Vulnerability, Impacts and Adaptation of Coastal Zones to Global Change - Vulnerability of Coastal Ecosystems and Adaptation - page 144

Projections
To make projections on the future rise in GMSL, it is necessary to
fully understand the mechanisms that are at work. Two main
processes, due to climate change, cause the rise in GMSL: the thermal
expansion of the upper layers of the ocean and the melting of land ice
on glaciers, polar ice caps and ice sheets. A third process results from
human intervention in the storing of water on land, associated mainly
with the construction of dams that retain water and the exploitation of
aquifers. We have here a good example of the combined effect of a
global systemic change (climate change) and a global cumulative
change (the exploitation of surface and ground waters on a global
scale). The retention of water in the roughly 30,000 dams, constructed
globally during the 20th Century, caused a small decrease in GMSL
between 1940 and 2007, with an estimated total value of 23 mm
[CHA 08]. Following increasing demand for water, the exploitation of
aquifers and the return of the used water to the hydrological network
at present cause a small increase in sea level. Currently, the net mean
annual variation in GMSL due to these intensive uses of freshwater is
positive and estimated at 0.38 mm, for the period 1993-2010
[IPC 13].
The two contributions of anthropogenic climate change to GMSL
rise will now be analyzed further. The rise due to thermal expansion is
approximately proportional to the increase in thermal energy in the
ocean, with a proportionality constant of 0.11 m per 10 24 J [KUH 12].
It is important to further analyze the origin of this increase in energy.
The increasing concentration of greenhouse gases in the troposphere,
or lower atmosphere, due to certain human activities, means that the
radiative forcing at the top of the troposphere is increasing. This
implies disequilibrium in the climate system that leads to an increase
in its thermal energy. It is estimated that, during the last decades, 93%
of that energy excess has been transferred to the ocean [IPC 13]
because its thermal capacity is much larger than the other subsystems
of the climate system. The remainder of the energy excess warms the
atmosphere and the continents and causes the melting of ice in
continental glaciers, ice sheets, ice caps and ice shelves. It can, then,
be concluded that in the absence of the ocean or with a smaller ocean,