Vulnerability, Impacts and Adaptation of Coastal Zones to Global Change - Vulnerability of Coastal Ecosystems and Adaptation - page 133

significant changes through the entire history of the evolution of the
planet. A relatively recent example of natural global changes are the
glacial-interglacial cycles of the Pleistocene, with an average period
close to 100,000 years. Their origin is related to small cyclical
changes in the eccentricity of the Earth's orbit and the obliquity of the
axis of rotation and also its movement of precession.
In the last millennia, and especially in the 20th and 21st Centuries,
some human activities have generated environmental changes that
have a global character due to their nature, their intensity and the size
of their geographical distribution. In general, these anthropogenic
global changes occur in periods of time much shorter than those of
natural global changes. Because of these different timescales, it is
often difficult to separate quantitatively the one from the other. Here,
we will be interested above all in global anthropogenic change, which
will simply be called global change, except when there is a question of
distinguishing the natural effects from the anthropogenic effects.
Human societies, through multiple activities carried out now and in
the past, interfere with the Earth system in such an intense way and to
such a temporal and spatial extent, that they threaten its various
subsystems and the biotic and abiotic processes on which the
sustainability of the societies themselves depend [STE 04].
The interference of human activities on the environment is, of
course, felt at a local level (urbanization, pollution of the air and
water, changes in land use, etc.), but it also has global consequences,
in particular on the global climate and on non-climatic aspects, such as
water and soil resources, biodiversity and natural resources.
In global change, it is useful to distinguish between systemic
global changes, which manifest themselves directly on the Earth
system scale, and cumulative global changes that occur at a local or
regional scale, but which have a global expression because they
arise almost all over the planet with such an intensity that they become
a global problem. Global climate change caused by anthropogenic
greenhouse gas emissions is a very important example of a systemic
global change. However, there are others, such as the reduction in the
concentration of stratospheric ozone, resulting mainly from the use of
chlorofluorocarbons or CFCs, and the variations in albedo due to