Tropical methane emissions: A revised view from SCIAMACHY onboard ENVISAT

Abstract

[1] Methane retrievals from near-infrared spectra recorded by the SCIAMACHY instrument onboard ENVISAT hitherto suggested unexpectedly large tropical emissions. Even though recent studies confirm substantial tropical emissions, there were indications for an unresolved error in the satellite retrievals. Here we identify a retrieval error related to inaccuracies in water vapor spectroscopic parameters, causing a substantial overestimation of methane correlated with high water vapor abundances. We report on the overall implications of an update in water spectroscopy on methane retrievals with special focus on the tropics where the impact is largest. The new retrievals are applied in a fourdimensional variational (4D-VAR) data assimilation system to derive a first estimate of the impact on tropical CH 4 sources. Compared to inversions based on previous SCIAMACHY retrievals, annual tropical emission estimates are reduced from 260 to about 201 Tg CH 4 but still remain higher than previously anticipated. Citation: Frankenberg, C.,

A novel pathway of direct methane production and emission by eukaryotes including plants, animals and fungi: An overview

“…This finding has sparked an interest in determining whether a direct source of unrecognised CH 4 generation exists in different structural/architectural hierarchies of plants (Bruhn et al, 2012;Carmichael et al, 2014), because before this discovery, different forms of combustion were the only processes known to form CH 4 in the presence of oxygen. Although the observation of plants acting as direct emitters of CH 4 is a paradigm shift and has received substantial criticism, it has indeed challenged the traditional view on the CH 4 biosynthetic pathway and opened another avenue to account for the fluctuation of the global CH 4 concentration and the recent satellite-observed discrepancy in CH 4 over tropical forests (Frankenberg et al, 2008(Frankenberg et al, , 2005.…”

Water vapor isotopologue retrievals from high-resolution GOSAT shortwave infrared spectra

“…Our basic retrieval approach for δD largely follows retrievals from SCIAMACHY (e.g., Frankenberg et al, 2005aFrankenberg et al, , 2008Frankenberg et al, , 2009) using the IMAP-DOAS (Iterative Maximum a Posteriori-Differential Optical Absorption Spectroscopy) algorithm (Frankenberg et al, 2005b) with instrument-specific adaptions and ECMWF meteorological data for pressure, temperature and a priori humidity profiles. CO 2 is the only interfering species, and the disk-integrated solar line-list is adapted from the full-physics CO 2 retrievals used for GOSAT (originally developed for TCCON retrievals).…”

Spatial patterns in oxygen and redox sensitive biogeochemistry in tropical forest soils

“…Methane (CH 4 ) is the product of several different redox reactions, and is a frequent end product of the anaerobic decomposition of organic matter (Ponnamperuma 1972). Although CH 4 effluxes typically exhibit high spatial variability, humid tropical forests are generally considered a net source of CH 4 (Frankenberg et al 2008). Given the spatial heterogeneity in O 2 availability and redox in soils, both production and consumption of CH 4 can occur simultaneously (Teh et al 2005).…”