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| Titel |
Present state of global wetland extent and wetland methane modelling: conclusions from a model inter-comparison project (WETCHIMP) |
| VerfasserIn |
J. R. Melton, R. Wania, E. L. Hodson, B. Poulter, B. Ringeval, R. Spahni, T. Bohn, C. A. Avis, D. J. Beerling, G. Chen, A. V. Eliseev, S. N. Denisov, P. O. Hopcroft, D. P. Lettenmaier, W. J. Riley, J. S. Singarayer, Z. M. Subin, H. Tian, S. Zürcher, V. Brovkin, P. M. Bodegom, T. Kleinen, Z. C. Yu, J. O. Kaplan |
| 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 ; 10, no. 2 ; Nr. 10, no. 2 (2013-02-04), S.753-788 |
| Datensatznummer |
250017500
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| Publikation (Nr.) |
 copernicus.org/bg-10-753-2013.pdf |
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| Zusammenfassung |
Global wetlands are believed to be climate sensitive, and are the
largest natural emitters of methane (CH4). Increased wetland
CH4 emissions could act as a positive feedback to future
warming. The Wetland and Wetland CH4 Inter-comparison of
Models Project (WETCHIMP) investigated our present ability to
simulate large-scale wetland characteristics and corresponding
CH4 emissions. To ensure inter-comparability, we used
a common experimental protocol driving all models with the same
climate and carbon dioxide (CO2) forcing datasets. The
WETCHIMP experiments were conducted for model equilibrium states as
well as transient simulations covering the last century. Sensitivity
experiments investigated model response to changes in selected
forcing inputs (precipitation, temperature, and atmospheric
CO2 concentration). Ten models participated, covering the
spectrum from simple to relatively complex, including models
tailored either for regional or global simulations. The models also
varied in methods to calculate wetland size and location, with some
models simulating wetland area prognostically, while other models
relied on remotely sensed inundation datasets, or an approach
intermediate between the two.
Four major conclusions emerged from the project. First, the suite of
models demonstrate extensive disagreement in their simulations of
wetland areal extent and CH4 emissions, in both space and
time. Simple metrics of wetland area, such as the latitudinal
gradient, show large variability, principally between models that
use inundation dataset information and those that independently
determine wetland area. Agreement between the models improves for
zonally summed CH4 emissions, but large variation between
the models remains. For annual global CH4 emissions, the
models vary by ±40% of the all-model mean
(190 Tg CH4 yr−1). Second, all models show
a strong positive response to increased atmospheric CO2
concentrations (857 ppm) in both CH4 emissions and
wetland area. In response to increasing global temperatures
(+3.4 °C globally spatially uniform), on average, the models
decreased wetland area and CH4 fluxes, primarily in the
tropics, but the magnitude and sign of the response varied greatly.
Models were least sensitive to increased global precipitation
(+3.9 % globally spatially uniform) with a consistent small
positive response in CH4 fluxes and wetland area. Results
from the 20th century transient simulation show that interactions
between climate forcings could have strong non-linear
effects. Third, we presently do not have sufficient wetland methane
observation datasets adequate to evaluate model fluxes at
a spatial scale comparable to model grid cells (commonly
0.5°). This limitation severely restricts our ability to
model global wetland CH4 emissions with confidence. Our
simulated wetland extents are also difficult to evaluate due to
extensive disagreements between wetland mapping and remotely sensed
inundation datasets. Fourth, the large range in predicted
CH4 emission rates leads to the conclusion that there is
both substantial parameter and structural uncertainty in large-scale
CH4 emission models, even after uncertainties in wetland
areas are accounted for. |
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