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Global Cooling-Wanna Bet?

Filed under: — stefan @ 8 May 2008 - (Español) (Deutsch) (Italian)

By Stefan Rahmstorf, Michael Mann, Ray Bradley, William Connolley, David Archer, and Caspar Ammann

Global cooling appears to be the “flavour of the month”. First, a rather misguided media discussion erupted on whether global warming had stopped, based on the observed temperatures of the past 8 years or so (see our post). Now, an entirely new discussion is capturing the imagination, based on a group of scientists from Germany predicting a pause in global warming last week in the journal Nature (Keenlyside et al. 2008).

Specifically, they make two forecasts for global temperature, as discussed in the last paragraphs of their paper and shown in their Figure 4 (see below). The first forecast concerns the time interval 2000-2010, while the second concerns the interval 2005-2015 (*). For these two 10-year averages, the authors make the following prediction:

“… the initialised prediction indicates a slight cooling relative to 1994-2004 conditions”

Their graph shows this: temperatures in the two forecast intervals (green points shown at 2005 and 2010) are almost the same and are both lower than observed in 1994-2004 (the end of the red line in their graph).

Fig. 4 from <em data-src=

That this cooling would just be a temporary blip and would change nothing about global warming goes without saying and has been amply discussed elsewhere (e.g. here). But another question has been rarely discussed: will this forecast turn out to be correct?

We think not – and we are prepared to bet serious money on this. We have double-checked with the authors: they say they really mean this as a serious forecast, not just as a methodological experiment. If the authors of the paper really believe that their forecast has a greater than 50% chance of being correct, then they should accept our offer of a bet; it should be easy money for them. If they do not accept our bet, then we must question how much faith they really have in their own forecast.

The bet we propose is very simple and concerns the specific global prediction in their Nature article. If the average temperature 2000-2010 (their first forecast) really turns out to be lower or equal to the average temperature 1994-2004 (*), we will pay them € 2500. If it turns out to be warmer, they pay us € 2500. This bet will be decided by the end of 2010. We offer the same for their second forecast: If 2005-2015 (*) turns out to be colder or equal compared to 1994-2004 (*), we will pay them € 2500 – if it turns out to be warmer, they pay us the same. The basis for the temperature comparison will be the HadCRUT3 global mean surface temperature data set used by the authors in their paper.

To be fair, the bet needs an escape clause in case a big volcano erupts or a big meteorite hits the Earth and causes cooling below the 1994-2004 level. In this eventuality, the forecast of Keenlyside et al. could not be verified any more, and the bet is off.

The bet would also need a neutral arbiter – we propose, for example, the director of the Hadley Centre, home of the data used by Keenlyside et al., or a committee of neutral colleagues. This neutral arbiter would also decide whether a volcano or meteorite impact event is large enough as to make the bet obsolete.

We will discuss the scientific reasons for our assessment here another time – first we want to hear from Keenlyside et al. whether they accept our bet. Our friendly challenge is out – we hope they will accept it in good sportsmanship.

(*) We adopt here the definition of the 10-year intervals as in their paper, which is from 1 November of the first year to 31 October of the last year. I.e.: 2000-2010 means 1 November 2000 until 31 October 2010.

Update: We have now published part 2 of this bet with our scientific arguments.

Update: Andy Revkin has weighed in at “dot earth”.

Update 5/11/08: so has Anna Barnett at Nature’s ‘climate feedback’ blog

228 Responses to “Global Cooling-Wanna Bet?”

  1. 201
    Ray Ladbury says:

    Furrycatherder, You are missing the point. It is not short-term ups and downs that matter–it is the long-term change. Humans, and even human civilization have survived short-term variation before. They may cause distress, but ultimately, even during a Grand Minimum, WEATHER is predictable enough to get in a crop that will keep us fed. Now contrast that with a climate change, where we cannot know whether the monsoon rains will come in May or August or even at all; and whether the monsoon rains will wash away the crop or not.
    Grand minima and maxima last for decades. CO2 persists for centuries. At best, a minimum now will give us a few decades to respond to the crisis of increased greenhouse warming. At worst, it will make people think the crisis is over, and we will have a much bigger problem in a few decades when the minimum is over. Given hmanity’s track record, I’d bet on the latter.

    In any case, it is awfully premature to declare the onset of a Grand Minimum. We are not yet even outside the normal range for the Solar Max/Min cycle.

  2. 202
    Ray Ladbury says:

    Russell, Skeptics make an effort to understand the evidence. Denialists do not. They are born of complacency, and alarmism merely nourishes them. Like all parasites, they will always seek out nourishment.

