Revised 1995 March, 20
Global Warming:
A Boon for Humans and Other Animals*
Thomas Gale Moore
Senior Fellow
Hoover Institution
Abstract
Contrary to the doom and gloom scenarios that
environmentalists propound, both evidence and theory suggest
that global warming would in general be beneficial for
mankind. Simple logic indicates that most of modern man's
activities would be unaffected by warming of 5 to 9 degrees
Fahrenheit. Agriculture and some services might actually
benefit. Moreover, past history shows two periods that were
significantly warmer than today and during both eras mankind
flourished. The first epoch, which has been dubbed by
climatologists "The Climatic Optimum," brought temperatures
which were as warm as the median prediction for the next
century. During this period, Homo Sapiens shifted from
surviving in small tribes through hunting and gathering to
settled farming communities and from the stone age to the
bronze age. During the second warming, "The Little Climate
Optimum," Europe enjoyed the High Middle Ages and went on
one of the largest building sprees ever recorded.
Why Global Warming Would be Good for You
Climate extremes would trigger meteorological chaos ---
raging hurricanes such as we have never seen, capable of
killing millions of people; uncommonly long, record-breaking
heat waves; and profound drought that could drive Africa and
the entire Indian subcontinent over the edge into mass
starvation. ... Even if we could stop all greenhouse gas
emissions today, we would still be committed to a
temperature increase worldwide of two to four degrees
Fahrenheit by the middle of the twenty-first century. It
would be warmer then than it has been for the past two
million years. Unchecked it would match nuclear war in its
potential for devastation.1
- Senate Majority Leader George J. Mitchell
Senator Mitchell's forecast and his history are both wrong. Warmer
periods bring benign rather than more violent weather. Milder
temperatures will induce more evaporation from oceans and thus more
rainfall---where it will fall we cannot be sure but the earth as a
whole should receive greater precipitation. Meteorologists now believe
that any rise in sea levels over the next century will be at most a
foot or more, not twenty.2 In addition, Mitchell flunks history:
around 6,000 years ago the earth sustained temperatures that were
probably more than four degrees Fahrenheit hotter than those of the
twentieth century, yet mankind flourished. The Sahara desert bloomed
with plants, and water loving animals such as hippopotamuses wallowed
in rivers and lakes. Dense forests carpeted Europe from the Alps to
Scandinavia. The Midwest of the United States was somewhat drier than
it is today, similar to contemporary western Kansas or eastern
Colorado; but Canada enjoyed a warmer climate and more rainfall.
Raising the specter of disaster as well, Vice President Al Gore has
called the threat of global warming "the most serious problem our
civilization faces."3 In fact, he has styled those who dispute it as
"self-interested" and compared them to spokesmen for the tobacco
industry who have questioned the relation of smoking to cancer. But
Gore is misinformed; many disinterested scientists, including
climatologists with no financial interest other than preventing
wasteful expenditures of society's limited resources, question the
evidence and the models that underlie the warming hypothesis.
In fact, the evidence supporting the claim that the earth has grown
warmer is shaky; the theory is weak; and the models on which the
conclusions are based cannot even replicate the current climate. It is
asserted, for example, that over the last hundred years the average
temperature at the earth's surface has gone up by 0.5 degrees
Centigrade or about 1 degree Fahrenheit. Given the paucity of data in
the Southern Hemisphere, the evidence that in the United States, with
the best records, temperatures have failed to rise; the British naval
records that find no significant change in temperatures at sea since
the mid- 1800s; and that the reported increases occurred mainly prior
to 1940 -- before the rapid rise in CO2 -- the public is entitled to
be wary. Moreover, even the National Academy of Sciences is skeptical
of the validity of the computer models and warns that the modeling of
clouds -- a key factor -- is inadequate and poorly understood.4
The dire forecasts of global warming hinge on a prediction that human
activity will provoke a continued upsurge in atmospheric carbon
dioxide. Many environmentalists believe that the burning of fossil
fuels, the release of methane from agricultural activities, and the
escape of other chemicals into the air over the next few decades will
lead to an effective doubling of greenhouse gases sometime in the next
century.
What is well known is that climate changes. The world has shifted from
periods that were considerably warmer--during the Mesozoic era when
the dinosaurs thrived the earth appears to have been about 18 degrees
Fahrenheit warmer than now--to spells that were substantially colder,
such as the Ice Ages when huge glaciers submerged much of the Northern
Hemisphere. One paleoclimatologist estimated that, during the
Precambrian period, the polar regions were about 36 degrees Fahrenheit
colder than they are in the contemporary world. During the last
interglacial, about 130,000 years ago or about when modern man was
first exploring the globe, the average temperature in Europe was at
least 2 to 5 degrees Fahrenheit warmer than at present.
Hippopotamuses, lions, rhinoceroses and elephants roamed the English
countryside. Areas watered today by the monsoons in Africa and east
Asia enjoyed even more rainfall then. Indeed during the last 12,000
years, that is since the end of the last glacial period, the globe has
alternated between times substantially warmer and epochs that were
noticeably cooler.
An examination of the record of the last twelve millennia reveals that
mankind prospered during the warm periods and suffered during the cold
ones. Transitions from a warm to a cold period or vice-versa were
difficult for people who lived in climates that were adversely
affected yet benefited others who inhabited regions in which the
weather improved. On average, however, humans gained during the
centuries in which the earth enjoyed higher temperatures. In writing
about the effect of climate change on human development, Senator and
now Vice-President Al Gore admits:
The archaeological and anthropological records indicate
that each time the ice retreated [during the ice ages],
the primitive peoples of the Eurasian landmass grew more
populous and their culture more advanced. Then, 40,000
years ago, the so-called cultural explosion of tools and
jewelry may have coincided with an unusually warm millen-
nium in Europe.10
Expected Effects of Global Warming
Although most of the forecasts of global warming’s repercussions have
been dire, an examination of the likely effects suggests little basis
for that gloomy view. Climate affects principally agriculture,
forestry, and fishing. Manufacturing, most service industries, and
nearly all extractive industries are immune to climate
shifts. Factories can be built in northern Sweden or Canada or in
Texas, Central America, or Mexico. Banking, insurance, medical
services, retailing, education and a wide variety of other services
can prosper as well in warm climates (with air-conditioning) as in
cold (with central heating). A few services, such as transportation
and tourism, may be more susceptible to weather. A warmer climate will
lower transportation costs: less snow and ice will torment truckers
and automobile drivers; fewer winter storms - bad weather in the
summer has less disruptive effects and is over quickly - will disrupt
air travel; a lower incidence of storms and less fog will make water
transport less risky. Hotter temperatures will leave mining and the
extractive industries largely unaffected; they might even benefit oil
drilling in the northern seas and mining in the mountains. A warmer
climate could, however, change the nature and location of tourism.
Many ski resorts, for example, might face less reliably cold weather
and shorter seasons. Warmer conditions would mean that fewer
northerners would feel the need to vacation in Florida or the
Caribbean. On the other hand, new tourist opportunities might develop
in Alaska, northern Canada and other locales at higher latitudes or in
upper elevations.
A rise in world-wide temperatures will go virtually unnoticed by
inhabitants of the advanced industrial countries. In his 1991 address
to its members, the President of the American Economic Association
asserted: "I conclude that in the United States, and probably Japan,
Western Europe and other developed countries, the impact on economic
output [of global warming] will be negligible and unlikely to be
noticed." As modern societies have developed a larger industrial base
and become more service oriented, they have grown less dependent on
farming, thus boosting their immunity to temperature variations.
Warmer weather means, if anything, fewer power outages and
less frequent interruptions of wired communications.
Only if warmer weather caused more droughts or lowered agricultural
output would even Third World countries suffer. Should the world
warm--and there is little evidence or theory to support such a
prognostication--the hotter temperatures would enhance evaporation
from the seas, producing more clouds and more precipitation world-
wide. Although some areas might become drier, others would become
wetter. Judging from history, Western Europe would retain plentiful
rainfall, while North Africa and the Sahara might gain moisture. The
Midwest of the United States might suffer from less precipitation and
become more suitable for cattle grazing than farming. On the other
hand, the Southwest would likely become wetter and better for crops.
A warmer climate would produce the greatest gain in temperatures at
northern latitudes and much less change near the equator. Not only
would this foster a longer growing season and open up new territory
for farming but it would mitigate harsh weather. The contrast between
the extreme cold near the poles and the warm moist atmosphere on the
equator drives storms and much of the earth’s climate. This difference
propels air flows; if the disparity is reduced, the strength of winds
driven by equatorial highs and Arctic lows will be diminished.
As a result of more evaporation from the oceans, a warmer climate
should intensify cloudiness. More cloud cover will moderate daytime
temperatures while acting at night as an insulating blanket to retain
heat. The Intergovernmental Panel on Climate Change has found exactly
this pattern both for the last 40 years, indeed for the whole of the
twentieth century.12 For the Northern Hemisphere in summer months,
daytime high temperatures have actually fallen; but in the fall,
winter and spring, both the maximum and especially the minimum
temperatures (nighttime) have climbed.
Warmer nighttime temperatures, particularly in the spring and fall,
create longer growing seasons, which should enhance agricultural
productivity. Moreover, the enrichment of the atmosphere with CO2 will
fertilize plants and make for more vigorous growth. Agricultural
economists studying the relationship of higher temperatures and
additional CO2 to crop yields in Canada, Australia, Japan, northern
Russia, Finland, and Iceland found not only that a warmer climate
would push up yields, but also that the added boost from enriched CO2
would enhance output by 17 percent.13 Researchers have attributed a
burgeoning of forests in Europe to the increased CO2 and the
fertilizing effect of nitrogen oxides.14 Professor of Climatology
Robert Pease writes that we may now be living in an “icehouse” world
and that a warming of about two degrees Celsius, which is what his
model indicates,
may actually make the earth more habitable. The higher
temperatures combined with more carbon dioxide will favor
plant and crop growth and could well provide more food for
our burgeoning global populations. Geologic history reveals
that warmer global temperatures produce more, not less,
precipitation, a fact reflected by a recent scientific
investigation that shows the Greenland ice-cap to be
thickening, not melting. So much for the catastrophic
prediction that our coastlines will be flooded by a rise
in sea level from polar meltwaters.15
The United States Department of Agriculture in a cautious report
reviewed the likely influence of global warming on crop production and
world food prices. The study, which assumed that farmers fail to make
any adjustment to mitigate the effects of warmer, wetter, or drier
weather--such as substituting new varieties or alternative crops,
increasing or decreasing irrigation--concludes that:
The overall effect on the world and domestic economies
would be small as reduced production in some areas would
be balanced by gains in others, according to an economic
model of the effects of climate change on world agricultural
markets. The model ... estimates a slight increase in world
output and a decline in commodity prices under moderate
climate change conditions.16 [Emphasis added.]
Economists Robert Mendelsohn, William D. Nordhous, and Daigee Shaw
researched the relationship of climate to land values in the United
States.17 After holding land quality, the proximity to urban areas and
the nearest coast, and income per capita constant, they found that
climate explained over two-thirds of the value of crop lands. They
concluded that for the lower-48 states, a rise in average temperature
of about 5 degees Fahrenheit and an 8 percent increase in rainfall
stemming from global warming would, depending on their model, reduce
the value of output between 4 and 6 percent or boost the value of
output slightly. This result ignored the effect of increased CO2 on
farm output. It is also consistent with the Department of Agriculture
study that suggests the U.S. might see a slight fall in output while
the rest of the world increased production.
Forestry is another sector that is potentially subject to change due
to an increase in world temperatures. Canadian agricultural economists
have examined the effect of a doubling of CO2 on forestry
production. They concluded that increased carbon dioxide would boost
productivity by 20 percent and that overall the harvest of timber in
Canada would climb by about 7.5 percent.18
Historical Evidence
History provides the best evidence for the effect of climate change on
humans, plants and animals, but a few researchers have challenged its
relevance. David Rind, a climate modeler and NASA scientist, has
questioned the applicability of past warming episodes to the modern
issue of climatic alteration caused by increased CO2 concentrations.19
He attributes the origin of past periods of warmth and cold to shifts
over time in the orbital position of the earth which impose more or
less energy on the poles, as contrasted to a general world-wide
warming that might result from the addition of man-made greenhouse
gases. [See Appendix A on factors determining climate]. He also argues
that the swiftness in warming that would occur following increased
levels of CO2 is unprecedented in history. On the latter point, he
ignores other research, such as that by a German academic, Burkhard
Frenzel, who writes, "During the Holocene, very rapid changes of
climate occurred. According to dendroclimatology [tree ring analysis
applied to climatology], they often lasted about 20 to 30 years, or
[were] even as brief as 2 to 3 years."20 Other climate historians have
found that a rapid cooling in the late glacial period--about 11,000
years ago--took about 100 to 150 years to complete and realized about
5 degree Fahrenheit variation in temperature within 100 years, more
than is being forecast for the next century.21
Although changes in the earth's orbital position may easily have
played a role in warming the earth after the last Ice Age, the effect
was world-wide rather than concentrated in northern latitudes. Ice
retreated in the Southern as well as in the Northern Hemisphere.
