The Key Argument of CO2 Alarmism

The key argument of CO2 greenhouse gas alarmism is presented in IPCC AR4 Glossary as follows: 

• An increase in the concentration of greenhouse gases leads to an increased infrared opacity of the atmosphere, and therefore to an effective radiation into space from a higher altitude at a lower temperature. This causes a radiative forcing...
  

Even a skeptic like Lindzen buys this argument, but let us nevertheless seek to understand the logic, or lack thereof. 

Note that IPCC here motivates the greenhouse effect without any reference to backradiation; the only possible reason for this omission is that IPCC does not believe in backradiation.  

As noted by Anders in a comment to the previous post, the cited argument requires that the lapse rate and temperature profile is not determined by greenhouse gases, but by something else. Only then does it make sense to claim that increasing the effective emission altitude will decrease the emission temperature and thus the outgoing radiation and thus cause radiative forcing.

But if the temperature profile is determined by something else than greenhouse gases (e.g. thermodynamics with gravitation), then the amount of greenhouse gases has no influence on the temperature profile.  

So we have here another example of Penguin logic: By assuming that the temperature profile depends on something else than greenhouse gases, IPCC concludes that increasing greenhouse gases will change the temperature profile to warming of the Earth surface.

Do you see the lack of logic?

Note that it is always important to choose the argument depending on whom you are addressing: Backradiation works quite well for a not so sophisticated audience, while the above argument suits e.g. members of Royal Societies, because it has a higher level of abstraction.