Revised February 22, 1995





Global Warming:
A Boon for Humans and Other Animals*

Thomas Gale Moore
Senior Fellow
Hoover Institution

moore@hoover.stanford.edu


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¡
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
ÒThe Climatic Optimum,Ó 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, ÒThe Little Climate Optimum,Ó
Europe enjoyed the High Middle Ages and went on one of the largest
building sprees ever recorded.

Global Warming:
A Boon for Humans and Other Animals*

Climate extremes would trigger meteorological chaos Ñ 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. É 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 Ñ Senate Majority
Leader George J. Mitchell

Senator MitchellÕs 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 Ñ 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 Òthe most serious problem our
civilization faces.Ó3 In fact, he has styled those who dispute it as
Òself-interestedÓ 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 societyÕs 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 earthÕs surface has gone up by 0.5¡ Centigrade or
about 1¡ 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 Ñ before the rapid rise in CO2 Ñ 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 Ñ a key factor Ñ 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. Studies of carbon (CO and CO2) in the atmosphere show that at
times in the last 8,000 years the level has been substantially higher
than it is today and greater than it is likely to reach any time
soon.5 Although fluctuations in CO2 correlate with climate shifts, the
record cannot distinguish whether they followed the temperature
changes or preceded them.6 Theory suggests either is possible.

What is well known is that climate changes. The world has shifted from periods
that were considerably warmer Ñ during the Mesozoic era when the dinosaurs thri
ved the earth appears to have been about 18¡ Fahrenheit warmer than now Ñ to sp
ells that were substantially colder, such as the Ice Ages when huge glaciers su
bmerged much of the Northern Hemisphere.7 One paleoclimatologist estimated that
, during the Precambrian period, the polar regions were about 36¡F colder than
they are in the contemporary world.8  During the last interglacial, about 130,0
00 years ago or about when modern man was first exploring the globe, the averag
e temperature in Europe was at least 2¡ to 5¡F warmer than at present.9  Hippop
otamuses, lions, rhinoceroses and elephants roamed the English countryside. Are
as watered today by the monsoons in Africa and east Asia enjoyed even more rain
fall then. Indeed during the last 12,000 years, that is since the end of the la
st 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. Transition
s from a warm to a cold period or vice-versa were difficult for people who live
d in climates that were adversely affected yet benefited others who inhabited r
egions 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-Presid
ent 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. É Then, 40,000 years ago,
the so-called cultural explosion of tools and jewelry may have coincided with a
n unusually warm millennium in Europe.10

Expected Effects of Global Warming
Although most of the forecasts of global warmingÕs repercussions have been dire
, an examination of the likely effects suggests little basis for that gloomy vi
ew. Climate affects principally agriculture, forestry, and fishing. Manufacturi
ng, most service industries, and nearly all extractive industries are immune to
 climate shifts. Factories can be built in northern Sweden or Canada or in Texa
s, Central America, or Mexico. Banking, insurance, medical services, retailing,
 education and a wide variety of other services can prosper as well in warm cli
mates (with air-conditioning) as in cold (with central heating). A few services
, such as transportation and tourism, may be more susceptible to weather. A war
mer climate will lower transportation costs: less snow and ice will torment tru
ckers and automobile drivers; fewer winter storms Ñ bad weather in the summer h
as less disruptive effects and is over quickly Ñ will disrupt air travel; a low
er incidence of storms and less fog will make water transport less risky. Hotte
r temperatures will leave mining and the extractive industries largely unaffect
ed; 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 a
nd shorter seasons. Warmer conditions would mean that fewer northerners would f
eel the need to vacation in Florida or the Caribbean. On the other hand, new to
urist 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 Pre
sident of the American Economic Association asserted: ÒI conclude that in the U
nited States, and probably Japan, Western Europe and other developed countries,
 the impact on economic output [of global warming] will be negligible and unlik
ely to be noticed.Ó11  As modern societies have developed a larger industrial b
ase 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 comm
unications.