Moreover, in the subsequent warming, from around 7,000 to 4,000 years
ago, the climate around the world appears to have improved. Although
the evidence for warming in the Southern Hemisphere is weaker, even if
higher temperatures had been localized in one hemisphere or one
continent, the effect on human beings would still tell us about the
benefits or costs of climatic change. Dr. Rind argues that greenhouse
warming would raise winter as well as summer temperatures while past
warmings, driven by orbital mechanics, have raised summer temperatures
alone. Even though his models suggest that these past warmings should
have boosted temperatures solely in June, July, and August, the
evidence, albeit a little tenuous for the three thousand year period
of Climatic Optimum, supports warmer winters. For the Little Climate
Optimum that coincided with the High Middle Ages, researchers have
found strong support for mild winters.
Moreover, at a recent conference the Russians have put forward the
hypothesis that past climate changes support the proposition that the
cause of the warming or cooling is irrelevant; the pattern has been
the same.22 This conclusion, disputed by some, is based on a large
number of past shifts in average weather conditions dating back
millions of years. The Russians contend that the climate models
overstate the amount of temperature change at the equator and
understate it at the poles.
Measurement of Human Well-being
Since statistics on the human condition are unavailable except for the
most recent centuries, I shall use indirect methods to demonstrate the
influence of climate on man’s well-being. A growth in the population,
major construction projects, a significant expansion in arts and
culture, all indicate that society is prosperous. If the population is
expanding, food must be plentiful, disease cannot be overwhelming, and
living standards must be satisfactory. In addition, if building, art,
science, and literature are vigorous, the civilization must be
producing enough goods and services to provide a surplus available for
such activities. Renaissance Florence was rich; Shakespeare flourished
in prosperous London; wealthy Vienna provided a welcome venue for
Haydn, Schubert, Mozart, and Beethoven.
Clearly climate is far from the only influence on man's
well-being. Governments that extort too much from their people
impoverish their countries. A free open economy stimulates growth and
prosperity. War and diseases can prove catastrophic. On the other
hand, a change in climate has frequently been a cause of war or aided
the spread of disease. A shift to more arid conditions, for example,
impelled the Mongols to desert their traditional lands to invade
richer areas. A cold wet climate can also confine people to close
quarters, which can abet contagion. Moreover, a shift towards a poorer
climate can lead to hunger and famine, which make disease more
virulent.
Throughout history climatic changes probably forced technological
innovations and adaptations. The shift from warm periods into Ice Ages
and back again likely accelerated the evolution of modern man. Each
shift would have left small groups of hominoids isolated and subject
to pressures to adapt to new weather conditions. These shifts,
especially to the more adverse conditions created by the spread of
extreme cold, would put strong selection pressure on the human
forebears that ultimately led to modern man. Even after Homo Sapiens
started spreading across the earth, climate shifts fostered new
technologies to deal with changed circumstances.
The influence of climate on human activities has declined with the
growth in wealth and resources. Primitive man and hunter-gatherer
tribes were at the mercy of the weather, as are societies which are
still almost totally bound to the soil. A series of bad years can be
devastating. If, as was the usual case until very recently,
transportation is costly and slow, even a regionalized drought or an
excess of rain can lead to disaster, although crops may be plentiful a
short distance away. Thus variation in the weather for early man had a
more profound influence on his life and death than do fluctuations in
temperature or rainfall in modern times when economies are more
developed. Since the time of the Industrial Revolution, climate has
basically been confined to a minor role in human activity.
Climate History
Since its origins, the earth has experienced periods significantly
warmer than the modern world - some epochs have been even hotter than
the most extreme predictions of global warming - and times much colder
than today. Today’s cool temperatures are well below average for the
globe in its more than four billion year history.23 During one of the
warmest such eras the dinosaurs roamed the earth and a rich ecological
world flourished.
Studies of climate history show as was mentioned above that sharp
changes in temperatures over brief periods of time have occurred
frequently without setting into motion any disastrous feedback systems
that would lead either to a runaway heating that would cook the earth
or a freezing that would eliminate all life. In addition, carbon
dioxide levels have varied greatly. Ice core data exhibit fluctuating
levels of CO2 that do not correspond to temperature changes.24 Most
past periods display a positive relationship between CO2 and
temperature, however, with a relationship roughly corresponding to
that of the Global Climate Models.25 During interglacial periods high
latitudes enjoyed temperatures that were about 5 to 11 degrees
Fahrenheit warmer than today.26 Middle latitudes experienced
temperatures only about 4 to 5 degrees Fahrenheit warmer. These warmer
periods brought more moisture to the Northern Hemisphere with the
exception during the Holocene of central North America. At the time of
the medieval warm period, temperatures in Europe, except for the area
around the Caspian Sea basin, were 1 to 3 degrees Fahrenheit higher
and rainfall more plentiful than today.27
This historical evidence is consistent with only some of the forecasts
of the computer climate models. Most climate estimates indicate that a
doubling of CO2 would generate greater rainfall in middle latitudes,
and history shows that warm climates do produce more wet weather.28 As
has been found in the historical record, land temperatures should
increase more than water thus strengthening monsoons. The models also
predict that sea-surface temperatures in the tropics would be higher
with increased CO2 but evidence from the past evinces no such
relationship.29
Carbon dioxide concentrations may have been up to sixteen times higher
about 60 million years ago without producing runaway greenhouse
effects.30 Other periods experienced two to four times current levels
of CO2 with some warming. Scientists have been unable to determine
whether the warming preceded or followed the rises in carbon
dioxide. For virtually all of the period from around 125 million to
about 75,000 years ago, CO2 levels were markedly higher than now.
The prevailing view among climatologists is that the Climatic Optimum
--9,000 to 4,000 years ago--resulted from orbital mechanics which
increased summer radiation in the Northern Hemisphere, although
winters received less heat than they do in the modern world.31 The
warmer summers melted the northern glaciers over several
millennia. Warmer lands in the interior of northern continents and
cooler oceans expanded the monsoons further north to bring greater
rainfall to the Sahara, Arabia and southern and eastern Asia.32 North
of the monsoon area, the climate was drier than today. Anatolia,
Northwestern Africa, parts of China and northern Japan experienced
less rainfall.33 By 4000 B.C., however, a slackening of the trade
winds had produced warmer Atlantic ocean water off northwestern
Africa, and as a consequence the Middle East, including Greece and
modern Turkey, were enjoying more reliable rain.
If orbital variations produced the Climatic Optimum, the Southern
Hemisphere should have been cooler. Between 10,000 B.C. and 7000 B.C.,
however, winter temperatures (June, July, August) below the equator
warmed to higher levels than now while summer temperatures (December,
January, February) were cooler than the modern world.34 Rainfall over
South America, Australia and New Zealand apparently was lighter than
the present. Although the Southern Hemisphere moved out of the Ice Age
with the Northern Hemisphere, its climate since then has not tracked
well weather patterns north of the equator.35 Data based on vegetation
suggest that annual temperatures in New Zealand were coldest between
20,000 and 15,000 years ago, warmed subsequently and peaked between
10,000 and 8,000 years before the present - somewhat earlier than they
did in the Northern Hemisphere.36 Temperatures appear to have been
falling over the last 7,500 years. By 1500 B.C., the climate was quite
similar to today’s.37
Whether the whole globe warmed or not during the period 7,000 to 4,000
years ago is really irrelevant to the question of how hotter
temperatures affect humans. If the Northern Hemisphere warmed, and
there is good evidence that it did, then comparing how people survived
in that portion of the globe provides information about how higher
global temperatures would influence mankind.
Modern man apparently evolved into his current genotype between 40,000
and 200,000 years ago, probably in Africa during an Ice Age.38 Around
150,000 years ago the extent of ice coverage reached a maximum,
followed around 130,000 years before the present (YBP) by a rapid
deglaciation.39 The warm interglacial era, during which temperatures
may have exceeded those forecast under a doubling of greenhouse gases,
lasted about 15,000 years until the onset of renewed glaciation at
115,000 YBP. Over the next 100,000 years the glaciers fluctuated with
the climate, but at no time did the average temperature equal the
level of the previous interglacial epoch or reach the warmth of the
last 10,000 years.40
In the thousands of years of the last Ice Age preceding the current
warm epoch, man existed as a hunter-gatherer in a world that looked
quite different from today’s. Herds of large animals such as bison,
mammoths, and elk roamed a largely treeless savanna in Europe. These
beasts made easy prey for human hunters that enjoyed as a consequence
a rich diet of wild animal meat plus, in season, local fruits and
vegetables. It was during the Ice Age that the level of the ocean fell
sufficiently that Asian peoples were able to migrate across what is
now the Bering Strait but then was dry land. Most archaeologists date
the first arrivals of humans in the Americas from around 15,000 years
ago, although some have claimed evidence for an earlier arrival. No
doubt the lower sea levels during the Ice Age also facilitated the
arrival of the aborigines in Australia some 35,000 years ago.
Climatologists consider that the last Ice Age ended about 12,000 to
10,000 years ago when the glaciers covering much of North America,
Scandinavia and northern Asia began to retreat to approximately their
current positions. In North America the glacial covering lasted longer
than in Eurasia because of topographic features that delayed the
warming. Throughout history warming and cooling in different regions
of the world have not been exactly correlated because of the influence
of oceans, mountains, prevailing winds, and numerous other
factors. Nevertheless, across the Northern Hemisphere large
temperature shifts have occurred roughly together - perhaps in some
areas they have lagged other zones by a century or more. The
correspondence between warming and cooling in the Northern Hemisphere
and that in the Southern is less well known and may be less well
correlated because of the predominance of water south of the equator
and the existence of Antarctica.
Human progress, a few improvements in hunting tools and some cave art,
was incredibly slow during the Ice Age - a period whose length dwarfs
the centuries since. Over the last 12 millennia of interglacial
warmth, however, modern man has advanced rapidly. The growth in
technology and living standards required a climate that was more
hospitable than existed throughout that frozen period.
During the last Ice Age humans survived through hunting and
gathering. Initially archeologists believed that these tribes, which
typically consisted of 15 to 40 people, eked out a precarious
existence.41 Many modern archeologists, however, feel, based on
studies of the few bands of hunter-gatherers that survived into the
twentieth century, that they normally found plentiful foods in their
forays and would rarely have been hungry. Modern primitive people,
however, may not have been typical of earlier groups. The ones that
did face food pressures would have adopted farming while those that
found plentiful supplies in their environment would be less concerned
with new ways of acquiring sustenance.42 Food pressures could have
arisen from either a change in climate that made previous ways-of-life
untenable or an expansion of population in the region that began to
overwhelm the natural supply.
As the earth warmed with the waning of the Ice Age, the sea level rose
as much as 300 feet; hunters in Europe roamed through modern Norway;
agriculture developed in the Middle East. For about 3,000 to 4,000
years the globe enjoyed what historians of climate call the Climatic
Optimum period--a time when average world temperatures--at least in
the Northern Hemisphere - were significantly hotter than today. At its
height between 4000 B.C. and 2000 B.C., H.H. Lamb, a leading climate
historian, judges that the world was 4 to 5 degrees Fahrenheit warmer
than the twentieth century.43 During the relatively short period since
the end of glaciation the climate has experienced periods of stability
separated by "abrupt transition."44 Lamb calculates that at its
coldest, during the Mini Ice Age, the temperature in central England
for January was about 4.5 degrees Fahrenheit colder than today.45 He
also concludes that in the central and northern latitudes of Europe
during the warmest periods, rainfall may have been 10 to 15 percent
greater than now and during the coldest periods of the Mini Ice Ages,
5 to 15 percent less.46 On the other hand, cooler periods usually
suffered from more swampy conditions because of less evaporation.
If modern humans originated 200,000 years ago, why did they not
develop agriculture for the first 190,000 years? Even if Homo Sapiens
originated only 40,000 years ago, people waited 30,000 years to grow
their first crops--an innovation which yielded a more reliable and
ample food supply. Farming developed first in the Middle East, right
after the end of the last Ice Age--a coincidence? The evidence
suggests that from 11,000 to 9,000 years ago the climate became warmer
and wetter in the Middle East shifting the ecology from steppe to open
woodland.47 This led to the domestication of plants and animals,
probably because the warmer, wetter weather made farming
possible. From its origins around 8000 B.C., agriculture spread
northward, appearing in Greece about 6000 B.C., Hungary 5000 B.C.,
France 4500 B.C. and Poland 4250 B.C.48 Is it chance that this
northward spread followed a gradual warming of the climate that made
agriculture more feasible at higher latitudes?
As Anthropologist Mark Cohen writes, "If, as the archaeological record
indicates, hunting and gathering was such a successful mode of
adaptation over such a long period of time, and if most human
populations are as conservative as anthropologists have observed them
to be, we are faced with answering the question why this form of
adaptation was ever abandoned."49 He gives estimates of the efficiency
of hunting and gathering that indicate that the latter was more
efficient than farming--at least for large game. He reports that when
large animals are available, hunting brings 10,000 to 15,000
kilocalories per hour of hunting. However, if large animals are
unavailable--because the environment is poor or because they have all
been killed--hunting of small game will return only a few hundred to
1,500 kilocalories per hour devoted to the effort. Collecting and
processing small seeds from such plants as wild wheat may produce only
700 to 1,300 kilocalories for each hour. Shellfish collection can
produce 1,000 to 2,000 kilocalories per hour of work. On the other
hand subsistence farming produces 3,000 to 5,000 kilocalories per hour
devoted to agriculture.50 This connotes that hunting large animals,
when and if they are available, is the most economical method of
subsistence, but if these beasts are exterminated or if the humans
move to areas without such species, domestication of plants and
animals can produce more food for the effort than any other strategy.
