The model accounts for the dynamic feedbacks that occur naturally in the Earth's climate system —
temperature projections determine the likelihood of extreme weather events, which in turn influence human behavior.
There was no mention of using a «mean» to
determine the start value of the
projection (in part because the IPCC were explicitly projecting
temperatures to rise, there was no expectation that
temperature measurements would drop so much that years later it makes the difference whether the models can be considered accurate).