FROM
https://archive.org/details/climateconsider03wardgoog/page/n381/mode/1upby Ward, Robert DeCourcy, 1867-1931 Assistant Professor of Climatology in Harvard University
1908/1918
Climate especially considered in relation to (WO)MAN
illustrates my view also
CHAPTER XI (last)
CHANGES OP CLIMATE
Popular Belief in Climatic Change—Evidence of Climatic Changes
Within Historie Times—What Meteorological Records Show
—Why the Popular Belief in Climatic Changes is Untrust-
worthy—Value of Evidence Concerning Changes of Climate—
Periodic OBcillations of Climate: The Sun-spot Period—Brück-
ner's 35-Year Cycle—Climatic Cycles of Longer Period—
Geological Changes in Climate—Condusion.
Popular Belief in Climatic Change. Belief in a
change in the climate of one’s place of residence,
within a few generations, and even within the mem-
ory of living men, is widespread. It is confined to
no special region or people. It finds support among
the most intelligent as well as among the uneducated.
Here it may be the view that the climate is growing
milder; there, that the winters are becoming more
severe; here, that there is increasing aridity; there,
that the rainfall is greater. Whenever a season
attracts attention because of weather conditions
which seem in any way unusual, this ‘belief is
strengthened. This popular impression has often
found support in the facts of distribution, or the
dates of flowering, or ripening, of certain cereals or
fruits. It is asserted that because grapes, or com,
338
CHANGES OF CLIMATE
339
or olives, for example, are now no longer grown in
parts of Europe where their cultivation was once
an important occupation, we must conclude that
the climate has changed from a favourable to an
unfavourable one.
Evidences of Climatic Changes within Historie
Times. Evidence is constantly being brought for-
ward of apparent climatic variations of greater or
less amount which are now going on. Such reports,
largely those of travellers or explorers in little-known
regions, are usually based on fluctuations in the ex-
tent of inland lakes; on the discovery of abandoned
dwelling sites, the ruins of aqueducts and irrigating
canals, and the like. Thus we have accounts of a
gradual desiccation which seems to have been going
on over a large region in central Asia, during histori-
cal times. In eastern Turkestan the lakes have been
reported as drying up, Lake Balkash falling one
metre in about fifteen years, and Lake Alakul gradu-
ally becoming a salt deposit. In his work on Turkes-
tan, Muschketoff gives numerous examples of
Progressive desiccation, and Rossikoff speaks of the
drying up of the lakes on the northem side of the
Caucasus. The same thing is reported of lakes in
the Pamir. Prince Kropotkin believes that the desic-
cation of central Asia in the past drove the inhabit-
ants out onto the lowlands, producing a migration
of the lowland peoples and thus bringing on the in-
vasions of Europe during the first centuries of our
era. In his recent work on the basin of eastern
340
CLIMATE
Persia, Transcaspia, and Turkestan, Huntington be-
lieves that, so far as it can be made out, the history
of these countries indicate* a gradual desiccation from
early historical times down to the present day. His
study of climatic changes in that region is one of the
most thorough ever made, for the evidences of archae-
ology, of tradition, of history, and of physiography
have been carefully matched and found to accord in a
very striking manner. Evidence has heen found of
the abandonment of successive village sites as the in-
habitants moved farther upstream in search of more
water, and patches of dead jungle show that vegeta-
tion once flourished where aridity now renders plant
growth impossible.
In northem Africa, certain ancient historical re-
cords have been taken by different writers to indicate
a general decrease of rainfall during the last 8000
years or more, the remains of cities and the rains of
irrigating works pointing to a larger population and
a greater water supply formerly than at present.
The presence of certain animals, now no longer found
there, is implied by ancient records, and from this
fact also, a change of climate is inferred. In his Cross-
ing of the Sahara between Algeria and the Niger,
Gautier found evidence of a former large population.