  3. 203
    Hank Roberts says:

    > the climate models won’t be “right”
    Wrong. The climate models work through the ups and downs of the solar cycle; even assuming a prolonged down instead of an up, the effect is as expected, and is small compared to the effect of added CO2.

    Think. If coal burning had been done on a large scale starting a century or more before the Maunder Minimum, what would climate have been like during that span?

  4. 204
    David Hindle says:

    Nature allows comment and reply. At this point, given the technicality of your arguments, you should be writing one, and sending it to the journal. Bets between scientists have a long history. They were mostly private, and cordial. Usually over relatively trivial points. I have a feeling also that ‘bets’ were generally made by a particular standard of scientist – usually Nobel or equivalent – at least the bets that became famous afterwards. Isn’t the most positive way to respond, to channel your energy into constructing a proper, scientific reply, and use the official channels for its submission, review, publication etc.?

    I can give you a very good example of exactly this process. Try reading the following (from the field of seismology):

    Smalley et al. Nature, 435, 1088-1090, 2005
    Calais et al. Nature, 438, E9 – brief communication arising, 2005

    That’s really how to do it. I’d be much happier happier if, in this case, you stuck to the ‘normal’ channels and waited until your counter-arguments were accepted and published in Nature. Then blog about it.

    [Response: That’s all well and good. But there is a big problem with that when you have such huge amounts of press coverage. Look at how long it took to get the comment published (almost 6 months). That does not fit in with the 24 hour news cycle. Note also that Nature only publishes a fraction of the comments it receives. We did discuss this particular issue a few weeks ago though. – gavin]

  5. 205
    David Hindle says:

    But Gavin, you are risking subverting the very process by which science is ‘done’. We don’t have a written constitution, but there are ‘rules’ which we all know and respect. Every scientist is frustrated at some point or other by manifestly bad articles which appear in Nature or Science. But I’m not happy that you claim the imperative of the news cycle means you can go your own route in this case. I think here, you have a more normal scientific objection, and there is a ‘correct’ way to deal with that. It isn’t (or wasn’t at least) a blog.

    It’s one thing to correct misapprehensions amongst journalists, or rebut nonsense from pseudo-scientific quarters with specious anti-AGW arguments. However, this particular case does not strike me as such. The news cycle argument could easily become a catch all whereby every peer reviewed article you disagreed with could be commented upon (scientifically) in a blog, run by you. You are running the risk of appointing yourselves as arbiters of what is good and bad in the literature. That is a very dangerous step. For all their faults, the peer-reviewed journals are the best system we’ve got. Their neutrality at least, can’t be questioned. Their crass stupidity at times, I’d not argue with. But for lack of an alternative, what else can we do?

    [Response: We went through all this on the other thread. The peer review route will remain dominant, but where did the idea that we have to be like monks under a vow of silence outside of the journals come from? It’s certainly not the case at meetings, workshops and coffee time – much more frank exchanges occur there! If I’d been asked to review this manuscript, I’d have said the same general things – is this now secret information that must be withheld from other interested parties? Our credibility comes from our backgrounds, publications and reputations in the field. We are not going to jeopardize that by running amok on a blog, but when the media gets the balance wrong or we see some misrepresentation being used by the antis, would you have us just sit back? I do not see any contradiction in commenting on papers that may well be fine technically, but that are misused and misrepresented in the media. Comments to journals are all very well, but having been involved in 4 in the last few months, they are a huge waste of time and, though necessary for the field, I do not need to do it for every paper I have an issue with. – gavin]

  6. 206
    Ray Ladbury says:

    David Hindle, Somehow, I think the integrity of science will survive this little exercise in applied Bayesian probability. In any case, I think that whether the Keenlyside have sufficient confidence in their predictions to take the bet will tell us something of value. We already know they were keen on going to press with their results. In any case, the American parties to the bet are the ones taking a risk–given current trends, who knows dollars one will need to make up 2500 euros in 10 years?

  7. 207


    I’m well aware of that. What I’m saying, and have always said, is that certain predictions have the potential to do harm, particularly if, as some of us have noted, there is a connection between solar cycles and weather.

    The absolute best thing that could happen to support AGW is 2008 breaks all the records, then 2009, then 2010, and so on. But if SC24 is a fizzle, 1998 will likely stand as a record for another 11 or 12 years, plus whatever it takes for SC25 to get going — perhaps 3 to 5 more years.

    In that intervening time, the people who’ve consistently asserted that the sun isn’t a significant influence — up and down, yes, but still a significant influence — aren’t going to look better.

    The worst case scenario, I think, is that SC24 and 25 are duds and people conserve just enough, but not any more, to get prices under control, but not enough to make a dent in CO2 level (and certainly not enough for my pet project — getting people off carbon so the global economy doesn’t really tank).

