Rapid Methane Emission Reductions within Stabilized Climate Scenarios

The Paris Agreement encourages member states to keep global warming below 2.0C, and more ambitiously, limit warming to 1.5C. Recent coupled Earth system model simulations adaptively adjusted emissions to reach these stabilization temperatures show that fossil fuel CO2 reductions cannot reach the goals of the Paris Agreement alone. Building upon this framework, we show how varying the relative contribution of cumulative sustained methane emissions reductions is independent of pathway and modifies the allowable emissions from fossil fuels to reach 1.5C, 2.0C, and 3.0C of warming. Our results show that methane emissions reductions can have a large impact on the allowable emissions budget, and with mitigation goals >75% methane emissions reductions combined with rapid decarbonization, may reach the Paris Agreement goals. 

 

Despite much shorter atmospheric perturbation lifetimes of methane compared to CO2, we find a surprisingly linear relationship of the climate impacts of a one-time release of CO2 versus the cumulative impact of sustained reduction in methane emissions at 2663.1 kgCO2/kgCH4/yr. The 5000-year timescale of atmospheric CO2 removal by ocean sediments translates into a methane emission equivalency of 0.53x CO2, much smaller than the currently proposed emissions trading 1 system value of 25x and the Global Warming Potential approach 100-year horizon of 27.8x. Thus, methane emissions must be treated as a sustained reduction versus an instantaneous reduction like CO2, and should be part of the most urgent decarbonization towards the Paris goals, while the concept of a market exchange value between methane and fossil fuel CO2 must be viewed critically. While acknowledging the indefinite commitment of rapid methane emissions mitigation, this combined with rapid decarbonization may help to prevent an overshoot of Paris Agreement temperature goals.