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New Study Estimates Impact of Soot on Global Warming and Timeframe of Actions to Be Taken

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Soot is considered one of the most important threats to the environment, along with carbon dioxide. Princeton University researchers have described the contribution of soot (“carbonaceous aerosols”) to phenomena of global warming and global dimming. Soot is born by incomplete combustion and comes mostly from diesel engines and coal burning.

Soot has two main components: black carbon and organic carbon.

While black carbon is dark in color and absorbs light, contributing to the warming of the atmosphere, organic carbon is light colored and reflective, having the reverse effect. Mixed in equal amounts, their effects on warming theoretically cancel each other, but both types of aerosols actually cool the climate through their effects on cloud formation. One particular case is when black carbon falls on snow or ice, darkening it and rising its temperature, which translates in more melted glaciers.

“Because of uncertainties in these many effects, and because of differences in whether and how these effects get incorporated into various models, past studies of soot’s contribution to global warming have ranged widely,” said Robert Kopp, a post-doctoral researcher jointly in Princeton’s Woodrow Wilson School of Public & International Affairs and its Department of Geosciences. “We took several key studies, put them all on a common footing, and assessed what emerged.”

Denise Mauzerall, associate professor of environmental engineering and international affairs, and Robert Kopp, attempted to estimate how much we would have to lower the soot pollution to reduce carbon dioxide emissions (coming namely from diesel and poorly-controlled coal sources). In order to avoid “dangerous anthropogenic interference with the climate system”, if these sources of soot remain at 1990s levels, the world would need to see a much more aggressive reduction in carbon dioxide.

“But effects on global climate aren’t the only reason to reduce soot emissions,” Mauzerall cautioned. “The public health case for reducing emissions of fine particles, including soot, is unequivocal, and aerosol pollution can have significant regional climate effects. For instance, soot pollution from India and China that is transported to the Himalayan glaciers can enhance glacier melting and hence influence water supplies in India, China and Bangladesh – potentially contributing to increased flooding in some regions in the short-term and reduced water availability in the longer term .”

Whereas carbon dioxide emissions tend to increase with income, some of the largest soot sources are in middle-income countries. In 1996, for example, China and India are believed to have accounted for about 40 percent of global black carbon emissions.

“Because some of the largest sources are in middle-income countries, and because the co-benefits of soot emission reductions can be felt quickly locally, black carbon reductions could serve as a catalyst for engaging these countries in climate change mitigation efforts,” Mauzerall suggested.

Reducing diesel-originated soot could be done either by installing more effective particulate filtering systems at tailpipes, thus increasing their price and decreasing their attractiveness, or by producing solely gasoline, hybrid or electric vehicles, just like in the U.S., and raising fuel consumption, because of poorer engine efficiency. It’s fair to say that current diesels are really much cleaner than the ones that existed ten years ago, and that (some) gasoline engines try to keep up with diesels, but the case doesn’t always apply to all kinds of machinery (trucks, locomotives).

We’ll have to continue using diesel for a while, and even gasoline, because when pure electrics will abound the market, soot and carbon dioxide will get reduced drastically. Money should go in that direction, and care less about patching the current problems. In other words, we should catch the sure wave, and not bounce back and forth between the old and the new one.

One more issue remains unclear, and this is maybe where Kopp and Mauzerall’s study would apply better: the industry. But that’s another story.

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