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Conclusion

Causes Of Mild Geological Climates

Hypotheses Of Climatic Change

Some Problems Of Glacial Periods

The Variability Of Climate

The Climatic Stress Of The Fourteenth Century

The Climate Of History

The Uniformity Of Climate

The Solar Cyclonic Hypothesis

Glaciation According To The Solar-cyclonic Hypothesis[38]



Least Viewed

Terrestrial Causes Of Climatic Changes

The Changing Composition Of Oceans And Atmosphere

The Sun's Journey Through Space

The Earth's Crust And The Sun

Post-glacial Crustal Movements And Climatic Changes

The Effect Of Other Bodies On The Sun

The Origin Of Loess

Glaciation According To The Solar-cyclonic Hypothesis[38]

The Solar Cyclonic Hypothesis

The Uniformity Of Climate






Hypotheses Of Climatic Change








The next step in our study of climate is to review the main hypotheses
as to the causes of glaciation. These hypotheses apply also to other
types of climatic changes. We shall concentrate on glacial periods,
however, not only because they are the most dramatic and well-known
types of change, but because they have been more discussed than any
other and have also had great influence on evolution. Moreover, they
stand near the middle of the types of climatic sequences, and an
understanding of them does much to explain the others. In reviewing the
various theories we shall not attempt to cover all the ground, but shall
merely state the main ideas of the few theories which have had an
important influence upon scientific thought.

The conditions which any satisfactory climatic hypothesis must satisfy
are briefly as follows:

(1) Due weight must be given to the fact that changes of climate are
almost certainly due to the combined effect of a variety of causes, both
terrestrial and solar or cosmic.

(2) Attention must also be paid to both sides in the long controversy as
to whether glaciation is due primarily to a diminution in the earth's
supply of heat or to a redistribution of the heat through changes in
atmospheric and oceanic circulation. At present the great majority of
authorities are on the side of a diminution of heat, but the other view
also deserves study.

(3) A satisfactory hypothesis must explain the frequent synchronism
between two great types of phenomena; first, movements of the earth's
crust whereby continents are uplifted and mountains upheaved; and,
second, great changes of climate which are usually marked by relatively
rapid oscillations from one extreme to another.

(4) No hypothesis can find acceptance unless it satisfies the somewhat
exacting requirements of the geological record, with its frequent but
irregular repetition of long, mild periods, relatively cool or
intermediate periods like the present, and glacial periods of more or
less severity and perhaps accompanying the more or less widespread
uplifting of continents. At least during the later glacial periods the
hypothesis must explain numerous climatic epochs and stages superposed
upon a single general period of continental upheaval. Moreover, although
historical geology demands cycles of varied duration and magnitude, it
does not furnish evidence of any rigid periodicity causing the cycles to
be uniform in length or intensity.

(5) Most important of all, a satisfactory explanation of climatic
changes and crustal deformation must take account of all the agencies
which are now causing similar phenomena. Whether any other agencies
should be considered is open to question, although the relative
importance of existing agencies may have varied.

I. Croll's Eccentricity Theory. One of the most ingenious and most
carefully elaborated scientific hypotheses is Croll's[10] precessional
hypothesis as to the effect of the earth's own motions. So well was this
worked out that it was widely accepted for a time and still finds a
place in popular but unscientific books, such as Wells' Outline of
History, and even in scientific works like Wright's Quaternary Ice
Age. The gist of the hypothesis has already been given in connection
with the type of climatic sequence known as orbital precessions. The
earth is 93 million miles away from the sun in January and 97 million in
July. The earth's axis "precesses," however, just as does that of a
spinning top. Hence arises what is known as the precession of the
equinoxes, that is, a steady change in the season at which the earth is
in perihelion, or nearest to the sun. In the course of 21,000 years the
time of perihelion varies from early in January through the entire
twelve months and back to January. Moreover, the earth's orbit is
slightly more elliptical at certain periods than at others, for the
planets sometimes become bunched so that they all pull the earth in one
direction. Hence, once in about one hundred thousand years the effect of
the elliptical shape of the earth's orbit is at a maximum.

