By JOSEPH WALLACE.
Every now and then some weather sage predicts extremely cold winters,
and another ventures to say that the sun is gradually losing heat and
in time Arctic cold will prevail over the globe. Whatever may have
been the changes during the vast cycles of time prior to the advent of
man, or whatever may be the changes in the time to come, one thing is
quite certain; that our climate has been much modified within the past
two or three thousand years.
"There have been fifteen climatic changes since the beginning of the
glacial age, each change lasting 10,500 years, and each change
reversing the season in the two hemispheres, the pole which had
enjoyed continuous summer being doomed to undergo perpetual winter for
10,500 years, and then passing to its former state for an equal term.
The physical changes upon the earth's surface during the past 80,000
years modified the changes of climate even in the Arctic regions, so
that the intense cold of the former epochs was much modified during
the latter epochs." Reckoning these climatic changes in their order,
we had entered the epoch of a more genial temperature about fifteen
hundred years ago; and if no disturbing change takes place during the
present epoch, we may reasonably expect a gradual modification of our
winters for nine thousand years to come. The changes to intense cold
from perpetual summer during the greater part of the glacial period
are supposed to have been caused by the high temperature of the north
pole as compared to that of the south pole, owing to the distribution
of land around the two, the south having almost none. Dr. Croll thinks
it was caused by the varying inclination of the earth's axis, which
produced the relative position of the two poles toward the sun to be
periodically reversed at distant periods. Dr. James Geikie agrees with
Croll on the reverse of seasons every 10,500 years during certain
periods of high ellipticity of the earth's orbit.
But it may be asked, "How could the fauna and flora propagate
themselves under such conditions?" The flora itself at the quaternary
age was of extreme vigor. We know this from the little which is left
us, but more especially from the presence of a large number of
herbivorous animals--stags, horses, elephants, rhinoceros, etc.--which
animated the plains and valleys of Europe and America at the same
time. Evidently they could not have lived and propagated themselves
without abundant vegetation for nourishment and development.
That which has deceived the adherents of the glacial theory, as
understood in its absolute sense, is, they have generally placed a too
high estimate on its extent and intensity. It needs but a little
effort of the reasoning powers to come to the conclusion that the
earth had cooled to the degree that all animal and vegetable life
could exist upon it, and that a portion of the earth's surface
permanently covered with snow and ice was absolutely indispensable to
the existence, perpetuity, and well-being of animal and vegetable
life. Again, they have attributed to the glaciers the rocks, gravels,
and other material which they have found spread here and there long
distances from the mountains. The transportation of the so-called
erratic rocks has appeared inexplicable in any other way, and the
piles of rock and gravel have been considered so many _moraines_, that
is, deposits of diverse material transported by the glaciers. They do
not regard the probability of other agents taking the place of
glaciers, and undervalue the moving power of water. Water in liquid
state has often produced analogous effects, and it has often been the
error of the glacialists to confound the one with the other. The
erratic rocks and the moraines are undoubtedly the ordinary
indications of the ancient gravels, but, taken isolatedly, they are
not sufficient proof. In order to convince they should be accompanied
with a third indication, which is the presence of striated rocks which
we find in the neighborhood of our actual glaciers. When all these
signs are together then there is hardly a possibility of error, but
one alone is not sufficient, because it can be the effect of another
cause.
No doubt the temperature was really lower at the quaternary age and at
the epoch generally assigned to man's advent in European countries,
but the difference was not so great as some say. A lowering of four
degrees is sufficient to explain the ancient extension of the
glaciers. We can look on this figure as the maximum, for it is proved
to-day that humanity played the main _role_ in the glacial phenomena.