Moreover hunter-gatherers can only survive if the density of their
population is low. Too many mouths would strain the environment and
preclude survival. Once, humans developed farming which could support
larger families and a denser population, however, the number of people
did explode. Primitive tribes, dependent on hunting, scavenging, and
collecting edibles to survive, had to hold their populations below
what they would individually have preferred or nature kept them in
check through periodic food shortages. A number of twentieth century
hunter-gatherers have practiced infanticide and induced abortions to
restrict the number and spacing of their children.51 Constant travel
by nomads may increase infant mortality, maternal mortality and
produce more miscarriages than a sedentary life and thus have kept the
numbers in check. In any case farming solved a major problem for
primitive peoples. Once people settled down into fixed abodes, the
population apparently ballooned.
Although many people view the current world’s huge population with
alarm, most ecologists take the size of the population of a species as
an indicator of its fitness. By this criterion, the domestication of
plants and animals improved greatly Homo Sapiens fitness. This essay
is not the place to discuss the capacity of the globe to sustain the
number of people expected to populate the world in the next century,
but certainly anything that produced greater numbers of people
thousands of years ago must have been beneficial for mankind.
Over history the number of humans has been expanding at ever more
rapid rates. Around 25,000 years ago, the world's population may have
measured only about 3 million.52 Fifteen thousand years later, around
10,000 B.C., the total had grown by one-third to 4 million. It took
5,000 more years to jump one more million, but in the 1,000 years
after 5000 B.C. it added another million. Except for a few disastrous
periods, the number of men, women and children has mounted with
increasing rapidity. Only in the last few decades of the twentieth
century has the escalation slowed. Certainly there have been good
times when man did better and poor times when people suffered--
although in most cases these were regional problems. However, as the
following chart shows, in propitious periods, that is, when the
climate was warm, the population swelled faster than during less
clement eras.
This chart is based on a paper by economist Michael Kremer who argues
that, until the Industrial Revolution, existing technology limited the
size of the population.53 As innovators discovered new techniques and
invented new tools, more people could be fed and housed and the
population expanded. Moreover, the greater the number of people, the
more innovations would be hit upon. He assumed that every individual
had an equal but very small probability of uncovering a new technique
or device and that the probability of being an innovator was
independent of the size of the population. Therefore the number of
inventions would be proportional to the number of people. Thus as the
world population expanded--slowly at first--the rate of
technological innovation escalated and hence the rate of growth of the
population that could be sustained. Only in recent times has
technological change become so rapid that it has run ahead of
population growth, leading to a rising standard of living, which in
turn has reduced the birth rate.
-----------------------------
CHART MISSING
-----------------------------
Source: Michael Kremer (August 1993): Table 1 and the Author.
Kremer's hypothesis signifies that for most of history the rate of
population growth should be proportional to the size of the
population. To link his model and data with climate change, I started
with his estimate of the world’s people in 10,000 B.C. and calculated
the rate of growth of the population over the next 5,000 years. For
each subsequent period, I also computed the rate of increase in
numbers of people. Comparing these expected rates with actual growth
revealed eras in which the number of humans has expanded faster than
predicted and periods during which the world’s people has grown more
slowly. The chart then shows the centuries in which the growth rate of
the globe’s populace has exceeded or fallen short of the rate expected
under this simple model. As can be seen, warm periods have done
considerably better than cold periods in terms of human expansion. The
warmest period since the end of the last Ice Age produced the highest
rate of population growth compared to what would have been expected--
in this era agriculture was spreading. Moreover, the Mini Ice Age,
which saw the coldest temperatures in the last 10,000 years, underwent
the slowest relative population expansion. This chart demonstrates
that mankind has prospered in warm periods and the hotter the better!
Another measure of the well-being of humans is how long they live. The
life of the hunter-gatherer was not as rosy as some have contended.
Life was short--skeleton remains from before 8000 B.C. show that the
average age of death for men was about 33 and that of women 28.54
Death for men was frequently violent, while many women must have died
in childbirth. Since women died so young, they had only around
thirteen years in which to bear children. Anthropologists have
estimated that on average they could have given birth to less than
five live babies, assuming that they bore a child every 22 months.55
An infant and childhood mortality rate of about 60 percent would have
kept the population stagnant.
Table 1 below shows some relevant data. The warmest periods, the
Neolithic, Bronze Ages and England in the thirteenth centuries enjoyed
the longest life spans of the entire record. The shortening of lives
from the late thirteenth to the late fourteenth centuries with the
advent of much cooler weather is particularly notable. Moreover, the
rise in life expectancies during the warm period could easily explain
the population explosion that took place during that period.
Table 1
Life Expectancy at Various Periods
Mesolithic people in Europe 31.5
Neolithic, Anatolia 38.2
Bronze Age, Austria 38
Classical Greece 35
Classical Rome 32
England 1276 A.D. 48
England 1376-1400 38
Source: Lamb [1977]: 264 from Comfort [1969].
Good childhood nutrition is reflected in taller adults. Skeleton
remains collected over wide areas of Eurasia from the period when
roving bands shifted from eating large animals and a few plants to
smaller prey and a much wider variety of foods attest to a decline in
height for both men and women of about five centimeters (two
inches).56 The shorter stature came at the end of the Ice Age when
large animals were disappearing. Some archaeologists have found that
average age of death for adults also declined during this
transitionary period.57 Studies of bone chemistry from Middle Eastern
skeletons indicate a reduction in meat consumption. The new diet
although more dependent on grains, fruits, and vegetables must have
been less nutritious than the old. As large game animals disappeared
with the end of the Ice Age, humans widened the variety of plants in
their diet, increasingly consuming vegetable matter that they had
ignored for thousands of years either because it was less nutritious,
more difficult to secure and process, or less tasty.
Table 2
Average Height of Icelandic Males
Period (A.D.) Mean Height
Medieval Warmth
874-1000 68"
1000-1100 68"
Mini Ice Age
1650-1796 66"
1700-1800 66"
Modern World
1952-1954 70"
Source: Lamb [1977]: 264 from Bergthorsson [1962].
Research on American Indians before the arrival of Europeans also
reveals a decline in health between early periods and later.58 The
evidence for the Americas is more mixed, however, than for
Europe. Based on the Eurasian studies and those of North American
aborigines it seems safe to conclude that health and nutrition were
declining before the advent of agriculture and that it may be that
agriculture was invented to stave off further decreases in food
availability. The absence of agriculture for most North American
peoples may have reflected that their nutrition fell less than it did
in Europe.
In southern Europe, the shift to agriculture coincides with a
reduction in skeleton size of 3 centimeters (1.2 inches) for men and 4
centimeters (1.6 inches) for women.59 Although some other
archaeological studies have found that agriculture led to shorter
people, a few have found the reverse. In Israel, for example, one
study found that people grew taller with the domestication of
animals.60 Overall the evidence supports the view that the diet may
have become less nutritious with the shift from large animal hunting
to food production but that its quality initially exceeded that of
medieval Europe. Table 2 on heights, however, signifies that food was
more plentiful and better during the medieval Period than during the
mini Ice Age.
In summary, the evidence overwhelmingly supports the proposition that
during warm periods, humans prospered. They multiplied more rapidly;
they lived longer; and they apparently were healthier. We now turn to
a closer examination of the two major warm epochs.
The First Climatic Optimum
Around 9,000 to 5,000 years ago the earth was much warmer than today;
perhaps 4 degrees Fahrenheit hotter, about the average of the various
predictions for global warming after a doubling of CO2.61 Although the
climate cooled a bit after 3000 B.C., it stayed relatively warmer than
the modern world until sometime after 1000 B.C., when chilly
temperatures became more common. During this Climatic Optimum epoch,
Europe enjoyed mild winters and warm summers with a storm belt far to
the north. Not only was the country less subject to severe storms, but
the skies were less cloudy and the days sunnier.
Notwithstanding the less stormy weather, rainfall was more than
adequate to produce widespread forests. Western Europe, including
parts of Iceland and the Highlands of Scotland, was mantled by great
woods.62 The timber, until average temperatures dipped temporarily for
about 400 years between 3,500 B.C. and 3,000 B.C., consisted of
warmth-demanding trees, such as elms and linden in North America and
oak and hazel in Europe. These species have never regained their once
dominant position in Europe and America. Not only did Europe enjoy a
benign climate with adequate rainfall, but the Mediterranean littoral,
including the Middle East, apparently received considerably more
moisture than it does today.63 The Indian subcontinent and China were
also much wetter during this Optimal period.64
As a Senator, Al Gore, writing on the prospect of further global
warming and its potential harm, contended that the temperature rise
over the last century has led to increased drought in Africa.65 To
bolster his argument, he presented a chart which shows a drop in
rainfall from 1930 to the early 1980s for portions of sub-Saharan
Africa. His conclusion, however, is based on a false premise: for most
of that period the earth was cooling, not warming! His chart actually
implies that further cooling would be undesirable. In fact, history
demonstrates and climatology attests that warming should drive the
monsoon rains that originate near the equator farther north, possibly
as far as the Sahara, contributing to a moister not a drier climate!
Compared to cooler periods in the last few thousand years, the Sahara
was much wetter and more fertile during the Climatic Optimum.66 Cave
paintings from the epoch depict hippopotamuses, elephants, crocodiles,
antelopes and even canoes.67 The water level in Lake Chad about 14
degrees north of the equator in central Africa was some 30 to 40
meters, that is, 90 to 125 feet higher, than it is today, indicating
much greater precipitation. Ruins of ancient irrigation channels in
Arabia, probably from the warmest millennia, derived their water from
sources well above current water supplies, indicating a wetter
climate.68 A warming would likely lead to similar conditions, not a
strengthening of African drought. With the cooling that started after
3000 B.C., North Africa dried up and the abundance of life
disappeared.
Research has shown, however, that some portions of the globe did
suffer from drier conditions. The Caspian Sea may have been at its
lowest level in over 80,000 years during the warmest recent period--
4,000 to 6,000 years ago--when it was some 20 to 22 meters--66 to 72
feet--below its modern height.69
The Southern Hemisphere seems to have flourished as well during the
warm millennia after the most recent Ice Age. Professor Lamb reports
that the southern temperate zone enjoyed both warmer weather and more
moisture than it does currently.70 Scholars have found that Australia
was consistently wetter than today in both the tropical and temperate
regions.71 Since the end of that epoch, the great deserts of Australia
have expanded and the climate has become both cooler and
drier. Apparently most of the other great desert regions of the world
enjoyed more rainfall during the Climatic Optimum than they do
now. Lamb contends that the period of temperature maximum was also a
period of moisture maximum in subtropical and tropical latitudes and a
good period for forests in most temperate regions.72 During this warm
era, Hawaii experienced more rainfall than in the twentieth century.73
Even Antarctica enjoyed warmer weather, about 4 to 5 degrees
Fahrenheit higher, and during the summer in some of the mountains the
weather was warm enough to produce running streams and lakes which
have subsequently frozen.74 Nevertheless, the basic ice sheet remained
intact.
As already mentioned, the invention of agriculture coincided with the
end of the last Ice Age and the melting of the glaciers.
Archaeologists have found the earliest evidence for husbandry and
farming in Mesopotamia around 9000 B.C.75 As the earth warmed, the
Middle East became wetter and the Iranian plateau shifted from an open
dry plain with roving bands of game to a more wooded environment with
less reliable food sources and a diminished supply of large animals.
No one really knows how man first domesticated plants and animals, but
the coincidence in time and the forcing nature of climate change
suggest that the warmer wetter weather, especially in the mountains,
may have encouraged new techniques.
The transition from the Ice Age to a warmer climate that led
eventually to agriculture is best documented in Europe. During the
cold period, most of Europe was a dry plain, an open savanna, in which
large herds of reindeer, mammoths, and bison roamed. As has been shown
by the cave drawings in France and Spain, the population secured a
good living by preying on these ungulates. As the climate warmed and
as rainfall increased, forests spread north limiting the habitat for
these large mammals. This forced humans into following northward the
dwindling herds or developing new sources of food. As the large
animals disappeared the local people shifted to exploiting red deer,
wild boar and smaller species. Those located near the seas or large
rivers found seafood a plentiful source of substance. On the other
hand, people who made their living at the edge of the ocean faced seas
that were rising about 3 feet each century and which often drowned
them when high tides and storms washed over their primitive villages.
