The study said the cloud -- a toxic cocktail of ash, acids, aerosols and other particles -- was damaging agriculture and changing rainfall patterns across the region, which stretches from Afghanistan to Sri Lanka.

The lives of millions of people were at risk from drought and flooding as rainfall patterns were radically altered, with dire implications for economic growth and health.

UN Environment Program chief Klaus Toepfer told a news conference: "We have an early warning. We have clear information and we already have some impact. But we need much, much more information.

"There are also global implications, not least because a pollution parcel like this -- which stretches 3 kilometers high -- can travel halfway round the globe in a week."

Toepfer said the cloud was the result of forest fires, the burning of agricultural waste, dramatic increases in the burning of fossil fuels in vehicles, industry and power stations, and emissions from millions of inefficient cookers.

He said the preliminary UN report into what it dubbed the "Asian Brown Cloud" was a timely reminder to the upcoming Earth Summit in the South African city of Johannesburg that action, not words, was vital to the future of the planet.

"The huge pollution problem emerging in Asia encapsulates the threats and challenges that the summit needs to urgently address," he said.

"We have the initial findings and the technological and financial resources available. Let's now develop the science and find the political and moral will to achieve this for the sake of Asia, for the sake of the world," he added.

Professor Victor Ramanathan said the cloud was cutting the amount of solar energy hitting the earth's surface beneath it by up to 15 percent.

"We had expected a drop in sunlight hitting the earth and sea, but not one of this magnitude," he said.

(China Daily August 13, 2002)