Maximum temperature increases (peak warming) is to first order determined by the cumulative emissions of the long-lived greenhouse gases until the peak and by the annual emissions of the short-lived greenhouse gases at the time of the peak.
Methane mitigation measures in the latter half of the century become important if carbon dioxide emissions have already been curbed, and warming thus peaks before 2100. Early action on methane is less important for limiting warming to below 2C.
Our results reinforce that short-lived climate forcer (reduction) measures are to be considered complementary rather than a substitute for early and stringent carbon dioxide mitigation. Near-term short-lived climate forcer (reduction) measures do not allow for more time for carbon dioxide mitigation.
Integrated approaches to find solutions to problems such as climate change, air pollution, and energy policy are critical. The physics of the Earth system indicate that stabilizing climate at any temperature means that, at some point, global CO2 emissions have to become zero. Near-term action to reduce short-lived climate forcers, like black carbon or methane, could help reduce warming in the coming decades and also provides possibly very important other societal benefits, such as cleaner air. However, it will not buy us time for delaying the reductions in carbon dioxide emissions which are required to stabilize the climate at safe levels.Our study shows the importance of integrated approaches to such complex problems. By taking into account the linkages between sources of short-lived climate forcers and climate forcers, we find that the long-term climate benefits of controlling these air pollutants and short-lived gases in scenarios that stabilize climate change – at 2, 2.5, or 3°C – might have been overestimated in earlier studies.
While reducing short-lived climate forcers can be a valid objective in its own right, for example, for their clear public health benefits, it is important that the expectations of what this will bring for climate stabilization and for reducing climate change over the coming decades are not overly optimistic.