The Global Warming Challenge

Evidence-based forecasting for climate change

The Global Warming Challenge

with 38 comments


The following terms were sent to Al Gore Tuesday, June 19th, 2007.

Al Gore has claimed that there are scientific forecasts that the earth will become warmer and that this will occur rapidly. University of Pennsylvania Professor J. Scott Armstrong, author of Principle of Forecasting: A Handbook for Researchers and Practitioners, and Kesten C. Green, of Monash University (and Armstrong’s Co-Director of, have been unable to locate a scientific forecast to support that viewpoint. As a result, Scott Armstrong offers a challenge to Al Gore that he will be able to make more accurate forecasts of annual mean temperatures than those that can be produced by current climate models.

The general objective of the challenge is to promote the proper use of science in formulating public policy. This involves such things as full disclosure of forecasting methods and data, and the proper testing of alternative methods. A specific objective is to develop useful methods to forecast global temperatures. Hopefully other competitors would join to show the value of their forecasting methods. These are objectives that we share and they can be achieved no matter who wins the challenge.

Al Gore is invited to select any currently available fully disclosed climate model to produce the forecasts (without human adjustments to the model’s forecasts). Scott Armstrong’s forecasts will be based on the naive (no-change) model; that is, for each of the ten years of the challenge, he will use the most recent year’s average temperature at each station as the forecast for each of the years in the future. The naïve model is a commonly used benchmark in assessing forecasting methods and it is a strong competitor when uncertainty is high or when improper forecasting methods have been used.

Specifically, the challenge will involve making forecasts for ten weather stations that are reliable and geographically dispersed. An independent panel composed of experts agreeable to both parties will designate the weather stations. Data from these sites will be listed on a public web site along with daily temperature readings and, when available, error scores for each contestant.

Starting at the beginning of 2008, one-year ahead forecasts then two-year ahead forecasts, and so on up to ten-year-ahead forecasts of annual “mean temperature” will be made annually for each weather station for each of the next ten years. Forecasts must be submitted by the end of the first working day in January. Each calendar year would end on December 31.

The criteria for accuracy would be the average absolute forecast error at each weather station. Averages across stations would be made for each forecast horizon (e.g., for a six-year ahead forecast). Finally, simple unweighted averages will be made of the forecast errors across all forecast horizons. For example, the average across the two-year ahead forecast errors would receive the same weight as that across the nine-year-ahead forecast errors. This unweighted average would be used as the criterion for determining the winner.

Terms of the challenge can be modified by mutual agreement.

If Al Gore accepts the challenge, each party would invest $10,000 in a mutually agreed Charitable Trust stock account on December 1, 2007. The charity will receive the total value in the fund when the official award is made at the annual International Symposium on Forecasting in 2018. Should Scott Armstrong win, the gift would be made to the Institute for Justice, in Arlington, Virginia. Should Al Gore win, he will designate the charity.

Details on the challenge and related materials such as the paper on climate forecasting by Armstrong and Green are provided at To facilitate open discussion, a blog is provided at

Written by climatebet

June 16, 2007 at 3:32 pm

38 Responses

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  1. Does making more accurate one- to ten-year-ahead forecasts of annual mean temperatures, measured by the average absolute forecast error, compared to a naive model, prove that there are no scientific forecasts that the earth will become warmer?

    Paul Mars

    June 18, 2007 at 8:30 am

  2. […] professor of forecasting methods at the Wharton School, an internationally ranked business school, challenged Al Gore to a $10,000 bet on the viability of current climate […]

  3. Terrific bet… Al, if you’re reading, I will side wager $500 with you and give a 2-to-1 payout if Dr. Armstrong is wrong. Hello…?

    Steve in Princeton

    June 22, 2007 at 9:07 pm

  4. Can the average Joe get into this bet? I’d second ‘Steve in Princeton’s’ side wager of $500 with 2 to 1 payout if Dr. Armstrong is wrong — seems like such a great sucker bet!

