Bryan Caplan  

Arnold's Standards of Science: Does Anything Measure Up?

The Subprime Mess, Daily Brief... Standards of Proof...

Like other global warming skeptics, Arnold objects to reliance on scientific consensus:

To me, scientific evidence is not "a whole bunch of scientists think X." To me, scientific evidence is "Here is an experiment or a naturally-occurring event where the results are extremely unlikely to occur unless X is true." That is what I find missing in the man-made global warming story.
I doubt that people claim that consensus is the same thing as scientific evidence. Instead, they rely on consensus because (a) It strongly correlates with scientific evidence, and (b) It is much easier for non-experts to check for consensus than to directly review the scientific evidence.

In any case, isn't Arnold's standard of scientific evidence strangely strict? Few results in economics rest on an "experiment or a naturally-occurring event where the results are extremely unlikely to occur unless X is true." The same goes for evolutionary biology. Some will be delighted to dismiss both as pseudo-sciences, but the real lesson is that Arnold's standard is excessive. Contrary to his account, the typical scientific conclusion rests on large body of diverse pieces of evidence. Most of these pieces of evidence are not, by themselves, very convincing; it is the totality of the evidence, not any particular finding, that provides the basis for scientific judgment.

Yes, this does leave room for herd mentalities and worse. But there is a sensible answer to these concerns: Put your money where your mouth is. Place your bets. The reluctance of global warming skeptics to do so (with one notable exception) makes me skeptical of their skepticism.

Of course, the fact that e.g. real estate prices in coastal regions remain high makes me skeptical that global warming will have dire consequences if it does happen, but that's a separate issue.

Comments and Sharing

COMMENTS (32 to date)
Maniakes writes:

Darwin didn't come up with evolution -- the idea had been floating around for a while -- he gets credit for it because he documented naturally-occurring events where the results are extremely unlikely to occur unless evolution were true.

Specifically, the species of birds found in the Galapagos were pretty much what you'd expect if mainland birds had flown there and evolved to fill all the niches that in more accessable places are normally filled by unrelated beings.

There's more rigororous modern evidence for evolution, most notably the similarities of evolutionary family trees as derived from the fossil record, analysis of accumulated mutations in junk DNA, and observation of common traits of modern species.

caveat bettor writes:

Sometimes, a consensus around a scientific hypothesis is erroneously accepted as scientific proof.

On Megan McArdle's site, I asked about the global cooling scientific consensus of the 1960s-80s. I also asked about the margarine and Crisco substitutions for butter and lard, scientifically driven during that same time period.

Thomas Kuhn was right: scientific consensus is quite vulnerable to group think. That might be a tautology, but no more than "survival of the fittest".

Sean writes:

One rather serious problem, caveat, is that there was never a 'global cooling scientific consensus'. See, e.g., here.

Brad Hutchings writes:

Bryan, my own skepticism is with the whole story. Let's assume the whole story has 15 parts to it, starting with the earth is warming, passing through with man is the cause through release of CO2, NH3, and other greenhouse gases, and ending with government damned well needs to do something to fix it. For the sake of argument, let's say that our confidence in each of these steps is 90%. Then freshman probability tells us that our confidence in the whole story ought to be 0.9 ^ 15 = .21, or 21%. Instead though, the proponents of the story make the calculation for "what is the chance none of this is true?". They get 0.1 ^ 15 = 10 ^ -15. They call people who don't buy the whole stories "deniers", when those "deniers" actually are asking the question, "what is the chance the whole story isn't true?". And that answer in our hypothetical is about 80%.

A lot of people on the AGW proponent side are anti or at least ambivalent to markets and individual freedom. A lot of skeptics are not confident in government's ability to fix or improve any problem there is, especially due to its scale. The attitudes cloud the debate. Frankly, I'd rather fight over whether meat is bad or Hummers are evil on their own terms than in a proxy context of AGW. But that's just how I like to argue.

caveat bettor writes:

Sean, with a nod to Karl Popper, could you provide me some references to mainstream support for global warming in the 60s-80s? Thanks in advance!

Floccina writes:

Of course, the fact that e.g. real estate prices in coastal regions remain high makes me skeptical that global warming will have dire consequences if it does happen, but that's a separate issue.

