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The Asian brown cloud is a layer of air pollution that covers parts of the northern Indian Ocean, India, Pakistan, and parts of South Asia, Southwest Asia, and China.1 2 Viewed from satellite photos, the Cloud appears as a giant brown stain hanging in the air over much of Asia and the Indian Ocean every year between January and March, possibly also during earlier and later months. The term was coined in reports from the UNEP Indian Ocean Experiment (INODEX).
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Causes
In some humidity conditions, it forms haze. It is created by a range of airborne particles and pollutants from combustion (e.g. woodfires, cars, and factories), biomass burning and industrial processes with incomplete burning.3 The cloud is associated with winter monsoon (November/December to April) during which there is no rain to wash pollutants from the air.
Observations
This pollution layer was observed during the Indian Ocean Experiment (INODEX) intensive field observation in 1999 an described in the UNEP impact assessment study published 2002.4 Scientists in India claimed that the Asian Brown cloud is not something specific to Asia.5 Subsequently, when the United Nations Environment Programme (UNEP) organized a follow-up international project, the subject of study was renamed the Atmospheric Brown Cloud with focus on Asia.
Although aerosol particles are generally associated with a global cooling effect, recent studies have shown that they can actually have a global warming effect in certain regions such as the Himalayas.6
Impacts
The second assessment study was published in 2008.7 It highlights regional concerns:
- Changes of rainfall patterns with the Asian monsoon. The observed weakening Indian monsoon and in China northern drought and
southern flooding is influenced by the clouds.
- Retreat of the Hindu Kush-Himalayan- glaciers and snow packs. The cause is attributed to rising air temperatures that are more pronounced in elevated regions, a combined warming effect of greenhouse gases and the Asian Brown Cloud. Also deposition of black carbon decreases the reflection and exacerbates the retreat. Asian glacial melting could lead to water shortages and floods for the hundreds of millions of people who live downstream.
- Decrease of crop harvests. Elevated concentrations of surface ozone is likely to affect crop yields negatively. The impact is crop specific.
The report also addresses the global concern of warming and concludes that the brown clouds have masked 20 - 80 per cent of greenhouse gas forcing in the past century. Thus, air pollution regulations can have large amplifying effects on global warming.
A recent CSIRO study found that the Asian Brown Cloud is also affecting rainfall in Australia.8
References
- ^ Srinivasan, J (10 September 2002). "Asian Brown Cloud – fact and fantasy" (PDF). Current Science 83 (5): 586–592, http://www.ias.ac.in/currsci/sep102002/586.pdf.
- ^ 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): 28371–28398. doi:, http://www.agu.org/pubs/crossref/2001/2001JD900133.shtml.
- ^ Taylor, David (1 January 2003). "The ABCs of Haze". Environmental Health Perspectives 111 (1): A20, http://www.ehponline.org/docs/2003/111-1/forum.html#thea.
- ^ UNEP Impact Study of the "Asian Brown Cloud"
- ^ http://www.ijoem.com/article.asp?issn=0019-5278;year=2008;volume=12;issue=2;spage=93;epage=95;aulast=Pandve Harshal T Pandve: "The Asian Brown Cloud"]
- ^ Ramanathan, Veerabhadran (2 August 2007). "Warming trends in Asia amplified by brown cloud solar absorption". Nature 448: 575–578. doi:.
- ^ Atmospheric Brown Clouds. Regional assessment report with focus on Asia
- ^ Rotstayn, Leon (2 May 2007). "Have Australian rainfall and cloudiness increased due to the remote effects of Asian anthropogenic aerosols?". Journal of Geophysical Research 112 (D09202): D09202. doi:, http://www.agu.org/pubs/crossref/2007/2006JD007712.shtml.
External links
- NASA Eyes Effects of a Giant 'Brown Cloud' Worldwide
- 'Asian Brown Cloud' poses global threat
- Project Proposal Project Asian Brown Cloud
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- This page was last modified on 19 November 2008, at 22:59.
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