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| Titel |
Barriers to predicting changes in global terrestrial methane fluxes: analyses using CLM4Me, a methane biogeochemistry model integrated in CESM |
| VerfasserIn |
W. J. Riley, Z. M. Subin, D. M. Lawrence, S. C. Swenson, M. S. Torn, L. Meng, N. M. Mahowald, P. Hess |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 7 ; Nr. 8, no. 7 (2011-07-20), S.1925-1953 |
| Datensatznummer |
250006052
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| Publikation (Nr.) |
 copernicus.org/bg-8-1925-2011.pdf |
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| Zusammenfassung |
| Terrestrial net CH4 surface fluxes often represent the difference
between much larger gross production and consumption fluxes and depend on
multiple physical, biological, and chemical mechanisms that are poorly
understood and represented in regional- and global-scale biogeochemical
models. To characterize uncertainties, study feedbacks between CH4
fluxes and climate, and to guide future model development and
experimentation, we developed and tested a new CH4 biogeochemistry
model (CLM4Me) integrated in the land component (Community Land Model; CLM4)
of the Community Earth System Model (CESM1). CLM4Me includes representations
of CH4 production, oxidation, aerenchyma transport, ebullition,
aqueous and gaseous diffusion, and fractional inundation. As with most
global models, CLM4 lacks important features for predicting current and
future CH4 fluxes, including: vertical representation of soil organic
matter, accurate subgrid scale hydrology, realistic representation of
inundated system vegetation, anaerobic decomposition, thermokarst dynamics,
and aqueous chemistry. We compared the seasonality and magnitude of
predicted CH4 emissions to observations from 18 sites and three global
atmospheric inversions. Simulated net CH4 emissions using our baseline
parameter set were 270, 160, 50, and 70 Tg CH4 yr−1 globally,
in the tropics, in the temperate zone, and north of 45° N, respectively;
these values are within the range of previous estimates. We then used the
model to characterize the sensitivity of regional and global CH4
emission estimates to uncertainties in model parameterizations. Of the
parameters we tested, the temperature sensitivity of CH4 production,
oxidation parameters, and aerenchyma properties had the largest impacts on
net CH4 emissions, up to a factor of 4 and 10 at the regional and
gridcell scales, respectively. In spite of these uncertainties, we were able
to demonstrate that emissions from dissolved CH4 in the transpiration
stream are small (<1 Tg CH4 yr−1) and that uncertainty in
CH4 emissions from anoxic microsite production is significant. In a
21st century scenario, we found that predicted declines in
high-latitude inundation may limit increases in high-latitude CH4
emissions. Due to the high level of remaining uncertainty, we outline
observations and experiments that would facilitate improvement of regional
and global CH4 biogeochemical models. |
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