Topic: The evolution of climate 1925 climatehistory

[Prometheus]

“ In the ancient days when the Oxus River entered
the Scythian Gulf of the expanded Caspian Sea, and
Lake Gyoljuk discharged permanently to the Tigris,
the lake of Seyistan had not been converted into dry
land by the giants. Kashmir was so cold and snowy
that agriculture was impossible. ... In the Lop
basin the rivers were full of water; Lop-Nor was
the “ Great Salt Lake ” ; the desert was comparatively
small and the zone of vegetation extensive ; and on all
sides there was a density of population and a degree of
prosperity far beyond those of to-day. And in the
Turfan basin the same was probably true.

“ A great change took place throughout the six basins
during the early centuries of the Christian era. The
lakes of Gyoljuk, Seyistan, the Caspian, Lop-Nor and
presumably Turfan were greatly reduced in size. In
the case of the first three, parts of the old lake-beds
were used as sites for villages. Except in Kashmir, the
change of climate appears to have brought disaster. . . .

“ Again there came a change (about a.d. 700). The
process of desiccation gave place to a slight but important
tendency toward increased rainfall and lower tempera-

1 ‘‘ The pulse of Asia,” p. 356. See also a new work by E. Huntington,
entitled 1 “ Climatic change».”
  154 THE EVOLUTION OF CLIMATE

ture. Kashmir became colder and more snowy, and
hence more isolated ; the rivers of Lop and Turfan
gained greater volume; and the lakes of Lop, the
Caspian and Turfan expanded once more. The habit-
ability of the arid regions began to increase ; migrations
came to an end ; and central Asia was prosperous for
a time. Finally (about 1350) a latest and slightest
change took place in the other direction, and we seem
to-day to be in the midst of an epoch of comparative
equilibrium, with no marked tendency towards climatic
change in either direction.” There was, however, a
period of comparatively high water in the Caspian in
the early part of the seventeenth century.

In Europe the evidence for climatic changes during
historical times is more difficult to follow, since variations
of rainfall leave fewer tracés in a moist than in an arid
or semi-arid country. A certain amount of material is
given by Brückner in his “ Klimaschwankungen.” He
finds that there was a great advance of the Alpine glaciers
from 1595 to 1610, while two Italian lakes without
outlet, the Lago di Fucina and Lake Trasimeno, attained
a high level about the same time. Other evidence for
western Europe is derived from the date of the wine-
harvest and from the records of severe winters. Like
the growth-curves of the big trees, they need a secular
correction to alter the general slope of the curve,
especially in the case of severe winters, but the larger
irregularities probably correspond to real variations of
climate. I have added in column 4 the numbers of
winters with sea-ice on some part of the Danish coast,
as tabulated from the records compiled by Captain
C. I. H. Speerschneider. The results are in general
agreement with column 3, particularly as showing that
the period 1401-50 was relatively mild; but the first
half of the seventeenth century is less instead of greater
than its two neighbours in this column.

The figures for the wine-harvest refer to the average
for the period 1816-80; — indicates that the harvest
  CLIMATIC FLUCTUATIONS SINCE A.D. 500 155

was so many days earlier than normal, corresponding to
a high summer temperature (May to August). The
table shows that cold winters were especially numerous
in the first half of the twelfth century and again in the
thirteenth. The end of the fifteenth century was
marked by hot summers and mild winters, or a
warmer climate; the beginning of the seventeenth

I.  Period,   Date of Wine   3-  No.  of Severe Winters.   4-  Winters with Ice on Danish   5-  Remark».
8*5      4      
875      7      
925      5      
975      6      
10*5      6      
1075            
1125      15      Cold winters
1175      10      
1225      13   )   
1275      13      Cold wintert
1325      13   7 )   
1375      II   4   
1425   + 5   «3   7   
•475   + 1   7   2   Warm
1525   +2-9   IO   5   
1575   + 2-2   14   «4 )   
1625   +4'i   *7   "   Cold
1675   + 27   >5   14 )   
1725   + 0-1   10   5   
•775      —   22   
1825   -0-9   ~   21   

century by cold (presumably snowy) winters and cool
summers. Thus the periods of increased rainfall in the
arid regions of Asia and America were marked by a
colder climate in the rainy regions of western
Europe.

