Giant pollution cloud hovers over Asia.

• Author: Chaudhry, Shivani

Scientists investigating the effects of pollutant particles on climate last March discovered a dense brown haze covering 9 million square kilometers - an area the size of the United States - over the Indian Ocean. The cloud, thought to have been blown out to sea during the winter monsoons, covers the Arabian Sea to the west of the Indian coast, the Bay of Bengal to the east, and the equatorial Indian Ocean to about 5 degrees south of the equator. It is about 3 kilometers thick, and contains soot, sulphates, nitrates, organic particles, fly ash, mineral dust, and high concentrations of gases such as carbon monoxide and sulfur dioxide.

The research team that made the discovery included scientists from the United States, Europe, India, and the Maldives, who had come to the region to work on the Indian Ocean Experiment (INDOEX), a study of the climatic effects of aerosols - small pollutant particles. V. Ramanathan, of the Scripps Institution of Oceanography, and a co-scientist in the project said, "what really shinned us (was) how pervasive these aerosols were and how they could survive at such long distances from where they originated."

The discovery has intensified debate about the impacts of human activity on climate change. The particles in the cloud are much darker than those found over North America and Europe, so the effects on climate may also be different. It is uncertain whether the overall result is one of warming or cooling. Aerosols, when mixed with clouds, act as reflective surfaces and have a cooling effect, but the soot particles in the...