Only if warmer weather caused more droughts or lowered agricultural output woul
d even Third World countries suffer. Should the world warm Ñ and there is littl
e evidence or theory to support such a prognostication Ñ the hotter temperature
s would enhance evaporation from the seas, producing more clouds and more preci
pitation world-wide. Although some areas might become drier, others would becom
e wetter. Judging from history, Western Europe would retain plentiful rainfall,
 while North Africa and the Sahara might gain moisture. The Midwest of the Unit
ed States might suffer from less precipitation and become more suitable for cat
tle 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 la
titudes and much less change near the equator. Not only would this foster a lon
ger 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 war
m moist atmosphere on the equator drives storms and much of the earthÕs 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 intens
ify cloudiness. More cloud cover will moderate daytime temperatures while actin
g 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, i
ndeed 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 (n
ighttime) have climbed.

Warmer nighttime temperatures, particularly in the spring and fall, create long
er growing seasons, which should enhance agricultural productivity. Moreover, t
he enrichment of the atmosphere with CO2 will fertilize plants and make for mor
e vigorous growth. Agricultural economists studying the relationship of higher
temperatures and additional CO2 to crop yields in Canada, Australia, Japan, nor
thern Russia, Finland, and Iceland found not only that a warmer climate would p
ush up yields, but also that the added boost from enriched CO2 would enhance ou
tput by 17 percent.13 Researchers have attributed a burgeoning of forests in Eu
rope to the increased CO2 and the fertilizing effect of nitrogen oxides.14  Pro
fessor of Climatology Robert Pease writes that we may now be living in an Òiceh
ouseÓ 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 tempera
tures combined with more carbon dioxide will favor plant and crop growth and co
uld well provide more food for our burgeoning global populations. Geologic hist
ory reveals that warmer global temperatures produce more, not less, precipitati
on, a fact reflected by a recent scientific investigation that shows the Greenl
and ice-cap to be thickening, not melting. So much for the catastrophic predict
ion that our coastlines will be flooded by a rise in sea level from polar meltw
aters.15

The United States Department of Agriculture in a cautious report reviewed the l
ikely 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 Ñ such as substituting new varietie
s or alternative crops, increasing or decreasing irrigation Ñ concludes that:

The overall effect on the world and domestic economies would be small as reduce
d production in some areas would be balanced by gains in others, according to a
n economic model of the effects of climate change on world agricultural markets
. The model É estimates a slight increase in world output and a decline in comm
odity prices under moderate climate change conditions.16

Economists Robert Mendelsohn, William D. Nordhous, and Daigee Shaw researched t
he 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 p
er capita constant, they found that climate explained over two-thirds of the va
lue of crop lands. They concluded that for the lower-48 states, a rise in avera
ge temperature of about 5¡F and an 8 percent increase in rainfall stemming from
 global warming would, depending on their model, reduce the value of output bet
ween 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 Dep
artment 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 incr
ease in world temperatures. Canadian agricultural economists have examined the
effect of a doubling of CO2 on forestry production. They concluded that increas
ed carbon dioxide would boost productivity by 20 percent and that overall the h
arvest 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 inc
reased 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 warmin
g that might result from the addition of man-made greenhouse gases. [See Append
ix A on factors determining climate]. He also argues that the swiftness in warm
ing that would occur following increased levels of CO2 is unprecedented in hist
ory. On the latter point, he ignores other research, such as that by a German a
cademic, Burkhard Frenzel, who writes, ÒDuring the Holocene, very rapid changes
 of climate occurred. According to dendroclimatology [tree ring analysis applie
d to climatology], they often lasted about 20 to 30 years, or [were] even as br
ief as 2 to 3 years.Ó20  Other climate historians have found that a rapid cooli
ng in the late glacial period Ñ about 11,000 years ago Ñtook about 100 to 150 y
ears to complete and realized about 5¡F variation in temperature within 100 yea
rs, more than is being forecast for the next century.21

Although changes in the earthÕs orbital position may easily have played a role
in warming the earth after the last Ice Age, the effect was world-wide rather t
han concentrated in northern latitudes. Ice retreated in the Southern as well a
s 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, t
he effect on human beings would still tell us about the benefits or costs of cl
imatic change. Dr. Rind argues that greenhouse warming would raise winter as we
ll as summer temperatures while past warmings, driven by orbital mechanics, hav
e raised summer temperatures alone. Even though his models suggest that these p
ast warmings should have boosted temperatures solely in June, July, and August,
 the evidence, albeit a little tenuous for the three thousand year period of Cl
imatic Optimum, supports warmer winters. For the Little Climate Optimum that co
incided with the High Middle Ages, researchers have found strong support for mi
ld winters.
Moreover, at a recent conference the Russians have put forward the hypothesis t
hat 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, dis
puted by some, is based on a large number of past shifts in average weather con
ditions dating back millions of years. The Russians contend that the climate mo
dels overstate the amount of temperature change at the equator and understate i
t at the poles.

