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Asian Brown Cloud
A summary of the large brownish haze layer and its impact on the radiative heating of the atmosphere and surface for South Asia; effects on regional temperature, rainfall, agriculture and health.

Executive SummaryExecutive Summary
[.pdf, 3226.1Kb]
(United Nations Environmental Program)

Part 1 The South Asian Haze: Air Pollution, Ozone and AerosolsPart 1 The South Asian Haze: Air Pollution, Ozone and Aerosols
[.pdf, 2732.1Kb]
(United Nations Environmental Program)

Part 2 Climate and Environmental ImpactsPart 2 Climate and Environmental Impacts
[.pdf, 4914.4Kb]
(United Nations Environmental Program)

Part 3 Global and Future ImplicationsPart 3 Global and Future Implications
[.pdf, 1067Kb]
(United Nations Environmental Program)

The first comprehensive report on the environmental impact of South Asian haze was released by UNEP and the Center for Clouds, Chemistry and Climate (C4) in August 2002. The report is largely based on the studies of the Indian Ocean Experiment (INDOEX) and its team of 200 scientists. It provides a summary of the large brownish haze layer and its impact on the radiative heating of the atmosphere and surface for South Asia and the Indian Ocean during the INDOEX campaign. It also discusses preliminary findings with respect to the effects of the haze on regional temperatures, rain fall, agriculture and health. However, the researchers cannot determine with confidence the relative contribution of biomass and fossil fuel burning to the brown cloud.

The report can be viewed in 4 PDF files from the UNEP web site or downloaded above.

Findings are based on limited sets of modeling studies. Because definitive conclusions cannot yet be drawn, these studies emphasize the importance of the haze on climate great need for further research into the problem of brown haze.

The report also includes a proposed strategic framework for Project Asian Brown Cloud (ABC).

  • Brown haze extends over South, Southeast and East Asia
  • Haze is concentrated 3 kilometers above the surface and can travel halfway around the globe in less than a week
  • Large surface cooling due to reduced sunlight perturbs the hydrological cycle
  • Black carbon and ash
  • Sulfates
  • Nitrates
  • Mineral dust
  • 75% of the cloud is man-made
  • Forest fires
  • Inefficient cooking fuels
  • Factories
  • Motor vehicle use
  • Significant reduction of solar radiation to the surface by as much as 15%
  • Altered regional monsoon patterns (less sea evaporation from sunlight means less rain)
  • Less rain in northwest India, Pakistan, Afganistan, and western PRC by as much as 40%
  • More rain and flooding in other areas
  • Reduction of photosythesis (drop in agricultural productivity)
  • Acid deposition and plant damage
  • Respiratory ailments

Source: UNEP and C4. The Asian Brown Cloud: Climate and Other Environmental Impacts UNEP, Nairobi

Go to the BAQ 2004 website
Regional and global effects

Secretariat: The World Bank & Asian Development Bank