Croll argued that these astronomical changes must alter the earth's
climate, especially by their effect on winds and ocean currents. His
elaborate argument contains a vast amount of valuable material. Later
investigation, however, seems to have proven the inadequacy of his
hypothesis. In the first place, the supposed cause does not seem nearly
sufficient to produce the observed results. Second, Croll's hypothesis
demands that glaciation in the northern and southern hemisphere take
place alternately. A constantly growing collection of facts, however,
indicates that glaciation does not occur in the two hemispheres
alternately, but at the same time. Third, the hypothesis calls for the
constant and frequent repetition of glaciation at absolutely regular
intervals. The geological record shows no such regularity, for sometimes
several glacial epochs follow in relatively close succession at
irregular intervals of perhaps fifty to two hundred thousand years, and
thus form a glacial period; and then for millions of years there are
none. Fourth, the eccentricity hypothesis provides no adequate
explanation for the glacial stages or subepochs, the historic
pulsations, and the other smaller climatic variations which are
superposed upon glacial epochs and upon one another in bewildering
confusion. In spite of these objections, there can be little question
that the eccentricity of the earth's orbit and the precession of the
equinoxes with the resulting change in the season of perihelion must
have some climatic effect. Hence Croll's theory deserves a permanent
though minor place in any full discussion of the causes of climatic
changes.

II. The Carbon Dioxide Theory. At about the time that the eccentricity
theory was being relegated to a minor niche, a new theory was being
developed which soon exerted a profound influence upon geological
thought. Chamberlin,[11] adopting an idea suggested by Tyndall, fired
the imagination of geologists by his skillful exposition of the part
played by carbon dioxide in causing climatic changes. Today this theory
is probably more widely accepted than any other. We have already seen
that the amount of carbon dioxide gas in the atmosphere has a decided
climatic importance. Moreover, there can be little doubt that the amount
of that gas in the atmosphere varies from age to age in response to the
extent to which it is set free by volcanoes, consumed by plants,
combined with rocks in the process of weathering, dissolved in the ocean
or locked up in the form of coal and limestone. The main question is
whether such variations can produce changes so rapid as glacial epochs
and historical pulsations.

Abundant evidence seems to show that the degree to which the air can be
warmed by carbon dioxide is sharply limited. Humphreys, in his excellent
book on the Physics of the Air, calculates that a layer of carbon
dioxide forty centimeters thick has practically as much blanketing
effect as a layer indefinitely thicker. In other words, forty
centimeters of carbon dioxide, while having no appreciable effect on
sunlight coming toward the earth, would filter out and thus retain in
the atmosphere all the outgoing terrestrial heat that carbon dioxide is
capable of absorbing. Adding more would be like adding another filter
when the one in operation has already done all that that particular kind
of filter is capable of doing. According to Humphreys' calculations, a
doubling of the carbon dioxide in the air would in itself raise the
average temperature about 1.3 deg.C. and further carbon dioxide would have
practically no effect. Reducing the present supply by half would reduce
the temperature by essentially the same amount.

The effect must be greater, however, than would appear from the figures
given above, for any change in temperature has an effect on the amount
of water vapor, which in turn causes further changes of temperature.
Moreover, as Chamberlin points out, it is not clear whether Humphreys
allows for the fact that when the 40 centimeters of CO{2} nearest the
earth has been heated by terrestrial radiation, it in turn radiates half
its heat outward and half inward. The outward half is all absorbed in
the next layer of carbon dioxide, and so on. The process is much more
complex than this, but the end result is that even the last increment of
CO{2}, that is, the outermost portions in the upper atmosphere, must
apparently absorb an infinitesimally small amount of heat. This fact,
plus the effect of water vapor, would seem to indicate that a doubling
or halving of the amount of CO{2}, would have an effect of more than
1.3 deg.C. A change of even 2 deg.C. above or below the present level of the
earth's mean temperature would be of very appreciable climatic
significance, for it is commonly believed that during the height of the
glacial period the mean temperature was only 5 deg. to 8 deg.C. lower than now.

