Brown Clouds

Brown clouds are giant brown layers of thick haze composed of pollutants like soot and other particles, hanging over much of Asia and Indian Ocean every year between January and March.

The UNEP Indian Ocean Experiment (INDOEX) first observed such a pollution layer during their field observations in 1999. They gave it the name “Brown Cloud” and published their findings in the United Nations Environment Program (UNEP) Impact Assessment Study, 2002.


Brown clouds are composed of a range of airborne particles and pollutions. Two-thirds of such pollutants originate in the burning of biomass, such as dried twigs, leaves, and dung. The remaining one-third of the pollutants comes from emissions from cars, other burning of fossil fuels, and industrial processes with incomplete burning. All these processes occur throughout the year. However, between December and April, there is no rain to wash away the generated pollutants from the air, and as such, brown clouds form.


Brown clouds constitute a thick layer of soot that traps up to 25 percent of the available sunlight, and this plays havoc with the ecology and environment.

Some particles that make up the brown clouds reflect sunlight and cool down the air. This reduces surface temperatures between 20 and 80 percent, and mask the full impact of global warming. However, other particles within the brown clouds, such as soot and black carbon, absorb sunlight and heat the air, contributing to global warming. This has led to a steady melting of the Himalayan glaciers, the source of many major rivers like Ganga, Yamuna, Indus, Jehlum, Bhramaputra, Irrawady and others. The Chinese Academy of Sciences estimates these glaciers having shrunk by 5 percent since the 1950s. At the current rate of retreat, the Himalayan glaciers could shrink by more than 75 percent by the year 2050, posing a major risk to the region’s water security.

The Brown clouds cause extreme weather conditions. The cooling of air over East Asia caused by the brown clouds has displaced the thermal equator, and consequently the monsoons southwards.This has weakened the Indian monsoons, caused droughts in the Northern parts of China and floods in South China. All these, and elevated concentration of surface ozone has had an adverse impact on agricultural production and resulted in reduced production of key crops such as rice, wheat and soybean in recent years.

Another impact of the brown cloud is particulate pollution that causes health problems like bronchitis, cardiovascular and respiratory diseases. These diseases cause nearly 350,000 premature deaths in China and India every year.

The brown cloud originates in Asia, but can move across continents within three to four days, as researchers from the Scripps Institution of Oceanography at the University of California, San Diego found out. The Brown Cloud phenomenon is thus a major global ecological and environmental issue, and if doomsday planners are to be believed, a sure recipe to a major catastrophe.


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Ramanathan, Veerabhadran (2001). “Indian Ocean experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze”. Journal of Geophysical Research 106 (D22): 2837128398. doi:10.1029/2001JD900133.

Gustafsson, rjan et al. (23 January 2009) “Brown Clouds over South Asia: Biomass or Fossil Fuel Combustion?” Science 323: pp. 495-498, DOI: 10.1126/science.1164857

Petit, C. W. (2003) “A darkening sky: A smoky shroud over Asia blocks both sun and rain” U.S. News & World Report (17 March 2003), 134(8): pp. 46-8

Ramanathan, Veerabhadran et al. (2002) The Asian brown cloud climate and other environmental impacts: impact study Center for Clouds, Chemistry and Climate, United Nations Environment Programme, Nairobi Kenya, ISBN 92-807-2240-9, accessed 8 December 2008}}

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