The domestication of plants appears to have occurred around the world
at about the same time: from 10,000 YBP to 7,500 YBP.76 The earliest
well documented employment of agriculture arose in the Middle
East. Planting of wheat and barley began in southwest Asia between
8000 B.C. and 7000 B.C. In north China’s Shensi Province between 4500
B.C. and 3500 B.C., peasants grew foxtail and millet and raised
pigs. Food production in this part of China extends back at least into
the sixth millennium B.C. In the Americas domestication of some grains
and chili peppers dates from between 7000 B.C. and 6000 B.C.;
anthropologists have documented maize in the Tehuacan Valley by 5700
B.C. and production may have started earlier. In South America the
evidence suggests that domestication of two species of beans and chili
pepper as well in the Andean highlands arose 8,500 years ago. Maize
appears in this area only about 3000 B.C. In Africa the evidence
implies the cultivation of plants after 3500 B.C. Domestication of
cattle occurred in the Sahara about 8,000 years before the present.77
As Professors Ammerman and Cavalli-Sforza put it, "One of the few
variables that would seem to be shared is timing: early experiments at
plant domestication occurred in southwest Asia, east Asia, and Central
America during the period between 8000 B.C. and 5500 B.C."78 The
coincidence of the invention of agriculture with a general warming of
the climate, an increase in rainfall, and a rise in carbon dioxide
levels, all of which would have made plant growth more vigorous and
more plentiful, cannot be accidental.
Domestication of plants and animals represented a fundamental shift in
man's involvement with nature. Prior to this humans simply took what
nature offered. People hunted or scavenged the local animals that
happened their way. Women gathered fruits and vegetables that grew
wild in their territory. With farming and herding, mankind, for the
first time, began to modify his environment. Humans determined what
would be grown, which plants would survive in their gardens, which
animals would be cultivated and bred, and which would be shunned or
eliminated. "Homo Sapiens" ceased being simply another species that
survived by predation coupled with grazing and became a manager of his
environment.
The shift from a hunter-gatherer existence to a sedentary one may be
the most important innovation in human existence. Prior to this
change, humans lived in small groups and moved frequently with the
seasons to find new sources of meat, fruit and vegetables. Being
mobile meant carrying few goods and only those that were light and not
fragile. Thus pottery, which is both heavy and easily breakable, was
not part of their culture. Any musical instruments must have been
small and portable. Many small children would have been a hindrance as
would elderly feeble individuals. Such small groups would have had
little opportunity to develop specialization. Virtually all males must
have participated in the hunt while all females, not giving birth or
caring for infants, must have helped gather edibles. These tribal or
family groups could not have supported elaborate priesthoods,
bureaucratic governmental structures, or even people who specialized
in artistic, cultural or intellectual activities. As a consequence
these societies were probably quite egalitarian with only a few, such
as the chief or elder and perhaps a medicine man, that stood out from
the rest.
The development of agriculture and the establishment of fixed
communities led to a population explosion and the founding of
cities. Agricultural societies produce enough surplus to support such
urban developments, including the evolution of trades and new
occupations. A large community could afford to have specialists who
made farm tools, crafted pots, and traded within the village and
between the locals and outsiders. The people in today's Palestine
established the first known city, Jericho, and thus the first step
towards specialization--which lies at the heart of economic
advancement - around 8000 B.C.79
Farming required the development of property rights in lands, although
initially pastures may have been held in common. Even though in the
beginning farm holdings were probably fairly equally distributed, over
time some families must have acquired larger holdings than
others. This increase in income inequality may offend modern
sensibilities, but it provided a major benefit. A wealthy class or a
rich ruler could afford to maintain individuals who would create
desirable objects, such as art, elaborate pots, and musical
instruments, and who could record eclipses, star movements or trade
with other centers.
Man's taming of animals and plants represents a movement towards
establishing property rights. In a hunter-gatherer's world no one owns
the wild beasts or the fruit and grains until they are collected. This
can work satisfactorily only as long as demands for the resources are
quite limited. But as the literature on the tragedy of the commons
shows, once pressures for more grow too large, the resource base can
be exhausted. In what is now called North America, many large species,
such as horses, were apparently hunted to extinction. Domestication--
privatization of animals and plants--became the answer to over
hunting and over grazing.
In Europe, the Optimum period produced an expansion of civilization
with the construction of cities and a technological revolution. The
Bronze Age replaced the New Stone Age.80 The more benign climate with
less severe storms encouraged travel by sea.
Trade flourished during this warm period. People from ancient Denmark
shipped amber along the Atlantic coast to the Mediterranean. As early
as 2000 B.C., the Celts apparently were sailing from Cornwall and
Brittany to both Scandinavia and southern Italy. Astrological
monuments built around this time, such as Stonehenge, indicate that
the skies were less cloudy than now.81 With the glaciers in the Alps
during the late Bronze Age being only about 20 percent of the size of
the ice in the nineteenth century, merchants made their way through
the Brenner Pass, the dominant link between northern and southern
Europe. Northern Europeans exchanged tin for manufactured bronze from
the south. Alpine people mined gold and traded it for goods crafted
around the Mediterranean. Baltic amber found its way to Scotland.
During the warm period prior to 3000 B.C., China enjoyed much warmer
temperatures. In particular midwinters were as much as 9 degrees
Fahrenheit hotter and rice was planted a month earlier than is now
common.82 Bamboo, valued for food, building material, writing
implements, furniture and musical instruments, grew much farther
north--about 3 degrees in latitude--than is now possible.83 Chinese
archaeologists have found evidence in a district near Sian that the
climate 5,000 to 6,000 years ago was warmer and wetter than the
present.
Prior to around 2500 to 1750 B.C., northwestern India, which is now
very dry, enjoyed greater rainfall than it does in the twentieth
century.84 In the Indus Valley, the Harappas created a thriving
civilization that reached its apogee during the warmest and wettest
periods, when their farmers were growing cereals in what is now a
desert.85 The area was well watered with many lakes. This civilization
disappeared around 1500 B.C. at a time when the climate became
distinctly drier.86 The earth was cooling. Historians and
archaeologists also attribute the failure of this civilization to poor
agricultural techniques that may have exacerbated drought.
Virtually all change can make some worse off and the warming after the
last Ice Age is no exception. Although as the population explosion
indicates most humans benefited, the growing warmth harmed some
people, especially those who lived near the coast or who had earned
their living hunting large animals. As the ice sheets melted, the sea
level rose sharply and probably peaked around 2000 B.C.87 During the
many centuries in which the waters mounted, storms often led to ocean
flooding of coastal communities. A few times each century, people
were forced to abandon well-established villages and move to higher
ground.
Cooler, More Varied, and Stormy Times
From the end of the Optimum period of sustained warmth until around
800 A.D. to 900 A.D., what we know of the world's climate and, in
particular, the European varied between periods of warmth and
cold. Based on the height of the upper tree lines in middle latitudes'
mountains, the temperature record following the peak warm period
around 5000 B.C. demonstrates a more or less steady decline right up
to the 20th century.88 As mentioned above, tree ring data for New
Zealand indicate that after temperatures reached a maximum around 6000
to 8000 B.C., the climate cooled in that part of the world.
After 1000 B.C. the climate in Europe and the Mediterranean cooled
sharply and by 500 B.C. had reached modern average temperatures.89 The
period from 500 B.C. to 600 A.D. was one of varied warmth, although
cooler on average than the previous 4,500 years. However, the climate
became more clement and somewhat more stable from 100 B.C. to 400
A.D., the period of the Roman Empire.90 The Italians grew grapes and
olives farther north than they had prior to this period. During these
centuries of varied weather, Classical Greece flourished and then
declined; the Roman Empire spread its authority through much of what
is now Europe, the Middle East and North Africa, only to be overrun by
barbarians from central Asia whose eruption out of their homeland may
have been brought on by a change in the climate.
The cooler climate after the start of the last millennium B.C. appears
to have contributed to a southern migration of people from northern
Europe.91 Archaeologists have also found evidence that Greeks adopted
warmer clothing after 1300 B.C. The population living in the Alps
diminished sharply with the cooler weather and mining
ceased. Classical historian Ray Carpenter attributes a depopulation of
Greece and Turkey between 1200 and 750 B.C. to long term drought that
must have reflected the increased coolness of the climate.92
Evidence for a cooler Mediterranean climate from 600 B.C. to 100
B.C. comes from remains of ancient harbors at Naples and in the
Adriatic which are located about one meter (three feet) below current
water levels.93 Further support for lower sea levels has been found on
the North African coast, around the Aegean, the Crimea, and the
eastern Mediterranean. Lower oceans imply a colder world leading to a
build-up of snow and ice at the poles and in major mountain
glaciers. By 400 A.D., however, temperatures had warmed enough to
raise water levels to about three feet above current elevations. The
ancient harbors of Rome and Ravenna from the time of the Roman Empire
are now located about one kilometer from the sea.94 Evidence exists
for a peak in ocean heights in the fourth century for points as remote
as Brazil, Ceylon, Crete, England, and the Netherlands, indicating a
world-wide warming.
Changes in the climate in Eurasia appear to have played a major role
in the waves of conquering horsemen who rode out of the plains of
central Asia into China and Europe. Near the end of the Roman Empire,
around 300 A.D., the climate began to warm and conditions in central
Asia improved apparently leading to a population explosion.95 These
people, needing room to expand and a way to make a living, invaded the
more civilized societies of China and the West. The medieval warmth
also seems to have also triggered an expansion from that area. During
this second optimum period, the homeland of the Khazars centered
around the Caspian Sea enjoyed much greater rainfall than earlier or
than it does now. The increased prosperity in this area produced a
rapidly rising number of young men that provided the manpower for
Genghis Khan to invade China and India and to terrorize Russia and the
Middle East.96
After 550 A.D. until around 800, Europe suffered through a colder,
wetter, and more stormy period. As the weather became wetter, peat
bogs formed in northern areas.97 The population abandoned many
lakeside dwellings while mountain passes became choked with ice and
snow, making transportation between northern Europe and the south
difficult. The Mediterranean littoral and North Africa dried up,
although they remained moister than now.
Inhabitants of the British Isles between the seventh and the ninth
centuries were often crippled with arthritis while their predecessors
during the warmer Bronze Age period suffered little from such an
affliction. Although some archaeologists have attributed the
difficulties of the dark age people to harder work, the cold wet
climate between 600 and 1000 A.D. may have fostered such ailments.98
During the centuries after the fall of the Roman empire and with the
deterioration of the climate, Greece languished. In 542 A.D., the
population was decimated by the plague, aggravated by cold damp
conditions; the Black Death struck again between 744 and 747.99 As a
consequence the number of people was sharply reduced. Greece was
partially re-populated in the ninth and tenth centuries when the
Byzantine Emperors brought Greek settlers from Asia Minor back into
the area. For the first time in centuries Greek commerce and
prosperity returned--probably due to an improved climate.100
In the ninth century, land hunger and a rising population in Norway
and Sweden spurred the Scandinavians on to loot and pillage by
sea. Their first descent was on the monastery of Lindisfarne in
northern England in 793. This was followed by raids on Seville in
Muslim Spain in 844 and later farther into the Mediterranean.101 In
870 they discovered Iceland and in the next century, Greenland. In 877
they began an invasion of England and conquered from the north to the
whole of the midlands--all of which became a Danish overseas kingdom
by the mid-tenth century. At the same time, they stormed France and
the king had to cede them Normandy as a fief. They also crossed the
Baltic (known as Rus in that time) and sent traders south to Islam and
Byzantium.
The High Middle Ages and Medieval Warmth
From around 800 A.D. to 1200 or 1300, the globe warmed considerably
and civilization prospered. This Little Climate Optimum generally
displays, although less distinctly, many of the same characteristics
as the first climate optimum.102 Virtually all of northern Europe, the
British Isles, Scandinavia, Greenland, and Iceland were considerably
warmer than at present. The Mediterranean, the Near East, and North
Africa, including the Sahara, received more rainfall than they do
today.103 North America enjoyed better weather during most of this
period. China during the early part of this epoch experienced higher
temperatures and a more clement climate. From Western Europe to China,
East Asia, India, and the Americas, mankind flourished as never
before.
