Conclusions - Climate Change: Identification and Projections - page 133

of a return to weak solar activity as in the 1700s-1800s, our identified
models instead give rise to fears of a drop in temperatures which could
cancel out the rise of the past century. This event is neither more nor less
probable than the alarming continuation of the rise predicted by the IPCC.
12.5. The climate change in question
Nobody denies that the 20 th Century has seen temperatures increase by
almost one degree, continuing a trend which started two centuries earlier.
But is it possible to speak of anthropogenic, and more or less irreversible,
climate change?
The analysis of the causes of this warming, as global identification
highlights them, provides parts of the answer. A primary cause is solar
activity. This is confirmed by the current stagnation, which belatedly results
in a drop in solar activity which started 30 or 40 years ago. A second cause is
the climate's natural variability: during the last quarter of a century, the
ocean has released quantities of heat which have contributed to the warming,
and the current stagnation can be explained by a recovery of this heat by the
oceans. This recovery is probably far from being complete.
With regard to these two explanations, the effects of human activity are
marginal, and difficult to assess via climatic observations. This could only be
confirmed theoretically, but this seems even more uncertain, and there does
not appear to be a real consensus on quantification.
In the future, a fall in solar activity could outweigh all other causes,
taking away any significance from the expression climate change (and a
fortiori climate disruption )
12.6. Prospects
Much still needs to be done to refine the quantification of identified
models. Firstly upstream, for paleoclimatic reconstructions, where a
consensus is far from being found, as well as for solar activity. Afterwards,
work needs to be done on the identification techniques themselves. We went
no further than the output error method, to ensure any manipulating by