Man-made ‘brown clouds’ darkening cities, threatening health in Asia

13 November 2008 – A three-kilometre-thick “brown cloud” of man-made pollution, which stretches from the Arabian Peninsula to China to the western Pacific Ocean, is making Asian cities darker, speeding up the melting of Himalayan glaciers and impacting human health, according to a new United Nations Environment Programme (UNEP) report.

Atmospheric Brown Clouds (ABCs), resulting from the burning of fossil fuels and biomass, has resulted in the formation of particles such as black carbon and soot which absorb sunlight and heat the air, experts write in the study released today in Beijing.

The clouds also “mask” the actual warming impact of climate change by anywhere between 20 and 80 per cent because they include sulfates and other chemicals which reflect sunlight and cool the surface.

The artificial lowering of temperature by ABCs is leading to sharp shifts in weather patterns, causing significant drying in northern China while increasing the risk of flooding in the Asian nation’s south. Monsoon precipitation over India and South-East Asia has dropped up to 7 per cent since the 1950s, with the summer monsoon both weakening and shrinking.

Meanwhile, the health and food security of 3 billion people in Asia are threatened by ABCs, which impacts air quality and agriculture.

Achim Steiner, UNEP’s Executive Director, voiced hope that “Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia” will serve as an early warning of the phenomenon, which he hopes will now be “firmly on the international community’s radar.”

He called on developed countries to help their poorer counterparts attain the technology needed to spur ‘green’ economic growth.

“In doing so, they can not only lift the threat of climate change but also turn off the soot-stream that is feeding the formation of atmospheric brown clouds in many of the world’s regions,” the Executive Director said.

The new publication points out 13 megacities as being ABC ‘hotspots’: Bangkok, Beijing, Cairo, Dhaka, Karachi, Kolkata, Lagos, Mumbai, New Delhi, Seoul, Shanghai, Shenzhen and Tehran. Soot levels in these cities comprise 10 per cent of the total mass of all man-made particles.

Since the 1970s, the Chinese city of Guangzhou, among other cities, has witnessed “dimming” – or reduction of sunlight – of more than 20 per cent, it notes.

The solar heating of the atmosphere by ABCs is “suggested to be as important as greenhouse gas warming in accounting for the anomalously large warming trend observed in the elevated regions” such as the Himalayan-Tibetan region, the study says, leading to the retreat of glaciers.

Further, the clouds contain toxic aerosols, carcinogens and other harmful particles, which could result in more people suffering from respiratory disease and cardiovascular problems.

While the effects of the clouds on food production and farmers’ livelihood could be immense, more research must be done to determine their precise role, it acknowledges, adding that the possible impact of ABCs could include elevated levels of ground-level ozone, which could result in massive crop losses of up to 40 per cent in Asia.

Scientists behind the report – produced by UNEP’s Project Atmospheric Brown Cloud – stress that brown clouds also can be found in parts of North America, Europe, Southern Africa and the Amazon Basin, and that they also require urgent and detailed research.


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