Introduction - Climate Change: Identification and Projections - page 7

thermometric measurements started to become widespread around the world.
Data from before this time can be qualified by paleoclimatology, and are
given in the form of reconstructions, created using traces, markers or
substitution measurements (proxies) left by the climate on the Earth and in
the oceans. These two types of data (instruments and proxies) cannot be used
in their raw form for the purposes of identification. They need to be linked
together in order to be processed as a continuous data stream through time.
Chapter 3 discusses a regrettable debate, a war of graphs where parties
exchange inconsistent arguments, often reduced to the display of climatic
signal lines. At times, these lines are contested to the point where the
credibility of paleoclimatic data in general is in doubt, thus jeopardizing the
very principle behind the identification of a climatic model. In practice, we
are able to totally disregard this controversy by processing all data available
without taking one side or the other. This collection of data is not exhaustive,
but its diversity is such that our conclusions cannot be accused of being
obtained through “cherry picking”.
Chapter 4 introduces the structure of the models which we would like to
identify. This is taken from the class of models known as EBM, or Energy
Balance Models. The simplest are static models, reduced to three or four
coefficients. They are too basic and unable to give an accurate picture of the
reality. The most complex models already constitute the first drafts of
GCMs, or General Circulation Models, for the atmosphere or oceans. These
have too many parameters and cannot be identified since there are many
which are redundant in terms of input/output. The characteristic feature of
the structure which is used is that each piece of input data is assigned a
balance sensitivity coefficient, but all are subject to the same transients of
heat transfer. A “black box” is created as a result, in which certain physical
coefficients appear in the form of combinations and remain out of reach in
their individually. This is the compromise made to find the right balance
between too many and too few parameters.
Chapter 5 brings together the assumptions relating to fundamental
climatic parameters of energy balance models, as well as their uncertainty
ranges. These are taken, directly or indirectly, from official IPCC
publications: SPM and AR5.
Chapter 6 examines the identification method. It is the simplest and most
reliable possible, that of the least square of output error (OE: Output Error