Date of this Version
In 2007, the Intergovernmental Panel on Climate Changes Working Group One, a panel of experts established by the World Meteorological Organization and the United Nations Environment Programme, issued its updated, Fourth Assessment Report, forecasts. The Report was commissioned at great cost in order to provide policy recommendations to governments. It included predictions of dramatic and harmful increases in average world temperatures over the next 92 years. Using forecasting principles as our guide we asked, are these forecasts a good basis for developing public policy? Our answer is "no." To provide forecasts of climate change that are useful for policy-making, one would need to forecast (1) global temperature, (2) the effects of any temperature changes, (3) the effects of alternative policies, and (4) whether the best policy would be successfully implemented. Proper forecasts of all four are necessary for rational policy making. The IPCC Report was regarded as providing the most credible long-term forecasts of global average temperatures by 31 of the 51 scientists and others involved in forecasting climate change who responded to our survey. We found no references to the primary sources of information on forecasting methods despite the fact these are easily available in books, articles, and websites. In our audit of Chapter 8 of the IPCC’s WG1 Report, we found enough information to make judgments on 89 out of a total of 140 forecasting principles. The forecasting procedures that were described violated 72 principles. Many of the violations were, by themselves, critical. We concluded that the forecasts in the Report were not the outcome of scientific procedures. In effect, they were the opinions of scientists transformed by mathematics and obscured by complex writing. Research on forecasting has shown that experts' predictions are not useful. Instead, policies should be based on forecasts from scientific forecasting methods. We have been unable to identify any scientific forecasts of global warming. Claims that the Earth will get warmer have no more credence than saying that it will get colder.
accuracy, audit, climate change, evaluation, expert judgment, mathematical models, public policy
Green, K. C., & Armstrong, J. S. (2007). Global Warming: Forecasts by Scientists versus Scientific Forecasts. Retrieved from https://repository.upenn.edu/marketing_papers/133
Date Posted: 16 July 2007
This document has been peer reviewed.