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← Why the laws of physics make anthropogenic climate change undeniable

Jos Gibbons's Avatar Jump to comment 10 by Jos Gibbons

All kind words (including future ones) are thanked simultaneously for brevity. As this is the first of my discussions I've had posted, it's only fair I answer some points.

Comment #865330 by God fearing Atheist

The AGW deniers are now going to tell Jos and his lecturer where they are wrong. In detail - lecture, page, and line/equation number, with full workings and evidence.

It doesn't take very long for us to see how true your predictions are, does it? ;) See also my response to some objectiosn below.

I haven't done physics since A level. What is the Clausius Clapeyron relation again?

Firstly, I'm glad to get questions like that, as it proves people are actually reading these PDFs!
“Again” suggests maybe it was on your A level syllabus. Maybe it was back then, but it wasn't for me.
Anyway, basically, it's the relation between the applied pressure and the temperatures at which phase transitions occur. You no doubt know you can melt ice by applying pressure rather than using a more direct way of heating it. You may also have heard tea-making on a mountain isn't much fun because you can't get the kettles to take water past about 70 degrees, at which it will boil at the much lower atmospheric pressure. (The first lecture course I've provided includes a discussion of the fact that, and reason why, atmospheric pressure exponentially declines with altitude; indeed, the change in altitude that gives an e-fold reduction is approximately the height of Mount Everest.) Well, the relation puts all this on a mathematical footing. Wikipedia provides multiple derivations as if its thermodynamic inexorability was in any question.

Comment #865332 by Alan4discussion

Many deniers I have encountered do not understand climate even at a school geography level, do not know the basic scientific measuring techniques, cannot follow basic reasoning, can't understand basic arithmetic, let along advanced maths, and refuse to recognise evidence as such. … I suspect many could not even quote you a law of physics, let alone understand one!

That's funny. All the ones I've encountered have “a science qualification”, like our friend rolan (see below). Now, I suppose they could all be lying, but it's much more charitable to think you and I have experienced very different critics of modern climatology's findings, and that the reason they never say what science the qualification is in is because “half a dozen of one, six of the other”. Now, as a physicist, I'd better go tell the economists why I just don't buy what they're saying ... Options' prices exhibiting behaviour analogous to diffusion, indeed ...

Comment #865395 by rolan

I find the term denier and the general condescending tone rather offensive.

I don't know how you detect tones in writing online, but as for whether “denier” is offensive, I have some sympathy with Peter Sinclair's (potholer54's) preference for calling such people opponents of … ACC, AGW, it mattering, whatever they may oppose. On the other hand, I think there are times it's OK to use the term denier, because:
* they are denying something, just as I deny a deity's being probable; and
* even if “denier” means something stronger, i.e. that they're full of bull, well … they are.

I have a science qualification

Is it in climatology? Actually, it wouldn't immunise you against thinking nonsense on this issue even if it is.

[I] resent the characterization of any critical analysis of the popular position on climate change as being some sort of Luddite, reactionary response.

Just to clarify, do you resent such a characterization being a matter of automatic policy, or do you happen to think all such characterizations that have happened so far have been unwarranted given the nature of the empirical evidence? Because as far as I know, such a characterization is never a matter of automatic policy (it certainly isn't when I do it), and I've yet to see an argument by the “don't call them deniers but, well, those guys” that actually works.

There is no argument that a doubling of CO2 concentrations should give rise to a temperature increase of about 1 degree K.

That's a load of bull right there. We have seen a 0.74 K $ rise from half of a doubling (a multiplication by almost exactly the square root of 2) despite natural (e.g. solar, orbital, volcanic) and polluting (the anthropogenic aerosols causing “global dimming”) factors acting to cool the planet at the moment, so the effect of doubling CO2 is more than double 0.74 K. In fact, we have a way of knowing what it really is (albeit not a brilliantly accurate one), namely that we know doubling CO2 adds 3.7 Watts per square metre to the radiative forcing, and we can see what radiative forcing has occurred and what temperature rise has accompanied it (since the warming is determined purely by the amount of radiative forcing rather than its causes). Many, many ways of finding the “climate sensitivity” (the warming due to the radiative forcing doubling CO2 provides) have been used, and they clustered around not 1 K, as you claim, but 3 K. Admittedly the error bars are wide on that, but they pretty much conclusively refute your 1 K claim. Only a few years ago it was “3 +/- 1.5”, which already said you were wrong. Now the bottom of that limit is eroding, and “2 to 4.5” is the confidence interval the consensus accepts. And what's more, values above – indeed, far above – 4.5 have a much better chance of being true than was previously imagined.

