To determine whether the Earth is heating up or not,
it is necessary to know the amount of received and escaped
energy.
Particular research programs, organised on an international
scale, have as objective, the precise formulation of this
radiation balance of the Earth. (picture
1)
 Sun |
 Earth |
 Solar radiations |
 Infrared radiations |
 Clouds |
 Heat
flux |
The Sun is the only external source of energy that “feeds”
the Earth-Ocean-atmosphere-system.
Therefore, we should determine very precisely the amount
of energy that reaches us, before it touches the surface
of the Earth (Solar constant). Changes in time are important
as well. (picture 2 & 3)
The Sun heats up the Earth by its radiations, especially
in the visible spectrum.
The Earth retransmits this energy in the form of infrared
radiations. Parts of these radiations are again absorbed
by the gasses in the atmosphere. This latter process is
what one calls the “greenhouse effect”, a
natural phenomenon. Without this effect, the average temperature
of the Earth would be about -18°C, because the heat
of the Earth system would escape quicker in space. Other
expressions of the radiation balance are studied as
well, either from the Earth’s surface, or from
out of space. Some natural phenomena (picture
4), but human activities too (picture
5) can have an influence on particular factors
of this balance. We think for example of "atmospheric
disturbances".
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