A gradual desiccation of the region is, therefore, be-
lieved to have taken place, but to-day the equatorial
rain-belt seems to be again advancing farther north,
giving an increased rainfall. Gautier divides the
history here into three periods: (1) dense population;
CHANGES OF CLIMATE
341
(2) aridity; and (3) the present change to steppe
character.
Farther south, several lakes have been reported as
decreasing in size, e. g., Chad, Ngami, and Victoria;
and wells and springs as running dry. In the Lake
Chad district, Chevalier reports the discovery of
vegetable and animal remains which indicate an in-
vasion of the Sudan by a Saharan climate. Neolithic
relics indicate the former presence there of prosper-
ous communities. Again, to note another instance,
it is often held that a steady decrease in rainfall has
taken place over Greece, Syria, and other eastern
Mediterranean lands, resulting in a gradual and in-
evitable deterioration and decay of their people.
These examples might be multiplied, for reports of
climatic changes of one kind or another are numerous
from many parts of the globe.
What.Meteorological Records Show. As concerns
the popular impression regarding change of climate,
it is clear at the start that no definite answer can be
given on the basis of tradition, or of general impres-
sion, or even of the memory of the “oldest inhabi-
tant.” Human memories are very untrustworthy,
and there are many reasons for their being particu-
larly untrustworthy in matters of this kind. The only
answer of real value must be based on what the in-
strumental records of temperature, and of rain and
snowfall show. Accurate instruments, properly ex-
posed and carefully read, do not lie; do not forget;
are not prejudiced. When such instrumental records,
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CLIMATE
scattered though they are, and difficult as it is to
draw general condusions from them, are carefully
examined, from the time when they were first kept,
which in a few cases goes back about one hundred and
fifty years, there is found no evidence of any progres- ‘
sive change in temperature, or in the amount of rain
and snow. Apparent signs of a permanent increase
or decrease in one or another element have been fairly
easy to explain as due to the method of exposing the
thermometer, or of setting up the rain-gauge. Little
care was formerly taken in the construction and loca-
tion of meteorological instruments. They were usu-
ally in cities, and as these cities grew, the temperature
of the air was somewhat affected. The rain-gauges
were poorly exposed on roofs or in court-yards. The
building of a fence or a wall near the thermometer,
or the growth of a tree over a rain-gauge, is
enough, in many cases, to explain any observed
change in the mean temperature or rainfall. Even
when the most accurate instrumental records are
available, care must be taken to interpret them cor-
rectly. Thus, if a rainfall or snowfall record of sev-
eral years at some station indicates an apparent
increase or decrease in the amount of predpitation,
it does not necessarily follow that this means a per-
manent, Progressive change in climate, which is to
continue indefinitely. It may mean simply that there
have been a few years of somewhat more predpita-
tion, and that a period of somewhat less precipitation
is to follow.
CHANGES OF CLIMATE
343
For the United States, Schott, some twenty years
ago, made a careful study of all the older records of
temperature and rainfall, including snow, from
Maine to California, and found nothing which led to
the view of a Progressive change in any one direc-
tion. There was evidence of slight variations of
temperature, occurring with the same characteristics
and with considerable uniformity over large areas.
These variations have the characteristics of irregular
waves, representing slightly warmer and slightly
cooler periods, but during the fluctuations the tem-
perature differed by only a degree or two on one side
or the other of the mean. Obviously, this is too
slight a range to be of any general or practical inter-
est, and in any case, these oscillations give no evidence
of a continuous change toward a warmer or a cooler
climate. Schott found that these waves of higher
and lower temperature followed one another at inter-
vals of about twenty-two years on the Atlantic coast.
In the interior, the intervals were about seven years.
The records of the closing of rivers to navigation, the
Hudson, for example, show no permanent change in
the dates for the last hundred years or so.
