Page 377 - Earth's Climate Past and Future

CHAPTER 19 • Future Climatic Change 353

FIGURE 19-11 Antarctic ice
sheet Fringing ice shelf margins
of the small, low-altitude West
Antarctic ice sheet may begin to
melt in a 2 × CO world, but the
2
higher, colder East Antarctic ice
sheet will be less vulnerable.
E A S T
(From F. Press and R. Siever,
A N T A R C T I C A Understanding Earth, 2d ed., © 1998
Amery by W. H. Freeman and Company,
A Pole of relative Ice Shelf and after Uwe Radok, “The
Ronne inaccessibility Antarctic Ice,” Scientific American,
entrance B August [1985]: 100, based on
South data from the International
C Pole
WEST Glaciological Project.)
D
ANTARCTICA
E
Dome C
Elevation (m) Ross Law
F H J K L
G Dome
4000 Ice Shelf M
3500
3000
2500
2000
1500
1000
0

Ronne C D Seawater J K Law
3
entrance
Depth (km) 2 A West Antarctic ice sheet F Ross Ice Shelf East Antarctic ice sheet L M
Dome
E
B
1
H
G
0
-1
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance (km)
sea ice, and probably most winter sea ice (Figure 19–12). 19-6 Greenhouse Surprises?
The belt of conifer forest will slowly move toward and
reach the Arctic Ocean. Sea ice around Antarctica would Because the mixture of slow and fast responses to the
also probably disappear. Changes at middle and lower large CO pulse of the future will create a climatic dise-
2
latitudes will be similar to but larger in magnitude than quilibrium unprecedented in Earth history, interactions
those for the 2 × CO world. within the climate system may produce unanticipated
2
In trying to project ice sheet changes so far in the phenomena, or “greenhouse surprises.”
future, we once again start with the fact that the ice One frequently mentioned possibility is that faster
sheets now exist but will be completely out of equilib- melting of Greenland ice could send enough fresh-
rium with the warmer climate all around them. The water to the North Atlantic Ocean to lower its salinity
Greenland ice sheet will become even more vulner- and thereby slow or stop the formation of deep water. A
able, but it is unclear whether or not irreversible melt- relatively small drop in salinity in the Labrador Sea begin-
ing would occur. West Antarctic ice will also be out ning in the 1970s lowered the density of the surface
of equilibrium with a warmer ocean, and the margins of waters enough to prevent them from sinking during win-
East Antarctica will also melt at rates that are hard to ters over the next two decades. Melting of the margins
predict. With increased ice sheet melting and thermal of the Greenland ice sheet or altered precipitation pat-
expansion of the ocean, sea level will rise faster and terns caused by greenhouse warming could conceivably
higher, reaching a level perhaps 1–2 m above that of the add enough low-salinity water to the North Atlantic to
present. slow or stop the formation of deeper water.