Wednesday, May 02, 2007

Why David Evans is wrong (along with all the other sceptics)

David Evans has a post up on Backseat driving, explaining why he has taken Brian on with a series of bets about global warming.

Usually, I don't bother addressing the sceptic stuff that can be found on a thousand blogs: people who want the facts can come looking for them, and I've got limited patience for wrestling with pigs (you both get mucky, but the pig enjoys it). However, David is a bit of a special case as he's actually been prepared to put a significant amount of his money where his mouth is. It turns out that his post is a fairly standard laundry list of excuses as to why he thinks climate science is a bit ropey. I could have some sympathy with some of his points, but there is one gaping hole in his analysis.

He starts off by acknowledging:
1. Carbon dioxide is a greenhouse gas. Proved in a laboratory a century ago.
and then continues with a string of tenuous arguments as to how it is possible that other factors could be behind most of the recent warming of the Earth.

At no point does he actually produce any evidence for his implied belief that CO2 has a negligible effect.

This, to me, is the crux of the matter. With no feedbacks at all, the sensitivity to doubled CO2 is about 1C, based on the well-understood radiative physics. It is also obvious that a warmer atmosphere has the potential to hold more water vapour (itself a GHG of course), and although the magnitude of this effect isn't known with certainty, the most plausible first-order estimate (supported by models and data) would be that relative humidity will stay roughly constant. This gives another 1C, making 2C in total. [The numbers here are intended as ballpark estimates, please let's have no quibbles about the precision.] Clouds may have a significant effect to enhance or offset warming. We know the climate has varied plenty in the past (indeed this is generally one of the septics' favourite talking points), so it seems implausible that they are a very strong stabilising force. Almost all models, using a wide range of physical parameterisations, suggest a significant positive amplification, giving the typical range of 2-4.5C for sensitivity. All analyses of observational evidence also point towards a value of close to 3C (exactly how close is still subject to some debate).

So we are left with the question: why on Earth would anyone believe that CO2 has almost no effect?

The claim that a world without anthropogenic forcing could possibly have warmed this much, whether true or not, is almost entirely irrelevant to the question of what we expect the anthropogenic effect to be. It's true that in the event of stronger natural variability, that might suggest a slightly larger possibility that a future downturn in the natural component could exceed the anthropogenically-forced response in the short term. But as I mentioned above, more variability also implies smaller stabilising feedbacks, so we'd also expect to see a larger sensitivity to CO2 in this case. Are we really supposed to believe that the planet is highly sensitive to some speculative and unquantified mechanism such as cosmic rays, and simultaneously insensitive to an effect that's been reasonably well understood for over 100 years? Why?

Detection and attribution has a lot to answer for in respect of this confusion. D&A essentially addresses the question "could an unforced planet have warmed as much as the observations"? However, this (frequentist) question has only tangential relevance to a (Bayesian) estimate of future warming. IMO, the arguments over whether or not we have "detected" AGW, and at what level of confidence, entirely misses the point. Imagine that someone points a gun in roughly your direction, and pulls the trigger. According to D&A, nothing interesting is going on until the bullet hits you, but at that point it's too late. An intelligent Bayesian would believe that there was a significant probability of serious harm before the bullet arrived - hopefully even before the trigger was pulled. Now, I'm not saying that climate change is going to suddenly kill us all, but just giving an analogy to explain the manner in which D&A fundamentally answers the wrong question. (As a secondary point, I believe it is the attempt to pretend that D&A methods can answer the interesting and useful questions that has lead to the uniform prior nonsense, but that isn't really my point here.)

So, until David and the rest can come up with some plausible arguments as to why CO2 actually has no effect, backed up by a sensible climate model which supports this claim, I'll continue to believe that it does in fact have a significant effect which will (with high probability) lead to continued warming. That is, as he more or less admitted at the start, solid science that is more than 100 years old.


Anonymous said...
This comment has been removed by a blog administrator.
James Annan said...