Are AGW belivers buying land in Maine 20 feet above sea level in hopes that they will one day have valuable ocean front property?

Al T writes:

Brian, is (A) true? It seems like a hypothesis that could be tested and maybe has been for all I know.

"I doubt that people claim that consensus is the same thing as scientific evidence."

But aren't you doing that later on in your post when you say, "the typical scientific conclusion rests on large body of diverse pieces of evidence." Or are you saying that scientific evidence and scientific conclusions are two very different processes? Arnold's requirements are strict, but that's why people are supposed to put a lot of trust into things "scientific" and not as much trust in other things.

It seems that a lot of things that were scientific consensus but based upon a large body of disparate observations have been since proven false. So how is a layman supposed to know when to trust something like F=ma but not trust the really popular racial theories of the early 20th century.

Al T writes:

"The reluctance of global warming skeptics to do so (with one notable exception) makes me skeptical of their skepticism."

But isn't this type of betting market very immature compared to the real estate market you describe?

Also, how do we find out what the consensus is among economists or climate scientists, especially relative to their weight in their field? I'm not an economist but my understanding of the 50's-70's was that it was filled with model building that stagflation proved utterly wrong. How do you know if you're in that situation now with climate modeling?

Sean writes:


I don't get it. What does 'mainstream support for global warming in the 60s-80s' have to do with your endlessly refuted 'global cooling' canard? Why the 60s-80s? What does Popper have to do with this?

Brad Hutchings writes:

So how is a layman supposed to know when to trust something like F=ma but not trust the really popular racial theories of the early 20th century.

Ideally, laymen understand the process of science. They see "truth" as a useful byproduct of science, but understand that science itself is a process. Ideally, the process is unclouded by politics, so careers don't end over observations about mean IQ or analyses of why women are underrepresented in the hard sciences that don't begin and end with "men are pigs". And ideally, they are skeptical about all proclaimed truth until it passes the tests of time.

Philosophically, I think that's the best argument for not rushing to do anything about global warming. The damage to science as a means for social improvement that would be caused by rushing into something expensive, ineffective, and/or unnecessary far exceeds any marginal damage we could do to the planet by waiting a decade or so. The nice thing about that argument is that it forces proponents of AGW action to claim ridiculous consequences of inaction, consequences which are not supported by any science in anyone's wildest dreams.

caveat bettor writes:

Sean, the nod to Popper was about falsifiability. The "canard" can be falsified if we are able to see scientific heterogeneity between global warming and global cooling scientists. I've only seen scientists write about global cooling in that time period.

I'm not one that looks back much, except for providing a context for the future. I frequent NASA's Goddard Institute for Space Studies site, and the data there seems to indicate a decade long cooling period.

Ben Kalafut writes:

Floccina: Those convinced by science (AGW supporters) are advocating cap-and-trade or even carbon taxes, both of which will (ignoring the gain from internalizing the ocean-acidification and warming externality) raise their own cost of living.

That does count for something.

Ben Kalafut writes:

If you've been following the science, you'd find that it has already passed the test of time. Irrational doubts are no justification for inaction.

Note also that ocean acidification is a fairly good justification for doing something now and not ten years from now. That problem becomes serious on much shorter timescales than AGW.

Matt writes:

The evidence is actually the inverse, global cooling was very likely unless X happened, where X is the lack of CO2 about 10,000 years ago. We missed a glacial cycle, we all know that, the ice core data is Nobel prize perfect, and ice core scientists deserve the Nobel in the aggregate for their work.

So, the ice core work is the actual, highly accurate measurement of the relationship between glacialization and CO2. This accurate measurement correlates very well with a Hamiltonian energy exchange among two of the major variables, albedo and CO2. The relationship obeys the photo transmission properties in the lab.

Don't confuse weather prediction with physics calculation. Arnold is looking for X to be a reasonable accurate estimate of the when and how much for temperature rise.

Sean writes:


I don't think you understand. Your claim was that there existed a *consensus* about global cooling, presumably among climate scientists. The link I provided you details the *actual* scope of cooling claims; while there were concerns voiced by a small number of scientists "the papers of the time present a clear consensus that future climate change could not be predicted with the knowledge then available." *Your* consensus is illusory, in other words.

