Geoscience Reference
In-Depth Information
- the cryosphere (sea ice, glaciers, other frozen areas),
- the land surface,
- the biosphere (flora and fauna);
forced or influenced by various external mechanisms, the most important of which is
radiation from the Sun.
Figure 4.1.
The climate system
The main drivers of the atmospheric and oceanic circulations are the rotation of
the Earth, the atmospheric composition, the total energy received at the surface from
the sun, and the radiative properties of the surface, and its topography and
roughness.
The natural variability of the Earth climate is due to several variables:
- the variation with time of the Earth orbital parameters, which regulate e.g. the
frequency of long-term ice-age periods (every 100,000 years) and which determine
the characteristics of the interglacial periods. Such variables include the
obliquity
(measuring the tilt of the ecliptic compared to the celestial equator), the
eccentricity
of the Earth's orbit around the Sun, and the
climatic precession
which is related to
the Earth-Sun distance at the summer solstice;
- the variations in solar activity, which modulate the amount of solar energy
received at the Earth's surface, with typical timescales from years to decades;
- different oscillations, such as the ENSO (El Niño Southern Oscillation, and its
two phases El Niño and La Niña), the NAO (North Atlantic Oscillation), etc.,
resulting from interactions between the ocean and the atmosphere, with timescales
ranging from a few years to several decades;
- volcanic eruptions, which emit massive quantities of gases and aerosols into
the atmosphere, and which are able to momentarily (for 1 to 2 years) change the
amount of solar energy received at the Earth's surface, and thus affect temperature;
