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[bluewave]

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[Snow_Miser]

I posted this quote from the IPCC in blizzard's thread, but I think it's necessary to post it here as well. With just the Lapse Rate, Water Vapor, and Albedo feedbacks alone in the GCMs, the models predict an equilibrium doubling to CO2 to be around 1.9 Degrees C.

From the IPCC:

"Using feedback parameters from Figure 8.14, it can be estimated that in the presence of water vapour, lapse rate and surface albedo feedbacks, but in the absence of cloud feedbacks, current GCMs would predict a climate sensitivity (±1 standard deviation) of roughly 1.9°C ± 0.15°C (ignoring spread from radiative forcing differences). The mean and standard deviation of climate sensitivity estimates derived from current GCMs are larger (3.2°C ± 0.7°C) essentially because the GCMs all predict a positive cloud feedback (Figure 8.14) but strongly disagree on its magnitude."

This means that the majority of amplification to reach 3.2 Degrees C in the models comes from the least certain feedback. The Cloud Feedback. Even assuming that the water vapor feedback is not exaggerated in the models (F2 and I have posted evidence in his thread that strongly suggest that it is, however), we still get an equilibrium doubling of only 1.9 Degrees C without the Cloud Feedback in the models. If the Cloud Feedback is negative, then the sensitivity is less than 1.9 Degrees C. Even more interesting, is that Dr. Dessler himself has co-authored a paper which suggests the Cloud Feedback to be negative.

From the paper:

"The global average SW, LW, and net cloud feedbacks are +0.30 ±1.10, −0.46 ±0.74, and −0.16 ±0.83 W m⁻² K⁻¹, respectively."

Keep in mind that the short term cloud feedback and the long term cloud feedback are different. But advocates of a positive cloud feedback have cited Dessler's previous work that claimed that the short term Cloud Feedback was positive.

So according to Dr. Dessler's own, and most recent work, and the logic from the GCMs, it is very possible that Climate Sensitivity is below 2 Degrees C, and many studies recently have come to that conclusion as well.