The date of the break up of the River Dwina at
Mitau was recorded intermittently from 1530 to 1709,
and regularly since that date, and the figures have been
11
  156 THE EVOLUTION OF CLIMATE

discussed by Rykatchef. Recasting them in our unit
of fifty years we find the mean dates to be :

1551-1600   ,60,-50   ,65,-1700   I7OI-5O   ,751-1800   ,80,-50
March 29   March 30   March 5   March 26   March 26   March 28

This again points to a cold period about the beginning
of the seventeenth century.

The climate of Iceland and Greenland in the Middle
Ages has been the subject of much controversy, the view
that there were extensive changes during that period
being warmly upheld by one party and as warmly com-
bated by the other party. The case for climatic change
has been well set out by O. Pettersson1. The Roman
authors (Pliny, Solinus, etc.) wrote that there was a
frozen sea about Thule (Iceland), but a party of monks
who visited the island about a.d. 795 during the months
of February to August, in which the ice is normally
most abundant in Icelandic waters, found the coast free,
though they met with a frozen sea a day’s joumey to
the northward. In the ninth century the Norsemen
visited Iceland regularly, and at times sailed round it,
apparently without interference from ice. The early
settlers practised agriculture with some success. In the
thirteenth century, however, the reports of ice off
Iceland became frequent—apparently the conditions
were worse than those of the present day, and much
more so than in the eighth and ninth centuries. Accord-
ing to Rabot, it appears from ancient records that
considerable areas cultivated in the tenth century are
now covered with ice. The first spread of the glaciers
took place in the first half of the fourteenth century.
In the fifteenth and sixteenth centuries the climate of
Iceland ameliorated somewhat, but in the seventeenth
there was a readvance, which destroyed several farms
about 1640 or 1650. Since then there has been a slight
retreat.

Climatic variations in historie and prehistorie time.”
  CLIMATIC FLUCTUATIONS SINCE A.D. 500 157

The ice conditions of Greenland are closely related to
those of Iceland, and the records of the Norse colonization
of Greenland bear out the conclusions drawn from the
latter island. Up to the close of the twelfth century
ice is hardly ever mentioned in the accounts of voyages,
though it is now a great hindrance. Eric, the pioneer
explorer of West Greenland, spent three successive
winters on the islands in Juliaanehaab Bay (latitude
6o° 45' N.), and explored the country during the summer;
“ this cannot be explained otherwise than by assuming
that the Polar ice did not reach Cape Farewell and the
west coast of Greenland in those days.” In the thirteenth
century ice is first specifically mentioned as a danger
to navigation, and at the end of the fourteenth century
the old Norse sailing route was on account of ice definitely
abandoned in favour of one further south. Shortly
afterwards the Norse colonies were wiped out by a
southward migration of the Eskimos. Even in Norway
itself the fourteenth century was a time of dearth,
short harvests and political troubles, when corn had to
be imported from Germany instead of being exported
to Iceland as in former years.

It should be noted that Pettersson’s conclusions are
considered invalid by H. H. Hildebrandsson1 on the
ground of the incompleteness of the records.

