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Betting on climate change

Filed under: — group @ 14 June 2005 - (Romanian) (Ukranian)

Guest contribution by James Annan of FRCGC/JAMSTEC.

“The more unpredictable the world, the more we rely on predictions” (Steve Rivkin). The uncertainty of an unknown future imposes costs and risks on us in many areas of life. A cereal-growing farmer risks a big financial loss if the price of grain is low at harvest time, and a livestock farmer may not be able to afford to feed his herd if the price of grain goes up. One way to reduce the risk is to hedge against it in a futures market. The two farmers can enter a forward contract, for one to deliver a set quantity of grain to the other for a fixed price at a future date. And indeed farmers do routinely use futures contracts to reduce their risks.

Weather is a major uncertainty affecting our futures (it is one of the main sources of risk for those farmers), and weather futures markets can be used to hedge on the monthly/seasonal time scale. In the longer term, changes in climate will also bring a range of costs and benefits, and a market in climate futures would allow anyone who is vulnerable to hedge against these risks too. But how can we assign fair prices to the contracts? One obvious starting point would be to look at model predictions and historical data. This is essentially what the IPCC does, eg with its estimate of 0.3+-0.1C /decade for anthropogenically-forced warming over the next 20 years in the absence of substantial mitigation of emissions (at the “likely” level, ie 66%-90% probability). If we want to work out the probability of global mean temperature being warmer 20 years from now, we could take this 0.1C in uncertainty of anthropogenic forcing (which I will assume to be 1 standard deviation of a Gaussian deviate), and add another 0.15C of independent natural internal variability, which gives a combined estimate of 0.3+-0.18C warmer overall or about a 5% chance of cooling. To this, we can add perhaps another 5% due to the possibility of a large volcanic eruption at the right time, making 10% in total. Now before you all write in telling me my assumptions are wrong, the real answer should be 20%, or 4%…that’s precisely my point. Of course my simplistic assumptions can be questioned, and I could have performed a more accurate calculation, but however carefully it is approached, this sort of forecasting inevitably involves subjective judgement and assumptions. The IPCC estimate depended on expert judgement, so someone who believed that they markedly overstated the anthropogenic influence might deduce that the chances of cooling were closer to 50%, and an advocate of the more extreme solar forcing theories might even confidently predict significant global cooling. So ultimately it seems like we have no really firm, provably correct and objective basis for setting a market price.

Fortunately, there is a solution to this problem. Efficient market theory states that the price in a free market should accurately reflect the aggregated information that is available, and so in 1990 economist Robin Hanson noted that we can turn the problem around: use the market as an aggregation mechanism to tell us what the odds are on any particular event. This, he claims, could be much more effective than relying on panels of government- (or self-)appointed experts and media pundits to predict the future, since the financial penalty would keep the incompetent away from the marketplace, and the real experts would be automatically rewarded for correcting any errors in the market prices. There is now a growing body of evidence in support of these theories, including for example the analysis of existing markets and results from a market which was set up specifically to investigate the idea further. Of course the market price does not exist in a vacuum: in practice, traders would perform calculations as I did above (but rather more carefully), and the market price would reflect their consensus. The market is a highly inclusive mechanism: rather than having to debate to the death, anyone who has an opinion can invest as much as they want (which will relate to their confidence), and in the long run the winners will drive out the losers. If I offer (and accept) bets on global cooling at 10:1 based on my rough calculation, someone who does a better job of estimation will probably be able to take money off me, earning a reward for their skill and effort.

The Foresight Exchange market is an internet-based game which runs an ideas futures market, covering a wide range of claims including a number of environmental issues. The basic betting mechanism is based on the concept of a pair of coupons labelled “Yes, claim X is true” and “No, claim X is false” (where X is a proposition whose truth is not yet known). These coupons can be bought and sold individually on the open market, and a pair of them can always be bought or redeemed for $1 from the bank. When the claim’s truth is determined, the correct coupon is redeemed for $1 and the false coupon becomes worthless. The market price of the Y coupon is the market’s estimate of the probability of the claim being ultimately proved true. Here are a couple of examples – indicating how confidently (or otherwise) the market predicted the re-elections of Clinton and Bush in 1996 and 2004 respectively.

The Foresight Exchange is a small market with a limited number of players, and is certainly not perfect – I presented a simple analysis in a poster at the EGU in April, and I have also discussed a couple of claims in more detail here and here. (These are a slightly different type of claim, where the payout of the Y coupon depends continuously on the value of a variable at a specified future time – such as the global mean temperature in 2030. The N coupon pays $1-Y as before.) As Hanson’s theory predicts, by participating in the game, I have both improved the price on these claims (increasing market skill) and simultaneously increased my wealth (received a reward for my contribution). Although this small and non-serious market has noticeable inefficiency, a real money market could certainly hope to do better. So what are the drawbacks? It seems that there are are surprisingly few. Fears that rich vested interests could rig the market are generally misplaced: it would cost them a lot of money to do so, potentially much more than the price of influencing a few high-ranking experts. Robin Hanson’s pages have a great deal of discussion about the various criticisms of the idea that have been offered, and also how the basic idea could be extended to cover a wide range of applications.

I’ve recently been trying to establish consensus on the subject of global temperature rise, by arranging bets with sceptics who claim that the IPCC TAR is overly alarmist. Richard Lindzen was the first I noted who forecast here that over the next 20 years, the climate is as likely to cool as warm, and said he would be prepared to bet on it. However, when challenged to a bet, it turns out that he expects odds of 50:1 in his favour, ie he will only bet on the chances of cooling being at the 2% level or higher, far short of his 50% claim. My quick and dirty estimate above based on the IPCC TAR suggests that they would put the probability at more like 10%, so his offer actually appears to affirm the IPCC position. He also suggested an alternative bet (see here for my comments on this article) based on the amount of warming: >0.4C warmer and I win $5,000, <0.2c and he wins $10,000. Again, no-one who believes the IPCC summary would find his offer attractive, since it has negative expected value. The chances of winning and losing are roughly equal, so there does not appear to be any possible justification for his expectation of a 2:1 ratio (in his favour) in the stakes. In both cases, in contrast to his words, his position seems to be more alarmist than the IPCC!

The list of sceptics who have refused to bet against the IPCC position has grown steadily since then, and now also includes Michaels, Jaworowski, Corbyn, Ebell, Kininmonth, Mashnich and Idso (all my blog posts and related comments are linked from here). While I would be happy to take money off any or all of them, there is more to this than sceptic-bashing and a few high-profile bets – it could also perhaps result in a working market that would generate a true consensus and, furthermore, provide the socially and economically valuable function of allowing the vulnerable to hedge against risks.

[2005/06/24: comments on this post are now closed. This post generated a record number of comments: thanks to all those who commented. For any further follow up, you are recommended to the discussion on the newsgroup sci.environment – William]

125 Responses to “Betting on climate change”

  1. 1
    Dan Allan says:

    I’m afraid I have significant issues with efficient market theory, both logically and empirically. I will forego the empirical cases where it has failed, and stick to what I perceive as the logical problem.

    Efficient market theory presumes, in effect, that, given the incentive making money (and the fear of losing it) a “correct” consensus will inevitably arise. With enough informed players, so the theory goes, every publicly traded equity will arrive at its “correct” price.

    Unfortunately, the theory fails to consider the possibility of all players misperceiving a situation in the same direction. Consider a simple case, the familiar math problem: “how many people are required in a room such that the likelihood is greater than 50% that two will have the same birthday?” If you give this problem to a room of math students, you will not only get many incorrect answers, but they will fail to congregate around the correct solution, because most who get it wrong will conclude that the number is a good deal higher than it is (if my memory serves, the answer is 21, which is paradoxically low. If I’m misremembering, I’m sure someone will be happy to correct me). There is nothing magical about allowing people to bet on their answers that will force the market “price”, i.e., the concensus response to come out to 21.

    Climate science is obviously orders of magnitude more complex than this simple probability problem, so the possibility of miscalculation is presumably that much greater. And there is no logical reason to assume that the miscalculations will somehow “average out”.

