The Global Warming Challenge

Evidence-based forecasting for climate change

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Armstrong extends the deadline for the Global Warming Challenge to Al Gore – and simplifies the bet

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After a series of cordial exchanges, Al Gore had said that he was too busy when the challenge was first offered. As a result, Scott Armstrong extended the deadline and simplified the process such that the only actions required of Al Gore are to 1) sign the letter and 2) deposit $10,000 in the Challenge Fund. The letter below explains the new simplified process.

November 28, 2007

Honorable Albert Gore
2100 West End Avenue
Suite 620
Nashville, TN 37203

Dear Mr. Gore,

Thank you for your previous emails and your letter concerning the Global Warming Challenge. You had mentioned that you were looking forward to reading my book, Principles of Forecasting; I believe the principles are critical to making accurate forecasts for global warming.

In earlier communications, your staff mentioned that you were too busy at the time to enter in the Global Warming Challenge. As a result, I am happy to extend the deadline beyond December 1st, 2007, to March 26th, 2008. In addition, I have found a way to make your task much easier. I propose that you place $10,000 on the Hadley Centre Forecasts.

This would merely require that you sign on the “I agree” line at the bottom of this letter. Each of us would then arrange to transfer $10,000 to a trust of your choosing. The money would be invested in mutual funds, and the proceeds would go to the winner’s charity on March 26th, 2018.

As a brief reminder, here is an overview of the original Global Warming Challenge (details can be found at

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.

Details on the 10-year bet would be handled with discussions between me the Hadley Centre. I would ask an independent board to aid in this process of finding an appropriate design and to monitor the progress of the bet. You would be kept up to date, and you would have the right to ask the board to consider changing aspects of the design.

In The Assault on Reason, you stated your interest in the use of science in addressing global warming:

“We must, for example, stop tolerating the rejection and distortion of science. We must insist on an end to the cynical use of pseudostudies known to be false for the purpose of intentionally clouding the public’s ability to discern the truth. Americans in both parties should insist on the reestablishment of respect for the rule of reason. The climate crisis, in particular, could cause us to reject and transcend ideologically based distortions of the best available scientific evidence.” p. 10

I believe we have a common goal. Although I expect to win, the purpose of the challenge is to promote interest in a scientific approach to forecasting. Climate experts have done much useful work to explain the past, but their approach to forecasting does not adhere to scientific principles.


J. Scott Armstrong

For the signature of Mr. Gore:

I agree to the terms of the Global Warming Challenge with the variations specified in this letter

Written by climatebet

November 30th, 2007 at 2:20 am

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