Are climate models like economics models?

Here’s another reader request:

You’ve spent a lot of time studying economic models.  You probably have an opinion about their overall reliability.

How should that opinion influence your view of the issue of
environmental change, given that many of the inferences about such
change come from general climate models that are, in some ways, very
similar to economic models?

I would prefer betting markets, but I don’t think they would suggest something much different from the current scientific consensus.  Economic models aside, economic empirics give us every reason to believe that (apart perhaps from environmental issues) today’s mixed economies with democratic capitalism have produced, and will continue to produce, entirely satisfactory outcomes.  Make of climate models what you may, there is lots of evidence that a) biodiversity is being hammered, and b) climate change will bring desertification, drought, and possibly coastal flooding to many parts of the world, among other dilemmas.  I don’t have a lot of faith in the exact predictive powers of climate models, or for that matter economic models, but uncertainty about outcomes should make us worry more not less.  Uncertainty usually has two tails, not just one.


The key difference between climate models and economic models is that economic models include volition, human choice.

CO2 molecules cannot change their minds in response to higher prices or different social norms, and act differently.

I'll keep this short, though I've thought about this a bit: the best boundary between science and social science is the boundary between the inanimate and the animate and cognizant player.

It is difficult to make a valid blanket statement about 'models' in general. Some models are more sensitive to their parameters than others. (Indeed, some models one could construct would be inherently unstable / ill-posed.)

The criticism of climate models as I understand it is not that they are getting the physics (that they actually model) wrong, which as other commenters are alluding is hard to do. The criticism is that they are so sensitive to parameter estimates with huge error bars (or parameters that are assumed to be constants when they may be dynamic, or...etc) that their signal-noise ratio is meaninglessly small.

I'm not sure I can agree that with Tyler that this sort of uncertainty should "make us worry more". We need a valid reason to "worry" in the first place and if the models are GIGO then we would not really have one.

Sonic, wasn't the important mental leap from Conrad Lorenz's weather models that "extreme sensitivity to initial conditions" was not just in the models, it was in nature too?

Uncertainty about outcomes should make us more concerned about possible bad outcomes, but should make us less confident in any particular policy's ability to prevent them.

Yes, obviously the path to fame and riches in America for the past eight years has been to predict dire consequences arising from global climate change.

It worked for one guy. One guy! For the rest, not so much. I haven't noticed any huge amounts of government funding, for example, being ladled out to climate change researchers. Corporate America not exactly embracing them either.

Either climate change researchers are very poor at predicting what will bring them economic gain, or they're following where the data leads them.

"uncertainty about outcomes should make us worry more not less."

This is a key point and one that climate skeptics seem to misunderstand.

Marty Weitzman has shown that there is a small, but real, chance of a true catastrophe and that chance only grows if we think the climate models are noisy predictions of the future.

"Economic models aside, economic empirics give us every reason to believe that (apart perhaps from environmental issues) today's mixed economies with democratic capitalism have produced, and will continue to produce, entirely satisfactory outcomes."

It is rare to see such a strikingly clear statement of how we got into our current mess, and how easy it is to rationalize policies that will just keep pushing us to the brink.
Rephrased, what Tyler is saying is “So long as we disregard the predictions of the imminent collapse of the global systems that sustain our basic needs and provide the free services that our extractive economy depends upon, everything is working fine! Carry on.†

I appreciate the concern in the following sentences, and it is too easy to dismiss this posting a platitude. I just want to know how the vast majority of the Earth that is not benefiting from participation in the democratic capitalist system can be dismissed with a parenthetical statement.

Climate models are really simulations. The equations for fluid motion and energy transfer are solved numerically on a grid using finite difference methods to move forward in time. Some of uncertainty arises from inadequate resolution but the most important source of uncertainties is from is specification of things like cloud formation, ocean temperatures, etc. Most predictive economic models are statistical fits to data with some assumptions about the relationship between variables. I think the assuming that climate models are "very similar to economic models" leads to misunderstanding of what the uncertainty in climate models mean.

As a high-school dropout who has more intelligence than ambition, I'll put it to you this way: both the "science" of climate change and the "science" of economics have failed to impress me with the rigor of their empirics.

