Global Warming: Forecasts by Scientists Versus Scientific Forecasts

Abstract

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. 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 eno...

Validation and forecasting accuracy in models of climate change

“…The logic of this comparison is that it clarifies whether the GCM forecasts are compatible with the 'stylised forecasting facts' (of trend or no trend) or not. If a trending univariate benchmark is measured to be more accurate ex ante than the naïve no-change benchmark argued for by Green and Armstrong (2007) amongst others, this supports the notion of global warming. (Of course, it tells us nothing about either its causes or possible effective policy responses.…”

“…financial) it has proved hard to beat. In addition, Green and Armstrong (2007) and Green et al (2009) have provided arguments for its use in climate forecasting, although we do not regard as strong over the forecast horizons we are considering here (10-20 years). In addition, we will also try a number of benchmarks which have performed better than the naïve in the various competitions: simple exponential smoothing, Holt's linear trend and the damped trend (Gardner, 2006).…”

“…A number of researchers have criticised the IPCC models and forecasts for their failure to provide any evidence of their predictive accuracy, despite the IPCC's strong claims (Green & Armstrong, 2007;Pielke Sr., 2008). At the heart of this argument is the need for the IPCC and GCM builders to apply rigorous standards of forecast evaluation to the IPCC forecasts of temperature change and other key variables.…”

Golden Rule of Forecasting: Be Conservative

“…Consider the IPCC dangerous manmade global warming forecasts that have been used as the basis for expensive government policies (Randall et al 2007). An audit found that procedures used to generate these forecasts violated 72 of the 89 relevant forecasting principles (Green and Armstrong 2007a). …”

Rebuttal of “Polar Bear Population Forecasts: A Public-Policy Forecasting Audit”

“…Given this procedure, a bias shared by all AGS authors is likely to have influenced the grading and skewed the results toward an unfavorable assessment. Because AGS and Green and Armstrong (2007) incorrectly portrayed the known relationship between GHGs and global warming and the use of GCMs as tools for estimating the climate response to GHG forcing, the problem of bias in the application of subjective auditing criteria by AGS cannot be overlooked.…”