Polluted haze over Indian Ocean may speed up Himalayan glacier melting

21 August, 2007:

Man-made haze of polluted air over the Indian Ocean may contribute more to climate change in the region than previously thought, possibly aiding the
melting of Himalayan glaciers that feed important Asian waterways.

Aerosol particles in the smog cause as much atmospheric warming as greenhouse gases such as carbon dioxide, according to an article in the journal Nature. That probably caused air temperatures to increase in the Himalayan-Hindu Kush region, where glaciers supply the Yangtze, Indus and Ganges rivers, say researchers.

Scientists generally have thought that aerosol particles – which in most cases contain soot from burned fuels such as coal, oil or wood – have a cooling effect, a researcher at the University of Colorado, the United States, said. The precise impact depends on the make-up of light-absorbing or light-scattering particles known to contribute both to atmospheric solar warming and to surface cooling.

Peter Pilewskie, associate professor at University of Colorado’s Laboratory of Atmospheric and Space Physics in Boulder, said in a separate editorial on the study that the new findings might seem to contradict the general notion of aerosol particles as cooling agents in the global climate system.

Since the new research suggests that the results might be representative of what is happening on a larger scale, scientists now must examine the impact of regional pollution from urban areas, airborne dust, and the effects of cloud and aerosol interaction in other places, Pilewskie said.

The researchers, led by Veerabhadran Ramanathan, professor of Applied Ocean Sciences at the University of California-San Diego, the United States, calculated heating rates using measurements of solar radiation, aerosol and soot levels collected near the island of Hanimaadhoo in the northern Maldives.

After conducting 18 aerial missions using unmanned vehicles designed to test atmospheric conditions, the team concluded that the polluted brown clouds increased warming trends in the lower atmosphere by about 50%.

The discovery also led the research team, which received funding from the National Science Foundation and other agencies in the United States, to suggest that scientists may have underestimated the impact of climate change in the region since the 1950s – with the profoundest effects in the elevated Himalayan glacial areas.

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

The report of the latest discovery in the journal Nature follows findings published in May 2007 that linked temperature increases in the Indian Ocean to changes in atmospheric heating. Oceanographers at the Commonwealth Scientific and Industrial Research Organization, Australia’s national science agency, had then said that the ocean’s temperature in certain subtropical latitudes has risen by 2 degrees Celsius (35.6 degrees Fahrenheit) in the past 40 years. The warming, they warned, would probably affect rainfall in the arid southern region of Australia, where the amount of rain has decreased.