Multi-Gas Forcing Stabilization with Minicam

This paper examines the role of climate forcing agents other than carbon dioxide using the MiniCAM integrated assessment model for both no-climate-policy and policy emissions scenarios. Non-CO, greenhouse-gas forcing is dominated by methane and tropospheric ozone. Assumptions about the prevalence of methane recovery and local air pollution controls in the no-policy cases are a critical determinant of methane and ozone-precursor emissions. When these factors are considered, emissions are substantially reduced relative to earlier estimates. This reduces their potential as climate mitigation agents through specific climate policies. Nevertheless, the addition of non-CO, greenhouse gas and ozone precursor abatement options significantly reduces mitigation costs in the first half of the 21st century (by up to 40%) compared to the case where only CO, abatement options are pursued. While the influences of aerosols are small by the end of the century, there is a significant interaction in the early 21st century between policies to reduce CO, emissions and SO, emissions, even in the presence of SO,-related pollution control policies. The attendant reduced aerosol cooling can more than offset the reduction in warming that accrues from reduced CO,. When non-CO, gases are included in the policy, the net effect is that global-mean climate change to 2050 is practically unaffected by mitigation policy.