Debates about the costs and benefits of reducing carbon emissions usually get conducted along very narrow lines. First you add up the amount people will have to pay in higher energy bills and then compare that with the benefits of avoiding big temperature increases. Et, voila. Except the problem with this approach is that it ignores many of the indirect benefits (and, yes, indirect costs) of shifting to cleaner forms of energy. And some of those secondary effects might be very significant.

Case in point: Shifting away from fossil fuels helps cut down on other, more conventional pollutants that cause all sorts of medical problems: SO2 and NOx and mercury and particulates. And how much is that worth? That's what a new study from Gregory Nemet, Tracey Holloway, and Paul Meier at the University of Wisconsin-Madison tried to figure out. The researchers surveyed 48 studies on the subject and found that, while estimates of the health benefits can vary quite a bit, they average $44 per ton of CO2 in wealthy countries and $81/ton in developing countries. That's bigger than the expected carbon price under a U.S. cap-and-trade system (around $20-$30 per ton). In other words, the air-quality improvements alone could offset the cost of cutting carbon. A cap could be "worth it" for public health reasons, regardless of how one feels about global warming.

Now, this public health angle is especially likely to make a difference in the developing world, where creaky coal plants and noxious car fumes are rampant—in many poorer countries, the health gains could entirely pay for the price of tackling carbon emissions. Indeed, there have already been a few examples of governments thinking along these lines. In India, the city of Delhi recently announced that it would shut down all three of its coal-fired plants and switch to natural gas, even though electricity prices will likely rise as a result. The city's not doing it for climate reasons—officials are trying to chip away at all the smog choking the air. But it's going to have a big impact on greenhouse gases all the same.

(Flickr photo credit: rowanhk)