Evidence for the medieval warming comes from contemporaneous reports
on weather conditions, from oxygen isotope measurements taken from the
Greenland ice, from upper tree lines in Europe, and from sea level
changes. These all point to a more benign, warmer, climate with more
rainfall but because of more evaporation less standing water. Not only
did northern Europe enjoy more rainfall but the Mediterranean littoral
was wetter. An early twelfth century bridge with twelve arches which
still exists over the river Oreto at Palermo exceeds the needs of the
small trickle of water that flows there now.104 According to Arab
geographers two rivers in Sicily that are too small for boats were
navigable during this period.105 In England at the same time, medieval
water mills on streams that today carry too little water to turn them
attest to greater rainfall. Although England apparently received more
rainfall than in modern times, the warm weather led to more drying out
of the land. Support for a more temperate climate in central Europe
comes from the period in which German colonists founded villages. As
average temperatures rose people established towns at higher
elevations. Early settlements were under 650 feet in altitude; those
from a later period were between 1,000 and 1,300 feet high; and those
built after 1,100 were located above 1,300 feet.106
H. H. Lamb counted manuscript reports of flooding and wet years in
Italy.107 He discovered that starting in the latter part of the tenth
century, the number of wet years climbed steadily, reaching a peak
around 1300. Over the same period northern Europe was enjoying warmer
and more clement weather. Not only was the temperature higher than now
in Europe during the twelfth and thirteenth century but the population
enjoyed mild wet winters. In the Mediterranean it was moist as well
with summer thunderstorms frequently reported.108
Studies have shown that some areas became drier during these
centuries. In particular, the Caspian Sea was apparently four meters--
over 13 feet--lower from the ninth through the eleventh century than
currently.109 After 1200 A.D. the elevation of the lake rose sharply
for the next two or three hundred years.110 In the Asian steppes, warm
periods with fine summers and often little snow in the winter produced
lake levels that were low by modern standards.111 A recent study of
tree rings in California's Sierra Nevada and Patagonia concluded that
the "Golden State" suffered from extreme droughts from around 900 to
1100 and again from 1210 to 1350 while the tip of South America during
the first 200 years also enjoyed little precipitation.112
The timing of the medieval warm spell, which lasted no more than 300
years, was not synchronous around the globe. For much of North
America, for Greenland and in Russia, the climate was warmer between
950 and 1200.113 The warmest period in Europe appears to have been
later, roughly between 1150 and 1300, although parts of the tenth
century were quite warm. Evidence from New Zealand indicates peak
temperatures from 1200 to 1400. Data on the Far East is meager but
mixed. Judging from the number of severe winters reported by century
in China, the climate was somewhat warmer than normal in the ninth,
tenth, and eleventh centuries, cold in the twelfth and thirteenth and
very cold in the fourteenth. Chinese scholar Chu Ko-chen reports that
the eighth and ninth centuries were warmer and received more rainfall,
but that the climate deteriorated significantly in the twelfth
century.114 He found records, however, that show that the first half
of the thirteenth century was quite clement and very cold weather
returned in the fourteenth century.115 Another historian found on the
basis of records of major floods and droughts that between the ninth
and eleventh century China suffered much fewer of these calamities
than during the fourteenth through the seventeenth.116 The evidence
for Japan is based on records of the average April day on which the
cherry trees bloomed in the royal gardens in Kyoto. From this record,
the tenth century springs were warmer than normal; in the eleventh
century they were cooler; the twelfth century experienced the latest
springs; the thirteenth century was average and then the fourteenth
was again colder than normal.117 This record suggests that the Little
Climate Optimum began in Asia in the eighth or ninth centuries and
continued into the eleventh. The warm climate moved west, reaching
Russia and central Asia in the tenth through the eleventh, and Europe
from the twelfth to the fourteenth. Some climatologists have theorized
that the Mini Ice Age also started in the Far East in the twelfth
century and spread westward reaching Europe in the fourteenth.118
Europe
The warm period coincided with an upsurge of population almost
everywhere, but the best numbers are for Europe. For centuries during
the cold damp "dark ages" the population of Europe had been relatively
stagnant. Towns shrank to a few houses clustered behind city
walls. Although we lack census data, the figures from Western Europe
after the climate improved show that cities grew in size; new towns
were founded; and colonists moved into relatively unpopulated areas.
Historians have failed to agree on why after the eleventh century, the
population soared. It might be more enlightening to ask why the
population remained stagnant for so long. As John Keegan, the eminent
military historian put it: "The mysterious revival of trade between
1100 and 1300, itself perhaps due to an equally mysterious rise in the
European population from about 40,000,000 to about 60,000,000, in turn
revived the life of towns, which through the growth of a money economy
won the funds to protect themselves from dangers beyond the walls".119
Although it is impossible to document it, the change in the climate
from a cold, wet one to a warm, drier climate--had more rainfall,
but more evaporation reduced bogs and marshy areas--seems likely to
have played a significant role. In the eighth through the eleventh
centuries, most people spent considerable time in dank hovels avoiding
the inclement weather. These conditions were ripe for the spread of
disease. Tuberculosis, malaria, influenza, and pneumonia undoubtedly
took many small children and the elderly--those over 30.
Written records confirm that the warmer climate brought drier and
consequently healthier conditions to much of Europe. Robert Bartlett,
citing H.E. Hallam in Settlement and Society, quotes the people of
Holland who invaded Lincolnshire in 1189 that "because their own marsh
had dried up, they converted them into good and fertile
ploughland."120 Moreover, prior to the twelfth century German settlers
on the east side of the Elbe frequently named their towns with mar,
which meant marsh, but later colonists did not use that
suffix. Bartlett's explanation is that the term had gone out of use,
but an alternative one is that the warmer climate had dried up the
marshes.121
With a more pleasant climate people spent longer periods outdoors;
food supplies were more reliable. Even the homes of the peasants would
have become warmer and less damp. The draining or drying up of marshes
and wetlands reduced the breeding grounds for mosquitoes that brought
malaria. In all the infant and childhood mortality rate must have
fallen spawning an explosion in population.
From the ninth century, with a climate still quite cool, to the
eleventh, medieval Europe was almost totally agricultural. The few
cities that existed consisted mainly of religious seats with their
support personnel. Even as late as the twelfth century, city dwellers
made up less than 10 percent of the population.122 Trade before the
eleventh century was virtually non-existent.123 People were tied to
the land through custom and necessity. The great feudal estates grew
what they ate and ate what they grew; they wove their own cloth and
sewed their own clothes; they built what little furniture was needed.
In a word they were almost entirely self-sufficient. The serfs that
tilled the land had inherited rights to enough land to sustain a
family. Typically the older son would follow his father. Any other
sons either joined the priesthood, became monks, vagabonds, or in
later centuries, mercenaries. Given the cold climate before the
eleventh century, the lack of medical care, and a restricted diet
fostering poor nutrition, few babies lived to adulthood. The problem
of an excess of labor was, therefore, nonexistent. The truth is that
the population was growing so slowly that a labor shortage persisted
and the feudal nobility established laws prohibiting serfs from
leaving their land.
Until the twelfth century when the weather became significantly more
benign, a Europe fettered by tradition remained cloistered in
self-sufficient units. The next two centuries, however, witnessed a
profound revolution which, by the end of the fourteenth century,
transformed the landscape into an economy filled with merchants,
vibrant towns and great fairs. Crop failures became less frequent; new
territories were brought under control. With a more clement climate
and a more reliable food supply, the population mushroomed. Even with
the additional arable land permitted by a warmer climate, the
expansion in the number of mouths exceeded farm output: food prices
rose while real wages fell. Farmers, however, did well with more
ground under cultivation and low wages payable to farm hands.124
The rise in the population may have contributed to the spread of
primogeniture. Prior to the twelfth century, infant and child
mortality coupled with short life expectancy required parents to be
flexible in designating their heirs. Robert Bartlett quotes an
estimate for the eleventh century that the probability of a couple
raising sons to adulthood was only 60 percent.125
Although the first sons born on the estates could follow their
fathers, other children, especially the men, had to find new
opportunities. The crusades furnished an occasion for both the sons of
serfs and of the nobility to enrich themselves and even to find new
land to cultivate. Others moved to virgin territory in eastern Europe,
Scandinavia or previously forested or swampy areas.126 The Franks and
Normans launched invasions of England, southern Italy, Byzantine
Greece, and the eastern Mediterranean. In 1130 the Tancred de
Hauteville clan, a notable example, founded the Kingdom of
Sicily. This family, a classic case of an "over-breeding, land-hungry
lesser nobility," consisted of 12 sons from two mothers who,
recognizing that their Norman property was inadequate, invaded
southern Italy in search of land and riches.127
During the High Middle Ages, the Germans advanced across the Elbe to
take land from pagan Serbs. The spread of knights and soldiers out of
France and Germany demonstrates that the population was multiplying
more rapidly in northern Europe than in southern. The rapid rise in
numbers north of the Alps fits the improved climate scenario: global
or continental warming brought greater temperature change and more
beneficial weather to higher latitudes.
The more skilled and enterprising who did not seek their fortune in
foreign lands typically flocked to towns and urban centers, becoming
laborers, artisans, or traders. Both those who moved to the new cities
and those who founded colonies were legally freed of feudal
obligations. This new liberty, making risk taking and innovation
possible, was essential for those in commerce.
The warmth of the Little Climate Optimum made territory farther north
cultivable. In Scandinavia, Iceland, Scotland, and the high country
of England and Wales, farming became common in regions which neither
before nor since have yielded crops reliably. In Iceland, oats and
barley were cultivated. In Norway, farmers were planting further north
and higher up hillsides than at any time for centuries. Greenland was
4 to 7 degrees Fahrenheit warmer than at present and settlers could
bury their dead in ground which is now permanently frozen. Scotland
flourished during this warm period with increased prosperity and
construction.128 Greater crop production meant that more people could
be fed, and the population of Scandinavia exploded.129 The rapid
growth in numbers in turn propelled and sustained the Viking
explorations and led to the foundation of colonies in Iceland and
Greenland.
The increasingly warm climate was reflected in a rising sea
level. People were driven out of the low lands and there was a large
scale migration of men and women from these areas to places east of
the Elbe, into Wales, Ireland, and Scotland. Flemish dikes to hold
back the sea date at least from the early eleventh century. Although
Pirenna and Bartlett attribute them to attempts to reclaim land from
the sea to provide new areas for farming, the evidence points towards
a higher water level that farmers in the low countries had to
battle.130 The earliest texts setting out rights on the reclaimed land
fail to mention any obligation to maintain the dikes, although later
ones spell out the requirement, suggesting that the problem of holding
back the sea became worse over time. Robert Bartlett quotes from a
Welsh chronicle on the influx of people from Flanders:
that folk, as is said, had come from Flanders, their land,
which is situated close to the sea of the Britons, because the sea
had taken and overwhelmed their land...after they had failed to
find a place to live in - for the sea had overflowed the coast
lands, and the mountains [sic] were full of people so that it was
not possible for everyone to live together there because of the
multitude of the people and the smallness of the land...131
In addition to the land north of the Alps, the warm rainier climate
benefited southern Europe, especially Greece, Sicily and southern
Italy. All of the Mezzogiorno in the Middle Ages did well.132 Nicolas
Cheetham, a former British diplomat who authored a recent book on
"Mediaeval Greece", reports that during the first half of the thirteenth
century, the plains and valleys of the Peloponnese were fertile and
planted with a wide variety of valuable crops and trees. They produced
wheat, olives, fruits, honey, cochineal for dyeing, flax for the linen
industry and, silk from the mulberry trees. The wealthy in
Constantinople prized highly the wines, olives, and fruit from
Greece. Thessaly's grain fed the Byzantine Empire.133 Patras exported
textiles and silk of very high quality. Extensive forests, which were
full of game, supplied acorns for hordes of pigs. Herders raised sheep
and goats in the mountain pastures, while in the valleys farmers kept
horses and cattle.134
The Mediterranean flourished in the twelfth century. Christian and
Moslem lands achieved great brilliance. Cordova, Palermo,
Constantinople and Cairo all thrived, engendering great tolerance for
contending religions.135 Christian communities survived and prospered
in Moslem Cairo and Cordova. The Rulers of Byzantine countenanced the
Moslems and often preferred them to "barbaric" Westerners.
In the West, Charlemagne, creator of the Holy Roman Empire, may have
inaugurated the era of the High Middle Ages while Dante, writing The
Divine Comedy, may have closed it. In A History of Knowledge, Charles
Van Doren contended that: "the...three centuries, from about 1000 to
about 1300, became one of the most optimistic, prosperous, and
progressive periods in European history."136 All across Europe, the
population went on an unparalleled building spree erecting at huge
cost spectacular cathedrals and public edifices. Byzantine churches
gave way to Romanesque, to be replaced in the twelfth century by
Gothic cathedrals. During this period construction began on the Abbey
of Mont-St-Michel (1017), St. Marks in Venice (1043), Westminster
Abbey in London (1045), the Cathedral of our Lady in Coutances (1056),
the Leaning Tower at Pisa (1067), the Cathedral of Santiago de
Compostela in northern Spain (1078), the Cathedral of Modena (1099),
Vézelay Abbey in France (1130), Notre-Dame in Paris (1163),
Canterbury in England (1175), Chartres (1194), Rouen's cathedral in
France (1201), Burgos' cathedral in Castile (1220), the basilica of
Saint Francis in Assisi (1228), the Sainte Chapelle in Paris (1246),
Cologne Cathedral (1248) and the Duomo in Florence (1298). Virtually
all the magnificent religious edifices that we visit in awe today were
started by the optimistic populations of the eleventh through the
thirteenth centuries, although many were not finished for
centuries. In southern Spain, the Moors laid the cornerstone in 1248
for perhaps the world’s most beautiful fortress, the Alhambra. The
Franks founded Mistra near ancient Sparta in the middle of the
thirteenth century.
It took a prosperous society to launch such major architectural
projects. In Europe, building the cathedrals required a large and
mostly experienced pool of labor. During the week of June 23 to June
29, 1253, the accounts of the construction at Westminister Abbey, for
example, showed 428 men on the job, including 53 stonecutters, 49
monumental masons, 28 carpenters, 14 glassmakers, 4 roofers, and 220
simple laborers.137 Nearly half of all workers were skilled
specialists. Even during the slowest season in November, the Abbey
employed 100 workers, including 34 stonecutters. Masons and
stonecutters earned the highest wages and usually hired a number of
workers as assistants. Master craftsmen moved from job to job around
Europe without any concern about national borders--the first truly
European Community. Historians have found that only 5 to 10 percent of
the masons and stonecutters were local people, but 85 percent of the
men who quarried the stones--an unhealthy and arduous job – were from
the vicinity.138 Thus during these centuries a European-wide market
flourished in skilled craftsmen.