I didn't put this post up as an open invitation for denialist kookery. Go away.

jollyspaniard said...

Well put. I'm going to plagarize those arguments in some of my own conversations.

David Evans said...

I have replied to this at

Full url:

Heiko said...

To get the 1C and 2C estimates has a number of straightforward steps for a chemical engineer like myself. I know how to easily deal with relative humidities or Stefan-Boltzmann.

What I've got to take on authority is the relationship between CO2 concentration / H2O concentration and the forcing.

The IPCC say this is well understood, but unfortunately that isn't the same as easily understood.
(link in German)

Now I believe the IPCC, when they say something is well understood, but it bugs me that I've got to take something on authority.

5 years ago I used to post a lot on a German environmental news group and learnt to appreciate the opinion of Hartmut Lehmann. The newsgroup is anonymous, he mightn't really be an expert on spectroscopy, but, he seemed quite credible to me nonetheless and claimed that the IPCC estimate for forcing was way too high.

I'd love to find an explanation for a scientifically literate layman that readily shows why the IPCC is right in their forcing calculation. As said, I do believe them, but this is purely because I accept that they ought to know what they are talking about.

James Annan said...


Your reply seems to be nothing more than argument from personal incredulity. The unfortunate fact that there is no simple enough explanation for your taste has no bearing on whether the complex explanation is correct, especially given what appears to be your willful refusal to consider the evidence that does exist. It is not argument from authority but rather from the evidence.

Furthermore, there is no "burden of proof" on either side and I'm not trying to put such a burden on you or anyone else. I'm simply asking where the weight of evidence is that justifies throwing out 100 years of solid science that indicates that CO2 is a significant greenhouse gas. "Something else could have contributed to the warming" simply doesn't begin to address that question.

James Annan said...


You mean where does the 3.7W/m^2 number come from? Not my field but there is an IPCC chapter (2) on it, which hopefully references the relevant literature. I don't think there is any back-of-the-envelope calculation from first principles, but rather a detailed calculation ("line by line" models) of the radiative properties of the atmosphere, based on theory and lab observations. The fact that GCMS get the overall planetary temperature roughly right (not to mention spatial and seasonal patterns) militates against them being too far out in the overall scheme of things (of course I realise there is some scope for tuning and error-cancelling).

Eli seems to know quite a lot about this, maybe if I rustle some carrot leaves he will come along and help...

Without knowning what Hartmut Lehmann has to say in English, it's hard to debate whether he is right or wrong! I have to say, when I see links to John Daly (via your google link) I tend to use that as a filter that there isn't a case to answer.

Heiko said...

Yes, I meant the 3.7 W/m2. The relevant IPCC TAR section on it is rather short, but does give references.

I broadly share you view of David Evan's counter argument, namely he doesn't understand how the effect of CO2 is calculated and in the absence of that understanding chooses not to trust the numbers. Pretty flimsy for a $6000 bet, but he lives in a free country and can do whatever he likes with his money.

I would agree with him though that, if he doesn't understand the evidence, he basically does have to accept "an argument of authority", if the word "argument of authority" is to be understood as having to take something on trust, because you are unable to check it independently for your self.

James Annan said...

I would agree with him though that, if he doesn't understand the evidence, he basically does have to accept "an argument of authority", if the word "argument of authority" is to be understood as having to take something on trust, because you are unable to check it independently for your self.

But it isn't generally understood to mean that. Argument by authority means invoking the unsupported opinion of someone who is not an expert in the relevant field. (Eg here and here.) Clearly in this case the authorities are genuine authorities, and they are also presenting their evidence. Compare to the examples on those pages.

Heiko said...

Hmm, from your second link:

"There are two basic forms of appeal to authority, based on the authority being trusted. The more relevant the expertise of an authority, the more compelling the argument. Nonetheless, authority is never absolute, so all appeals to authority which assert that the authorities' claims are definitely true are fallacious.

