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Asian brown cloud

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This article is about the Indian Ocean brown cloud. For China, see Air pollution in China.

The Indian Ocean brown cloud or Asian brown cloud is a layer of air pollution that recurrently covers parts of South Asia, namely the northern Indian Ocean, India, and Pakistan.[1][2] Viewed from satellite photos, the cloud appears as a giant brown stain hanging in the air over much of the Indian subcontinent and the Indian Ocean every year between October and February, possibly also during earlier and later months. The term was coined in reports from the UNEP Indian Ocean Experiment (INDOEX). It was found to originate mostly due to farmers burning stubble in Punjab and to lesser extent Haryana and Uttar Pradesh. The debilitating air quality in Delhi is also due to the stubble burning in Punjab.[3]

The term atmospheric brown cloud is used for a more generic context not specific to the Asian region.[4]

Causes

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The Asian brown cloud is created by a range of airborne particles and pollutants from combustion (e.g., woodfires, cars, and factories), biomass burning[5] and industrial processes with incomplete burning.[6] The cloud is associated with the winter monsoon (October/November to February/March) during which there is no rain to wash pollutants from the air.[7]

Observations

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This pollution layer was observed during the Indian Ocean Experiment (INDOEX) intensive field observation in 1999 and described in the UNEP impact assessment study published 2002.[3] Scientists in India claimed that the Asian Brown cloud is not something specific to Asia.[8] 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.

The cloud was also reported by NASA in 2004[9] and 2007.[10]

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.[11]

Impacts

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Health problems

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One major impact is on health. A 2002 study indicated nearly two million people die each year, in Asia alone, from conditions related to the brown cloud.[12]

Regional weather

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A second assessment study was published in 2008.[13] It highlighted regional concerns regarding:

  • Changes of rainfall patterns with the Asian monsoon, as well as a delaying of the start of the Asian monsoon, by several weeks.[14][15] The observed weakening Indian monsoon and in China northern drought and southern flooding is influenced by the clouds.
  • Increase in rainfall over the Australian Top End and Kimberley regions. A CSIRO study has found that by displacing the thermal equator southwards via cooling of the air over East Asia, the monsoon which brings most of the rain to these regions has been intensified and displaced southward.[16]
  • 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 are likely to affect crop yields negatively. The impact is crop specific.

Cyclone intensity in Arabian Sea

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A 2011 study found that pollution is making Arabian Sea cyclones more intense as the atmospheric brown clouds has been producing weakening wind patterns which prevent wind shear patterns that historically have prohibited cyclones in the Arabian Sea from becoming major storms. This phenomenon was found responsible for the formation of stronger storms in 2007 and 2010 that were the first recorded storms to enter the Gulf of Oman.[17][18]

Global warming and dimming

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The 2008 report also addressed the global concern of warming and concluded that the brown clouds have masked 20 to 80 percent of greenhouse gas forcing in the past century. The report suggested that air pollution regulations can have large amplifying effects on global warming.[clarification needed]

Another major impact is on the polar ice caps. Black carbon (soot) in the Asian Brown Cloud may be reflecting sunlight and dimming Earth below but it is warming other places by absorbing incoming radiation and warming the atmosphere and whatever it touches.[19] Black carbon is three times more effective than carbon dioxide—the most common greenhouse gas—at melting polar ice and snow.[20] Black carbon in snow causes about three times the temperature change as carbon dioxide in the atmosphere. On snow—even at concentrations below five parts per billion–dark carbon triggers melting, and may be responsible for as much as 94 percent of Arctic warming.[21]