    I am in no way a skeptic about global warming. But I am very much a skeptic about efficient market theory.

    [Response:I’m not going to defend efficient market theory to the death. But it seems to me that your example doesn’t work. If enough people bet on the wrong answer, people who bet on the right answer will make money/be rewarded. In that case, people would pretty quickly learn who to trust for the right answer – William]

  2. 2
    Chris Randles says:

    I know what you are getting at Dan re #1.

    I suspect people betting on 184 would not be happy to part with much money on that basis. I did a simple but wrong calculation that said 52% chance with 20 people. A better calculation came out at 50.7% with 23 people but that is also wrong. Anyway it is possible that the distribution of opinions could be skewed in the opposite direction to what you intended.

    Yes I agree there is a problem with the possibility of lots of people misperceiving the problem. However there would be a powerful incentive to spot such situations and this is likely to lead to fast absorption of new information. Research may become more focused which may be good for decision making but bad for the science.

    How should sceptics, who believe the uncertainty is greater than that implied by the IPCC, act? Perhaps they might be more inclined to take out insurance bets rather than to gamble to win in the manner suggested. Could this be what we are seeing from the mentioned people who refuse to enter sensible bets rather than them actually being more alarmist than the IPCC?

    Perhaps we also need a market to estimate the amount of uncertainty in the estimate of warming and/or perhaps the amount of natural variability over a multi-decadal period.

  3. 3
    Tom Fiddaman says:

    To amplify #1, individuals perform poorly on dynamically complex cognitive tasks, where feedback is remote in time and space, even in the absence of noise. In ordinary tasks this is not a big problem as one can learn through repetition and experimentation. Markets are similar – even if people make systematic errors in valuation, cash flow ultimately reveals the truth and errors are selected out within a time scale of at worst a decade or so.

    In a climate market, the revelation of information about the true state of the world is going to be slow, so foolish ideas could persist for a long time. Think of how oil markets have performed as signals of long run scarcity over the past few decades. There’s every reason to think that foolishness would arise if market participation is broad, given that people apparently don’t appreciate even the first-order dynamics of carbon accumulation – see Assessing Public Understanding of Global Warming.

    Seems to me that another big challenge would be to determine the methods and authority by which global mean temperature is judged, and maintain its integrity and institutional stability. The USDA maintains very strict control of information prior to crop reports, but the time scale of that problem is short. Perhaps the RealClimate team would agree to be sequestered on a remote island for 25 years if we gave them a really nice supercomputer.

    I don’t want to rain on the idea of a market though – if nothing else it could serve as a motivating aggregator of information and barometer of public opinion. That the skeptics won’t take fair bets is rather compelling.

  4. 4
    Doug says:

    If I were a famous scientist, I would not take the bet for fear that it would make me look silly. In the end, the money won wouldn’t be worth it.

    In a case like this with the high odds suggested by Lindzen, it sounds reasonable to me. If the alarmists have 95% confidence of warming, they should have 98% confidence of no cooling, so 50 to one odds is an even bet. (I’m being approximate of course, I’m no statistician, but by an even bet I intend to mean the expected value of the bet equals the size of the bet.)

    So I guess the question is: Just how confident are the alarmists?

    Probability of 2 people with the same birthday:

    For 23 people .507
    For 30 people .706
    For 50 people .970
    For 60 people .995

    Birthday problem answers from Fundamentals of Probability by Saheed Ghahramani p 41 ex 2.6

  5. 5


    A couple of things.

    1) The bet proposed in World Climate Report ( that you refer to as “Michaels” was made in December 1998 and pertained to the trend in monthly UAH 2LT global temperature anomalies from 1998-2007. As you mentioned on your blog (, we cherrypicked the starting point to illustrate just how warm the average El Nino-elevated global average temperature was in 1998 ( More than five years later you have come to us with an interest in taking the bet, and then act somewhat surprised in our decision to ‘pass’ on it. Obviously, it would be quite advantageous to be able to get in on a bet at halftime while holding the house to its pre-game line. Had you approached us in 1999 things would have been different.

    2) As far as betting what the next 20 years holds in store in terms of temperature change the time period is too short to really start differentiating between trends that are too close together. For instance, in your scenario of a 20-yr temperature change of 0.3ºC +/- 0.18ºC, assuming a natural noise level (observed standard deviation of detrended annual global temperatures from 1977-2004) of 0.085ºC, a statistically significant difference in the trend that leads to the lowest end of your range (a change of 0.12ºC) and the trend that leads to the highest end of your range (0.48ºC) doesn’t begin to rise above the level of noise until around year 16 or 17. Thus, given natural variability, 20 years is only enough time to start tell apart (in a statistical significant fashion) trends that are at least disparate by about 0.15ºC/decade.

    But, perhaps that is enough for wagering purposes.

    Recall that in their 2001 Third Assessment Report, the IPCC gives a range of temperature increase between 1990 and 2100 of 1.4 and 5.8ºC based upon the simulated output from 7 different climate models run under 35 different emissions scenarios – each of which the IPCC claimed as having an equal probability of occurrence. At World Climate Report, we believe, that instead of having an equal likelihood of occurrence, that the temperature rise during the next 50 to 100 years will lie closer to the low end of the IPCC projected range than to the high end of the range and thus the overall impacts will tend towards the modest rather than the extreme. We have written this opinion numerous times (most recently here, However, the high end of the IPCC range (or even higher) is often waved about in order to hype the issue and draw “concern” from the general public such that they stand behind efforts to limit carbon dioxide emission. We contend that the high end of the range in unreasonable. So perhaps there is room for a wager.

    The IPCC temperature change range from 1990 to 2100 (11 decades) represents a range of rates of temperature change of 0.13ºC/decade to 0.53ºC/decade. Given the theoretical 20-yr signal-to-noise threshold of 0.15ºC/decade established above, in 20 years, a temperature trend that lies between 0.12 and 0.25ºC/decade (in the bottom portion of the IPCC range) should be able to be statistically differentiated from a trend that lies between 0.40 and 0.53ºC/decade (in the top portion of the IPCC range).

    Since the IPCC contends that all emissions scenarios are equally likely, there should be equal likelihood that the rate of temperature change should fall within either of the two ranges I just defined. Therefore, we need not take the odds to be any different from 1:1.

    In fact, let’s extend the low end of the low range infinitely downward, and the upper end of the high range infinitely upward (this should be amiable since there are numerous papers who suggest the high end of the IPCC range is too low and yet hardly extend the low end of the range downward) – doing so will allow the ultra alarmists and the ultra skeptics to have their positions included as well.

    Thus, the wager that I propose is as follows. Even odds. I (or whoever is on my side) get a future warming rate (as determined over the next 20 years) of 0.25 ºC/decade or less – indicating that I (we) believe that future climate change will be modest. And you (or whoever is on your side) get a warming rate of 0.40ºC/decade or greater-indicating that future climate change will be extreme. Anything in the middle (between 0.26 and 0.39ºC/decade) is a wash (since we can’t tell those values apart anyway).

    This should effectively separate out the alarmists from the realists.

    Does this seem reasonable?

  6. 6
    Brian S. says:

    I don’t understand the estimate “0.3+-0.1C/decade for anthropogenically-forced warming over the next 20 years” – the linked IPCC site ( says .1 to .2 C over the next several decades. Can someone clarify?

    [Response:I suspect that it should read 0.3 over 20 years, not /decade. Fact-checking is in progress…; completed. “/decade” should not have been there and is now struck out – William]

  7. 7
    Ed says:

    If there is a perception that necessary information is lacking, it devolves from making an investment decision into pure gambling based on chance. A skeptic of human induced global climate warming can reasonably view a bet on temperatures in 20 years as a game of chance, not an investment decision. That a handful of skeptics choose not to participate in this market may mean only that they do not play games of chance.

