What Controls the Temperature of the Earth?
The question remains, can GH gasses effect the temperature of the Earth. My opinion is yes but maybe not in the way most would understand.
As we saw earlier the temperature of the planet is governed by the equation:
From this we can see several ways that the temperature of the Earth TE can be effected.
TE could increase if any of the following scenarios were to occur:
- If the solar irradiance J increases. This is of course a possibility but is no way related to human activity
- The absorptivity a of the Earth increases or there is a decrease in reflectivity. This is possible and may be due to human activity. Urbanisation, dark building surfaces and road ways, land clearing, localised snow melts may all contribute to an increase in a and result in a warming of the Earth
- The emissivity e of the earth decreases. This is where GH gasses may have an effect.
I would like to elaborate on the third point.
GH gases may decrease the emissivity of the Earth when an emitting surface of high e is replaced by an emitting surface of low e .This is exactly what happens when a GH gas absorbs in the so called transparent IR window. The GH gas of low e effectively takes the place of the earth’s surface having a high e. Thus, IR absorption by a GH gas decreases the effective emissivity of the Earth, thus raising the temperature. This is a far more satisfactory explanation then back radiation heating the surface!
However, there is a flip side to this argument. There are 66 W/m2 of IR radiation radiated from the surface, 26 units are absorbed (by the GH gasses), and 40 passes through the IR window. This is where the GH effect occurs. More radiation will be absorbed and therefore less will be emitted to space when GH gas concentrations increase.
However, what happens to the 102 units of energy absorbed by the atmosphere due to convection and the 67 units absorbed from the direct sunlight. How is this energy emitted to space?
All up 235 units of IR radiation are emitted to space, 40 directly from the Earths surface, 195 from the atmosphere (including clouds). How is this 195 units radiated to space? – by Greenhouse Gases in the atmosphere. If these gases were not present this energy could not be emitted.
By increasing GH gas concentrations the ability for the atmosphere to radiate energy to space is increased. GH gasses have a higher emissivity than air. The emissivity of the atmosphere increases thus cooling the Earth.
It would seem plausible that the cooling effect of GH gasses would be greater than the warming effect! In any sense it is a colossal oversight to disregard this cooling effect when considering the effect of increasing GH gas concentrations on the warming of our planet.
Why is this not considered in the CSIRO’s explanation?