The first form of the appeal to authority is when a person presenting a position on a subject mentions some authority who also holds that position, but who is not actually an authority in that area. For instance, the statement "Arthur C. Clarke recently released a report showing it is necessary to floss three times daily" should not convince many people of anything about flossing, as Arthur C. Clarke is not a known expert on dental hygiene. Much advertising relies on this logical fallacy in the form of endorsements and sponsorships.

The second form, citing a person who actually is an authority in the relevant field, carries more weight in that the authority is more likely to be correct. However the possibility of a mistake remains."

I am not a native speaker, but my impression is that the expression "appeal to authority" is often used with negative connotations, but it doesn't have to be.

Put it another way, if somebody argues that something is true, because a trusted authority says so, how would you refer to that argument?

David Evans said...

James and Heiko,

Yes, I meant "argument by authority" in the positive sense of having to take it on trust from someone who really is an authority on the matter.

The essence of the point I was groping towards is that science, historically, has rarely progressed by calculations and models. Rather it has been by repeatable experiments and by observation.

You know the usual cautionary litany of theories held by authorities that turned out to be spectacularly wrong: heavier-than-air flight not possible, sun orbits the earth,...

I'm not throwing out 100 years of solid science that indicates that CO2 is a significant greenhouse gas. I acknowledge it, and agree that the extra carbon causes some warming.

But, I question the models that say that the extra carbon causes a particular amount of warming, because they are opaque to lazy me. Our ignorance on feedbacks and other effects is potentially huge (for example, unaware of global dimming until a few years ago). Experimental or observational evidence of the amount of warming due to carbon, on the other hand, would be very convincing -- especially because it would be replicated by other groups, so I would have great confidence it was true.

So I see a large area of unknowns in the debate. Which leaves people free to apply their prejudices and hopes into that void, without being definitively contradicted. Then come two political calculations. First, the evidence for blaming carbon emissions was pretty good in the 1990's, but it has weakened since, and most people don't seem to have noticed. Second, alternative explanations are being given short shrift by people whose jobs and position rest in part on carbon emissions being the cause. The human herd has not assimilated the new information properly, thus potentially misjudging the situation, so a bet is not an unreasonable way to exercise my prejudices and hopes!

David Evans said...

An annotated spreadsheet is a good way to present a calculation such as the carbon sensitivity. People can see the numbers, and each number can be described (with links) in nearby text boxes.

I found this an effective way of explaining plant models to scientists in carbon accounting. They were free to play with the calculations, and they could examine every assumption. As soon as I put in a macro or any programming, however, they lost interest and became distrustful. It was quite a marked effect.

guthrie said...

David, what I find fascinating about history of science is the way that the methods of sciene have changed over the centuries. Whilst for a long time it was correct that experiments not calculation were the mainstay of advances, that is no longer the case. I think that over the past century improved mathematical abilities allied to better experimental techniques have meant that the naieve experimental view of science is no longer applicable. Instead it is the interplay of theory and experiments that drives it.

For example, the Higg's Boson has been predicted by calculation, now physicists are looking for it, to prove or disprove the set of calculations in it.
THen biologists are predicting things based upon models of genomes and what is known of previous behaviours in evolutionary biology.

Thus, in the case of climate change, we have an interaction of calculation and experimentation. Look at the stratospheric warming satellite recalibration for an example. The theory said X, the experiments said Y, then they found that Y was wrong.

James Annan said...

When I google "argument by authority" I struggle to find any links which attribute a "positive sense" to this phrase. Rather, it invariably refers to the logical fallacy of the form "this toothpaste must be good because Einstein say so", where the only support for the claim is that an "authority" is supposed to have said so - and furthermore the "authority" is generally not even knowledgeable about the subject.

It's true that Wikipedia also mentions another weaker form where the authority actually is an authority in a relevant field - but note here that it still refers to the case where the supporting evidence is merely the word of the authority.

