IPCC issued its first temperature prediction in 1990 (I actually use the prediction from the supplement to the 1990 report issued in 1992). Its 1995 report dramatically lowered this prediction. 2001 nudged this up a bit, and 2001 elevated the entire curve another small increment, keeping the slope the same. My hypothesis for what is going on here is that the various changes over time to the IPCC predictions reflect incrementally improved fits to observed temperature data, as more observations have come in since 1990.
In other words, the early 1990s showed how important aerosols were in the form of dramatically lowered temperatures (after Mt. Pinatubo), and immediately put the 1990 predictions well off track. So the IPCC recognized the importance of aerosols and lowered its predictions, putting the 1995 IPCC back on track with what had happened with the real climate since its earlier report. With the higher observed temperatures in the late 1990s and early 2000s the slightly increased predictions of temperature in 2001 and 2007 represented better fits with observations since 1995 (for the 2001 report) and 2001 (for the 2007 report).
Imagine if your were asked to issue a prediction for the temperature trend over next week, and you are allowed to update that prediction every 2nd day. Regardless of where you think things will eventually end up, you'd be foolish not to include what you've observed in producing your mid-week updates. Was this behavior by the IPCC intentional or simply the inevitable result of using a prediction start-date years before the forecast was being issued? I have no idea. But the lesson for the IPCC should be quite clear: All predictions (and projections) that it issues should begin no earlier than the year that the prediction is being made
http://sciencepolicy.colorado.edu/prome ... _ipcc.html