Key Points:

Dirty brown clouds created by millions of cooking fires in Asia contribute as much to global warming as greenhouse gas emissions and are a major factor in the melting of the Himalayan glaciers, say scientists.

Experts had previously thought the clouds, which hang in a haze over the Indian Ocean, actually acted to deflect sunlight and cool the atmosphere.

The findings have serious implications and will give weight to the voice of those seeking to get India and other developing nations to do more to use renewable energy and find alternatives to wood-burning stoves.

"All we are saying is there is one other thing contributing to atmospheric warming and that is the brown cloud," said Veerabhadran Ramanathan, a senior scientist at the University of California who led the research into the clouds, which was carried out in the spring of last year.

Mr Ramanathan and his colleagues dispatched unmanned measuring devices at different altitudes into the pollution, technically known as atmospheric brown clouds, over the Indian Ocean in March last year, above the Maldives.

They were able to measure aerosol concentrations, soot levels and solar radiation and concluded that the pollution added to the heating of the atmosphere by around 50 per cent.

They suggested that half of recent global temperature increases could be the result of the pollution.

Mr Ramanathan, whose team's findings are contained in Nature magazine, said: "The conventional thinking is that brown clouds have masked as much as 50 per cent of the global warming by greenhouse gases through the so-called global dimming.

"While this is true globally this study reveals that over southern and eastern Asia, the soot particles in the brown clouds are intensifying the atmospheric warming trend caused by greenhouse gases by as much as 50 per cent."

In Asia there is widespread concern about the plight of Himalayan glaciers, many of which are in rapid retreat.

Scientists fear that if they melt entirely - some are already retreating at a rate of 15m a year - many rivers fed by the glaciers will disappear for months at a time.

"In those cases the rivers would only run when there was sufficient seasonal rain from the monsoon to feed them."

Billions of people in Asia rely on water from rivers such as the Yangtze, the Ganges and the Indus.

Mr Ramanathan is working on a project in the foothills of the Himalayas to find alternatives to wood-burning stoves for more than 1000 families.

"If the pollution increases, the glacier retreat will be much worse than projected," he and his colleagues wrote.

"It now depends on what energy path India, China and Asia will take.

"If the rapid melting of these glaciers, the third-largest ice mass on the planet, becomes widespread and continues for several more decades, that will have unprecedented downstream effects on southern and eastern Asia."

Professor Syed Iqbal Hasnain, a glacier expert at the Centre For Policy Research in Delhi, said the brown clouds could be a factor in the melting of the glaciers.

But more research was needed to understand the entire background to what was happening.

- Independent