    The best case scenario, I think, is for the climate folks to say “Look, we’ve got a decade or two reprieve — let’s push as hard and fast as we can before the sun resumes its normal level of activity and global warming comes in with a vengeance.” Bets and other such silliness don’t give me a warm and fuzzy feeling about this.

  8. 208
    wmanny says:

    Ray, I attempted to respond to your calling me a kook (which the moderator allowed) and for the record my reply was censored by the moderator, possibly because I did not call you any names in return. Will the moderator print this? Hmmm. I will say I am enjoying the process of letting my science colleagues in on this site’s true colors regarding dissent! They have been telling me for years about RC’s supposedly disinterested stance, and they have been surprised to learn otherwise. They, in fairness to RC, have the advantage of knowing that I, like Nixon, am not a kook.

  9. 209
    wmanny says:

    Wow. Different moderator on board at the moment, perhaps, so, Ray, I’ll try it again: I am not a kook, and neither are you, so let’s give the ad hominems a rest. I used the religion analogy in debate without giving proper consideration to its loading. Re-phrasing, then, I know that Gavin is a scientist, but I believe he is overly attached to the politics of AGW if he is so loath to countenance criticism of Gore’s overstatement. I thank you for your decency in noting that Gore is doing what politicians do when he uses the cyclone’s spector to motivate people through fear and compassion. Gore, whom I do not hate, by the way (though on this site dissent and hatred seem to be conflated at times) has overstated his case, says me. You say he has not, and so be it.

  10. 210
    Hank Roberts says:

    Reread that comment because you misread or misquoted what he said.

  11. 211
    David Hindle says:

    Ray Ladbury: Suppose Noel Keenlyside or Mojib Latif or both are billionaires. Their accepting the bet would probably tell you that 2500 euros is peanuts to them and they can indulge you. They might even ‘raise’ until you fold. Or suppose Noel Keenlyside earns less than me. Not accepting the bet would probably tell us that he hasn’t got money to burn, and more generally that european scientists are financially very risk averse.

    Currently, Keenlyside et al. have the published article, and RC has a blog reaction and offer of a bet. Keenlyside et al. are quite entitled to ignore you completely unless you are prepared to challenge them through official channels. The worse thing is, I may well agree with most of your criticisms. But still, this particular series of posts more closely resembles a tirade than science.

  12. 212
    Ray Ladbury says:

    Walter Manny, Apology (of sorts) well taken. Note that I did not explicitly state that you were a kook–merely that the attribution of religiosity to a scientist doing his job crosses into the borders of that dangerous land. I apologize if you took my warning as an epithet.
    As to Gore, he makes such a good whipping boy for the political right, that they feel safe in ignoring the science. The science, however, is not going away. And by ignoring the science, they continue to cede the high to Mr. Gore and his allies. It appears that John McCain has realized this–at least until November. I’m not sure how much I can believe him. Even George Bush in 2000 talked about regulating greenhouse gasses. And whether you like Mr. Gore or not, you must give him credit for consistency. He advocated for a carbon tax long after Bill Clinton discarded the idea (whether out of a weakness for lobbying dollars or a weakness for cigars, who can say?).

  13. 213
    Ray Ladbury says:

    David Hindle, All a bet does is ask the question: Are you sure about that? And I think that is a rather important question. After all, the press latched onto this like a pit bull on a burglar’s shin, and I don’t think it’s a bad thing to point out that this is one of many predictions and has its issues. Science is a human activity. So is gambling (actually, chimps to it, too, but that just means it’s more fundamental). And a bet can also be taken as a way of establishing a subjective probability. Now a better way would be to allow the authors and their allies to wager whatever amount they wish and then allow those dissenting from Keenlyside to subscribe to shares of that wager. But that is likely more trouble than it’s worth. Come on, haven’t you ever been tempted to use the term “horse puckey” in a review?

  14. 214

    Thank you for putting the bet out there. I think risking money goes a long way in seeing how strong your beliefs are.

    Dagny McKinley
    organic apparel

  15. 215

    You might as well make the bet. Paying out the money will be the least of your problems if temperatures don’t continue to rise. The public has a very short attention span for fads. If the climate cools down your careers will be feeling the heat.

    [Response: Climate change is (unfortunately) a growth industry. But it is not an environmental cause de jour, more like a cause de siecle. – gavin]

  16. 216
    Jeffrey Davis says:

    re: 215

    As long as the underlying physics is correct, there’s not a “problem”: energy will keep getting added to the Earth’s climate system. Eventually, that’ll show up in higher air temps. It really can’t happen any other way. There are cooler waters in the oceans that can dampen that for awhile, but the energy that goes into the oceans doesn’t disappear.

