environmental physics office hours ( arnaud czaja) thursdays, 13.00-14.00 (huxley room 726)
TRANSCRIPT
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Environmental Physics
Office Hours (Arnaud Czaja)
Thursdays, 13.00-14.00(Huxley Room 726)
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Lecture 8Water vapour feedback
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8.1 Motivation:Water vapour and the
greenhouse effect
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“Top ofAtmosphere” (TOA)
Surface
A simple model of the greenhouse effect(lecture 7)
Radiation of surface
Atmospheric layer(absorbs all radiationfrom surface and re-emitsat its own temperature)
Solar input
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“Top ofAtmosphere” (TOA)
Surface
A simple model of the greenhouse effect(lecture 7)
Radiation of surface
Atmospheric layer(absorbs all radiationfrom surface and re-emitsat its own temperature)
Solar input
A measure of the greenhouse effect:
G = upward radiation
of surface minus
upward Radiation at TOA
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I
=upward (longwave)radiation at TOA
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Observed Greenhouse effect24
WminITG clears
Water vapour content2
2
kgminM OH
Sea surface temperature
KinSST
180
50
50
10
303
273
NB: All are annual mean data (from Held & Soden, 2000)
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Pierrehumbert et al., 2006, AGU Monograph.
Trapping of radiation by CO2 (330ppmv) only
Trapping of radiation by CO2 + observedwater vapour
No atmospheric absorbers
Upward radiation at TOA from full radiative calculation (January)
Trapping of radiation by CO2 + water vapourat saturation
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Pierrehumbert et al., 2006, AGU Monograph.
Trapping of radiation by CO2 (330ppmv) only
Trapping of radiation by CO2 + observedwater vapour
No atmospheric absorbers
Upward radiation at TOA from full radiative calculation (January)
Trapping of radiation by CO2 + water vapourat saturation
Water vapour vs. CO2:
-more abundant (amount of CO2 in atmosphereis only a few percent of that of water vapour)
-larger impact on greenhouse effect (as a result of being more abundant)
-a strong function of climate (and thus can notbe considered externally prescribed as is CO2to a certain extent)
--------> FEEDBACK!!
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What is meant by a function of climate:
sate
eRH
Upper tropospheric RH on April 27, 1999Low level enthalpy
qLTCh vp
0 1002.5
3.5
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What is meant by a function of climate:
sate
eRH
Upper tropospheric RH on April 27, 1999Low level enthalpy
qLTCh vp
0 1002.5
3.5Some control though….Clausius-Clapeyron relation(2nd law of thermodynamics)
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Dependence of globally averaged water vapour upon surface temperature (IPCC-AR4 models)
Held and Soden (2007)
Δe
Δe
ΔTs
ΔTsClausius-Clapeyron
scaling (7% / K)satisfied!
SRES A1B
20th century(control)
0 1K
0 4K