Jökull - 01.12.1969, Side 104

Fig. 8. A 30 year running mean temperature
of Central England (Manley 1959) (top) and
Iceland (below).
ed temperature. The correlation is remarkably
good.
Some information regarding Icelandic gla-
ciers during the last centuries is represented
in Fig. 9, by Thorarinsson (1956). Even if the
graph is not fairly accurate before regular
measurements begin about 1930, it indicates
strongly a climatic improvement in this century
but very little general variations from 1700 to
1900, in good accordance with the temperature
graph.
The number of famine years is an important
basis of the temperature and ice graphs in
Fig. 6. Steffensen (1958) and Tliorarinsson
(1956) have pointed out that the stature of
Icelanders, as indicated by bone measurements,
is highly correlated with the economic condi-
tions of the nation in the past centuries. The
curve of the male stature, obtained in this
manner, is very much parallel to the curve of
severe years.
Earlier estimates of the drift ice incidence at
Iceland are generally quite different from the
graph in Fig. 6. According to Koch (1945), the
average ice incidence in the 13th century was
2—5 weeks in every 20 years, i.e. 0.2—0.6 months
per year, whereas in my graph the correspond-
ing annual ice incidence is 1 l/í, to 21/4 months.
This great difference is in the author’s opinion
due to the fact that in his graph Koch only
counts the ice directly mentioned in historical
documents. In these times only heavy ice years
are mentioned, the contribution of light ancl
moderate ice years being mainly omitted.
The mild period before 1200 indicated by the
graphs presented is confirmed by many historical
data. After the settlement about 870 grain was
grown in most parts of the country, but in
the fourteenth century it was only grown in a
few places in South-Iceland and then only
barley. In the sixteenth century grain growing
had been completely abolished. Thorarinsson
(1956) has pointed out tliat glaciers must have
been much less extensive at the time of settle-
ment than later on.
The most remarkable possibility of testing
the temperature and ice graphs in Figs. 5 and
6 lies probably in core drilling in the Icelandic
glaciers and analyses of heavy oxygen or hydro-
gen. This work has now just begun, and promis-
100 JÖKULL 19. ÁR