Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 332

Table6.3 Potentialsea-levelrisefromallterrestrialicemeltfrom
estimatesbytheUSGeologicalSurvey(1999)

Volume (km 3 ) Source Percentage Level rise (m)

Glaciers, etc. 180 000 0.55 0.5

Greenland 2 600 000 7.90 6.5

Antarctic a 30 109 800 91.49 73.5

Total 32 889 800 100 80.5

a

Of which the West Antarctic Ice Sheet would contribute 5-6
m. Note: this excludes any rise from thermal expansion of the
oceans. Also note that Antarctic land ice is largely stable and
unlikely (unless there are surprises) to make a major contri-
bution to sea-level rise, if at all, in the 21st century. However,
since 1999 new evidence suggests that terrestrial ice melt may
be faster, especially from Greenland (see text). The US Geolo-
gical Survey data have been rounded to the nearest half metre.

terrestrial ice melted would be somewhere around 80 m. (This melt does not include
the sea-level rise from thermal expansion, and the melt would probably take a few
thousand years.) In 1999 the US Geological Survey published the estimates shown in
Table 6.3 for the breakdown of this 'all-melt' potential.
Those concerned that the IPCC consensus view of sea-level rise might be too
conservative can point to the work of marine biologists from Mexico and Germany
(Blanchon et al., 2009). Corals track sea level and so these researchers isotope-dated
corals from the last interglacial using 230 Th. They not only confirmed what had been
known for a few decades, that sea levels at times during the last interglacial were
6 m higher, but also found that there were rapid jumps in sea level of 2-3 m, during
which the rate of sea-level rise was more than 36 mm year − 1 . This rate is faster than
the IPCC's forecast based on models.
On the one hand a worst-case 6 m rise (as in the last interglacial) over a few (two,
three or four) centuries seems modest against a very long-term potential rise of around
80 m in the event of all terrestrial ice melting over very many centuries. The long-term
all-melt scenario is far greater that the IPCC's 2007 forecast for the end of the 21st
century, but may occur should an event like the Initial Eocene Thermal Maximum
(IETM) be triggered (see Chapter 3). The 6 m rise seen in the last interglacial took
place at a time when temperatures were not far from what they are anticipated to
become later in the 21st century; although, of course, due to thermal inertia it will
take a long time for Greenland, let alone Antarctica, to melt. On the other hand, at
more than 392 ppm, current atmospheric carbon dioxide levels are already exceeding
the peak level of just over 300 ppm seen during the last interglacial.
The reason for the disparity of the last interglacial sea-level peak (approximately
5-6 m) and the potential rise if all our planet's ice melted (approximately 80 m) is
due to the aforementioned huge thermal inertia inherent in very large ice caps: it
takes a while for ice caps of a very large mass to adjust to extra warming. Conversely,
if we stopped further global warming geo-biosphere inertia would ensure that some