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According to observations (identified models):
+0.4°C
results from solar and volcanic activity;
+0.2°C from human activity;
+0.2°C from natural random fluctuations.
These values are simply guideline ones and the spreads indicated in the
graphs are of a different nature.
In our case, the dispersion results from that of the paleoclimatic
reconstructions used, both for the identification and the simulations, and we
will not extract ranges of probability or debatable confidence indices from
them. It is important to specify that, even though the display period adopted is
limited to 1850-2013, all of the millennium-old data contributes to the result.
In light of this, the variety of IPCC simulations results in part from the
internal variability of the climate simulated that large coupled models
are able to reproduce, in the same way as numerical wind tunnels simulate
the turbulence of real flows. It also comes from the dispersion of coefficients
of the climatic models themselves, in this case, those of the coefficients and
parameters of the models which are not determined by the rigorous laws of
fundamental physics (fluid mechanics, thermodynamics, etc.) The relatively
small amount of dispersion in the results therefore would appear to reflect
the consensus of numerous independent experts on the least certain
characteristics of the climate machine. We will see that this is not the case.
9.3.
Representative concentration pathways (RCPs)
The simulations to be carried out in light of the 5th IPCC report were
defined in 2008 by the Working Group on Coupled Modelling (WGCM) of
the World Climate Research Program, in the context of the CMIP5: Coupled
Model Intercomparison Project, Phase 5, [TAY
12]
. The scenarios regarding
human activity are called RCPs: Representative Concentration Pathways
[MEI 11].
The RCPs replaced the emission scenarios of previous projects. The
essential new point is that the RCPs offer scenarios directly in terms of
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