Nevertheless, variations in atmospheric carbon dioxide do not
necessarily seem competent to produce the relatively rapid climatic
fluctuations of glacial epochs and historic pulsations as distinguished
from the longer swings of glacial periods and geological eras. In
Chamberlin's view, as in ours, the elevation of the land, the
modification of the currents of the air and of the ocean, and all that
goes with elevation as a topographic agency constitute a primary cause
of climatic changes. A special effect of this is the removal of carbon
dioxide from the air by the enhanced processes of weathering. This, as
he carefully states, is a very slow process, and cannot of itself lead
to anything so sudden as the oncoming of glaciation. But here comes
Chamberlin's most distinctive contribution to the subject, namely, the
hypothesis that changes in atmospheric temperature arising from
variations in atmospheric carbon dioxide are able to cause a reversal of
the deep-sea oceanic circulation.

According to Chamberlin's view, the ordinary oceanic circulation of the
greater part of geological time was the reverse of the present
circulation. Warm water descended to the ocean depths in low latitudes,
kept its heat while creeping slowly poleward, and rose in high latitudes
producing the warm climate which enabled corals, for example, to grow in
high latitudes. Chamberlin holds this opinion largely because there
seems to him to be no other reasonable way to account for the enormously
long warm periods when heat-loving forms of life lived in what are now
polar regions of ice and snow. He explains this reversed circulation by
supposing that an abundance of atmospheric carbon dioxide, together with
a broad distribution of the oceans, made the atmosphere so warm that the
evaporation in low latitudes was far more rapid than now. Hence the
surface water of the ocean became a relatively concentrated brine. Such
a brine is heavy and tends to sink, thereby setting up an oceanic
circulation the reverse of that which now prevails. At present the polar
waters sink because they are cold and hence contract. Moreover, when
they freeze a certain amount of salt leaves the ice and thereby
increases the salinity of the surrounding water. Thus the polar water
sinks to the depths of the ocean, its place is taken by warmer and
lighter water from low latitudes which moves poleward along the surface,
and at the same time the cold water of the ocean depths is forced
equatorward below the surface. But if the equatorial waters were so
concentrated that a steady supply of highly saline water kept descending
to low levels, the direction of the circulation would have to be
reversed. The time when this would occur would depend upon the delicate
balance between the downward tendencies of the cold polar water and of
the warm saline equatorial water.

Suppose that while such a reversed circulation prevailed, the
atmospheric CO{2} should be depleted, and the air cooled so much that
the concentration of the equatorial waters by evaporation was no longer
sufficient to cause them to sink. A reversal would take place, the
present type of circulation would be inaugurated, and the whole earth
would suffer a chill because the surface of the ocean would become cool.
The cool surface-water would absorb carbon dioxide faster than the
previous warm water had done, for heat drives off gases from water. This
would hasten the cooling of the atmosphere still more, not only directly
but by diminishing the supply of atmospheric moisture. The result would
be glaciation. But ultimately the cold waters of the higher latitudes
would absorb all the carbon dioxide they could hold, the slow
equatorward creep would at length permit the cold water to rise to the
surface in low latitudes. There the warmth of the equatorial sun and the
depleted supply of carbon dioxide in the air would combine to cause the
water to give up its carbon dioxide once more. If the atmosphere had
been sufficiently depleted by that time, the rising waters in low
latitudes might give up more carbon dioxide than the cold polar waters
absorbed. Thus the atmospheric supply would increase, the air would
again grow warm, and a tendency toward deglaciation, or toward an
inter-glacial condition would arise. At such times the oceanic
circulation is not supposed to have been reversed, but merely to have
been checked and made slower by the increasing warmth. Thus
inter-glacial conditions like those of today, or even considerably
warmer, are supposed to have been produced with the present type of
circulation.

The emission of carbon dioxide in low latitudes could not permanently
exceed the absorption in high latitudes. After the present type of
circulation was finally established, which might take tens of thousands
of years, the two would gradually become equal. Then the conditions
which originally caused the oceanic circulation to be reversed would
again destroy the balance; the atmospheric carbon dioxide would be
depleted; the air would grow cooler; and the cycle of glaciation would
be repeated. Each cycle would be shorter than the last, for not only
would the swings diminish like those of a pendulum, but the agencies
that were causing the main depletion of the atmospheric carbon dioxide
would diminish in intensity. Finally as the lands became lower through
erosion and submergence, and as the processes of weathering became
correspondingly slow, the air would gradually be able to accumulate
carbon dioxide; the temperature would increase; and at length the
oceanic circulation would be reversed again. When the warm saline waters
of low latitudes finally began to sink and to set up a flow of warm
water poleward in the depths of the ocean, a glacial period would
definitely come to an end.

