FIGURE 4. Hindcast/forecast decadal variations in global mean temperature, as compared with observations and standard climate model projections.

Model projections are twentieth century-RF followed by A1B scenario simulations ('20C-RF/A1B'); 'Stabilization' forecasts assume greenhouse gas concentrations fixed at year 2000 levels. Each point represents a ten-year centred mean; vertical bars indicate ensemble spread; verification and forecast periods are indicated (dark shading begins 2008, indicating the start of the true forecast period). Three additional decadal means (joined by a dotted line) show the evolution of the initialized and un-initialized 2005 predictions extended till 2030. Correlation of both hindcasts and climate model projections with observations are given in brackets. Correlation of the twentieth century-RF simulation with observations is greater than that of the hindcasts, but only marginally at the 5% significance level. Observed global mean temperature anomalies are from HadCRU3²⁸.