A new United Nations study warns that a toxic cloud of pollution hanging over much of South Asia may be responsible for causing widespread disease and environmental damage in the region. Scientists say much of the damage results from deforestation.

The study from the U.N. Environment Program says a three-kilometer deep Asian brown cloud of ash, soot, acids and other particles may be responsible for a steep increase in respiratory diseases, drought and flooding across South Asia.

The report says most of the pollution making up the so-called "Asian brown cloud" comes from wood and dung-burning stoves, cooking fires and other low-tech pollutants, as well as from biomass burning - the clearing of forest and vegetation by burning.

The report, which was compiled by more than 200 scientists, is based on data compiled by ships, planes and satellites in the Indian Ocean area between 1995 and 2000.

Syed Hasnain is a professor of environmental science at New Delhi's Jawarhalal Nehru University. Although he is not involved in the U.N.-sponsored study, he says there is no question that low-tech pollutants are having a dramatic impact on climate change in South Asia.

"Because of the burning and all that - the forest fires and bio-mass burnings - the ambient temperature is increasing, so that the normal circulation pattern that was there earlier is disrupted," said Prof. Hasnain. "Another important impact of the monsoonal change in this part of the world is that there is less snow cover over the Himalayas and central Asia.

So over the years, particularly in the last few years, there is less snow cover. That also creates a temperature adjustment which creates the Asian monsoonal rainfall."

Professor Hasnain and other scientists say that, as a result, rainfall has increased in Bangladesh, Nepal and northeastern India. However, precipitation in Pakistan and northwestern India has decreased, resulting in prolonged periods of drought.

So far this year, forecasters in India say there has been a shortfall of about 25 percent in the monsoon rains, so far, mainly affecting western, central and northern India. However, in Bangladesh, Nepal and eastern India, heavier than unusual rains have resulted in massive flooding, submerging hundreds of villages and forcing tens of thousands of people into relief camps.

Preliminary findings from the U.N. report were released Monday. The final report is expected to be issued later this month at the World Summit on Sustainable Development in Johannesburg, South Africa.