This hypothesis has been so skillfully elaborated, and contains so many
important elements that one can scarcely study it without profound
admiration. We believe that it is of the utmost value as a step toward
the truth, and especially because it emphasizes the great function of
oceanic circulation. Nevertheless, we are unable to accept it in full
for several reasons, which may here be stated very briefly. Most of them
will be discussed fully in later pages.

(1) While a reversal of the deep-sea circulation would undoubtedly be of
great climatic importance and would produce a warm climate in high
latitudes, we see no direct evidence of such a reversal. It is equally
true that there is no conclusive evidence against it, and the
possibility of a reversal must not be overlooked. There seem, however,
to be other modifications of atmospheric and oceanic circulation which
are able to produce the observed results.

(2) There is much, and we believe conclusive, evidence that a mere
lowering of temperature would not produce glaciation. What seems to be
needed is changes in atmospheric circulation and in precipitation. The
carbon dioxide hypothesis has not been nearly so fully developed on the
meteorological side as in other respects.

(3) The carbon dioxide hypothesis seems to demand that the oceans should
have been almost as saline as now in the Proterozoic era at the time of
the first known glaciation. Chamberlin holds that such was the case, but
the constant supply of saline material brought to the ocean by rivers
and the relatively small deposition of such material on the sea floor
seem to indicate that the early oceans must have been much fresher than
those of today.

(4) The carbon dioxide hypothesis does not attempt to explain minor
climatic fluctuations such as post-glacial stages and historic
pulsations, but these appear to be of the same nature as glacial epochs,
differing only in degree.

(5) Another reason for hesitation in accepting the carbon dioxide
hypothesis as a full explanation of glacial fluctuations is the highly
complex and non-observational character of the explanation of the
alternation of glacial and inter-glacial epochs and of their constantly
decreasing length.

(6) Most important of all, a study of the variations of weather and of
climate as they are disclosed by present records and by the historic
past suggests that there are now in action certain other causes which
are competent to explain glaciation without recourse to a process whose
action is beyond the realm of observation.

These considerations lead to the conclusion that the carbon dioxide
hypothesis and the reversal of the oceanic circulation should be
regarded as a tentative rather than a final explanation of glaciation.
Nevertheless, the action of carbon dioxide seems to be an important
factor in producing the longer oscillations of climate from one
geological era to another. It probably plays a considerable part in
preparing the way for glacial periods and in making it possible for
other factors to produce the more rapid changes which have so deeply
influenced organic evolution.

III. The Form of the Land. Another great cause of climatic change
consists of a group of connected phenomena dependent upon movements of
the earth's crust. As to the climatic potency of changes in the lands
there is practical agreement among students of climatology and
glaciation. That the height and extent of the continents, the location,
size, and orientation of mountain ranges, and the opening and closing of
oceanic gateways at places like Panama, and the consequent diversion of
oceanic currents, exert a profound effect upon climate can scarcely be
questioned. Such changes may be introduced rapidly, but their
disappearance is usually slow compared with the rapid pulsations to
which climate has been subject during historic times and during stages
of glacial retreat and advance, or even in comparison with the epochs
into which the Pleistocene, Permian, and perhaps earlier glacial periods
have been divided. Hence, while crustal movements appear to be more
important than the eccentricity of the earth's orbit or the amount of
carbon dioxide in the air, they do not satisfactorily explain glacial
fluctuations, historic pulsations, and especially the present little
cycles of climatic change. All these changes involve a relatively rapid
swing from one extreme to another, while an upheaval of a continent,
which is at best a slow geologic process, apparently cannot be undone
for a long, long time. Hence such an upheaval, if acting alone, would
lead to a relatively long-lived climate of a somewhat extreme type. It
would help to explain the long swings, or geologic oscillations between
a mild and uniform climate at one extreme, and a complex and varied
climate at the other, but it would not explain the rapid climatic
pulsations which are closely associated with great movements of the
earth's crust. It might prepare the way for them, but could not cause
them. That this conclusion is true is borne out by the fact that vast
mountain ranges, like those at the close of the Jurassic and Cretaceous,
are upheaved without bringing on glacial climates. Moreover, the marked
Permian ice age follows long after the birth of the Hercynian Mountains
and before the rise of others of later Permian origin.

