ic change
9
. The advance or retreat of a glacier is, though, They essentially convert a small change in climate, such
an easily-observed and strong signal of climatic change, as a temperature change of 0.1°C per decade over a longer
as long as it is observed over a long enough period. If the time period, into a pronounced length change of several
time interval of the analysis is longer than the time it takes hundred metres or even kilometres (Figure 6B.4) – a sig-
a glacier to adjust to a change in climate, the complica- nal that is visible and easily understood.
tions involved with the dynamic response disappear
10,11
.
Over time periods of decades, cumulative length and Past glacier fluctuations and current
mass change can be directly compared. Special problems trends
are encountered with heavily debris-covered glaciers with
reduced melting and strongly limited ‘retreat’, glaciers The Late Glacial and Holocene (the period
that end in deep-water bodies causing enhanced melting since about 21 000 years ago)
and calving, and glaciers undergoing periodic mechanical
instability and rapid advance (‘surges’) after extended pe- At the time of the peak of the last ice age about 21 000
riods of stagnation and recovery. But glaciers that are not years ago, glaciers covered up to 30 per cent of the land
2
.
influenced by these special problems are recognized to be Glacier fluctuations can be reconstructed back to that
among the best indicators of global climate change
12,20
. time using a variety of scientific methods. Understand-
Figure 6B.4: Shrinking of Vernagtferner, Austria. This glacier in the European Alps lost almost 30% in area and
more than 50% in mass between 1912 and 2003.
Source: Data and photos, taken by O. Gruber (1912), H. Schatz (1938), H. Rentsch (1968) and M. Siebers (2003), provided by
the Commission for Glaciology of the Bavarian Academy of Sciences and Humanities (www.glaziologie.de)
CHAPTER 6B GLACIERS AND ICE CAPS 119