Greenland
Antarctica
Melting on the lower
Ice shelves, with
parts of the surface,
subglacial melting.
icebergs calve off from
Icebergs calve off
ice sheet edges into ice
from ice shelves
fjords and the sea
S
no
w accumula
tio
n
Equilibrium
line
Ice sheet
Ice shelf
I
c
e

f
l
o
w
Iceberg
i
o
n
calving
b
l
a
t
I
c
e
A
f
l
Iceberg
o
w
Ocean calving
Subglacial
Ocean
melting
Bedrock
Figure 6A.1: Ice sheets.
Source: based on material provided by K. Steffen, CIRES/Univ. of Colorado
climate and air composition dating back hundreds of mil- completely. Although this would take many thousands of
lennia. During glacial periods, ice sheets contained more years, recent observations show a marked increase in ice-
than twice as much ice as that in Greenland and Antarc- sheet contributions to sea-level rise. In addition, ice-sheet
tica today. Sea level would rise by about 64 m if the cur- melting strongly influences ocean salinity and tempera-
rent mass of ice in Greenland and Antarctica were to melt ture, and also global thermohaline circulation as a con-
CHAPTER 6A ICE SHEETS 101