    [Response:Information isn’t lacking – there is lots and lots of it. Knowing which bit is correct is lacking. As to your skeptic, it would depend on what sort of skeptic they were. If they were a skeptic that claimed to have information – many of them do, many of them claim to “know” that future warming will be lower than the IPCC consensus – then it should be possible to find odds for a bet – as the post says. If they were a skeptic that claimed that we have no idea at all about the future – warming is as likely as cooling – then again, there is room for a bet, since if you think warming/cooling is 50/50, then presumably your odds on warming-by-0.3-over-20-years would be far less than 50%, which again means there is scope for a bet. That all the skeptics (and calling them a handful seems unreasonable – it includes some quite prominent ones) so far contacted won’t put their money where their mouth is seems quite significant – William]

  8. 8
    Tom Cecere says:

    Surowiecki argues in “The Wisdom of Crowds” that if the bettors are sufficiently independent that the result is nearly always equal to or superior to the result of the panel of experts. The auction market does not depend upon classical efficient market theory as much as it depends upon people’s natural caution — the fact that losing hurts more than winning gives pleasure. This tends to tone down “wild” claims that normally take precedence either in a group of similarly-minded people or in the race to be noticed by the media.

    You can have dollar limits on the bets, not take them from corporations, etc., but all you’re doing is interfereing with the information flow that helps the accuracy. If, for example, Big CO2 Inc. wanted to put a billion dollars down on global cooling, 2 things would happen — the web would be full of “sign up and take some money from Big CO2 Inc.” emails, and, more importantly, some of the people who think it’s a slam dunk for global warming might temper their predictions just a bit because some clown put so much money down on the opposite outcome.

    None of this, of course, changes the science; but policy depends upon good predictive models.

  9. 9
    Thomas Palm says:

    Tom, the problem with your scenario is that Big CO2 Inc might very well put down a billion dollar to push down the estimate, even if they suspected they would lose, because this reduced estimate of warming might mean less regulation and them saving more than a billion dollar.

    In theory one may consider that small CO2 inc might bet on high warming, because their more efficient industry emits less CO2 and would thrive with demands for reduced CO2 emissions, however, companies that profit from the current situation will have a lot more money available than companies that might profit from any future situation.

  10. 10
    Franz says:

    I think it is a good idea, but it is by far not a solution to every problem that global warming creates. One drawback is, that you can only bet against the consensus. That means if you fear your island is going to be submerged by the rising seas, and everybody expects that it will be, there is no way you can be reimbursed for your losses. One can only hedge against outcomes which are still unknown.

    It also leaves out those who are creating the situation in the first place. One idea might be a global carbon tax that buys insurance against identified and not identified risks of global change. Of course there is little hope to get anything like that implemented in the current political climate.


  11. 11
    Michael Jankowski says:

    Lindzen may have put his foot in his mouth (I don’t see a direct quote in the “Reason” article, so I guess it’s possible his wager invitation was taken out-of-context), but what about the rest?

    Most skeptics believe not only that much/all of the recent warming is natural but that we should be warming as part of the ascent from the LIA. Such people would want to leverage their bet in case “natural warming” occurs/continues. If the issue at hand is anthropogenic global warming, a skeptic will either want to remove the potential for natural warming from the equation or expect to be compensated more heavily for being correct.

    [Response: One of the classic fallacies advanced by climate change contrarians involves the notion of a ‘recovery from the Little Ice Age (LIA)’ or some variant on this theme. This is based on the simply false supposition that the LIA represents some perturbation to the climate from which it must naturally rebound. In fact, quite the opposite appears to be the case. As discused elsewhere on this site, modeling studies indicate that the modest cooling of hemispheric or global mean temperatures during the 15th-19th centuries (relative to the warmer temperatures of the 11th-14th centuries) appears to have been associated with a combination of lowered solar irradiance and a particularly intense period of explosive volcanic activity. When these same models are forced with only natural radiative forcing during the 20th century [see e.g. Crowley (2000)] they actually exhibit a modest cooling trend. In other words, the same natural forcings that appear responsible for the modest large-scale cooling of the LIA should have lead to a cooling trend during the 20th century (some warming during the early 20th century arises from a modest apparent increase in solar irradiance at that time, but the increase in explosive volcanism during the late 20th century leads to a net negative 20th century trend in natural radiative forcing). In short, given natural forcing factors alone, no ‘rebound’ from the LIA should have been expected at all. The only way to explain the upturn in temperatures during the 20th century, as shown by Crowley (2000) and many others, is indeed through the additional impact of anthropogenic forcing, on top of any natural forcing. – Mike]

    Let’s say I’ve got a friend who thinks he can bring rain with a song-and-dance and is willing to bet he can make it rain tomoorw. The forecast calls for an 80% chance of rain tomorrow – should I wager? Of course not. I’m pretty sure his rain dance won’t do the trick, but if Mother Nature is sending signals that rain is likely, I don’t want her rain to be confused with that of the rain dance. I’d much prefer to take that wager when the forecasts suggest a slim chance of rain (although 50% would be perfectly “fair”). Along the same vein, those who feel global warming is most/all natural variability shouldn’t/won’t take a straight-up wager unless the indications are that natural variability will be neutral or provide for a cooling effect. Are there any such forecasters, such as the solar cyclists?

  12. 12
    Dano says:

    Back to the point, no one wants to put their money where their mouth is, irrespective of whether a person believes in efficient market theory. This is the point: when cornered, septics won’t back their beliefs.



  13. 13
    Franz says:

    It may take some time until a market is set up, and betting about temperature might not be the most interesting one, because its connection to the damages is not yet fully understood. But it might be worthwhile to figure out the bets that are already going on.

    For example Exxon is extremely visible in lobbying against any carbon regulations and in financing climate sceptics. One could say that Exxon’s managers are gambling with the future of the company. Suppose there would be large damages that could be attributed to global change in 30 or 50 years. The scientist then could easily dissect any of the arguments which the sceptics are spreading now. There will be lots of documents and memos showing that the executives themselves did not believe the nonsense whose spread they payed. The McFagans of 2050 will happily go to court and bleed them dry. So how about put options on Exxon stock that expire in 30 or 50 years?

    If one wants to make money from expected climate change one could check the results of climate models. Which countries and areas might profit, where are the losers? How about put options upon real estate that we expect to become desert or on beach front property? The opposite ist probably harder to do. Can we identify areas that are barren now, and which might become green. Of course they should be stable enough that you can invest there.

    I think there should be some demand in consulting fonds in long term strategies that hedge against damages by global warming. It will take some time, but I think you are on the right track

  14. 14
    Dan Hughes says:

    This is somewhat off-topic, but along the lines of #5, #6 and #7.

    Who or what is “Big Co2 Inc” and “Small CO2 Inc”? IMO that are no such things.

    It is all of us who demand products and services that require production of CO2 that are the cause of the “problem”. And in particular those of us in the “first world” countries, and within these countries those of us with above-average incomes consuming our above-average number of unnecessary products and services (computers, books, CDs, Internets, individual transportation, recreation, etc. etc etc.). We are “those creating the situation in the first place”.

    In the end, all of society pays for all regulations; businesses do not pay for regulations in a vaccuum. And we determine which businesses profit and which do not. If you don’t want to support “Big CO2” don’t buy their products and services. That way you will not be among “those creating the problem in the first place” and won’t be paying a carbon tax either.

  15. 15
    Tom Cecere says:

    Thomas Palm –

    Thanks for your comments. It seems to me, however, that no board of directors would approve a market dominating purchase because it would either ruin the market and simply tie up the billion dollars until the bet is over, or, more likely, the odds would be so attractive that tens of thousands of us would trip all over ourselves to put down $100 to get $10,000 on what looks like a sucker bet.

    And, adding insult to injury, as the years go on and global warming becomes harder to deny, BIG CO2 will have the regulatory/legal costs as well. I just hope I’m around long enough to see the day!

  16. 16
    dave says:

    Re #6 decadal temperature changes

    Richard Kerr in Getting Warmer, However You Measure It (Science, Vol 304, Issue 5672, 805-807 , 7 May 2004) gives the surface trend as 1.7C/decade – reporting on Fu et. al. 2004. Fu himself cites the result of Jones and Moberg in the Tropical Glacier Retreat topic here at realclimate; their result gives 1.3C/decade in the tropics.

