Date: 21-Feb-11
Country: NORWAY
Author: Alister Doyle

Strict curbs on soot and ozone air pollution would limit global warming by 0.5 degree Celsius (0.9 F) in a step toward achieving tough world climate goals, a U.N.-backed study showed on Friday.

Stricter limits on "black carbon" soot and tropospheric ozone -- a greenhouse gas that is a big component of smog -- would also clear the air and so reduce human deaths and improve crop yields, especially in Asia, it said.

"Rapid implementation of proven emission reduction measures would have immediate and multiple benefits for human well-being," it said.

Proposed measures include cuts in flaring of natural gas, curbing gas leaks from pipelines and reducing methane emissions from livestock. Poor countries should make wider use of cleaner-burning stoves, and open-field burning of farm waste should be banned.

The study, backed by the U.N. Environment Program, the World Meteorological Organization and the Stockholm Environment Institute, will be reviewed by environment ministers from around the world during a meeting in Nairobi from February 21-25.

Full implementation of proposed measures to clamp down on black carbon and ozone would reduce future global warming by 0.5 degree Celsius (0.9 Fahrenheit), within an estimated range from 0.2 to 0.7 degrees Celsius, the report said.

Almost 200 countries agreed in Cancun, Mexico, in December to limit a rise in world temperatures to below 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times, mainly by curbing emissions of carbon dioxide, the main greenhouse gas.

Many studies show that existing pledges for cuts in greenhouse gas emissions are insufficient to reach the 2 degree goal, which is viewed as a threshold to dangerous change from floods, heatwaves, desertification and rising sea levels.

"This is not an alternative to carbon dioxide reductions, it's complementary," Johan Kuylenstierna, of the Stockholm Environment Institute who was scientific coordinator of the report, told Reuters.

The study also estimated that less air pollution could avoid 2.4 million premature human deaths a year and the annual loss of 52 million metric tons, or about 2 percent, of world production of maize, rice, soybean and wheat.

"The most substantial benefits will be felt immediately in or close to the regions where action is taken to reduce emissions, with the greatest health and crop benefits expected in Asia," it said.

Black carbon, caused by incomplete burning mainly of fossil fuels and wood, is blamed for accelerating global warming by soaking up heat from the sun. Soot can darken snow and ice when it lands, hastening a thaw such as in the Arctic or Himalayas.

Ozone is not directly emitted but is produced from precursors including methane and carbon monoxide. The troposphere is the lower atmosphere -- higher up, ozone is beneficial as un ultra-violet sunshield.

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