For the Southern hemisphere our records are naturally
much rarer and of less antiquity than for the northern
hemisphere, and until the tree-rings are investigated we
cannot carry our study back beyond the sixteenth
century. From some researches into the municipal
archives of Santiago de Chile, latitude 33§° S., published
by B. V. Mackenna in 1877, we can infer, however, that
the general course of variation since 1520 was similar
to that of corresponding regions in North America.
Santiago lies in a semi-arid region where a temporary
shortage of water is severely feit, the average annual
rainfaU being only 364 mm. (14.3 inches). The early

1 Sur le prétendu changement du climat européen en tempt hittorique.”
  158 |jTHE EVOLUTION OF CLIMATE

traveUers, however, make no specific mention of drought,
and in 1540 Pedro de Valdivia crossed the desert of
Atacama with a column of troops and cattle without
inconvenience—a feat which would be difficult nowadays.
In 1544 there were heavy rains and great floods in June.
The next record is for the year 1609, recording another
heavy flood on the Mapocho, which was repeated nine
years later in 1618. The first recorded drought occurred
in the years 1637 to 1640; there was another flood in
1647, after which came a series of severe droughts
interrupted by occasional floods, which lasted until the
close of the eighteenth century. The first half of the
nineteenth century was again comparatively rainy.
The records thus indicate a wet period centred about
1600, followed by a dry period during the eighteenth
century, exactly parallel to the records from the United
States and Europe.

BIBLIOGRAPHY

Huntington, E. “ The climatic factor as illustrated in arid America
Washington, Carnegie Institution, 1914.

--------------. “ The fluctuating climate of North America.” Geogr. J.,

40, 1912, pp. 264, 392.

-------------- “ The pulse of Asia.” Boston and New York, 1907.

. “ World power and evolution.” New Haven, 1919.

Pettersson, O. “ Climatic fluctuations in historie and prehistorie time.”
Svenska Hyirogr.—Biol. Komm. Skrifter, H. 5.

Rabot, Ch. “ Essai de chronologie des variations glaciaires.” Buil. geogr.
bistorique et descriptive, No. 2, 1902.

Brfickner, E. “ Klimaschwankungen seit 1700” . . . Vienna, 1890.

Hildebrandsson, H. H. “ Sur le prétendu changement du climat européen
en temps historique.” Upsala, Nova Actae Regiae Soc. Set. (4),
Vol. 4, No. 5, 1915.

Brooks, C. E. P. “ An historical notice of the variations of climate in Chile.”
Washington, Dept. Agric., U.S. Weatber Bureau, Montbly Weatber Rev.
47. *9*9. P- 637-
  CHAPTER XVIII

^CLIMATIC FLUCTÜATION8 AND THE EVOLUTION OF MAN

The origin of man from an ape-like ancestor1 is generally
admitted, but owing to the incompleteness of the
palseontological record we are still in ignorance as to
the circumstances, while the place is generally put
vaguely as somewhere in Asia, and the time as the late
Tertiary (Prof. Elliot Smith places it near the Siwalik
hills in the Miocene). For this early period we are
reduced to speculation, in which we may reasonably
utilize the facts which we have gained about climatic
variation.

The chief problem to be explained is why man’s
arboreal ancestor left the safe shelter and easy food
supply of his primseval forest and ventured forth into
the plains. An article by PrcfessPX. J- Barrell,® of Yale
University, gives a plausible account of the change,
putting it down to necessity, and not to choice. His
theory is that the human ancestor lived in the forests
spread over Asia, then a vast well-watered plain, during u"
the middle Tertiary period. Then the gradual uplifting
of the Himalayas and other mountain ranges caused a
decrease in the rainfall of central Asia, so that ultimately
the forests were unable to thrive, and gradually gave
place to steppe conditions. The change was slow
enough to give the less specialized inhabitants of the

1 Or lemur-like ancestor. There is evidence to show that man’s ancestor
was a nocturnal animal, whose food-supply was governed by the phases
of the moon.

1 “ Scientific monthly,” New York, 4, 1917, pp- i6-*6.

