Atmospheric CH₄ in the first decade of the 21st century: Inverse modeling analysis using SCIAMACHY satellite retrievals and NOAA surface measurements

Abstract

[1] The causes of renewed growth in the atmospheric CH 4 burden since 2007 are still poorly understood and subject of intensive scientific discussion. We present a reanalysis of global CH 4 emissions during the 2000s, based on the TM5-4DVAR inverse modeling system. The model is optimized using high-accuracy surface observations from NOAA ESRL's global air sampling network for 2000-2010 combined with retrievals of column-averaged CH 4 mole fractions from SCIAMACHY onboard ENVISAT (starting 2003). Using climatological OH fields, derived global total emissions for 2007-2010 are 16-20 Tg CH 4 /yr higher compared to [2003][2004][2005]. Most of the inferred emission increase was located in the tropics (9-14 Tg CH 4 /yr) and mid-latitudes of the northern hemisphere (6-8 Tg CH 4 /yr), while no significant trend was derived for Arctic latitudes. The atmospheric increase can be attributed mainly to increased anthropogenic emissions, but the derived trend is significantly smaller than estimated in the EDGARv4.2 emission inventory. Superimposed on the increasing trend in anthropogenic CH 4 emissions are significant inter-annual variations (IAV) of emissions from wetlands (up to AE10 Tg CH 4 /yr), and biomass burning (up to AE7 Tg CH 4 /yr). Sensitivity experiments, which investigated the impact of the SCIAMACHY observations (versus inversions using only surface observations), of the OH fields used, and of a priori emission inventories, resulted in differences in the detailed latitudinal attribution of CH 4 emissions, but the IAV and trends aggregated over larger latitude bands were reasonably robust. All sensitivity experiments show similar performance against independent shipboard and airborne observations used for validation, except over Amazonia where satellite retrievals improved agreement with observations in the free troposphere. Citation: Bergamaschi, P., et al. (2013), Atmospheric CH 4 in the first decade of the 21st century: Inverse modeling analysis using SCIAMACHY satellite retrievals and NOAA surface measurements,

The global methane budget 2000–2012

“…Pison et al, 2013) or for a limited number of flux categories (e.g. Bergamaschi et al, 2013). Indeed, the assimilation of CH 4 observations alone, as reported in this synthesis, cannot fully separate individual sources, although sources with different locations or temporal variations could be resolved by the assimilated atmospheric observations.…”

“…Atmospheric inversions based on SCIAMACHY or GOSAT CH 4 retrievals have been carried out by different research groups (Monteil et al, 2013;Cressot et al, 2014;Alexe et al, 2015;Bergamaschi et al, 2013;Locatelli et al, 2015). For GOSAT, differences between the use of proxy and full-physics retrievals have been investigated.…”

Performance simulations for a spaceborne methane lidar mission

“…At the same time, however, natural methane sources have the potential to significantly amplify human-induced climate change, for instance due to the strong dependence of methane wetland emissions on climate, release from permafrost soils and continental shelves, and potential destabilization of methane hydrates from the ocean floors [Kort et al, 2012;Walter-Anthony et al, 2012;Portnov et al, 2013]. While total global methane emissions from anthropogenic and natural processes at the Earth's surface are reasonably well determined [Bergamaschi et al, 2013], estimates of emissions by source sector vary by up to a factor of 2, and current ground-based observational networks fail to constrain methane emissions at regional scales [Dlugokencky et al, 2011]. with a Fourier transform interferometer like the Greenhouse Gases Observing Satellite.…”

“…The MERLIN data will primarily be supplied to inverse numerical models [Basu et al, 2013;Bergamaschi et al, 2013] that use the globally observed concentration gradients to infer methane surface fluxes with a foreseen grid resolution of 1000 km and a temporal resolution of 1 month, which represents a considerable improvement from the current state of the art. The MERLIN scientific advisory group set up a list of user requirements the mission has to fulfill to meet its goal.…”

A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) – Part 2: Optimization scheme and identical twin experiment of atmospheric CO<sub>2</sub> inversion

“…The 4D-Var method is a popular inversion method and has been widely used in inversion studies for atmospheric carbon dioxide (CO 2 ) (e.g., Chevallier et al, 2005;Rödenbeck, 2005;Baker et al, 2006a), methane (CH 4 ) (e.g., Bergamaschi et al, 2013) and carbon monoxide (CO) (e.g., Kopacz et al, 2010;Hooghiemstra et al, 2012).…”