2006-02-08

Methane and Kuhn

I'm reading Kuhn, "The structure of scientific revolutions". I'm only up to chapter 7 so far, and not desperately impressed. Perhaps it gets better later. Anyway, by curious co-incidence, a piece of it is relevant to the "methane debate", recently energised by Keppler et al. (btw, don't miss the clarification). We had a "discussion group" about this at work: mostly ice core folks whose ultimate interest was interpreting delta-C-13 in ice cores; but most of the discussion was trying to make sense of the paper. And the thing that came up repeatedly is that the *mechanism* for the methane production is unknown. Given that, its really not clear what to measure. At some point, the mechanism will be understood, or at least there will be a testable hypothesis, and suddenly there will be a mini-paradigm-shift (K states that P-shifts are not always major revolutions; they are allowed to be little things in their own area).

To illustrate this: the paper measures methane production from both dead and living leaves. The dead stuff produces much less methane (order of magnitude). Is this because the methane in this case is the breakdown product of some molecule produced by the living plant? In which case a time series would be instructive. But the paper doesn't present this. Then again: for living plants, the paper asserts that production is bigger in sunlight. The measurements weren't terribly well controlled, as the paper notes make clear: "sunshine" is defined as what you get in Heidelburg. And then the problem is: if you expose the plant to sunlight, it will get warmer. And elsewhere they note the strong temperature sensitivity of their results. So all of this is rather typical of the early stages: something odd is found, but the measurements are all in a bit of a fog and its not clear exactly what you are trying to measure.

A bit more commentary on the results: all this turns out to come from about 10 living plants, extrapolated to the planet. So the error bars are huge. It may turn out that these plants are quite atypical. Or, they may turn out to be quite typical. In which case, the methane budget is overthrown? Well, probably not that either. The sinks in the methane budget seems to be well known (mostly atmos oxidation); the sources (wetlands, rice paddies, gas leaks) have pretty big error bars. Most of the overall budgets people construct from these various sources add up to about the same number, but that is because people know the number they are supposed to get: viz, the number that makes the current observed increase work out about right. So (especially if the new results come in at the low end of their range) they can be fitted into the existing methane budget quite easily.

[Update: when I wrote the above, I didn't put any numbers in cos I was doing it from memory. But now I have the data: this (may not be subscription). From which you see, firstly, that Nature says the current methane source-sinks is negative (-47 Tg/y; thats based on a range of sources of 500-600 and deciding, for some unknown reason, that 530 is the best value; IPCC seems to use much the same data but get an *increase*, which is correct...), from those estimates: whereas the atmos measurements clearly show an increase (14 Tg/y). So at the very least, flipping that to +47 could be done without surprising anyone: ie, there is room for an extra source of 94 Tg/y. Kepplers estimates are 62-236 Tg/y, so the lower end can be accomodated without trouble: it would even help! And there is even more scope for fiddling (or, put another way, accomodating the new source without changing much else): Nature sources the current balance to IPCC table 4.2. Is the wetlands source 115, 237, 225, 145 or 92 Tg/y? Is rice 100, 88, 25-54, 60 or 53? Confused?]

7 Comments:

Anonymous Anonymous said...

John Fleck says -

If you would allow me to fly off on a complete tangent here....

I think this is a good example of the problem created by the Nature-media nexus. You've done a good job of sketching out the problems with interpreting the paper, which puts in clearly in the realm of "interesting result, much more work needed before we understand what's going on." But the public's and media's misunderstanding of the Nature stamp of approval led to this study being treated as something that answered questions rather than raising them.

Bryden's Nature paper on the thermohaline circulation is a similar example, which was trumpeted in the media as a definitive result when it fact it's really just raising interesting questions.

More research is needed.

4:39 pm  
Blogger Belette said...

You are exactly correct - I almost wrote that into the post, so its not a tangent at all. It is a problem with Nature. As someone at our discussion meeting said, its a shame in a way that this got into Nature, it would have been better published somewhere quiet, discussed and replicated/extended/refuted, and *then* brought into the public.

Perhaps Nature could actually have a section for stuff like this, and label it "preliminary results" or somesuch...

7:11 pm  
Blogger Dano said...

This is not just a problem with Nature, gents.

The 'lowfat diet no good for lowering disease risk' paper is undergoing the very same issue (I made this point at John's place today).

Just saying in a newspaper article that 'more research needed' won't do it either.

I, personally, don't know if it is a lack of science-educated reporters (present company excluded), or thought of papers that audience can't handle complex explanations, or the audience really can't handle complexity, or whatever. But I come across this all the time. I call it 'bridging', but 'liasing' or 'interpreting' is OK too, and in my view this is another layer that is needed to do better 'splainin'.

Best,

D

11:19 pm  
Blogger nige said...

Problems with Kuhn's analysis

Dr Imre Lakatos, Science and Pseudo-Science, pages 96-102 of Godfrey Vesey (editor), Philosophy in the Open, Open University Press, Milton Keynes, 1974:

‘Scientists have thick skins. They do not abandon a theory merely because facts contradict it. They normally either invent some rescue hypothesis to explain what they then call a mere anomaly or, if they cannot explain the anomaly, they ignore it, and direct their attention to other problems. Note that scientists talk about anomalies, recalcitrant instances, not refutations. History of science, of course, is full of accounts of how crucial experiments allegedly killed theories. But such accounts are fabricated long after the theory had been abandoned. ... What really count are dramatic, unexpected, stunning predictions: a few of them are enough to tilt the balance; where theory lags behind the facts, we are dealing with miserable degenerating research programmes. Now, how do scientific revolutions come about? If we have two rival research programmes, and one is progressing while the other is degenerating, scientists tend to join the progressive programme. This is the rationale of scientific revolutions. ... Criticism is not a Popperian quick kill, by refutation. Important criticism is always constructive: there is no refutation without a better theory. Kuhn is wrong in thinking that scientific revolutions are sudden, irrational changes in vision. The history of science refutes both Popper and Kuhn: on close inspection both Popperian crucial experiments and Kuhnian revolutions turn out to be myths: what normally happens is that progressive research programmes replace degenerating ones.’

7:53 pm  
Blogger Belette said...

I think this is based on a mis-reading (or more likely a not-reading) of Kuhn himself. Kuhn specifically mentions all this; old theories die away as those brought up with them die off. Fairly relevant to GW: most of the septics are old, many emerius.

1:14 pm  
Anonymous Anonymous said...

A string theorist widely called Dr *#&% M*^£ is only about 32 and he denies global warming.

Don't tell me that Stoat dismisses him as a mere "anomaly" or "recalcitrant instance"?

:-)

12:08 am  
Blogger Belette said...

Old before his time I guess... :-) Actually I thing dr Stringy accepts the obs; he just denies the future.

10:04 am  

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