    I don’t know where Kerr got his 1.7 figure from. What is the “fact checking” William is doing to get this 3.0/20 years = about 1.5/decade number? How is this number baselined? This temperature calculation should also be rising decade to decade? Is it?

    [Response: This is obviously a slip of a decimal point. The warming trend over the last 30 years is 0.17 C/decade. -gavin]

  17. 17
    dave says:


    Please convert my numbers in this post. 1.7C should be 0.17C, etc.



  18. 18
    Glen Raphael says:

    Lindzen’s sort of lopsided bet seems appropriate and useful to me. Maybe a little agressive, but not hugely so. Bets like that would help us gauge how much confidence the alarmists have in their prediction. The big fear of a skeptic taking a bet is that the alarmists might turn out to be right by accident. The most reasonable skeptical view isn’t certainly in a particular prediction but merely some degree of confidence that you don’t have the certainty you claim and that the certainty you actually have isn’t sufficient to justify extreme measures.

    If alarmists are 95% confident that the IPCC temperature range encompasses the likely possibilities, they should be willing to offer 20:1 odds that the temperature will be in that range. If they’re only 90% confident, 10:1. If they’re only 66% confident, 2:1. But to offer no better than even odds on warming vs no warming is to agree with the strongest possible skeptical position – it’s saying that in your opinion we have no information better than flipping a coin as to whether it will get warmer. To turn around your criticism of Lindzen, your mouth claims 90% but your wallet claims 50%.

  19. 19
    Terry says:

    Looks like we’re in luck! Junkscience is working out the terms of exactly the type of bet you are talking about. Looks like they are pretty serious. They are actively soliciting comments, so you should contact them directly.

    Please keep us posted on what bet you arrive at.

    See: … search for “Lindzen.”

  20. 20
    Joel Kuni says:

    Your article is very interesting! If I understand your wager correctly, you want to bet that anthropogenic influences will be responsible for at least a tiny fraction of the warming of the earth that most people expect to occur in the next few decades.

    The fact that nobody has taken you up on this bet suggests the possibility that you are fighting a classic straw man. In other words, perhaps there are no scientists anywhere who assert that the activities of humans won’t cause at least a trivial, inconsequential, temporary amount of warming.

    Or maybe nobody is willing to accept your wager because nobody thinks you will be able to prove the extent to which any warming that occurs will be due strictly to the activities of humans and definitely would not have occurred if the last human on earth had dropped dead a century ago.

    Personally I would not accept a mathematical model as “proof” of such an extraordinary claim unless the model can accurately predict the daily temperatures in every major city on the globe at least five years in advance.

    All the models I’ve seen rely on the assumption that an increase in atmospheric greenhouse gases will necessarily increase the long-term average temperature of the globe and that all the other mechanisms that cause or counteract warming are understood and modeled fairly accurately. Yet that is the very issue under dispute.

    The fact that a particular model accurately predicts a warming trend does not in any way prove that the model accurately explains WHY the warming actually occurred.

    If my model predicts that my house will warm up after I light a match and the house does in fact warm up, it does not prove to me that the warming would not have occurred anyway due to some other factor I neglected to model such as the heat generated by the refrigerator. Nor does it prove that the house does not contain an air conditioner that will prevent the temperature from ever rising above a certain acceptable level.

    Without relying on a mathematical model to demonstrate that some of the warming of the globe has been due to human influences, what proof do you propose to offer when it comes time to settle the wager?

    By the way, it has not escaped me that nobody has accepted the wager offered by Chip in #5. His proposed wager and method of proof seem sound to me. Would those of you who refuse to accept Chip’s wager care to explain your reticence to the rest of us?

  21. 21
    Phillip says:

    One of the problems with this analysis is the statistics. I recall this MIT paper that maintaine that the probability distribution is highly skewed towards higher temperatures.

    Although it looks at the IPCC horizon of 2100, rather than simply 20 years ahead, it implies there is effecively zero probability that the global mean temperature might be equal to or lower than that recorded in 1990.

    On the basis of the MIT study, if I was in Richard Lindzen’s shoes, I too would be demanding much longer odds than the author in this instance seems willing to offer.

    To put it another way, the author should quickly snap up the 50:1 odds on offer over a 20 year horizon.

    Massachusetts Institute of Technology
    Joint Program on the Science and Policy of Global Change
    Uncertainty Analysis of Global Climate Change Projections:

  22. 22
    Steve Bloom says:

    Re #18: The alternative bet offered by Lindzen (warming over the next twenty years of less than .2c vs. greater than .4c, not “warming vs. no warming” as you misquoted it) was stated to be even odds per the IPCC. Note that the .2c figure just misses the low end of the IPCC scenarios. Yet he still wanted 2 to 1 odds? Presumably his version of an even-odds bet would allow him to win even if the IPCC is correct.

  23. 23
    geniusNZ says:

    > If alarmists are 95% confident that the IPCC temperature range encompasses the likely possibilities, they should be willing to offer 20:1 odds.

    Haha you think the best things these people have to do with their money is make bets they are not making any money on? that would jsut be plain stupid Besides if you are lets say 90% sure and that is the corect odds no one will take a 95% bet that doesnt mean the politicians shouldnt act on a 90% probability – letting the market set the rate is more appropriate.

  24. 24
    Mark Bahner says:

    James Annan writes, “My quick and dirty estimate above based on the IPCC TAR suggests that they would put the probability (of cooling) at more like 10%, so his offer actually appears to affirm the IPCC position.”

    Your “quick and dirty” estimate is completely wrong. The IPCC TAR puts the odds that the world will cool from 1990 to 2030 at MUCH less than 1%. By my “quick and dirty” estimate, it’s less than 0.2% (i.e., less than 1 in 500).

    People interested in a scientific analysis of the probabilities given in the IPCC TAR should see the analysis performed by Thomas Wigley and Sarah Raper, which was published in Science magazine in 2001 (“Interpretations of High Projections for Global-Mean Warming”). Interested readers can read the article for details about how the analysis was done, but basically Wigley and Raper presented probability density functions, based on all of the IPCC TAR scenarios. James Annan apparently hasn’t read this article, but here are the the probability values from Table 1 of that paper, for temperature increases from 1990 to 2030, in degrees Celsius.

    Percentage Temperature Rise (deg C)

    1% <0.36
    5% <0.48
    25% <0.66
    50% <0.80
    75% <0.95
    95% <1.17
    99% <1.31

    If James Annan truly thinks the IPCC TAR is correct, he should be willing to give odds of more than 500-to-1 against cooling from 1990 to 2030.

  25. 25
    Dan Hughes says:

    My comment #14. I must have been looking at the wrong page. The citations to previous comments should be to #s 8, 9, 10. And now #15 too.

    I again say that we are “Big CO2 Inc”.

  26. 26
    Roger Pielke Jr. says:

    James- Very nice work. For those interested in interesting questions about how IPCC contributors, non-IPCC experts, different disciplines, the public, etc. a prediction market can be a fantastic tool. I urge caution in interpreting very public bets among prominent people, which brings in a whole bunch of other factors other than those at play in a market setting (like the difference between a stock price and a stock picker). I really think that this could be an exciting development in understanding expert opinion on climate issues. Last comment, it’d be useful to focus the bets on variables of direct interest to decision makers. Global average temperature is not particularly relevant.

