The Role of Non-CO2 Greenhouse Gases in Climate Policy: Analysis Using the MIT IGSM

Abstract

First steps toward a broad climate agreement, such as the Kyoto Protocol, have focused attention on agreement with less than global geographic coverage. We consider instead a policy that is less comprehensive in term of greenhouse gases (GHGs), including only the non-CO2 GHGs, but is geographically comprehensive. Abating non-CO2 GHGs may be seen as less of a threat to economic development and therefore it may be possible to involve developing countries in such a policy who have thus far resisted limits on CO2 emissions. The policy we consider involves a GHG price of about $15 per ton carbon-equivalent (tce) levied only on the non-CO2 GHGs and held at that level through the century. We estimate that such a policy would reduce the global mean surface temperature in 2100 by about 0.57 degrees C; application of this policy to methane alone would achieve a reduction of 0.3 to 0.4 degrees C. We estimate the Kyoto Protocol in its current form would achieve a 0.30 degrees C reduction in 2100 if all Annex B Parties except the US maintained it as is through the century. Furthermore, we estimate the costs of the non-CO2 policies to be a small fraction of the Kyoto restriction. Whether as a next step to expand the Kyoto Protocol, or as a separate initiative running parallel to it, the world could make substantial progress on limiting climate change by pursuing an agreement to abate the non-CO2 GHGs. The results suggest that it would be useful to proceed on global abatement of non-CO2 GHGs so that lack of progress on negotiations to limit CO2 does not allow these abatement opportunities to slip away.