Delaying methane mitigation increases the risk of breaching the 2°C warming limit

Abstract:

Methane (CH₄) mitigation is often proposed as one option for tackling climate change in the short-term with co-benefits for air quality and global health. However, recent observations show that atmospheric CH₄ concentration ([CH₄]) is tracking future scenarios of unmitigated CH₄ emissions. Here we use an Earth system model of intermediate complexity including a representation of the CH₄ cycle to investigate the effect of immediate versus delayed CH₄ mitigation on changes in global mean surface temperature as well as complying with the 1.5 and 2°C warming limits. We assume scenarios with different timing of CH₄ mitigation over the next three decades, all reaching the same amount of anthropogenic CH₄ emissions in 2100 as in a reference low emission scenario (SSP1-2.6). We also assume that all non-CH₄ forcings would evolve according to SSP1-2.6. Our model simulations suggest that CH₄ mitigation initiated between 2020 and 2030 would result in 0.1-0.2°C less warming by 2100 than if CH₄ mitigation is delayed to 2050. The lack of CH₄ mitigation in the 21^st century (i.e. anthropogenic CH₄ emissions evolving according to SSP3-7.0) would imply ~0.5°C more warming by 2100 than if mitigation is initiated between 2020 and 2030. We estimate that such a lack of CH₄ mitigation (under SSP1-2.6) could increase global mean temperature rise to ~2.3°C relative to 1850-1900. Conversely, CH₄ mitigation between 2020 and 2030 could allow to keep global warming below 2°C relative to 1850-1900, whereas delaying CH₄ mitigation to between 2040 and 2050 could overshoot the 2°C warming target for two to four decades in the 21^st century. Our results imply that immediate cuts in anthropogenic CH₄ emissions, along with CO₂ mitigation, are needed to increase the likelihood of limiting global warming to 2°C above pre-industrial levels.