Methane emissions or surface concentrations

Methane can either be prescribed at the surface, or the emissions may be specified. The following emission sources for methane have been compiled by Sander Houweling:

Abbreviation	Category	Assumed 1997 emission (Tg/yr)
stat	Stationary	266
rice	Rice fields	80
wetl	Wetlands	145
bmbs	Seasonally dependent biomass burning	29
bmbns	Seasonally independent biomass burning	20
Sum		540

Stationary sources include ruminants, termites, oceans, waste treatment, soil oxidation, a.o. Note that soil oxidation is a sink that is included in the stationary sources. See also table 3.1 of [Houweling, 2000]. The TM input files are ch4Category.d, i.e. ch4stat.d, ch4rice.d, ch4wetl.d, ch4bmbs.d and ch4bmbns.d. These are calculated with geiach42tm3 from resp. ch4stat_SH.d, ch4rice_SH.d, ch4wetl_SH.d, ch4bmbseas_SH.d and ch4bmbnoseas_SH.d. Here SH stands for Sander Houweling. The default year is 1990. How were these files constructed? Most likely the sources are as in table 4.1 of [Houweling et al., 1998]:
Emissions from rice cultivation and biomass burning are anthropogenic should be moved from here ! For biomass burning [Hao et al., 1991] is still used. For emissions from rice cultivation [Matthews et al., 1991] is used. Interannual variability in emissions from biomass burning and rice fields is not simulated at the moment.
The geographical distribution and seasonality of natural wetland emissions is based on a process model by [Walter, 1998], that parameterizes the microbial methane production and consumption as well as soil and plant transport as a function of soil and vegetation properties, temperature and hydrology. This model was tuned to mainly high latitude wetlands and one tropical wetland. The NH to SH ratio of sources is 1.38, lower than the 1.86 from [Hein et al., 1997] that was used before in TM.
The geographical distribution of methane sources from oxidation in soils by microbes has been updated (originally [Fung et al., 1991]), introducing a seasonal variation, based on the process model of [Ridgwell et al., 1999], that takes into account temperature and soil moisture variations. The seasonal variation is mainly important outside the tropics. Emissions from industrial waste water, including food and paper industries and oil refineries, have been introduced, accounting for 25 Tg (CH$_{4}$)/yr, following [Lelieveld et al., 1998].
Stationary natural emissions include termites, wild animals, oceans and volcanos? The geographical distribution of emissions from termites are based on [Sanderson, 1996].
The total emissions from volcanoes (3.5 Tg(CH$_{4}$)/yr) are based on [Lacroix, 1993]. Geographical distribution?
Methane emissions from wild animals have been calculated as described in [Houweling et al., 1998], chapter 3, which used the methodology of [Bouwman et al., 1997]. 3-6 percent of the net primary produced vegetation is assumed to be consumed by wild ruminants. A constant fraction of this is emitted as methane. The NPP distribution from the integrated model, IMAGE ([Minnen et al., 1996], [Kreileman, 1996]) was used, after elimination of cultivated regions with the land use database of [Matthews, 1983]. As in [Bouwman et al., 1997] it is assumed that the ecosystem NPP in forested areas consists for 20 percent of consumable grass and leaves. For this, the vegetation database of [Olson et al., 1983] was used. This can be downloaded from NOAA NGDC:

http://www.ngdc.noaa.gov/seg/eco/cdroms/gedii_a/datasets/a05/ow.htm

or from CDIAC:

http://cdiac.esd.ornl.gov/epubs/ndp/ndp017/ndp017.html

Oceans ?
The total emissions are based on the inverse modelling study of [Houweling et al., 1998] (chapter 3) and [Lelieveld et al., 1998], except for volcanoes ([Lacroix, 1993]).
See the section on boundary conditions for methane concentrations at ground level.