    George Winski

    June 22, 2007 at 10:46 pm

  5. Here’s a link to a journal article that presents highlights of a study that uses one natural process (Earth Magnetic Field Variation) variable that can predict global temperatures 6 to 7 years in the future… And there’s no one other variable that can do that.

    Edward Moran


    June 23, 2007 at 5:13 am

  6. Sounds like fun, but….

    This is a focus on temperature alone. It sounds as though only surface temperature is being measured. Getting agreement as to the sampling sites should in itself be entertaining. Let’s avoid urban/industrial areas, deforrested areas, new agricultural digs etc. Let’s include the polar cap areas, Siberia, mountain tops, deserts etc.

    What about also measuring upper atmospheric temperatures at the same time? The upper atmospheric temperatures have risen less than those at the earth’s surface; a worrysome flaw in the greenhouse theory.

    No matter the outcome of this contest, nothing will emerge to address causation. I “bet” that average global temperature will increase as expected from the cyclic natural events so well doumented by Prof. S. Fred Singer.

    Charles G. Battig, MD

    June 23, 2007 at 12:41 pm

  7. Rising temperatures at the moment is more important than what have caused them, I think. Global warming is so obvious especially in tha last 20 years.


    June 23, 2007 at 5:59 pm

  8. More on the “$20,000” bet

    Following on from this post, I emailed J Scott Armstrong, he pointed me to this web site/blog and the bet is outlined in more detail in this post.

    At a glance, he is using the most obvious and trivial trick

    James' Empty Blog

    June 24, 2007 at 1:40 am

  9. Why are we debating about this when it actually has no relevance to the Global Warming issue?

    We should stop arguing about if the records or forcasts are accurate, or if Global Warming is actually ‘real’ and focus on sustainable energy sources and way to decrease the harmful effects of emissions and pollution on the environment. Even if the world doesn’t warm due to Global Warming, if we actually do something about the other issues that surround it, we would be doing something productive for the Earth and future generations. Better to be safe than sorry.

    If Al Gore actually took on this challenge (which would be rather one sided, because he is not qualified for this sort of work) and lost, wouldn’t that just mask all the global awareness about the Earth he has put forward and how we are damaging the environment?

    This challenge is tossing away the real issue here.


    June 24, 2007 at 3:02 am

  10. Professor Armstrong’s sound bite is only an attempt of bait and switch, taking the eye off the ball, a childish prank. The requirement of the human species to take care of the earth can not be altered by a half wit scholar with an alternative agenda. The assertion that the earth is not sick proves his ploy. To visit any conservation area you may have visited when you were a child proves this. Fix the earth now!


    June 24, 2007 at 5:02 pm

  11. fix the earth now?? Rcheery really, the earth is not an engine, what should we replace the spark plug?
    Why do people think we can save the earth or change the climate change? Try saving your city or fellow man then get back with me. Oh wait, that would be an inconvience.


    June 25, 2007 at 12:01 pm

  12. weethan, I am at a loss to understand your point. Are you saying “let’s not debate whether global warming is a) happening or b) predictable or c) caused by largely or primarily by humans, let’s just act as if it is?”

    If so, I think you must have a real misunderstanding of the costs of reducing greenhouse gas emissions. If it were easy or costless to do that, then I would agree with you. But it’s not.


    June 25, 2007 at 3:08 pm

  13. Weethan and Rcherry, So are you now conceeding that you’ve lost the “tax us because of global warming” scare argument and now your new ploy is “tax us to save the earth” guilt argument? Talk about bait and switch. Sorry, but we’re not buying this argument either. When your suggestions become tenable the invisible hand of the market place will adopt them. Don’t take yourselves so seriously. You’ll overheat and contribute to global warming. Now let’s all just chill out, take it easy, and I won’t force you to buy a handgun if you won’t ram your socialist stealth taxes ideas down my throat. That’s not to say you aren’t free to sell all your belongings and contribute their proceeds to developing alternative energy sources. Go for it. Put your money where your mouth is. We won’t stop you.

