In summary, small quantities of radiation from excited Greenhouse gases, at frequencies corresponding to a transparent window of the atmosphere, provide direct feed back of heat towards the earth, causing some heating, and towards outer space producing cooling. The proportion of this free radiation, relative to the amount of excitation energy trapped in the Greenhouse gas, is a characteristic of the gas and will be independent of both the total heat energy present and the concentration of a given Greenhouse gas.
[The calculations show] that there is little significant difference between the spatial distributions of heat captured by the Greenhouse gases along a vertical column within the troposphere, for a range of concentrations equal to that defined at present, nominally 380 ppm of CO2 and possible future concentrations of 760 ppm and 1140 ppm. While it is not possible to calculate the actual proportion of energy returning to the earth via these very low frequency photons passing through a transparent atmosphere, the proportion relative to that held by excited CO2 molecules will always be exactly the same, irrespective of the total amount or density of carbon dioxide present.
The findings clearly show that any gas with an absorption line or band lying within the spectral range of the radiation field from the warmed earth, will be capable of contributing towards raising the temperature of the earth. However, it is equally clear that after reaching a fixed threshold of so-called Greenhouse gas density, which is much lower than that currently found in the atmosphere, there will be no further increase in temperature from this source, no matter how large the increase in the atmospheric density of such gases.
I have been misunderstanding this. What they are arguing, effectively, is that half the heat trapped winds up escaping and having a cooling effect, and the other half of course has a warming effect, and that beyond a certain concentration the quantity of CO2 doesn’t matter.
It is my understanding that ALL models of CO2 accumulation posit a relatively decreasing effect per unit as quantities increase. No sane mind can fail, then, performing basic logic on this idea, to grasp that at some point further increases do NOTHING, which is what this paper argues.
James Hanson got his start worrying about Earth becoming Venus. Unless we move into Venus’ orbit, this will not happen. How hard is it to grasp that any planet as much closer to the Sun as Venus is will also be that much hotter? We are of course much hotter than Mars, which in turn is much hotter than Pluto.