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Causes Of Mild Geological Climates

Conclusion

Hypotheses Of Climatic Change

Some Problems Of Glacial Periods

The Climatic Stress Of The Fourteenth Century

The Variability Of Climate

The Climate Of History

Glaciation According To The Solar-cyclonic Hypothesis[38]

The Uniformity Of Climate

The Solar Cyclonic Hypothesis



Least Viewed

The Sun's Journey Through Space

The Changing Composition Of Oceans And Atmosphere

Terrestrial Causes Of Climatic Changes

The Effect Of Other Bodies On The Sun

The Earth's Crust And The Sun

Post-glacial Crustal Movements And Climatic Changes

The Origin Of Loess

The Uniformity Of Climate

The Solar Cyclonic Hypothesis

Glaciation According To The Solar-cyclonic Hypothesis[38]






The Solar Cyclonic Hypothesis








The progress of science is made up of a vast succession of hypotheses.
The majority die in early infancy. A few live and are for a time widely
accepted. Then some new hypothesis either destroys them completely or
shows that, while they contain elements of truth, they are not the whole
truth. In the previous chapter we have discussed a group of hypotheses
of this kind, and have tried to point out fairly their degree of truth
so far as it can yet be determined. In this chapter we shall outline
still another hypothesis, the relation of which to present climatic
conditions has been fully developed in Earth and Sun; while its
relation to the past will be explained in the present volume. This
hypothesis is not supposed to supersede the others, for so far as they
are true they cannot be superseded. It merely seems to explain some of
the many conditions which the other hypotheses apparently fail to
explain. To suppose that it will suffer a fate more glorious than its
predecessors would be presumptuous. The best that can be hoped is that
after it has been pruned, enriched, and modified, it may take its place
among the steps which finally lead to the goal of truth.

In this chapter the new hypothesis will be sketched in broad outline in
order that in the rest of this book the reader may appreciate the
bearing of all that is said. Details of proof and methods of work will
be omitted, since they are given in Earth and Sun. For the sake of
brevity and clearness the main conclusions will be stated without the
qualifications and exceptions which are fully explained in that volume.
Here it will be necessary to pass quickly over points which depart
radically from accepted ideas, and which therefore must arouse serious
question in the minds of thoughtful readers. That, however, is a
necessary consequence of the attempt which this book makes to put the
problem of climate in such form that the argument can be followed by
thoughtful students in any branch of knowledge and not merely by
specialists. Therefore, the specialist can merely be asked to withhold
judgment until he has read all the evidence as given in Earth and Sun,
and then to condemn only those parts that are wrong and not the whole
argument.

Without further explanation let us turn to our main problem. In the
realm of climatology the most important discovery of the last generation
is that variations in the weather depend on variations in the activity
of the sun's atmosphere. The work of the great astronomer, Newcomb, and
that of the great climatologist, Koeppen, have shown beyond question that
the temperature of the earth's surface varies in harmony with variations
in the number and area of sunspots.[15] The work of Abbot has shown that
the amount of heat radiated from the sun also varies, and that in
general the variations correspond with those of the sunspots, although
there are exceptions, especially when the spots are fewest. Here,
however, there at once arises a puzzling paradox. The earth certainly
owes its warmth to the sun. Yet when the sun emits the most energy, that
is, when sunspots are most numerous, the earth's surface is coolest.
Doubtless the earth receives more heat than usual at such times, and the
upper air may be warmer than usual. Here we refer only to the air at the
earth's surface.

Another large group of investigators have shown that atmospheric
pressure also varies in harmony with the number of sunspots. Some parts
of the earth's surface have one kind of variation at times of many
sunspots and other parts the reverse. These differences are systematic
and depend largely on whether the region in question happens to have
high atmospheric pressure or low. The net result is that when sunspots
are numerous the earth's storminess increases, and the atmosphere is
thrown into commotion. This interferes with the stable planetary winds,
such as the trades of low latitudes and the prevailing westerlies of
higher latitudes. Instead of these regular winds and the fair weather
which they bring, there is a tendency toward frequent tropical
hurricanes in the lower latitudes and toward more frequent and severe
storms of the ordinary type in the latitudes where the world's most
progressive nations now live. With the change in storminess there
naturally goes a change in rainfall. Not all parts of the world,
however, have increased storminess and more abundant rainfall when
sunspots are numerous. Some parts change in the opposite way. Thus when
the sun's atmosphere is particularly disturbed, the contrasts between
different parts of the earth's surface are increased. For example, the
northern United States and southern Canada become more stormy and rainy,
as appears in Fig. 2, and the same is true of the Southwest and along
the south Atlantic coast. In a crescent-shaped central area, however,
extending from Wyoming through Missouri to Nova Scotia, the number of
storms and the amount of rainfall decrease.


