Why 33 deg. C for the Earths Greenhouse Effect is Misleading
Pretend you have no idea who Roy Spencer is, other than a climate scientist who recently published an article on global warming feedbacks in JGR. Now read this post…
The value of 33 deg. C represents the difference between the observed average surface temperature of the Earth, and the estimated surface temperature if there was no atmosphere.
But what many people don’t realize is that the 33 deg. C of surface warming is not actually a measure of the greenhouse warming – it represents the balance between TWO competing effects: a greenhouse warming effect of about 60 deg. C (the so-called “pure radiative equilibrium” case), and a convective cooling effect of about 30 deg. C. When these two are combined, we get the real-world observed “radiative-convective equilibrium” case.
This has been known since at least 1964 (Manabe and Strickler, 1964). It was also discussed in Dick Lindzen’s 1990 paper, Some Coolness Regarding Global Warming, which is when I became aware of its significance.
These climate basics, which have been known since the 1960s, also raises an intriguing question: If the surface warming effect of 2XCO2 before surface cooling by convection is 1 deg. C, and (as even the IPCC knows) 50% of that natural greenhouse warming is then short-circuited by convection, might this then tell us that negative feedbacks in the climate system can be expected to reduce anthropogenic global warming to only 0.5 deg. C?
I believe this is entirely possible.
How could this happen, since there is so much evidence that water vapor feedback is positive? Because, even if water vapor feedback is positive, an increase in the solar shading effect of clouds (negative cloud feedback) could more than overwhelm the positive water vapor feedback, leading to little net warming.
Where is the wacky? Is he just making numbers up, or is there something to these posts?