At a scholarly site such as Climate of the Past it appears to me that half the papers are summaries of what happens when you tweak computer programs and datasets this way or that. Past posts on this forum of similar tendencies in the sphere of economics speak for themselves.

Should serious policy makers stake their careers on such thin reeds? It seems foolish to me.

When Rich posted this question on the other thread, I was ecstatic, and hoped that Tyler or Alex would answer him. Alas, I think Tyler misses (what I take to be) Rich's main point.

Tyler (if you're still reading), I know you are not as rabid a free marketeer as some of us, but I think you would generally endorse this history:

In the 1950s, the "consensus" among the most credentialed economists--the ones who taught at the best schools, the ones advising presidents, and the ones with the most prestigious publications--was that free markets, left to their own devices, could lead to human misery. At the very least, fine-tuning by government could greatly improve living conditions for future generations. Indeed, Noble Laureate Paul Samuelson declared as late as the late 1970s (right?) that the Soviet Union might soon overtake the US in economic output.

It's true, there were some "deniers." But most of them were cranks like Ludwig von Mises and Friedrich Hayek who couldn't even put their crotchety objections into a model. In fact, that was part of their whole point--they objected to the whole enterprise of modeling, saying it couldn't capture all the relevant variables, blah blah blah. Sooo 19th century.

Admittedly, there was a big gun here or there who came out against the consensus, like Milton Friedman. But even though he did publish some smart critiques in the peer-reviewed literature, it was soon apparent that he was just trying to be rich and famous by appealing to conservatives. He spent most of his career writing pop books and giving speeches to the choir, rather than engaging in serious research like the true scholars at MIT and Harvard. (I hear that Friedman took money from the denier Volcker Fund, proof that he wasn't objective.)

When you boiled down the rhetoric of these planning deniers, it usually wasn't a scientific objection to the rigorous mathematical approach of Samuelson et al. Rather, it was a knee jerk political reaction. "Waaa, I don't want to pay higher taxes. Waaa, I'm afraid of jack-booted thugs running the economy." Oh please.

[/analogy not too far from reality]


One final point: I think you are totally dodging the important question here, Tyler, when you say:

I don't have a lot of faith in the exact predictive powers of climate models, or for that matter economic models, but uncertainty about outcomes should make us worry more not less. Uncertainty usually has two tails, not just one.

I think what Rich may have had in mind is this: If we are uncertain about macro models, should that make us more willing to give Paulson et al. the power to run things? I say no, do you?

If you agree the answer is no, then why would our uncertainty about the effects of humans on the climate, cause us to give more power to the government to regulate our lives? Since when do we give politicians the benefit of the doubt?

One thing held in common by all computer models: They rely on data. A reliable model would produce an accurate forecast with good data.

It seems to me that, given good data, economic models would could be useful but still prone to go awry because of human elements, but I could be wrong.

Climate models are, in fact, extremely difficult to produce because of the complexity of the system. As I have surveyed the literature available online I have discovered that some think there is a simple linkage between the temperature of the Sun at any given time and the climate on earth. Other models give little weight to Sun temperature. I have also read of a theory that the total rainfall on the face of the earth is nearly constant, but that there is no data available to prove or disprove this theory. It seems like total rainfall on the planed might be an important statistic to any climate model, but we are incapable, so far, of measuring this.

I have to vote for economic models over climate models. Economic systems are complex, but we seem to have learned a lot about collecting good data and determining which numbers are salient to the model.

I embarked on a 'Who is really right" campaign when I was director of public policy analysis back at Enron and had the advantage of getting the alarmists to cooperate because Enron was "green." (The skeptics are always ready to cooperate....) I worked with probably 15 scientists and have over 150 emails for when the history of the debate is written some years from now. One big name middle-of-the-roader/alarmist was particularly helpful, and he was a paid consultant.)

Maybe the most important thing I learned is the gulf between the modelers and the empiricists. The modelers have much higher sensititity estimates than the empiricists. Indeed, before slicing and dicing the explanations, we do have the fact that the world has warmed remarkably little since the end of the Little Ice Age in the mid-19th century compared to what models predict given the buildup of GHGs in the atmosphere today. Some say ocean delay and aerosol offsets and such, but the other explanation is that the positive feedbacks that get the predicted 2x equilibrium warming from 1.2C (neutral feedbacks) to the predicted 3C (IPCC mid-range model average) are overstated badly.

