December 25, 2012

The return of major dust bowls

Janet Larsen, Earth Policy Institute - When most people hear the term “dust bowl,” they think of the American heartland in the 1930s, when a homesteading wheat bonanza led to the plowing up of the Great Plains’ native grassland, culminating in the greatest environmental disaster in U.S. history.

Despite warnings from researchers and some farmers, history repeated itself in the Soviet Virgin Lands Project in the 1950s to early 1960s. Some 100 million acres of grassland were plowed under in Russia, Kazakhstan, and western Siberia during Premier Nikita Khrushchev’s push to produce ever more food from the land. When drought hit, the topsoil started to blow away. By 1965, nearly half the newly planted area was degraded by wind erosion. Yields plummeted. Ultimately farmers staged a retreat, abandoning much of that land.

Unfortunately, dust bowls are not just relics of the past. Today two new dust bowls are forming: one in northern China and southern Mongolia and the other in Africa south of the Sahara. Whereas the dust bowls in the United States and the Soviet Union were the result of overplowing, the main culprit in Asia and Africa is overgrazing. Although arid or semiarid grasslands are typically better suited for grazing livestock than for farming, once they are overstocked their protective grass covering deteriorates and they face erosion all the same.

Forty percent of China’s land area is grassland. Following agricultural reforms that began in the late 1970s, in which collectively owned livestock were transferred to household ownership, China’s cattle herds grew from 52 million in 1980 to nearly 105 million in 2000, according to the U.N. Food and Agriculture Organization (FAO). Meanwhile, China’s population of sheep and goats ballooned from close to 180 million to 280 million. Such a high concentration of grazing animals has put unsustainable pressure on the land. For comparison, the United States—a country with comparable grazing capacity—hosts a similar number of cattle but only 9 million sheep and goats.

Noting that an extraordinary 90 percent of China’s grasslands are degraded, the Chinese government has embarked on restoration programs, including re-vegetation, grazing bans, and livestock confinement. The government also has moved nomadic herders off the land or limited their movement under the guise of environmental protection. Evidence from the field, however, reveals that disrupting traditional grazing patterns can exacerbate land degradation and leave pastoralists more vulnerable to the vagaries of the weather.

...Meanwhile, much damage has been done, and China’s dust bowl rages on. More than a quarter of China’s land area is covered by desert, and each year spreading sands claim additional territory. Expanding deserts in the arid northwest are merging. Since 1950, more than 24,000 Chinese villages have been abandoned or are seriously in danger of succumbing to traveling dunes, with some 35 million people directly affected.

The effects reach far beyond the desert margins. Spring is the dust storm season. The snow melts and the wind picks up, transporting dust and sand particles from northern China and Mongolia as far as Beijing and on to Korea and Japan, sometimes even crossing the Pacific to cloud parts of North America. The China Meteorological Administration reports that a single severe dust storm in 2006 dumped 330,000 tons of dust from the west onto Beijing: a stunning 44 pounds for each of the city’s residents. In 2007, a dust storm originating in China’s spreading Taklimakan Desert circled the globe in just under two weeks.

Desert scholar Wang Tao notes that in the first decade of the twenty-first century, China experienced 87 dust storms. Records of very strong dust storms (in which visibility is reduced below 200 meters) show an increase over recent decades, from 5 in the 1950s to 13 in the 1970s, 23 in the 1990s, and 21 between 2000 and 2009. (See data.)

As bad as Asia’s dust storms are, the largest source of dust in the atmosphere on a global scale is Africa. Dust has long traveled out of Africa’s deserts and drylands, which make up two thirds of the continent’s land area; in fact, dust blowing out of Chad’s Bodélé Depression is thought to help fertilize the lush Amazon rainforest. Nearly 75 percent of Africa’s drylands are degraded. With land suffering the double whammy of drought and overuse, dust carried out of West Africa has increased over the last 40 years. Studies suggest that the larger influx of African dust may even be teaming up with rising ocean temperatures to damage Caribbean coral reefs.

In the Sahelian zone south of the Sahara the squeeze is on, with fast-growing populations trying to eke out a living by farming or grazing herds on ever less productive land. Desertification is particularly acute in Burkina Faso, Chad, and Niger, as well as in Nigeria, Africa’s most populous country, where an estimated 868,000 acres are lost to desert each year. Conflicts over land between herders (largely Muslim) and farmers (largely Christian) are legion, with both groups exacerbating erosion. Nigerian pastoralists, largely in the country’s north, have dramatically expanded their herds, putting additional pressure on soils already vulnerable because of erratic rainfall. In 1990, Nigeria had 14 million cattle, 12 million sheep, and 23 million goats. By 2010, cattle populations had climbed just slightly to 17 million, but the number of sheep tripled to 36 million, and goats jumped to 56 m illion.

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