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Environmental Physics: Climate Dynamics aspects Arnaud Czaja Space & Atmospheric Physics.

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Presentation on theme: "Environmental Physics: Climate Dynamics aspects Arnaud Czaja Space & Atmospheric Physics."— Presentation transcript:

1 Environmental Physics: Climate Dynamics aspects Arnaud Czaja Space & Atmospheric Physics

2 Overview (Lectures #7-14) Greenhouse effect (#7, i.e. today) Water Vapour feedback (#8) Cooling mechanisms for the planet (#9) Climate models (#10) + MATLAB session Climate timescales (#11) Climate sensitivity (#12) Modes of climate variability (#13) Discussion of a hot Topic (#14)

3 Our own EP Climate Model! Atmosphere Tropics Extra Tropics Ocean

4 Our own EP Climate Model! Atmosphere Tropics Extra Tropics Ocean (i) Use of model is not mandatory and thus the model is not examinable (ii) MATLAB session on Thursday Feb 7 (5-6pm) (come if you wish, this is not mandatory)

5 Lecture 7 The Greenhouse effect

6 Student: Oh yeah! It’s the trapping of radiation by the atmosphere

7 Lecture 7 The Greenhouse effect Lecturer: Let’s be a bit more precise!!

8 7.1 Motivation: Observations of Earth from Space

9 Total radiation seen by a satellite (GERB project in Space & Atmospheric Physics) NB: Photon energy is the main form of energy exchanged between the earth and space

10 LW SW Long wavelength photons (emitted by the Earth) Short wavelength photons (reflected from the Sun) +

11 Terrestrial radiation λ≈10-20μm 1 erg s -1 cm -2 = 10 -3 W m -2

12 Sun radiation Solar radiation λ≈0.2-1μm

13 To zero order… Solar photons are absorbed by the atmosphere (clouds, water vapour, ozone) …but much less so than are the terrestrial photons. This is because of the atmospheric composition, with tri-atomic molecules efficient at interacting with λ≈10-20μm photons (“greenhouse absorbers”).

14 Atmospheric composition (fraction of total molecules) Main Greenhouse gas (GHG) is Water vapour (variable ≈1% ) Man influenced GHG Pre-industrialIPCC (2007) CO2280ppmv380 ppmv CH4700ppbv1800 ppbv N2O270ppbv320 ppbv NB: 1ppmv = 1 molecule out of a million 1ppbv = 1 molecule out of a billion N2 O2 CO2

15 What is meant by variable H2O… Upper tropospheric RH on April 27, 1999Low level enthalpy 0100 2.5 3.5

16 7.3 Observations of the greenhouse effect (G)

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18 Observed Greenhouse effect Water vapour content Sea surface temperature 180 50 10 303 273 NB: All are annual mean data (from Held & Soden, 2000)

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20 Imperial College London 28 May 2003 20 Solar spectr um Lean (1991) [adapted by Lockwood]

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