Huge haze clouds over the Indian Ocean contribute as much to atmospheric warming as greenhouse gases and play a significant role in the melting of the Himalayan glaciers, according to a study published Thursday.
Scientist Veerabhadran Ramanathan and his colleagues sent unmanned measuring devices into the haze pollution, known as Atmospheric Brown Clouds, over the Indian Ocean in March 2006 near the island of Hanimadhoo.
Measuring aerosol concentrations, soot levels and solar radiation, the team concluded that the pollution - mostly caused by the burning of wood and plant matter for cooking in India and other South Asian countries - enhanced heating of the atmosphere by around 50 percent and contributed to about half of the temperature increases blamed in recent decades for the glacial retreat.
Ramanathan said his team's research shows that the brown clouds are therefore an additional factor in the melting of glaciers, along with overall global warming caused by greenhouse gas emissions.
Until this study, which is published in the journal Nature, scientists believed the brown clouds mostly deflected sunlight, cooled the atmosphere and did not contribute much to the effects of global warming. But Ramanthan said their observations show that particles also absorbed sunlight and warmed the atmosphere much more than previously believed.
"All we are saying is that there is one other thing contributing to atmospheric warming and that is the brown cloud," said Ramanathan, a chief scientist at the University of California San Diego's Scripps Institution of Oceanography in La Jolla, Calif.
Prof. Syed Iqbal Hasnain, a senior fellow at the Centre For Policy Research in New Delhi and a glacial expert, agreed that brown clouds could be a factor in the melting of the glaciers that supply water to most Asian rivers. But he said more research was needed to understand why the Himalayan glaciers in China are also melting at a dramatic rate.
"Glaciers across Himalaya are receding but their response is dependent on many factors like size, orientation and intensity of monsoonal moisture," he said in an e-mail message from New York. "There is a great urgency on the part of the international scientific community to establish high altitude research stations across Himalaya and monitor climate accurately to develop scientifically correct models."
Scientist have expressed concerns that the Himalayan glaciers will melt entirely and the rivers will run dry for months at a time, fed only by annual rains like the monsoon that sweeps across the subcontinent every summer. Exacerbated by India and China's fast-growing, coal-fed economies, scientists have predicted that the glaciers are melting at a rate up to 15 meters (49 feet) a year and could further decline with temperatures projected to rise as much as 6.4 degrees Celsius by 2100.
While much of the melting has been blamed on global warming, Ramanthan said the new findings offer another way to tackle the problem of the melting glaciers. He said he was hopeful the findings would spur regional governments to step up efforts to replace wood-burning stoves, for example, with solar powered cookers and biogas plants that capture methane and carbon dioxide emissions and convert them to fuel.