In using the phrase, you are inappropriately characterising the situation as a property of the argument when in fact it is a property of your reaction - ie, you cannot/will not examine the evidence.

Heiko, when an argument is presented by an authority, and theeir evidence is essentially unchallenged, I'd call it a "strong argument" :-)

James Annan said...


IMO the best test of science is when it predicts things that we did not already know. Experiments in themselves are little more than stamp-collecting, it is the theory that allows us to generalise and predict (which is of course the cornerstone of any decision support). In that context, the resolution of several high-profile conflicts between models and observations in favour of the models has to be seen as a striking success for the theory. As well as the satellite obs (NB there is still a range of observational analyses, of course David cherry-picks the lowest outlier in order to claim there is still a disagreement, but given the range of analyses it is clear at a minimum that several groups are underestimating their errors), the recent ocean cooling thing, and perhaps even the THC switch-off fuss can be seen as ways in which models have proved to be a powerful tool. Of course going back to 1988 we have Hansen's famous prediction which has been completely vindicated, despite the outrageous way in which some have tried to misrepresent it.

Heiko said...

From the google search (hits number 3, 9 and 12):

And in many of the more substantive links where "argument of authority" refers to a logical fallacy, a qualifier is often added, like

"A (fallacious) appeal to authority"

followed somewhere down by an explanation like:

"An appeal to authority is a logical fallacy: authorities can be wrong, both in their own field and in other fields; therefore referencing authority does not automatically imply truth. However, referencing authority may carry a high enough probability of truth that it would be correct to base decisions on it.

An appeal to authority is only a reliable argument if:

* evidence is available to back up the point (it is better to use the evidence as argument rather than the authority, but sometimes this is not an option) and is known to the authority being referenced
* the authority is an expert, specifically in the field being discussed, and not merely popular, high-ranking or famous
* the authority is not obviously biased. It is important to note that if the authority is heavily biased, that does not make their claims false, only unreliable. See Circumstantial Ad Hominem.
* the authority is interpreted correctly, and not quoted out of context
* the authority is representative of the majority of experts the field. It is better to have at least a second opinion from another expert, than to go on what could be an unrepresentative sample.
* most importantly, the argument does not try to claim absolute truth based on authority"


Particularly this description of when argument by authority is not fallacious seems to fit the IPCC reports pretty well.

Maybe we could agree to call it a "strong argument by authority" ;-)

guthrie said...

James, I meant my post as a correction to Davids comments about historical science in particular.
I disagree that experiments are little more than stamp collecting- designing experiments that really work is difficult in itself, far more so than simply looking at a stamp and checking which country it comes from.
Also, without the experimental data that showed that CO2 absorbed IR, people would only now be working things out. I stand by my assertion that for science to progress, interplay between theory and experiment is entirely necessary.

James Annan said...


I wasn't disagreeing with you, just putting things a different way. Yes, experiments are important - models by themselves are just untested hypotheses. My main field of research is basically how to combine models with measurements (data assimilation) so I wouldn't want to downplay the importance of either.

PeppyKiwi said...

An interesting paper in this context was published in the Proceedings of the National Academy of Sciences of the USA in March 2002. The author was Daniel H. Rothman, then of the Department of Earth, Atmospheric and Planetary Sciences at MIT. The essence of the paper is illustrated in Fig 4 on page 4170, in which the estimated partial presure of CO2 is plotted against time covering the last 500 million years. Rothman himself says:
"Fig. 4 reveals that CO2 levels have mostly decreased for the last 175 My. Prior to that point they appear to have fluctuated from about two to four times modern levels with a dominant period of about 100 My."

It is notable that three of the four largest peaks in CO2 levels roughly coincide with periods of high glaciation (i.e., lower global temperature). The most recent cool period coincides with relatively low CO2 levels, while one of the peaks of CO2 level coincides with an interglacial period.

