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The IPCC Is Never Wrong -1- Why Kevin Trenberth Is Right

Thus spoke Dr Kevin E Trenberth, Head of the Climate Analysis Section at the National Center for Atmospheric Research in the (very welcome!) Gray/Trenberth written debate hosted by the Tea Party of Northern Colorado:

I have found that the only scientists who disagree with the IPCC report are those who have not read it and are poorly informed

Contrarily to what the most argument-challenged readers of this blog might think, I fully agree with Dr Trenberth’s statement. Only, I arrive at his same conclusion starting from a very different point of view (wonder if Morano will ever try to sing a different tune?).


I have read several chapters of the IPCC AR4 (2007) (sadly, I have not read the whole thing in full from start to end and seriously wonder if anybody ever has). Fact is, they are all written in a scientifically very valid way. As the science of climate is still full of uncertainties, then whatever the future, may it be hot, may it be cold, it will be impossible to ever find in the IPCC reports any item that may be actually considered as fundamentally wrong or misleading.

Everything is in there and its opposite, by wise [UPDATE: “wise” means “wise” in a POSITIVE way…do not mix it up with “weasel” or anything else with a bad connotation] use of words like “could”, “might” and “likely”. Even if we meet again in 2050 and global cooling is in full swing, still the IPCC reports will be, in a sense, correct. Take for example AR4-SYR-SPM (Synthesis Report, Summary for Policymakers)

page 5: Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations

page 7: Continued GHG emissions at or above current rates would [note how they had so many would‘s to distribute, they added one too many here] cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century

The meaning of “very likely” is explained in the box Treatment of uncertainty” in the Introduction of the Synthesis Report (page 27):

Where uncertainty in specific outcomes is assessed using expert judgment and statistical analysis of a body of evidence (e.g. observations or model results), then the following likelihood ranges are used to express the assessed probability of occurrence: virtually certain >99%; extremely likely >95%; very likely >90%; likely >66%; more likely than not > 50%; about as likely as not 33% to 66%; unlikely <33%; very unlikely <10%; extremely unlikely <5%; exceptionally unlikely <1%.

Since “very likely” stops at 90%, it means that the IPCC experts agree that there is a 10% probability that most of observed temperature increases might not be due to “increase in anthropogenic GHG concentrations“. And that there is a 10% probability that the 21st century will not see anything larger than the 20th century has seen.

So if anything like that actually happens, well, the IPCC AR4 has already included that possibility, has it not?

Interestingly, if the IPCC work were to be presented as a scientific article, and the p-value associated to the null hypothesis (that observed temperature increases have nothing to do with increased GHG concentrations) were 0.1 or 10%, most if not all journals would deny publication.


  1. John DeFayette
    2009/12/23 at 09:05


    I’m sorry to arrive on the scene so late, but I hope you can help me with an old, nagging questions that I have regarding the IPCC’s AR4. To be clear, I have read the whole of the WGI report. There is absolutely no need to read beyond that, since WG’s II and III are mere science fiction once you understand the lack of conclusion in WGI.

    In my opinion you are correct in asserting that the document is well written. For those who can read beyond the summaries the scientific evaluations are mostly honest in their admission of our ignorance regarding our climate.

    However, the politicians weighed in heavily even with the report’s body, and here is the question:

    Who decided, and when was the decision made, to add the uncertainty category “more likely than not” to the uncertainty table in AR4?

    The question is fundamental since it turns a perfectly reasonable document into a political club. Clearly, an honest IPCC panel hammered out a reasonable likelihood scale in July 2005, published as an annex to AR4 in 2007. Table 4 in the uncertainty guidelines document indicates the terminology “as likely as not” for the probability zone around 50% (from 33% to 66%). This is perfectly reasonable, since a 50-50 likelihood or thereabouts has the same meaning as a coin toss. The document further instructs the authors of AR4 to refrain from messing with these terms.

    To my dismay, I find the final AR4 littered with a new term, “more likely than not” plopped right there at the 50-yard line where I would expect to find a balanced “as likely as not.” A short search leads me to Box 1.1 of AR4 Chapter 1 as well as Box TS.1 in the Technical Summary, where I find that the AR4 authors have simply added the new term “…in order to provide a more specific assessment of aspects including attribution and radiative forcing.” With this wondrous little change the AR4 is no longer a document that must admit that human activity may or may not (we don’t really know) cause an increase in hurricanes, in heavy precipitation events, in heat waves, droughts and more. Instead it says “more likely than not” in these cases. Obviously, the original terminology only allowed for a vague “we don’t know” whether the coin will land heads up; it sounds much better to say that the coin is more likely to land heads up than tails up.

