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| Titel |
Analysis of present day and future OH and methane lifetime in the ACCMIP simulations |
| VerfasserIn |
A. Voulgarakis, V. Naik, J.-F. Lamarque, D. T. Shindell  , P. J. Young, M. J. Prather, O. Wild, R. D. Field, D. Bergmann, P. Cameron-Smith, I. Cionni, W. J. Collins, S. B. Dalsøren, R. M. Doherty, V. Eyring, G. Faluvegi, G. A. Folberth, L. W. Horowitz, B. Josse, I. A. MacKenzie, T. Nagashima, D. A. Plummer, M. Righi, S. T. Rumbold, D. S. Stevenson, S. A. Strode, K. Sudo, S. Szopa, G. Zeng |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 5 ; Nr. 13, no. 5 (2013-03-05), S.2563-2587 |
| Datensatznummer |
250018472
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| Publikation (Nr.) |
 copernicus.org/acp-13-2563-2013.pdf |
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| Zusammenfassung |
| Results from simulations performed for the Atmospheric Chemistry and Climate
Modeling Intercomparison Project (ACCMIP) are analysed to examine how OH and
methane lifetime may change from present day to the future, under different
climate and emissions scenarios. Present day (2000) mean tropospheric
chemical lifetime derived from the ACCMIP multi-model mean is
9.8 ± 1.6 yr (9.3 ± 0.9 yr when only including selected models), lower than a
recent observationally-based estimate, but with a similar range to previous
multi-model estimates. Future model projections are based on the four
Representative Concentration Pathways (RCPs), and the results also exhibit a
large range. Decreases in global methane lifetime of 4.5 ± 9.1% are
simulated for the scenario with lowest radiative forcing by 2100 (RCP 2.6),
while increases of 8.5 ± 10.4% are simulated for the scenario with
highest radiative forcing (RCP 8.5). In this scenario, the key driver of the
evolution of OH and methane lifetime is methane itself, since its
concentration more than doubles by 2100 and it consumes much of the OH that
exists in the troposphere. Stratospheric ozone recovery, which drives
tropospheric OH decreases through photolysis modifications, also plays a
partial role. In the other scenarios, where methane changes are less
drastic, the interplay between various competing drivers leads to smaller
and more diverse OH and methane lifetime responses, which are difficult to
attribute. For all scenarios, regional OH changes are even more variable,
with the most robust feature being the large decreases over the remote
oceans in RCP8.5. Through a regression analysis, we suggest that differences
in emissions of non-methane volatile organic compounds and in the simulation
of photolysis rates may be the main factors causing the differences in
simulated present day OH and methane lifetime. Diversity in predicted
changes between present day and future OH was found to be associated more
strongly with differences in modelled temperature and stratospheric ozone
changes. Finally, through perturbation experiments we calculated an OH
feedback factor (F) of 1.24 from present day conditions (1.50 from 2100
RCP8.5 conditions) and a climate feedback on methane lifetime of
0.33 ± 0.13 yr K−1, on average. Models that did not include
interactive stratospheric ozone effects on photolysis showed a stronger
sensitivity to climate, as they did not account for negative effects of
climate-driven stratospheric ozone recovery on tropospheric OH, which
would have partly offset the overall OH/methane lifetime response to climate change. |
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