As a (hopefully intelligent) layperson, I conclude from this paper that:
- Current levels of CO2 are much lower than average for the last 500My.
- That a number of significant peaks in CO2 level coincided with lower global temperature over extended periods of time (tens of millions or years).
- That by itself, CO2 level is unlikely to be "the dominant" driver of global temperature.

Does this make sense?


James said...

Is there a place on this blog or elsewhere, in which you discuss David Evans' paper of November 28, 2007: "Carbon Emissions Don't Cause Global Warming"? He seems to summarize evidence that indicates "for sure" (his phrase) that carbon emissions are not the (main) cause of what we popularly call "global warming."

Unknown said...

One thing I don't see mentioned in the evans post, the rebuttal above or any of the comments is the effect of ocean sequenstration of CO2. The world's oceans absorb a lot of CO2 and sequester it from the atmosphere. Thus, it is possible, even likely, that the bulk of human generated CO2 has not manifested itself in the atmosphere. The oceans have been acidifying, this is measurable and factual. At some point, the oceans will no longer absorb CO2 from the atmosphere and then anthropogenic CO2 will start accumulating in the atmosphere at much higher rates. Another unfavorable side-effect is that acidification of the oceans will kill many life forms, force others into new (and likely reduced) habitats and generally have a negative effect of the health of the oceans and the planet as a whole. And then too we will see much faster CO2-influenced climate change.

IcedVolvo said...

Well then James you had better explain how during the recent past (geologically speaking) CO2 levels of 5000ppm (about 10-15x present) did not send the earth into complete meltdown?

Can't? Then perhaps a refresher course in spectroscopy and an understanding of the atmosphere would help!

Then perhaps you could explain the absorption anomaly, you know thats the problem where we plug all we know about physics into a computer model and find out that the difference (in other words the ERROR) between the predicted and measured amount of energy arriving at the surface is ~30W/m-2 or about 10 times the WHOLE contribution of CO2.

When we get the physics and computer models better than order of magnitude then we can start worrying!

James Annan said...

CO2 at 16x pre-industrial would lead to a temperature rise of around 12C according to the simplest assumptions. There is a lot of uncertainty about both the CO2 level and the temperature at that time, but the presence of fossils in the antarctic seems generally supportive of the mainstream. Are you disputing that the planet was in fact generally much warmer back then?

As for models being uncertain, I don't see why you should take comfort in the fact that there are still many uncertainties in how climate change will impact us.

IcedVolvo said...

Actually the temperature was significantly colder than now, even accounting for the increasing solar output your lack of knowledge of the geological history of the earth is gob smacking! Photosynthesising plants have been steadily converting CO2 to O2 since life began and the levels of CO2 have been steadily decreasing until recently and yet planetary temps have remained reasonably constant.

However the lack of understanding of how absorption works through thick layers (i.e. planetary atmospheres) relegates your comments (based on first order models) simply ignorant.

As to models not being accurate, the whole basis IS the prediction of models, none of the warming that has occurred in the 20thC is unusual or unprecedented. IT IS ONLY THE COMPUTER MODELS which are predicting catastrophe so if we can't even get a comparatively trivial model of the absorption/transmission in clear skies to within an order of magnitude WHY are placing so much emphasis on the infinitely more complicated climate models?

James Annan said...

Your comments are too vague to make much sense. When is this significantly colder period you are talking about? See this figure. The whole Mesozoic period is widely acknowledged to have been substantially warmer than the present, and with substantially higher CO2, although there is not a perfect correlation between the two (eg changes in continental configuration and the growth of mountain ranges can both have significant impacts).

As for the "steady" temperature, in fact there has been a clear drift to cooler temperatures over the last few million years (eg this figure here). The modern severe ice age cycles only started up within the last million years.

IcedVolvo said...

Temps have been warmer than present for quite long periods (as much as 10C warmer!!!) but they have also been as cool or cooler (e.g. between the Cretaceous and Jurassic and earlier in the Palaeozoic) where temps were <= today's temps) and yet CO2 ranged from 2000-4000ppm!