So here is the crux of the matter. There is no "skeptic" model and there cannot be because the microphysics of climate that MIT's Richard Lindzen and some others believe to be reality cannot be incorporated into the macro models. Models simply do not have the resolution and computing power to have a "Lindzen" version.

What is fascinating to me about this debate is the micro-macro dichotomy. It might turn out that Lindzen is the "F.A. Hayek" of the debate because he was right and he was micro oriented.

By the way, Lindzen is the top theoretician in the debate. My middle-of-the-roader often remarked how Lindzen was the smartest guy of them all but was a theoretical risk taker too.

Hope this helps....

What is interesting is that there is an objective and rational examination regarding present climate modelling. That a group of diverse posters can discuss this subject without devolving into ad hominem is extraordinary.

Rob Bradley, I meant only that climatology has proceed further since Enron collapsed in 2001. The real evidence keeps mounting.

Your contention that models aren't perfect is shared by everyone, but your statement that there is a "microphysics of climate" that cannot be incorporated into the "macro models" leaves me puzzled. Would you please point to the section of the 2007 IPCC 4th report that explains this? Are you talking about feedbacks? Surely there is some progress on this front, (although there may be a long way to go,) and so the possibility of modeling has not been rejected.

You also appear to assume that the incorporation of the "microphysics of climate" (whatever it is) will PROVE the skeptics' position, instead of disproving it. You adduce no evidence other than a selection of some results, plus the fallacy of argument from authority. Which argument itself is supported by nothing but the assertion that "Lindzen is the top theoretician in the debate."

(I also want to point out an analogical misconception. Returning to Joan's description: since the climate models are in fact solved as cells or grids, characterizing them as "macro" is an analogy mistaken from economics.)

"Uncertainty usually has two tails, not just one."

True. And the most catastrophic tail is not global warming , its global cooling. I would go so far as to say that global warming could be considered a good insurance policy against another ice age.

"Tyler why don't you call it climate empirics? Or perhaps better, complex physical system empirics: The classroom assignment would be to try to find one complex physical system which can receive a continuous extra input without flipping into a new dynamic state. Are there any at all?"

Huh? Have you ever heard of homeostasis. You apply some input to a living thing and the body adjusts to the input. The input can be continuously applied. In fact any complex system which has negative feedback will have this property. This is the basis of Gaia theory. Hell an even better example is the climate system itself. Increase carbon dioxide and this acts as a fertilizer for plants which in turn suck up more carbon dioxide. This is one of the reasons Freemon Dyson does not believe in global warming.

The amount of C02 coming from sinks and the amount of C02 coming from sources is very nearly equal. Why exactly should they be equal? The fact that they are indicates the existence of a negative feedback.


What does Freeman Dyson know about global warming? Real Climate did a perfectly good deconstruction of Dyson's article in the NYRB. But Dyson is hardly a research scientist working on global climate issues. We might as well ask what his views on oncology are, to set policy for cancer treatment.

Plants actually reduce their uptake of CO2 in an increased CO2 environment.


"The modelers have much higher sensititity estimates than the empiricists."

That's flatly incorrect. Compare Table 8.2 to Figure 9.20 in the IPCC AR4 WG1 report.

If anything, it's the opposite. None of the GCMs run at the high sensitivities included in the "fat right tail" that Weitzman is worried about.

"Indeed, before slicing and dicing the explanations, we do have the fact that the world has warmed remarkably little since the end of the Little Ice Age in the mid-19th century compared to what models predict given the buildup of GHGs in the atmosphere today."

That's also incorrect; GCMs hindcast post-1850 warming rather well. See chapter 8 in the report, starting with FAQ 8.1. See also Rahmstorf et al.'s 2007 comparison of 1988 projections in Science.

"By the way, Lindzen is the top theoretician in the debate."

That's kind of a bizarre statement. Lindzen has hardly contributed anything to the climate sensitivity literature since his 2001 "infrared iris" paper that was debunked.

"But actually the case today on feedback effects being less than strongly positive has grown significantly since 2001,"

On the contrary, climate sensitivity publications since the IPCC TAR have continued to accumulate in the usual Charney range.

"and the temperature anomoly between predicted and real has grown too."