Economic activity blossomed throughout the continent. Banking,
insurance, and finance developed; a money economy became well
established; manufacturing of textiles expanded to levels never seen
before. Farmers were clearing forests, draining swamps and expanding
food production to new areas.139 The building spree mentioned above
was made possible by low wages resulting from a population explosion
and by the riches that the new merchant classes were creating. In
England, virtually all of the churches and chapels which had
originally been built of wood were reconstructed in stone between the
twelfth and fourteenth centuries.140 With the clergy still opposing
buying and selling for gain, those who became wealthy often
constructed churches or willed their estate or much of it to religious
institutions as acts of redemption.141 They supplied much of the funds
to erect the great Gothic cathedrals.
Starting in the eleventh century European traders developed great
fairs that brought together merchants from all over Europe. At their
peak in the thirteenth century they were located on all the main trade
routes and served not only to facilitate the buying and selling of all
types of goods but also functioned as major money markets and clearing
houses for financial transactions. The fourteenth century saw the
waning of these enterprises probably because the weather became so
unreliable and poor that transport to and from these locations with
great stocks of goods became impractical. Belgian historian Henri
Pirenne attributes their decline to war, which may indeed have played
a role, but the failure of crops and the increased wetness must have
made travel considerably more difficult.142 Wet roads were muddy
rendering it arduous to transport heavy goods. Crop failures made for
famines and more vagabonds who preyed on travelers.
During the High Middle Ages, technology grew rapidly. New techniques
expanded the use of the water mill, the windmill, and coal for energy
and heat. Sailing improved through the invention of the lateen sail,
the sternpost rudder and the compass. Governments constructed roads
and contractors developed new techniques for use of stone in
construction. New iron casting techniques led to better tools and
weapons. The textile industry began employing wool, linen, cotton, and
silk and, in the thirteenth century, developed the spinning
wheel. Soap, an essential for hygiene, came into use in the twelfth
century. Mining, which had declined since the Romans, at least partly
because the cold and snow made access to mountain areas difficult,
revived after the tenth century.
Farmers and peasants in medieval England launched a thriving wine
industry south of Manchester. Good wines demand warm springs free of
frosts, substantial summer warmth and sunshine without too much rain,
and sunny days in the fall. Winters cannot be too cold - not below
zero Fahrenheit for any significant period. The northern limit for
grapes during the Middle Ages was about 300 miles above the current
commercial wine areas in France and Germany. These wines were not
simply marginal supplies, but of sufficient quality and quantity that,
after the Norman conquest, the French monarchy tried to prohibit
British wine production.143 Based on average and extreme temperatures
in the most northern current wine growing regions of France and
Germany compared to current temperatures in the former wine growing
regions in England, Lamb calculates that the climate in springs and
summers were somewhere between 0.9 and 3.4 degrees Fahrenheit warmer
in the Middle Ages.144
Not only did the British produce wines during the Little Climate
Optimum but farmers grew grapes in East Prussia, Tilsit, and south
Norway.145 Many areas cultivated in Europe were much further up
mountains than is possible under the modern climate. Together these
factors suggest that the temperatures in central Europe were about
1.8 to 2.5 degrees Fahrenheit higher than during the twentieth century.
Europe's riches and a surplus of labor enabled and emboldened its
rulers to take on the conquest of the Holy Land through a series of
Crusades starting in 1096 and ending in 1291. The Crusades, stimulated
at least in part by a mushrooming population and an economic surplus
large enough to spare men to invade the Muslim empire, captured
Jerusalem in 1099--a feat not equaled until the nineteenth century. A
major attraction of the first crusade was the promise of land in a
"southern climate."146
Even southern Europe around the Mediterranean enjoyed a more moist
climate than currently.147 In the reign of the Byzantine Emperor
Manuel I Comnenus, art and culture flourished and all the world looked
to Constantinople as its leader.148 Under the control of the Fatimid
caliphate, Egypt cultivated a "House of Science," where scholars
worked on optics, compiled an encyclopedia of natural history, with a
depiction of the first known windmills, and described the circulation
of the blood. In Egypt block-printing appeared for the first time in
the West.149 The caliphate turned Cairo into a brilliant center of
Moslem culture. In Persia, Omar Khayyam published astronomical tables,
a revision of the Muslim calendar, a treatise on algebra and his
famous Rubáiyát.150
As European commerce expanded, traders reached the Middle East,
bringing back not only exotic goods, but new ideas and information
about classical times. Drawing on fresh information about Aristotelian
logic, St. Thomas Aquinas defined medieval Christian doctrine in his
Summa Theologica. Possibly the oldest continuous university in the
world was founded in Bologna for the study of the law in 1000
A.D. Early in the twelfth century a group of scholars under a license
granted by the chancellor of Notre-Dame began to teach logic, thus
inaugurating the University of Paris. Cambridge University traces its
foundation to 1209 and Oxford to slightly later in the thirteenth
century. Roger Bacon, one of the first to put forward the importance
of experimentation and careful research, studied and taught at Oxford
in the thirteenth century.
Secular writing began to appear throughout northern Europe. In the
twelfth century the medieval epic of chivalry, the Chanson de Roland,
was put into writing. Between 1200 and 1220 an anonymous French poet
composed the delightful and optimistic masterpiece, Aucassin et
Nicolette. An anonymous Austrian wrote in Middle High German the
Nibelungenlied.151
The Arctic
From the ninth through the thirteenth centuries agriculture spread
into northern Europe and Russia where it had been too cold to produce
food before. In the Far East, Chinese and Japanese farmers migrated
north into Manchuria, the Amur Valley and northern Japan.152 As
mentioned above, the Vikings founded colonies in Iceland and
Greenland, a region that may have been more green than historians have
claimed. It was also during this period that Scandinavian seafarers
discovered "Vinland"--somewhere along the East Coast of North
America. The subsequent Mini Ice Age cut off the colonies in Greenland
from Europe, and they eventually died off. Even today, during this
warm period of the late twentieth century, the British climate
forecloses large-scale grape production and Greenland is unsuitable
for farming.
The Eskimos apparently expanded throughout the Arctic area during the
medieval warm epoch.153 Starting with Ellesmere Land around 900 A.D.,
Eskimo bands and their culture spread from the Bering Sea into the
Siberian Arctic. Two centuries later, these people migrated along the
coast of Alaska and into Greenland. During this period the Eskimos’
main source of food came from whaling, which had to be abandoned with
the subsequent cooling. The Mini Ice Age forced the Thule Eskimos
south out of northern Alaska and Greenland. These hardy aborigines had
abandoned Ellesmere Land by the sixteenth century.
At the same time that the Eskimos were moving north, Viking explorers
were venturing into Greenland, Vinland, and even the Canadian
Arctic. Scandinavian sailors found Iceland in 860, Greenland around
930, and reached the shores of North America by 986.154 By the turn of
the millennium, when the waters south-west of Greenland may have been
at least 7 degrees Fahrenheit warmers than now, Vikings were regularly
visiting Vinland for timber.155 They were received with great
hostility by the natives and eventually abandoned contact, although
the last trip may have occurred as late as 1347, when a Greenland ship
was blown off course.156 At the height of the warm period,
Greenlanders were growing corn and a few cultivated grain. Some
archaeologists have found evidence that Vikings from Greenland may
have visited remote portions of the Canadian archipelago and even may
have sailed through the Northwest Passage to the West Coat of America
traveling as far south as the Gulf of California. At least one
scientists believes that this visit is the origin of the Aztec belief
in the visit of “fair” people from the East.157
The Far East
As noted above, the warming in the Far East seems to have preceded
that in Europe by about two centuries. Chinese Economist Kang Chao has
studied the economic performance of China since 200 B.C. In his
careful investigation, he discovers that real earnings rose from the
Han period (206 B.C. to 220 A.D.) to a peak during the Northern Sung
Dynasty (961 A.D. to 1127).158 This coincides with other evidence of
longer growing seasons and a warmer climate. He explains the fall in
worker productivity after the twelfth century as stemming from
population pressures, but a change in climate may have played a
significant role. Chao reports that the number of major floods
averaged fewer than 4 per century in the warm period of the ninth
through the eleventh centuries while the average number was more than
double that figure in the fourteenth through the seventeenth centuries
of the Mini Ice Age.159 Not only floods but droughts were less common
during the warm period. The era of benign climate sustained about 3
major droughts per century, while during the later cold period, China
suffered from almost 13 each hundred years.
The wealth of this period gave rise to a great flowering of art,
writing, and science. The Little Climate Optimum witnessed the highest
rate of technological advance in Chinese history. During the 300 years
of the Sung Dynasty, farmers invented 35 major farm implements--that
is, over 11 per century, a significantly higher rate of invention than
in any other era.160 In the middle of the eleventh century, the
Chinese invented movable type employing clay pieces.161
During the Northern Sung Dynasty Chinese landscape painting with its
exquisite detail and color reached a peak never again matched.162 Adam
Kessler, curator of the Los Angeles County Museum of Natural History
dates the earliest Chinese blue-and-white porcelain to the twelfth
century.163 The Southern Sung produced pottery and porcelains
unequaled in subtlety and sophistication. Literature, history and
scholarship flourished as well. Scholars prepared two great
encyclopedias, compiled a history of China, and composed essays and
poems. Mathematicians developed the properties of the circle.
Astronomers devised a number of technological improvements to increase
the accuracy of measuring the stars and the year.164
Chinese civilization has waned and waxed for about 3500 years, yet
during all those centuries only once has it ventured to spread its
culture or its people beyond its normal borders. Beginning with the
twelfth century A.D., however, Chinese explorers and merchant ships
plied the Indian Ocean and landed on the East African coast.165
Although favorable weather may not have motivated these voyages, which
ended in the fourteenth century, they coincided with both the warmest
temperatures in much of the world and the time of the richest per
capita incomes in China. Certainly the more clement climate meant
fewer storms and easier sea travel.
Japan also prospered during the Little Climate Optimum. In the Heian
Period (794 A.D. to 1192) the arts thrived as emperors and empresses
commissioned vast numbers of Buddhist temples. Murasaki Shikibu,
perhaps the world's first female novelist, composed Japan's most
famous book, The Tale of Genji. Other classical writers penned essays:
Sei Shonagon--another court lady--wrote Makura-no-Soshi (the Pillow
Book). The Japanese aristocracy vied in composing the best poems. All
of this attests a prosperous economy with ample food stocks to support
a leisured and cultivated upper class.
Over the four hundred years between 800 A.D. and 1200, the peoples of
the Indian subcontinent prospered as well. Society was rich enough to
produce colossal and impressive temples, beautiful sculpture,
elaborate carvings, many of which survive to this day.166 The
Lingaraja Temple, one of the finest Hindu shrines, as well as the
Shiva Temple date from this period.167 Seafaring empires existed in
Java and Sumatra, which reached its height around 1180. Ninth century
Java erected the vast stupa of Borobudur; other temples--the Medut,
Pawon, Kelasan and Prambanan--originate in this era. In the early
twelfth century, the predecessors of the Cambodians, the Khmers, built
the magnificent temple of Angkor Wat.168 In the eleventh century
Burmese civilization reached a pinnacle. In or around its capital,
Pagan, between 931 and 1284, succeeding kings competed in constructing
vast numbers of sacred monuments and even a library.169 Today the area
is a dusty plain littered with the crumbling remains of about 13,000
temples and pagodas, built in a more hospitable era.
Archaeologists studying the compositions of forests in New Zealand
have found that the South Island enjoyed a warmer climate between 700
A.D. and 1400, about the time when Polynesians were colonizing the
South Pacific Islands and the Maoris were settling in New Zealand.170
Partially confirming that warming are data from Tasmania of tree rings
which show a warm period from 940 to 1000 and another from 1100 to
1190.171
The Americas
Less is known about civilizations in the Americas during the Little
Climate Optimum or even how the prevailing weather changed. Much of
the currently arid areas of North America were apparently wetter
during this epoch. The Great Plains areas east of the Rocky Mountains,
the upper Mississippi Valley and the Southwest received more rainfall
between 800 A.D. and 1200 than they do now.172 Radiocarbon dating of
tree rings indicates that warmth extended from New Mexico to northern
Canada. In Canada, forests extended about sixty miles north of their
current limit.173
Starting around 800 to 900 A.D., the indigenous peoples of North
America extended their agriculture northward up the Mississippi,
Missouri, and Illinois river basins. By 1000 they were farming in
southwestern and western Wisconsin and eastern Minnesota.174 They grew
corn in northwestern Iowa prior to 1200 in an area which is now
marginal for rainfall.175 Indian settlements on the northern plains of
Iowa were abandoned with colder drier weather that set in after 1150
to 1200. After that time, the natives substituted bison hunting for
growing crops. In general the land east of the Rocky Mountains enjoyed
wetter conditions from 700 to 1200 and then turned drier as it
experienced greater intrusions of colder Arctic weather.
The Anasazi civilization of Mesa Verde flourished during the warm
period, but the cooling of the climate at the end of the medieval
warmth around 1280 probably led to its disappearance.176 This climatic
shift brought drier conditions to much of the region, leading to a
retreat from the territory and forcing the Pueblo Indians to shift
their farming to the edge of the Rio Grande River.