The beds of rivers and the alluvia are there to tell that all the
water was not in a solid state at that time, that the glaciers were
much more extended than in our days, and that the courses of the
rivers were infinitely more abundant. When this is understood we can
reasonably reduce the extension of the ancient glaciers, the lowering
of the temperature at the quaternary age, and account for the
uninterrupted life of the fauna and flora. However, we must not fall
into the opposite excess and assert, as some have done, that the
glacial period is comparatively recent, the traces of which are too
plain and fresh in some localities to assign to it an age prior to
man, and that the temperature has rather lowered itself since this
epoch. The ancient extension of the glaciers has been followed by a
corresponding growth and extension of animal life, thus proving that
the permanence of glaciers is a wise provision and absolutely
essential to man and the high orders of animals and vegetation. The
ancient extension does not prove alone that it was much colder than in
historic times, for the animals themselves are proof of this. At that
time the plains of Europe, and of France in particular, were animated
by herds of reindeer, gluttons, camels, and marmots, which one does
not find to-day except in the higher latitudes or more considerable
heights. The mammoth and rhinoceros are no exception to this, for
naturalists know they were organized to live in cold countries.
Space will not permit us to pursue this point further, or speculate on
the probable climatic conditions of the ice age; but we can carry
ourselves back a few thousand years and describe the climate of Europe
and neighboring countries of Africa and Asia. Herodotus describes the
climate of Scythia in terms which would indicate in our day the
countries of Lapland and Greenland. He shows us the country completely
frozen during eight months of the year; the Black Sea frozen up so
that it bore the heaviest loads; the region of the Danube buried under
snow for eight months, and watered in summer by the abundant rains
which gave to the river its violent course. The historian adds that
the ass cannot live in Scythia on account of the extreme cold which
reigns there. The following century Aristotle makes the same remarks
concerning Gaul. His contemporary, Theophrastes, tells us that the
olive tree did not succeed in Greece more than five hundred furlongs
from the sea. We can assure ourselves that both the ass and the olive
thrive in these countries at the present day.
Three centuries later, Cæsar speaks frequently and emphatically of the
rigor of winters and early setting in of cold in France, the abundance
of snow and rain, and the number of lakes and marshes which became
every moment serious obstacles to the army. He says he is careful not
to undertake any expedition except in summer. Cicero, Varro,
Possidonius, and Strabo insist equally on the rigor of the climate of
Gaul, which allows neither the culture of the vine nor the olive.
Diodorus of Sicily confirms this information: "The cold of the winters
in Gaul is such that almost all the rivers freeze up and form natural
bridges, over which numerous armies pass quite safely with teams and
baggages; in order to hinder the passengers to slip out upon the ice
and to render the marching more secure, they spread straw thereon."
Virgil and Ovid insist on the severity of cold in the regions of the
Danube. The first describes the inhabitants of these miserable
countries withdrawing themselves into caves dressed with the skins of
wild beasts. Ovid, who had passed several years of his life in that
region, is more precise in his description. He says the wine has
changed itself here (Black Sea) into a solid frozen mass; one gives it
to drink by pieces. Fearing of being accused of poetic exaggeration he
appeals to the testimony of two ancient governors of Moesia, who could
establish the facts like himself. The author who would give such
accounts of the Black Sea in our days would risk his reputation for
veracity.
Italy, too, experienced its part of the cold in early days. Virgil
tells us of the snows being, heaped up, rivers which carried ice
along, the sad winter which split the stone and bound up the course of
large streams, and all this in the warmest part of Italy, at the base
of the walls of Taranto. Heratius affirms that the Soracte, a
neighboring mountain of Rome, was whitened with thick snow, rivers
frozen, and the country covered with snow. To-day the snow stays very
little upon the Soracte and never in the country around Rome. During
the four or five centuries which followed, writers speak of the
severity of climate in Northern Italy, the lagoons on the Adriatic
being frozen over. Algiers was much colder then than now. The Danube,
Rhine, and other rivers in Europe, the Nile in Africa, the Amazon in
South America, the Mississippi and Missouri in North America, had
quite different volumes two thousand years ago than their present
actual ones, and they especially rolled much greater masses of water.
There is everything to show a modification of climate in our own days.
If this goes on in the future as in the past, there will be a marked
difference in the temperature two or three hundred years from now.
Even a degree in a thousand years would effect a great change in the
course of time. The lowering of four degrees established the ancient
extension of glaciers, though it did not interrupt animal or vegetable
life. Fifty-four of the fifty-seven species of _Mollusca_ have
outlived the glacial age, and all our savage animals--even a certain
number which have disappeared--date equally from the quaternary, and
were contemporary with the great extension of the glaciers.--_Popular
Science News_.
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