Asia — f you’ve noticed a haze over the city, here’s a possibly big reason for it. A dirty brown haze, sometimes more than a mile thick, is darkening skies over vast areas of Asia, the Middle East, southernAfrica and the Amazon Basin, changing weather patterns and threatening health and food supplies.
The huge smog-like plumes, caused mainly by the burning of fossil fuels and firewood, are known as ”atmospheric brown clouds”. When mixed with emissions of carbon dioxide and other gases blamed for warming the earth’s atmosphere like a greenhouse, they are the newest threat to the global environment, according to a report commissioned by the UN Environment Program and released on Thursday.
Soot levels in the air were reported to have risen alarmingly in Mumbai, New Delhi, Kolkata and 10 other megacities Bangkok, Beijing, Cairo, Dhaka, Karachi, Lagos, Seoul, Shanghai, Shenzhen and Tehran.
Brown clouds were also cited as dimming the light by as much as 25% in some places including New Delhi, Karachi, Shanghai and Beijing. The clouds have been found to be more than a mile thick around glaciers in the Himalaya and Hindu Kush mountain ranges. They hide the sun and absorb radiation, leading to new worries not only about global climate change but also about extreme weather conditions.
One of the most serious problems resulting from the brown haze that envelopes vast areas of Asia, the Middle East, southern Africa and the Amazon Basin, is the retreat of the glaciers in the Himalayas and Hindu Kush and in Tibet, according to lead researcher Veerabhadran Ramanathan, a professor of climate and oceansciences at the University of California in San Diego.
The glaciers feed most Asian rivers and “have serious implications for the water and food security of Asia,” Ramanathan said.
Monsoon rains over India and south-east Asia have decreased between 5% and 7% overall since the 1950s, the report says, naming brown clouds andglobal warming as a possible cause.
Likewise, they may have contributed to the melting of China’s glaciers, which have shrunk 5% since the 1950s. The volume of China’s nearly 47,000 glaciers has fallen by 3,000 sq km in the past 25 years, according to the Chinese Academy of Sciences.
Health problems associated with particulate pollution, such as cardiovascular and respiratory diseases, are linked to nearly 350,000 premature deaths in India and China every year, said Henning Rohde, a University of Stockholm scientist who worked on the study.
Soot winds up on the surface of the glaciers that feed the Ganga, Indus, Yangtze and Yellow rivers, which makes the glaciers absorb more sunlight and melt more quickly and also pollutes the rivers, the researchers say.
The worst-hit appears to be the Chinese city of Guangzhou, where sunlight in winter had dimmed by more than 20% since the 1970s. For India as a whole, the dimming trend has been running at about 2% per decade between 1960 and 2000 – more than doubling between 1980 and 2004, it adds.
Brown clouds are caused by an unhealthy mix of particles, ozone and otherchemicals from cars, coal-fired power plants, burning fields and wood-burning stoves. First identified by Ramanathan in 1990, the clouds were depicted on Thursday as being more widespread and causing more environmental damage than previously known.
The phenomenon complicates the climate change scenario, because the brown clouds also help cool the earth’s surface and mask the impact of global warming by an average of 40%, said the report. The enormous cloud masses can move across continents within three to four days. Although they also form over the eastern US andEurope, winter snow and rain tend to lessen the impact in those areas.