Vulnerability, Impacts and Adaptation of Coastal Zones to Global Change - Vulnerability of Coastal Ecosystems and Adaptation - page 149

that the rise in GMSL is maintained by the thermal inertia in the
ocean. Even if it is imagined that all greenhouse gas emissions cease
abruptly in 2016, the GMSL would continue to rise for centuries or
millennia. The green line refers to a scenario where the global
emissions are reduced by 80% before 2050. Current engagements
correspond to reductions in emissions agreed voluntarily by the
countries that have established quantified mitigation. The four other
lines correspond to different SRES [SRE 00] scenarios, to scenario
RCP2.6, and to a scenario where the probability of not exceeding an
increase of 2 ° C in the mean global temperature is 50%.

There are still considerable uncertainties over the effect of global
warming on the behavior of polar caps. Recent observations show that
changes in the dynamic of the polar ice have often been under-
estimated. From the beginning of the 1990s, the loss of ice mass in the
Arctic and the western Antarctic ice sheets has accelerated
considerably. In the period 1992-2011, the mean annual rate of ice
mass loss has been 142 gigatonnes in Greenland and 71 gigatonnes in
the Antarctic. [SHE 12]. The models currently available indicate that
beyond a certain threshold of increase in the mean global temperature
of the atmosphere, global warming will lead to an irreversible and
almost complete disappearance of the Greenland ice sheet.
Calculations show that this threshold is situated between 2 and 4 C

compared to the pre-industrial temperature [RID 10]. The process of
ice melting in Greenland will last more than a millennium leading to a
rise in GMSL close to 6 m.

°

The Antarctic ice sheet is more stable, particularly in its eastern
part. It is estimated that the melting of the whole Antarctic ice sheet
would contribute to a rise in sea level of more than 60 m. The western
part of the Antarctic is less stable and, if it melted, would lead to an
increase in GMSL of nearly 4 m. It is important to note that a large
proportion of the western Antarctic ice sheet is situated below mean
sea level, which renders it particularly unstable in a case of continuing
global warming. Although the uncertainty over the future behavior of
this part of the Antarctic is considerable, its melting is likely to begin
before the end of the century [IPC 13].