Scott Armstrong's notional bet with Al Gore provides evidence that the IPCC's preference for complexity has increased the size of forecast errors by as much as 45% over a seven year period. (Armstrong is represented by forecasts from the simple no-trend model, and Gore by the IPCC model "business as usual" projected warming rate of 0.03Â°C per annum.) Earlier, Green, Armstrong, and Soon's (2009) validation study found that the "business as usual" projection from the IPCC's complex forecasting models increased the size of forecast errors by seven times relative to the simple no-change model for the period of exponentially increasing atmospheric CO2 from 1851 to 1975.
A longer version of this essay is available from the popular climate change site, Watt's Up With That?, here.
Kesten and Scott's conference paper abstract and slides are available from ResearchGate, here.
Their paper, "Simple versus complex forecasting: The evidence" and their Simplicity Checklist are available from the Simple-Forecasting.com pages of the ForecastingPrinciples.com (ForPrin.com) website. (You can do your own ratings of the IPCC procedures, to check if your ratings might lead to a different conclusion.) The original Green, Armstrong, and Soon validation study of IPCC forecasting is available here.