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)
Our own EP Climate Model! Atmosphere Tropics Extra Tropics Ocean
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)
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”).
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
What is meant by variable H2O… Upper tropospheric RH on April 27, 1999Low level enthalpy 0100 2.5 3.5