Asian Brown Cloud Particulate Pollution Amplifies Global Warming

A new analysis of pollution-filled “brown clouds” over south Asia by researchers at the Scripps Institution of Oceanography in La Jolla, Calif., suggests that the region may be able to arrest some of the alarming melting of Himalayan and other tropical glaciers by reducing its air pollution.

The team, led by atmospheric chemist V. Ramanathan of Scripps, found that atmospheric brown clouds enhanced solar heating of the lower atmosphere by about 50%. The results are in a paper in this week’s issue of the journal Nature.
The combined heating effect of greenhouse gases and brown clouds, which contain soot, trace metals and other particles from urban, industrial and agricultural sources, is enough to account for the retreat of Himalayan glaciers in the past half century, the researchers concluded. These glaciers supply water to major Asian rivers, including the Yangtze, Ganges and Indus. These rivers are the chief water supply for billions of people in China, India and other south Asian countries.

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

The scientists based their conclusions on data gathered by a fleet of unmanned aircraft during a landmark field campaign conducted in March 2006, in the skies over the Maldives, an island nation in the Indian Ocean south of India.

The conventional thinking is that brown clouds have masked as much as 50 percent of global warming by greenhouse gases through 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 in fact amplifying the atmospheric warming trend caused by greenhouse gases by as much as 50 percent.
—V. Ramanathan

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