I have a comment on the answer you provided to a question on temperature as a function of CO2. In your reply (see Global Warming: How does global warming vary as a function of CO2?), you portrayed temperature change as a linear function of CO2. To my knowledge this is not correct. The response is logarithmic.
Submitted by: Onar
Answer:
Actually, we both are approximately correct. In the first paragraph of our answer, we state that each new increment of a radiatively-active greenhouse gas that is added to a planetary atmosphere produces less warming than the preceding equivalent increment. Hence, we clearly imply that atmospheric temperature change is not a linear function of CO2. To illustrate the truth of this statement, however, we do use a linear analysis for the three situations investigated -- Earth, Mars and Venus - but this approach is taken purely for illustrative purposes, as we also clearly state.
The results obtained by this method, although crude, are nevertheless adequate to demonstrate that planetary surface temperature is not a linear function of atmospheric CO2 concentration, i.e., it shows that a given incremental addition of CO2 to the atmospheres of these three planets does not produce the same increase in near-surface air temperature. On Earth, for example, we described how Idso (1988) demonstrated that a 300 to 600 ppm doubling of the air's CO2 content had the potential to warm the surface of the planet by approximately 0.4°C. On Mars, on the other hand, we demonstrated how the average of all such 300 ppm increments of CO2 from 0 to 8500 ppm had the potential to create a comparable warming of only 0.19°C. And on Venus, with its incredibly massive CO2 atmosphere, we demonstrated how the average of each 300 ppm increment of CO2 from 0 to 89,300,000 ppm had a greenhouse warming capacity of but a miniscule 0.0017°C.
The reason we approached the problem as we did is that it presumes no prior knowledge of the nature of the relationship between the greenhouse effect of a given increment of a radiatively-active gas and the base concentration of that gas at the time its atmospheric concentration is increased by the specified increment, which means that it bears the burden of no preconceived ideas. The relationship, therefore, is totally data-derived and representative of nothing but reality, although only approximately so because of the linear derivation of the data points. For a more exact derivation, one is referred to the publications of Idso (1988, 1989).
References
Idso, S.B. 1988. The CO2 greenhouse effect on Mars, Earth, and Venus. The Science of the Total Environment 77: 291-294.Idso, S.B. 1989. Carbon Dioxide and Global Change: Earth in Transition. IBR Press, Tempe, AZ.