The ONLY other time in the billion year history of the earth that CO2 AND temps have both been low is in the Late Carboniferous/Early Permian ~300mya.

There is little support there for CO2 being a powerful driver of climate.

But if CO2 is such a powerful driver of climate then why is it that CO2 levels of 5000-7000ppm did not result in complete greenhouse runaway and even supported temps as low or lower than present for millions of years (eg the Ordovician Ice Age)?

It is certainly not true to say there has been any cooling trend in the last 500my! However if you look at the more recent Tertiary period then there has been cooling for the last few 00,000 years but the CO2 levels were falling (from 3000>300ppm) for 200 million years before that cooling started. So again there's no support for CO2 being the driver!

Over the long term there is NO correlation between CO2 and global temperature and direct evidence that CO2 levels 20x higher than current (i.e. 7000ppm) do not resul t in some runaway greenhouse effect.

Temp data from here

CO2 data from here

Correlated temp/CO2 data from here

James Annan said...

Oh good grief. The Scotese scribbles, I should have guessed. Did you not realise that they are just sketched lines? Can you find any scientific basis for them?

Regardless, it is clear that none of those graphs actually show cooler temperatures than the present (and the Cretaceous/Jurassic boundary is clearly indicated as several degrees WARMER than today, directly contradicting your claim).

I don't expect a "runaway" greenhouse and it is not part of any standard theory, so you can forget the silly straw men.

pworam said...

I haven't officially come down on one side of the global warming debate or another. However, alarmists always give me pause; I think an alarmist posture shuts down the ability to hear opposing views.

I am also very leery of computer modeling in the climate sciences. I've done some statistical modeling under the supervision of someone whom I consider to be a brilliant statistician. In the process, the strengths and weaknesses of modeling were evident. While I view computer models as very valuable tools, they are subject to data forcing (trying to get the results to make sense) and are not always reliable. This is especially true when the modelers aren’t fully qualified, don't fully understand the full extent of the interplay between all of the variables being modeled, or when certain variables are omitted. Extensive testing and verification through independent observation is, therefore, critical for supporting the conclusions of computer modeling. From what I can gather, observation does not seem to support man made global warming.

Guthrie - correct me if I'm wrong, but the Higgs Boson was predicted without the aid of a model, using high level mathematics that could also test and prove the existence of the particle. Such is not the case with current climate models.

And, James, thanks for hosting this debate, but try and keep it cordial.

Unknown said...


Thanks for the facts and logic - they seem in short supply in this area.

I've been trying to track down any model validation/correlation efforts against the paleoclimatic data. All efforts seem to be focussed on the use of complex models looking at just the last 50-100 years worth of climate data and all the problems that entails.

The paleoclimate data sets contain large temp swings and CO2 levels and orbital/solar affects are known. Before any complex model is developed I would have thought a correlation effort involving simpler models against the paleoclimate data would be a first logical step to ensure the major factors/basics are understood.

But I have not found any documented attempts, in particular efforts which explain the cooling onset in the presence of relatively large CO2 concentrations. I'm sure the initial warming trend can be explained, but the models would also need to match the cooling cycles as well and in particular the time delays.

Is anyone aware of any efforts in this area?

Anonymous said...

Since Dale Evans claims many aspects are still "up in the air", so to speak, would it not be prudent to START to stabilize and reduce carbon emissions NOW, just in case the worse case happens?
I mean that is the least we can do.

Hank Roberts said...

> Clarke ... says you should floss ...

Don't rely on claims of dentistry -- go 'round back and count the teeth!

Anonymous said...

The 'Bush Doctrine' (sometimes known as the 'one percent doctrine') says that any great danger that has a 1% probability must be treated as a certainty because the potential impacts are so large. Thus Climate Change Deniers must prove that the probability of severe weather disruption due to CO2 is less than one percent. Any risk level above one percent demands immediate response.

Hank Roberts said...