The current temperatures are still squarely within the error bars of the GCM predictions. Indeed, you can see larger deviations between models and observations in the past. Take for instance the 1940s, when observed temperatures were higher than the models hindcast. You don't see people claiming that the 1940s disprove the climate models and demonstrate that there is more warming than the models predict. But somehow they feel they can do that for the 2000s.

"Have you ever heard of homeostasis. You apply some input to a living thing and the body adjusts to the input. The input can be continuously applied."

"...indicates the existence of a negative feedback."

You beg the question, then you assume it is an absolute.

Negative feedback in systems is NOT guaranteed for every possible input, and it is NOT guaranteed for ever-increasing amounts of regular inputs.

Without negative feedback, there are no complex natural systems which can survive an ever-increasing amount of any natural (or exotic) component without flipping into another state. For example, almost every chemical naturally found in the body is toxic in ever-increasing amounts.

But even with negative feedback, stability on a higher continuous throughput isn't guaranteed, by any means. In the case of carbon dioxide, the results show that it begins to inhibit plant growth beyond a certain point. "Moderation in all things" is almost a complex systems law.

The question, as before, is the existence of feedback, negative and positive, in climate.


"The fact that there is little to no discussion of the sub-grid scale problem of models"

What are you talking about? Read pretty much any GCM paper with the world "parameterization" in it and you will find plenty of discussion of sub-grid scale problems with the models.

"and how this offers downside to the strong positive feedbacks"

Sub-grid scale physics errors, e.g. in cloud dynamics, can lead to even stronger positive feedbacks as well as less strong; it's the two-tails issue again.

"There is an active peer-reviewed literature supporting less positive feedback effects."

If you're going to bring up authors like Lindzen and Schwartz, there is an even larger literature on why such papers are wrong.

The sad fact is that the last decade or so of research hasn't compellingly reduced the uncertainty in climate sensitivity in either direction.

"The 3C-3.2C for 2X--one top scientist I know says that accumulating evidence is for 2C--a good 50% below the IPCC."

I can point you towards "top scientists" who think the evidence is accumulating for 4 C. What's your point?

Personally, 2 C wouldn't surprise me, and neither would 4. The IPCC canonical range is 1.5-4.5.

"And it gets back to the fact that we have little anthropogenic warming compared to what we should have given a century of GHG buildup,"

That "fact" is remains as wrong as it was the first time you asserted it. Please consult the references I cited.

"and the fact that warming seems to have stalled in the last five to 10 years."

See my response to that, as well.

I just want to clarify a few of the points Rob Bradley has been making. (Full disclosure: Rob founded the Institute for Energy Research, and hired me last year for it. That's why I am going to speak so confidently about his views, because I know them well. FWIW, I never worked for Enron. :))

The most important point Rob has been making is that an "idiot check" look at the history from pre-industrial times to the present suggests that the IPCC climate sensitivity best-guess may be very pessimistic. So that's what Rob meant by contrasting the models with the empirics.

To give a flavor of this gap, we can use the AR4's own numbers. (The following argument is taken from page 10 of my paper [pdf] on Nordhaus.) The IPCC reports a best guess of +1.6W/m/m of total radiative forcing (including solar activity, aerosols from man and volcanoes, etc.) through 2005 (p. 205 of the AR4). This total forcing went hand-in-hand with an estimated warming over this period of only 0.7 degrees C. Now starting at pre-industrial times, if we instead had just doubled CO2 (and not done any aerosols etc.) then the estimated forcing would be +3.7W/m/m (p. 140 of AR4). So that means even on its own terms, there has been an "observed" (if you will) medium-term climate sensitivity of 1.6C, just over half the best guess of 3C reported in the AR4.

Now before people have a hissy fit, give me a chance to show I understand the IPCC position. (And then after I say this, feel free to say I'm an idiot...:)) The definition of climate sensitivity involves the LONG-run equilibrium impact on temperature; even if we stopped all forcings tomorrow, there would still be extra warming in the pipeline because of positive feedbacks induced from the changes humans have already effected. I.e. the observed warming of 0.7C would rise, even if we stopped pumping more CO2 into the air tomorrow.

