July 15, 2010

Best hope for saving Arctic sea ice is cutting soot emissions

The quickest, best way to slow the rapid melting of Arctic sea ice is to reduce soot emissions from the burning of fossil fuel, wood and dung, according to a new study by Stanford researcher Mark Z. Jacobson.
He examined the effects of soot – black and brown particles that absorb solar radiation – from two types of sources. He analyzed the impacts of soot from fossil fuels – diesel, coal, gasoline, jet fuel – and from solid biofuels, such as wood, manure, dung, and other solid biomass used for home heating and cooking in many locations. He also focused in detail on the effects of soot on heating clouds, snow and ice.
What he found was that the combination of both types of soot is the second-leading cause of global warming after carbon dioxide. That ranks the effects of soot ahead of methane, an important greenhouse gas. He also found that soot emissions kill more than 1.5 million people prematurely worldwide each year, and afflicts millions more with respiratory illness, cardiovascular disease and asthma, mostly in the developing world where biofuels are used for home heating and cooking.

Jacobson found that eliminating soot produced by the burning of fossil fuel and solid biofuel could reduce warming above parts of the Arctic Circle in the next 15 years by up to 1.7 degrees Celsius. For perspective, net warming in the Arctic has been at least 2.5 degrees Celsius during the last century and is expected to warm significantly more in the future if nothing is done.
The most immediate, effective and low-cost way to reduce soot emissions is to put particle traps on vehicles, diesel trucks, buses, and construction equipment. Particle traps filter out soot particles from exhaust fumes.
Soot could be further reduced by converting vehicles to run on clean, renewable electric power.
Jacobson found that although fossil fuel soot contributed more to global warming, biofuel-derived soot caused about eight times the number of deaths as fossil fuel soot. Providing electricity to rural developing areas, thereby reducing usage of solid biofuels for home heating and cooking, would have major health benefits, he said.
Soot from fossil fuels contains more black carbon than soot produced by burning biofuels, which is why there is a difference in impact.
Black carbon is highly efficient at absorbing solar radiation in the atmosphere, just like a black shirt on a sunny day. Black carbon converts sunlight to heat and radiates it back to the air around it. This is different from greenhouse gases, which primarily trap heat that rises from the Earth’s surface. Black carbon can also absorb light reflecting from the surface, which helps make it such a potent warming agent.

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