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| Titel |
Use of the HadGEM2 climate-chemistry model to investigate interannual variability in methane sources |
| VerfasserIn |
Garry Hayman, Fiona O'Connor, Douglas Clark, Chris Huntingford, Nicola Gedney |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078150
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| Zusammenfassung |
| The global mean atmospheric concentration of methane (CH4) has more than doubled during
the industrial era [1] and now constitutes -
20% of the anthropogenic climate forcing by greenhouse gases [2]. The globally-averaged
CH4 growth rate, derived from surface measurements, has fallen significantly from a high of
16 ppb yr-1 in the late 1970s/early 1980s and was close to zero between 1999 and 2006 [1].
This overall period of declining or low growth was however interspersed with years of
positive growth-rate anomalies (e.g., in 1991-1992, 1998-1999 and 2002-2003). Since 2007,
renewed growth has been evident [1, 3], with the largest increases observed over polar
northern latitudes and the Southern Hemisphere in 2007 and in the tropics in 2008. The
observed inter-annual variability in atmospheric methane concentrations and the associated
changes in growth rates have variously been attributed to changes in different methane
sources and sinks [1, 4].
In this paper, we report results from runs of the HadGEM2 climate-chemistry model [5]
using year- and month-specific emission datasets. The HadGEM2 model includes the
comprehensive atmospheric chemistry and aerosol package, the UK Chemistry Aerosol
community model (UKCA, http://www.ukca.ac.uk/wiki/index.php). The Standard
Tropospheric Chemistry scheme was selected for this work. This chemistry scheme simulates
the Ox, HOx and NOx chemical cycles and the oxidation of CO, methane, ethane and
propane.
Year- and month-specific emission datasets were generated for the period from 1997 to
2009 for the emitted species in the chemistry scheme (CH4, CO, NOx, HCHO, C2H6, C3H8,
CH3CHO, CH3CHOCH3). The approach adopted varied depending on the source sector:
Anthropogenic: The emissions from anthropogenic sources were based on
decadal-averaged emission inventories compiled by [6] for the Coupled Carbon
Cycle Climate Model Intercomparison Project (C4MIP). These were then used
to derive year-specific emission datasets by scaling the emission totals for
the different years and source sectors using sector and species-specific scaling
factors based on the annual trends given in various EDGAR time series: (a)
version 4.2 for all species (except NMVOCs) and version 4.1 for NMVOCs; (b)
v3.2. This approach was also applied to the emissions from aviation (only for
oxides of nitrogen) and international shipping.
Biomass burning: Month-specific emission inventories are available from the
Global Fire Emissions Database (GFED, v3.1) for the years 1997 to 2009 [7].
The emissions were rescaled to give the same decadal mean as used in the Hadley
Centre’s earlier HadGEM2 runs (25 Tg CH4 per annum).
Other: Sources such as termites and hydrates for methane were taken from the
GEIA website and the dataset of Fung et al. [8]. The datasets contain a single
annual cycle, which was assumed to apply for all years.
For CH4, there are also emissions from wetlands. These were either based on the dataset
of Fung et al. [8] or derived from the JULES (Joint UK Land Earth Simulator) land
surface model [9, 10]. The standard version of JULES uses a simple methane wetland
emission parameterization, developed and tested by [11] for use at large spatial
scales.
The surface concentrations from the different model runs have been compared
to surface atmospheric CH4 measurements. In addition, growth rates have been
derived. These comparisons will be reported and used to assess the contribution
of different methane sources to the interannual variations in the methane growth
rate.
References
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