See also

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References

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  1. ^ Srinivasan (10 September 2002). "Asian Brown Cloud – fact and fantasy" (PDF). Current Science. 83 (5): 586–592. Archived from the original (PDF) on 5 November 2004.
  2. ^ Ramanathan, Veerabhadran; Crutzen, P. J.; Lelieveld, J.; Mitra, A. P.; Althausen, D.; Anderson, J.; Andreae, M. O.; Cantrell, W.; et al. (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. Bibcode:2001JGR...10628371R. doi:10.1029/2001JD900133.
  3. ^ a b Ramanathan, Veerabhadran et al. (2002) The Asian brown cloud climate and other environmental impacts: impact study Archived June 5, 2004, at the Wayback Machine Center for Clouds, Chemistry and Climate, United Nations Environment Programme, Nairobi Kenya, ISBN 92-807-2240-9, accessed 8 December 2008
  4. ^ Haag, Amanda Leigh (2007). "The even darker side of brown clouds". Nature Reports Climate Change. 1 (709): 52–53. doi:10.1038/climate.2007.41.
  5. ^ Gustafsson, Örjan; Kruså, Martin; Zencak, Zdenek; Sheesley, R. J.; Granat, Lennart; Engström, Erik; Praveen, P. S.; Rao, P. S. P.; Leck, Caroline; Rodhe, Henning; et al. (2009). "Brown Clouds over South Asia: Biomass or Fossil Fuel Combustion?". Science. 323 (5913): 495–498. Bibcode:2009Sci...323..495G. doi:10.1126/science.1164857. PMID 19164746. S2CID 44712883.
  6. ^ Taylor, David (1 January 2003). "The ABCs of Haze". Environmental Health Perspectives. 111 (1): A21–A22. doi:10.1289/ehp.111-a21a. PMC 1241333. Archived from the original on 2006-08-28.
  7. ^ 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
  8. ^ Pandve, Harshal T. (2008). "The Asian Brown Cloud". Indian Journal of Occupational and Environmental Medicine. 12 (2): 93–5. doi:10.4103/0019-5278.43269. PMC 2796752. PMID 20040987.
  9. ^ "NASA Eyes Effects of a Giant 'Brown Cloud' Worldwide (2004)". Archived from the original on 2019-02-07. Retrieved 2007-08-21.
  10. ^ Global Aerosol System 2000-2007 (NASA Earth Observatory)
  11. ^ Ramanathan, Veerabhadran; Ramana, MV; Roberts, G; Kim, D; Corrigan, C; Chung, C; Winker, D (2 August 2007). "Warming trends in Asia amplified by brown cloud solar absorption". Nature. 448 (7153): 575–578. Bibcode:2007Natur.448..575R. doi:10.1038/nature06019. PMID 17671499. S2CID 4420513.
  12. ^ Ahmad, K. (2002). "Pollution cloud over south Asia is increasing ill health". Lancet. 360 (9332): 549. doi:10.1016/S0140-6736(02)09762-3. PMID 12241664. S2CID 35909421.
  13. ^ "Archived copy" (PDF). Archived from the original on 2008-11-18. Retrieved 2008-11-18.{{cite web}}: CS1 maint: archived copy as title (link) CS1 maint: bot: original URL status unknown (link)
  14. ^ Brown cloud delaying monsoon.
  15. ^ Paper reporting the delaying of the monsoon being caused by brown cloud[permanent dead link‍]
  16. ^ Rotstayn, Leon; Cai, Wenju; Dix, Martin R.; Farquhar, Graham D.; Feng, Yan; Ginoux, Paul; Herzog, Michael; Ito, Akinori; et al. (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. Bibcode:2007JGRD..11209202R. doi:10.1029/2006JD007712. hdl:2027.42/94749. Archived from the original on 2007-09-30.
  17. ^ "Link Between Air Pollution and Cyclone Intensity in Arabian Sea". National Science Foundation. 2011-11-02. Retrieved 2011-11-07.
  18. ^ Evan, Amato T.; Kossin, James P.; Chung, Chul; Ramanathan, V. (2011-11-03). "Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols". Nature. 479 (7371): 94–97. Bibcode:2011Natur.479...94E. doi:10.1038/nature10552. PMID 22051678. S2CID 4423931.
  19. ^ Biello, David (August 1, 2007). "Brown Haze from Cooking Fires Cooking EarthToo.The brown haze over Asia warms the atmosphere just as much as greenhouse gases". Scientific American.
  20. ^ Biello, David (June 8, 2007). "Impure as the Driven Snow: Smut is a bigger problem than greenhouse gases in polar meltdown". Scientific American.
  21. ^ Boswell, Randy (October 19, 2009). "Burning crops darken Arctic sky, speed polar melt". Canwest News Service. Archived from the original on February 6, 2010.

Further reading

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