Global Warming: Forecasts by Scientists versus Scientific Forecasts*
J. Scott Armstrong†, The Wharton School, University of Pennsylvania
Kesten C. Green, Business and Economic Forecasting Unit, Monash University
Paper prepared for ISF 2007 in New York
June 23, 2007
Abstract
In 2007, a panel of experts established by the World Meteorological Organization and the United Nations Environment Programme issued its updated, Fourth Assessment Report, forecasts. The Intergovernmental Panel on Climate Change's Working Group One Report predicts dramatic and harmful increases in average world temperatures over the next 92 years. We asked, are these forecasts a good basis for developing public policy? Our answer is "no".
Much research on forecasting has shown that experts' predictions are not useful. Rather, policies should be based on forecasts from scientific forecasting methods. We assessed the extent to which long-term forecasts of global average temperatures have been derived using evidence-based forecasting methods. We asked scientists and others involved in forecasting climate change to tell us which scientific articles presented the most credible forecasts. Most of the responses we received (30 out of 51) listed the IPCC Report as the best source. Given that the Report was commissioned at an enormous cost in order to provide policy recommendations to governments, the response should be reassuring. It is not. The forecasts in the Report were not the outcome of scientific procedures. In effect, they present the opinions of scientists transformed by mathematics and obscured by complex writing. We found no references to the primary sources of information on forecasting despite the fact these are easily available in books, articles, and websites. We conducted an audit of Chapter 8 of the IPCC's WG1 Report. We found enough information to make judgments on 89 out of the total of 140 principles. The forecasting procedures that were used violated 72 principles. Many of the violations were, by themselves, critical. We have been unable to identify any scientific forecasts to support global warming. Claims that the Earth will get warmer have no more credence than saying that it will get colder.
*Neither of the authors received funding for this paper.
† Information about J. Scott Armstrong can be found on Wikipedia.
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