(After Kullmer.)

Based on nine years' nearest sunspot minima and nine years' nearest
sunspot maxima in the three sunspot cycles from 1888 to 1918. Heavy
shading indicates excess of storminess when sunspots are numerous.
Figures indicate average yearly number of storms by which years of
maximum sunspots exceed those of minimum sunspots.]

The two controlling factors of any climate are the temperature and the
atmospheric pressure, for they determine the winds, the storms, and thus
the rainfall. A study of the temperature seems to show that the peculiar
paradox of a hot sun and a cool earth is due largely to the increased
storminess during times of many sunspots. The earth's surface is heated
by the rays of the sun, but most of the rays do not in themselves heat
the air as they pass through it. The air gets its heat largely from the
heat absorbed by the water vapor which is intimately mingled with its
lower portions, or from the long heat waves sent out by the earth after
it has been warmed by the sun. The faster the air moves along the
earth's surface the less it becomes heated, and the more heat it takes
away. This sounds like a contradiction, but not to anyone who has tried
to heat a stove in the open air. If the air is still, the stove rapidly
becomes warm and so does the air around it. If the wind is blowing, the
cool air delays the heating of the stove and prevents the surface from
ever becoming as hot as it would otherwise. That seems to be what
happens on a large scale when sunspots are numerous. The sun actually
sends to the earth more energy than usual, but the air moves with such
unusual rapidity that it actually cools the earth's surface a trifle by
carrying the extra heat to high levels where it is lost into space.

There has been much discussion as to why storms are numerous when the
sun's atmosphere is disturbed. Many investigators have supposed it was
due entirely and directly to the heating of the earth's surface by the
sun. This, however, needs modification for several reasons. In the first
place, recent investigations show that in a great many cases changes in
barometric pressure precede changes in temperature and apparently cause
them by altering the winds and producing storms. This is the opposite of
what would happen if the effect of solar heat upon the earth's surface
were the only agency. In the second place, if storms were due
exclusively to variations in the ordinary solar radiation which comes to
the earth as light and is converted into heat, the solar effect ought to
be most pronounced when the center of the sun's visible disk is most
disturbed. As a matter of fact the storminess is notably greatest when
the edges of the solar disk are most disturbed. These facts and others
lead to the conclusion that some agency other than heat must also play
some part in producing storminess.

The search for this auxiliary agency raises many difficult questions
which cannot yet be answered. On the whole the weight of evidence
suggests that electrical phenomena of some kind are involved, although
variations in the amount of ultra-violet light may also be important.
Many investigators have shown that the sun emits electrons. Hale has
proved that the sun, like the earth, is magnetized. Sunspots also have
magnetic fields the strength of which is often fifty times as great as
that of the sun as a whole. If electrons are sent to the earth, they
must move in curved paths, for they are deflected by the sun's magnetic
field and again by the earth's magnetic field. The solar deflection may
cause their effects to be greatest when the spots are near the sun's
margin; the terrestrial deflection may cause concentration in bands
roughly concentric with the magnetic poles of the earth. These
conditions correspond with the known facts.

