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Black Carbon – Solutions from Soot?

April 4, 2013

Nature’s Secrets by Meg Lowman

Breathing the sooty plume from a maladjusted diesel engine or a smoldering cooking fire has always been ill-advised. But a new study finds that soot is warming the climate about twice as fast as scientists had estimated.

Richard Kerr, Science Magazine (25 January 2013)

For a typical mom in rural India, breakfast does not involve take-away Starbucks, microwaved oatmeal, frozen waffles, or sparkling tableware extracted from an automatic dishwasher. Instead, it usually consists of leaning over a wood-burning stove for many hours, inhaling particulates while cooking for your family. This scenario exists for millions of moms in India, China, South America, Indonesia, and Africa. While traditional cooking has a fairly small energy footprint compared to western cooking, it also emits black carbon, otherwise known as soot.

Soot results from the incomplete combustion of fossil fuels or biomass. Common sources of soot are wild fires, diesel engines, wood stoves, and agricultural burn-off. When soot plumes settle on surfaces, the dark particles absorb heat and accelerate warming. The good news is that soot disintegrates from the atmosphere after only a few days or weeks; but the bad news is that soot is on the increase. Soot has a three-fold impact on global temperatures — its dark particles absorb sunlight, shrink cloud droplets, and darken ice/snow (leading to accelerated melting). Scientific evidence indicates that black carbon may have caused up to 50% of the recent Arctic ice melt. In addition, soot causes lung disease in women and children who use wood-burning stoves.

The eradication of soot could slow down the planet’s current warming trends, providing more time to develop cleaner energy technologies such as solar, wind, nuclear, and hydrogen. A recent study published in the Journal of Geophysical Research claims that soot is warming our planet twice as fast as scientists had predicted, adding 1.1 watts per square meter to our climate system (second only to carbon dioxide which adds 1.66 W/m²). But, all soot is not equal. According to the JGR study, reducing soot from diesel engines and from coal currently burned under less optimal conditions are top priorities. A distant third is to reduce soot plumes from cook stoves, but this scenario also poses enormous ethical issues. Should villagers in developing countries who use very little energy during their entire lifetimes (as compared to Americans and other developed countries) be enforced to give up their cooking practices to stabilize global temperatures? Nonetheless, the recent clarification of soot’s significance to our atmosphere could also lead to positive social outcomes. If developed countries take the lead to design cleaner stoves, developing countries could become the beneficiaries of healthier cooking conditions.

Scientists and policy-makers alike consider the reduction of soot a “low-hanging fruit” which can be plucked quickly to delay the consequences of rising global temperatures. What about a million-dollar prize for designing a clean cook-stove? It must be not only durable, but also produce food that tastes good to the users to guarantee acceptance. Solar-powered stoves reduce soot by as much as 90%, but replacing hundreds of millions of cook-stoves in developing countries is no easy task. On the other hand, some energy experts believe that changing the cook-stoves of 3 billion people may actually be easier than altering the energy culture of 300 million Americans.

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