Jökull - 01.12.1969, Page 103

DISCUSSION
It must be empliasized that the temperature
and ice graphs in Figs. 5 and 6 are only based
on a limited type of data. Although this data
is the most important, there are various pos-
sibilities to check the conclusions with the aid
of historical documents and geological clata. A
few possibilities will be mentioned here.
The most important check available for the
time being is the oxygen isotope analysis of
glacier ice core in Camp Century, Greenland
(Dansgaard et al. 1969). Fig. 7 gives the varia-
tion of the 018/016 ratio cluring the last 1000
years. In general, the correlation with the
temperature in Fig. 6 is remarkable, liigh ratio
of O18 being associated with high temperature,
as would be expected. The strong cooling in
the 12th century is very marked in both cases,
and it is in fact the main characteristic of the
climate during the last 1000 years. Shorter
climatic fluctuations cannot be expected to be
similar in Iceland and this remote place in
Greenland, some 2000 km away, and therefore
one should only compare the broad lines in
these graphs. For example, the very warm
period in Iceland in the years 1920 to 1964
seems to have been quite different at the west
coast of Greenland where the 1920’s and 1930’s
were particularly warm, but a cooling set in
before 1950.
The graphs in Figs. 6 and 7 seem to throw
a new light on the socalled 'Tittle ice age”
which is maintained to have begun in the 16th
century and lasted until about 1900. It is true
that in both graphs this period is a little colder
than any other during the last 1000 years. But
it is not nearly as marked as one might have
expected. It must though be remembered that
a certain cooling may have more serious eco-
nomic consequences in a cold periocl than in
relatively mild climate. For example the
number of famine years then rises much more
rapidly for every degree of cooling.
Tlre most important check of the tempera-
ture graph during the last 250 years is the
temperature record of Central-England, publ-
ished by professor Gordon Manley (1959). A
30-year running mean of the Central-England
temperature is shown in Fig. 8, together with
the corresponding part of the Icelanclic estimat-
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AD
Fig. 7. Variation of the 018/010 ratio in
Camp Century, Greenland. After Dans-
gaard et al. (1969).
JÖKULL 19. ÁR 99