    Chris McLaughlin
    Orange Park, FL

    chris mclaughlin

    June 25, 2007 at 6:35 pm

  14. Ooops, give me back one of those “e”s in conceding, please. I might need it, later.

    chris mclaughlin

    June 25, 2007 at 6:40 pm

  15. “Rising temperatures at the moment is more important than what have caused them”

    If you don’t know what is causing them, spending trillions on a solution is ill advised, to say the least. But then again, I am not part of the “reality based” left, so what do I know?


    June 25, 2007 at 7:04 pm

  16. Al Gore’s global warming hysteria is making him big bucks every time he sells foolish people carbon offsets. Fools like you that think human activity is responsible for climate change rather than solar activity are so arrogant. You think everything in the universe can be controlled and manipulated by the human race! The only thing being manipulated is the population of fools buying into the climate change hysteria. You think computer models that don’t take into account atmospheric and oceanic effects (because they are not understood well enough to model) are somehow worth changing your lifestyles? Go ahead! Al Gore and gaia will thank you!


    June 25, 2007 at 8:48 pm

  17. Why not 1000 Points? why only 10? we can get data for 40 years on more that 1000, and the warming is a global total not just a few points? I mean some places are bound to get colder from the jetstrem shifting, so 10 is a damn small test set. So why not 1000, 10,000?

    I smell a rat.


    June 25, 2007 at 9:30 pm

  18. Most things in life are costly, JChandler, it’s just that some things are more important that other things – and global warming and all the issues surrounding it cannot be dealt with a “sit back and watch what happens” kind of attitude.

    If we reduce greenhouse gases and other emissions, and if people actually accepted that it has other implications other than just warming, we would be a lot better off. Instead we are just debating about a rise in temperature, which hasn’t really got to do with anything other than who is right and who is wrong.

    Maybe we should be investing in energy sources such as hydro and solar? Or are the governments too obsessed with the coal boom to even care if it’s harming the environment?

    And how costly is all this research and improvement in energy and other areas? Or is that just another misconception…?


    June 26, 2007 at 6:23 am

  19. And chris mclaughlin, I really have no idea what you post is about, because I can’t seem to string together what your comment means at all. You’re somehow talking about handguns, sarcasm that I’m “overheating” and pointing out that I’m conceeding to something I didn’t even mention?

    I think you’ve missed my point…


    June 26, 2007 at 6:27 am

  20. Armstrong is cheating.

    His naive (no change) model automatically tracks any warming from year to year, so he isn’t really betting strongly against warming. And he weights short term predictions equally to long term ones. In the short term, however, random noise dominates.

    He should really bet that temperatures AFTER N years won’t be warmer than the average of the past N years. Al Gore gets to predict warming using the model of his choice. After N years, we take an M year average to get a good grip on the mean temperature, and the winner is the one who is the closest.

    Ignatius Gorgonzola

    June 26, 2007 at 9:02 am

  21. Population Ehrlich made a bet about resource depletion. He lost. Also lost was the billions of dollars blown preparing for the disaster that never came.

    Walter E. Wallis

    June 26, 2007 at 7:18 pm

  22. I’ll back you, especially if any Hollywood types want to increase the bet!


    June 26, 2007 at 7:28 pm

  23. Weethan…On what basis, and using whose criteria, are you going to make that investment decision (Maybe we should be investing in energy sources such as hydro and solar?)

    Because it feels good, or seemed like a good idea at the time, or everybody in Hollywood said I should?

    “Most things in life are costly”… indeed. On what basis do you claim that it’s better to invest in solar energy than to dig wells in Africa for sanitary water sources for the poor?

