Physicists Disagree about Climate Change

Here is a statement from Hal Lewis, a physics professor at UC Santa Barbara, in answer to a question from CBS News:

I know of nobody who denies that the Earth has been warming for thousands of years without our help (and specifically since the Little Ice Age a few hundred years ago), and is most likely to continue to do so in its own sweet time. The important question is how much warming does the future hold, is it good or bad, and if bad is it too much for normal adaptation to handle. The real answer to the first is that no one knows, the real answer to the second is more likely good than bad (people and plants die from cold, not warmth), and the answer to the third is almost certainly not. And nobody doubts that CO2 in the atmosphere has been increasing for the better part of a century, but the disobedient temperature seems not to care very much. And nobody denies that CO2 is a greenhouse gas, along with other gases like water vapor, but despite the claims of those who are profiting by this craze, no one knows whether the temperature affects the CO2 or vice versa. The weight of the evidence [suggests] the former.

That’s reasonable. Here is a statement from another physicist, a friend of mine and Andrew Gelman’s:

Like a lot of scientists — I’m a physicist — I assumed the “Climategate” flap would cause a minor stir but would not prompt any doubt about the threat of global warming, at least among educated, intelligent people. The evidence for anthropogenic (that is, human-caused) global warming is strong, comes from many sources, and has been subject to much scientific scrutiny. Plenty of data are freely available. The basic principles can be understood by just about anyone, and first- and second-order calculations can be performed by any physics grad student. Given these facts, questioning the occurrence of anthropogenic global warming seems crazy. (Predicting the details is much, much more complicated). [He seems to miss the point here. The usual claim is that man-made warming is large relative to other global temperature changes. That’s not predictable “by any physics grad student” and to call it a “detail” is misleading. — Seth] And yet, I have seen discussions, articles, and blog posts from smart, educated people who seem to think that anthropogenic climate change is somehow called into question by the facts that (1) some scientists really, deeply believe that global warming skeptics are wrong in their analyses and should be shut out of the scientific discussion of global warming, and (2) one scientist may have fiddled with some of the numbers in making one of his plots. This is enough to make you skeptical of the whole scientific basis of global warming? Really?

At risk of sounding v smug, my views have changed only a little. I already thought the consensus was more fragile than it appeared. That’s just a general truth about modern science. I was already skeptical of climate models because I knew how easily modelers fool themselves. I began to believe the consensus was not just fragile but wrong when I heard the story of the Yamal tree ring data — the long refusal to supply the raw data and, when the researcher’s hand was forced and the data finally supplied, the way it contradicted the claims that had been made. Climategate didn’t vastly change what I thought; it provided more evidence for ideas I already had.

Another friend of mine used to be a math professor. He has views similar to the views of my physicist friend. “Look,” I said to him, “if you want to argue that humans are causing major global warming you should at least show it’s warmer now than in the past. Even that isn’t true. The Medieval Warm Period.” “That was only in Europe,” he replied. Actually, there is evidence of the same thing in the Gulf of Mexico.

26 Replies to “Physicists Disagree about Climate Change”

  1. Seth:
    Nobody fiddled with the data. Part of the data, the tree ring data, has been funky since the early 60s. For unknown reasons, since 1961 the tree ring data has been diverging from temperature data at the same location. Rather than throw the baby out with the bathwater, they used the “trick” of decreasing the weight of the tree ring data over time since then.
    So tree ring data should trump direct temp measures, pollen distributions, stalagtite and stalagmite measures, annual ice deposition thickness, and isotope concentrations?
    We live in an age of Shibboleths. There is no such thing as artery clogging saturated fat, cholesterol tells us next to nothing about heart disease, and even with your work there isn’t a fully sound theory about metabolism.
    But skepticism without measure leads to gullibility. AGW and Climate Breaking are the simplest hypothesis, are consistent with paleontological evidence of past warmings, and do not have the burden of proof you demand.

  2. You are sure the “temperature” (which means what?) data are right and the tree-ring data wrong because . . . ?

    As for the idea that “nobody fiddled with the data” — have you read this?

  3. “my views have changed only a little”

    And it’s wonderfully convenient that these views are consistent with your both your politics and attitudes about large institutions generally. It is fun, being a cynical contrarian sceptic.

  4. Jonlongstrider: The point of the chart that got fiddled with was to show the long-term trend based on proxy data. If the proxy data “diverges” almost immediately after leaving the period it was calibrated against, what makes us think it didn’t “diverge” in the past? Two perfectly plausible hypotheses about this include:

    (1) tree rings just aren’t a good long-term proxy, and the apparent fit with temperature in the past was just a result of data-snooping

    (2) tree rings are a decent proxy but top being so when the temperature exceeds X.

