Short-term Predictions - Climate Change: Identification and Projections - page 127

models and observations between 1998-2012 is to a substantial degree
caused by internal variability, with possible contributions from forcing error
and some models overestimating the response to increasing greenhouse gas
forcing.”
It is strange to read a claim of “ very high confidence ” in what is in fact a
simple observation: the reproduction by IPCC models of the rapid warming
over the last half-century. The statement that the models fail to reproduce the
current climate pause is also an observation, but the IPCC prefers to assign
no level of confidence to this whatsoever. However, medium confidence is
given to a diagnosis which arises from the evidence: internal variability,
substantial forcing errors and overestimations of the greenhouse effect in the
models, which could also apply to earlier periods.
Reading the entirety of Chapter 9 of the AR5, it seems that the IPCC is
more and more circumspect with regard to its large models and their
simulations - while maintaining their confidence in the most alarmist
predictions 5 . We would highlight that this Chapter 9 concludes with a single,
and rather revealing FAQ: “Are climate models getting better, and how
would we know?” (p. 824). We can deliberate over the response:
“Climate models of today are, in principle, better than their predecessors.
However, every bit of added complexity, while intended to improve some
aspect of simulated climate, also introduces new sources of possible error
(e.g. via uncertain parameters), and new interactions between model
components that may, if only temporarily, degrade a model's simulation of
other aspects of the climate system. Furthermore, despite the progress that
has been made, scientific uncertainty regarding the details 6 of many
processes remains.”
5 Doublethink?
6 And the devil is in the detail.