chapter - Atmospheric and Oceanic Science

9.1. Introduction
The emissions of greenhouse gases (GHG) resulting from certain activities
have been the main cause of the unusual heating of the planet during the last 150
years, this process that continues is known as Climatic Change. Actually, it is a
global warming of the planet that also involves an important climatic change not
only in temperature but also in the other climatic variables such as precipitation,
winds and humidity.
9.2. Causes of climatic changes
Global climatic change
The changes in the Earth climate were and are produced by diverse natural
processes that affect the climatic system or some of its components. In order to conclude
that the trend to the global warming is due to human activity, it has been necessary
to discard or at least to measure the effect of these processes.
The variations of the Earth orbit around the sun have induced important climatic
changes in the past. However, these changes are very slow and significantly influence
the climate, only after thousands years. The undergoing process of global warming
is a process that started not before two centuries ago. Therefore, the changes in
the terrestrial orbit must be disregarded as its possible cause, which in any case at
present astronomic circumstances would drive to a cooling of the planet.
For the same reason, the geological processes that modify the geography of
the Earth have to be disregarded. The drift of the continents, the raising and destruction
of the mountain chains modify not only local but also global climate. These
processes and the concurrent climatic changes that they originate are very slow and
only important at a million year timescale.
Other possible natural causes of climatic change that could have an effect in
the scale of time from decades to centuries are the variations of the solar radiation
and of the volcanic activity, but they have not been as important as to explain the
observed warming. Although solar radiation has been increasing in the last two centuries,
its contribution to the warming from the beginning of the industrial period
has been six times lower than that of the CHG.
Volcanic activity produces explosions that when, due to its intensity, injects
gases into the stratosphere, they remains in it for several years. This material
increases the reflection of the solar light, thus contributing to the cooling of the
planet. The absence of eruptions of this type in the first half of the twentieth century
contributed to the warming in this period in a similar magnitude to the increase
of the solar radiation.
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