The purpose of your request is a pretty obvious non-sequitur. Unfortunately, it does follow that because there was no consensus about global warming during the period, there was a consensus about global cooling. The facts, caveat, tell us that there was consensus on *neither* position.

Al T writes:

"Here's exactly the problem that availability cascades pose: What if the heads being counted to certify an alleged "consensus" arrived at their positions by counting heads?"

Troy Camplin writes:

His definition works well for the following fields: quantum physics, Newtonian physics, and chemistry. If you try to apply this to complex systems with emergent properties (cellular biology, evolutionary biology, economics, sociology, psychology, anthropology, or climatology), then you will fail far more often than not to meet this standard of evidence. The real problem is that everyone thinks of science as what includes the first three listed, which does give us some pretty specific and absolute results. The more complex something is, the less likely we are to get this kind of data, meaning we end up hearing people accusing fields like economics of being nothing but nonsense because it can't give us absolute answers, like physics does. Well, economics is 4 levels of magnitude more complex than physics, so we shouldn't be expecting those kinds of results. The less complex something is, the more likely it is to be described with math; the more complex something is, the more likely it is to be described with language. Of course, people don't like the ambiguities that come along with a reliance on language over math (or even a reliance on statistics, increasingly the only math worth mentioning for extremely complex systems).

Badger writes:

"Scientific consensus" always smells to me like the pre-Volcker consensus on the Keynesian Phillips curve. Or the consensus that central planning beats markets. Always followed by the usual "the debate is over." This is not science. This is politics.

Lord writes:

Coastal real estate offers high returns that would make it insensitive to climatic conditions until they were upon us.

Brad Hutchings writes:

Sorry Ben. It (being the whole 15+ step story that makes my SUV responsible for destruction of the earth as we know it) has not stood the test of time. Individual pieces may or may not have, but the whole story most certainly has not. And regardless of what you like, it will take another two decades to do anything anyway, so we're going to have to wait it out. When people realize that they can't smoke without buying a carbon offset or that they have to ride a bicycle to work 2 days a week or get federal air quality permission for a divorce, they'll vote against the solutions. And forget India and China. They want the lifestyle we have, and they're not going to put their ambitions on hold until Toyota can ship 50 million hydrogen powered Priuses per year.

Besides... there isn't a person I know across the country that wouldn't love to have the 85 degree December day I'm enjoying in SoCal. If they'd had these in the San Francisco Bay Area, I never would have left ;-).

Les writes:

Your expression "scientific judgment" is an oxymoron. Judgment is not science. Science is hard factual evidence. Hard factual evidence comes from rejecting hypotheses, based upon empirical research.

Judgment, and consensus, are used when the evidence is lacking or unconvincing, but a decision is needed.

To confuse "judgment" or "consensus" with science is to proclaim ignorance of the philosophy of science.

Troy Camplin writes:

No, back when I was doing molecular biology, there was a great deal of judgement involved. There is no such thing as the facts speaking for themselves. You do have to interpret the results of your experiments.

Barkley Rosser writes:


I am a fan of generally. However, the piece you cited about the views about global cooling over three decades is one of the most misleading and inaccurate pieces they have ever published. This is in fact an example of herd mentality, with this particular piece of crap being widely repeated.

I was there, and there was no consensus either way. There is a rather large amount of scientfic lit back then (the claim in your link that it was all some scare story in Newsweek is simply false) in which leading climatologists were discussing a close call: global cooling versus global cooling. It should be kept in mind that the record had been (and is agreed to have been in the IPCC reports) that there was a gradual global cooling from the mid-1930s to the mid-1970s, since when we have had an accelerating global warming.

The debate then was CO2 versus particulates (aerosols) and SO2. There was no consensus, but plenty of people were taking the possibility of global cooling very seriously. Just to pick on one such, Stephen Schneider, now one of the leading advocates of doing something dramatic to deal with global warming. Do a deep search to the early 1970s of his scientific pubs, and you will find him posing the alternatives as a tossup. So, cool it.

US writes:

Like AI T, I think of a) more as a hypothesis than a fact. I think the covariation varies widely among different branches of science, and it seems obvious that the more politically infested the subject, one way or the other, the lower covariation. You need to convince me that the scientific evidence is a main contributor to the consensus, instead of the 10+ other reasonable explanations I can come up with, before I will even start to accept the premise that scientific consensus is something I should care about.