    Nothing is as costly as making a mistake in how a society invests its accumulated wealth…and you haven’t a clue as to how to make those decisions other than everyone you know says “global warming, the sky is falling…we can’t afford to wait and see what happens”…

    What we can’t afford is to run off throwing money at problems that don’t exist when there are plenty of problems that DO. That would be very costly indeed.

    doug in colorado

    June 26, 2007 at 10:13 pm

  24. The fact is that Gore won’t bet or debate his assertions. Why should he? He’s making money on the hysteria that he has caused. I just hope he has to pay it all back when this whole fiasco is over.

    John Nicklin

    June 27, 2007 at 12:33 am

  25. As I pointed out below, Armstrong’s bet essentially drowns the effect of global warming in noise, by using a “naive” model that would itself track warming.

    Consider the following scenario: suppose Al Gore is right, and predicts that temperatures will rise 0.1 deg per year, with an added yearly random term of 0.5 degrees. In other words, T=T0+0.1*year+Gaussian*0.5

    Let’s assume that Al takes Armstrong’s $20,000 bet as stated. I just did a Monte Carlo simulation shows that Al will win just $5600 over the 10 year interval of the bet, with a 1 sigma random variation of $5700. Al Gore’s model might be right, but the way the bet is structured whittles his advantage down by forcing him to bet on short intervals.

    Now if Armstrong wanted to bet on 5 year averages before the start and after the end of the 10 year interval, then Al would win virtually the entire $20,000, because Al would be betting on what models actually predict – LONG TERM rises in temperature – and not on year to year random noise.

    Ignatius Gorgonzola

    June 27, 2007 at 2:05 am

  26. My bet, don’t hold your breath waiting for Gore to respond. This is about politics, not science.


    June 27, 2007 at 2:38 am

  27. doug in colorado, don’t you see that Global Warming is just not one issue? Even if it proves to be false, which I doubt is very likely, power sources like coal and oil are ruining the physical environment in hundreds of ways that are proven to exist a long time ago. Acid rain, air pollution and other such devastating implications of inneffective power use are proven to exist and are harming the surround environment and the communities that are subjected to them.

    Instead of building another coal factory and digging up more coal from the earth, why don’t the governemnts just build a solar or hydro power plant? They’re renewable and less costly than the “dig up and burn” method and last alot longer. The reason the government doesn’t build those sorts of power plants because they don’t gain the same amount of revenue from selling the power or paying people to extract coal – or selling it off to other countries. Not because this will increase taxes or anything – it’s because of simple, plain, greed.

    I’m not saying we shouldn’t spend money to help people with poor living conditions, the fact is that building new renewable energy power plants isn’t costly, it’s just replacing the old method – instead of building a coal one, why not a hydro-electric one?

    For example: Electric of Hybrid cars. Why doesn’t everyone buy them instead? Most people would say it is too costly – but that is a downright LIE. An electric car takes the same amount of labour to build and manufactor as any other automobile, but they are only expensive because some people are too greedy to let those sort of non-pollution cars enter market. Why? Because they’re so afraid the price of their oil will go down that they make deals with the companies to sell out their cars.

    Oh – and wait a minute – lets go back to your argument.

    “than to dig wells in Africa for sanitary water sources for the poor?”

    Yeah, I’d like to know that too. WHY isn’t the government doing anything about those sorts of problems apart from throwing support here and there when they decide to blow up their city in a war? It’s a OBVIOUS problem, right? It’s OBVIOUS that someone needs to do something about it other than the charitable organisations, right?

    Then WHY isn’t that happening?

    Simple – people in power are to consumed with profit, their own economy and their own life and way of thinking to even care about what issues need to be attended to. If there are issues to be dealt with suddenly and it’s on a global scale, they want nothing to do with it.

    And doesn’t that just bring us straight back to Global Warming…?


