The El Niño–Southern Oscillation and wetland methane interannual variability

Global measurements of atmospheric methane (CH 4 ) concentrations continue to show large interannual variability whose origin is only partly understood. Here we quantify the influence of the El Niño–Southern Oscillation (ENSO) on wetland CH 4 emissions, which are thought to be the dominant contributor to interannual variability of the CH 4 sources. We use a simple wetland CH 4 model that captures variability in wetland extent and soil carbon to model the spatial and temporal dynamics of wetland CH 4 emissions from 1950–2005 and compare these results to an ENSO index. We are able to explain a large fraction of the global and tropical variability in wetland CH 4 emissions through correlation with the ENSO index. We find that repeated El Niño events throughout the 1980s and 1990s were a contributing factor towards reducing CH 4 emissions and stabilizing atmospheric CH 4 concentrations. An increase in emissions from the boreal region would likely strengthen the feedback between ENSO and interannual variability in global wetland CH 4 emissions. Our analysis emphasizes that climate variability has a significant impact on wetland CH 4 emissions, which should be taken into account when considering future trends in CH 4 sources.