Jökull - 01.12.1969, Síða 108

On Climatic Fluctuations and their Possible Causes
TRAUSTI EINARSSON,
DEPARTMENT OF ENGINEERING, AND SCIENCE INSTITUTE, UNIVERSITY OF ICELAND
After a short summary of the last 70—100
years, and the Post-Glacial time, the main dis-
cussion is devoted to the Pleistocene. To ex-
clude all geologically slow causes of climatic
changes, the time span considered is limited
to the last 100—200 thousand years. We have
then to deal with fluctuations of up to 40—50
thousand years’ durations (Dansgaard and
Tauber, 1969). The grouping of the possible
hypotheses follows Schwarzbach (1961) with
some additions, Table I.
We are here concerned with the primary
causes that triggered these great climatic fluc-
tuations, not with the many secondary terre-
strial factors that would no doubt enter the
picture. The interplay of the latter has for
instance been discussed by Emiliani and Geiss
(1959) and by Donn ancl Ewing (1966). For a
full understanding of all main effects botli
primary and secondary factor would have to
be taken into account.
TABLE 1
Grouþing of primary climatic hypothesis
(mainly after Schwarzbach).
A. TERRESTRIAL CAUSES
1. Changes of continents; extension, eleva-
tion, mountain ranges.
2. The ocean. a. Changes of extension or cur-
rents. b. Changes in salinity. c. Variable
amount of dissolved COo as a cause of 4, d.
3. Volcanic causes. Heat given off or ash in
the air.
4. The atmosphere. a. Self-regulated circula-
tion changes in the troposphere or in the
stratosphere. b. Changes of average cloud
cover. c. Changes in average humidity. d.
Changes of the CO2- content. e. Influence
of a variable magnetic field on the state
104 JÖKULL 19. ÁR
in the stratosphere or in the uppermost
troposphere.
5. Pole wandering or continental drift.
B. CHANGES OF THE EARTH’S ORBIT
AND THE AXIS OF ROTATION
1. Calculable changes (the Milankowitch
hypothesis).
2. Unknown changes.
C. SOLAR AND COSMIC CAUSES
1. Changes of the solar constant. Sunspots.
2. Traversing of the solar system through
interstellar clouds.
The hypotheses A-l, 3, 5 are rejected. B-1 is
rejected on the following grouncls. The aver-
age of the March and September temperature
for cold climate regions (Miller, 1959, Table of
35 representative stations, pp. 238—39) is 0.1°
C above the annual average (2.4° C), and the
average for January and July is 0.2° C above
the annual mean. These facts are interpretecl
to show that, first, the annual mean is prac-
tically independent of a 23.5° inclination of
the axis and, second, that on the average the
annual heat curve is so symmetric that what
for reasons of the three astronomical factors is
gained in the northern summer, will be lost in
winter. The very small fluctuations in these
factors, on which the B-1 hypothesis is based,
cannot, therefore, be assumed to have any re-
motely significant climatic influence. Broecker
(1966) assumes two different (self-regulated)
states of the atmosphere, glacial and intergla-
cial, on which the three astronomical factors
should have a modulating effect. But it is argu-
ed in the present paper that postulates of such
different states, each dominating for a very
long time, are unacceptable for the fact that
the superposed annual fluctuation is one to two