The global methane emissions were estimated for 2000-2012 using the CarbonTracker Europe-CH4 (CTE-CH4) data assimilation system. In CTE-CH4, the anthropogenic and biosphere emissions of CH4 are simultaneously constrained by global atmospheric in-situ methane concentration observations. We use three configurations developed in Tsuruta et al. (2016) to assess the sensitivity of the CH4 flux estimates. The posterior emission (2007-2012) estimates were evaluated by comparing simulations to surface mole fractions at in-situ observation sites, to dry air total column-averaged mole fractions (XCH4) observations from the Total Carbon Column Observing Network (TCCON) network, and to XCH4 retrievals from the Greenhouse gases Observing SATellite (GOSAT).

The estimated posterior mean global total emissions during 2000-2012 is 516±51 Tg CH4 yr-1 on average, and the emissions during 2007-2012 are 18 Tg CH4 yr-1 higher than those of the period 2001-2006, mainly driven by an increase in emissions from the south America temperate region, the Asia temperate region and Asia tropics. The sensitivity of the flux estimates to the underlying ecosystem map was large for the Asia temperate region and Australia, but not significant in the northern latitude regions, i.e. the north American boreal region, the north American temperate region and Europe.