## tisdag 5 april 2011

### Simple Climate Model: Thermodynamics, Radiation and Observation

In the spirit of my article in Slaying the Sky Dragon, consider the following facts:
• The Earth with atmosphere absorbs 240 W/m2 sunlight and emits 240 W/m2 IR.
• The Earth surface temperature is 288 K.
• By Stefan Boltzmann 240 W/m2 corresponds to an effective blackbody temperature of 255 K (with an albedo of 0.3). The difference 288 - 255 = 33 C can be seen as the total warming effect of the atmosphere.
• 40 W/m2 is emitted directly from the Earth surface through an "atmospheric window".
• The climate system acts as an air conditioner in a combined thermodynamic-radiation cycle processing the remaining 200 W/m2.
• The effect of this process is to reduce the lapse from the base (dry adiabatic) value of 9.81 C/km to the observed 6.5 C/km, thus with a reduction of 3.5 C/km per 200 W/m2 or total cooling effect of 18 C, since the temperature is observed to be 255 K at a height of 5 km.
• The reduction of the lapse results mainly from the thermodynamics by evaporation/condensation, which has a cooling effect by lowering the temperature at low altitudes by evaporation and increasing the temperature by condensation at higher altitudes.
• Suppose now the atmospheric window is decreased by additional greenhouse gases by 4 W/m2, which are to be handled by the combined thermodynamic-radiation process.
• Suppose the 4 W/m2 are splitted equally between thermodynamics and radiation.
• Additional 2 W/m2 to be processed by thermodynamics means 1% reduction of the lapse rate with corresponding cooling effect of about 0.18 ~ 0.2 C.