Geoscience Reference
In-Depth Information
Melting icesheets
The IPCC sea-level rise projections for 2100 with no curbs to carbon emissions are
between 57 cm and 98 cm. The largest uncertainty within these estimates is the contribu-
tion that the melting of Greenland and Antarctica will make by the end of the century. At
the moment it is estimated that Greenland is losing over 200 gigatonnes of ice per year, a
six-fold increase since the early 1990s. While Antarctica is losing about 150 gigatonnes of
ice per year, a five-fold increase since the early 1990s. Most of this loss is from the north-
ern Antarctic Peninsula and the Amundsen sea sector of West Antarctica. Greenland and
Antarctica constitute one of the most worrying potential climate surprises. If the large ice
sheets there completely melted, their contribution to global sea-level rise would be as fol-
lows: Greenland, about 7 m; West Antarctic ice sheet, about 8.5 m; East Antarctic ice sheet,
about 65 m; compared with just 0.3 m if all the mountain glaciers melted. Palaeoclimate
data show that the huge East Antarctic ice sheet developed 35 million years ago due to the
progressive tectonic isolation of Antarctica and that it has in fact remained stable in much
warmer climates. So climate scientists have a very high degree of confidence that the East
Antarctic ice sheet will remain stable in this century. In fact there is evidence that the
warmer wetter climate is allowing a small increase in snow accumulation on the ice sheet.
However, scientists are now very worried that the melting of Greenland or the West
Antarctic could significantly accelerate in next 100 years. Even if we have already started
the processes of melting the whole of these ice sheets, there is of course a physical con-
straint to the speed that the ice can melt. This is due to the time it takes for heat to penetrate
into the ice sheets. Imagine dropping an ice cube into a hot cup of coffee you know it will
melt entirely, but it takes time for the heat to penetrate into the middle of the ice cube. Also
most of the ice from ice sheets goes through ice streams, which have a limit on how much
ice they can mobilize. The worst case scenario according to leading glaciologists is that
these ice sheets could add between 1 m to 1.5 m to the sea level by the end of the century,
which would threaten many coastal populations around the world. There is also scientific
debate about what happens to both the Greenland and Antarctic ice sheets beyond the next
100 years; even if significant melting does not occur this century, we may have started a
process that causes irreversible melting during the next one. Thus our carbon emission over
the next few decades could determine the long-term future of these ice sheets and the liveli-
hoods of billions of people who live close the coast.
