The leading pollutant blamed for climate change is carbon dioxide, but a new study says another form of carbon ranks a close second. So-called black carbon is a kind of soot produced by diesel engines, power plants, and the burning of wood. A major source of black carbon is cook stoves in the developing world, and scientists are now trying to clean those stoves up. The World’s Rhitu Chatterjee has the story. (Photo: Rhitu Chatterjee) Download MP3
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JEB SHARP: Scientists generally agree the main pollutant that’s changing the climate is carbon dioxide, produced by the burning of fossil fuels. Wealthy nations, and the rich in developing nations, are mostly to blame for those emissions. But another form of carbon also plays an important role in climate change. And this form of carbon is often produced by poor households. As the World’s Rhitu Chatterjee reports, scientists are hoping to enlist those households to help cool the earth.
RHITU CHATTERJEE: It’s a typical evening rush hour in India’s capital city, New Delhi. Buses, cars, and motorcycles choke the street and the air’s so hazy that it can be difficult to see. The pollution here and across South Asia can be severe and contains an under-appreciated cause of climate change. A kind of soot that researchers call black carbon. It’s a powerful absorber of sunlight, several hundred times more potent than carbon dioxide. Some researchers had previously suggested that the black carbon in India’s air came largely from diesel vehicles and coal power plants. But 6,000 miles from India, in a lab at Stockholm University geochemist Orjan Gustafson recently made a surprising discovery.
ORJAN GUSTAFSON: Okay, here we see the soot-laden filters.
CHATTERJEE: Gustafson has collected soot from India on air filters. The filters look like they came from a vacuum cleaner, covered with dust.
GUSTAFSON: That’s what we see now here is this grayish, brownish coverage on the filter. That contains the soot particles.
CHATTERJEE: Gustafson wanted to know where this soot was coming from. So he used a technique called radiocarbon analysis. That enabled him to determine how much of the soot came from fossil fuels, from cars, motorbikes, and power plants, versus how much of it came from burning wood, crops and other organic matter.
GUSTAFSON: We found that one-third of the soot comes from fossil fuel combustion and about two-thirds comes from biomass/biofuel combustion.
CHATTERJEE: Now that two-thirds comes from a number of different sources. But Gustafson thinks that the vast majority comes from one source, cooking. In the village of Walia Waas outside of New Delhi, its morning. You can smell the smoke, and see thin wisps of it rising from the houses. Families cook meals of vegetables and wheat breads on traditional stoves. A young mother named Nitu takes a ball of dough, pats it back and forth between her palms till its round and flat and ready to be placed on the stove top.
CHATTERJEE: She says she spends several hours every morning and evening at the stove. The stove is called a chulha. It’s made of mud and hollow. Open at the top and on one side and it burns twigs and cakes of dried buffalo-dung and creates a lot of smoke. But Nitu says that doesn’t bother her.
CHATTERJEE: She says all she cares about is that her family eats her food. She says her family likes the food cooked on the chulha. But climate researchers now see these stoves as a significant threat to the region’s climate. Atmospheric scientist V Ramanathan of the University of California San Diego says consider this fact. There are roughly a 150 million rural households in India, virtually all of them with cook-stoves.
V RAMANATHAN: If we can replace those cook stoves with stoves which either completely eliminate or cut down the black carbon emissions by about 70-80%, that would almost have a dramatic impact on black carbon concentration in India.
CHATTERJEE: And replacing dirty cook stoves all over Asia, South America and Africa could have a similar effect on black carbon levels worldwide. Now that won’t stop climate change. In the long run scientists say the big problem is carbon dioxide emissions, not black carbon. But carbon dioxide can stay in the atmosphere for a hundred years. So reductions in emissions today will only bear fruit in the distant future. Black carbon on the other hand is very short lived. Again, Ramanathan.
RAMANATHAN: If you reduce the black carbon today, they’ll be gone few weeks from now. So the effect will be immediate.
CHATTERJEE: And that means targeting black carbon can have a big effect on climate in the short term.
RAMANATHAN: You know we have lost some time in terms of taking remedial actions to slow down climate change. And while we are figuring out how to reduce CO2, reducing black carbon would let us gain some time back.
CHATTERJEE: That idea has become popular among many in the global environmental community. Scientists, entrepreneurs, and environmental groups have rushed in to help replace dirty cook-stoves in the developing world. Ramanathan launched a pilot project in a northern Indian village last year. He’s testing a new model of stove that pollutes less than traditional ones. But getting villagers to use these stoves may not be so easy. Ibrahim Rehman is a scientist at New Delhi’s Energy and Resources Institute and a collaborator on Ramanathan’s cook-stove project. Rehman has spent most of his career trying to get rural Indians to adopt cleaner cook-stoves, not for environmental reasons, but to protect the health of women and children from indoor smoke.
IBRAHIM REHMAN: You see cooking is a very cultural trait.
CHATTERJEE: And people are particular about cooking their food in a certain way. Rehman says others before him have tried to get villagers to switch to solar cook-stoves. But people didn’t like them.
REHMAN: Solar cookers in the rural areas is not a very practical idea at the moment because they are really not able to take care of different customs, practices, food habits of local communities.
CHATTERJEE: The stoves he’s testing now are similar to the traditional ones. They burn dung, and plant material, only more efficiently. But whether they will be adopted by the local people remains to be seen. Back in Walia Waas, Nitu’s family already owns a modern gas stove, the kind used by millions of urban Indians. It puts out no soot. And yet, as Nitus’ mother in-law Veervati explains, the family rarely uses it.
CHATTERJEE: We use the gas stove occasionally, she says, for example, to cook for unexpected visitors. But for her daily meals she says she prefers to cook on the chulha. It may put out smoke, but it makes the food taste the way it’s supposed to. For The World, I’m Rhitu Chatterjee, New Delhi.
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