Jökull - 01.01.2020, Side 28

Glacier extent in Iceland, 1890–2019
Figure 13: Area (with respect to the maximum LIA extent) of the main Icelandic ice caps and all the glaciers in total since
the end of the 19th century. Open circles denote additional data points that are not derived from outlines in the GLIMS
data set (see caption of Figure 12). The step rise in the curves for Vatnajökull and all glaciers is due to the surge in Brúar-
jökull in 1963–1964. The left y-axis applies to the area of Vatnajökull (V) and all glaciers (blue line), whereas the right
y-axis applies to the smaller ice caps (L=Langjökull, H=Hofsjökull, M=Mýrdalsjökull). – Flatarmál meginjökla landsins
og einnig allra jökla landsins samtals. Skyndileg aukning í flatarmáli Vatnajökuls árið 1964 kemur til vegna framhlaups
Brúarjökuls 1963–1964. Vinstri y-ásinn á við Vatnajökul og alla jökla (blá lína), en hægri y-ás á við Langjökul, Hofsjökul
og Mýrdalsjökul.
varies between −7.2 km2 a−1 (∼1973 to ∼2000) and
−44 km2 a−1 (∼2010 to ∼2014). The rate of rela-
tive area change is in general inversely related to the
size of the glacier. It is greatest in magnitude for
the smaller intermediate-size glaciers (3–10 km2) and
varies between −0.37 % a−1 (∼1945 to ∼1973) and
−2.5 % a−1 (∼2010 to 2014). This may for example
be compared with −0.07 % a−1 (in ∼1945 to 1973)
and −0.52 % a−1 (∼2010 to 2014) for Hofsjökull.
DISCUSSION
The general pattern of glacier area changes reflects
the fluctuations in the climate in Iceland since the end
of the 19th century, as seen in variation in the sum-
mer temperature in Stykkishólmur (Figure 2), with
occasional exceptions due to surges. This temperature
record may be considered representative of the rather
spatially uniform decadal temperature variations in
Iceland (Crochet, 2011), in agreement with model
studies of the response of Icelandic glaciers to climate
variations (Aðalgeirsdóttir et al., 2011; Flowers et al.,
2007, 2008; Schmidt et al., 2017). Areal changes are
not an unequivocal indicator of climate changes, as
glacier response to climate change depends on sev-
eral non-climatic factors. But area changes are more
easily extracted from various remote sensing data and
historical information about glacier variations than
glaciological or geodetic mass balance. Information
about variations in glacier extent can be useful to
complement available data about mass-balance vari-
ations in analyses of glacier–climate interactions, and
past changes in ice volumes can be derived from
glacier extent variations with the volume–area scal-
ing method (Bahr et al., 2015; Aðalgeirsdóttir et al.,
2020).
Glacier-area changes and outlet-length variations
are related, as the main area changes generally take
place in the ablation area. The terminus variation
measurements of the Iceland Glaciological Society
(collected since the 1930s, see spordakost.jorfi.is) re-
flect the general pattern of area changes of glaciers
in Iceland. The in-situ length-change observations
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