Also, what a lot of people seem to forget when discussing this subject is this: The very foundation of good science is a good healthy skepticism - skepticism is a great contributor to getting rid of bad and incorrect ideas. This is my main caveat when it comes to the global warming discussion - to a lot of people, scientists or not, skepticism is simply inadmissible. But skepticism is what drives scientific progress, if we never question what we know, we will never learn anything new, and we will be having great difficulties knowing if we are wrong.

US writes:

A small correction/addendum: A high level of political implications related to scientific results needs not of course necessarily result in a lower correlation with the 'scientific evidence'. What often happens, and what most certainly takes place in this debate, is that the (never impartial) scientists look very hard for the 'scientific evidence' that support their own agenda, and tend to overlook the rest of the scientific body, meaning that even if there's a high degree of correlation between 'consensus' and 'evidence', it might still be of limited relevance, given that the scientists are not attempting to disprove their theories, as they should, but merely look for confirmation of preconceived ideas, something that is both quite easy to do and has little to nothing to do with science.

Sean writes:


I'm have a really hard time believing you've even bothered to read the piece, considering that every 'point' you made is addressed therein. Just to take two random examples:

"There was no consensus, but plenty of people were taking the possibility of global cooling very seriously."

Golly, doesn't Connolley write that:

"Finally, its clear that there were concerns, perhaps quite strong, in the minds of a number of scientists of the time."

I found this comment odd:

"...the claim in your link that it was all some scare story in Newsweek is simply false..."

Gee, where did Connolley write that? Certainly not in the piece I linked to!

Ben Kalafut writes:

Brad Hutchings:

If you think the story is "how your SUV is responsible for the destruction of the earth", and if you really think this is about how nice the weather will be, it's clear you're not interested in serious discussion.

caveat bettor writes:

Could we historically normalize what "scientific consensus" is? And does the pre-Copernican 1400 years of the Ptolemaic view of planetary orbits fall into that consensus?

Larry writes:

Has anyone proved scientifically as per required that jumping in front of a moving train is detrimental to health of a human being ? Which human being was used in such experiment ?

Ben Kalafut writes:

I don't think we should confuse a "consensus of those who call themselves scientists" with a "scientific consensus", Caveat Bettor.

But that aside, it's pretty clear that the consensus on this matter is quite a bit different from that in favor of the phlogiston theory of heat. "Known physics tells us X" is categorically different from "this is the best theory we've got so far".

Note that when climatologists reference the consensus, it's a statement of humility. "This is what we, the experts on the subject, the most qualified skeptics, agree on. This isn't merely my research group's latest conjecture."

Barkley Rosser writes:


Point granted. The piece is pretty reasonable, although it starts out not looking like it will be. They had another one that was not that I have read.

Just as one sees some popular skeptics (rather than scientific ones) going on about how the current consensus is probably wrong because there was this consensus about global cooling in the 70s, one sometimes sees people responding to them by claiming that there was no serious discussion of global cooling possibilities, and that it was just all a few scare stories in the popular press. The link you provided is more balanced; there was serious discussion of the possibility of global cooling by serious scientists, but there was no consensus either way.

Michael Sullivan writes:

Of course, the fact that e.g. real estate prices in coastal regions remain high makes me skeptical that global warming will have dire consequences if it does happen, but that's a separate issue.

this makes me skeptical that it will have dire consequences in the near term, but not particularly in the long term.

Suppose you were 100% certain that a piece of property would be struck my a predictable disaster in 150 years, rendering it completely worthless, and we had no idea how to avoid said disaster other than abandoning the property.

How much would that cause you discount it's value (in terms of your willingness to pay for it) today? Not that much, I expect.

It's not clear that knowledge about a very small vs. say 10-20% probability of something bad happening 100+ years out is going to be resolvable over the normal noise of price fluctuation.

That coastal real estate is not plummeting makes me fairly confident we won't see a complete catastrophe in the next 30 years (or at least, if we do, that it will be a catastrophe *no one* could reasonably have expected today).

But nobody is seriously claiming there will be 10+m sea level rise in 30 years. More like 1-4m in 75-150 years as an expected likely - worst case range, with some worries that our tail numbers might significantly understate both the probability and magnitude of the worst effects.

Comments for this entry have been closed
Return to top