    If either of those are the case, tree rings couldn’t have shown us if the MWP was warmer than today because the temps they show in the past are probably “diverging” just as recent ones are. No

  5. (hit submit by accident there..) No argument has been made to exclude those hypotheses. Instead choices were made with respect to plotting the data that deliberately hide the otherwise obvious potential problem from those who read the resulting chart.

  6. It’s always a bad sign when new data only confirms what you already believe, especially on a controversial issue. A priori the chance that you are one of the small fraction of people in the world who are right on the issue, given incomplete and contradictory data, is very low. Yet of course you will think you are right, because if you didn’t, you would change your opinion. So the great majority of people think they are right, but are at least slightly wrong. Hence new data should cause almost everyone to change their opinion. But it does not, because most people are biased and will interpret and adapt the new data to reinforce their pre-existing beliefs. If you, too, find the new data only confirming what you already believe, it is overwhelmingly more likely that you are committing this logical error than that you were in the lucky minority that happened to be right before.

    OTOH if you find your opinion changing in response to new data, that doesn’t prove you are right or logical, but it is evidence in that direction.

  7. That Hal Lewis quote is a really good one for the purpose of contrasting the two viewpoints. I just don’t see any part of Lewis’s quote as “reasonable”.

    For instance, the statement that continued warming is more likely good than bad because “people die of cold, not warmth”…I’ve just typed and deleted four different responses because I am having trouble coming up with anything other than an insult. There may (or may not) be an abstract sense in which a warmer climate would be better. But the fact is that the manmade world (and the terrestrial ecosystem) is highly optimized to the current climate. Reservoirs are built where the rain falls. Coastal cities, towns, and houses are built at an appropriate location for the current ocean level. To suggest that the major effect of warming is that fewer people will die of cold isn’t just wrong, it is _obviously_ wrong. It’s _ridiculously_ wrong.

    And as for the claim that change is “almost certainly not” too big for “normal adaptation” to handle…well, that obviously depends on what “normal adaptation” means, and also on how much change we are talking about. Considering Levin doesn’t think the temperature is changing much at all — he says so a few sentences later — well, if you believe that then I guess you can believe that “normal adaptation” is going to do OK. But that’s arguing from a false premise: temperatures are going up, and going up fast. (And global warming isn’t just about temperatures, it also affects rainfall patterns and storms and so on). It’s not clear if Levin (or you, Seth) would agree that if climate change is very large and rapid, “normal adaptation” would suffice? I hope you would agree that there is _some_ magnitude of climate change for which “normal adaptation” would not be enough.

    Lewis says increasing temperature causes an increase in CO2 rather than the other way around, and that “the disobedient temperature seems not to care very much” about increasing levels of CO2. Confusingly, he also says that CO2 is a greenhouse gas. But it’s hard to interpret these statements as anything other than a denial that increasing levels of CO2 lead to an increase in temperature.

    So, I think this entire Lewis quote is something very close to nonsense. The fact that you, Seth, say it is “reasonable”…I just hardly know what to say.

    Moving on through your post: you insert a comment in my quote, that I “seem to miss the point here. The usual claim is that man-made warming is large relative to other global temperature changes. That’s not predictable “by any physics grad student” and to call it a “detail” is misleading.”

    First, that is not the usual claim. The usual claim is that man-made warming is large enough that it may be catastrophic. I’ve never understood the importance of comparing it to historical variability, unless you are one of the people who believes anything natural is good. (Malaria? Smallpox?). Even if we had some philosophical agreement that anything natural is good, it wouldn’t necessarily follow that something unnatural, but of the same magnitude as a natural effect, is good. If we agree that it’s a good thing that people die of the flu — culls the herd, and all that — it doesn’t necessarily mean that if I go out and kill 10,000 people, I’ve done a good thing.

    Second, it is not “missing the point,” nor “misleading” to say that any grad student can do the first- and second-order calculations of the magnitude of a change. This is important because there are people out there who claim that the whole concept of any human-caused influence on the climate is a scam. Ironically, and seemingly contradicting my claim about any physics grad student, you just quoted a physicist who apparently believes the amount of CO2 in the atmosphere does not affect global temperatures! In your post, you have simultaneously proven the relevance of my point, while also apparently disproving my assertion. Actually, I’m sure Lewis is capable of performing the calculations; he presumably is sure (why?) that effects beyond the first orders are big enough to cancel out the leading terms.

    I’m just at a loss. You people are nuts!

  8. Phil, can you explain why Lewis — who surely understands physics at a better-than-grad-student level — has the views he has? Not the view that warmth is good for people but the other views.

