Scott vs. Al


Scott Armstrong seeks input on a global warming forecasting contest that will be offered to Al Gore 26 Jun 2007

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On Wednesday, June 27, I will present a Global Warming Forecasting Challenge to Al Gore (see

I am still making changes to the challenge, and I will contact Al Gore next Tuesday. Please send suggestions about making the challenge interesting, useful, fair, and attractive. The challenge appears below.


J. Scott Armstrong
Professor of Marketing, 747 Huntsman, The Wharton School, U. of PA,
Phila, PA 19104
home phone 610 622 6480
Home address: 645 Harper Ave., Drexel Hill, PA 19026
Fax at school: 215 898 2534

DRAFT 8: June 17, 2007

A Global Warming Challenge

Al Gore has claimed that there are scientific forecasts that the earth will become warmer. Wharton School Professor J. Scott Armstrong, author of Principle of Forecasting: A Handbook for Researchers and Practitioners, and Kesten C. Green, Armstrong’s Co-Director of, have been unable to locate a single 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 climate models.

The purpose of the challenge is to focus public policy on the proper use of science in formulating public policy.

Al Gore is invited to select any 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, the forecasts for the ten future years’ mean temperature at each station will be the same as the most recent year’s observation at that station prior to making any forecasts.

The challenge will involve making forecasts for 10 weather stations that are reliable and geographically dispersed. An independent panel 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.

One- to ten-year-ahead forecasts of annual "mean temperature" will be made annually for each weather station for each of the next ten years. The calendar year would end on December 31. Forecasts must be submitted by the end of the first working day in January. The criteria for accuracy would be the average absolute error at each weather station and each of the next ten years into the future. Simple averages will be made of the forecast errors for each number of years into the future. For example, the two-year ahead forecast errors would receive the same weight as the nine-year-ahead forecast errors.

Terms of the challenge can be modified by mutual agreement.

If Al Gore accepts the challenge, each party would post $10,000 on December 1, 2007. The money will be invested in a Charitable Trust stock account to be established at a brokerage house. The charity designated by the winner 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.

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