Why does CO2 not match the temperature line?

I have had a long and depressing Twitter debate with a contrarian who denies that CO2 doubling will cause a temperature increase of 1.2*C. This means that I cannot take the debate onwards to discuss feedbacks. He is of the group I classify as DIY amateur climatologists, guys (and it is always the male of the species) who have their own theory of what is going on. His is that the calculations showing the changes between CO2 energy absorption in 1970 and the late 90s contain simple errors that he has noticed but climate scientists are unable to notice. His argument is here. I have made a response, which I post here to try to summarise the debate about the fundamentals. But it is depressing, having to run the fundamentals over and over again. I want to engage on the real McCoy, on climate sensitivity.


"Seeing graphs, like this:
http://cosmoscon.files.wordpress.com/2011/12/co2-vs-temp.jpg
leads me to believe that CO2 is saturated."

Your graph simply reproduces the graph you show on this page: http://cosmoscon.com/2012/09/11/global-temperature-and-co2-update-september-2012/

Co2 is increasing in a more or less linear way, temperature is increasing from 1978-1999, then the increase reaches a plateau.  The plateau happens when CO2 reaches 370 ppm i.e. in 1999.

This divergence between the steady increase in CO2 and the temperature line would be significant if it were posited that CO2 is the sole determinant of temperature. It is not. Forcings include solar variations, ocean currents and particles, and feedbacks also affect the resultant. Solar output is in decline in recent years, the PDO has been cold since 2006, and aerosols, so I am told, have increased over the same period.

I wish I could point you to a computer simulation that integrates all of these, but sadly I cannot.

However I can point you to the graph on this page, when models are run with CO2 alone, natural forcings alone and with both together.

Source:  http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/figspm-4.htm

I know you dismiss models out of hand. My response to that is to ask - would you accept it if each calculation were to be worked out by hand? If yes, you are being unrealistic. If no, you are simply requiring that climate science should stop totally since climate science requires huge calculations.

Basically, you are running the CO2 is saturated argument, which was made by Angstrom and basically prevailed until the 1960s.  It is fully answered here: http://www.skepticalscience.com/saturated-co2-effect-advanced.htm

As I have said many times on Twitter, your main skeptical climate scientists Pat Michaels and Dick Lindzen both admit that CO2 doubling will cause an increase of ~1*C.  Surely that must give you pause for thought.