I am not claiming that the models are internally inconsistent; I'm not saying my above argument just blew up the models from within, or showed that their climate sensitivity estimate is too high. My point is simply that when the IPCC talks of the "long run" impact of doubling CO2, even according to its own calibrations, the long run is longer than 100 years.

Let me put it to you this way. If industrialists had been proposing to build factories etc. back in 1890, the climate scientists (using AR4 knowledge) would have said, "Well if you do that, keep in mind the impact on temperatures for the kind of forcings you're talking about--plus the volcanic eruptions that we magically know will happen--through the year 2005 will cause an equilibrium global warming of about 1.3C."

But the greedy, self-generation-centered industrialists go ahead anyway with their plans. And thus far they would have seen only half the predicted warming. Now it's true maybe the other half is still in the pipelines, but the point is, when the general public hears how accurate these "hindcasts" are, I think they would be very surprised to see how much of this calibrated, back-tested warming is still (supposedly) waiting in the wings.

Last point, I have taken the IPCC's own estimates of aerosol forcings at face value. It is my understanding that there is large uncertainty on these, and that in order to get even the 50% climate sensitivity match (with observed warming) I describe above, you need to choose the aerosol forcings in order to best fit the model to historical trends.

Putting it in other words--and this is more faithful to Rob Bradley's point, I think--if we just relied on the historical increase in CO2, and the historical increase in global temperatures--then the "observed" medium-run climate sensitivity is even lower than the 1.6C I mentioned above.

Big-picture, news you can use, take-home point: I think the general public believes that climate modelers are doing a simple extrapolation when they get their results. E.g. "in the past CO2 went up by such-and-such, and temperature in turn went up by such-and-such. So if these trends continue, bye bye San Francisco..."

But that's not really accurate. The simple observed trends in CO2 (or even all forcings) and the observed temperature increases do not match up with the AR4's best guess climate sensitivity. Now it's true, Gavin et al. can give good reasons for why that's the case.

But in the context of this thread--which was getting at the fact that the "smartest guys in the room" in the economics profession were enamored with their cutting edge models and ended up being totally wrong on very important things--there could be a similar problem here. This isn't a rigorous point, I grant you, but I am not reassured by the tremendous confidence with which some climate scientists (I'm not saying Gavin here) say that they know how things will turn out in 80 years. Come on! This is similar to Hayek's notion of "the fatal conceit." A bunch of really smart guys think they can run the world because their models show them how to save humanity from itself.

We can debate the science until we are blue in the face, but let me ask two questions.

If the science is really settled along IPCC lines even with the huge uncertainty ranges, why do we have this undertow of dissent that is keeping a number of voices from joining the "skeptic" camp--at least skeptic of climate alarmism? A number of scientists are keeping quiet about the concerns they have--that is a fact that I have seen first hand at two major Texas universities, and I imagine it is also the case at a lot more places.

Any why do top alarmist scientists avoid debating top skeptic scientists? Why don't we have a two-on-two debate at the Heartland Conference in March 2009, and arrange for C-SPAN to show it? The "skeptics" could take the postion that the warming range is below the IPCC model range. Any takers that you know of from the alarmist side?

And on real world warming, we are 150 years out of a Little Ice Age and for 2007/2008, say, we are about 1F higher globally. And how much of this is anthtropogenic? And we are going to see 2x in a couple of decades from pre-industrial and what is the anthropogenic warming likely to be? Less than 1C? Why isn't the warming accelerating?

Is it crazy to suggest that the bottom of the IPCC range may be the top of what the real answer will turn out to be? Is it not fair to say that mainstream climate science has been badly politicized?

For some of us who have been following the neo-Malthusian 40-year alarm (dating from Ehrlich's The Population Bomb), it would seem that a little humility is in order on what we don't know and the fact that market failure must be balanced with analytic failure and government failure.

"why do we have this undertow of dissent?"

Because Exxon and others have, from the crudest short-term profit motives, been funding so-called "think tanks" and astroturf groups to generate that undertow, consciously using as a model tobacco company responses to another inconvenient truth. Do some googling on terms like "Exxon astroturf".

Plus climate change is an inconvenient truth. Many Americans, with that relentless optimism that is such an attractive part of the national character, find it really hard to look unpleasant facts in the face and will listen to anyone who tells them they don't have to (the popularity of that "line about "the American way of life is not negotiable" is a classic example. Who are they going to negotiate it with - the rising sea levels?).

