Multi-gas scenarios to stabilize radiative forcing

Using the results of a recent model comparison study performed by the Energy Modeling Forum, we have shown in this paper that including non-CO₂ gases in mitigation analysis is crucial in the formulation of a cost-effective response. In the absence of climate policies, the emissions of non-CO₂ greenhouse increase from 2.7 GtC-eq/year in 2000 to 5.1 GtC-eq/year in 2100 (averaged across all the models). A multi-gas reduction strategy stabilizing radiative forcing at 4.5 W/m² (compared to pre-industrial) reduces the emissions (on average) to 2.5 GtC-eq. Such an approach leads to a cost reduction of 30–40% compared to a CO₂ only reduction strategy for the same target. The choices of a target and how the gases are valued form an essential part of developing multi-gas strategies. Model results show that using IPCC global warming potentials (GWPs) as basis for substitution has large consequences for the timing of methane reductions. In this context, further research and assessment on multi-gas metrics, going beyond the mere physical aspects, are important for both research and policy-making.