IPCC science

This thread is for discussion of the IPCC and scientific matters.

125 Thoughts on “IPCC science

  1. Richard C (NZ) on October 1, 2013 at 9:59 am said:

    IPCC’s pause ‘logic’

    by Judith Curry

    Well here it is, the pause discussion is buried in Box 9.2 of the IPCC Working Group I Report.


    JC summary

    My original intention for this thread was to go through and try to map the IPCC’s logical argument. I quickly got dizzy owing to seemingly unwarranted assumptions and incomplete information (such as: did the climate models use the correct external forcing for the first decade of the 21st century, or not?). I was then going to illustrate how any reasonable propagation of uncertainty of individual assertions/arguments through their main argument would produce much lower confidence in their overall conclusions. For example, they seem to have eliminated high CO2 sensitivity as a problem. Not to mention high confidence in increasing trend following 2012 (this high confidence comes right after blowing the prediction of the previous decade). And of course not to mention the relevant journal articles that didn’t get mentioned.

    Apart from these obvious flaws, reading that text and trying to follow it is positively painful. Can someone remind me again how and why all this is supposed to be useful?


    Their “main argument” from the summary is:

    “….the observed recent warming hiatus,…….., is attributable in roughly equal measure to a cooling contribution from internal variability and a reduced trend in external forcing”

    There are enormous implications to drawn from this, already identified from the leaks. No point going on here because this statement and it’s rationale will be (or should be) dissected remorselessly.

  2. Richard C (NZ) on October 1, 2013 at 1:00 pm said:

    >”…this statement and it’s rationale will be (or should be) dissected remorselessly”

    Like this:

    ‘IPCC in denial. “Just-so” excuses use ocean heat to hide their failure’


    Tutorial for Science Journalists:

    A few questions serious journalists might want to ask instead of just cut and pasting press releases from activists.


  3. Richard C (NZ) on August 27, 2014 at 7:23 pm said:

    ‘The 50-50 argument’

    by Judith Curry, August 24, 2014

    Pick one:

    a) Warming since 1950 is predominantly (more than 50%) caused by humans.

    b) Warming since 1950 is predominantly caused by natural processes.

    When faced with a choice between a) and b), I respond: ‘I can’t choose, since i think the most likely split between natural and anthropogenic causes to recent global warming is about 50-50′. Gavin [Schmidt] thinks I’m ‘making things up’, so I promised yet another post on this topic.

    […extensive analysis…]

    The IPCC notes overall warming since 1880. In particular, the period 1910-1940 is a period of warming that is comparable in duration and magnitude to the warming 1976-2000. Any anthropogenic forcing of that warming is very small (see Figure 10.1 above). The timing of the early 20th century warming is consistent with the AMO/PDO (e.g. the stadium wave; also noted by Tung and Zhou). The big unanswered question is: Why is the period 1940-1970 significantly warmer than say 1880-1910? Is it the sun? Is it a longer period ocean oscillation? Could the same processes causing the early 20th century warming be contributing to the late 20th century warming?

    Not only don’t we know the answer to these questions, but no one even seems to be asking them!


    I am arguing that climate models are not fit for the purpose of detection and attribution of climate change on decadal to multidecadal timescales. Figure 10.1 speaks for itself in this regard (see figure 11.25 for a zoom in on the recent hiatus). By ‘fit for purpose’, I am prepared to settle for getting an answer that falls in the right tercile.

    The main relevant deficiencies of climate models are:

    # climate sensitivity that appears to be too high, probably associated with problems in the fast thermodynamic feedbacks (water vapor, lapse rate, clouds)
    # failure to simulate the correct network of multidecadal oscillations and their correct phasing
    # substantial uncertainties in aerosol indirect effects
    # unknown and uncertain solar indirect effects

    So, how to sort this out and do a more realistic job of detecting climate change and and attributing it to natural variability versus anthropogenic forcing? Observationally based methods and simple models have been underutilized in this regard. Of great importance is to consider uncertainties in external forcing in context of attribution uncertainties.

    The logic of reasoning about climate uncertainty, is not at all straightforward, as discussed in my paper Reasoning about climate uncertainty.

    So, am I ‘making things up’? Seems to me that I am applying straightforward logic. Which IMO has been disturbingly absent in attribution arguments, that use climate models that aren’t fit for purpose, use circular reasoning in detection, fail to assess the impact of forcing uncertainties on the attribution, and are heavily spiced by expert judgment and subjective downweighting.


    Note: In the original of the Nic Lewis quote from Bishop Hill, the word “without” was given emphasis, viz:

    [Lewis] – “Since the CMIP5 models used by the IPCC on average adequately reproduce observed global warming in the last two and a half decades of the 20th century without any contribution from multidecadal ocean variability, it follows that those models (whose mean TCR is slightly over 1.8°C) must be substantially too sensitive.”

  4. Richard C (NZ) on August 27, 2014 at 9:46 pm said:


    I am arguing here that the ‘choice’ regarding attribution shouldn’t be binary, and there should not be a break at 50%; rather we should consider the following terciles for the net anthropogenic contribution to warming since 1950:


    # # #

    I argue that the ‘choice’ should be in terms of all risk factor possibilities (including anthro, solar, ocean oscillations etc, which JC covers) rather than in narrow, unary, out of date, IPCC terms of anthro attribution-only thinking i.e. risk scenarios for the future are a far more useful and responsible tool because the respective probability weighting of each factor can be revised (even discarded) as the situation evolves over time.

    A cooler regime setting in over the next 5 years (or just continued stasis) automatically eliminates the top 2 attribution choices above (>66% and JC’s 33-66%), along with the risk assigned to them. Radical cooling after say 2020 would eliminate all but the “negligible” element of the lower attribution choice (<33%) i.e. attribution 'choice' in those terms is somewhat premature in view of the "pause" in global warming.

    Only if warming resumes in the next 3 – 5 years can JC's 33-66% attribution 'choice' even come back into contention let alone be selected. In other words, in terms of risk, the attribution period of 1951 – 2010 becomes less relevant as time goes on. It is out of date thinking.

  5. Richard C (NZ) on September 11, 2014 at 8:19 pm said:

    I stumbled on a University of Cambridge document that “synthesizes” AR5:

    The IPCC’s Fifth Assessment Report, Working Group 1


    Curiously, on page 6 there is this definition of climate change (my emphasis):


    Natural and human factors drive climate change by altering the Earth’s energy budget. At present there is a net uptake of the Sun’s energy by the Earth system; that is, more energy is entering the Earth system than is being lost back to space. The outcome is an increase in heat energy stored by the Earth. This imbalance is driving the rise in global temperature. AR5 concludes that over 90% of the excess heat is stored in the ocean.”

    There’s no attribution for this statement so I assume it is by the University of Cambridge authors rather than the IPCC.

    Here’s the thing. Drop the two words “and human” and the remaining definition is one which I’m sure any solar-centric critic of the MMCC hypothesis would agree with. I certainly do.

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