Plus of course the Right is full of batshit crazy conspiracy theorists telling themselves they are "brave contrarians".

Oh, on the ExxonMobil criticism, I would focus instead on Enron and what it was doing to promote climate alarmism. I have detailed this at:

I have a book coming out next month, Capitalism at Work: Business, Government, and Energy that gets into the history of Malthusianism and Enron/Ken Lay's climate alarmism in some detail. Climate alarmism has created a number of unintended consequences, and one of them was Enron's Kyoto push.


"I think what Tyler will find when he spends more time on the debate is that the balance of evidence is easily toward the bottom end of the IPCC warming range,"

Why is it that you repeat this assertion over and over without ever citing any evidence in its support?

Two quick points:

(1) I don't know if Rob Bradley has more recent work to cite, but Mendelsohn and Neumann wrote a book on US impacts. (The listed publication date on Amazon is 2004, but I think that might be a reprint? I thought it had come out earlier, like in 2000.) In the book they find that there are net benefits up to around 2.5C, and then the net benefits shrink above that. (I forget at what point it turns into a net harm, maybe 3C but don't quote me on that.)

Incidentally, Rob emailed Mendelsohn last year and asked if his work extrapolated to the entire world (not just the US, where they have the most detailed impact studies) and Mendelsohn said yes, that their latest work was consistent with the idea that 2 - 2.5C of global temperature increase would shower net benefits on world. (I saw the email.)

Now let me confess that a year ago when I started work on my paper dealing with Nordhaus' model, I was prepared to just stipulate the damage estimates from stipulated climate change. After all, how the heck was I supposed to pick one damage estimate over another, since my background was in capital theory?

But I was more confident in Mendelsohn et al.'s estimates when I read what things they had tweaked. For example, in assessing the agricultural impact of warming, they would allow the farmers to change the crops they planted in the face of rising temperature etc. At the time, the most drastic impacts were being generated by studies that assumed farmers had to keep planting the same crops, even as conditions changed. Another hilarious example: Mendelsohn's commissioned study on the recreational sector got much lower damages than other studies, because his didn't just focus on winter activities (skiing etc.) and how they would be hurt by global warming; he also focused on summer activities (boating etc.) and how they would now have longer seasons. Again, seems pretty reasonable.

Now like I said, I think this stuff I am talking about was true when they first issued their book, back in 1999 - 2001 range I believe. Presumably the "alarmist" impact studies aren't as crude as the ones Mendelsohn et al. were reacting to.

(2) I understand there are a lot of nutjobs saying over-the-top things like, "This is all a hoax cooked up by Al Gore to run the world." However, you've also got James Hansen saying people who fund skeptics should be prosecuted for crimes against humanity, and you've got Joesph Romm saying over at the Cato blog that unless we take immediate action to stabilize at 450ppm, we invite the destruction of modern civilization (not putting words in his mouth). So there are people making extreme statements on both sides.

There are, in my non-climatologist opinion, serious holes in the consensus view. E.g. isn't it true that the "greenhouse signature" (the differential warming of the surface versus the top of the troposphere) in the tropics isn't quite what it should be, if the GHG forcing is responsible for much of the 20th century warming? And yes, I've read Gavin's (I think he wrote it) explanation at RealClimate, but I still think it's fishy that the warming preceded CO2 increases by hundreds of years, historically.

So Rob Bradley (and my) point is, in light of these holes--and these holes, even if I've understood them properly, are not fatal to the theory--it is also significant that the alleged climate sensitivity has only revealed itself by about 50% so far at best. I.e. you've got some PhD experts (like Lindzen) saying, "This consensus is wrong," and then you've got many more PhD experts saying it's right, and so if an outsider is trying to judge, it is significant that thus far this dangerously high sensitivity of the earth's temperature to GHG emissions has yet to be observed. Again, I understand that the observations are consistent with the models, but the models maintain this high sensitivity to CO2 by calibrating other factors (such as aerosols) to partially mask the alleged effects of CO2 so far.

So what Rob was getting at in the above ("is it so crazy...?") was that if Lindzen et al. are right, and the consensus is spurious, scientists in 50 years will probably wonder why there was such confidence in the consensus models, when the empirical observations THUS FAR have not demonstrated this high sensitivity.


