A Window Into the IPCC Process

I thought this article by Steve McIntyre was an interesting window on the IPCC process.  Frequent readers of this site know that I believe that feedbacks in the climate are the key issue of anthropogenic global warming, and their magnitude and sign separate mild, nearly unnoticeable warming from catastrophe.  McIntyre points out that the IPCC fourth assessment spent all of 1 paragraph in hundreds of pages on the really critical issue:

As we’ve discussed before (and is well known), clouds are the greatest source of uncertainty in climate sensitivity. Low-level (“boundary layer”) tropical clouds have been shown to be the largest source of inter-model difference among GCMs. Clouds have been known to be problematic for GCMs since at least the Charney Report in 1979. Given the importance of the topic for GCMs, one would have thought that AR4 would have devoted at least a chapter to the single of issue of clouds, with perhaps one-third of that chapter devoted to the apparently thorny issue of boundary layer tropical clouds.

This is what an engineering study would do – identify the most critical areas of uncertainty and closely examine all the issues related to the critical uncertainty. Unfortunately, that’s not how IPCC does things. Instead, clouds are treated in one subsection of chapter 8 and boundary layer clouds in one paragraph.

It turns out that this one paragraph was lifted almost intact from the work of the lead author of this section of the report.  The “almost” is interesting, though, because every single change made was to eliminate or tone down any conclusion that cloud feedback might actually offset greenhouse warming.  He has a nearly line by line comparison, which is really fascinating.  One sample:

Bony et al 2006 had stated that the “empirical” Klein and Hartmann (1993) correlation “leads” to a substantial increase in low cloud cover, which resulted in a “strong negative” cloud feedback. Again IPCC watered this down: “leads to” became a “suggestion” that it “might be” associated with a “negative cloud feedback” – the term “strong” being dropped by IPCC.

Remember this is in the context of a report that generally stripped out any words that implied doubt or lack of certainty on the warming side.

  • Thomas J. Arnold.

    It is the ‘new scientific way’ make the science fit the hypothesis and if the science doesn’t fit, then change the wording! Feed back is the bane of the IPCC, they cannot or won’t or don’t want to admit that it is a major factor (or one of them, the oceans are another) in the amelioration of the planet’s atmosphere.

    How can models be precision fine-tuned to climate when we don’t know what drives the whole process. Other than to say, “it is the sun and some other things”!…… Maybe a little simplistic but a kernal of truth.

  • hunter

    When there is no accountability, and the process is opaque, it is difficult to keep prejudice and self-interest out of any enterprise, no matter how lofty it may claim to be.

  • Rob J Mitchell

    Of course they didn’t look at clouds. If they did they would have noticed the obvious cause of the global warming, the 5% reduction in low cloud cover. I’ts responsible for 0.35 deg C warming between 1980-2000, which includes strong negative feedback due to the accompanying reduction in the dominant greenhouse gas, water vapor.

    Of course climate models based on the maths of a perpetual motion machine (system dominated by positive feedback) are bound to be accurate!

  • Alan D. McIntire

    Here’s a link to the actual paper:


    Obviously weather is based 100% on water in its various forms, solid, liquid and gas. Until climatologist have accurate models predicting water vapor levels, changes in temperature lapse rate, and cloud cover, they’ll be practicing astrolology, not climatology- A. McIntire

  • Orson

    This 16 page paper on falsifying the AGW hypothesis through ocean heat content deserves your attention. The skeptic community as well as the open-minded could well use your expert skills in simplifying the argument and evidence – much as you already have on the missing tropical hotspot.


    “Have Changes In Ocean Heat Falsified The Global Warming Hypothesis?”
    by William DiPuccio, Thursday, 16 July 2009.