The Global Warming Challenge

Evidence-based forecasting for climate change

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Chorus does not justify climate prophecies

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Armstrong and Green’s work was featured in the Sydney Morning Herald’s July 7, 2007 article, “Chorus does not justify climate prophecies” by Michael Duffy:

The next week promises some excitement for those who believe global warming threatens our future. Today they can enjoy the Live Earth concert in Sydney. But on Thursday they will have to suffer ABC TV’s showing of The Great Global Warming Swindle, a British documentary sceptical of the orthodoxy…

…Professor Scott Armstrong is at the Wharton School at the University of Pennsylvania. Dr Kesten Green is with the Business and Economic Forecasting Unit at Monash University. They’re experts in forecasting techniques. (Many people are unaware that forecasting is a subject with many academic experts and a body of research going back to the 1930s. The website forecastingprinciples.com attracts more than 200,000 visitors a year.) Their paper is Global Warming: Forecasts by Scientists Versus Scientific Forecasts. It was written for the 27th Annual International Symposium on Forecasting.

Armstrong and Green looked at the Intergovernmental Panel on Climate Change’s Working Group 1 report from earlier this year. This is the major source for the orthodoxy.

They focused on chapter eight, which sets out the methodology used for the forecasts in the report. They found that the panel, despite its immense assembly of scientific talent, appeared to have no idea of how to make a reliable forecast. Although the chapter has 788 references, none relates to forecasting methodology.

Armstrong and Green rated the methodology used by the panel against 89 principles of good forecasting derived from years of research. They found that the panel report breached 72 of those principles. They concluded that the forecasts the weather was likely to change in many negative ways were worthless.

What are some of the main principles of forecasting? One involves the notion, so popular among orthodoxy advocates, of consensus. While consensus might say something about testable scientific theories, it says nothing about forecasts.

Armstrong and Green say: “Agreement among experts is weakly related to accuracy. This is especially true when the experts communicate with one another and when they work together to solve problems, as is the case with the Intergovernmental Panel on Climate Change process.”

Another principle involves uncertainty and complexity. The more of each you have, the less sure you should be of your forecasts. Climate forecasts involve so many factors and so much uncertainty that Armstrong and Green believe they’re useless.

Many people believe these complex forecasts can be trusted because computer models are used. But so much uncertainty and subjectivity is involved in the input that Armstrong and Green say the use of these computer models is just a modern version of an old practice: the use of mathematics to make personal opinions sound more impressive. (Robert Malthus’s predictions on population increase and food decline, very influential in the 19th century, were presented with a lot of mathematics. They were wrong.)

Armstrong and Green note: “To our knowledge, there is no empirical evidence to suggest that presenting opinions in mathematical terms rather than in words will contribute to forecast accuracy.”

Armstrong has just offered Al Gore a $US20,000 ($23,000) bet that the Intergovernmental Panel on Climate Change temperature forecasts are wrong.

Written by climatebet

July 9th, 2007 at 11:37 pm

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