Lay summary

Future role of Methane Emissions in the climate System (FuMES)


In its most recent assessment report the IPCC stated that the observed warming of the climate system is most likely caused by increased anthropogenic greenhouse gas emissions.  Methane (CH4) emissions caused by human activities have led to a doubling of atmospheric CH4 concentrations since pre-industrial times, making CH4 to be the second most important long-lived greenhouse gas after CO2 (in terms of radiative forcing).  With a 25-times larger global warming potential than CO2 (on a 100-yr time horizon), methane would become even more important as driver of climate change if its atmospheric concentrations continued to rise.  In light of this development several mitigation options to reduce anthropogenic CH4 emissions have been proposed.  However, CH4 emissions from natural wetlands might increase in a warmer climate and offset future efforts to reduce anthropogenic emissions. Substantial uncertainties in the understanding of the complex interactions between atmospheric methane and other atmospheric quantities like OH, CO, O3, tropospheric UV fluxes, aerosols and clouds make reliable projections difficult.


To contribute to a clarification of these uncertainties we propose here to run an ensemble of short- and long-term model simulations using the state-of-the-art atmosphere-chemistry-climate model SOCOL coupled to a dynamic global vegetation model. The following questions will be addressed in detail:


-        What is the relative importance of individual source and sink processes for the short- and long-term variability of the atmospheric methane abundance? Which processes determine the strength of individual methane sources and sinks?


-        How will methane emissions from natural wetlands change in a warmer climate?


-        How will the oxidation capacity of the troposphere and, therefore, the main atmospheric methane sink change in future? What are the implications for air quality?


-        How do proposed methane mitigation measures compare with a climate-change related aggravation of natural methane emissions?


The envisaged model system will be able to simulate the atmospheric methane cycle in a self-consistent manner, including atmospheric methane sinks, CH4 uptake in soils as well as methane emissions from wetlands and other sectors. Furthermore, the model will capture the relevant feedback effects between methane emissions and the coupled chemistry-climate system of troposphere and stratosphere, including land-surface processes. The application of this novel model is expected to allow for a more reliable estimate of the future role of atmospheric methane in the climate system.