Air Pollution Might be as Important as CO2 in Affecting Global Climate


American Geophysical Union, Fall Meeting 2007

Soot and other forms of black carbon spread by biomass and fossil fuel burning are disrupting monsoon patterns in Asia, accelerating the melting of snow and sea ice, especially in polar regions, and creating giant metropolitan and regional-scale hot spots around the world, says a researcher at Scripps Institution of Oceanography at UC San Diego.

The effects of such pollution were scarcely considered by climate scientists a decade ago, but Scripps atmospheric science professor V. Ramanathan will present findings in two invited American Geophysical Union 2007 Fall Meeting lectures that show that this newly acknowledged force is as great in some regions as the climate effects of carbon dioxide and other greenhouse gases.

Atmospheric brown clouds (ABCs) filled with sub-micron-sized particles are often generated by industrial activity in and around cities. Ramanathan has observed, however, that such clouds can travel across continents and ocean basins before dissipating. Along the way, they spur formation of often rainless clouds filled with particles that both absorb and reflect light. Their mass and longevity is sufficient to alter climate patterns, including a temperature gradient between the Northern and Southern hemispheres that is a key regulator of Asian monsoon cycles.

ABCs are also altering atmospheric conditions over several world regions by increasing air temperatures and diminishing the amount of sunlight that reaches the ground. Most of Southeast Asia, eastern China, Indonesia, sub-Saharan Africa, Mexico and Central America, and most of Brazil and Peru are among these hot spots.

"Populations of about 3 billion are living under the influence of these regional ABC hot spots," said Ramanathan.

Ramanathan argues that reducing soot emissions can be one means of mitigating large-scale climate changes, especially by significantly reducing the retreat of sea ice and glaciers. Ramanathan's work, especially the Maldives AUAV (autonomous unmanned aerial vehicles) Campaign of 2006, has demonstrated that brown clouds are already accelerating the melting of Himalayan glaciers that provide drinking water to billions of people in South Asia.

"Given black carbon's much shorter lifetime compared to CO2 and its significant contribution to global radiative forcing, a major focus on decreasing black carbon emissions offers an opportunity to reduce the effects of global warming trends in the short term," Ramanathan said. "Reductions in black carbon are also warranted from considerations of regional climate changes and human health."

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