Brown clouds fuelling Asian glacier meltdown

Pollution filled "brown clouds" are intensifying the impact of global warming over south Asia which is melting glaciers vital to the region's water supplies.

The combined heating effect of greenhouse gases and brown clouds is enough to account for the retreat of Himalayan glaciers over the past 50 years, says a paper by a team from Scripps Institution of Oceanography at the University of California, San Diego.

Professor V Ramanathan, lead author of the paper published in the journal Nature this month, said: “The conventional thinking is that brown clouds have masked as much as 50 percent 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 percent.”

The team found that brown clouds, which contain soot, trace metals and other particles from urban, industrial and agricultural sources, enhanced solar heating of the lower atmosphere by about 50 percent.

This melting of the glaciers has implications for the region’s population.

They supply water to the major Asian rivers including the Yangtze, Ganges and Indus, which in turn supply billions of people in China, India and other south Asian countries.

The Nature article concludes: “The rapid melting of these glaciers, the third-largest ice mass on the planet, if it becomes widespread and continues for several more decades, will have unprecedented downstream effects on southern and eastern Asia.”

Achim Steiner, United Nations under-secretary general and executive director of the UN Environment Programme (UNEP), which helped support the research, said: “The main cause of climate change is the build up of greenhouse gases from the burning of fossil fuels. But brown clouds, whose environmental and economic impacts are beginning to be unravelled by scientists, are complicating and in some cases aggravating their effects.

“The new findings should spur the international community to ever greater action.”

The research was based on data gathered by aircraft last year over the Maldives during the region’s dry season when polluted continental air travels south to the Indian Ocean.

David Gibbs

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