IPCC science

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

129 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.

  6. Richard C (NZ) on April 20, 2015 at 3:13 pm said:

    ‘Detection of Enhanced Greenhouse Warming: What the IPCC Said Back In 1990
    Changing goal posts or better science?’

    Ronald Bailey|Apr. 8, 2015

    “Detection of the Greenhouse Gas Effect in the Observations” in the 1990 IPCC report

    8.4 When Will The Greenhouse Effect be Detected?

    The fact that we have not detected the enhanced greenhouse effect leads to the question when is this likely to occur? As noted earlier, this is not a simple yes/no issue. Rather it involves the gradual accumulation of evidence in support of model predictions, which in parallel with improvements in the models themselves, will increase our confidence in them and progressively narrow the uncertainties regarding such key parameters as the climate sensitivity. Uncertainties will always remain. Predicting when a certain confidence level might be reached is as difficult as predicting future climate change – more so, in fact, since it requires at least estimates of both future signal and future noise level.

    Nevertheless, we can provide some information on the time-scale for detection by using the unprecedented change concept mentioned briefly in Section 8.14. This should provide an upper bound to the time of detection since more sophisticated methods should produce earlier results. We take a conservative view as a starting point namely that the magnitude of natural variability is such that all of the warming of the past century could be attributed to this cause. (Note that this is not the same as denying the existence of an enhanced greenhouse effect. With such a noise level the past warming could be explained as a 1°C greenhouse effect offset by 0.5°C natural variability.) We then assume, again somewhat arbitrarily that a further 0.5°C warming (i.e., a total warming of 1°C since the late nineteenth century) is required before we could say with high confidence, that the only possible explanation would be that the enhanced greenhouse effect was as strong as predicted by climate models. Given the range of uncertainty in future forcing predictions and future model-predicted warming when would this elevated temperature level be reached?

    Figure 8.5

    The answer is given in Figure 8.5. [Basically, the upper curve is assumes a fast warming rate and the lower one a slow warming rate. If fast, warming will be detected by 2002; if slow no detection until 2047.]

    Figure 8.5 Text: If a further 0.5°C warming were chosen at the threshold for detection of the enhanced greenhouse effect then this would be reached sometime between 2002 and 2047.

    On the basis of this simple analysis alone we might conclude that detection with high confidence is unlikely to occur before the year 2000. If stringent controls are introduced to reduce future greenhouse gas emissions and if the climate sensitivity is at the low end of the range of model predictions then it may be well into the twenty-first century before we can say with high confidence that we have detected the enhanced greenhouse effect.



    “I have earlier reported the various per decade warming rates in the observational record. The highest rate is +0.16°C per decade and the lowest is +0.13°C per decade. Assuming those rates had been maintained since 1990 (and they have not been so) mean global temperature would have risen by between +0.4°C and +0.325°C by now.

    In other words, enhanced greenhouse warming above the noise of natural climate variability would not yet have crossed over the benchmark (+0.5°C) set by the IPCC back in 1990. Interesting.”

  7. Richard C (NZ) on April 6, 2016 at 9:31 am said:

    ‘RCP 8.5: The “Mother of all” Junk Climate Science’

    David Middleton / 9 hours ago April 5, 2016

    Representative Concentration (or Carbon)Pathway 8.5 assumes a “rising radiative forcing pathway leading to 8.5 W/m² in 2100.”

    It is generally assumed, with little dissent, that each doubling of the atmospheric CO2 concentration will add 3.7 W/m² to the net infrared radiative flux.

    A doubling of the supposedly stable pre-industrial CO2 level (280 ppmv to 560 ppmv) should yield 3.7 W/m² of additional forcing to the net infrared radiative flux. In order to get 8.5 W/m², the atmospheric CO2 concentration would have to rise to 1,370 ppm…


    # # #

    Theoretical CO2 forcing as at 2015: 1.9 W.m-2

    TOA energy imbalance 2000 – 2010: 0.6 W.m-2

  8. Richard C (NZ) on June 26, 2016 at 2:30 pm said:

    Report Graphics – Chapter 8: Anthropogenic and Natural Radiative Forcing
    WORKING GROUP I – Climate Change 2013: The Physical Science Basis [AR5]

    Figure 8.15 – Radiative forcing of climate between 1750 and 2011

    BIG PROBLEM. Total net anthropogenic forcing is +2.3 W.m-2, natural solar is negligible, but the earth’s energy imbalance is only +0.6 W.m-2.

    Worse, the surface energy budget, as cited by AR5 WG1 Chapter 2, shows the +0.6 imbalance is simply solar energy (SWdown) supplying surface heat accumulation (+0.6) predominantly in the oceanic heat sink:

    Stephens et al (2012) Figure 1 Surface budget

    +SWdown -SWup -SHup -LHup -LWnet(up) = Surface imbalance

    +188 -23 -24 -88 -52.4 = +0.6 W.m-2

    +188 -187.4 = +0.6 W.m-2

    Solar energy down is greater than energy up at the surface.

  9. Richard C (NZ) on July 9, 2016 at 2:14 pm said:

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