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Abstract. Possible implications of a GWP-based implementation of GHG reductions on future man-made climate change are explored. Abatement scenarios are established in terms of "COx equivalents" using GWP100; one scenario reducing COx only, and one reducing short-lived gases, mainly CH4. Future temperature changes are calculated by using a simple climate model. Equal emission scenarios in terms of COx equivalents do not imply equivalent climate responses and large differences in the magnitude and rate of temperature change are calculated.

Current climate policies are based on the use of Global Warming Potentials (GWPs) to compare emissions of various greenhouse gases. Yet, from an economic point of view, more efficient methods exist. We compare the potential costs of implementing some long-term goal for stabilization of the climate in three cases: Reduce CO2 emissions only, reduce emissions of the four greenhouse gases CO2, CH4, N2O and SF6 using the standard IPCC GWPs and reduce emissions of the same four gases with efficient and flexible, time dependent metrics. A multi-gas approach with GWPs reduces the costs by 8 percent when compared with CO2 reductions only, whereas the costs may be reduced by an additional 2 percent if using flexible metrics. If compared with the use of GWPs, we find that efficient weights increase the cost savings of including non-CO2 gases in climate policy by 15-40%, depending on the stabilization goal.

In this paper, we present a climate-policy game with international emissions trading, where governments first select their amounts of emissions permits. These permits are transferred to firms, and then traded competitively on an international market. Compared with a game without trading, we find that the potential efficiency gains from permit trading, which have been identified in other studies, are totally undone if governments also employ a tax or subsidy on domestic emissions. The only effect of permit trading in this case is a redistribution of income away from those most affected by climate change.