These frequent and more powerful events have caused a major loss of topsoil in Niger, Mali, southern Algeria, Chad, Burkina Faso, Mauritania, and northern Nigeria. Main causes of the dramatic change are deforestation and desertification through dry farming without soil conservation measures, loosening the parched soil which is then easily carried away by the high winds that occur in the region.

The African winds blow dust concentrations westward every year, depositing tons of dust and spores in the South Atlantic Ocean, and over a thousand miles away in Central and South America. As these dust clouds drift over the Atlantic, they screen out the sun and cool the ocean water, reducing evaporation, cloud formation, and rainfall. Dust settling in the Atlantic promotes algae bloom, a notorious fish and seafood killer. African dust storm health statistics are not readily available, but reports indicate many suffer from respiratory problems and there are a number of deaths from lung failure every year.

Northwest China. The huge area of China that borders Mongolia and Kazakhstan is semi-arid, with low annual rainfall. Dryland farming without appropriate conservation measures, and overgrazing of the vast high plains pastureland, have exposed loose, dry soil to the strong winds that come down out of the high mountains of Central Asia. These winds blow eastward toward China’s major cities . Beijing, China’s largest city, suffers a series of crippling dust storms every spring. When the dust storms strike, the sky turns orange, and breathing the air is hazardous to health. In recent years, the wind also picks up coal ash piled up outside manufacturing plants, and mixes it in with the soil dust. Coal ash contains high levels of mercury, so the dust storms originating in northwest China now deliver highly toxic clouds of dust, grit, and poisonous air to the cities of China.

Chinese dust storms don’t stop at the borders of China. Other Asian countries are in the path of the east-blowing jet stream, as are Hawaii, and continental United States. In 2001, a dust storm originating in northwest China took two weeks to cross the Pacific Ocean, finally delivering a dust plume 4 miles (7km) thick that hung for days in a dense haze over the Rocky Mountains from Canada to Colorado.

Middle East. Dust storms are an uncomfortable fact of life on the Arabian Peninsula, the vast dry area between the Red Sea and the Persian Gulf, which includes Iraq, Kuwait, and Saudi Arabia. In spring and summer, the subtropical jet stream pushes up from the south at the same time that the polar jet stream pours down from Europe, creating what is known locally as a shamal, a strong wind that blows across the region at over 40 mph (64kph). The shamal picks up fine desert sand in Jordan and Syria, plus silt from the Tigris and Euphrates basins, and blows it southeast as far as India and the horn of Africa.

A strong shamal can create a dust and sandstorm front hundreds of miles wide and over 10,000 ft (3,000m) high. It usually blows continuously for 3 to 5 days, making breathing difficult, gumming up machinery, and sandblasting paint off cars and structures. In 2005, a shamal-driven dust storm brought Baghad to a standstill, one hospital treating more than a thousand patients for respiratory distress. People living in the area can expect 20 to 50 days of shamal sandstorms every year.

As global warming progresses, dust storms around the world will most likely grow in size and frequency, and last longer. And dust storms don’t recognize national boundaries. African dust storms end up in South America, Chinese dust storms in North America, and Middle Eastern dust storms in India and Africa. The dust clouds often pick up other pollutants as they travel, making these storms a serious part of the air pollution problem around the world. We hope that better soil conservation practices, and environmentally safer manufacturing practices in developing countries, will one day reduce the damage in health and treasure presently inflicted on the world population by dust storms.