Guest essay by Saburo Nonogaki
It has been said that the averaged earth surface temperature would be 255K if no green-house-effect(g-h-e) gases were contained in the atmosphere, and is 288Ｋ at present where the atmosphere contains g-h-e gases. The estimation of 255K is based on the earth’s long-term radiative equilibrium and Stefan-Boltzmann’s law which states that the total amount of radiative energy from a black body at absolute temperature T is proportional to T 4.
As the earth’s long-term radiative equilibrium will be reached also in the case where the atmosphere contains g-h-e gases, we obtain the following equation under the condition that the long-term input energy from the sun remains constant.
(1–a )T 4 = constant (1)
Here, T is the averaged earth surface absolute temperature and a the ratio of radiative energy retained by the g-h-e gases in the atmosphere to the total radiative energy. By replacing T in equation (1) with 255Ｋ and 288Ｋ, we obtain the following equation.
(1–0)×2554 = (1–a )×2884 (2)
From equation (2), we obtain the value of a as follows.
a = 0.385 (3)
Jack Barrett* has reported that, in the case of 100m-thick atmosphere, the doubling of pre-industrial concentration of CO2 will result in the increase in infrared absorption by g-h-e gases by 0.5%. The reason why the increase is so small is based mainly on the