It has been well pointed out that if a list were care-
fully compiled of heavy snowstorms, of droughts, of
floods, of severe cold, of mild winters, of heavy rains,
and of other similar meteorological phenomena, for
one of the early-settled sections of the United States,
beginning with the date of the first white settlements
and extending down to the present day, we should
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CLIMATE
have the following situation: Dividing this list into
halves, each division containing an equal number of
years, it would be found, speaking in general terms,
that for every mild winter in the first half, there would
be a mild winter in the second; for every long-
continued drought in the first division, there would
be a similar drought in the second; for every “old-
fashioned ” winter in the first group, there would be
an “ old-fashioned ” winter in the second. And so
on, through the list. In other words, weather and
climate have not changed from the time of the land-
ing of the earliest pilgrims on the inhospitable shores
of New England down to the present day.
Why the Popular Belief in Climatic Changes. is
Untrustworthy. Why is the popular belief in a
change of climate so widespread and so firmly fixed,
when instrumental records all go to show that this
belief is erroneous? It is not easy to answer this
question satisfactorily, but several possible explana-
tions may be given. The trouble arises chiefly from
the fact that we place absolute trust in our memories,
and attempt to judge such subtle things as climatic
changes on the basis of these memories, which are at
best short, defective, and in the highest degree un-
trustworthy. We are likely to exaggerate past
events; to remember a few exceptional seasons which,
for one reason or another, made a deep impression
on us, and we thus very much overrate some special
event. To make use of an illustration given by an-
other, individual severe winters which, as they occur,
CHANGES OF CLIMATE
345
may be some years apart, seem, when looked back
upon from a distance of several years later, to have
been close together. It is much as in the case of the
telegraph poles along a railroad track. When we
are near the individual poles, they seem fairly far
apart, but when we look down the track, the poles
seem to stand close together. The difference in the
impressions made upon youthful and adult minds
may account for part of this misconception regard-
ing changes of climate. To a youthful mind a heavy
snowstorm is a memorahle thing. It makes a deep
impression, which lasts long and which, in later years,
when snowstorms are just as heavy, seems to dwarf
the recent storms in comparison with the older. The
same is true regarding heavy rains, or floods, or
droughts.
Changes of residence may account for some of the
prevailing ideas about climate. One who was
brought up as a child in the country, where snow
drifts deep and where roads are not quickly broken
out, and who later removes to a city, where the tem-
peratures are slightly higher, where the houses are
warmer, and where the snow is quickly removed from
the streets, naturally thinks that the winters are
milder and less snowy than when he was a boy.
Similarly, a change of residence from a hill to a val-
ley, or vice versa, or from the coast to the interior,
may easily give the impression of a changing climate.
Even in cases where individuals have kept a record of
thermometer readings during a long series of years,
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CLIMATE
and are sure that the temperatures are not as low
or as high as they used to be, or who are convinced
that the rainfall is lighter or heavier than it was some
years before, the chances are that the location of the
thermometer, or the exposure of the rain gauge, has
been changed sufBciently to account for any observed
difference in the readings.
Value of Evidence Conceming Change» of CU-
mate. The body of facts which has been adduced as
evidence of Progressive changes of climate within his-
torical times is not yet sufliciently large and complete
to warrant any general correlation and study of these
facts as a whole, especially from the point of view of
possible causation. But there are certain considera-
tions which should be bome in mind in dealing with
this evidence, certain corrections, so to speak, which
should be made for possible Controls other than cli-
matic, before condusions are reached in favour of
climatic changes. In the first place, it has been noted
above that changes in the distribution of certain
fruits and cereals, and in the dates of the harvest,
have often been accepted as undoubted evidence of
changes in climate. Such a conclusion is by no means
inevitable, for it can easily be shown that many
changes in the districts of cultivation of various
crops naturally result from the fact that grapes, or
com, or olives, are in time found to be more profitably
grown, or more easily prepared for market in another
locality. Thus the area covered by vineyards in
northem Europe has been very much restricted in the
CHANGES OF CLIMATE
347
last few hundred years, because grapes can be raised
better and cheaper farther south. Cultivation in one
district is abandoned when it is more profitable to im-
port the product from another. It is easy, but not
right, to conclude that the climate of the districts first
used has changed. Wheat was formerly more gen-
erally cultivated far north in the British Isles than is
the case at present, because it was profitable. Later,
after a readjustment of the taxes on breadstuffs, it
was no longer profitable to grow cereals in that
region, and the area thus cultivated diminished.
