The Montreal Protocol entered force in 1989 and was initially designed to phase out ozone depleting CFCs. It was later amended to also phase out the use of HCFCs.

More recently there have been renewed discussion about amending the Montreal Protocol to reduce the use of HFCs, a class of high global warming potential (GWP) gases. According to the EPA, “the global warming potentials of HFCs range from 140 (HFC-152a) to 11,700 (HFC-23).” In particular, Canada, Mexico and the United States recently proposed a phasedown (as opposed to a phaseout) to 15% of baseline. So far, 91 countries have indicated their support for such an amendment. (See also: Recent International Developments in Saving the Ozone Layer)

In light of these discussion, I thought it might be worth re-considering the somewhat dated World GHG Emission Flow Chart below (which is based on data from 2000). Instead of depicting volumes of emissions on the right-hand side, if the chart were re-configured to weight emissions by GWP, things would look a lot different. In particular, CO2′s share would fall dramatically, while the share for CH4 (i.e., methane, a.k.a. natural gas), HFCs, PFCs and SF6 would all grow significantly.