The notion that humans could take rapid action on global warming by curbing emissions of black carbon – more commonly known as soot – took root in various forums a couple of years ago. It’s one of those ideas that has wide appeal, precisely because reducing soot makes so much sense for an entirely different set of reasons, namely that it maims and kills thousands of people every year.

The climate impacts, however, are not nearly so simple. How much of the sun’s energy black carbon absorbs in the atmosphere depends on the size of the particles and how they interact with other airborne particles. Clearly black carbon sitting atop a blanket of snow will absorb sunlight and hasten melt, but does the black carbon itself wash away or stick around to continue the process? And everything depends on the ratio of black carbon to lighter-coloured organic carbon emitted by any number of combustion processes, from diesel engines in the United States to simple cook stoves in India.

Couple all of that with the fact that researchers have performed various analyses using different assumptions, and it can be quite difficult to pin things down. But in a paper published online Monday in the Proceedings of the National Academy of Sciences, a pair of Princeton University researchers attempts to bring some order to the discussion.

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The researchers essentially compare four published analyses, adjusting for differing assumptions to make sure that all of the models are speaking the same language. They then take the mean of the results from the various models to produce a best estimate of .22 watts per square meter. Though well below some of the higher estimates, which actually suggested that black carbon’s impact could be second only to carbon dioxide, this figure is still an order of magnitude larger than that used by the Intergovernmental Panel on Climate Change.

The idea of targetting black carbon for climate purposes has cropped up in the international climate talks and climate bills in the US Congress. This particular magazine has covered the issue in a feature as well as an accompanying editorial. Most recently, controlling black carbon made the list of quick-start policies endorsed by a group of thinkers in the Hartwell Paper, which advocates for a radical shift in course on climate policy.

Part of the logic behind all of these proposals is that global warming’s impacts could be moderated very quickly by reducing soot, which typically filters out of the atmosphere in days to weeks. The Princeton researchers analyzed black carbon reductions in light of a greenhouse gas target equivalent to 500 parts per million of carbon dioxide in 2100, which offers a 50/50 chance of staying below 2.5 degrees. In that scenario, curbing black carbon buys you eight extra years to cut reduce greenhouse gases and still meet the target.