Farther than this we cannot yet go. The calculations of Humphreys seem
to indicate that the direct electrical effect of the sun's electrons
upon atmospheric pressure is too small to be of appreciable significance
in intensifying storms. On the other hand the peculiar way in which
activity upon the margins of the sun appears to be correlated not only
with atmospheric electricity, but with barometric pressure, seems to be
equally strong evidence in the other direction. Possibly the sun's
electrons and its electrical waves produce indirect effects by being
converted into heat, or by causing the formation of ozone and the
condensation of water vapor in the upper air. Any one of these processes
would raise the temperature of the upper air, for the ozone and the
water vapor would be formed there and would tend to act as a blanket to
hold in the earth's heat. But any such change in the temperature of the
upper air would influence the lower air through changes in barometric
pressure. These considerations are given here because the thoughtful
reader is likely to inquire how solar activity can influence storminess.
Moreover, at the end of this book we shall take up certain speculative
questions in which an electrical hypothesis will be employed. For the
main portions of this book it makes no difference how the sun's
variations influence the earth's atmosphere. The only essential point is
that when the solar atmosphere is active the storminess of the earth
increases, and that is a matter of direct observation.

Let us now inquire into the relation between the small cyclonic
vacillations of the weather and the types of climatic changes known as
historic pulsations and glacial fluctuations. One of the most
interesting results of recent investigations is the evidence that
sunspot cycles on a small scale present almost the same phenomena as do
historic pulsations and glacial fluctuations. For instance, when
sunspots are numerous, storminess increases markedly in a belt near the
northern border of the area of greatest storminess, that is, in southern
Canada and thence across the Atlantic to the North Sea and Scandinavia.
(See Figs. 2 and 3.) Corresponding with this is the fact that the
evidence as to climatic pulsations in historic times indicates that
regions along this path, for instance Greenland, the North Sea region,
and southern Scandinavia, were visited by especially frequent and severe
storms at the climax of each pulsation. Moreover, the greatest
accumulations of ice in the glacial period were on the poleward border
of the general regions where now the storms appear to increase most at
times of solar activity.


decreasing sunspots.

Heavy shading, more rain with increasing spots. Light shading, more rain
with decreasing spots. No data for unshaded areas.

Figures indicate percentages of the average rainfall by which the
rainfall during periods of increasing spots exceeds or falls short of
rainfall during periods of decreasing spots. The excess or deficiency is
stated in percentages of the average. Rainfall data from Walker:
Sunspots and Rainfall.]


decreasing sunspots.

Heavy shading, more rain with increasing spots. Light shading, more rain
with decreasing spots. No data for unshaded areas. Figures indicate
percentages of the average rainfall by which the rainfall during periods
of increasing spots exceeds or falls short of rainfall during periods of
decreasing spots. The excess or deficiency is stated in percentages of
the average. Rainfall data from Walker: Sunspots and Rainfall.]

Even more clear is the evidence from other regions where storms increase
at times of many sunspots. One such region includes the southwestern
United States, while another is the Mediterranean region and the
semi-arid or desert parts of Asia farther east. In these regions
innumerable ruins and other lines of evidence show that at the climax of
each climatic pulsation there was more storminess and rainfall than at
present, just as there now is when the sun is most active. In still
earlier times, while ice was accumulating farther north, the basins of
these semi-arid regions were filled with lakes whose strands still
remain to tell the tale of much-increased rainfall and presumable
storminess. If we go back still further in geological times to the
Permian glaciation, the areas where ice accumulated most abundantly
appear to be the regions where tropical hurricanes produce the greatest
rainfall and the greatest lowering of temperature at times of many
sunspots. From these and many other lines of evidence it seems probable
that historic pulsations and glacial fluctuations are nothing more than
sunspot cycles on a large scale. It is one of the fundamental rules of
science to reason from the known to the unknown, from the near to the
far, from the present to the past. Hence it seems advisable to
investigate whether any of the climatic phenomena of the past may have
arisen from an intensification of the solar conditions which now appear
to give rise to similar phenomena on a small scale.

