"Brown clouds" increase warming in Asia

Reduction of air pollution could slow down glacier melt

"Brown Clouds" over Bengal © NASA / VisibleEarth
Read out

The glaciers of the Himalayas and other tropical regions are melting faster and faster. Now a study published in "Nature" proves a major role for this process for the "Brown Clouds" over South Asia. These clouds of pollutant and fine particulate emissions help warm the atmosphere, but at the same time raise hopes that reducing air pollution could at least slow down climate change in the region.

The "white giants" in the Himalayas are an important resource for much of Asia. Because they supply the lifelines of the densely populated plains, rivers like the Yangtze, the Ganges or the Indus, with water. In recent decades, however, the glaciers on the "roof of the world" have shrunk dramatically. "The rapid melting of these glaciers, the planet's third-largest ice mass, could have unparalleled effects on South and East Asia if it continues or even increases, " scientists at the Scripps Institute of the University of California, San Diego, call Professor V. Ramanathan.

They investigated the role of the "brown clouds", pollutant clouds of soot, greenhouse gases and other emissions, in this process. For some time, it has been known that the particulate matter of such pollutant clouds plays a key role in climate development: some of the aerosols absorb sunlight and heat the atmosphere, but on the other hand the particles shield the surface from part of the sunlight and have a cooling effect. similar to normal clouds.

Measuring campaign with robotic aircraft

Which effect predominates and what is left of climate effects is up to now largely unexplained. However, according to Ramanathan and his colleagues, the "dimming effect" of pollutant clouds may have so far masked even the full extent of anthropogenic warming. The researchers analyzed data collected by unmanned aerial vehicles during a March 2006 Maldives campaign.

Nature cover © Scripps / Nature

The Maledives Autonomous Unmanned Aerial Vehicle Campaign (MAC) took place during the regional dry season, at a time when large volumes of industrial pollution, slash-and-burn and traffic drift from the Indian continent across the Indian Ocean. The measurement aircraft produced a profile of the Ru concentrations and the light absorption over the entire vertical extent of the pollutant clouds and allowed for the first time a deeper insight into the structure and combined effects of these clouds. display

Suspended global cooling, but warming in Asia

Analysis of the data, including using a climate model, revealed that warming in Asia is even more pronounced in higher altitudes than on Meeresh hey. The largest warming registered the scientists exactly at the height, in which most of the Himalayan glaciers lie.

Air Pollution Over Pakistan NASA / Visible Earth

"The conventional view assumes that brown clouds could have masked up to 50 percent of global warming by so-called global dimming, " explains Ramanathan. This is true on a global scale, but our study shows that over southern and eastern Asia the cloud particles in the clouds increase the atmosphere's warming trend by as much as 50 percent verstrken.

These results should encourage the international community to take even more decisive action, especially at the next, decisive climate summit in Indonesia this December, said Achim Steiner, executive director of the United Nations Environment Program (UNEP). "It is likely that by reducing emissions we can address both climate change and air pollution, and thus brown clouds."

(Scripps Institution of Oceanography, 02.08.2007 - NPO)