Short-term Predictions - Climate Change: Identification and Projections - page 126

3)Internal climate variability reached its peak around 2000 (see
Figure 11.3), and its subsequent short-term prediction can do nothing else
but decrease;
4) In any case, human action identified is too weak to compensate - at
least in the short-term - for the above downward trends.
Let us look again at point 3 above. By way of comparison, when a
barometer is very high, we can predict - in the absence of any other
information - that it will fall in the following days. The only error which
could be made is on when this drop will take place. However, when the
barometer gives an intermediate reading, it is not possible to predict whether
the next movement will be up or down: the optimal prediction is the mean
value (1014 mb), but this will be inevitably contradicted, in one direction or
another, at some point in the future. A posteriori , it so happens that, by
chance, the start date for the retroactive prediction (2000), corresponds to an
extreme in internal variability. Another date (e.g. 1990), would have given
less spectacular results but, in 2000, one would have to be willingly
blinkered to predict anything other than a stagnation, if not a cooling at the
start of the 21 st Century.
Nevertheless, the IPCC had predicted nothing of the sort, and had no
chance of predicting what actually happened at the start of the 21 st Century,
or even to explain it a posteriori , due to its refusal to take into account the
nonetheless blatant solar activity. This is also due to its tendency to
minimize the contribution of internal variability between the years 1980-
2000, aiming to point the finger of blame squarely at CO 2 . It has difficulty in
explaining these circumstances. Indeed, this can be seen in the executive
summary of Chapter 9 in the AR5, devoted to the evaluation of models
(p.743):
“There is very high confidence that models reproduce the general features
of the global-scale annual mean surface temperature increase over the
historical period, including the more rapid warming in the second half of the
20 th Century, and the cooling immediately following large volcanic
eruptions 4 . Most simulations of the historical period do not reproduce the
observed reduction in global mean surface warming trend over the last 10 to
15 years. There is medium confidence that the trend difference between the
4 Interestingly, the first part of this citation is in bold in the original text, but not the second.