The Alarmists have held since the 70's that Climate Sensitivity would be in the +4.5°C to +6°C range.

The Moderates in the 70's assigned a range of +1.8°C to +3°C.

Over time the models of the Moderates have crept upward in their bottom range in the face of reality. The 66% range is the "best guess" as of 2020.

It reflects the Moderate Faction position that 2XCO2 will cause +2.6°C to +3.9°C of warming.

In this study there was a HUGE fight about including an Alarmist model. That model is the "outlier" at +5.7°C. The Moderates didn't want to include it at all and their models assign a "less than" 5% likelihood of temperatures reaching that high at 2XCO2. As well as a less than 5% chance that warming will be as low as +2°C.

After this report, there was a BIG push to "decertify" the Alarmist model and not include it in future reports. That has been done. The next report won't include models which are so dramatically different from the others.