chapter - Atmospheric and Oceanic Science

Global climatic change
On the base of these and other facts, the Inter-governmental Panel for the
Climatic Change (IPCC 2001a) in its report of the year 2001 has concluded that the
trend to warming observed in the twentieth century has an important component of
human origin.
9.7. The climate in the twenty first century
The evolution of the emission of GHG in the future will depend on numerous
factors whose prediction is quite complex. They are the economic and demographic
growth, the technological changes and even the development towards a society
with more or less equity. Finally, but not less important, it will depend of the collective
answers of the humanity to reduce or at least to diminish the rate of growth
of the emission.
Since all these factors are very difficult to foresee, the only possibility is to
build possible socioeconomic scenarios of the future. The building and characteristics
of these scenarios are discussed in chapter 13. The different scenarios suppose
dissimilar levels of economic activity that imply in turn different emissions scenarios.
It is possible to build as many emission scenarios as arise from the combinations
of the driven factors of the level of economic activity and of its characteristics,
without certainty on which will be the one really happening. However, for a
given scenario of GHG emissions throughout time, it will be a corresponding scenario
of concentration evolution of these gases.
The effect of GHG concentrations in the climate is studied with the help of
global climate models (GCM) that simulate the climatic system in almost all its
complexity. These models represent the physical processes of the sea, the atmosphere,
the soil and the cryosphere, and simulate its evolution using huge computers.
In chapter 11, they are described in more detail. Only the most sophisticated
GCM have been capable of reproducing, forced by the observed evolution of GHG
concentrations, the global climate global changes observed during the industrial
period. This generates certain confidence in their capacity to simulate the global
changes of the future climate.
The different GCM project different values of the global temperature, still
under the same socio-economic scenarios. Nevertheless, they all give the same
qualitative response, important warming throughout the twenty first century for any
of the socioeconomic scenarios.
The GCM are a reliable methodology to assess climate changes at global
scale, but they still have a limited capacity to simulate the climate at regional scale,
understanding for such the one that goes from a locality up to a continent. Although
the different models are consistent among one another in terms of their predictions
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