Limiting warming by CO2 and methane mitigation in an expanded scenario space

Anthropogenic methane (CH ₄ ) is currently contributing over 0.5 °C to global warming, and mitigation of CH ₄ emissions is a powerful option to limit warming in the near-term. However, assessments of the effect of greenhouse gas (GHG) mitigation rely on scenarios from Integrated Assessment Models (IAMs) that typically include highly non-linear emission trajectories due to economic optimization and assume similar mitigation ambition for CO ₂ and CH ₄ . Conversely, climate targets are often linear, with a primary focus on reducing CO ₂ emissions. Here, we present a complementary approach for scenario generation to systematically map peak warming resulting from two main political choices: a linear reduction in CO ₂ or GHG emissions to net zero by a certain year and the simultaneous change in CH ₄ emissions. We show that without CH ₄ mitigation, peak warming will inevitably exceed 1.7 °C (50% likelihood), and the likelihood of limiting warming to below 2 °C drops below 50% when net zero CO ₂ emissions are achieved after 2050. Irrespective of the stringency of CH ₄ mitigation, limiting warming to 1.5 °C is no longer plausible. We also show that a sustained linear reduction in CH ₄ emissions by 10% (~35 MtCH ₄ /year) until 2050 increases the 2 °C-compatible global remaining carbon budget by ~165 GtCO ₂ . Our results emphasize both the immediate necessity and benefit of strong near-term CH ₄ mitigation, and provide a basis for setting CH ₄ mitigation targets compatible with different global temperature limits.