159
  i6o THE EVOLUTION OF CLIMATE

forest time to change their habits and evolve into forms
suitable to a terrestrial life, and the chief of the animals
which took advantage of this period of grace was the
pre-human. Forced to live on the ground, with a dimin-
ishing food supply, only the most progressive individuals
were able to survive, and evolution was rapid. The
changing type was saved from being submerged in the
great mass of the original type in the forests which
continued to exist further south by the impassable wall
of mountains. Major Cherry1 considers that there is
sufficiënt evidence to prove that a portion of this evolu-
tion took place on the seashore, an environment which
would have been much more favourable to a small ape-
like animal than the open steppe would have been. It
is quite likely that the earliest migrations, such as that
which carried Pithecanthropus to Java, took place along
the shore. But after a time, when increasing brain-
power and the use of primitive stone implements enabled
man to take the offensive against the larger animals,
the centre of activity changed to the steppes. A
familiar view of the early development of man was
advocated by W. D. Mathew,* who writes : “ In view
of the data obtainable from historical record, from
tradition, from the present geographical distribution of
higher and lower races of men, from the physical and
physiological adaptation of all and especially of the
higher races, it seems fair to conclude that the centre of
dispersal of mankind in prehistorie times was central
Asia, north of the great Himalayan ranges, and that
when by progressive aridity that region became desert
it was transferred to the regions bordering it to the
east, south and west. We may further assume that the
environment in which man primarily evolved was not
a moist tropical climate, but a temperate and more or
less arid one, progressively cold and dry during the
course of his evolution. In this region and under these

1 “ Science progren,” 15, 19*0, p. 74.

* “ Climate and evolution.”
  EVOLUTION OF MAN   161

conditions, the race first attained a dominance which
enabled it to spread out in successive waves of migration
to the most remote parts of the earth.”

We do not know anything of the migrations of the
Eolithic and earlier Palaeolithic races, except that they
spread rapidly over a considerable portion of the earth.
Both migration and evolution, especially mental evolu-
tion, must have been accelerated by the great changes
of climate which were taking place. In the Mindel-
Riss interglacial period we know of two types,
the Pilt down man (Eoanthropus dawsoni) and the
Heidelberg man {Homo heidelbergensis), the latter a true
man, though probably not on the direct line'of evolution
of Homo sapiens. The stress of the succeeding second
Glacial period was too great for Eoanthropus, which
appears to have died out, but Homo, probably an Asiatic
or African type similar to H. Heidelbergensis, survived.
The next form, associated with Mousterian implements,
is Neanderthal man (H. neanderthalensis), who closely
resembled modern man, and all the remains of races
which lived subsequently to the last glaciation are those
of modern man (H. sapiens), including the magnificent
Cro-Magnards and the negroid Grimaldi race. Thus
each glaciation has been marked by a step upwards in
the scale of humanity; does this mean that the coming
of the super-man is contingent on another glacial epoch ?

BIBLIOGRAPHY

Barrell, J. “ Probable relations of climatic change to the origin of the
Tertiary Ape-man.” Scientific Monthly, New York, 4, 1917, p. 16.
Mathew, W. D. “ Climate and evolution.” Annals New Tork Acai. Sci.,
24, i9i5,p. aia.

London, British Museum. “ A guide to the fossil remains of man . .
London, 1918.
  CHAPTER XIX

CLIMATE AND HISTORY

It is a remarkable fact in human history that civilization
began in regions which are at present inhabited chiefly
by backward. races, and the centres of progress have
shifted from one country to another with the passage
of time. Many accidental factors—position on trade-
routes, possession of special mineral advantages, and so
on, have undoubtedly played a part in this, but it will
not be difficult to show that climatic fluctuations have
also had their share.

A brilliant study of Ellsworth Huntington1 has shown
that there are certain optimum conditions of climate
which are most suitable for efficiënt work. These
conditions, which were determined by an analysis of the
output of work in American factories, were then found
to be just those which prevail in the most progressive
regions of the globe, which are located in the temperate
storm-belts, and it is shown in certain instances that
fluctuations in the position of this storm-belt coincided
with fluctuations in the centres of civilization. A few
additional examples of this may be given. •

The beginnings of civilization may reasonably be
placed with the transition from the Palaeolithic to the
Neolithic type, a transition which involved much more
than just the polishing of stone weapons. It involved
also the beginnings of agriculture, crude pottery, and

1 “ Civilization and climate.”