Around 900, the Chimu Indians in South America developed an extensive
irrigation system on Peru's coast to feed their capital of between
100,000 to 200,000 souls--a huge number for the era.177 The Toltec
civilization, which occupied much of Mexico, reached its apogee in the
thirteenth century.178 By 1200, the Aztecs had built the pyramid of
Quetzalcoatl near modern Mexico City.179 The Mayas' civilization,
however, reached a peak somewhat earlier, before 1000, and declined
subsequently for reasons that remain unclear. It is possible that the
warming after 1000 led to additional rainfall in the Yucatan, making
the jungle too vigorous to restrain and causing a decline in farming,
while at the same time improving agricultural conditions in the
Mexican highlands and farther north into what is now the southwestern
United States.
Thus warmer times brought benefits to most people and most regions,
but not all. As is always the case with a climate shift, the changes
benefited some while affecting other adversely. Change is disruptive;
at the same time it produces new ideas and new ways of coping with the
world. Nevertheless, for most of the known world, the Little Climate
Optimum of the ninth through the thirteenth centuries brought
significant benefits to the local populations. Compared with the
subsequent cooling it was nirvana.
The Mini Ice Age
The Little Ice Age is even less well defined than the medieval warm
period. Climatologists are generally agreed that, at least for
Europe, North America, New Zealand and Greenland, temperatures fell
after 1300 to around 1800 or 1850, although with many ups and
downs. There was a cold period in the first decade of the fourteenth
century, another around 1430 and again in 1560. The end of this period
of increasingly harsh temperatures could have been as early as 1700,
1850 or even 1900 for Tasmania. The worst period for most of the
world occurred between 1550 and 1700.180 One reasonable interpretation
of the data is that the world has been cooling since around 4500
B.C. with a temporary upswing during the High Middle Ages.
Europe and Asia cooled substantially from around 1300 to 1850,
especially after 1400, with temperatures falling some 2 to 4 degrees
Fahrenheit below those of the twentieth century. This indicates that
temperatures may have dipped by as much as 9 degrees Fahrenheit in the
two hundred years from 1200 to 1400, a drop of about the same
magnitude as the maximum rise forecast from a doubling of CO2. These
frigid times did bring hardships, and as the chart shows world
population growth slowed. For much of these centuries, famine and
disease stalked Europe and Asia.
Glaciers in North America and northern Europe peaked between the late
1600s and 1730 to 1780. In the Alps these ice sheets reached their
maximum between 1600 and 1650. The coldness came later below the
equator where the glaciers reached their extreme between 1820 and
1850.181
Oxygen isotope ratios from oak trees in Germany document a steady
decline in average temperatures from 1350 to about 1800, with the
exception of a few small upsurges and one strong temperature spike in
the first half of the eighteenth century.182 Since late in the 19th
century they confirm a recovery to much higher levels. Icelandic
records of sea ice attest to an increase between 1200 and the middle
of the fourteenth century and then, starting in the latter half of the
sixteenth century, a marked upswing in ice which appears to have
peaked around 1800.183 As H. H. Lamb points out, "in most parts of the
world the extent of snow and ice on land and sea seems to have
attained a maximum as great as, or in most cases greater than, at any
time since the last major Ice Age."184
The Little Ice Age, especially the century and a half between 1550 and
1700 - the exact timing varied around the globe - produced low
temperatures throughout the year and considerable variation in weather
from year to year and from decade to decade. It included some years
that were exceptionally warm.185 The polar cap expanded as did the
circumpolar vortex, driving storms and the weather to lower
latitudes. Although much of Europe experienced greater wetness than
during the earlier warm epoch, this dampness was more the product of
less evaporation due to the cold than an excess of precipitation.
The cooling after the High Middle Ages can be seen in the lowering of
tree lines in the mountains of Europe, changes in oxygen isotope
measurement, and advances of the glaciers and of sea ice. This cooling
diminished the abundance and quality of wine production in France,
Germany and Luxembourg as depicted in historical documents such as
weather diaries and farm records.186 The ocean, which had reached
relatively high levels both in the late Roman period and again during
the High Middle Ages, fell to lower elevations in the seventeenth and
nineteenth centuries.187 As a result of an expanded ice cap, the
circumpolar vortex, which funnels weather around the globe, moved
south and spawned increasingly cold and stormy weather in middle
latitudes. With the exception of southern United States and central
Asia, both of which enjoyed more rainfall, this brought a worsening of
the climate and disasters to people almost everywhere. During the
coldest period of the seventeenth century, snow fell in the high
mountains of Ethiopia above 10,000 feet which today never see
snow. The subtropical monsoon rains decreased and receded farther
south causing droughts in East Asia and parts of Africa.188
The expansion of the circumpolar vortex produced some of the greatest
windstorms ever recorded in Europe. A terrible tempest destroyed the
Spanish Armada in 1588. Fierce gales wracked Europe in December 1703
and on Christmas Day 1717.189 The contrast between the cold northern
temperatures which moved south and the warm subtropical Atlantic
undoubtedly generated a fierce jet stream. Although we lack any
information, this may also, have enhanced tornado activity on the
plains of the United States.190
The reduced temperatures had the following general effects: (1) Arctic
sea ice expanded in the Atlantic eventually cutting off Greenland; (2)
glaciers advanced in Iceland, Norway, Greenland, and the Alps; (3) the
upper tree line in North America and central Europe lowered; (4)
enhanced wetness spawned bogs, marshes, lakes, and floods; (5) rivers
and lakes froze more frequently; (6) the number and strength of
storms, some of which were extraordinarily destructive, intensified
sharply; (7) harvests failed engendering famine and higher prices for
basic foods; (8) peasants abandoned farms that no longer enjoyed
reliable weather; (9) disease for both animals and humans spread.191
As early as 1250, floating ice from the East Greenland ice cap was
hindering navigation between Iceland and Greenland.192 Over the next
century and a half the prevalence of icebergs became worse and by 1410
sea travel between the two outposts of Scandinavia ceased. Based on
the ratio of isotopes of oxygen in teeth of ancient Norsemen,
researchers have estimated that the climate in Greenland cooled by
about 3 degrees Fahrenheit between 1100 and 1450.193 For about 350
years, from the third quarter of the fifteenth century to 1822, no
ships found their way to Greenland and the local population
perished.194
The deteriorating climate in Europe was heralded by harvest failure in
the last quarter of the thirteenth century. Compounding the
insufficiency was a shift of land from farming, which because of the
change in climate was more chancy, to enclosure and sheep rearing.195
Average yields, which were already low by modern standards, worsened
after the middle of the thirteenth century.196 One of the first severe
bouts of cold wet weather afflicted Europe from 1310 to 1319, leading
to large scale crop failures.197 Food supplies deteriorated sharply
generating famine for much of Europe in 1315-18 and again in 1321.198
Harvest deficits and hunger preceded the Black Death by 40 years.199
According to Lamb, for much of the continent, "the poor were reduced
to eating dogs, cats and even children."200 This scanty food output
contributed to a decline in population which was aggravated by
disease. The history of many villages shows that they were abandoned
before the beginning of the plague not afterwards. By 1327, the
population in parts of England--especially those later devastated by
the plague--had fallen by 67 percent.201 People poorly nourished were
quickly carried off by disease. Between 1693 and 1700 in Scotland,
seven out of the eight harvests failed and a larger percentage of the
population starved than died in the Black Death of 1348-50.202
In two terrible years, 1347 and 1348, famine struck northern Italy,
followed by the Black Death, which decimated most of those not already
carried away by lack of food.203 Bubonic plague spread across the Alps
after 1348, killing in the next two years about one-third of northern
Europe's people. Life expectancy fell by ten years in a little over a
century: from 48 years in 1280 to 38 years in the years 1376 to
1400.204 Crops often failed; peasants abandoned many lands that had
been cultivated during the earlier warm epoch. Between 1300 and 1600
the growing season shrank by three to five weeks with a catastrophic
impact on farming.205 In Norway and Scotland, the population declined
and villagers deserted many locales well before the plague reached
those areas.206 The capitals of both Scotland and Norway moved south
before both areas lost their autonomy.
The cooling after 1300 may also have contributed to the bubonic
plague, the greatest disaster to ever befall Europe. The disease
appears to have originated around 1333 in China, shortly after major
rains and floods in 1332, which are reputed to have caused 7 million
deaths, while disturbing wildlife and displacing plague-carrying
rats.207 The Black Death then spread to central Asia around 1338-9,
which, with the increased coldness, was also drying out. By 1348
rodents carrying fleas infested with bubonic plague had marched or
been carried from the Crimea into Europe. Historians have estimated
that as many as one-third of all the people in Europe died in the
raging epidemic that swept the continent.208 This outburst of the
plague, like a similar one in the sixth century, occurred during a
period of increasing coolness, storminess, and wet periods, followed
by dry hot ones. The unpleasant weather is likely to have confined
people to their homes where they were more likely to be exposed to the
fleas that carried the disease. In addition the inclement weather may
have induced rats to take shelter in human buildings, exposing their
inhabitants to the bacillus.
Not only did the cold facilitate the spread of the plague, but it
caused much other human suffering. In July of 1789, just prior to the
French Revolution, wet weather and air temperatures between 59 and 85
caused an ergot blight in the rye crop of Brittany and other parts of
France. This blight caused hallucinations, paralysis, abortions and
convulsions and came after a very cold winter that had created severe
food shortages.209 Earlier in that century wet cold summers had
produced two famine years in Europe.
The end of the medieval warmth had devastating effects on populations
that lived at the edge of habitable lands. For example, historians
have estimated the population of Iceland at the end of the eleventh
century at about 77,000, and early in the fourteenth it still numbered
over 72,000. By the end of the eighteenth century, after several
hundred years of coolness and stormy weather, the number of Icelanders
had been cut in half to 38,000.210
The poorer climate in Europe after the thirteenth century brought a
halt to the economic boom of the High Middle Ages. Innovation slowed
sharply.211 Except for military advances, technological improvements
ceased for the next 150 years. Population growth not only ended but,
with starvation and the black death, fell. Without the drive of
additional numbers of people, colonial enterprise ceased and no new
lands were reclaimed nor towns founded. The economic slump of 1337
brought on the collapse of the great Italian bank, Scali, leading to
one of the first recorded major financial crises.212 Construction on
churches and cathedrals halted.
The hardships of the fourteenth century induced a search for
scapegoats. In 1290 after some years of crop failures, the king of
England expelled the Jewish population from the country. The French
king followed this example in 1306 and again in 1393.213 In 1349, the
Christians of Brabant massacred the local Jews and expelled the
remainder twenty-one years later.
The Mini Ice Age at its coldest devastated the fishing industry. From
1570 to 1640, during the most severe period, Icelandic documents
record an exceptionally high number of weeks with coastal sea
ice. Except for a few years, fishermen from the Faeroe Islands
suffered from a lack of cod from 1615 to 1828--cod needs water warmer
than 3.6 degrees Fahrenheit to flourish. During the worst periods,
1685 to 1704, fishing off southwest Iceland failed totally.214 In
the very icy year of 1695, Norwegian fishermen found no cod off their
coast. Lamb calculates that the sea around the Faeroe Islands was
probably 7 to 9 degrees Fahrenheit colder than it has been over the
last century.215
The Mini Ice Age brought hard times to Southern Europe as well. Severe
winters and wet summers created shortages and famines in the south of
France and in Spain. The great variability in the weather made
agricultural output quite uncertain and contributed to a farming
crisis in the Iberian Peninsula. Although one cannot know for sure
that it was the weather, the whole of the Mediterranean littoral
declined economically in the seventeenth century.216
The cold had devastating effects elsewhere in the world. In China,
frosts killed the orange trees in Kiangsi province between 1646 and
1676.217 Per capita incomes fell as food prices rose. As already
mentioned, cooler weather brought an end to the Anastazi Indian pueblo
culture, as well as ending native American farming in the upper middle
west.
According to Nicolas Cheetham, in the second half of the thirteenth
century warfare in Greece and the necessity of keeping a large
military establishment under arms reduced its previous prosperity. War
does exact a high toll on economies, but it seems extraordinarily
coincidental that economic troubles occurred at the time Europe was
experiencing a deteriorating climate. In 1268, the King of Naples, in
gratitude for military service send wheat, barley and cattle to the
Peloponnese.218 Was this needed because of crop failures solely due to
military disruptions? Although not necessarily weather related, in
1275 Geoffroy de Briel, a major figure in medieval Greece, died during
a military campaign of dysentery, a disease often exacerbated by cold
wet conditions.219
Notwithstanding the cooling climate and the ravages of disease after
1300, European civilization recovered with the advent of the
Renaissance in the fifteenth century. This burst of cultural activity
represented a continuation, an expansion, and a deepening of the
artistic and intellectual activity of the High Middle
Ages. Ironically, the outpouring of art, science and literature that
made up the Renaissance may have been sustained by the plague. The
colder climate made agriculture more chancy, reduced the territory
available for farming, and cut yields. Yet without the one-third drop
in Europe's population caused by the Black Death, food supplies would
have been too meager to support a large artistic and cultured class
that promoted and supported the arts. The reduced agricultural output,
however, was still large enough to support the even more diminished
population. In China, which experienced a slower decline in numbers,
real wages fell and the people became increasingly impoverished.220
But in Europe, as a result of such a terrible death rate over a very
short period, real incomes for the survivors actually climbed.221
From around 1550 to 1700 the globe suffered from the coldest
temperatures since the last Ice Age. Lamb estimates that in the 1590s
and 1690s the average temperature was 3 degrees Fahrenheit below the
present. Grain prices increased sharply as crops failed. Famines were
common. The Renaissance had ended; Europe was in turmoil. The
Continent suffered from cold and rain, which produced poor growing
conditions, food shortages, famines and finally riots in the years
1527-29, 1590-97, and the 1640s. The shortages between 1690 to 1700
killed millions and were followed by more famines in 1725 and 1816.222
China, Japan, and the Indian subcontinent were also afflicted with
severe winters between 1500 and 1850-80. Despite the development of a
new type of rice that permitted the cultivation of three crops a year
on the same land--up from two--the population of China, as well as
that of Korea and the Near East, declined for two centuries after
1200, undoubtedly reflecting a deteriorating climate.223 The
abandonment of sea trade by the Chinese most likely resulted from
deteriorating weather and less population pressure.
