Climate skeptics like Lindzen, Singer and Spencer (and Monckton and WUWT and Lubos...) are skeptical to CO2 alarmism, but they are all eager to state that they understand that CO2 is a greenhouse gas GHG with in principle a warming effect (even if this effect is so small that it can never be observed). They are skeptical to all of the dogmas of CO2 alarmism of melting ice caps, rising sea level, bad weather and threatened ice bears, but there is one thing for which the skepticism is missing: CO2 as a GHG with some warming effect. Maybe 3.7 W/m2 upon doubling.
People questioning the warming effect of CO2 are called "climate deniers" and they are not highly valued by neither climate alarmists nor climate skeptics.
What is then the difference is between climate skeptics and climate deniers? Why are climate skeptics not skeptical to the capacity of CO2 to cause warming, when they are skeptical to just about everything else coming from the climate alarmist camp?
I think the answer is credibility, scientific credibility. If you like a denier questions everything from IPCC including CO2 as a GHG, then you could easily be viewed as a crank that does not understand anything at all and therefore can question everything. Like a fool asking more questions than many wise men can answer.
And you don't want to be (viewed as) a crank. To send the signal that your are not a crank, it may be a good idea to pretend to understand the deep physics of the spectrum of CO2 based on deep quantum mechanics by saying that you very well understand that certainly CO2 is a GHG, because advanced computer codes like Modtran produce spectra which can be interpreted this way.
The difference between climate skeptics and deniers thus seems to be that skeptics gain credibility by pretending to understand something, which may be incorrect, while deniers lose credibility by admitting to not to understand, what possibly cannot be understood.
PS Here is a recent statement by Spencer representative of a skeptics view on the radiative forcing of 3.7 W/m2 from doubled CO2:
- I’m just saying I think the no-feedback temperature response is pretty sound…although I admit it must be computed based upon theory, and can’t be observationally verified.