"The Middle East has to be part of our program because here the problem is that the dust and pollution can interact," Ramanathan said on the sidelines of a conference on atmospheric pollution in the Gulf city of Dubai.

"I presumed this region was clean, but the dust haze in the desert is a lot less than here in the city. Then I saw this picture," he said, pointing to aerial shots of a cloud hanging over Dubai, a modern city of skyscrapers on the edge of desert.

"This haze is about 300 meters (yards) above the ground, I would say. It could be coming locally or from several hundred kilometers away," he said, adding no research had been done into the effects of oil refineries along the Gulf coastline.

Ramanathan's team, backed by the United Nations Environment Program (UNEP), first identified a blanket of chemicals and dust from cars, aerosols and agricultural and industrial waste across most of South Asia in 1999.

The discovery provoked denials from Indian officials who felt India was being singled out as a culprit and was seen by some as vindicating the Bush administration in 2001 when it pulled out of the global Kyoto climate treaty.

Ramanathan, an atmospheric scientist at the Scripps Institution of Oceanography at the University of California, said the major contributors to a worldwide circle of pollution were Los Angeles, Delhi, Bombay, Beijing and Cairo.

"Pollution in the eastern United States can go in four or five days to Europe and in a week it goes from Europe to South Asia. This is fast transport which converts a local problem into a regional and global problem," the Indian scientist said.

He and the UNEP have ditched the reference to Asia, now preferring "Atmospheric Brown Cloud" or just "Brown Cloud," he said.

GLOBAL DRYING?

Most scientists studying global warming due to ozone depletion are predicting a warmer but wetter world because of the melting of polar icecaps.

But Ramanathan said he suspected the effect of the shroud of pollution across the globe would be to dry the planet.

"We're interested to see if the planet will be warmer and wetter or warmer and drier. My research suggests a large drying effect, especially in the Tropics," Ramanathan said, referring to the area stretching from South Asia to Africa.

"The haze is reducing sunlight to the oceans and one of the things sunlight does is evaporate water from the ocean which gives us rain in the water cycle," he said.

He said recent research by his team in an agricultural plain running across north India near the Himalayas showed that 10 to 17 percent of sunlight was not reaching the ground.

The team made use of advanced satellite imagery, but the focus of environmental work needed to shift to the processes going on inside the pollution band itself, Ramanathan said.

"We need ground observatories which can probe the atmosphere, which can be integrated with satellite observation...We need to use laser instruments and unmanned aircraft to monitor up to four km (2.5 miles) in the air," he said.