  27. 27
    Roger Pielke Jr. says:

    One interesting point relevant to policy about bets focused on global average temperature (GAT) — it appears from this discussion that there is unanimous agreement among those who disagree on what future GAT will be that there is no need to discount for policy interventions. That is, the IPCC projections are not conditioned upon assumptions about policies being implemented related to emissions. A functioning market would make this more apparent (e.g., if the market price is equal to the IPCC midpoint scenario), of course, but it appears to me that in the debate motivated by James so far that there is no expectation that emissions reductions policies will have a discernable effect on the climate (as measured by GAT) by 2030 (the terminal point of the bet). From a policy perspective, this suggests a number of possibilities, among them, (a) that the benefits of emissions reduction (as related to GAT) lie beyond 2030, (b) that everyone implicitly agrees that emissions reductions are unlikely (I doubt this is the case), (c) that emissions reductions of any conceivable amount will have no noticable effect on GAT, and so on. If bettors expect that emissions reductions will have a discernable influence on GAT over this period, then it should be apparent in the market value for GAT, which would be less than the IPCC’s non-policy mid-point projection.

    [Response:I took me several reads of your first few sentences to make sense of them… but now I have, I partially agree. I would say that out to a short horizon like 2030, you may be mostly right. I think “the IPCC projections are not conditioned upon assumptions about policies being implemented related to emissions” is wrong, since there are a variety of projections, which are conditioned explicitly on the emission scenarios. Well, its in the SPM (of course it is, everything is :-)) fig 5. Which shows that though the emission scenarios vary a lot out to 2030/50, CO2 levels vary much less (of course). And then there is fig 5d, which I always misinterpret. Anyway, I wouldn’t discount (b) as much as you seem to. And, of course, there is a lot of mental inertia behind IS92a – William]

    [Response: Actually, Roger is correct. IPCC SRES scenarios do not take into account any regulatory or legislative action to specifically curtail emissions. Their mandate was to provide plausible storylines for how emissions may develop in the absence of any such action. Like William though, I agree with conclusion (a). I doubt that the other statements are widely supported by anyone serious. – gavin]

  28. 28
    James Annan says:

    Thanks to all for the comments.

    I’ll reply to some of the specific points in turn, but firstly, as Brian (#6) spotted, the 0.3+-0.1C estimate from the IPCC was of course the 20 year total, as I hope the linked page and rest of the calculation made clear.

    #4: Your sums are the wrong way round, if I believe cooling has a 10% chance (as per my rough calc) then I would certainly choose the cooling side of Lindzen’s offer. (I’m assuming that the probability of precisely 0 temperature change being either zero, or at least very very small – NASA GISS quotes to 0.01C.)

    #5: Sorry Chip, I should have included your name in that list. I’m glad to see that you are now at least prepared to consider a new bet.

    You seem to have gone to quite some length in creating an impressive straw man, which doesn’t really need dealing with in detail, since I can simply jump to the end-point and agree that warming in excess of 0.325C/decade is indeed unlikely over the next few decades.

    I hope that innocent bystanders have noticed how useful the betting paradigm has been in generating consensus – me, Chip Knappenberger and the IPCC report all agree that warming is unlikely to be greater than 0.325C/decade in the immediate future (probably “very unlikely”, in IPCC-speak). Wasn’t that easy?

    I’ll correct one detail of the straw man, since it seems to crop up a lot. Chip says:

    35 different emissions scenarios – each of which the IPCC claimed as having an equal probability of occurrence

    but the IPCC Special Report on Emissions Scenarios quite explicitly contradicts that claim, eg here:

    Preferences for the scenarios presented here vary among users. No judgment is offered in this report as to the preference for any of the scenarios and they are not assigned probabilities of occurrence

    This is reinforced again in the summary, even more explicitly (with my bold emphasis):

    Probabilities or likelihoods are not assigned to individual SRES scenarios. None of the SRES scenarios represents an estimate of a central tendency for all driving forces and emissions, such as the mean or median, and none should be interpreted as such. The statistics associated with the frequency distributions of SRES scenarios do not represent the likelihood of their occurrence.

    #18: Obviously the odds on the bet have to lie somewhere between the honest beliefs of the opponents. With Lindzen estimating 50% warming and me at about 90%, there is a lot of room (my calc is very rough but given the gulf in opinions, high precision should not be required). I actually offered 2:1 (=67%), not 50% as you claim. Lindzen would not drop below 98%, at which odds I would prefer his side.

    #24: Oh, hi Mark, good to hear from you again. Mark, have you replied regarding your CO2 bet yet? The one I explicitly ACCEPT although I would like to up the wager to something worthwhile? I do look forward to hearing from you on this.

    As for your ref to Wigley and Raper, I refer you to what the IPCC SRES actually says, as quoted in my reply to Chip. Their choices for probabilities of emissions scenarios are for them to defend if they wish. I’m not going to get involved in debating every paper in the field, or even some of the more important ones – the issue is to find what the market consensus is on global warming over the next couple of decades. So far, I’ve had a handful of offers which all apparently endorse the IPCC TAR and none which contradict it.

    #26,27: Sure, there are lots of ways of developing the idea in more policy-relevant ways (including different variables, and perhaps more interestingly, climate change bets which are conditional on policy), but simple SAT seemed like the most obvious place to start. Robin Hanson’s pages have a wealth of ideas.

  29. 29

    Putting Your Mouth Where Your Money Is
    In a discussion on Tim Lambert’s blog, Daniel Davies remarks:
    [blockquote]If anyone’s interested in what large and wel…

  30. 30


    Thanks for the comments in #28.

    As you point out, the IPCC does not explicitly state that the SRES scenarios all are of equal likelihood, but, given what they do tell us (as you indicated) 1) we should not rely on the frequency distribution to develop probability of occurrence, and 2) “No judgment is offered in this report as to the preference for any of the scenarios and they are not assigned probabilities of occurrence,” it seem to me that the best we can do is to make the simple assumption that they are equally likely (with departures from equal probability randomly distributed). If you have a better idea, let me know.

    As far as your call for a wager, it seems as if you are only interested in calling out the skeptics – a group in which you consider me (and Pat Michaels) to be part of. As we have written numerous times, our stance is clear – we believe that the warming during the next 50 to 100 years will lie close to the low end of the IPCC projected range.

    [Response:This seems an odd thing to write. For you, I don’t know: could you quote some instances? For Michaels, it seems to be untrue: this is 3/4 oC, by implication over the coming century, which is well below the IPCC range. Could you quote something from M in support of your statement? – William (update: oops, I’m wrong: that was 50 years not 100: see #35 – William)]

    Thus, if you consider this to be in agreement with the IPCC, then apparently you can still be a skeptic and agree with the IPCC. Further, since you agree with us that the warming rate during the next several decades will be below 0.325ºC/decade, then, as I have pointed out, due to the level of natural variability, a 20-yr time period is too short to really differentiate between your beliefs and ours (if there exist any). This being the case, I welcome you to the group of “skeptics”, as evidently, you can’t prove yourself not to be.

    Since we (you, me, the IPCC) all are in agreement as to the likelihood of the rate of (near) future temperature change, the real impetus in your call for a wager should be geared towards calling out the alarmists – those folks who entertain the idea that the IPCC extreme temperature change scenarios are the most probable. After all, it is these folks who keep driving the press coverage and the political wrangling over this issue of anthropogenic climate change. So let’s see how many of them are willing to put their money where their mouths are.

    I propose to join with you and together we’ll issue a call to wager along the lines of which I outlined in comment #5 – even odds for those who believe that future climate change will be modest (an average 20-yr temperature trend of less than 0.25ºC/decade) vs. those who think it will be extreme (an average 20-yr temperature trend of greater than 0.40ºC/decade).

    What do you say?

  31. 31
    Mark Bahner says:

    James Annan writes to me, concerning my comment (#24) on the probabilities for different degrees of warming in the IPCC TAR: “As for your ref to Wigley and Raper, I refer you to what the IPCC SRES actually says, as quoted in my reply to Chip.”

    Please provide a copy/paste of the exact paragraph of “what the IPCC SRES actually says.” Please do not simply link to the page, and please do not provide a copy/paste of only a portion of a sentence.


    [Response:From SRES Box 6.4

    There is no single most likely, “central”, or “best-guess” scenario, either with respect to other SRES scenarios or to the underlying scenario literature. Probabilities or likelihoods are not assigned to individual SRES scenarios. None of the SRES scenarios represents an estimate of a central tendency for all driving forces and emissions, such as the mean or median, and none should be interpreted as such. The statistics associated with the frequency distributions of SRES scenarios do not represent the likelihood of their occurrence. The writing team cautions against constructing a central, “best-estimate” scenario from the SRES scenarios; instead it recommends use of the SRES scenarios as they are.


