Tiny particles of pollution may carry large consequences for Earth's water supply

December 07, 2001

A new study conducted by researchers at the Scripps Institution of Oceanography at the University of California, San Diego, argues that particles of human-produced pollution may be playing a significant role in weakening Earth's water cycle much more than previously realized. The study was funded by the National Science Foundation (NSF) and other federal agencies.

Tiny aerosols primarily made up of black carbon, the Scripps scientists argue, can lead to a weaker hydrological cycle, which connects directly to water availability and quality, a major environmental issue of the 21st century. The paper, based on results obtained during the international Indian Ocean Experiment (INDOEX), is published in the December 7 issue of the journal Science.

"By combining a unique set of field measurements with models, INDOEX scientists have provided strong evidence that human-produced atmospheric pollution may be having a profound effect on the Earth's water cycle, weakening it as pollution increases," said Jay Fein, director of NSF's climate dynamics program, which funded the research. "The large extent and magnitude of the effect is an unexpected discovery which will have important implications for environmental policy."

"Initially we were seeing aerosols as mainly a cooling agent, offsetting global warming; in this article we are saying that perhaps an even bigger impact of aerosols is on the water budget of the planet," said Scripps scientist V. Ramanathan, who along with Scripps scientist Paul Crutzen, a co-author of the new study, led the INDOEX science team as co-chief scientists. "Through INDOEX we found that aerosols are cutting down sunlight going into the ocean. The energy for the hydrological cycle comes from sunlight."

The $25 million INDOEX project involved more than 150 scientists across several disciplines from Austria, France, Germany, India, Maldives, the Netherlands, Sweden and the United States. The project was sponsored primarily by the National Science Foundation and the Department of Energy, and funded in part by NASA and the National Oceanic and Atmospheric Administration. It focused on the Indian Ocean region in a Smultiplatform" analysis approach of satellites, aircraft, ships, surface stations and balloons. The project was designed to assess the nature and magnitude of the chemical pollution over the tropical Indian Ocean and to assess the significance of the region's aerosols.

Early on INDOEX researchers documented a human-produced brownish-gray haze layer of about 10 million square kilometers over the Indian-Asian region. The particles within the haze, researchers discovered, were causing a three-fold decrease in solar radiation reaching the earth's surface as compared with the top of the atmosphere. The aerosols, typically in the submicrometer- to micrometer-size range, were a mixture of sulfates, nitrates, organic particles, fly ash and mineral dust, formed by fossil fuel combustion and rural biomass burning.

"One of the key revelations from INDOEX is that air pollution is not only an industrial phenomenon," said Crutzen. "The part of the atmosphere that you would expect to be the cleanest -- areas without a lot of industrialization -- in fact can be very highly polluted, especially during the dry season."

In the Science paper, Ramanathan, Crutzen, J.T. Kiehl (National Center for Atmospheric Research, Boulder, Colorado), and Daniel Rosenfeld (The Hebrew University of Jerusalem), say the aerosol issues raised from INDOEX are a "major environmental concern."
Media contact:
Cheryl Dybas
(703) 292-8070/cdybas@nsf.gov

Program contact:
Jay Fein
(703) 292-8527/jfein@nsf.gov

National Science Foundation

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