Costs and Benefits of Efforts to Mitigate Warming
If mankind had to choose between a warmer or a cooler climate, humans,
most other animals and, after adjustment, most plants would be better
off with higher temperatures. Not all animals or plants would prosper
under these conditions; many are adapted to the current weather and
might have difficulty making the transition. Society might wish to
help natural systems and various species adapt to warmer temperatures
(or cooler, should that occur). Whether the climate will warm is far
from certain; that it will change is unquestionable. The weather has
changed in the past and will no doubt continue to vary in the
future. Human activity is likely to play only a small and uncertain
role in climate change. The burning of fossil fuel may generate an
enhanced greenhouse effect or the release into the atmosphere of
particulates may cause cooling. It may also be simply hubris to
believe that Homo Sapiens can affect temperatures, rainfall and winds.
As noted, not all regions or all peoples benefit from a shift to a
warmer climate. Some locales may become too dry or too wet; others
may become too warm. Certain areas may be subject to high pressure
systems which block storms and rains. Other parts may experience the
reverse. On the whole, though, mankind should benefit from an upward
tick in the thermometer. Warmer weather means longer growing seasons,
more rainfall overall, and fewer and less violent storms. The optimal
way to deal with potential climate change is not to strive to prevent
it, a useless activity in any case, but to promote growth and
prosperity so that people will have the resources to deal with any
shift.
It is much easier for a rich country such as the United States to
adapt to any long term shift in weather than it is for poor countries,
most of which are considerably more dependent on agriculture than the
rich industrial nations. Such populations lack the resources to aid
their flora and fauna in adapting, and many of their farmers earn too
little to survive a shift to new conditions. These agriculturally
dependent societies could suffer real hardship if the climate shifts
quickly. The best preventive would be a rise in incomes, which would
diminish their dependence on agriculture. Higher earnings would
provide them with the resources to adjust.
The cost of trimming emissions of CO2 could be quite high. William
Cline of the Institute for International Economics - a proponent of
major regulatory initiatives to reduce the use of fossil fuels - has
calculated that the cost of cutting emissions from current levels by
one-third by 2040 as 31/2 percent of World Gross Product.224 Given his
assumption that cutbacks of CO2 emissions are done by the least cost
methods and his bias, we can be certain that in the real world outlays
to slow warming would be considerably higher. In terms of the
estimated level of world output in 1992, his estimate would amount to
roughly $900 billion annually, an amount that could slow growth and
impoverish some who survive on the margin. These resources could be
better spent on promoting investment and growth in the poorer
countries of the world.
Should warming become apparent at some time in the future and should
it create more difficulties than benefits, policy makers would have to
consider preventive measures. Based on history, however, global
warming is likely to be positive for most of mankind while the
additional carbon, rain, and warmth should also promote plant growth
that can sustain an expanding world population. Global change is
inevitable; warmer is better; richer is healthier.
* A shorter version of this paper appeared as "Why Global Warming would
be Good for You" in the Winter
1995 issue of The Public Interest.
1Mitchell [1991]: 70-71.
2Committee on Science, Engineering, and Public Policy [1991]. Policy
Implications of Greenhouse Warming, p. 24.
3Healy [1994].
4Policy Implications of Greenhouse Warming, p. 18.
5Crowley & North [1991]:, 70.
6Crowley & North [1991]: 82-83.
7Levenson [1989,]: 25.
8Huggett [1991]: 74.
9Crowley & North [1991]: 117.
10Gore [1992]: 62 & 63.
11Schelling [1992]: 6.
12Folland et al. [1992]Climate Change 1992, Table C2, p. 152.
13Parry et al. [1988] as summarized in Kane [1991]: 7.
14Kauppi, et al. [1992]: 70-74.
15Letter to the editor, Wall Street Journal, February 16, 1990.
16Kane et al. [1991]
17Mendelsohn,[1994]: 753-771.
18Van Kooten [1990]: 704.
19Rind [1993]: 39-49.
20Frenzel [1993]: 7.
21Flohn [1983]: 404.
22Broccoli [1994]: 282.
23Giles[1990]: 23.
24Frenzel [1993]: 8.
25Crowley [1993]: 23.
26Frenzel [1993]: 10.
27Frenzel [1993]: 11.
28Crowley [1993]: 21.
29Crowley [1993]: 25.
30Rind [1993]: 41.
31Webb III, et al.. [1993]: 517
32Webb III, et. al. [1993]: 521.
33Webb III, et. al. [1993]: 523.
34Webb III, et. al. [1993]: 525.
35Morley and Dworetzky [1993]: 133-134.
36McGlone et al. [1993]: 311.
37McGlone et al. [1993]: 313.
38Genetic support for the 200,000 years ago estimate comes from
Vigilant,et al. [1991]: 1503-1507. The oldest human remains
found by archeologists are from 40,000 years ago.
39Crowley & North [1991]: 116.
40Crowley & North [1991]: 20.
41Ammerman and Cavalli-Sforze [1984]: 4.
42Boserup [1981]: 39-40.
43Lamb [1968]: 6.
44Wendland & Bryson [1974].
45Lamb [1968]: 12.
46Lamb (1988): 30.
47Ammerman & Cavalli-Sforza [1984]: 28.
48Ammerman & Cavalli-Sforza [1984]: 41.
49Cohen.[1977]: 1.
50Cohen [1989]: 56.
51Boserup [1981]: 34.
52Kremer [1993]: 683.
53Kremer [1993]: 681-716.
54Boserup [1981]: 36-37.
55Boserup [1981]: 38.
56Cohen [1989]: 112.
57Cohen [1989]: 113.
58Cohen [1989]: 114-115.
59Cohen [1989]: 119.
60Cohen [1989]: 119.
61Lamb (1988): 22.
62Giles, [1990]: 133.
63Claiborne [1970]: 324.
64Lamb [1982]: 120.
65Gore [1992]: 76.
66Lamb [1988]: 21.
67Giles [1982]: 115-116.
68Lamb [1977]: 270.
69Lamb [1977]: 133.
70Lamb [1968]: 61.
71Lamb [1982]: 131.
72Lamb [1982]: 131.
73Lamb [1968]: 61.
74Lamb [1968]: 62.
75Claiborne [1970]: 243.
76Ammerman & Cavalli-Sforze [1984]: 16.
77Ammerman & Cavalli-Sforza [1984]: 14-16.
78Ammerman & Cavalli-Sforze [1984]: 16.
79Lamb [1977]: 256.
80Lamb [1982]: 126.
81Lamb [1977]: 254.
82Limb [1982]: 124.
83Ko-chen [1973]: 228 & 229.
84Lamb [1977]: 251.
85Lamb [1977]: 389.
86Claiborne [1970]: 295.
87Lamb [1977]: note 1, p. 257.
88Lamb [1982]: Fig. 43, p. 118.
89Lamb [1988]: 22.
90Lamb [1988]: 23.
91Lamb [1977]: 419.
92Carpenter [1966]
93Lamb [1977]: 257.
94Lamb [1977]: 258.
95 Claiborne [1970]: 344-347.
96Lamb [1977]: 250.
97Lamb [1968]: 63.
98Lamb [1977]: 261.
99Cheetham [1981]: 18 & 20.
100Cheetham [1981]: 26.
101Keegan [1993]: 288.
102Lamb [1968]: 64.
103Lamb [1968]: 64-65.
104Lamb [1968]: 8.
105Lamb [1977]: 271.
106Bartlett [1993]: 162.
107Lamb [1977]:, 427.
108Lamb [1977]: 429.
109Lamb [1977]: 133.
110Lamb [1977]: 439.
111Lamb [1977]: 136.
112Stine [1994]: 546-549.
113Lamb [1977]: 435.
114Chu [1973]: 235.
115Chu [1973]: 237 & 238.
116Chao [1986]: 203.
117Lamb [1977]: Tables 17.3 and 17.4, pp. 443 & 447.
118Chu [1973]: 239-240.
119Keegan [1993]: 149.
120Bartlett [1993]: 155 from Hallam [1965]: 166.
121Bartlett [1993]: 162.
122Pirenne [n.d., c. 1938]: 59.
123Pirenne [n.d., c. 1938]: 12.
124Donkin, [1973]: 90.
125Bartlett [1993]: 48.
126Bartlett [1993]: Chapter 6.
127Bartlett [1993]: 48.
128Lamb [1977]: 437.
129Claiborne [1970]: 348-364.
130Pirenne [n.d.]: 76 and Bartlett [1993]: 114-115.
131Bartlett [1993]: 115.
132Cheetham [1981]: 37.
133Cheetham [1981]: 28.
134Cheetham [1981]: 85.
135Cheetham,[1981]: 35-36.
136Van Doren [1991]: 111.
137Gimpel [1983]: Table p. 68.
138Gimpel [1983]: 69.
139Bartlett [1993]: 2.
140Donking [1973]: 110-111.
141Pirenne [n.d.]: 50.
142Pierenne [n.d.]: 103.
143Lamb [1977]: 277.
144Lamb [1977]: 278-279.
145Lamb [1977]: 279.
146Keegan, [1993]: 291.
147Lamb [1968]: 8.
148Langer [1968]: 269.
149Langer [1968]: 206 & 286.
150Carruth [1993]: 161.
151Carruth [1993]: 134, 170, & 171.
152McNeill [1963]: 559.
153Lamb [1977]: 248.
154Lamb [1977]: 252.
155Lamb [1988]: 159.
156Lamb [1977]: 252.
157Lamb [1977]: 252.
158Chao [1986]: 219.
159Chao [1986]: 203.
160Chao [1986]: 195.
161Carruth [1993]: 151.
162Langer [1968]: 366.
163Kesseler [1994]: A17.
164Langer [1968]: 367.
165Claiborne [1970]: 288.
166McNeill [1963]: 559.
167Carruth [1993]: 151.
168Langer [1968]: 372.
169Deland [1987]: 9, 29-32.
170Lamb [1977]: 430-431.
171Cook et al. [1991): 1267.
172Lamb [1988]: 42.
173Lamb [1988]: 42.
174Lamb [1977]: 249.
175Lamb [1982]: 177.
176Gore [1992]: 78.
177Carruth [1993]: 142-143.
178Langer [1968]: 386.
179Carruth [1993]: 168.
180Lamb [1977]: 463.
181Lamb [1988]: 166.
182Lamb [1977]: Fig. 17.12, p. 450.
183Lamb [1977]: Fig. 17.13, p. 452.
184Lamb [1977]: 461-462.
185Lamb [1977]: 465-466.
186Lamb [1977]: 246.
187Lamb [1977]: 432.
188Fairbridge [1984]: 181-190.
189Lamb [1988]: 158.
190Lamb [1977]: 467.
191Lamb [1977]: 451-452.
192Lamb [1988]: 159.
193Monastersky [1994]: 310.
194Lamb [1988]: 159.
195Lamb [1977]: 7.
196Donkin [1973]: 91.
197Lamb [1977]: 454.
198Donkin [1973]: 90.
199Lamb [1977]: 266.
200Lamb [1977]: 7.
201Lamb [1977]: 454.
202Lamb [1977]: 471.
203Langer [1968: 317.
204Lamb [1982]: 189.
205Lamb [1988]: 32.
206Lamb [1988]: 36.
207Lamb [1977]: 456
208Lamb [1977]: 262.
209Lamb [1988]: 165.
210Lamb [1977]: 265 taken from Thorarinsson [1961].
211Gimpel [1983]: 150.
212Gimpel [1993]: 151.
213Pirenne [n.d.]: 134.
214Lamb [1988]: 153-54, 155.
215Lamb [1988]: 156 & 160.
216Lamb [1977]: 469.
217Lamb [1977]: 471.
218Cheetham [1981]: 98 & 99.
219Cheetham [1981]: 101.
220Kremer, [1993]: Appendix A, p. 714 & Chao [1986]: Table 9.2, p. 218.
221Rosenberg & Birdzell, Jr. [1986]: 54.
222Ladurie [1971]: 64-79.
223Carruth, [1993]: 166 & 168.
224Cline [1992]: 8.