The Asian Brown Cloud, as the blanket of pollutants over South Asia and the Tibetan plateau is called, is not only weakening the monsoon but is responsible for half the warming observed in the Himalayas, Syed Iqbal Hasnain, senior fellow at The Energy and Resources Institute, said here Monday evening.

He was delivering a talk organised by the Indian Mountaineering Foundation on the melting of Himalayan glaciers due to climate change. Scientists fear the melting will lead to water scarcity in the north and south of the Himalayas, affecting well over a billion people.

"With 70% of the Indian population using biomass for cooking, the Asian Brown Cloud covers the entire sub-continent at a height of around 3,000 feet," said Hasnain, a former vice chancellor of Kozhikode University and formerly from New Delhi's Jawaharlal Nehru University.

The effect of this cloud gets worse in the cold atmosphere of the Himalayas where the soot gathers and impedes wind, he explained. Apart from the weak monsoon that is causing consternation in India now, the cloud also held up the westerly winds in winter.

"There was not much of a winter in Kashmir this year," Hasnain pointed out. "And hardly any winter snow." It had a bad effect on horticulture.

Scientists have measured the average temperature in the Himalayas had risen by 1.2 degrees Celsius in the last 100-odd years.

Hasnain said 0.6 degrees of this was due to increase in the concentration of carbon dioxide -- the commonly known villain in global warming -- and the other 0.6 degrees is due to black carbon (BC), as the soot is called by scientists.

Hasnain said the effect of BC in reducing monsoon rainfall had also been shown by a recent study carried out by the Indian Institute of Technology, Delhi. "We have measured BC up on the East Rathong glacier in Sikkim. The concentration is three times as should be."

He explained that BC is reducing albido -- the ability of snow to reflect heat -- and thus accelerating melting of the glaciers. East Rathong glacier has reduced in area from 7.125 sq km in 1962 to 0.46 sq km in 2009, a loss of 93 percent.

Another glacier Hasnain has been studying -- Kolahai in Kashmir -- has receded 10 metres per year since 1965.

"The smaller glaciers, those below 10 square kilometres, are disappearing much faster than the big ones like the Gangotri glacier," Hasnain said. "And these small glaciers are the majority among the 15,000-odd glaciers in the Himalayas."

He rued that hydroelectric projects being planned in the lower slopes of the Himalayas were not taking glacier melt into account.

"When these glaciers start melting, they form lakes, and there is a serious danger of these lakes bursting, which will bring huge amounts of silt, rocks and dirt to choke the dams being built downstream."