Vulnerability, Impacts and Adaptation of Coastal Zones to Global Change - Vulnerability of Coastal Ecosystems and Adaptation - page 141

to flooding. The problem will not stop at the end of the century. It is
very probable that the rise in GMSL will continue over several
centuries because of the thermal inertia of the ocean and the
persistence of the melting of the polar ice in Greenland and
Antarctica. It is estimated that the current atmospheric concentration
of greenhouse gases leads to an inevitable rise in the GMSL by 2.6 m
in the next 2,000 years [LEV 13]. To respond to these challenges, it
will be necessary to develop adaptation strategies embracing several
centuries.

4.3.3. The rise of the global mean sea level - observations and
projections

On geological timescales, the GMSL has been affected by the
formation of polar icecaps during former glaciations (the last began
during the Carboniferous period and continued into the Permian,
360 to 260 million years ago), by changes in the shape of oceanic
basins and by change in the configuration of the continents. During
the quaternary glaciation, the GMSL varied by about 100 m in the
glacial-interglacial cycles of the Pleistocene. These changes are
principally due to the periodic increase and decrease in the polar caps'
ice mass, associated with changes in the global mean temperature of
the atmosphere. Since the peak of the last glacial period around
18,000 years ago, the GMSL has risen by approximately 120 m.
However, during the last interglacial period around 129 to 116
thousand years ago, the global mean temperature of the atmosphere at
the surface being around 2

C greater than the corresponding
temperature in the pre-industrial era (before the middle of the 18th
Century), the GMSL was very probably more than 5 m higher
compared to the current value [IPC 13]. Recent reconstructions of the
evolution of the GMSL during the last 2,100 years [KEM 11],
represented in Figure 4.3, indicate a stable period between 100 B.C
and 950 A.D., followed by a rise of around 0.2 m up to the end of the
20th Century. After this period, the GMSL has risen by an average of
2.1 mm per year, which represents the highest rate of increase in the
last 2,000 years.

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