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Cutting soot, ozone will keep climate change in check, says UN

chimney.jpgCutting black carbon and ground level ozone emissions will be the best way to slow temperature rise due to climate change, according to a United Nations Environment Program report discussed today in Nairobi, Kenya.

Curbing these emissions from cars, stoves, forest fires, and other sources could reduce the increase in temperature expected by 2070 by 0.5 degrees Celsius, states the report. The cuts could be achieved using existing technology and current policies, and they would help protect climate, public health, water and food security, and ecosystems.

The report was presented at the annual meeting of the UNEP governing council, a body of 58 ministers who advice the general assembly on environmental matters.


Carbon dioxide is a potent greenhouse gas and it stays around in the carbon cycle for many decades. This means that any effort we make today to curb emissions will have theirs results far in the future. In contrast, ‘black carbon’ and ozone molecules stay for only days to weeks. They are called “short lived climate forcers” and curbing these emissions will produce immediate results.

And unlike carbon dioxide, black carbon particles are not a greenhouse gas. They are black particles present in soot that absorb sunlight, and warm the atmosphere. They are emitted whenever biomass is burned.

The other chemical in the mix, trophospheric ozone, is responsible for the blanket of brown smog in major cities. It forms from methane, nitrogen oxides, volatile organic compounds and carbon monoxide, which are often released by human activity. Ozone at the ground level has been tied to respiratory illnesses such as asthma. It is the third most important contributor to emissions after carbon dioxide and methane.

These particles have a profound impact on climate, states the report. In high latitudes, black carbon particles darken snow and ice. This increases their absorption of sunlight, which worsens the melting of glaciers in the Arctic, the Himalayas and other places.

In the lower atmosphere, black carbon and ozone disrupt the circulation patterns of the monsoon, threatening the livelihoods of millions of people in Asia.

The report suggests 16 measures for cutting these emissions that, together with carbon dioxide reductions, will “greatly improve the chances” of keeping the Earth’s temperature within 2 degrees Centigrade relative to pre-industrial levels. This is the threshold beyond which warming will have dangerous consequences, such as the bleaching of coral reefs, according to the Parties to the United Nations Framework Convention on Climate Change (UNFCCC).

Measures for cutting methane include controlling emissions from livestock, reducing gas emissions from oil and gas pipelines, de-gasifying coal mines, and others.

Measures for reducing black carbon include phasing out old, dirty diesel engines, introducing cleaner burning cook stoves, eliminating high-emitting vehicles, stopping the open-field burning of agricultural waste, and others.

The measures suggested in the report are aggressive and may not actually be achievable in the real world, says Ellen Baum, senior scientist at the non-profit Clean Air Task Force. She calls the proposals an ambitious “thought experiment” that sheds light on measures other than carbon dioxide reductions that can help mitigate climate change.

The report was put together by more than 50 authors who used existing literature as well as two new climate-chemistry-aerosol models.

Image: photo by mira66 via Flickr under Creative Commons.

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