> line by line

Yep. Belatedly, since Eli apparently didn't hear your rustling among the carrots as to explaining that 3.7 number is explained:

"The simple formulae for RF of the LLGHG quoted in Ramaswamy et al. (2001) are still valid. These formulae are based on global RF calculations where clouds, stratospheric adjustment and solar absorption are included, and give an RF of +3.7 W m–2 for a doubling in the CO2 mixing ratio. (The formula used for the CO2 RF calculation in this chapter is the IPCC (1990) expression as revised in the TAR. Note that for CO2, RF increases logarithmically with mixing ratio.) Collins et al. (2006) performed a comparison of five detailed line-by-line models and 20 GCM radiation schemes. The spread of line-by-line model results were consistent with the ±10% uncertainty estimate for the LLGHG RFs adopted in Ramaswamy et al. (2001) and a similar ±10% for the 90% confidence interval is adopted here. However, it is also important to note that these relatively small uncertainties are not always achievable when incorporating the LLGHG forcings into GCMs. For example, both Collins et al. (2006) and Forster and Taylor (2006) found that GCM radiation schemes could have inaccuracies of around 20% in their total LLGHG RF (see also Sections 2.3.2 and 10.2).

Using the global average value of 379 ppm for atmospheric CO2 in 2005 gives an RF of 1.66 ± 0.17 W m–2; a contribution that dominates that of all other forcing agents considered in this chapter. This is an increase of 13 to 14% over the value reported for 1998 in Ramaswamy et al. (2001). This change is solely due to increases in atmospheric CO2 and is also much larger than the RF changes due to other agents. In the decade 1995 to 2005, the RF due to CO2 increased by about 0.28 W m–2 (20%), an increase greater than that calculated for any decade since at least 1800 (see Section 6.6 and FAQ 2.1, Figure 1). "

David Evans said...

I am David Evans (not the David Evans that appears to deny global warming). I posted the following by GARY GUTTING in my blog on Blogger called “It Started in Philadelphia” on October 13 of this year.
“… Consider, for example, current discussions about climate change, specifically about whether there is long-term global warming caused primarily by human activities (anthropogenic global warming or A.G.W.). All creditable parties to this debate recognize a group of experts designated as “climate scientists,” whom they cite in either support or opposition to their claims about global warming. In contrast to enterprises such as astrology or homeopathy, there is no serious objection to the very project of climate science. The only questions are about the conclusions this project supports about global warming.

There is, moreover, no denying that there is a strong consensus among climate scientists on the existence of A.G.W. — in their view, human activities are warming the planet. There are climate scientists who doubt or deny this claim, but even they show a clear sense of opposing a view that is dominant in their discipline. Non-expert opponents of A.G.W. usually base their case on various criticisms that a small minority of climate scientists have raised against the consensus view. But non-experts are in no position to argue against the consensus of expert opinion. As long as they accept the expert authority of the discipline of climate science, they have no basis for supporting the minority position. Critics within the community of climate scientists may have a cogent case against A.G.W., but, given the overall consensus of that community, we non-experts have no basis for concluding that this is so. It does no good to say that we find the consensus conclusions poorly supported. Since we are not experts on the subject, our judgment has no standing.

It follows that a non-expert who wants to reject A.G.W. can do so only by arguing that climate science lacks the scientific status needed be taken seriously in our debates about public policy. There may well be areas of inquiry (e.g., various sub-disciplines of the social sciences) open to this sort of critique. But there does not seem to be a promising case against the scientific authority of climate science. As noted, opponents of the consensus on global warming themselves argue from results of the discipline, and there is no reason to think that they would have had any problem accepting a consensus of climate scientists against global warming, had this emerged…”

Hank Roberts said...

aside -- there's a new expert at WTF who writes at RC " for the record, I have a fair amount of experience in decision making in the face of uncertainty. For example, see my Goggle Knols and Excel spreadsheets for Bayesian Analysis, Decision Trade-Offs, and Nash Equilibrium"