Measurement of Human Well-being
Since statistics on the human condition are unavailable except for the most rec
ent centuries, I shall use indirect methods to demonstrate the influence of cli
mate on manÕs well-being. A growth in the population, major construction projec
ts, a significant expansion in arts and culture, all indicate that society is p
rosperous. If the population is expanding, food must be plentiful, disease cann
ot be overwhelming, and living standards must be satisfactory. In addition, if
building, art, science, and literature are vigorous, the civilization must be p
roducing enough goods and services to provide a surplus available for such acti
vities. Renaissance Florence was rich; Shakespeare flourished in prosperous Lon
don; wealthy Vienna provided a welcome venue for Haydn, Schubert, Mozart, and B
eethoven.

Clearly climate is far from the only influence on manÕs 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 catastrop
hic. 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, i
mpelled 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 con
tagion. Moreover, a shift towards a poorer climate can lead to hunger and famin
e, which make disease more virulent.

Throughout history climatic changes probably forced technological innovations a
nd 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 grou
ps of hominoids isolated and subject to pressures to adapt to new weather condi
tions. These shifts, especially to the more adverse conditions created by the s
pread of extreme cold, would put strong selection pressure on the human forebea
rs that ultimately led to modern man. Even after Homo Sapiens started spreading
 across the earth, climate shifts fostered new technologies to deal with change
d circumstances.

The influence of climate on human activities has declined with the growth in we
alth 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 so
il. A series of bad years can be devastating. If, as was the usual case until v
ery 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 shor
t distance away. Thus variation in the weather for early man had a more profoun
d influence on his life and death than do fluctuations in temperature or rainfa
ll in modern times when economies are more developed. Since the time of the Ind
ustrial Revolution, climate has basically been confined to a minor role in huma
n activity.

Climate History
Since its origins, the earth has experienced periods significantly warmer than
the modern world Ñ some epochs have been even hotter than the most extreme pred
ictions of global warming Ñ and times much colder than today. TodayÕs cool temp
eratures are well below average for the globe in its more than four billion yea
r 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 te
mperatures 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, howe
ver, with a relationship roughly corresponding to that of the Global Climate Mo
dels.25 During interglacial periods high latitudes enjoyed temperatures that we
re about 5¡ to 11¡F warmer than today.26 Middle latitudes experienced temperatu
res only about 4¡ to 5¡F 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, exce
pt for the area around the Caspian Sea basin, were 1¡ to 3¡F higher and rainfal
l more plentiful than today.27

This historical evidence is consistent with only some of the forecasts of the c
omputer climate models. Most climate estimates indicate that a doubling of CO2
would generate greater rainfall in middle latitudes, and history shows that war
m climates do produce more wet weather.28 As has been found in the historical r
ecord, land temperatures should increase more than water thus strengthening mon
soons. The models also predict that sea-surface temperatures in the tropics wou
ld be higher with increased CO2 but evidence from the past evinces no such rela
tionship.29

Carbon dioxide concentrations may have been up to sixteen times higher about 60
 million years ago without producing runaway greenhouse effects.30 Other period
s experienced two to four times current levels of CO2 with some warming. Scient
ists 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 milli
on to about 75,000 years ago, CO2 levels were markedly higher than now.

The prevailing view among climatologists is that the Climatic Optimum Ñ 9,000 t
o 4,000 years ago Ñ resulted from orbital mechanics which increased summer radi
ation 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 coo
ler 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, th
e climate was drier than today. Anatolia, Northwestern Africa, parts of China a
nd northern Japan experienced less rainfall.33 By 4000 b.c., however, a slacken
ing of the trade winds had produced warmer Atlantic ocean water off northwester
n Africa, and as a consequence the Middle East, including Greece and modern Tur
key, were enjoying more reliable rain.