    You don’t see a problem when you argue based on what any physics grad student can do and I give an example of a physics professor who disagrees?

    Ben, my “politics”? what are you talking about? I’m a member of the Green Party. I fail to see the consistency.

  9. Seth asks: Phil, can you explain why Lewis — who surely understands physics at a better-than-grad-student level — has the views he has? Not the view that warmth is good for people but the other views.

    I reply: No. To ask me to explain why someone else has the views that they have, based on a single paragraph of nonsense…you’re asking too much of me.

    Seth asks: You don’t see a problem when you argue based on what any physics grad student can do and I give an example of a physics professor who disagrees?

    I reply: First, I have to correct you on a minor point. What I’m claiming that any physics grad student can do is to calculate things like: what would the earth’s temperature be if it had the same albedo that it actually has, but no atmosphere? What would the earth’s temperature be if the amount of CO2 were doubled but nothing else changed? This latter question is what I meant by the “first-order” problem.

    I see no evidence that Lewis would have any problem solving those problems. I do not think Lewis would disagree with these calculations. Perhaps he would — maybe he lost his physics chops when he retired — but I doubt it.

    But I think you’re intended point isn’t to ask about those specific calculations, it’s to say “do you think there’s a problem when a presumably intelligent physicist who claims familiarity with the issue disputes anthropogenic global warming?” If that’s your question, then yes, I do see a problem. Two problems. But I think the problems I see are different from the one that you see.

    The first problem I see is that this guy is just not thinking clearly about this subject. He says that even if global warming happens as expected it will be good because fewer people will die of cold, as if that’s the main expected effect. He says global temperatures are not in fact increasing, which is simply false. He says CO2 is a greenhouse gas (meaning it absorbs and re-radiates infrared radiation) but that as for trebling or quadrupling its atmospheric concentration “no one knows” if that affects temperature. These are just not reasonable statements, whether they come from a physicist or someone else.

    The second problem I see is that some intelligent people think these unreasonable statements are in fact reasonable!

  10. posted for Bruce Charlton:

    The whole Climate Change business hinges upon computer modelling:

    This is John Wixted of UCSD :

    “To think about the relationship between CO2 emissions and global warming, the most important step to take is to imagine that scientists had never invented climate models that presume to predict the future. In the absence of those models, what would you think about CO2 emissions? That’s the question.

    The reason to drop the climate models from consideration is that models of complex systems cannot predict the future in any area of science, so climate models should not be trusted until they are uniquely shown to be able to do that. So far, the models have not passed any serious test, and the excuse given is that, in the short term, unpredictable weather variations can mask predictable long-term climate trends. In the long-term, the argument goes, the models may be shown to be right after all. But get back to me in the long term because, for now, I have no reason at all to believe that the models are accurate (and neither do you).

    Scientists who are infatuated with their own climate models seem to have a different view, namely, that the models should be trusted until those models are proven wrong. By definition, this cannot happen in the short term (because of unpredictable weather), so the models are protected from disconfirmation until decades go by. That’s not a reasonable view because, in light of the general predictive utility of complex-system modeling, the odds are very high that the climate models are incorrect.”

    But I must admit that probably the biggest influence on me was Freeman Dyson, whom I respect hugely. Just search his name and ‘climate’ to get a flavour of his views.

  11. Seth, you could remove the statement about deaths from cold from Lewis’s statement, and it would still be nonsense for reasons I have outlined.

    Bruce and John: The whole “Climate Change business” does not hinge on computer modeling.

    Bruce or John (I can’t tell who said it): Freeman Dyson was an excellent mathematician and physicist, but has always been absolutely terrible as a futurist. His main stance on climate change is that the problems won’t be nearly as bad as people think because technology will allow cheap and easy adaptation — we’ll genetically engineer plants to take up the CO2, or else we’ll adopt special planting methods over virtually the entire surface of the earth to recapture in biomass what we are putting out through burning fossil fuels…and this will be cheap and easy and won’t have negative side effects (yep, seriously. He proposes that we increase the rate of plant growth by an average of 1/10 of an inch per year over the entire surface of the earth).

    Dyson is, and has always been, a technological optimist to an almost incredible degree. For instance, he thought in the 1950s that we would land people on Mars by the mid-60s (using nuclear-powered spacecraft), and that we would send people to the outer solar system by the 1970s. Please allow me to revel in the irony of someone who says not to trust predictions of complex systems, especially if they don’t have a track record of success…but then cites the authority of a man with a 60-year track record of failure who predicts the progress of technology far into the future and, on that basis, claims that adapting to climate change is going to be a piece of cake.

