Photo: Bruce Richmond/USGS
Ice and Sea-level Change
Sea level is rising at an increasing rate which is associ- bal sea level rise over the 21st century in the range of
ated with global warming. The rate of sea-level rise is about 20 to 80 cm. However, the upper bound of this
now 3.1 mm per year; the average for the 20th century projection is very uncertain.
was 1.7 mm per year. Climate change is also projected to increase the fre-
More than a third of sea-level rise is from meltwater quency and severity of extreme sea-level events such
from glaciers and ice sheets with most of the remain- as storm surges. This will exacerbate the impacts of
ing rise being due to thermal expansion of the oceans. sea-level rise.
The contribution of meltwater to sea-level rise can be The impacts of sea level rise in any region will depend
expected to continue and accelerate as more land ice on many interacting factors, including whether the
melts. Over the long term the ice sheets of Greenland coastal region is undergoing uplift or subsidence, and
and Antarctica have the potential to make the larg- to what degree development has altered natural flood
est contribution to sea-level rise, but they are also the protection such as coastal vegetation.
greatest source of uncertainty. Rising sea levels will potentially affect many millions of
For the next few decades, the rate of sea-level rise people on small islands and at and near coasts world-
is partly locked in by past emissions and will not be wide. A wide range of adaptation and mitigation meas-
strongly dependent on 21st century greenhouse gas ures will be required to assist people to cope with the
emissions. However, sea-level projections closer to consequences; these will require cooperation among
and beyond 2100 are critically dependent on future nations as well as among all levels of government, the
greenhouse gas emissions. private sector, researchers, non-government organiza-
The IPCC Fourth Assessment Report projects a glo- tions and communities.
14 GLOBAL OUTLOOK FOR ICE AND SNOW