A new report by the United Nations Environment Program and the World Meteorological Organization, proposes a climate-change stopgap: by controlling two noxious ground-level pollutants, black carbon (or soot) and ozone. Reducing levels of these substances would slow the rate of climate change in the first half of the 21st century while carbon dioxide levels are brought down over the longer term.

Both black carbon and ozone contribute to climate change but both could be reduced relatively easily and inexpensively.

Black carbon particles attract heat, warming the air around them if they remain suspended, and melting snow and ice if they settle on glaciers. The main sources of black carbon are dirty diesel generators and primitive cooking stoves in the developing world. Cleaner cooking methods and  particle filters on diesel vehicles would greatly reduce the problem.

Ozone at ground level acts as a heat-trapping blanket. Ozone levels can be substantially reduced by exerting tighter control over activities that release methane into the air, such as cattle farming, waste-water treatment and coal mining. In many instances, methane can be readily captured and fburned to make energy or, if necessary, simply flared.

NASA image of China on 22 February 2011
The haze is mostly black carbon and ozone.