Changes in the facility, or in the cost, of importation
of certain articles of food from a distance are speedily
followed by changes in the districts over which these
same crops are grown. Similarly, the introduction of
some new plant, better suited to the local soil and
climate, will result in the replacement of the older pro-
duct by the newer. In France, Angot has made a
careful compilation of the dates of the vintage from
the fourteenth century down to the present time, and
finds no support for the view so commonly held there
that the climate has changed for the worse. The dates
of the vintage do, however, indicate some oscillation
of the climatic elements. In the period 1775-1875,
the average date of the grape harvest in Aubonne was
about ten days earlier than during the preceding cen-
tury, but three days later than during the second
century preceding. At the present time, the average
date of the grape harvest in Aubonne is exactly the
same as at the close of the sixteenth century. After
348
CLIMATE
a careful study of the conditions of the date tree, from
the fourth century b. c., Eginitis concludes that the
climate of the eastern portion of the Mediterranean
basin has not changed appreciably during twenty-
three centuries. In China, a comparison of the
ancient and present-day conditions of cultivation, of
silk production, and of bird migrations, has led Biot
to a similar conclusion. In some cases, the reported
cultivation of cereals, or other soil products, in cer-
tain climates at present unfavourable has been shown
to be purely a myth; as in the case of a supposed
extended cereal cultivation in Iceland in former
times.
Secondly, a good many of the reports by explorers
from little-known regions are contradictory. Thus
Lake Aral, which was diminishing in area for many
years, is recently reported by Berg as increasing.
Lake Balkash, which was rapidly drying up, has also
begun to fill again. Partly submerged trees are
noted as having been seen by Berg, who in June,
1902, found the lake waters quite fresh. As the lake
has no outlet, this is an interesting fact. In Africa,
Lake Victoria, which, it was generally agreed, was
sinking in the period 1878-1892, has since shown a
tendency to rise. Lake Rukwa, east of Tanganyika,
has risen within the last few years. Reports that the
Sea of Azov is drying up have been explained as due
to a silting up of the lake. Lake Chad is very prob-
ably subject to oscillations, sometimes spreading be-
yond its usual limits as the result of several years of
CHANGES OF CLIMATE
349
heavy rainfall. Such diverse reports show the need
of caution in jumping at condusions of climatic
change. An increased use of water for irrigation
may cause the level of water in a lake to fall, as has
been the case to some extent in Great Salt Lake.
Periodic oscillations, giving higher and then lower
water, do not indicate Progressive change in one di-
rection. Many writers have thus seen a law in what
was really a chance coincidence. Partsch believes
that the ancient settlements on the interior lakes of
northern Africa show that these lakes contained no
more water formerly than they do now. Some have
claimed that the supposed desiccation of the climate
of northem Africa resulted from deforestation, but
no certain evidence exists of the presence or destruc-
tion of such forests, and if deforestation did take
place, no considerable change of climate could have
resulted.
Thirdly, where a Progressive desiccation seems to
have taken place, the question should be asked, Is less
rain actually falling, or have the inhabitants less
capacity, less energy, less ability, than formerly? Is
the change from a once cultivated area to a barren
expanse the result of decreasing rainfall, or of the
emigration of the former inhabitants to other lands?
The difference between a country formerly well irri-
gated and fertile, and a present-day, sandy, inhospit-
able waste may be the result of a former compulsion
of the people, by a strong goveming power, to till
the soil and to irrigate, while now, without that com-
350
Language in this board is ENGLISH