Can you please point me to more reading on the "hot spot" discussions? Specifically, why I was confusing two different things? I want to understand this distinction so I don't make any similar mistake in the future...

One last comment about this point you made:

You can equally well say that empirical observations THUS FAR have not demonstrated or even favored low sensitivity. Indeed, from the shape of the estimated climate sensitivity probability distributions, it's been easier to observationally disfavor low sensitivities than high ones.

This is pretty funny, and I'm not trying to be a smart aleck. We are arguing over the "estimated climate sensitivity probability distributions here, after all. That's the very issue under discussion. Lindzen thinks the distributions put out by the IPCC are way too high.

And now you are saying that the observed low warming so far, disproves low estimates more than it disproves high estimates? What in the world would the temperature data have to look like, if (say) aerosols on net were positive forcings, and the climate sensitivity were 1C, and there were no significant positive feedbacks? Wouldn't the temperature data look pretty much like what we've seen historically?

Now you can say, "Yeah but that doesn't fit the models!" I know, and so does Lindzen. He thinks the models are wrong.

So you're sounding like a fundamentalist who proves the authenticity of the Bible by pointing to a passage from the gospel of John.

(I hope you realize I'm making an analogy just to show why I didn't like your particular quoted response above. I'm not saying the evidence for your view is as strong/weak as that for the Bible.)

Lee Arnold said:

Bob Murphy, please point out in the Mendelsohn and Neumann book where they discuss the global warming effects upon U.S. wildlife biodiversity.

I don't know that they discussed that; I never claimed they did. (My office literally got moved today, and so my books are all in piles right now. I don't see the book handy to check if they cover that issue.)

If I might read into your question, I assume you are saying, "Global warming is destroying wildlife biodiversity, and any alleged benefits to summer water parks will be trumped by mass extinctions."

That's a big issue, and we're not going to get anywhere arguing it here. I brought up Mendelsohn only because Rob Bradley had cited him as an expert who is not as alarmed about moderate warming as others, and then someone asked Bradley for a cite.

The reason I personally think Mendelsohn is important, is that he showed how a lot of the more alarming studies assumed very little adaptation in response to warming. Now it's true, just because Scientist A may have overestimated the damage to farmers in Iowa, that alone doesn't mean we should embrace global warming with open arms.

Bob Murphy, both you and Rob Bradley have expressed the point of view that you can't get anywhere arguing about things -- and then do a good deal of it.

Mendelsohn's work does not appear to touch upon ecological issues, so it's no wonder he would not be alarmed about moderate warming.

Now, let's get back to the original discussion.

Tyler Cowen's post at the very top expressed the point of view that, given the real evidence of effects upon biodiversity and desertification etc., "uncertain outcomes should make us worry more not less."

Despite questions about climate models!

Please take it from the top, and address this quote directly.

And let's hear whether you think economic models used by Mendelsohn or anyone else are more valid than the climate models.

I replied to your comment above, but the response is held up in the spam filter because of the hyperlinks I used. I'll try reposting later if it never shows up.

To PI:

I have offered several lines of evidence, the main one being the actual warming relative to GHG forcing we have over our heads right now. You trust the models. If 3C is a good number, why haven't we seen 1C or more of anthropogenic warming by now? Why is the warming deaccelerating rather than accelerating? Why do some top names on your side not want to go public with their concerns about models? I'm repeating myself, but I do not think you want to think that the "consensus" may be artificial.

I think a fundamental rethinking is in order, and maybe page 805 in the IPCC report is a good place to start.

I'm signing off, but invite you to read Climate Alarmism Resonsidered (2003) that is at
for my worldview on the subject.

Well guys, we've flushed a genuine denialist.

Of course what we are doing is suppressing science. He, on the other hand, is merely defending sceptical inquiry.

The risks that we might be wrong, and that temperatures might be a lot higher, a lot sooner, than we think, well he's not going to address that.

After all, we are simply Paul Ehrlich and the population bomb all over again.