    June 27, 2007 at 6:06 am

  28. […] who work in the weather forecasting world have asked the Goracle to man up and take their $10,000 bet as to whom can produce the more accurate climate model. Al Gore has claimed that there are […]

  29. 1. The Earth was created by, ad is regulated by, God.
    2. To think that humans could do something that would have an effect of such magnitude (i.e. cause global warming, or stop global warming) is arrogant and ridiculous.
    3. The idea that the melting of the polar ice caps would flood the Earth is also stupid. When water freezes it expands and takes up a greater volume of space than if it was in its liquid state. See where I am going with this yet? If the ice caps melted coastlines would recede. Don’t believe me? Get a cup, drop a few ice cubes in it, then fill it to the very top with water. Then wait for the ice to melt and watch what happens. It wont overflow I can promise you that, the water level will actually go down.


    June 28, 2007 at 5:23 am

  30. “For example: Electric of Hybrid cars. Why doesn’t everyone buy them instead? Most people would say it is too costly – but that is a downright LIE. An electric car takes the same amount of labour to build and manufactor as any other automobile, but they are only expensive because some people are too greedy to let those sort of non-pollution cars enter market.”
    Wrong wrong wrong wrong. To assemble the cars maybe so. To manufacture the batteries costs lots of money. To mine the matterials to build the batteries cost money and creates a lot of pollution. To dispose of the batteries cost money and pollution. To replace the batteries after 100K miles or so costs money. To charge the batteries costs electricity, which in this part of the country is coal generated. You guys wont let us build nukes. You might consider a econ class if your going to argue this stuff.


    June 29, 2007 at 12:30 am

  31. “The idea that the melting of the polar ice caps would flood the Earth is also stupid. When water freezes it expands and takes up a greater volume of space than if it was in its liquid state.”

    True, but that’s only the case for the North Pole. Antarctica, which has a greater amount of ice than the North Pole, has most of its ice situated on top of the actual land mass. If Antarctica ice melted, the water would flow off the land mass into the ocean, rising the sea levels dramatically.

    “Wrong wrong wrong wrong. To assemble the cars maybe so. To manufacture the batteries costs lots of money. To mine the matterials to build the batteries cost money and creates a lot of pollution. To dispose of the batteries cost money and pollution. To replace the batteries after 100K miles or so costs money. To charge the batteries costs electricity, which in this part of the country is coal generated.”

    And batteries for electric cars make them cost triple that than normal cars? That’s so wrong – it’s just bigger companies buying the majority of electrical and hybrid cars out and forcing the brands that still manufacture electric cars struggle to sell their product. If you compared a car battery of an electric car to the amount of oil that is needed in a petrol based car’s lifetime, you would see the immediate difference. Plus electric car batteries last a lot longer now – and if hydro-electric power supply was used, like where I currently live, there would be no extra emissions at all.

    So which type of car is better for the environment? Or is that part of your argument flawed also?


    June 29, 2007 at 10:06 am

  32. I think that the crucial issue here is the need to bring the debate back towards reality. Dr. Armstrong does not seem to be challenging the theory of Global Warming, just the extreme and unhelpful claims made by Mr. Gore.

    When alarmism comes to dominate a discussion that has tremendous implications for everyone the world over, we all lose. I applaud any effort to force this undeniably important conversation back onto surer ground.


    June 30, 2007 at 4:52 pm

  33. Instead of solar, etc. why not follow the lead of the French, Japanese and others and use nuclear power? Oh yeah, I forgot , the environmentalists just don’t get the attention over there that we give to them. They are the number 1 reason we have no new oil refineries in 30 years. I praise their name each time Big Oil rips me off at the pump. Unwittingly, they have empowered the Big Oil machine. Take a refinery off line for maintenance and they can jack the price. How Convenient that must be!! I hear that Exxon is considering forming a chapter of Sierra Club as it has been their leading contributor to the bottom line.

    Ray Blevins

    July 1, 2007 at 1:05 am

  34. Nuclear power, although it does not produce greenhouse gases, still has other environmentally and socially hazardous implications. You still have to mine the uranium and other materials to actually make the power station support itself, it takes a very long time to build, and it has numerous health risks and waste products that cannot safely or easily be destroyed or prevented to a more-than-satisfactory degree; even in today’s standards. Hydro-electric, solar and wind is the direction to head in. They are all renewable energy sources; but nuclear is not renewable.


