Jökull - 01.10.1998, Side 34

verse around 1960 as was the case in Iceland and in
the Alps (Chaohai, 1992).
The response of the termini varies between the
monitored glacier tongues as can be seen from graphs
of the individual data series in Sigurðsson (this vol-
ume). Due to the small number of glaciers in the data
set, we are, however, unable to draw any conclusions
regarding regional differences of glacier variations in
Iceland during the monitoring period.
Figure 5 shows summer temperature (May to
September) and yearly precipitation (October previ-
ous year to September) in Kirkjubæjarklaustur S-Ice-
land (a) and Reykjavík SW-Iceland (b) from 1931 to
1995. Variations in glacier ablation are primarily re-
lated to variations in the summer temperature, where-
as changes in the accumulation may be expected to
correlate with variations in the precipitation record.
There is a good correlation between the temperature
records from Kirkjubæjarklaustur and Reykjavík, as
is expected, since there is in general a good correla-
tion between temperature measurements from differ-
ent meteorological stations in Iceland (Einarsson,
1991). It can, therefore, be assumed that the tempera-
ture records from Kirkjubæjarklaustur and Reykjavík
give an estimate of temperature variations that oc-
curred on Icelandic glaciers in this time period. The
figure shows that the temperature was relatively high
from 1931 to 1960, especially in the years 1931 to
1940. After about 1960 the climate cooled markedly,
the temperature reached a minimum between 1980
and 1985 and the climate has been slowly warming
since then. There are no similar systematic trends in
the precipitation records in spite of large short term
fluctuations (note the shifted precipitation scale in
Figure 5a,b).
The temperature and precipitation records in Fig-
ure 5 indicate that glacier fluctuations in Iceland (cf.
Figure 4) were primarily controlled by variations in
the summer temperature. The rapid glacier retreat
from 1931 to 1960 is related to high summer temper-
atures in the decades after 1930. The retreat slowed
down and turned to advance in the period 1965 to
1970 when the climate had become cooler and the
fraction of advancing glaciers reached its maximum
in the period 1975 to 1990 after the summer tempera-
ture had reached its minimum around 1980.
In spite of the strong correlation between glacier
variations and summer temperature, which is appar-
ent from figures 4 and 5, the figures show that the re-
lationship between glaciers and climate is not simple.
The decade from 1931 to 1940 is the warmest decade
in the instrumental record in Iceland. In spite of this,
between 10 and 20% of the glacier termini were ad-
vancing in this period, and more than 40% of the ter-
mini were still retreating during most of the very cold
summers from 1970 to 1980.
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