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Conclusion

Causes Of Mild Geological Climates

Hypotheses Of Climatic Change

The Uniformity Of Climate

Some Problems Of Glacial Periods

The Climate Of History

The Variability Of Climate

The Climatic Stress Of The Fourteenth Century

The Solar Cyclonic Hypothesis

Glaciation According To The Solar-cyclonic Hypothesis[38]



Least Viewed

The Changing Composition Of Oceans And Atmosphere

Terrestrial Causes Of Climatic Changes

The Sun's Journey Through Space

The Effect Of Other Bodies On The Sun

Post-glacial Crustal Movements And Climatic Changes

The Earth's Crust And The Sun

The Origin Of Loess

The Solar Cyclonic Hypothesis

Glaciation According To The Solar-cyclonic Hypothesis[38]

The Climatic Stress Of The Fourteenth Century






Some Problems Of Glacial Periods








Having outlined in general terms the coming of the ice sheets and their
disappearance, we are now ready to discuss certain problems of
compelling climatic interest. The discussion will be grouped under five
heads: (I) the localization of glaciation; (II) the sudden coming of
glaciation; (III) peculiar variations in the height of the snow line and
of glaciation; (IV) lakes and other evidences of humidity in unglaciated
regions during the glacial epochs; (V) glaciation at sea level and in
low latitudes in the Permian and Proterozoic eras. The discussion of
perhaps the most difficult of all climatic problems of glaciation, that
of the succession of cold glacial and mild inter-glacial epochs, has
been postponed to the next to the final chapter of this book. It cannot
be properly considered until we take up the history of solar
disturbances.

I. The first problem, the localization of the ice sheets, arises from
the fact that in both the Pleistocene and the Permian periods glaciation
was remarkably limited. In neither period were all parts of high
latitudes glaciated; yet in both cases glaciation occurred in large
regions in lower latitudes. Many explanations of this localization have
been offered, but most are entirely inadequate. Even hypotheses with
something of proven worth, such as those of variations in volcanic dust
and in atmospheric carbon dioxide, fail to account for localization. The
cyclonic form of the solar hypothesis, however, seems to afford a
satisfactory explanation.

The distribution of the ice in the last glacial period is well known,
and is shown in Fig. 6. Four-fifths of the ice-covered area, which was
eight million square miles, more or less, was near the borders of the
North Atlantic in eastern North America and northwestern Europe. The ice
spread out from two great centers in North America, the Labradorean east
of Hudson Bay, and the Keewatin west of the bay. There were also many
glaciers in the western mountains, especially in Canada, while
subordinate centers occurred in Newfoundland, the Adirondacks, and the
White Mountains. The main ice sheet at its maximum extension reached as
far south as latitude 39 deg. in Kansas and Kentucky, and 37 deg. in Illinois.
Huge boulders were transferred more than one thousand miles from their
source in Canada. The northward extension was somewhat less. Indeed, the
northern margin of the continent was apparently relatively little
glaciated and much of Alaska unglaciated. Why should northern Kentucky
be glaciated when northern Alaska was not?

In Europe the chief center from which the continental glacier moved was
the Scandinavian highlands. It pushed across the depression now occupied
by the Baltic to southern Russia and across the North Sea depression to
England and Belgium. The Alps formed a center of considerable
importance, and there were minor centers in Scotland, Ireland, the
Pyrenees, Apennines, Caucasus, and Urals. In Asia numerous ranges also
contained large glaciers, but practically all the glaciation was of the
alpine type and very little of the vast northern lowland was covered
with ice.

In the southern hemisphere glaciation at low latitudes was less striking
than in the northern hemisphere. Most of the increase in the areas of
ice was confined to mountains which today receive heavy precipitation
and still contain small glaciers. Indeed, except for relatively slight
glaciation in the Australian Alps and in Tasmania, most of the
Pleistocene glaciation in the southern hemisphere was merely an
extension of existing glaciers, such as those of south Chile, New
Zealand, and the Andes. Nevertheless, fairly extensive glaciation
existed much nearer the equator than is now the case.

In considering the localization of Pleistocene glaciation, three main
factors must be taken into account, namely, temperature, topography, and
precipitation. The absence of glaciation in large parts of the Arctic
regions of North America and of Asia makes it certain that low
temperature was not the controlling factor. Aside from Antarctica, the
coldest place in the world is northeastern Siberia. There for seven
months the average temperature is below 0 deg.C., while the mean for the
whole year is below -10 deg.C. If the temperature during a glacial period
averaged 6 deg.C. lower than now, as is commonly supposed, this part of
Siberia would have had a temperature below freezing for at least nine
months out of the twelve even if there were no snowfield to keep the
summers cold. Yet even under such conditions no glaciation occurred,
although in other places, such as parts of Canada and northwestern
Europe, intense glaciation occurred where the mean temperature is much
higher.

The topography of the lands apparently had much more influence upon the
localization of glaciation than did temperature. Its effect, however,
was always to cause glaciation exactly where it would be expected and
not in unexpected places as actually occurred. For example, in North
America the western side of the Canadian Rockies suffered intense
glaciation, for there precipitation was heavy because the westerly winds
from the Pacific are forced to give up their moisture as they rise. In
the same way the western side of the Sierra Nevadas was much more
heavily glaciated than the eastern side. In similar fashion the windward
slopes of the Alps, the Caucasus, the Himalayas, and many other mountain
ranges suffered extensive glaciation. Low temperature does not seem to
have been the cause of this glaciation, for in that case it is hard to
see why both sides of the various ranges did not show an equal
percentage of increase in the size of their icefields.

From what has been said as to temperature and topography, it is evident
that variations in precipitation have had much more to do with
glaciation than have variations in temperature. In the Arctic lowlands
and on the leeward side of mountains, the slight development of
glaciation appears to have been due to scarcity of precipitation. On the
windward side of mountains, on the other hand, a notable increase in
precipitation seems to have led to abundant glaciation. Such an increase
in precipitation must be dependent on increased evaporation and this
could arise either from relatively high temperature or strong winds.
Since the temperature in the glacial period was lower than now, we seem
forced to attribute the increased precipitation to a strengthening of
the winds. If the westerly winds from the Pacific should increase in
strength and waft more moisture to the western side of the Canadian
Rockies, or if similar winds increased the snowfall on the upper slopes
of the Alps or the Tian-Shan Mountains, the glaciers would extend lower
than now without any change in temperature.

Although the incompetence of low temperature to cause glaciation, and
the relative unimportance of the mountains in northeastern Canada and
northwestern Europe throw most glacial hypotheses out of court, they are
in harmony with the cyclonic hypothesis. The answer of that hypothesis
to the problem of the localization of ice sheets seems to be found in
certain maps of storminess and rainfall in relation to solar activity.
In Fig. 2 a marked belt of increased storminess at times of many
sunspots is seen in southern Canada. A comparison of this with a series
of maps given in Earth and Sun shows that the stormy belt tends to
migrate northward in harmony with an increase in the activity of the
sun's atmosphere. If the sun were sufficiently active the belt of
maximum storminess would apparently pass through the Keewatin and
Labradorean centers of glaciation instead of well to the south of them,
as at present. It would presumably cross another center in Greenland,
and then would traverse the fourth of the great centers of Pleistocene
glaciation in Scandinavia. It would not succeed in traversing northern
Asia, however, any more than it does now, because of the great
high-pressure area which develops there in winter. When the ice sheets
expanded from the main centers of glaciation, the belt of storms would
be pushed southward and outward. Thus it might give rise to minor
centers of glaciers such as the Patrician between Hudson Bay and Lake<