Cumulative mean According to climate scenarios for the end of the 21st
annual ice loss
century, changes in global temperature and precipitation
(mm w.e.)
range between +1.1 to +6.4 °C and –30 to +30 per cent, re-
0
spectively
1
. Such an increase in mean air temperature will
-2 000 continue the already dramatic glacier changes. Cold con-
tinental-type glaciers will react in the first instance with
-4 000
a warming of the ice and firn temperatures, whereas gla-
-6 000
ciers with ice temperatures at the melting point will have
to convert the additional energy directly into melting
7,8
.
-8 000
-10 000 Low-latitude mountain chains like the European Alps or
1975 1980 1985 1990 1995 2000 2005
the Southern Alps of New Zealand, where glaciers are
typically medium-sized and found in quite steep moun-
tains, will experience rapid glacier changes in adaptation
to the modified climate. A modelling study shows that
the European Alps would lose about 80 per cent of their
glacier cover should summer air temperatures rise by
3°C, and that a precipitation increase of 25 per cent for
each 1°C would be needed to offset the glacial loss
19
.
In heavily glacier-covered regions like Patagonia (Argenti-
na, Chile) or the St. Elias Mountains (Alaska), the landscape
is dominated by relatively few large and rather flat valley
glaciers. Because long, flat valley glaciers have dynamic
Figure 6B.6: Mass balance reference glaciers in nine mountain
response times beyond the century scale
10,11
, rapid climate
ranges. The 30 glaciers lost on average more than 9.5 m water
change primarily causes (vertical) thinning of ice rather
equivalent in thickness over the period 1976–2005.
than (horizontal) retreat and area reduction. For such cases,
Source: Data from the World Glacier Monitoring Service, Zurich, Switzerland
conditions far beyond equilibrium stages, perhaps even
run-away effects from positive feedbacks (mass balance/al-
titude), must be envisaged
20,25
. Downwasting or even col-
lapse of large ice bodies could become the most likely future
Outlook for glaciers scenarios related to accelerating atmospheric temperature
rise in these areas, and have already been documented
26,27
.
The total increase of global mean air temperature of
about 0.75 °C since 1850 is clearly manifested in the Under the present climate scenarios
1
, the ongoing trend
shrinking of glaciers and ice caps worldwide
1
. The sensi- of worldwide and fast, if not accelerating, glacier shrink-
tivity of glaciers in humid-maritime areas to this warm- age on the century time scale is of a non-periodical na-
ing trend has been found to be much higher than that of ture and may lead to the deglaciation of large parts of
glaciers in dry-continental areas
7,21
. many mountain regions in the coming decades.
122 GLOBAL OUTLOOK FOR ICE AND SNOW