$ 0.74 plus or minus 0.18. Since the main proof “about 1 K” is wrong doesn't rely on this, I didn't include the error bars in the main body of the discussion, since the important error bars are on everything else.

Lecture 7 - Forcing, feedbacks, and the climate response

Ah, good – people really are reading these things! Although in your case, quite selectively. The flawed logic that gets a 1 K figure, and the reasons why it is flawed, are also included in that PDF. Incidentally, whenever I contradict rolan on what the PDF says, I invite others to check in a "Don't take my word for it" manner.

explains the uncertainties in trying to estimate the climate sensitivity to this change from models and the difficulty (the lecture says that it cannot be done) in trying to use experimental data for such an estimation. It also states that the precise effect on and by various actors in the system (e.g. cloud cover) is currently unknown. It's the climate sensitivity which is unknown.

More selective reading is in evidence.
* As I said above, the upper and lower bounds on the sensitivity are in a ratio of more than 2 to 1. But even the minimum, a 2 K response, is much higher than you entertained. What's more, a 2 K rise is the most we are willing to tolerate, and many think even that's too high; so, if at least (and probably more than) 2 K worth of a rise comes from doubling CO2, which we've half-done already, we really do need to put the brakes on anthropogenic GHGs fast!
* Could you quote where the lecturer says it “cannot be done”?
* It's at times like these we all need to remember “uncertainty” doesn't mean that yes/no questions cannot be answered, but that variables have non-zero errors. Indeed, it's clear from his context that he discusses the ways errors can accumulate in the context of the Central Limit Theorem, as opposed to in addition implying the final answer has an enormous error on it. The PDF discusses in detail the fact that the only errors that have to add rather than partially cancelling each other are the small ones. It also makes clear the only effect whose sign is not known is that of cloud cover change's effect (because clouds both warm and cool depending on a number of their properties). After these, the main other big uncertainty is a matter of heat capacities. However, neither you nor he quantify their figures particularly well (although ironically the 2 to 4.5 K range is wider than any “no doubt it's about 1 K” claim you make), and overall the discussion in lecture 7 shows we can get a ballpark figure on the sensitivity and gradually narrow its error bars.

This is a big deal as most of the IPPC predictions are predicated on multi-degree changes in temperature.

That would only make your moaning a big deal if there was major doubt about the sensitivity being in the multi-degree range. (BTW, if you insist on measuring changes in K rather than Celsius, technically you can't call it “degree”, since K isn't in degrees.) As I've explained above, there is no doubt about that; what we're unsure of is whether it's slightly multi or very multi.

It is unclear that a 1 (or 2 or 3 or whatever) degree change in global temperature is significant in relation to long-term cyclic, global temperature variation.

How long term are we talking? Because our 0.74 K rise has already made us hotter than we've been in the last 2,000 years. And what's more, even if the last time our mean temperature was this high was N years ago, that doesn't mean things are no worse than they were N years ago because the rate of heating matches too (as it can determine whether perturbations have reversible or permanent effects, and our ice caps are an especially worrying example of this). The temperature rise we have seen already is definitely significant because its speed is so huge – not surprising, given that in a little over a century we've increased CO2 by 41 %, several times a larger percentage change than from its low to high in the previous 800,000 years, taking it to its highest levels in the past 15 to 20 million years. And as I said before, none of the natural phenomena, cycles or otherwise, are currently in a warming period, so all the warming is anthropogenic.

This is a pulling-signal-out-of-noise problem, and so far, the experimental data doesn't seem to have matched model predictions.

Those are both unqualified lies. The only models that don't fit data are the ones that assume the greenhouse effect isn't important.

We just don't know enough to make accurate predictions

Maybe not. But we can place lower bounds on what will happen that are much higher than your “definitely about 1 K” nonsense confesses.

don't tell me that the science is settled, blather on about scientific consensus, and pull out numbers from somewhere within the error bars as definitive fact.

“The science is settled” is an annoying phrase for its vagueness, so let's go into specifics. The science is settled on SOME things. It is settled, for example, on no value for the sensitivity under 2 K being the least bit plausible. I'm sorry scientific consensus (which, as I've explained ad nauseum, is not simply a consensus of scientists but a consensus that formed for scientific reasons) means so much less to you on the climate than it does when you use technology (Mr Internet user), but as you can see I gave error bars rather than pulling out numbers inside them.

Comment #865446 by JuJu

It looks good; I'll go through it in detail later. Thanks. While we're adding links, here is the climate equivalent of the Talk.Origins list of creationist arguments.

Tue, 30 Aug 2011 07:26:17 UTC | #865466