  12. First, the dialogue is tremendously useful.
    Second, I looked at the “fiddling with data reference”
    Seth referred to above and think wonder three things:
    1) How much more time do I need to figure out what the author is doing?
    2) What are the confidence intervals around the 1-2 degree anomalies?
    3) If he had to work that hard to find an anomaly, what is the likelihood this represents the work of a conspiracy to fool the planet into believing the planet is heating when it isn’t? Cui bono?

  13. Seth, that Freeman Dyson article at is a really good one, when it comes to seeing why people shouldn’t put a whole lot of weight on Dyson’s beliefs on this! He says himself, “it is definitely a tactical mistake to use somebody like me for that job, because I am so easily shot down. I’d much rather the job would be done by somebody who is young and a real expert. But unfortunately, those people don’t come forward.”

    I also don’t think I’ve mischaracterized Dyson’s views. That particular article doesn’t emphasize his technological optimism. He doesn’t say global warming isn’t happening — indeed, he specifically says that it is: “No doubt that warming is happening. I don’t think it is correct to say “global,” but certainly warming is happening. I have been to Greenland a year ago and saw it for myself. And that’s where the warming is most extreme. And it’s spectacular, no doubt about it. And glaciers are shrinking and so on.”

    Dyson does say in that interview that he doesn’t think most of this is due to anthropogenic effects, a claim I hadn’t previously seen. It’s an odd claim, not exactly contradicting other things he has said, but close: he has said “Everyone agrees that the increasing abundance of carbon dioxide in the atmosphere has two important consequences, first a change in the physics of radiation transport in the atmosphere, and second a change in the biology of plants on the ground and in the ocean.”

    Check out the long article by Dyson at
    Among other things, he says ” I consider it likely that we shall have “genetically engineered carbon-eating trees” within twenty years, and almost certainly within fifty years. Carbon-eating trees could convert most of the carbon that they absorb from the atmosphere into some chemically stable form and bury it underground. Or they could convert the carbon into liquid fuels and other useful chemicals. Biotechnology is enormously powerful, capable of burying or transforming any molecule of carbon dioxide that comes into its grasp.”

    Or, check out the article he wrote at in which he says “If we use genetic engineering to put more biomass into roots, we can probably achieve much more rapid growth of topsoil. I conclude from this calculation that the problem of carbon dioxide in the atmosphere is a problem of land management, not a problem of meteorology.”

    In all of Dyson’s publications, he emphasizes that (1) he is not an expert on climate change and does not intend to become one, (2) the climate is changing, and particularly the colder parts of the earth are warming, and (3) even major climate change will not be harmful. In the two that I cited, he also mentions using biotechnology to remove carbon dioxide from the air.

    I definitely agree with Dyson about item (1), above!

  14. Quick response to Scot on question (3): I would say the likelihood of conspiracy is close to 0%. Cui bono? No one, because no one need benefit. Conspiracies are unnecessary to explain massive consensuses based on questionable evidence. Exhibit A, I give you world religion.

  15. Ted – I think you can find more productive ways to cheer on those in your tribe than trying to bait me.

    Seth – My impression from reading your work and postings is that your an enthusiastic believer in the power of individuals to do good and you are deeply suspicious, concerned, and dismissive of the power of institutions to do good. I think that’s a deep and fundamental part of your world view. Would you dispute that?

  16. Ben, yes, I dispute that. Some institutions work well, some don’t. I have often praised Spy magazine, for example. That was an institution. I’m a member of Slow Food — another institution. I’ve praised printed books for their power to teach cheaply — although written by individuals, they are published by publishing companies, which are institutions. I’ve praised — yet another institution.

  17. Seth, embrace who you are. You have spent your entire life being a gadfly, a contrarian, and doubter. You’ve been marvelously successful at that. But to claim that you are not pro-institutional, be real! Your examples prove my point. Spy magazine, green party snort.

    But we are getting pulled away from the topic at hand. My point was and is that for you to join the consensus that we have sufficient confidence about the source and the likely consequences of global warming at this point to spin up a vast and coordinated response would demand not once by twice that you create some allegiance to really vast institutions. One the side of the consensus about sources you’d have to join assent to agree with institutional science in a way that you’ve spent most of your life being a contrarian about. And to support the vast response we need to spin up you’d have to work, or at least allow that it’s possible, to make the institutions that coordinate those responses functional. Both these are deeply hard given where your political center of mass is.

    I am not, by choice, arguing about the merits of the contrarian arguments around the global warming consensus. Though I consider them broadly wrong. I am highlighting that like the majority of those who take them seriously your engagement with them runs true to your politics in ways that create what I consider an unfortunate synergy. You all have recently gotten all into trying to play the group think card, a move that suffers a tad from projection.

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