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Tiny pollution particles may control earth's water supply
ACCORDING TO a United Nations Population Fund report released Nov. 7, water use has grown six-fold over the past 70 years. "Water may be the resource that defines the limits of sustainable development," the report notes.
A new study undertaken by researchers at 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.
Tiny aerosols primarily made up of black carbon, the authors 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 Science.
"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 Professor V. Ramanathan, who 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.
As sunlight heats the ocean, water escapes into the atmosphere and falls out as rain. So as aerosols cut down sunlight by large amounts, they may be spinning down the hydrological cycle of the planet."
They also note that these aerosol particulates may be suppressing rain over polluted regions. Within clouds, aerosols can limit the size of cloud droplets, stifling the development of the larger droplets required for efficient raindrops.
Early in the project, 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, the 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.
In the Science paper the authors say that the aerosol issues raised from INDOEX are a "major environmental concern."
Not only do they question the role aerosols are playing on the regional and global hydrological cycle, but, they say, globally averaged, the aerosol increases the solar heating of the atmosphere accompanied by a reduction in the solar heating of the surface of the planet and these effects maybe quite comparable with the forcing due to greenhouse gases.
The immediate next step, the authors argue, is to develop a reliable global inventory of aerosol emission rates, life times, and concentrations.
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