IV. The Volcanic Hypothesis. In the search for some cause of climatic
change which is highly efficient and yet able to vary rapidly and
independently, Abbot, Fowle, Humphreys, and others,[12] have concluded
that volcanic eruptions are the missing agency. In Physics of the Air,
Humphreys gives a careful study of the effect of volcanic dust upon
terrestrial temperature. He begins with a mathematical investigation of
the size of dust particles, and their quantity after certain eruptions.
He demonstrates that the power of such particles to deflect light of
short wave-lengths coming from the sun is perhaps thirty times more than
their power to retain the heat radiated in long waves from the earth.
Hence it is estimated that if a Krakatoa were to belch forth dust every
year or two, the dust veil might cause a reduction of about 6 deg.C. in the
earth's surface temperature. As in every such complicated problem, some
of the author's assumptions are open to question, but this touches their
quantitative and not their qualitative value. It seems certain that if
volcanic explosions were frequent enough and violent enough, the
temperature of the earth's surface would be considerably lowered.

Actual observation supports this theoretical conclusion. Humphreys
gathers together and amplifies all that he and Abbot and Fowle have
previously said as to observations of the sun's thermal radiation by
means of the pyrheliometer. This summing up of the relations between the
heat received from the sun, and the occurrence of explosive volcanic
eruptions leaves little room for doubt that at frequent intervals during
the last century and a half a slight lowering of terrestrial temperature
has actually occurred after great eruptions. Nevertheless, it does not
justify Humphreys' final conclusion that "phenomena within the earth
itself suffice to modify its own climate, ... that these and these alone
have actually caused great changes time and again in the geologic past."
Humphreys sees so clearly the importance of the purely terrestrial point
of view that he unconsciously slights the cosmic standpoint and ignores
the important solar facts which he himself adduces elsewhere at
considerable length.

In addition to this the degree to which the temperature of the earth
as a whole is influenced by volcanic eruptions is by no means so clear
as is the fact that there is some influence. Arctowski,[13] for example,
has prepared numerous curves showing the march of temperature month
after month for many years. During the period from 1909 to 1913, which
includes the great eruption of Katmai in Alaska, low temperature is
found to have prevailed at the time of the eruption, but, as Arctowski
puts it, on the basis of the curves for 150 stations in all parts of the
world: "The supposition that these abnormally low temperatures were due
to the veil of volcanic dust produced by the Katmai eruption of June 6,
1912, is completely out of the question. If that had been the case,
temperature would have decreased from that date on, whereas it was
decreasing for more than a year before that date."

Koeppen,[14] in his comprehensive study of temperature for a hundred
years, also presents a strong argument against the idea that volcanic
eruptions have an important place in determining the present temperature
of the earth. A volcanic eruption is a sudden occurrence. Whatever
effect is produced by dust thrown into the air must occur within a few
months, or as soon as the dust has had an opportunity to be wafted to
the region in question. When the dust arrives, there will be a rapid
drop through the few degrees of temperature which the dust is supposed
to be able to account for, and thereafter a slow rise of temperature. If
volcanic eruptions actually caused a frequent lowering of terrestrial
temperature in the hundred years studied by Koeppen, there should be more
cases where the annual temperature is decidedly below the normal than
where it shows a large departure in the opposite direction. The contrary
is actually the case.

