Wednesday, June 30, 2010

Swiss Re on sceptic arguments re AGW

A comprehensive refutation of sceptic arguments from an unexpected source - Swiss Re, a reinsurance firm. Here is their topic list:

  • A) Global warming:

    • A1 Global temperature cannot be calculated because of unreliable measurements
    • A2 Global warming is an artefact of the Urban Heat Island effect
    • A3 The most important argument of IPCC (Mann et al. “hockey stick” curve) has proved to be incorrect
    • A4 Satellite data show no warming of the troposphere in contrast to model predictions
    • A5 Sea level isn’t rising everywhere
    • A6 There is no apparent increase of extreme events
    • A7 In earlier times the climate was much warmer than today
  • B) Forcing factors:

    • B1 Other factors have potentially caused the present warming
    • B2 Water vapour is the most important greenhouse gas, CO2 is unimportant
    • B3 Climate change is driven by the sun
    • B4 Climate change is driven by cosmic rays
    • B5 Anthropogenic CO2 emissions are much smaller than natural CO2 emissions
    • B6 Volcanoes emit more greenhouse gases than human activities
    • B7 There was global cooling between 1940 and 1970 although CO2 concentration increased
  • C) Carbon dioxide (CO2)

    • C1 CO2 measurements in ice cores are not reliable
    • C2 CO2 increase is just the result of temperature change
    • C3 CO2 is just a fertiliser for plants and therefore positive
    • C4 The observed increase in CO2 is much smaller than assumed in climate models
    • C5 The greenhouse effect of CO2 is small because CO2 absorption bands are saturated


  1. This is quite capably done. Crisp, well cited, pretty complete.

  2. A3 is the party line. They ignore the problem that all the so-called independent reconstructions are anything but. They also ignore the problem with uncertainty. The argument isn't so much that the various paleoclimate reconstructions are inaccurate, but that the uncertainty in the reconstruction past a few hundred years before the present, before about 1600 AD, is so large that no conclusion about differences between the present and the past can be drawn.

    If it's not important to the argument, then given the controversy, paleoclimate reconstructions should have been left out of AR4 altogether.

  3. Well, the party line "HS is broken" is rarely stated clearly, but seems in most sceptics minds to be methodological - non-centred PCA etc. The subsequent reconstructions will not be using such methodological deviations. I think replication assures that the HS curves are correctly deduced from the data - with currently, somewhat higher internal variability.

    Then it comes back to the shared data. The data isn't perfect, but there's now a lot of it, and despite much CA handwaving, it isn't shown to be broken. And the sources are getting more varied - even though Loehle's sediments have obvious problems with temporal resolution, they still get not vastly different results.

    I don;t think paleo should be left out of the AR4 because of controversy. Indeed, that would rightly be controversial itself - suppression of evidence etc. The fact that it is peripheral to AGW (and it is) could have been more emphasised.

    My own view is that it would be miraculous if we could be sure of accurately telling the temperature 1000 yrs ago, and I don't quite believe in miracles. But there's too much evidence to ignore.

  4. There are lots of things that, taken by themselves, are not of paramount importance. Yet they go into the textbook or literature review as parts of the overall picture.

    And as Nick says, the subsequent replications absolutely do use different methodologies from the initial two papers, and more and different sorts of data. So if one is going to say they aren't independent, one will have to say exactly what one means by that.

    I'm with Nick; putting these records together with any level of accuracy was never going to be easy.

    As for uncertainty - even without looking at the uncertainty limits placed by each author on their own calculation, if you so much as glance at the spaghetti plot, you immediately sense a good deal of uncertainty - because the plot is such a mess.

  5. The subsequent replications still use statistical techniques that are almost certain to produce something that looks like a hockey stick even if all the series are pure noise. Jeff Id at The Air Vent has done a lot of work on this. His most recent post should be instructive:

  6. DeWitt,
    "The subsequent replications still use statistical techniques that are almost certain to produce something that looks like a hockey stick"
    I'd like to see some evidence of that. It was said a lot in the early days of M&M, but then seemed to fade. As Mosh has said, the proxies aren't expected to provide the blade of the HS; they provide the shaft. The blade (globally) is instrumental.

    Jeff doesn't seem to provide any such evidence - seems to me that his post is really a proposal for activity (which I think is a very good thing).

  7. I'm new to your site and really like your use of empirical data to support your scientific conclusions. This is how all science, especially climate science should be done.

    Given that, can someone explain (in a gentle rational way please) why climate scientists continue to defend the "Hockey Stick" paper MBH 98??: "it has been shown that the points of critique in the cited papers do not affect the results of Mann et al. in a relevant way (von Storch and Zorita. 2005)"

    With all due respect to von Storch and Zorita, (and other climate scientists as well), in my opinion, this paper seems to be the Poster Child for how NOT to do climate science. The data is suspect, the statistics are bad, the algorithm (which was with held for as long as possible) is bogus, etcetera, etcetera. Furthermore, dozens of other peer reviewed papers clearly document both the Medieval Warming Period and the Little Ice Age as global phenomenon.

    Rather than defend this work, climate scientists should run as far away as possible from this research. Their continued defense of demonstrably bad research paints them all with the broad brush of scientific fraud. Can anyone explain?

  8. Lou, I would turn the question around. Why do people keep attacking MBH 98? The normal process of science is that when a new achievement is claimed, many people try similar analyses, which either confirm the conclusion or not.

    Here you can see the process working.Nine new analyses (and there have been others on global data etc) all showing similar results, whatever methods were used. Are they all getting it wrong?

    Mann's statistics were not bad (principal components analysis is mainstream), and his algorithm was reasonable - non-centred PCA is not optimal, but has similar effect to centred PCA. As for the data, it's never perfect, but we're getting more and more of it, and all leading to similar results.