Loss of Topsoil
The rate of soil erosion now vastly exceeds soil formation. Soil is washed away ten times faster than it is replenished in the US and 50 times faster in China and India. In some areas of the Great Plains, agricultural topsoil has decreased in thickness from 12 inches to less than four inches. As a result of erosion in the last 40 years, 30 percent of the world's arable land has become unproductive. Just as it takes hundreds of years for a clear-cut forest to return to an old growth state, an inch of topsoil can take 500 years to form, and at least six inches are needed for crop production.
Where land is dry and bare, soil is easily eroded by winds. Americans are familiar with the 1930's Dust Bowl of the Great Plains, which took place after years of over plowing followed by successive droughts. The same phenomenon occurred in the Soviet Union in the 1960s and is now frequent in northern Africa and China. In 2001, the western US was blanketed with dust from a huge storm in China and Mongolia.
Where land is dry and bare, soil is easily eroded by winds. Americans are familiar with the 1930's Dust Bowl of the Great Plains, which took place after years of over plowing followed by successive droughts. The same phenomenon occurred in the Soviet Union in the 1960s and is now frequent in northern Africa and China. In 2001, the western US was blanketed with dust from a huge storm in China and Mongolia.
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