Ice and Sea-level Change
Summary
Sea-level rise is a major impact of global warming. There
is clear scientific consensus that sea level is rising partly
in response to past emissions of greenhouse gases from
human activity. Melting glaciers and ice sheets are re-
sponsible for more than a third of the current rate of
Sea-level change: Sea level can change, both globally and lo-
sea-level rise and the contribution of meltwater to the
cally, due to changes in the shape of the ocean basins, chang-
oceans can be expected to continue and accelerate as
es in the total mass of water in the ocean, and changes in
more land ice melts. Over the long term the ice sheets of ocean water density. Relative sea level is measured by a tide
Greenland and Antarctica have the potential to make the gauge with respect to the land upon which it is situated, and
largest contribution to sea-level rise, but they are also the
includes land uplift/subsidence. Mean sea level is the aver-
greatest source of uncertainty.
age sea level over a period long enough to average out effects
from waves, tides and other short term fluctuations.
Sea level will rise during the 21st century and after and
Components of the Cryosphere Potential Sea-level rise (cm)
hence adaptation measures will be required during the
Antarctica ice sheet 5660
21st century and beyond. The rate and magnitude of sea-
Greenland ice sheet 730
level rise, particularly beyond the mid 21st century, de- Glaciers and ice caps
pends on future emission of greenhouse gases. Signifi-
(lowest and [highest] estimates) 15 [37]
cant and urgent reductions in emissions are essential if
Permafrost (Northern Hemisphere) ~7
we wish to avoid committing future generations to a sea-
Snow on land (Northern Hemisphere)
level rise of metres over centuries. Both adaptation and
(annual minimum ~ maximum) 0.1 ~ 1
Sea ice and ice shelves 0
mitigation strategies need to be seriously considered,
as together they can provide a more robust response to
Source: IPCC 2007
26
human-induced climate change than either can alone.
Sea-level rise is both an international and a national is- Introduction to sea level issues
sue. Preparation and implementation of adaptation and
mitigation plans requires partnerships between nations, Coastal regions, particularly some low-lying river deltas, have
as well as between all levels of government, the private very high population densities. It is estimated that in excess
sector, researchers, non-governmental organizations of 150 million people live within 1 metre of high tide level,
and communities. Rising sea level is a mainstream is- and 250 million within 5 metres of high tide
1,2
. Also, there
sue in need of urgent and informed decision making are billions of dollars invested in coastal infrastructure im-
and action. mediately adjacent to the coast (Figure 6C.1). Sea-level rise
154 GLOBAL OUTLOOK FOR ICE AND SNOW