The three researchers created a naive ‘benchmark’ forecast of temperature over the 16-year period since 1992 (when the IPCC issued it’s 3° per century forecast of global warming). Their naive forecast was that the temperature over the rest of the period would be the same as the mean temperature in 1992. When compared with both HADCRUT (UK Met.Office) and UAH (Satellite) observations, their naive ‘forecast’ performed as well as the UN’s elaborate global circulation models. When ‘back-cast’ against the HADCRUT series of temperatures between 1850 and 1975—a year chosen to minimize ‘cherry picking’ the data—the naive forecast significantly outperformed the IPCC modeled forecasts.
The chart extracted from the Green, Armstrong and Soon paper shows the use of the naive forecast alone as a ‘benchmark’ forecast of temperature after 1850 (HADCRUT):
“We used each year’s mean global temperature as a forecast of each subsequent year in the future and calculated the errors relative to the measurements for those years. For example, the year 1850 temperature measurement from Hadley was our forecast of the average temperature for each year from 1851 through 1950. We calculated the differences between this benchmark forecast and the Hadley measurement for each year of this 100-year forecast horizon. In this way we obtained from the Hadley data 157 error estimates for one-year-ahead forecasts, 156 for two-year-ahead forecasts, and so on up to 58 error estimates for 100-year-ahead forecasts; a total of 10,750 forecasts across all horizons.
[The chart] shows that mean absolute errors from our benchmark model increased from less than 0.1°C for one-year-ahead forecasts to less than 0.4°C for 100-year-ahead forecasts. Maximum absolute errors increased from slightly more than 0.3°C for one-year-ahead forecasts to less than 1.0°C for 100-year-ahead forecasts. “
The conclusion that the three forecasters reach is:
“Global mean temperatures were found to be remarkably stable over policy-relevant horizons. The benchmark forecast is that the global mean temperature for each year for the rest of this century will be within 0.5°C of the 2008 figure. There is little room for improving the accuracy of forecasts from our benchmark model…our analysis shows that errors from the benchmark forecasts would have been so small that they would not have been of concern to decision makers who relied on them. “
In the discussion they note three principles for policy forecasting that these results suggest must be applied to climate forecasts:
- Validation tests should properly be conducted on forecasts from evidence-based forecasting procedures. The models should be clearly specified, fully-disclosed, and replicable. The conditions under which the forecasts apply should be described.
- Speculation is not sufficient for forecasting. The belief that “things have changed” and the future cannot be judged by the past is common, but invalid.
- Finally, success in forecasting climate change and the effects of climate change must then be followed by valid forecasts of the effects of alternative policies.