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| Titel |
Climate versus emission drivers of methane lifetime against loss by tropospheric OH from 1860–2100 |
| VerfasserIn |
J. G. John, A. M. Fiore, V. Naik, L. W. Horowitz, J. P. Dunne |
| 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 ; 12, no. 24 ; Nr. 12, no. 24 (2012-12-19), S.12021-12036 |
| Datensatznummer |
250011677
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| Publikation (Nr.) |
 copernicus.org/acp-12-12021-2012.pdf |
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| Zusammenfassung |
| With a more-than-doubling in the atmospheric abundance of the potent
greenhouse gas methane (CH4) since preindustrial times, and indications
of renewed growth following a leveling off in recent years, questions arise
as to future trends and resulting climate and public health impacts from
continued growth without mitigation. Changes in atmospheric methane lifetime
are determined by factors which regulate the abundance of OH, the primary
methane removal mechanism, including changes in CH4 itself. We
investigate the role of emissions of short-lived species and climate in
determining the evolution of methane lifetime against loss by tropospheric
OH, (τCH4_OH), in a suite of historical (1860–2005) and future
Representative Concentration Pathway (RCP) simulations (2006–2100),
conducted with the Geophysical Fluid Dynamics Laboratory (GFDL) fully coupled
chemistry-climate model (CM3). From preindustrial to present, CM3 simulates
an overall 5% increase in τCH4_OH due to a doubling of the
methane burden which offsets coincident increases in nitrogen oxide
(NOx emissions. Over the last two decades, however, the
τCH4_OH declines steadily, coinciding with the most rapid
climate warming and observed slow-down in CH4 growth rates, reflecting a
possible negative feedback through the CH4 sink. Sensitivity simulations
with CM3 suggest that the aerosol indirect effect (aerosol-cloud
interactions) plays a significant role in cooling the CM3 climate. The
projected decline in aerosols under all RCPs contributes to climate warming
over the 21st century, which influences the future evolution of OH
concentration and τCH4_OH. Projected changes in
τCH4_OH from 2006 to 2100 range from −13% to +4%. The
only projected increase occurs in the most extreme warming case (RCP8.5) due
to the near-doubling of the CH4 abundance, reflecting a positive
feedback on the climate system. The largest decrease occurs in the RCP4.5
scenario due to changes in short-lived climate forcing agents which reinforce
climate warming and enhance OH. This decrease is more-than-halved in a
sensitivity simulation in which only well-mixed greenhouse gas radiative
forcing changes along the RCP4.5 scenario (5% vs. 13%). |
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