IÓ2
  CLIMATE AND HISTORY

163

later, the domestication of animals. One of the earliest
Neolithic cities known is probably that of Anau, near
Askabad in Transcaspia, excavated by Pumpelly in
1904. From the thickness of the accumulated debris
the date of first settlement is placed at or before 8000 B.c.,
i.e. 10,000 years ago, or during the period which in
Europe is assigned to the concluding stages of the
Wurm glaciation. Pumpelly’s time-estimates are based
on careful comparison with accumulations in Merv and
other cities. At present the mean annual rainfall in
that part of Turkestan is below ten inches a year, and
the country is practically desert, and is entirely unfitted
for agriculture. But with the remains of the ice-sheet
still over Scandinavia and depressions following a more
southerly course along the Mediterranean basin and into
Southern Asia, the rainfall was considerably heavier, and
the climate in general was more suited to a progressive
race. At the outset we find this Neolithic race living
in rectangular houses built of uniform sun-dried bricks ;
they were skilful potters, cultivating cereals, but at first
without domestic animals.

The beginning of Neolithic civilization in Crete is
placed by Evans at about 12000 b.c., while on the basis
of excavations by de Morgan at Susa in Persia, Montelius
places the origin of Neolithic culture in this part of
Asia as early as about 18000 b.c. At Susa the deposits
are 130 feet thick, and of these the upper 40 feet cover
a period of 6000 years.

Thus we see that what may be considered as the
great step from savagery to civilization took place while
the present centres of progress in Europe and America
were still in the Ice Age. At this time the climate of
Southern Asia must have resembled the present climate
of north-west Europe in heavier rainfall and the day-to-
day fluctuations of weather—in fact, the districts where
civilization began probably had at that time the most
stimulating climate in the northern hemisphere.

With the vanishing of the ice-sheets and the setting
  164

[Prometheus]

THE EVOLUTION OF CLIMATE

in of the mild climate of the Maritime phase the Neo-
lithic culture sjpread rapidly to Europe, and by 2000 B.c.
even the Baltic regions were well inhabited, and it is
probable that the Aryan race was developing in the
Russian steppes. About this time Anau was abandoned
owing to increasing aridity.

With the coming of the Bronze Age in western
Europe, about 1800 b.c., however, the climate again
became colder and rainier, corresponding to the Peat-
bog phase or “ Classical ” rainfall maximum, the
deterioration culminating in the Early Iron Age. This
period was marked by a great southward spread of the
Aryan peoples, and ushered in the Heroic Age of Greece.
The races of the Mediterranean, as we have seen, con-
tinued to thrive throughout this rainy period, and their
power did not diminish until its close, about a.d. 400.
This downfall was accelerated if not caused by the
pressure of nomad peoples driven out of Asia by
the increasing drought. These Asiatic migrations in-
cluded the great marches of the Tartar hordes and,
aided by religious enthusiasm, the conquests of the
Moslems.

The early Middle Ages, after the downfall of Rome,
appear to have been characterized by a dry warm climate.
This was the age of the Vikings, when’ the Norse races
rosé to dominance in western Europe, finally invading
and occupying large areas óf France and Britain, and
even extending their power to Sicily. With the increas-
ing cold and wet of the “ Mediasval ” rainfall maximum
came a final burst of Norse migration, which left the
homeland poor and scantily populated, and the centre
of activity and progress lay once again with the Mediter-
ranean peoples, and especially with Italy and Spain.
The Tartar invasions ceased, and against the increasing
power of Europe the Moslem wave broke and receded.
At the close of this rainy period political dominance
again moved north. From that time the fluctuations
of climate have been of minor importance, and corres-
  CLIMATE AND HISTORY   165

pondingly there have been no great shiftings of political
power from latitude to latitude.

BIBLIO GRAPHY.

Tyler, J. M. “The New Stone Age in Northern Europe.” London
1921.