  32. 32
    Mark Bahner says:

    Chip Knappenberger writes, “As you point out, the IPCC does not explicitly state that the SRES scenarios all are of equal likelihood,…”

    To quote from Wigley and Raper’s 2001 Science article I referred to in my comment number #24 (see page 452 of Volume 293 of Science, dated 20 July 2001, first paragraph):

    “For emissions, the SRES rport (2) states that ‘There is no single most likely, ‘central,’ or ‘best guess’ scenario, either with respect to the SRES scenarios or to the underlying literature’ and does not assign probabilities or likelihoods to individual scenarios [see also 93)]. WE THEREFORE ASSUME ALL 35 EMISSION SCENARIOS TO BE EQUALLY LIKELY.”

    Emphasis added. :-/

  33. 33
    Mark Bahner says:

    James, please provide the COMPLETE quote of the warming rate given in the IPCC TAR summary.

    [Response: (Comment edited): From IPCC TAR:

    On time-scales of a few decades, the current observed rate of warming can be used to constrain the projected response to a given emissions scenario despite uncertainty in climate sensitivity. Analysis of simple models and intercomparisons of AOGCM responses to idealised forcing scenarios suggest that, for most scenarios over the coming decades, errors in large-scale temperature projections are likely to increase in proportion to the magnitude of the overall response. The estimated size of and uncertainty in current observed warming rates attributable to human influence thus provides a relatively model-independent estimate of uncertainty in multi-decade projections under most scenarios. To be consistent with recent observations, anthropogenic warming is likely to lie in the range 0.1 to 0.2°C/decade over the next few decades under the IS92a scenario. This is similar to the range of responses to this scenario based on the seven versions of the simple model used in Figure 22.


  34. 34
    Steve Bloom says:

    Re #30: The betting issue aside, being one of those “alarmists” I guess I don’t share your confidence that (projecting out the high end of your figure) 2.37c in 2100 would be “modest” in the sense that we can reasonably presume it will lack major consequences. Hopefully you’re right. On the other hand, I buy insurance policies for risks I consider to be much lower.

  35. 35
    J. Sperry says:


    In your response to #30, you appear to misrepresent P. Michael’s article, in which he clearly points out that the 0.75 oC estimate is for the next 50 years (from Oct. 2003), not over the coming century. And of course, this estimate is based on NASA’s Jim Hansen, who is not exactly in the skeptic crowd. Chip’s characterization that this is the low end of the IPCC range (min. of 1.4 by 2100) doesn’t sound odd to me.

    [Response: I concur – Michaels’ estimate is for 2050. However, comparing it to Hansen’s estimate is misleading and I discussed why very early on. Basically, Hansen is saying that is the smallest possible rise in temperature to be expected given sufficient regulatory and legislative effort (particularly to reduce methane, black carbon and CO2 emissions). Michaels’ is claiming that this is the most that can be expected given no action whatsoever. I would hardly call that argeement. -gavin]

    [Response:I confess – Michaels is for 2050. I’m surprised: why is Michaels considered such a skeptic when he agrees with the IPCC (OK, I know, he’s only just within the range and there is the tone to be considered). JA is right: this *is* bringing out how close everyones positions really are – William]

  36. 36
    Mark Bahner says:

    James Annan has repeatedly represented the “IPCC consensus” for warming over the next few decades to be 0.1 to 0.2 degrees Celsius per decade.

    When I asked him to provide the complete quote supporting his representation, Gavin Schmidt provided this quote:

    “To be consistent with recent observations, anthropogenic warming is likely to lie in the range 0.1 to 0.2°C/decade over the next few decades under the IS92a scenario.”

    But all Gavin Schmidt’s provided quote does is show clearly and unequivocally that James Annan is WRONG. Let me repeat the quote, in it’s entirety:

    “To be consistent with recent observations, anthropogenic warming is likely to lie in the range 0.1 to 0.2°C/decade over the next few decades UNDER THE *******IS92a******* SCENARIO.”

    Emphasis added.

    That 0.1 to 0.2 degrees Celsius over the next two decades represents the warming ONLY for the IS92a scenario (under different climate sensitivities). This fact should be **obvious** to anyone who bothers to read the sentence carefully!

    I request that James Annan please admit his error. Failing that, I request that Gavin Schmidt, William Connolley to acknowledge James Annan’s error.

    [Response: You’re wrong, as JA points out, since much of the warming over the next few decades is contrained by commitment and current levels and doesn’t much vary by scenario. Now, how about you decide whether you’re going to accept JAs bet or not? – William]

  37. 37
    Joel Shore says:

    I saw Michaels give a talk in the physics department at the University of Rochester a few (~3?) years ago and the title of his talk was something like: “Global Warming: No Big Deal.” After a general trashing of various things including surface observations and climate models, he admitted that his prediction for the globally-averaged warming (of ~1.5 C by 2100) is within the IPCC range…albeit at the low end. However, he claimed that this warming would be no big deal because:

    (1) Most of the warming would actually occur near the surface in areas with shallow cold dry air masses, such as in Siberia and northern Canada where it would not have a large effect. [I forget if he had anything to say regarding melting of land ice and glaciers raising sea levels.]

    (2) Various other arguments that basically amounted to saying that the effects of the warming were being exaggerated.

    I don’t know if this has been his opinion all along or an opinion that he has evolved to as it has become less and less credible to claim that little or no warming will occur.

    [It is also interesting to note that Michaels conveys a quite different tone in such seminars as he does in his generally more strident editorials for the masses. In particular, he basically admitted that his was a minority viewpoint within the climate science community but mumbled various things about Thomas Kuhn and how hard it is to overturn an established paradigm…and something about public choice theory.]

  38. 38

    Gavin has, on several occasions, contended that Pat Michaels has taken Hansen’s (PNAS, 2001) warming estimate for the next 50 years out of context (for the latest see #35). However, Gavin’s characterization of Hansen’s estimate is wrong. Hansen IS NOT saying that a rise of 0.75 degC is “the smallest possible rise to be expected given sufficient regulatory and legislative effort.” Instead, Hansen says that 0.5ºC is the minimum expected warming value by 2050 and that the maximum realized warming will be 1.0ºC (assuming some public concern and action). He thus arrives at a expected warming value of 0.75 ºC +/- 0.25 ºC by 2050 given how he expects things (including public concern and action) to evolve over the next 50 years.

    Both sides keep claiming that the other has taken some of Hansen’s text out of context, so I include the whole pertinent section below:

    – Global Warming, 2000-2050. A byproduct of the above analysis is the conclusion that future global warming can be predicted much more accurately than is generally realized. We show elsewhere (8) that a forcing of 1.08W/m2 yields a warming of 3/4 °C by 2050 in transient climate simulations with a model having equilibrium sensitivity of 3/4 °C per W/m2.

    – We contend that a forcing much smaller than 0.85 W/m2 is unlikely, because fossil fuels are expected to be the primary energy source for at least several decades. Rapid introduction of nonfossil energies or CO2 sequestration might reduce the forcing by a few tenths of 1 W/m2. However, much of the warming in the next 50 years will be from presently “unrealized warming” caused by the existing planetary radiative imbalance of at least 0.5 W/m2 (8, 37). Slowing CO2 emissions in the second quartile of the century, although crucial for stabilizing atmospheric composition later in the century, would have only a small effect on the warming in 2050. These considerations suggest a minimum warming of 0.5°C by 2050.

    – At the other extreme, CO2 growth exceeding exponential at 1.5%/year would be inconsistent with historical trends and with the negative feedback caused by human concern about climate change. Thus the maximum CO2 forcing is 1.28-1.54 W/m2 (Table 1). BC and O3 are unlikely to be much greater in 2050 than today. Indeed, China has already begun to reduce its air pollution (38) and other developing countries are probably near their limits. Continued global warming would produce at least moderate public concern, thus limiting added forcing to about 1.5 W/m2 and realized warming to about 1°C.

