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| Titel |
Chemical feedbacks in climate sensitivity studies |
| VerfasserIn |
Simone Dietmüller, Michael Ponater, Robert Sausen |
| 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 |
250075364
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| Zusammenfassung |
| Interactively coupled climate chemistry models extend the number of feedback
mechanisms in climate change simulations by allowing a variation of several radiatively
actice chemical tracers that are prescribed in conventional climate models. Different
perturbation experiments including chemical feedbacks were performed using the
chemistry-climate model system EMAC coupled to the mixed layer ocean model MLO.
The influence of the chemical feedbacks O3, CH4 and N2O on climate response
and climate sensitivity is quantified for a series of CO2-perturbation simulations:
Equilibrium climate sensitivity is dampened, if chemical feedbacks are included. In
case of a CO2 doubling simulation chemical feedbacks decrease climate sensitivity
by -3.6% and in case of a 4*CO2 simulation by -8.1%. Analysis of the chemical
feedbacks reveals, that the negative feedback of ozone, mainly the feedback of
stratospheric ozone, is responsible for this dampening. The radiative feedbacks of CH4 and
N2O are negligible, mainly because the model system does not allow interactive
emission feedbacks at the Earth’s surface for these gases. The feedback of physical
parameters is significantly modified by the presence of chemical feedbacks. In case of
the CO2-perturbation experiments the negative stratospheric ozone feedback is
accompanied by a negative stratospheric H2O feedback change of the same order of
magnitude. So the dampening effect of the direct O3 radiative feedback is enhanced. A
non-linearity in the damping is found with increasing CO2 concentrations. Reasons are the
nonlinear feedbacks of ozone, temperature, and stratospheric water vapor. Additional
6*CO2 simulations with and without chemical feedbacks included show, that the
presence of chemic feedbacks helps to prevent a runaway greenhouse effect, as the O3
distribution can react to the upward shift of the tropopause. Also experiments driven by
anthropogenic NOx- and CO-emissions were performed, where chemically active
trace gases act both as radiative forcing and radiative feedback. The comparison to
CO2-perturbation experiments shows, that the variation of the perturbation type induces
different feedback processes resulting in a different influence on climate sensitivity. |
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