PARIS -- The "Asian brown cloud", a vast haze of soot particle hovering over south Asia, is at least partly to blame for China's recent climatic disasters -- drought in the north and floods in the south -- according to a NASA study published this week in U.S. journal *** Science.**** Surabi Menon of NASA and Columbia University and James Hansen of NASA's Goddard Institute said in the study there was a clear link between increased amounts of man-made soot and the kind of climate change witnessed in the south Asian region over the past few years.

"Reducing the amount of black carbon, or soot, may help diminish the intensity of floods in the south and droughts in the northern areas of China, in addition to having human health benefits," Hansen said in a statement.

Menon and Hansen conducted four computer simulations using scientific data from 46 ground stations in China to examine whether airborne soot affected China's water cycle.

They found the soot particles affected the climate by absorbing sunlight, which then heated the air and made the atmosphere more unstable.

This created rising air that formed clouds and brought rainfall to heavily polluted southern China. It was balanced out by an increase of sinking air -- which prevented clouds and rain from forming -- in northern China, contributing to the droughts there.

The researchers took other factors into account, including ocean surface temperature and the presence of other greenhouse gases, in their computer models, AFP reported. In a related commentary in science, scientists William Chameides and Michael Bergin said: "The contribution of black carbon to global warming may be substantial, perhaps second only to that of carbon dioxide."

Soot is generated from industrial pollution, traffic, outdoor fires and household burning of coal and biomass fuels, such as cow dung and field residues. It occurs when the combustion of coal and other fuels is incomplete.

It continues to be produced in large amounts in Asia, especially in China and India, because cooking and heating are done using wood, coal and biomass fuels at low temperatures, which prevents complete combustion taking place.

Based on their simulations, the authors predicted soot-induced cooling over China, extended warming over northern Africa and cooling over the southern United States, amidst overall global warning.

The Asian brown cloud phenomenon has stirred controversy recently, as scientists across the globe warn of its radical consequences and regional scientists retort that it does not exist and is not specifically Asian.

In August the UN Environment Program (UNEP) said the pollution haze was damaging agriculture, modifying rainfall patterns and endangering the population.

Using global models to study the phenomenon, the UNEP said the cloud could reduce precipitation over northwest India, Pakistan, Afghanistan, western China and the western part of Central Asia by as much as between 20 and 40 percent.

But Indian scientists slammed the findings last week as "exaggerated and distorted", saying it was not a thick, choking cloud but only a wintertime haze.

They said the report reflected a trend of blaming developing Asian countries for global pollution.