    – Given these constraints on climate forcing trends, we predict additional warming in the next 50 years of 3/4 +/- 1/4°C, a warming rate of 0.15 +/- 0.05°C per decade. A slower warming rate will occur in the second half of the century, assuming that the climate forcing growth rate begins to trend downward before 2050.

    Quoted from: Hansen, J.E., and M. Sato, 2001. Trends of measured climate forcing agents. Proceedings of the National Academy of Sciences, 98, 14778-14783.

    [Response: I recommend that anyone interested read the whole paper (linked above). The CO2 minimum forcing estimate of 1.08 W/m2 by 2050 assumes flat emission growth (i.e. no further increases in CO2 emissions), and thus is the absolute minimum (and something I would be willing to bet against!). With continued growth of emissions, forcing estimates rise to up to 1.54 W/m2 but may be somewhat less. Other terms such as from CH4, O3 and black carbon are posited to decrease substantially as per the ‘alternative scenario’ outlined by Hansen in a number of publications. Unlike the IPCC scenarios, Hansen is actually trying to make a prediction of what is likely to happen. This is different to SRES because of a) the inclusion of the effects of policies specifically designed to reduce emissions and b) he implies that there is a probablity assigned to his scenario – i.e. he claims this is more likely that any particular SRES storyline. This is a perfectly valid exercise and does have use in the policy debate, however, it cannot be used to argue that anthropogenic forcing is not a problem and that no efforts should be made to tackle it (as Michaels implied recently on CNN). It is precisely because he thinks that unrestrained emissions growth would be a problem that Hansen feels confident in positing that some efforts will be made to restrain emissions.
    This is an entirely different argument than those that have been made by Michaels. In 1987 and again in 1997 (referred to here), Michaels claimed that climate sensitivity was between 1.0 and 1.5 deg C (for a doubling of CO2), thus projected increases of GHGs would only lead to a small change. Since the 1998, Michaels has insisted that temperature trends can be simply be linearly extrapolated out to 2050 and further and that the resulting (small) changes are nothing to be concerned about. Since then his argument has remained consistent, however the rate of warming has not. In 1998, Michaels was projecting 0.125 C/decade as the likely long-term trend (0.13 a year later), and now he claims 0.17 C/decade (~0.75/4.5). I would be interested in knowing what Michaels now considers to be the best estimate of the climate sensitivity, since if he remains convinced that it is much smaller than the number used by Hansen above (around 3 C for a doubling of CO2), then any claim of ‘agreement’ is coincidental in the extreme. -gavin]

  39. 39
    Mark Bahner says:

    William Connolley writes in comment #35, “I confess – Michaels is for 2050. I’m surprised: why is Michaels considered such a skeptic when he agrees with the IPCC (OK, I know, he’s only just within the range…”

    I think you have a mispelling…don’t you mean, “septic?” (Isn’t that the word you routinely use?)

    [Response:You’re thinking of this. Be more discriminant. Michaels is marginal for his k: he agrees with the IPCC (I and many other discover to our surprise) but does his best to disguise it by his choice of words – William]

    Isn’t the reason Pat Michaels is considered a “skeptic” obvious? It’s that he doesn’t think governments need to pass any new regulations to “stop” (or even slow down) global warming.

    [Response:Not as far as I’m concerned, since I’m talking about the science not the politics. Michael Tobis had a nice post which might help you – William]

  40. 40
    Steve Latham says:

    Re #20 and some others: WAIT A MINUTE!

    “…you want to bet that anthropogenic influences will be responsible for at least a tiny fraction of the warming of the earth that most people expect to occur in the next few decades.”

    You mean that if the earth warms in the next few decades as the IPCC models predict (at least within the bounds of the prediction), this debate will be no closer to being resolved? Crap! On what non-anthropogenic basis do the skeptics expect the earth to warm over the next few decades? What’s the non-anthropogenic mechanism? Since the earth is now warmer than it has been for the last couple thousand years (or, less controversially, now that it is warmer than average), I would have thought that those who think anthropogenic global warming is bunk would expect the GAT to go back to a more ‘normal’ value.

    Maybe the skeptics will argue that there is some kind of inertia to the latest warming trend. On the other hand, in a laypersons debate on another site, the argument was made that the earth is now on a cooling trend since 1998.

    I think the ‘main debate’ should be whether or not there is anthropogenic global warming. People who agree that there is, but lean toward the low predictions, are not really skeptics at all, in my mind. After the ‘main debate’ is over, which I believe it should be, then you can haggle all you want about how much warming will occur.

    It’s not for climatologists to determine whether X degrees Celcius is worth worrying about or not. The fish I study (and the livelihoods and cultures of those who fish them) are already threatened by high water temperatures and the lack of glacial moderation of those temperatures. They might not be able to handle just the continuation over time of the recent high temperatures, never mind some additional modest warming.

    Please, ‘skeptics’, define your positions. It would be best not to lump y’all into a single category. And if you think that anthropogenic global warming exists and is in part responsible for recent trends, let the public know so that folks like the ones I deal with can properly lay at least some of the blame.

  41. 41
    Brian S. says:


    It would either further the consensus or facilitate betting if you clarified that you do NOT think the temperature rise will be less than the IPCC TAR likely minimum increase of .1 C for the next 2 decades. In other words, either you agree with the floor (yeah consensus!) or there’s a significant spread between your likely range of temperature increases, and the IPCC range of .1 to .2 C/decade, which means there may be something worth betting on.

  42. 42
    Terry says:


    What did Junkscience say when you contacted them? Have they responded yet? Do you think the bet he is suggesting is fair?

  43. 43
    Mark Bahner says:

    “…and the IPCC range of .1 to .2 C/decade,…”

    The IPCC range is not 0.1 to 0.2 degrees Celsius per decade. That value only refers to the climate sensitivity around IPCC scenario IS92a:

    “To be consistent with recent observations, anthropogenic warming is likely to lie in the range 0.1 to 0.2°C/decade over the next few decades UNDER THE IS92a SCENARIO.”

    Emphasis added.

  44. 44
    dave says:

    Re #16, 17:

    Gavin told me that in #16 that I had got the decimal points wrong, which I had acknowledged in the unfortunately posted #17. I had hoped you would do some editing.

    OK, all that aside, I STILL WANT TO KNOW, where do these decadel figures come from – Gavin says it is 0.17C/decade, the same number published by Kerr as cited in #16.

    OK – how is that being calculated?

    LOOK, if you’re going to present an entire thread talking about betting on a twenty year increase 0.3 over two decades, PLEASE tell us how these figures are being caluculuted, OK? And, I don’t want to hear about the IPCC (2001) estimate that states the that decadel changes will be between .10 and .20 per decade. That was 2001; this is 2005.

    What’s the latest stuff and how is that being calculated? If I’ve missed something in cited material, tell me so, and — otherwise respond.

    [Response:I presume you’ve been pointed to this before, but the answer for the numbers is in the IPCC TAR SPM. If you haven’t read that document before, and are interested in climate change, then you should read it now. If you follow links to the future-climate-change chapter, you’ll find where the numbers come from.
    You don’t want to hear about the IPCC TAR? Well thats tough because its the best summary we have, until the AR4 comes out in a year or two – William]

    [Response: An additional note. Download the GISS temperature anomalies from and calculate the trend over the last 30 years. -gavin]

  45. 45
    Lynn Vincentnathan says:

    These economic/gambling games are fun and revealing, esp. the odds the skeptics are willing to bet on that warming or cooling will occur. However, we should be cognizant of what the stakes are, what GW means, including loss of human life from GW, which is happening even now — 160,000 per year according to WHO. Even though economists can calculate a price on human life, e.g. for court settlement purposes (with a greater price for the rich and important people), and chemists can figure a human to be worth $2 in chemicals (that was 40 years ago, so it must be at least $10 now), there is no amount of money that can bring back a life. Also, money (whether in paper or coin or plastic card form) is not good when stranded on a desert island, or globally warmed earth that is greatly diminished of supportive biota and other conditions for life.

