Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 274

Sea Level Rise in the Arctic and Around the Planet
We have seen in the previous section that many of the large reservoirs of water held on land
in the form of glaciers and ice sheets are melting. The ultimate fate of this water must be to
enter the sea. If we think of the sea as a simple bathtub, then unless the ocean basins can ex-
pand in some way, we can predict that the mean global sea level must be going up. However,
measuring sea level is much more complicated than meets the eye. For example, Earth's
crust is not a stable and inflexible entity. In some places, it is being thrust up or pushed down
by plate tectonics. In others, it is being pushed down by the weight of an overlying ice sheet,
and in other areas, it is bouncing up because of the removal of such ice. Therefore, meas-
urements taken at a coast may be subject to geological subsidence (such as the east coast
of the United States around New York) or postglacial uplift 14 (as in coastal western Canada
and in much of western Scandinavia). In some areas, sea level will be elevated because of
the gravitational pull of a mountain range and/or an ice sheet. In addition, atmospheric and
ocean current interaction can result in regional elevation and depression of the sea surface
(such as is associated with the ENSO), while the Coriolis effect can result (in the Northern
Hemisphere) in the right-hand side of currents being higher than the left (for example, the
Gulf Stream off the east coast of North America). The latter is a tricky problem because
ocean currents are not straight highways. They meander around - often with back eddies
- to further confuse us. These difficulties can be overcome, and since 1993, satellite data
has become available to measure the term global mean sea level . This is the area-weighted
mean of all the sea surface height anomalies measured by the satellite's altimeter on a single
10-day flight track repeat cycle. If you follow up this topic with some further reading, you
will also probably come across the term eustatic sea level . This is a theoretical sea level that
overcomes local effects by representing the level of all the water in the oceans as if they
were contained in a single basin. Eustatic change is an alteration to the global sea levels due
to changes in either the volume of water in the world oceans or net changes in the volume of
the ocean basins. It is not concerned with density changes of water, such as thermal expan-