  17. 217
    Sully says:

    As a reasonably informed non-scientist with no dog in this hunt I’m heartened by the bet but wish it was significantly larger. At 2500 Euros it puts some skin in the game but not as much skin as is being asked of those who will most suffer from reduced economic growth if a carbon tax is instituted.

    [edit – discussions of who called who what are off topic]

    The question before me as a voter is how much pain should we inflict on ourselves now to avoid pain later. That is a cost benefit question which can’t be resolved if people are name calling rather than presenting evidence.

  18. 218
    Ray Ladbury says:

    Sully, You seem to neglect the fact that if we do not act now, we will pay a whole lot more in the future, and maybe not even the distant future. Moreover, many of the problems we face may be amenable to improved science and technology. Others will be amenable to greater efficiency. These could actually foster growth in the future. Each of us has a lot more than 2500 euros riding on this proposition, and every evidence points toward the winning bet being on acting soon.

  19. 219
    Jess Whitaker says:

    I’m happy to see someone has addressed this article. However, I’m a little confused as to why you failed to explain your eagerness to bet money. Ignorant climate skeptics could and probably would use this review of Keenlyside’s study to argue scientists “believe” global warming rather than deduce its occurrence from hard data. Not everyone has those temperature trends in their back pocket.

  20. 220
    jonny says:

    Why 2500? Why not 100,000? or 10? I think that you should point out that they might not take your bet because it is too much money.

    Anyone who plays p o k e r knows how that works. Even if you have a 51% chance of winning, you don’t go all in. The amount of the bet is important.

  21. 221
    Ray Ladbury says:

    Jonny, 2500 euros represents a sufficient commitment to be meaningful and is within the means of most professionals to raise if they need to. It is large enough that one would not commit to it frivolously and small enough that it is not beyond the means of a team of professionals. One could also take it as a statement of how confident the RC team are of continued warming.

  22. 222
    Chuck Booth says:

    Re # 219
    “Ignorant climate skeptics could and probably would use this review of Keenlyside’s study to argue scientists “believe” global warming rather than deduce its occurrence from hard data.”

    But, they’ve been doing that all along, despite an extensive peer-reviewed literature on the subject, and despite a decade of IPCC reports. Even if they learn of it, the bet won’t influence the skeptics either way – their minds are already made up.

  23. 223
    Sean Rogers says:

    Re: #222

    Those who are smart should not have their minds totally made up either way at this point – skeptic or AGW believer. I think bets like this are good, because they represent confidence in one’s position…however, the average Joe would do best to wait out at least the next 10 years and see where the science/trends stand at that point.

    If RC wins this bet, that proves something about their science. If this other group that predicts cooling turns out to more correct, that also proves something.

  24. 224
    Jim Eager says:

    Re Sean Rogers @223: Except that the ghg pump will continue ticking as we wait. Waiting 10 years means that there will be at least* 10×2.5 ppmv more CO2 in the atmosphere, or 412 ppmv total, minimum.

    (*Not counting an acceleration in either antropogenic emissions or in CO2 and CH4 emissions from natural sinks–not a safe assumption in either case.)

  25. 225

    Umm, I can’t seem to find the page of the original post in English.
    Can someone help with a link?

    [Response: Click on the US/UK flag icon. – gavin]

  26. 226
    Marcus says:

    Re #223: Sean Rogers, there was this great set of articles in EOS, the journal of the American Geophysical Union, which were titled “The Greenhouse Debate: Time for Action?” They were a correspondence between two groups of authors, one group advocating, much like you, a 10 year delay before implementing a GHG policy because they judged the costs of delay to be small compared to the benefits of learning over that 10 year period. The other group advocating starting immediately with a phased in approach to GHG control, noting that after waiting for 10 years, they were sure someone else would repeat the “wait for 10 years” argument. The publication date of this edition of EOS? December 31, 1991. That was more than 16 years ago. Hansen talked in front of Congress is 1988, almost 2 decades ago. Heads of state signed the UN Framework Convention in 1992. Kyoto was approved over a decade ago. The evidence since then has only been better and stronger – how long should the average Joe wait? Had we started implementing a carbon pricing policy in 1988, we would be in a much better position today with respect to increased energy costs. And given that it is unrealistic (and unreasonable) to expect developing nations to make much of a commitment until several years after the developed world (and especially the US) shows some good faith efforts, you’d in effect be delaying their entrance until almost mid-century…

  27. 227
    Ray Ladbury says:

    Marcus, Arguably, we would be better off not just in terms of climate, but also in economic terms, as the price of oil has dealt a severe jolt to the global economy. I would also not that those yelping the loudest for delay are precisely those with the least understanding of the science.

  28. 228
    james jones says:

    Be ready to pay up. Looks like temps from 2001 to 2010 will be lower sorry.