If orbital variations produced the Climatic Optimum, the Southern Hemisphere sh
ould have been cooler. Between 10,000 b.c. and 7000 b.c., however, winter tempe
ratures (June, July, August) below the equator warmed to higher levels than now
 while summer temperatures (December, January, February) were cooler than the m
odern world.34 Rainfall over South America, Australia and New Zealand apparentl
y was lighter than the present. Although the Southern Hemisphere moved out of t
he 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 befor
e the present Ñ somewhat earlier than they did in the Northern Hemisphere.36 Te
mperatures appear to have been falling over the last 7,500 years. By 1500 b.c.,
 the climate was quite similar to todayÕs.37

Whether the whole globe warmed or not during the period 7,000 to 4,000 years ag
o 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, th
en comparing how people survived in that portion of the globe provides informat
ion 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 ag
o the extent of ice coverage reached a maximum, followed around 130,000 years b
efore the present (ybp) by a rapid deglaciation.39 The warm interglacial era, d
uring which temperatures may have exceeded those forecast under a doubling of g
reenhouse gases, lasted about 15,000 years until the onset of renewed glaciatio
n 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 prev
ious 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 t
odayÕs. Herds of large animals such as bison, mammoths, and elk roamed a largel
y treeless savanna in Europe. These beasts made easy prey for human hunters tha
t enjoyed as a consequence a rich diet of wild animal meat plus, in season, loc
al 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 t
he Bering Strait but then was dry land. Most archaeologists date the first arri
vals 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 year
s ago when the glaciers covering much of North America, Scandinavia and norther
n Asia began to retreat to approximately their current positions. In North Amer
ica the glacial covering lasted longer than in Eurasia because of topographic f
eatures that delayed the warming. Throughout history warming and cooling in dif
ferent regions of the world have not been exactly correlated because of the inf
luence of oceans, mountains, prevailing winds, and numerous other factors. Neve
rtheless, across the Northern Hemisphere large temperature shifts have occurred
 roughly together Ñ perhaps in some areas they have lagged other zones by a cen
tury or more. The correspondence between warming and cooling in the Northern He
misphere and that in the Southern is less well known and may be less well corre
lated because of the predominance of water south of the equator and the existen
ce of Antarctica.

Human progress, a few improvements in hunting tools and some cave art, was incr
edibly slow during the Ice Age Ñ a period whose length dwarfs the centuries sin
ce. Over the last 12 millennia of interglacial warmth, however, modern man has
advanced rapidly. The growth in technology and living standards required a clim
ate that was more hospitable than existed throughout that frozen period.

During the last Ice Age humans survived through hunting and gathering. Initiall
y archeologists believed that these tribes, which typically consisted of 15 to
40 people, eked out a precarious existence.41 Many modern archeologists, howeve
r, feel, based on studies of the few bands of hunter-gatherers that survived in
to the twentieth century, that they normally found plentiful foods in their for
ays and would rarely have been hungry. Modern primitive people, however, may no
t have been typical of earlier groups. The ones that did face food pressures wo
uld have adopted farming while those that found plentiful supplies in their env
ironment 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 t
o 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 develo
ped in the Middle East. For about 3,000 to 4,000 years the globe enjoyed what h
istorians of climate call the Climatic Optimum period Ñ a time when average wor
ld temperatures Ñ at least in the Northern Hemisphere Ñ were significantly hott
er than today. At its height between 4000 b.c. and 2000 b.c., H.H. Lamb, a lead
ing climate historian, judges that the world was 4¡ to 5¡ Fahrenheit warmer tha
n the twentieth century.43  During the relatively short period since the end of
 glaciation the climate has experienced periods of stability separated by Òabru
pt transition.Ó44 Lamb calculates that at its coldest, during the Mini Ice Age,
 the temperature in central England for January was about 4.5¡F colder than tod
ay.45 He also concludes that in the central and northern latitudes of Europe du
ring 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.4
6 On the other hand, cooler periods usually suffered from more swampy condition
s because of less evaporation.

If modern humans originated 200,000 years ago, why did they not develop agricul
ture for the first 190,000 years? Even if Homo Sapiens Sapiens originated only
40,000 years ago, people waited 30,000 years to grow their first crops Ñ an inn
ovation 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 Ñ a coinciden
ce? The evidence suggests that from 11,000 to 9,000 years ago the climate becam
e 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 bec
ause the warmer, wetter weather made farming possible. From its origins around
8000 b.c., agriculture spread northward, appearing in Greece about 6000 b.c., H
ungary 5000 b.c., France 4500 b.c. and Poland 4250 b.c.48 Is it chance that thi
s northward spread followed a gradual warming of the climate that made agricult
ure more feasible at higher latitudes?