The rest of this chapter will be devoted to a resume of certain
tentative conclusions which have no bearing on the main part of this
book, but which apply to the closing chapters. There we shall inquire
into the periodicity of the climatic phenomena of geological times, and
shall ask whether there is any reason to suppose that the sun's activity
has exhibited similar periodicity. This leads to an investigation of the
possible causes of disturbances in the sun's atmosphere. It is generally
assumed that sunspots, solar prominences, the bright clouds known as
faculae, and other phenomena denoting a perturbed state of the solar
atmosphere, are due to some cause within the sun. Yet the limitation of
these phenomena, especially the sunspots, to restricted latitudes, as
has been shown in Earth and Sun, does not seem to be in harmony with
an internal solar origin, even though a banded arrangement may be normal
for a rotating globe. The fairly regular periodicity of the sunspots
seems equally out of harmony with an internal origin. Again, the solar
atmosphere has two kinds of circulation, one the so-called "rice
grains," and the other the spots and their attendant phenomena. Now the
rice grains present the appearance that would be expected in an
atmospheric circulation arising from the loss of heat by the outer part
of a gaseous body like the sun. For these reasons and others numerous
good thinkers from Wolf to Schuster have held that sunspots owe their
periodicity to causes outside the sun. The only possible cause seems to
be the planets, acting either through gravitation, through forces of an
electrical origin, or through some other agency. Various new
investigations which are described in Earth and Sun support this
conclusion. The chief difficulty in accepting it hitherto has been that
although Jupiter, because of its size, would be expected to dominate the
sunspot cycle, its period of 11.86 years has not been detected. The
sunspot cycle has appeared to average 11.2 years in length, and has been
called the 11-year cycle. Nevertheless, a new analysis of the sunspot
data shows that when attention is concentrated upon the major maxima,
which are least subject to retardation or acceleration by other causes,
a periodicity closely approaching that of Jupiter is evident. Moreover,
when the effects of Jupiter, Saturn, and the other planets are combined,
they produce a highly variable curve which has an extraordinary
resemblance to the sunspot curve. The method by which the planets
influence the sun's atmosphere is still open to question. It may be
through tides, through the direct effect of gravitation, through
electro-magnetic forces, or in some other way. Whichever it may be, the
result may perhaps be slight differences of atmospheric pressure upon
the sun. Such differences may set in motion slight whirling movements
analogous to terrestrial storms, and these presumably gather momentum
from the sun's own energy. Since the planetary influences vary in
strength because of the continuous change in the relative distances and
positions of the planets, the sun's atmosphere appears to be swayed by
cyclonic disturbances of varying degrees of severity. The cyclonic
disturbances known as sunspots have been proved by Hale to become more
highly electrified as they increase in intensity. At the same time hot
gases presumably well up from the lower parts of the solar atmosphere
and thereby cause the sun to emit more heat. Thus by one means or
another, the earth's atmosphere appears to be set in commotion and
cycles of climate are inaugurated.

If the preceding reasoning is correct, any disturbance of the solar
atmosphere must have an effect upon the earth's climate. If the
disturbance were great enough and of the right nature it might produce a
glacial epoch. The planets are by no means the only bodies which act
upon the sun, for that body sustains a constantly changing relation to
millions of other celestial bodies of all sizes up to vast universes,
and at all sorts of distances. If the sun and another star should
approach near enough to one another, it is certain that the solar
atmosphere would be disturbed much more than at present.

Here we must leave the cyclonic hypothesis of climate and must refer the
reader once more to Earth and Sun for fuller details. In the rest of
this book we shall discuss the nature of the climatic changes of past
times and shall inquire into their relation to the various climatic
hypotheses mentioned in the last two chapters. Then we shall inquire
into the possibility that the solar system has ever been near enough to
any of the stars to cause appreciable disturbances of the solar
atmosphere. We shall complete our study by investigating the vexed
question of why movements of the earth's crust, such as the uplifting of
continents and mountain chains, have generally occurred at the same time
as great climatic fluctuations. This would not be so surprising were it
not that the climatic phenomena appear to have consisted of highly
complex cycles while the uplift has been a relatively steady movement in
one direction. We shall find some evidence that the solar disturbances
which seem to cause climatic changes also have a relation to movements
of the crust.

FOOTNOTES:

[Footnote 15: The so-called sunspot numbers to which reference is made
again and again in this book are based on a system devised by Wolf and
revised by A. Wolfer. The number and size of the spots are both taken
into account. The numbers from 1749 to 1900 may be found in the Monthly
Weather Review for April, 1902, and from 1901 to 1918 in the same
journal for 1920.]





Next: The Climate Of History

Previous: Hypotheses Of Climatic Change



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