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UN Report Highlights Dangers Of ‘Atmospheric Brown Clouds’

November 14, 2008

Thick smog clouds that loom over Asia threaten the livelihood of crops and contain particles that actually reflect the sun’s rays away from the earth, the U.N. reported on Thursday.

These so-called “atmospheric brown clouds” are primarily caused by the burning of fossil fuels and firewood. They can be more than one mile thick and result in changing weather patterns in areas across Asia, the Middle East, southern Africa and the Amazon Basin.

First identified by the report’s lead researcher in 1990, brown clouds are composed of a dangerous mix of soot, particles and chemicals. They have been linked to the melting of Himalayan glaciers and extreme weather conditions that impact agricultural production, according to the report commissioned by the U.N. Environment Program.

“Imagine for a moment a three-kilometer-thick (1.8-mile-thick) band of soot, particles, a cocktail of chemicals that stretches from the Arabic Peninsula to Asia,” said Achim Steiner, head of Kenya-based UNEP, which funded the report with backing from Italy, Sweden and the United States.

“All of this points to an even greater and urgent need to look at emissions across the planet.”

During this summer’s Beijing’s Olympics, brown clouds caught international attention. They hide the sun and absorb radiation, leading to new worries not only about global climate change but also about extreme weather conditions.

Previous studies on brown clouds have been conducted, but the most recent research shows that the phenomenon is not unique to Asia, with pollution hotspots seen in North America, Europe, South Africa and South America.

The enormous cloud masses can move across continents within three to four days. Although they also form over the eastern U.S. and Europe, winter snow and rain tend to lessen the impact in those areas.

Soot levels in the air were reported to have risen alarmingly in 13 megacities: Bangkok, Beijing, Cairo, Dhaka, Karachi, Kolkata, Lagos, Mumbai, New Delhi, Seoul, Shanghai, Shenzhen and Tehran.

Brown clouds were also cited as dimming the light by as much as 25 percent in some places including Karachi, New Delhi, Shanghai and Beijing.

Since the 1950s, the report found a 5 to 7 percent decrease in monsoon rains over India and southeast Asia linked to brown clouds.

“The emergence of the atmospheric brown cloud problem is expected to further aggravate the recent dramatic escalation of food prices and the consequent challenge for survival among the world’s most vulnerable populations,” the report said.

But the U.N., which began studying the problem six years ago, still finds “significant uncertainty” in understanding how brown clouds affect conditions regionally, said the lead researcher, Veerabhadran Ramanathan, a professor of climate and ocean sciences at the University of California in San Diego.

“The main message is that it’s a global problem. Everyone is in someone else’s backyard,” Ramanathan said.

Image Caption: Fires and Thick Smoke Across Southeast Asia. (NASA)

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