Methane (CH₄) is a powerful greenhouse gas, second only to carbon dioxide (CO₂) in the contribution to global mean temperature increase over the last two centuries. For the last four decades at least, more than 60% of global CH₄ emissions have originated from anthropogenic activities such as fossil fuel exploitation, livestock production, agriculture and waste. Recent trends of observed atmospheric CH₄ levels are tracking future scenarios of unmitigated emissions, making it a serious challenge for climate change mitigation.

A key outcome of the 2015 Paris Agreement is the international commitment to hold the increase in global mean temperature to well below 2°C above pre-industrial levels, and pursue efforts to limit global warming to 1.5°C above pre-industrial levels. Limiting global warming to 1.5 or 2°C above pre-industrial levels will require reaching net-zero CO₂ emissions as well as deep reductions in CH₄ and other non-CO₂ emissions by or around the year 2050.

For many years, researchers and policymakers have focused on CO₂ mitigation. It is only recently – following the 2021 UN Climate Change Conference held in Glasgow, Scotland – that more than 100 countries (representing 70% of the global economy) jointly agreed to urgently act on reducing CH₄ emissions to comply with the Paris Agreement climate goal.

While policymakers now accept the need for urgent CH₄ mitigation, it is necessary to assess the importance of immediate versus delayed CH₄ mitigation to comply with the temperature goal in the Paris Agreement – particularly taking into account potential Earth system feedbacks.

In our latest article published in Communications Earth & Environment, we use an Earth system model with a coupled CH₄ cycle to assess the importance of immediate versus delayed CH₄ mitigation to comply with the 2°C warming limit above pre-industrial levels. In particular, we aim at investigating the role of feedbacks in the carbon and methane cycles in the context of the timing of CH₄ mitigation to achieve the Paris Agreement climate goal, as well as the long-term climate impacts of delaying or failing to mitigate CH₄ in the current century, which have not been explored previously.

We drive the model with anthropogenic CH₄ emissions according to two scenarios: a scenario featuring immediate CH₄ mitigation, and a scenario without CH₄ mitigation throughout the 21^st century. We design four additional scenarios of anthropogenic CH₄ emissions with initiation of global-scale CH₄ mitigation ranging from the year 2020 to year 2050 (Figure 1). We prescribe the same future anthropogenic forcings – including CO₂ emissions reaching net zero around mid-century in all scenarios – implying that the only difference in outcomes between scenarios results from the difference in anthropogenic CH₄ emissions.

Our results suggest that global warming relative to the pre-industrial period could be limited to well below 2°C if global-scale CH₄ mitigation is initiated before the year 2030 (Figure 2). However, delaying CH₄ mitigation to the year 2040 or beyond will increase the risk of breaching the 2°C warming limit above pre-industrial levels, even if net-zero CO₂ emissions are achieved.

According to our model simulations featuring low CO₂ emission scenarios, every 10-year delay in CH₄ mitigation will result in additional peak warming of about 0.1°C. Our results show that the peak warming is amplified by the carbon-climate feedback whose strength increases with delayed CH₄ mitigation (Figure 2). The simulated contribution from the carbon-climate feedback to the peak warming ranges from about 0.03°C to 0.06°C for CH₄ mitigation initiated in 2020 and 2050, respectively. In contrast, our model simulations suggest a negligible contribution from wetland CH₄ emissions to temperature change for every 10-year delay in CH₄ mitigation under the scenarios explored in the study.

Despite that CH₄ stays in the atmosphere for only about 10 years, we demonstrate that delaying CH₄ mitigation by 2-3 decades will have an impact on global warming over many centuries (Figure 2). Most importantly, we show that a failure to mitigate CH₄ in the current century implies a high risk for global warming to exceed the 2°C warming limit for several centuries in the future, even under net-zero CO₂ emissions (Figure 2).

Our study supports recent concerns about a sustained atmospheric CH₄ growth and the associated potential challenge for achieving the Paris Agreement climate goal even under stringent CO₂ mitigation. We demonstrate that the carbon-climate feedback amplifies the warming response for delayed versus early CH₄ mitigation – with the feedback strength increasing for every 10-year delay in CH₄ mitigation. In addition, we show that aggressive reductions of CO₂ emissions without CH₄ mitigation could still push the Earth system beyond the 2°C warming limit for several centuries in the future.

Therefore, we highlight the need for immediate cuts in anthropogenic CH₄ emissions globally, along with stringent CO₂ mitigation, in order to increase the likelihood of holding the rise in global mean temperature to well below 2°C above pre-industrial levels. We emphasize that actions associated with the Global Methane Pledge should not be delayed, because every year of delayed CH₄ mitigation implies additional global warming – making it harder and harder to achieve the Paris Agreement climate goal.