    July 1, 2007 at 6:01 am

  35. The reason the earth is sick, is because there is little immediate money in fixing it and there was money in the poisoning. So make the repair of the earth profitable or don’t…. for a more immediate profitable goal.


    July 2, 2007 at 12:45 am

  36. A few facts: I ride my bike to work. I don’t eat meat. Car exhaust smells bad.

    With those facts out in the open, you should know that I’m doing ‘my part’ to reduce global warming. But not because I believe in the whole man-made global warming hyperbole, but simply because I like a clean, grean environment in which to live.

    Al Gore is a shyster (I could very well have added this to my above list of facts.) Nevertheless, I don’t enjoy sucking on exhaust fumes on my ride to work. But I strongly believe that the most fair, the most effective, and the most efficient means of change is through the marketplace.

    I also strongly believe science should be objective. There’s a lot of junk being passed off as ‘science’ by many whose zeal exceeds their knowledge. I heartily endorse this wager as a means of returning the debate to a solid scientific foundation.


    October 11, 2007 at 4:01 pm

  37. It is now pollitically correct to change the term “Global Warming” to “Climate Change”
    The reason for this change is so that it is easier to explain the current 10 year Cooling Cycle on Climate Change. Global Cooling for the last 10 Years = Climate Change.

    You won’t see this in Mainstream US Media.. It took the Australians to break the news!

    See what the head of the IPCC has actually acknowledged about the current Global Cooling at the following link:

    John B

    March 27, 2008 at 6:35 pm

  38. Well, here we are, almost one year after Al Gore refused to man up. Gore declined the wager, and he absolutely runs and hides from any neutral, moderated debate on his repeatedly falsified global warming hypothesis. So, what has another year revealed?

    1. Since 1998, temperatures have declined or remained flat; they have not increased. At all.

    2. The r-squared correlation between Sunspots and global temps is right on track: very few Sunspots, and declining temperatures.

    3. Carbon dioxide, an extremely beneficial plant nutrient, has steadily increased — at the same time that the Earth’s temperature has fallen. Therefore, CO2 can not cause global warming; effect can not precede cause.

    Inescapable conclusion: anthropogenic global warming [AGW] is a purely financial scam, aimed directly at American taxpayers. AGW has been repeatedly falsified via the Scientific Method [peer-review]. The only basis for Gore and the UN’s alarmism comes from computer models, which are uniformly inaccurate. Empirical [real world] measurements, on the other hand, show significant cooling over the past year. Gore’s climate models are wrong. All of them.

    Before he left office, UN Sec-Gen Kofi Annan floated a proposed .7% “World Tax” [which would exempt all non-industrialized countries, preposterously including China, Russia, Brazil and most smaller countries]. The UN’s World Tax is to be paid into the UN to “combat global warming.” [Note also that the UN has steadfastly refused to allow any independent accounting of its spending.] Kofi Annan’s successor, Ban Ki Moon, realizing that a “World Tax” is bad P.R., dropped the term “World Tax,” and placed the proposed tax in the UN’s “Millennium Development Goals” program. But it still proposes a .7% tax, primarily aimed at U.S. taxpayers [our GDP is ~$14 trillion, so a .7% tax = about $100 billion per year – to be paid to the opaque and unaccountable U.N. kleptocrats].

    The global warming scam is all about MONEY – American taxpayers’ money, and how the U.N. can get its hands on a revenue stream to replace the lost Oil-For-Food income.

    Now that global temperatures are declining, maybe it’s time for The Gorebot and his acolytes to begin arm-waving over a colder climate. After all, “climate change” allows them to continually move the goal posts – which by now are in the next county.


    April 24, 2008 at 1:06 pm

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