Judy Curry comments on the Raymond T. Pierrehumbert Article In Physics Today Titled “Infrared Radiation And Planetary Temperature” in her post
Pierrehumbert on infrared radiation and planetary temperatures [from Climate Cash]
I agree with Judy that this is a very informative and valuable article on the role of CO2 and other greenhouse gases in the Earth’s (and other planet) atmospheres. However, there is one major error in my view in the article.
Ray concludes that
“… increasing CO2 would warm the atmosphere and ultimately result in greater water-vapor content—a now well-understood situation known as water-vapor feedback.”
This significantly overstates our understanding of the water vapor feedback on Earth since phase changes of water are intimately involved. In a world without these feedbacks, but in which evaporation from the surface increases if surface temperature increases from the added CO2, his conclusion would be correct.
However, as summarized by Graeme Stephens in my post
where he wrote (see), for example,
“Models contain grave biases in low cloud radiative properties that bring into question the fidelity of feedbacks in models”
“The presence of drizzle in low clouds is ubiquitous and significant enough to influence the radiative properties of these clouds and must play some role in any feedbacks”
“….our models have little or no ability to make credible projections about the changing character of rain…”
major uncertainties remain.
The water vapor feedback in the real climate system remains incompletely understood.