Environmental Engineering Reference
In-Depth Information
climate transition. Berger et al. (2003) and Berger and Loutre (2002) note
that the Anthropocene may initiate a 50,000-year interruption of Northern
Hemisphere glaciation, during much of which time the Northern Hemi-
sphere may be almost ice-free.
During the last interglacial period (the Eemian), global sea level was
at least 3 m, and probably more than 5 m, higher than at present. But
some studies suggest that the high sea levels during the last interglacial
period have been proposed to result mainly from disintegration of the West
Antarctic ice sheet, with model studies attributing only 1-2 m of sea level
rise to meltwater from Greenland. Cuffey and Marshall (2000) suggest that
the Greenland ice sheet was considerably smaller and steeper during the
Eemian, and plausibly contributed 4-5.5 m to the sea level highstand dur-
ing that period. New results from ice cores indicate that a significant ice
sheet was covering Greenland during the warm Eemian period and that the
reduction of the Greenland ice sheet at most contributed a sea level rise of
1-2 m of the observed 5 m (Dahl-Jensen et al., 2005).
Total loss of the Antarctic ice sheet would make the Anthropocene look
something like the largely ice-free pre-Miocene climates that prevailed
more than 30 million years ago. Antarctica is less subject to direct ablation
by melting than is Greenland, and so the conditions for deglaciation of
Antarctica are much more dependent on poorly understood aspects of ice
dynamics. Many important processes, including ice streams and ice shelves,
are not represented at all in the models used to study the problem. There
have been few modeling studies, and little confidence can be placed in the
few that have been done. Conventional thinking has it that the current East
Antarctic ice sheet would be very difficult to get rid of by anthropogenic
warming (Huybrechts, 1993). Indeed, Vizcaino et al. (2008) find that the
Antarctic ice sheet
grows
in volume even when the global mean warming
exceeds 4°C for 1,000 years. In a study of Antarctic glacial fluctuations, Pol-
lard and Deconto (2005) find that substantial portions of Antarctica deglaci-
ate in under 10,000 years in response to CO
2
concentrations on the order
of 840 ppm, but express doubt that their results are applicable to the more
extensive Antarctic glacier of today. Modeling studies, however, support the
possibility of deglaciation of the West Antarctic ice sheet if subjected to local
oceanic warming of as little as 5°C over a few thousand years, and there is
moreover good support for episodic deglaciation of the West Antarctic Ice
Sheet in Pliocene conditions (Pollard and DeConto, 2009). Based on the
pattern scaling given in Section 4.1, this would correspond roughly to a 5°C
global mean warming, but much caution should be exercised in applying
these transient climate response patterns to long-term climate behavior,
