Tuesday, October 06, 2009

Something brief on Anthropogenic Global Warming (AGW)

Ian has asked "why that one source (Yamal) is so important to your overall belief in this subject".

The short and direct answer is that the Yamal data underlies much of the advocacy surrounding AGW, specifically that it seems to be the major grounds for believing that our present climate is warmer than it was in the Medieval Warm Period (MWP). This is the graph accepted by the IPCC in 1990 to show the change in temperature over the last thousand years. Note that the MWP is warmer than the present.

This was replaced after 1998 with the 'hockey stick':

The principal scientific source for the 'Hockey Stick' relied on data from Yamal (see this wikipedia page for more background).

Now, it could well be the case that even without the Yamal data, the evidence for the late twentieth century being warmer than the MWP is robust. I'm open to that being the case. My concerns are different, because, in the end, I'll believe what scientists tell me on matters of scientific fact (in other words, when they stop using words like 'consensus' and just say 'this is how it is' - after all nobody talks about a consensus when discussing, eg, gravity, or the sun being at the centre of the solar system.)

I think that:
a) the science supporting the AGW hypothesis, and the alarmist predictions built on it, is not as robust as it is claimed to be. I think this because i) the IPCC does not take into account the peaking of fossil fuel resources; ii) the (on-going) Svenmark research exploring solar/cosmic ray influence on climate; and, yes, iii) the sort of arguments that McIntyre makes;
b) in other words, I think that scepticism about AGW is not illegitimate, I believe that it is intellectually respectable;
c) because I think this, I find the attempts to repress debate (either by suppressing the data, eg with Biffra) or by ridiculing, scorning and doubting the moral fibre of sceptics to be distinctly lacking in virtue. If the science is robust then it will stand up to the most virulent of partisan criticism, and will emerge all the stronger for it (this is not to say that some criticism isn't simply partisan and deserving of scorn, only to ask for discrimination);
d) because of the prevalence of c) I have come to see that there are aspects of idolatry involved in the AGW consensus. In particular I believe that many people accept AGW because it fits into a wider picture of belief about what is wrong with the world today. As it happens, I share that wider picture of belief (basically, the 'Limits to Growth' argument), I just don't believe that we can build a better future on the back of c) - that is, I really do believe that it is the truth that sets us free and that fear paralyses us (and I think the AGW consensus is trying to force change by amplifying the fear. I see this as morally wrong and spiritually unsound);
e) my motivation in sharing information like that about Yamal, therefore, is much more to do with wanting to combat that idolatry than wanting to object to the bigger picture, and all that it entails. The difference in personal behaviour required in responding to AGW or responding to Peak Oil is pretty small.

That ended up being less brief than planned. I should add that for some time (eg in my early LUBH talks) I accepted the AGW consensus. Two things started to shift me on it: first the IPCC ignorance of Peak Oil, second reading this book. I became more sceptical the more I studied the question. Now I would class myself as an agnostic/mild sceptic on the specific AGW issue, but definitely a critic on the 'wider aspects' of what is involved.


  1. Two brief points about the 1990 graph.

    In the 1990 IPCC report (Fig. 7.1(c), p202, see http://tinyurl.com/ypvurw), this image was described there as “a schematic diagram”, and not as a plot of real data. The report cautions that “it is still not clear whether all of the fluctuations indicated are truly global.”

    Second and more importantly, the above graph covers the period 900 AD to 1975, just before the start of by far the strongest and most sustained period of warming in the temperature record (or the recent proxy record for that matter).

    So to use this graph to say that the MCA had global temperatures higher than today (whether that today is taken to be 1990 or 2010) is somewhat misleading, as is claiming that this was the view of the IPCC in 1990. You have not made either of these claims directly, but by putting this graph up against the Hockey Stick (which you then criticise), I don't think this is an unreasonable reading of your post. You grant that you are willing to listen to what scientists say when they do not talk about consensus, but just say "this is how it is". AR4 WG1 SFP uses the word "consensus" once: to note that there is no consensus on dynamic ice flows. I haven't checked the other documents, but I suspect they may be similar. The recently released NRC report also doesn't use the word consensus in its summary. It is largely the politicians who use the language of consensus.

    And since you have more recently said that the relation of the MCA to today's atmospheric temperatures is not critical, do you still think that the Yamal data underlies much of the advocacy surrounding AGW? Is this an overstatement of your case? Or have you changed your mind in the last six months or so?

  2. Hi Byron, what does MCA stand for? (medieval climate average?)
    As I understand it, there actually IS something of a consensus that the Medieval period saw temperatures at least as high as today, and that, in fact, previous eras (eg Roman) saw temperatures that were even higher.
    More interestingly, what reading Montford has given me is a much greater sense of how tenuous many of these reconstructions are. The instrumental data is very recent (say to about 1850, the first graph above is based on the central England temperatures, which is the longest consistent series that we have), all other temperature charts for the past are based on proxies and inferences.
    I haven't changed my mind on this aspect of the question in the last six months, rather the opposite, but I would emphasise point e) in the original post.

  3. MCA = Medieval climate anomaly. This is discussed at length in AR4 WG1, chapter 6. See for example p.469: "A number of studies that have attempted to produce very large spatial-scale reconstructions have come to the same conclusion: that medieval warmth was heterogeneous in terms of its precise timing and regional expression (Crowley and Lowery, 2000; Folland et al., 2001; Esper et al., 2002; Bradley et al., 2003a; Jones and Mann, 2004; D’Arrigo et al., 2006).
    The uncertainty associated with present palaeoclimate estimates of NH mean temperatures is signifi cant, especially for the period prior to 1600 when data are scarce (Mann et al., 1999; Briff a and Osborn, 2002; Cook et al., 2004a). However, Figure 6.10 shows that the warmest period prior to the 20th century very likely occurred between 950 and 1100, but temperatures were probably between 0.1°C and 0.2°C below the 1961 to 1990 mean and significantly below the level shown by instrumental data after 1980." Have you read this chapter of AR4?

    Do you have any papers for the (global?) claim re ancient temps? Or for the claim about a consensus re medieval period?

    And do you take my two points about the 1990 IPCC graph? (Schematic and not running to "now" in any case).

    I believe that many people accept AGW because it fits into a wider picture of belief about what is wrong with the world today
    Are there similar structures of belief about what is wrong (or right) with the world that motivate many people's acceptance of some of the very poor arguments against AGW? (Leaving aside the question of the better arguments)


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