Peak warming and remaining carbon budgets under different methane emission targets

Methane (CH₄) is the second most important anthropogenic greenhouse gas after CO₂, and CH₄ mitigation is a main option to limit near-term warming. Yet, the required CH₄ mitigation to stay below specific temperature limits remains uncertain. Furthermore, prevalent scenarios from Integrated Assessment Models (IAMs) typically exhibit highly non-linear and correlated CO₂ and CH₄ emissions, due to economic optimization and aggregation of greenhouse gases (GHGs). By contrast, climate targets are often framed as linear reductions in emissions with a primary focus on mitigating CO₂ emissions.

Here, we present a simple, complementary approach for scenario generation that aligns more closely with the current framing of emission targets and remains largely independent of many assumptions in IAMs. Using this scenario generation approach and the simple climate model FaIR, we systematically map peak warming resulting from a linear reduction to net zero CO₂ or GHG emissions combined with different changes in CH₄ emissions. We estimate that without CH₄ mitigation, peak warming of 1.7 °C is already unavoidable. We provide minimum CH₄ mitigation targets compatible with different peak temperatures when combined with specific net zero CO₂ or GHG emission targets. We further quantify how the remaining carbon budget (RCB) depends on the stringency of CH₄ mitigation. Our results show that without sizable CH₄ mitigation, RCBs are far smaller than commonly communicated.

These findings emphasize both the necessity and the benefit of strong near-term CH₄ mitigation, and can support policymakers in setting CH₄ emission targets compatible with globally agreed-upon temperature limits.