A still more important argument is the fact that the earth is now in an
intermediate condition of climate. Throughout most of geologic time, as
we shall see again and again, the climate of the earth has been milder
than now. Regions like Greenland have not been the seat of glaciers, but
have been the home of types of plants which now thrive in relatively low
latitudes. In other words, the earth is today only part way from a
glacial epoch to what may be called the normal, mild climate of the
earth--a climate in which the contrast from zone to zone was much less
than now, and the lower air averaged warmer. Hence it seems impossible
to avoid the conclusion that the cause of glaciation is still operating
with considerable although diminished efficiency. But volcanic dust is
obviously not operating to any appreciable extent at present, for the
upper air is almost free from dust a large part of the time.

Again, as Chamberlin suggests, let it be supposed that a Krakatoan
eruption every two years would produce a glacial period. Unless the most
experienced field workers on the glacial formations are quite in error,
the various glacial epochs of the Pleistocene glacial period had a joint
duration of at least 150,000 years and perhaps twice as much. That would
require 75,000 Krakatoan eruptions. But where are the pits and cones of
such eruptions? There has not been time to erode them away since the
Pleistocene glaciation. Their beds of volcanic ash would presumably be
as voluminous as the glacial beds, but there do not seem to be
accumulations of any such size. Even though the same volcano suffered
repeated explosions, it seems impossible to find sufficient fresh
volcanic debris. Moreover, the volcanic hypothesis has not yet offered
any mechanism for systematic glacial variations. Hence, while the
hypothesis is important, we must search further for the full explanation
of glacial fluctuations, historic pulsations, and the earth's present
quasi-glacial climate.

V. The Hypothesis of Polar Wandering. Another hypothesis, which has
some adherents, especially among geologists, holds that the position of
the earth's axis has shifted repeatedly during geological times, thus
causing glaciation in regions which are not now polar. Astrophysicists,
however, are quite sure that no agency could radically change the
relation between the earth and its axis without likewise altering the
orbits of the planets to a degree that would be easily recognized.
Moreover, the distribution of the centers of glaciation both in the
Permian and Pleistocene periods does not seem to conform to this
hypothesis.

VI. The Thermal Solar Hypothesis. The only other explanations of the
climatic changes of glacial and historic times which now seem to have
much standing are two distinct and almost antagonistic solar hypotheses.
One is the idea that changes in the earth's climate are due to
variations in the heat emitted by the sun and hence in the temperature
of the earth. The other is the entirely different idea that climatic
changes arise from solar conditions which cause a redistribution of the
earth's atmospheric pressure and hence produce changes in winds, ocean
currents, and especially storms. This second, or "cyclonic," hypothesis
is the subject of a book entitled Earth and Sun, which is to be
published as a companion to the present volume. It will be outlined in
the next chapter. The other, or thermal, hypothesis may be dismissed
briefly. Unquestionably a permanent change in the amount of heat emitted
by the sun would permanently alter the earth's climate. There is
absolutely no evidence, however, of any such change during geologic
time. The evidence as to the earth's cosmic uniformity and as to secular
progression is all against it. Suppose that for thirty or forty thousand
years the sun cooled off enough so that the earth was as cool as during
a glacial epoch. As glaciation is soon succeeded by a mild climate, some
agency would then be needed to raise the sun's temperature. The impact
of a shower of meteorites might accomplish this, but that would mean a
very sudden heating, such as there is no evidence of in geological
history. In fact, there is far more evidence of sudden cooling than of
sudden heating. Moreover, it is far beyond the bounds of probability
that such an impact should be repeated again and again with just such
force as to bring the climate back almost to where it started and yet to
allow for the slight changes which cause secular progression. Another
and equally cogent objection to the thermal form of solar hypothesis is
stated by Humphreys as follows: "A change of the solar constant
obviously alters all surface temperatures by a roughly constant
percentage. Hence a decrease of the heat from the sun would in general
cause a decrease of the interzonal temperature gradients; and this in
turn a less vigorous atmospheric circulation, and a less copious rain or
snowfall--exactly the reverse of the condition, namely, abundant
precipitation, most favorable to extensive glaciation."