    Scanning the two-year-old news I find no references to enraged citizens. I wonder if it is possible to find the authors who are responsible for this semantic scam?

    Best regards.

    • 2009/12/23 at 10:50

      John – many thanks for that. I have taken the liberty to post your comment as a blog, enriching it with a couple of notes and all the necessary links and images of the original texts

  2. kuhnkat
    2009/10/16 at 00:54


    Off the top of my head, the section including Dendrochronology.

    The section that has no definitive work on basis for GreenHouse effect, yet claims for certain temp increases for doubling CO2.

    Maybe the same, but, the section on modeling. Some of the major shortcomings of the models have come out since, yet were known at the time. Well, that is my assumption. If the modellers didn’t know it says bad things about their knowledge and ability. Claiming that models are only projections and scenarios while pushing action based on them.

    Their claimed belief in the accuracy of their temperature records. HadCrut can not even show us their records now. GISS is failing on their own practice of using poor sites, adding and dropping sites apparently at will, and questionable adjustments. Papers proving UHI in the Chinese record which are ignored by HadCrut and GISS while they ignore the same problems with their own records.

    What would be criminal suppression of comments if it were in relation to businesses.

    Misadventures in relation to using certain Dendro papers.

    Have you read the Comments that Steve McI has been involved in getting posted for free availability??


  3. 2009/10/15 at 21:46

    Part #2, in case it hasn’t been noticed yet, is titled “‘Settled Science’ Of Chinese Whispers”

  4. 2009/10/15 at 07:45

    Thank you for the linkback, Maurizio. I’ve been a reader of your blog for over a year now. You, sir, are indefatigable.

    • 2009/10/15 at 21:50

      thank you Ray…haven’t had the time to read the debate as yet. But it was a good thing you got it running. At last!

  5. kuhnkat
    2009/10/15 at 04:32


    there are, inarguably, sections of the report that are as you describe. Yet, you ignore those that are corrupt. Why??

    • 2009/10/15 at 06:09

      Could you please point them out? As I said, I have read plenty of it, but far from everything…

  6. Rick Fanning
    2009/10/14 at 19:27

    Word games with word games. It doesn’t instill any more confidence in the IPCC reports. All of their “could”, “should”, “would” and “might” hasn’t panned out so far. We shall see.

    • 2009/10/14 at 20:41

      to the contrary…it should instill ALL confidence in the IPCC reports. As long as one sticks to the original reports.

  7. Lucklucky
    2009/10/14 at 16:43

    I make my words those of Kuhnkat. I don’t think IPCC makes science since it doesn’t recognize its knowledge limitations and those should be upfront.

    • 2009/10/14 at 18:19

      Lucklucky – you are wrong. Please read the various reports. They recognize their knowledge limitations upfront. The problem is that none of that gets into any of the derived documents, policy briefings, newspaper articles. The source is good, but the Chinese whispers pollute its message.

  8. KuhnKat
    2009/10/14 at 14:39

    Except, how accurate is their quantification of the probabilities??

    I believe they are more sure than they should be based on much of the Science included in the reports. That is, they understate issues against AGW and overstate issues for AGW. I would remind you of the Fingerprint and Hockeystick for examples of how they have distorted the Science.

    • 2009/10/14 at 14:43

      That is the meaning of “expert judgment”.

  9. Alan McIntire
    2009/10/14 at 14:22

    Could, should, maybe, might,
    Weasel words are always right!

    • 2009/10/14 at 14:33

      And still…I shall not get tired of repeating: “wise”, not “weasel”. There is a difference.

  10. Klem
    2009/10/14 at 12:36

    You are so correct. The UN IPCC has covered it’s ass so well by using these wishy washy non scientific terms that the reports become so generalized that no matter what happens to the climate the reports will still be valid. Well done, I had never viewed them that way before.

    • 2009/10/14 at 12:44

      Klem – Let me be clear: those terms are scientific. The IPCC reports are well-written from a scientific point of view.

      This is the way science moves forward, most of the time: “out on a limb”, but in full acknowledgment that one is “out on a limb”. That’s why any policy strictly based on science, especially in a relatively new field such as AGW, is an oxymoron.

  1. 2012/03/21 at 00:58
  2. 2010/01/25 at 23:29
  3. 2009/10/15 at 10:33

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