Curbing our expectations: Global temperature impacts from strong mitigation of individual climate forcers

Achieving the goals of the Paris agreement, or a stabilization of the global climate, requires strong and sustained mitigation of a range of anthropogenic emissions. A key stepping stone in this effort would be a measurable reduction in the current rate of global warming, which has been approximately constant over time since the 1970s, or a statistically significant deviation of the time evolution of observations from a predetermined baseline expectation. The various components that contribute to anthropogenic climate change are however markedly different in their total, present day impact, and time scales from emissions reductions to an expected climate system response. Here, we investigate when a significant change in global mean surface temperature could be expected, relative to an emission pathway consistent with current global policies, for a broad range of long and short-lived climate forcers. By combining reduced complexity and Earth System modelling, we investigate a comprehensive set of idealized emission mitigation choices for the near term, while still taking into account natural variability. As expected, mitigation of anthropogenic emissions of CO₂ stands out as the most efficient, both in the short and longer term, although very strong mitigation is required to have a clear effect. Further, we find that strong mitigation policy targeting black carbon (BC) emissions would have a rapid, discernible effect, but a low net effect in the longer term. Mitigation of CH₄ stands out as an option that combines rapid effects on surface temperature with long term gains.