This brings us to the end of the main hypotheses as to climatic changes,
aside from the solar cyclonic hypothesis which will be discussed in the
next chapter. It appears that variations in the position of the earth at
perihelion have a real though slight influence in causing cycles with a
length of about 21,000 years. Changes in the carbon dioxide of the air
probably have a more important but extremely slow influence upon
geologic oscillations. Variations in the size, shape, and height of the
continents are constantly causing all manner of climatic complications,
but do not cause rapid fluctuations and pulsations. The eruption of
volcanic dust appears occasionally to lower the temperature, but its
potency to explain the complex climatic changes recorded in the rocks
has probably been exaggerated. Finally, although minor changes in the
amount of heat given out by the sun occur constantly and have been
demonstrated to have a climatic effect, there is no evidence that such
changes are the main cause of the climatic phenomena which we are trying
to explain. Nevertheless, in connection with other solar changes they
may be of high importance.

FOOTNOTES:

[Footnote 10: James Croll: Climate and Time, 1876.]

[Footnote 11: T. C. Chamberlin: An attempt to frame a working hypothesis
of the cause of glacial periods on an atmospheric basis; Jour. Geol.,
Vol. VII, 1899, pp. 545-584, 667-685, 757-787.

T. C. Chamberlin and R. D. Salisbury: Geology, Vol. II, 1906, pp.
93-106, 655-677, and Vol. III, pp. 432-446.

S. Arrhenius (Kosmische Physik, Vol. II, 1903, p. 503) carried out some
investigations on carbon dioxide which have had a pronounced effect on
later conclusions.

F. Frech adopted Arrhenius' idea and developed it in a paper entitled
Ueber die Klima-Aenderungen der Geologischen Vergangenheit. Compte
Rendu, Tenth (Mexico) Congr. Geol. Intern., 1907 (=1908), pp. 299-325.

The exact origin of the carbon dioxide theory has been stated so
variously that it seems worth while to give the exact facts. Prompted by
the suggestion, of Tyndall that glaciation might be due to depletion of
atmospheric carbon dioxide, Chamberlin worked up the essentials of his
early views before he saw any publication from Arrhenius, to whom the
idea has often been attributed. In 1895 or earlier Chamberlin began to
give the carbon dioxide hypothesis to his students and to discuss it
before local scientific bodies. In 1897 he prepared a paper on "A Group
of Hypotheses Bearing on Climatic Changes," Jour. Geol., Vol. V (1897),
to be read at the meeting of the British Association at Toronto, basing
his conclusions on Tyndall's determination of the competency of carbon
dioxide as an absorber of heat radiated from the earth. He had
essentially completed this when a paper by Arrhenius, "On the influence
of carbonic acid in the air upon the temperature of the ground," Phil.
Mag., 1896, pp. 237-276, first came to his attention. Chamberlin then
changed his conservative, tentative statement of the functions of carbon
dioxide to a more sweeping one based on Arrhenius' very definite
quantitative deductions from Langley's experiments. Both Langley and
Arrhenius were then in the ascendancy of their reputations and seemingly
higher authorities could scarcely have been chosen, nor a finer
combination than experiment and physico-mathematical development.
Arrhenius' deductions were later proved to have been overstrained, while
Langley's interpretation and even his observations were challenged.
Chamberlin's latest views are more like his earlier and more
conservative statement.]

[Footnote 12: C. G. Abbot and F. E. Fowle: Volcanoes and Climate;
Smiths. Misc. Coll., Vol. 60, 1913, 24 pp.

W. J. Humphreys: Volcanic dust and other factors in the production of
climatic and their possible relation to ice ages; Bull. Mount Weather
Observatory, Vol. 6, Part 1, 1913, 26 pp. Also, Physics of the Air,
1920.]

[Footnote 13: H. Arctowski: The Pleonian Cycle of Climatic Fluctuations;
Am. Jour. Sci., Vol. 42, 1916, pp. 27-33. See also Annals of the New
York Academy of Sciences, Vol. 24, 1914.]

[Footnote 14: W. Koeppen: Ueber mehrjaehrige Perioden der Witterung
ins besondere uezer die II-jaehrige Periode der Temperatur. Also,
Lufttemperaturen Sonnenflecke und Vulcanausbrueche; Meteorologische
Zeitschrift, Vol. 7, 1914, pp. 305-328.]





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