onsdag 15 september 2010

Simplistic Climate Science

Climate science is a young science with a variety of contradictory simplistic theoretical arguments offering a wide range of predictions such as climate sensitivity (global warming from doubled CO2) anywhere between 0 and 5 C. Some of the simplistic arguments may capture some true essence of global climate, others are completely misleading, following the device by Einstein.

Consider now the following simplistic argument:

The Earth surface temperature is set by the lapse rate (decrease of temperature with height) since the effective top of the atmosphere TOA temperature is determined to -18 C. The observed lapse rate is 6.5 C/km corresponding a TOA at a height of 5 km and an Earth surface temperature of 15 C with a temperature drop of 33 = 5 x 6.5 C.

The lapse rate of an atmosphere in equilibrium without convective motion and phase change (evaporation/condensation) may range from 0 (isothermal) to 9.8 C/km (adiabatic). In such an
atmosphere (without also radiation) there would be no heat transport from the Earth surface to TOA.

Suppose we now view the observed lapse rate of 6.5 C/km as being obtained from the adiabatic rate 9.8 by adding effects of convection/phase change transporting an observed 180 W/m2 from the Earth surface to TOA (with 60 out a total of observed 240 transported by radiation).
This corresponds to giving thermodynamics the leading role as concerns the lapse rate, that is,
global warming/cooling.

We would then view the reduction of the lapse rate from 9.8 to 6.5 as an effect of the heat transport from the Earth surface to TOA by convection/phase change: Increased heat transport coupled to increased convection/phase change, would then correspond to a further reduction of the lapse rate and thus correspond to global cooling.

Now, increased CO2 would require more heat to be transported by convection/phase change (under constant insolation of 240 W/m2), which with the above argument could cause global cooling.

We have thus presented a simplistic argument suggesting that climate sensitivity may very well be negative: more CO2 could cause global cooling. Is this argument correct? Maybe. At least it appears to be as plausible as any other simplistic argument floating around suggesting a climate sensitivity in the range 0 - 5 C. Maybe even more plausible, if the lapse rate is determined by thermodynamics rather than radiation.

2 kommentarer:

  1. Claes & Anders:

    This paper may be of interest to you:


  2. Yes, evaporation/condensation is an important part of the thermodynamics.