Climate Impacts of Methane Removal

Abstract:

Quantifying the impacts of methane removal, whether through avoided emissions or direct removal technologies, is crucial to guide future policy decisions on mitigating climate change. However, past modelling work on these impacts has been limited to examining ‘concentration-driven’ pathways, where the concentration is specified over time, thereby ignoring the feedbacks that are present in the methane cycle. We address this issue by examining ‘emissions-driven’ pathways using the United Kingdom Earth System Model, a global coupled atmosphere-ocean model, that now has interactive wetland emissions, atmospheric methane chemistry, and soil uptake. To quantify the impacts, we define a new metric, effective cumulative removal, that accounts for the shorter lifetime of methane to allow for a direct comparison with carbon dioxide. We find that effective cumulative removal of methane is proportional to reductions in both global mean surface temperature and ozone. Furthermore, we quantify the amount of methane removal required to hit specific policy-relevant targets, such as delaying the onset of 2 degree warming in pessimistic scenarios (SSP3-7.0) or reducing the peak temperature in optimistic scenarios (SSP1-2.6). In summary, this new modelling development of interactive methane emissions allows us to quantify the climate and atmospheric chemistry impacts of methane removal across a wide range of scenarios over the coming century.