While the Global Warming Potential (GWP) of the IPCC remains the talisman for measuring radiative forcing, a new study in the journal Science (Shindell, et al., Improved Attribution of Climate Forcing to Emissions, 326 Science 716-18 (2009) (subscription required) provides convincing evidence that methane emissions are more important than previously assessed. The researchers calculated radiative forcing of GHGs regulated under Kyoto in a coupled composition climate model that also incorporated the impacts of aerosols ( atmospheric particles such as dust, sea salt, sulfates and black carbon) and tropospheric ozone precursor emissions. The study concluded that when the neglected interactions between oxidants and aerosols is incorporated into an analysis of radiative forcing, methane’s GWP rises from 25 to 33, and likely would be further increased by including ecosystem responses.
This could be an interesting reading for students in conjunction with other recent analyses discussed on this cite that discuss the potential value of more aggressively restricting short-term pollutants, such as black carbon and volatile organic compound as an intermediate strategy to address climate change. Of course, in the case of aerosols, many forms of which exert a powerful cooling effect, this might argue in favor of slowing down efforts to reduce such emissions. At the same time, there are clear health benefits in removing aerosols such as sulfates, so this could lead to an interesting discussion about how we weigh the trade offs in policy making fora. As is almost always the case in the field of climate change, there is likely no free lunch!