That glorious sunset that frames the Taj Mahal? Would you ooh and aah quite so fervently if you knew what was causing it - to wit, smog?

The Times, London [Images], quotes a study published in Nature magazine to underline what environmentalists are calling the Asian Brown Cloud -- an enormous blanket of smog that covers much of the subcontinent.

There is, say scientists, more than aesthetics involved -- they say this smog cover is causing Himalayan glaciers to melt; the consequences could be catastrophic for over two billion people in India, China and Bangladesh, who are downstream along the rivers that are sourced from the Himalayas - including the big three, the Indus, Gangus and Yangtze.

How it works, the Times quotes Nature magazine as saying, is that the smog cover is comprised of gases and of black soot particles known as aerosols, that absorb the sun's heat, and by retaining it, push up temperatures at the higher altitudes.

This heat melts the glaciers; as the pace of meltdown accelerates, populations come at risk as rivers swollen by the melted ice overflow their banks.

The magazine points out that two-thirds of the 46,000 glaciers in the Himalayas are shrinking, leading to increasingly severe floods downstream and, eventually, when the meltdown is complete, to widespread drought.

A research team from the Scripps Institution of Oceanography in California says the Asian Brown Cloud is more to blame than greenhouse gases, previously assumed to be the villain of the piece.

'My one hope is that this finding will intensify the focus of Asian scientists and policy makers on the glacier issue,' Veerabhadran Ramanathan, who led the research, is quoted in the Times as saying. 'These glaciers are the source for major river systems, so at least two billion people are directly involved in this.'

The smog cloud is created, the researchers say, out of the enormous plume of smoke from factories, power plants and wood or dung fires that stretch across the Indian subcontinent, into SouthEast Asia.

The researchers led by Professor Ramanathan's team examined the cloud using three unmanned aircraft fitted with instruments to measure temperature, humidity and aerosol levels.

The aircraft were launched from the Maldives island of Hanimadhoo, the Times reports, and carried out 18 missions over the Indian Ocean in March 2006, flying through the cloud at different altitudes.

They found that the cloud amplified the effects of solar heating on the surrounding air by 50 per cent; and also that some aerosols in the cloud reflected sunlight, cooling the earth beneath in a process known as 'global dimming' that is also worrying climate change experts.

Others absorbed heat radiation from the sun because of their dark color.

When the data was fed into a computer model for climate change, researchers found that Himalayan temperatures had risen 0.25C (0.45F) a decade since 1950, which is twice the average rate of global warming.

'If we continue to use outdated technology to achieve industrialisation, this is only going to get worse,' Professor Ramanathan is quoted as saying.

The only silver lining in the smog is that unlike greenhouse gases, which can stay in the atmosphere for 200 years, aerosols drop to the ground after two to three weeks.

The reason that qualifies as good news is that Asian countries can tackle the problem relatively quickly, by finding alternatives to fuels such as coal, diesel, wood and dung, which account for the majority of aerosols in the air.