Spinning the literature on cloud feedback

Chapter 8 of the IPCC AR4 report is about "Climate Models and Their Evaluation".
One of the weaknesses of these models is in how they deal with clouds, and in particular, feedback to the climate from cloud formation.  This is acknowledged by the IPCC, for example on page 593, "The relatively poor simulation of these clouds in the present climate is a reason for some concern."

The main section on cloud feedbacks is pages 635-638, section 8.6.3.2.  Clouds exert a negative feedback on global warming, since warming leads to more evaporation of water, which leads to more cloud formation, which reflects sunlight. In the jargon of climate science, the global mean cloud radiative feedback (CRF) is negative.

This section illustrates the usual biased commentary by the IPCC on the literature of the field. For example, a paper by skeptic Richard Lindzen and colleagues is referred to with the remark "Lindzen et al (2001) speculated that ...".  A paper by Somerville (Cloud optical thickness feedbacks in the CO2 climate problem,  Advances in Space Research, 5, 209-212, 1985) that explains clearly the negative feedback mechanism, is not cited.

Steve McIntyre notes that substantial parts of this section are very similar to a review article by Bony et al, 2006, but that key parts of the text have been changed in a way to downplay the negative feedback. The review article has 14 authors, and all of them are involved with writing the chapter, one as coordinating lead author (David Randall) and three others as lead authors. 

Here are some comparisons between the two versions:


 Bony et al 2006
 IPCC chapter 8
 Boundary layer clouds have a strongly negative CRF
(Harrison et al. 1990; Hartmann et al. 1992) and covera very large fraction of the area of the Tropics (e.g., Norris 1998b).
 Boundary-layer clouds have a strong impact on the net
radiation budget (e.g., Harrison et al., 1990; Hartmann et al.,
1992) and cover a large fraction of the global ocean (e.g., Norris,
1998a,b).
It has been argued based on the Clausius–Clapeyron
formula that in a warmer climate, water clouds of a
given thickness would hold more water and have a
higher albedo (Somerville and Remer 1984; Betts and
Harshvardhan 1987).
 -
 Klein and Hartmann (1993) showed an empirical correlation between mean boundary layer cloud cover and lower-tropospheric stability (defined in their study as the difference of 700-hPa and near-surface potential temperature). When imposed in simple two-box models of the tropical climate (Miller 1997; Clement and Seager 1999; Larson et al. 1999) or into some GCMs’ parameterizations of boundary layer cloud amount [e.g., in the National Center for Atmospheric Research (NCAR) Community Climate System Model verion 3 (CCSM3)], this empirical correlation leads to a substantial increase in low cloud cover in a warmer climate driven by the larger stratification of warmer moist adiabats across the Tropics, and produces a strong negative feedback. The observed relationship between low-level cloud amount and a particular measure of lower tropospheric stability (Klein and
Hartmann, 1993), which has been used in some simple climate
models and in some GCMs’ parametrizations of boundary layer
cloud amount (e.g., CCSM3, FGOALS), led to the suggestion that a global climate warming might be associated with an increased low-level cloud cover, which would produce a negative cloud feedback (e.g., Miller, 1997; Zhang, 2004).

In the first example, the "strongly negative CRF" is deleted from the IPCC version.
In the second, the argument for higher albedo is not mentioned at all.
In the third, the word "strong" has been removed, and questioning language such as "suggestion" and "might" have been inserted.

The two versions were written by the same 14 authors, at more or less the same time (2006), but the science has been distorted in the IPCC version, to try to weaken the argument for negative feedback (and thus strengthen the argument for dangerous global warming).