chapter - Atmospheric and Oceanic Science

The dynamics of the climatic system like that of other complex systems might
generate changes in its equilibrium statistical conditions without being forced by
any external cause. This is called internal variability. Using global climate models,
it is possible to discard with great probability, that the internal variability had generated
the global observed trend, since in simulations of the climate for thousands
of years, these models do not reproduce trends of the global temperature during
periods of 100 years, so pronounced as the current trend of the last century.
The change of the chemical composition of the atmosphere, when it affects
the so called greenhouse gases is another of the causes of climatic changes. From
the beginning of the industrial period the concentration of these gases has been
altered by the emission of human origin.
The emission of soot and other particles, as well as of sulphates and nitrates
originated in human activities increases the formation of aerosols. These emissions
add to the natural ones and are a potential source of both global and regional climatic
changes. A direct effect of the aerosols is to reflect the solar light to the outer
space contributing to the cooling, although in the case of soot they can have a
greenhouse effect. Besides, they alter the process of formation of the clouds and
their duration. About their effect on global climate there is still a great uncertainty.
Anyway, whereas the emission of aerosols of human origin grows in a linear way,
those of GHG are growing exponentially, and thus, the relative effect will be losing
importance with time at worldwide scale. This topic will be approached in more
detail in chapter 10.
9.3. Solar and terrestrial radiation
Global climatic change
All the bodies emit and absorb the electromagnetic radiation in a different way
according to their temperature. In general, emissions are very close to those of a
black body and proportional to the fourth power of the absolute temperature
(Stefan-Boltzman law). For each temperature, emissions are practically within a
certain range of wave lengths according to the law deduced by Planck. The maximum
of the emission varies with the temperature so that the warm bodies emit in a
shorter wave length than cold ones.
The Earth receives energy from the sun in the form of electromagnetic radiation.
This radiation coming from a body with high temperature (about 6000°K) is
of very short wave length, passing through the atmosphere with little absorption. A
part of it is reflected to outer space by the clouds, the atmosphere itself and the terrestrial
surface and the rest is absorbed in the surface of the planet. In turn the terrestrial
surface, the atmosphere and the clouds emit electromagnetic radiation with
a longer wave length since they are at much lower temperatures, 200 a 300°K.
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