1Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212, IPSL-LSCE, CEA-CNRS-UVSQ, 91191, France
2Université de Versailles Saint Quentin en Yvelines, France
3NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, CO, USA
4South African Weather Service, Stellenbosch, South Africa
5Jet Propulsion Laboratory, Pasadena, CA, USA
6Centre for Australian Weather and Climate Research/CSIRO, Marine and Atmospheric Research, Victoria, Australia
Abstract. The recent increase of atmospheric methane is investigated by using two atmospheric inversions to quantify the global distribution of sources and sinks for the 2006–2008 period, and a process-based model of CH4 emissions by natural wetland ecosystems. Global emissions derived from inversions are found to have increased by 19 Tg on average in 2007 (16 to 21 Tg) and by 13 Tg in 2008 (6 to 20 Tg), as compared to the 1999–2006 period. A positive anomaly of tropical emissions is found to be the main contributor to the global emission anomaly of 2007 (~60–75%), with a dominant share attributed to natural wetlands (~66%). Abnormally high wetlands emissions from high latitudes are also detected by both inversions in 2007, contributing 15–30% of the global anomaly. Good agreement is found between the results of the wetland ecosystem model and the inversions for 2007. The inferred distribution of the source anomaly in 2007 is shown to be consistent with the observation of a more pronounced increase in near surface methane atmospheric growth rate at high latitudes, because the dilution of surface fluxes by convection is strong in the tropics and weak at high latitudes. The source anomaly in 2008 is found to be much larger in the wetland ecosystem model than in the inversions, suggesting a too strong sensitivity of bottom-up modeled emissions to precipitation. Changes in OH radicals during 2006–2008 are found to be less than 1% in inversions, with only a small impact on the inferred methane emissions.