World leaders meeting at the Earth Summit in Brazil are challenged by critical environmental threats to the atmosphere; the diversity of animals, birds, and plants; the soil; and the oceans and coastal areas. Soil
In the past 45 years, an area approximately the size of China and India combined has experienced moderate to extreme soil degradation as a result of human activities, according to UN studies.
This area - nearly 3 billion acres - represents almost 11 percent of the earth's vegetated surface. The largest areas of degraded land are in Asia (1.1 billion acres) and Africa (793 million acres).
Most soil degradation is caused by water and wind erosion resulting from agricultural activities, overgrazing, deforestation, and fuel-wood collection. About 741 million acres worldwide are so damaged that they have lost nearly all of their original biological capacity. Moderate soil degradation, according to the Washington-based World Resources Institute, includes loss of most topsoil, shallow rills and gullies, nutrient decline, and low water retention. Extreme degradation occurs where deforestation an d overgrazing happen on soils naturally poor in nutrients and other materials.
Agriculture is an important sector, if not the backbone, of the national economies of many developing countries, often providing them with sufficient growth to enable people to earn a living. But agriculture is also a culprit, both in soil degradation and in off-farm effects that include water quality.
Runoff of fertilizers, pesticides, and soils often contaminates surface and ground-water aquifers. Human and livestock pressures may also compact soil and damage or destroy native vegetation.
In the United States, an estimated 970 million tons of eroded agricultural soils annually run into reservoirs, reducing their flood-control benefits, clogging waterways, and increasing the operating costs of water-treatment facilities. Worldwide, more than 25 billion tons of productive topsoils erode each year.
While the world's population is expected to double by about the middle of the next century, little good land is left for agricultural expansion. Thus, continued degradation of soils will almost certainly make adequate food production increasingly difficult.
At the Fourth Session of the Preparatory Committee of the UN Conference on Environment and Development in April, delegates addressed concerns from third-world countries about desertification - the loss of arable land - but there is still some question whether delegates will agree to consider a future treaty. According to observers who have followed the issue, some delegates may try to link desertification to a future forest convention beyond the Earth Summit.
Delegates also agreed to strengthen the international framework that governs land management, including problems posed by deforestation, desertification, and drought. In addition, they agreed to develop policies to reclaim degraded lands and conserve areas of risk.