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Is All CO2 Created Equal? Maybe Not.

Does it matter where carbon-dioxide is emitted? From a climate perspective, at least, the standard answer has always been, "Not really." Carbon-dioxide mixes pretty evenly and uniformly throughout the atmosphere, so that the heat-trapping gases coming out of a factory in China have the same effect on global temperatures, pound for pound, as the greenhouse gases emitted by, say, cars in Delaware. (This is in contrast to a number of other air pollutants, whose effects are often localized—sulfur dioxide only causes acid rain in discrete areas.)

But a new study just published in Environmental Science and Technology by Stanford's Marc Jacobson adds a slight twist to this standard view. Older research has found that local "domes" of high CO2 levels can often form over cities. What Jacobson found was that these domes can cause serious health impacts in the area: Among other things, they worsen the effects of localized air pollutants like ozone and particulates, which cause respiratory diseases and the like. As a result, Jacobson estimates that local CO2 emissions cause anywhere from 300 to 1,000 premature deaths in the United States each year. And presumably the problem's much worse in developing countries.

It'd be interesting to see more work on this subject, because if true, it slightly complicates the logic of a cap-and-trade system for emissions. After all, the idea behind a carbon-trading market is that a ton of CO2 has the exact same effect no matter where it's emitted—be it a factory in rural North Dakota or a power plant in L.A. But Jacobson's work suggests that the two aren't totally equal—that ton of emissions from the power plant in L.A. has a much bigger impact on human health. Now, maybe trying to account for those disparities would just make a cap-and-trade system hopelessly complicated. Still, Jacobson argues, they should at least be considered.

(Flickr photo credit: Stefan Gara)