onsdag 21 april 2010

Maximal Green House Effect Without Effect

If the atmosphere had a maximal Green House Effect GHE by blocking all outgoing infrared radiation, what would then be the surface temperaturebe on Earth? Let's first collect the data describing the present situation from the top picture of the previous post:
  • Out of incoming 100% from the Sun, 51% is absorbed by the surface of the Earth,
  • 30% is delivered back by conduction-convection/evaporation-condensation and 21% as infrared radiation.
  • The temperature at the Earth surface is 15 C, and at the top of the stratosphere 0 C.
Suppose now all of 21% outgoing infrared radiation would be blocked by a maximal GHE, so that all of the incoming 51% would have to be delivered back by convection-evaporation-condensation. What would the temperature increase be? Well, if we assume proportionality we get 21/30 x 15 = 10 C.   The maximal GHE thus may be 10 C.

What is then the present GHE? We did an estimate in the previous post and obtained about
50%.  So the present GHE may be 5 C. Without the present GHE the temperature would be about 15 - 5 = 10 C. The temperature gradient would then be maintained by convection-evaporation/condensation-conduction, not by any radiation.

With 10% the present GHE of CO2 would thus be 0.5 C. Doubling the CO2 could thus be expected to give at most 0.5 C. This conforms with Lindzens more elaborate analysis.

This argument includes feed back since it is part of the convection-evaporation/condensation. 

We thus have another (simple, but maybe relevant) argument indicating a small climate sensitivity of less than 0.5 C, based on observations of the present Earth surface temperature from the present radiative forcing.

The climate sensitivity estimate of 0.15 C in previous post, based on an even simpler argument using less data, may be a minimal climate sensitivity. It is easy argue that it should be doubled. By simple arguments we thus estimate the climate sensitivity to 0.3 - 0.5 C, about 10 times smaller than the IPCC value of  1.5 - 4.5 C based on even simpler (probably irrelevant) arguments.

It is natural to also make the following thought experiment: Suppose the effect of conduction-convection-evaporation/condensation was eliminated and only the GHE was left. What would then be the surface temperature? Right: 0 C, the same as at the top of the stratopshere.  Any temperature gradient in the atmosphere would be eliminated by radiation and the temperature would become constant through the atmosphere. From this one can argue that the GHE has no effect, right? An effect without effect? 

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