Soot warming earth even more than thought

Richard A. Kerr Science 25 January 2013: Vol. 339 no. 6118 p. 382 DOI: 10.1126/science.339.6118.382

Soot Is Warming the World Even More Than Thought

A new study finds that soot is warming the climate about twice as fast as scientists had estimated.

With roughly 8 million tons of soot produced each year by burning everything from coal in power plants to oil in ship’s boilers, that’s bad news for the planet.

Scientists began the 232-page study—published last week in the Journal of Geophysical Research: Atmospheres—4 years ago in response to calls for drastic reductions in emissions of soot, called black carbon in the scientific literature. Soot particles roughly 100 nanometers in diameter were obviously absorbing solar energy and passing it on to the atmosphere, adding to the warming caused by greenhouse gases.

Under the auspices of the International Global Atmospheric Chemistry Project, 31 researchers from nine countries in a range of disciplines came together to assess the climate effects of soot. Working from published field observations, the authors looked at all the effects of soot on the planet’s retention of solar energy as well as the effects of other products of soot-producing combustion. They then tried to understand why different researchers got different answers from their climate models. “It’s a deeper view,” Bond says.

The new, deeper view—which drew 600 comments from 20 peer reviewers—finds a prominent role for soot in global warming.

All the ways soot can affect climate—among them by:

  • absorbing sunlight
  • shrinking cloud droplets and thus brightening clouds
  • darkening ice and snow

This adds 1.1 watts per square meter (W/m2) to the climate system, the study concludes.

That’s a big number,” Bond says. It puts soot second behind carbon dioxide, which accounts for 1.66 W/m2.

Soot’s contribution to the warming is roughly twice as large as estimated in the 2007 assessment made by the Intergovernmental Panel on Climate Change.


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