Failing to note in fact, the real lessons of Ehrlich:

- human fertility dropped in a way that had never before occurred in human history, largely as a result of unprecedented changes in SE Asia

So you see problem => human action => (partial) solution

- much of what Ehrlich said re the environmental threats of human population are still true

- no one (I think) regards 12 billion humans with equanimity, but that's where we are going

- the main break on mass starvation has been better supply of food during famines, a highly 'non market' solution. Famine is not caused primarily by scarcity

So he makes a false analogy, sets up a straw man (none of us has said we are doomed, what we've said is we don't know, and we can't risk the consequences), and then ignores the real lessons (about positive human action) that resulted in part from the concerns about overpopulation.

Oh and by the way, he says the world isn't warming any more. that straight in the face of the scientific evidence.

Good to know that we are suppressing the truth.


I see my comment never made it out of the spam filter. Here it is again, sans hyperlinks (so less informative). I see Ben above later raised one of the points I made here.

"Can you please point me to more reading on the "hot spot" discussions?"

A mix of blogs, reports, and journal articles: RealClimate here and here, the 2006 CCSP report, Santer et al. (2005), Thorne et al. (2007), Allen and Sherwood (2008).

"Specifically, why I was confusing two different things?"

The discrepancy between models and observations regarding tropical tropospheric temperature trends is real (although we don't know whether the discrepancy is due to the models or observations). But those trends are not "the greenhouse signature"; they should be there if the warming was due to other causes too. A signature is something unique you should see from greenhouse warming but not other kinds of warming. The actual greenhouse signature is stratospheric cooling, which is observed in reality.

"And now you are saying that the observed low warming so far, disproves low estimates more than it disproves high estimates?"

I have no idea why you keep claiming the current warming is "low", other than continued confusion between the transient and equilibrium response. The observed warming is most compatible with sensitivities in the IPCC range, and less compatible with sensitivities outside that range.

And yes, you can disfavor very low sensitivities easier than very high sensitivities. That's why the climate sensitivity pdfs have heavy right tails but not left tails. The reason why is interesting. If you approach the problem from the perspective of estimating individual feedbacks and then adding them up, the fat right tail comes in because of nonlinearity between feedback and response; see Roe and Baker (2007). If you approach the problem from the perspective of using total warming to constrain the total feedback, the fat right tail enters for different reasons, involving the amount of noise in the system relative to the forcing, the long response time of the oceans, and the existence and uncertainty of other forcings.

"Now you can say, "Yeah but that doesn't fit the models!" I know, and so does Lindzen. He thinks the models are wrong."

So? If you think the models are wrong in some unspecified way, then you have no way of saying whether climate sensitivity is high or low; there is no model independent way of estimating it. (Your attempts correspond to using an extremely poor linear model with no heat capacity.)

If Lindzen thinks the models are wrong, fine. Then he should say that we don't know what climate sensitivity is, in which case you're back to Tyler's two-tails argument. (Sensitivity could be lower than the models say, but it could also be higher, and the latter error is worse from a damages point of view.) More importantly, he should give an argument why the models are so wrong that their sensitivity estimates are way off. Considering that sensitivity mostly boils down to measuring the response and the response time (barring new feedbacks that kick in later), and you can do that with two equations, it will be very difficult to make that case. (That is, there are both physics-based and observation-based reasons to think that sensitivity is in the IPCC range.)

If Lindzen or anyone else says that climate sensitivity is lower than what the models say, they really mean that they think the models are wrong and they know why: they have some reason to believe the models err in one direction but not the other. Then it's incumbent upon them to give an argument supporting that. Lindzen gave one, the infrared iris, and it turned out not to be supported by the data. If he has another, I haven't heard it.

Note that you get sensitivity estimates in the IPCC range regardless of whether you use simple energy conservation models and compare them to data, or if you use big AOGCMs and try to calculate them from physics. You also get consistent answers if you look at the instrumental record, volcanic "natural experiments", and paleoclimate data. The uncertainty in climate sensitivity has hardly changed since the Charney report in 1979. I listed some of the fundmental reasons why above.

"So you're sounding like a fundamentalist who proves the authenticity of the Bible by pointing to a passage from the gospel of John."

Wow, can anyone present a skeptical climate argument without comparing their opponents to theists?

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Another ice age" is in the tails of the distribution for thousands or tens of thousands of years from now, not the next century. If you're so worried about another ice age, you should be arguing that we should save our fossil fuels for then when we need it, instead of using them up now when we don't.

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