    As Roy Rappaport (“Distinguished Lecture,” American Anthropologist, 1993, p. 299) states: “Monetization…forces the great range of unique and distinct materials and processes that together sustain or even constitute life into an arbitrary and specious equivalence. Phenomena that relate to each other essentially in terms of their qualitative distinctiveness are represented and understood in terms of a logic that reduces all qualitative distinctions to mere quantitative differences, a logic that…attempts to “bottom line” the world”

    Nevertheless, if efficient market theory and betting on GW help build consensus, that’s great. I doubt poor drought-stricken farmers in India (& now in Australia), who have a high rate of suicide due to inability to pay loans, would be able to participate & hedge their future losses. We will also need to figure some monetary ways of facilitating GW mitigation & compensation/penalties. It’s just that none of this can bring back the dead or replace actual net agricultural losses due to GW each year.

  46. 46
    David says:

    Chip your choice of language is “interesting”, when descibing change as “modest” “in the middle” and “extreme”. The smallest warming/sea level rise in TAR figure 5 will place a wide range of human and natural systems under very considerable pressure (and based on estimates of the melt-down point for greenland place us teetering on the edge of dangerous climate change). The mid range warmings will tip well into the realm of dangerous climate change, and the upper range; well it is pretty much game over for the world as we know it. You have also brushed over the fact that the warming rate increases rapidly in the mid and upper scenarios so using the centenial trend applied to the next 20 years is inappopriate.

    >However, the high end of the IPCC range (or even higher) is often waved about in order to hype the issue and draw “concern” from the general public such that they stand behind efforts to limit carbon dioxide emission.

    You could be accussed of the same. Your language suggests coping will be easy; we can only hope. For climate scientists I know, the low end is troubling enough; their ain’t a need to hype the upper end.


  47. 47
    Joel Kuni says:

    In #40, Steve asks “On what non-anthropogenic basis do the skeptics expect the earth to warm over the next few decades? What’s the non-anthropogenic mechanism?”

    My answer – On the basis of billions of years of historical global warming periods, some of which happened rapidly and without any human influence whatsoever – and whose specific causes remain a mystery. For example:

    Around 14,000 years ago (about 13,000 radiocarbon years ago), there was a rapid global warming and moistening of climates, perhaps occurring within the space of only a few years or decades. In many respects, this phase seems to have resembled some of the earlier interstadials that had occurred so many times before during the glacial period. Conditions in many mid-latitude areas appear to have been about as warm as they are today”

    [Response:You’ve misunderstood the question. If you don’t believe that CO2 forces climate change, then why do you think the temperature should go up in the future, rather than down? As of 150 years ago, the thousand-year trend was downwards if anything: . If you believe in random natural shifts, you presumably believe they are as likely to be downwards as upward. And the billion year scale is irrelevant. And the various YD and D-O type events probably only occur when the Laurentide ice sheet is around – William]

  48. 48
    Joel Kuni says:

    Lynn, in #45 you refer to losses of human life that are supposedly already occurring due to global warming. Don’t forget to add back the lives that are being saved because there are fewer deaths due to hypothermia, frostbite, etc. Most of the warming occurs in the coldest parts of the earth and at night, not in the warm regions of the planet.

    Also, the longer growing season and the increased concentrations of CO2 obviously improve crop yields, thus preventing deaths due to malnutrition and starvation.

    The WHO apparently wants us to believe they know of people in New Delhi who died because, due to global warming that has already occured, the high temperature was 108.37 degrees rather than the pleasant 108 degrees it would have been otherwise. I guess they think we’re stupid.

    I would like to know how the WHO justifies showing pity for overheated equator-dwellers while showing no pity at all for the Inuit victims of frostbite and malnutrition in northern Canada.

  49. 49
    James Annan says:

    Ok, round two.

    # 16,17,39 (dave): Sorry I thought your earlier retraction meant you’d found out. NASA GISTEMP is the obvious source of surface temperature data. As for new results, you (and I) will have to wait for AR4, I’m afraid. I would be surprised if it was very different to the 2001 TAR version as far as the next few decades go, but I certainly have no priviledged information about that.


    it seem to me that the best we can do is to make the simple assumption that they are equally likely (with departures from equal probability randomly distributed). If you have a better idea, let me know.

    You can make any assumptions you like, but the scenarios are essentially a question of socioeconomic forecasting and that is not my field. If the people writing the SRES had written your comment above, I would have probably taken their word for it. As it is, I view the scenarios as much as a choice as a random input – ie, how much carbon do we want to burn? Which is one reason for my focus on the 20-30 year time scale, which is essentially a matter of climate science and committed change.

    I’m sorry if you feel slighted by being bracketed with some of the more outlandish forecasts that cooling was more likely than not (Corbyn, Jaworowski) or even close to a 50% chance (Lindzen). It would perhaps advance the debate if you explicitly distanced yourself from these sort of statements. After all, you did offer to bet on significant cooling in 1998, a bet which you would have lost had anyone taken you up on it. Certainly, if you agree that ongoing warming (of 0.15C+-0.05/decade over the next few decades) is likely, then you don’t disagree with the IPCC TAR on that matter at least. But I think it would be very hard to reconcile your extended prediction of ~+1.5C in 2100 with your assumption that all scenarios are equally likely.

    I will happily take on any alarmists who say anything that I believe to be false (ie extreme predictions which I believe are substantially less likely than they claim). I would be interested (genuinely) to hear of any examples that you think provide a bettable proposition.

    Mark: I’m still waiting for your confimation of full details (including the max stake you are comfortable with) on this bet (see the last section) :-)

    As for the IS92a thing: yes, it is a reasonably middle-of-the-road scenario, although now a bit outdated. For the purposes of a short forecast, it doesn’t make a whole lot of difference – the IPCC TAR says 0.1-0.2C/decade with IS92a, and Wigley and Raper, using a different set of scenarios, get….about 0.2C/decade after 4 decades. Sorry, but I’m not going to get excited over a discrepancy (if you can call it that) of that magnitude. I guess there may be a gnat’s crotchet of disagreement if you look closely. If you want to bet against them, good luck to you. If you want to bet against me or the TAR, you’ll have to bet against what we (it) actually says, rather than what you want to pretend it says.

    So, calling for bets has apparently stopped people making unreasonable predictions, and replaced it with people putting unreasonable predictions into the mouths of their opponents. I guess we can call that progress, of sorts :-)

  50. 50
    Jim Carson says:

    This thread seems a little close to getting “involved in political or economic implications,” but what the heck, it’s fun.

    Since no one’s actually addressed the legitimate point made by Michael Jankowski and others that while the bet might prove warming, it can never prove GHG-induced warming, how about we make a bet that does?

    James Annan, et. al. have increasing faith in their climate models, so let’s bet on that. James and company can put forth a model that uses any data set they like, so long as it’s independent, consistent, wide-ranging (good approx of global) and expected to remain so for the duration of the bet. Calculation of R-squared is made on the raw and modeled temperatures for the prior twenty years. The bet will then be whether the R-squared for the next twenty years will be higher or lower. The only serious point of contention should be the level of R-squared which proves the hypothesis of anthropogenic global warming. You might be surprised how low an R-squared I’d be willing to bet $1000 against. As for contracts, I’d suggest up-front purchase of US T-Bills, held by an interested law firm.

    This type of bet has several benefits:

    1) We’d actually be betting on GHG-induced warming, not just warming.
    2) We can shorten the duration of the bet, or place multiple bets (5, 10 and 20 years, e.g.)
    3) We can have a jolly old time charting the progress on this and other websites.

    For Lynn (post 45): I swear I don’t intend any sarcasm when I say, “Cheer up!” If you’re trying to persuade people, this is probably not the best forum for your message. If you really believe all that, you need to find a way to stop thinking about it because that much negativity will destroy a person.