Huntington, Ellsworth, “ World Power and Erolution.” New Haren, 1919.
Haddon, A. C., “ The wanderings of peoplei.” Cambridge Univerrity
Preis, 1919.
  APPENDIX

THE FACTORS OF TEMPERATURE

To calculate the probable temperature of January or
July at any point, the following procedure should be
adopted :

Draw a circle round the point of angular radius ten
degrees (i.e. set the compass to cover ten degrees of
latitude) and divide this into two halves by a line passing
from north to south through the centre. By means of
squared tracing paper, or otherwise, measure : (a) the
amount of ice in the whole circle; (b) the amount of
land in the western half; (c) the amount of land in the
eastern half.   (a) is expressed as a percentage of the

area of the whole circle; (b) and (c) as percentages of
the area of a semicircle.

The term “ ice ” includes ice-sheets such as that of
Greenland or Antarctica, and also frozen sea or sea
closely covered by pack-ice ; the latter figure may vary
in different months.

The temperature in January or July is then calculated
from the following formula :

Temperature = basal temperature + ice coeff. X per
cent. of ice + land west coeff. x per cent of land to
west + land east coeff. X per cent of land to east.

The basal temperatures and the appropriate coeffidents
are given in the following table.

In calculating the effect of a given slight change of
land and sea distribution, it is not necessary to employ
the basal temperature. Instead the equation can be
treated as a differential, and the change of temperature
166
  APPENDIX   167

due to the change of land and ice calculated from the
figures in columns 3 to 5. The figures are given in
degrees absolute, 273°o=32°F. To convert differences
to Fahrenheit, multiply by l°8.

In the case of the calculation of the effect of com-
paratively slight and irregular changes in land and sea

Latitude.   Basal Temp. (Water Zone).   Ice Coeff.   West Coeff.   Land, East Coeff.
Jan.  70 N.   298-8   _o-49   -o-43   — 0*20
60   277-4   — 0-07   -0-31   
5°   276-8   — 0-09   -0-29   CO9
40   282-5   —   -0-17   0*04
30   289-6   —   — 0-08   0*03
      —   — 0*01   — 0*01
10   298-6   —   — O-OI   0*03
O   299-3   —   0*01   0*00
10 S.   298-2   —   0-04   — 0*01
20   296-2   —   0-07   0*00
30   293-5   —   0-06   0*03
40   289-3   —   0*09   — 0*03
Juljr.      — o-i6      
70 N.   279-3         
60      —   — O-OI   O-II
5°   285-8   —   0*04   0-06
40   29I-t   —   0*05   0*07
30   296-8   —   0-08   — 0*01
20   297-6   —   0-07   0*02
10   298-8   —   0-03   — 0*01
0   298-6   —   0*02   — 0*01
xo S.   296-9   —   0-04   -0-03
20   293-1   —   0*02   — 0*02
30   288-2   —   — 0*01   — 0*01
40   284-0   ~   0-00   -0-03

distribution in a limited area, such as those of the
Littorina Sea referred to on p. 128, it may be found
that a ten-degree circle is too wide an area to employ,
the changes from land to sea at one point being nullified
by changes from sea to land at another more distant
point. In such a case a smaller unit such as a circle of
five degrees radius can be employed. As a rough
  i68 THE EVOLUTION OF CLIMATE

approximation it may be said that the effect of the
conversion of a square mile of land into sea, or inee versa,
on the temperature of a neighbouring point is inversely
proportional to its distance. Since the area of a five-
degree circle is one-quarter that of a ten-degree circle,
while the average distance of the land composing it is
one-half, we have to divide our regression coefficients
by two in order to fit the new data.

This method was applied to obtain the probable
temperature distribution on the shores of the Littorina
Sea at its maximum extension, and gave results which
agreed remarkably well with those calculated by geologists
from the animal and plant life of the time.

See London Q.J.R. Meteor. Sae., 43,1917, pp. 169-171.
.