As Anthropologist Mark Cohen writes, ÒIf, as the archaeological record indicate
s, hunting and gathering was such a successful mode of adaptation over such a l
ong period of time, and if most human populations are as conservative as anthro
pologists have observed them to be, we are faced with answering the question wh
y this form of adaptation was ever abandoned.Ó49 He gives estimates of the effi
ciency of hunting and gathering that indicate that the latter was more efficien
t than farming Ñ at least for large game. He reports that when large animals ar
e available, hunting brings 10,000 to 15,000 kilocalories per hour of hunting.
However, if large animals are unavailable Ñ because the environment is poor or
because they have all been killed Ñ hunting of small game will return only a fe
w 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 2,00
0 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 economi
cal method of subsistence, but if these beasts are exterminated or if the human
s move to areas without such species, domestication of plants and animals can p
roduce more food for the effort than any other strategy.

Moreover hunter-gatherers can only survive if the density of their population i
s low. Too many mouths would strain the environment and preclude survival. Once
, humans developed farming which could support larger families and a denser pop
ulation, however, the number of people did explode. Primitive tribes, dependent
 on hunting, scavenging, and collecting edibles to survive, had to hold their p
opulations below what they would individually have preferred or nature kept the
m in check through periodic food shortages. A number of twentieth century hunte
r-gatherers have practiced infanticide and induced abortions to restrict the nu
mber and spacing of their children.51 Constant travel by nomads may increase in
fant mortality, maternal mortality and produce more miscarriages than a sedenta
ry life and thus have kept the numbers in check. In any case farming solved a m
ajor problem for primitive peoples. Once people settled down into fixed abodes,
 the population apparently ballooned.

Although many people view the current worldÕs 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 gr
eatly Homo Sapiens  fitness. This essay is not the place to discuss the capacit
y of the globe to sustain the number of people expected to populate the world i
n the next century, but certainly anything that produced greater numbers of peo
ple 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 worldÕs population may have measured only about 3
million.52 Fifteen thousand years later, around 10,000 b.c., the total had grow
n 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 Ñ although in most cases these were region
al 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, unt
il the Industrial Revolution, existing technology limited the size of the popul
ation.53 As innovators discovered new techniques and invented new tools, more p
eople could be fed and housed and the population expanded. Moreover, the greate
r 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 t
echnique or device and that the probability of being an innovator was independe
nt of the size of the population. Therefore the number of inventions would be p
roportional to the number of people. Thus as the world population expanded Ñ sl
owly at first Ñ the rate of technological innovation escalated and hence the ra
te of growth of the population that could be sustained. Only in recent times ha
s technological change become so rapid that it has run ahead of population grow
th, leading to a rising standard of living, which in turn has reduced the birth
 rate.

KremerÕs hypothesis signifies that for most of history the rate of population g
rowth should be proportional to the size of the population. To link his model a
nd data with climate change, I started with his estimate of the worldÕs people
in 10,000 b.c. and calculated the rate of growth of the population over the nex
t 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 reveal
ed eras in which the number of humans has expanded faster than predicted and pe
riods during which the worldÕs people has grown more slowly. The chart then sho
ws the centuries in which the growth rate of the globeÕs populace has exceeded
or fallen short of the rate expected under this simple model. As can be seen, w
arm periods have done considerably better than cold periods in terms of human e
xpansion. The warmest period since the end of the last Ice Age produced the hig
hest rate of population growth compared to what would have been expected Ñ in t
his era agriculture was spreading. Moreover, the Mini Ice Age, which saw the co
ldest temperatures in the last 10,000 years, underwent the slowest relative pop
ulation expansion. This chart demonstrates that mankind has prospered in warm p
eriods 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 Ñ sk
eleton 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, whi
le 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 est
imated that on average they could have given birth to less than five live babie
s, assuming that they bore a child every 22 months.55 An infant and childhood m
ortality rate of about 60 percent would have kept the population stagnant.

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].

Table 1 below shows some relevant data. The warmest periods, the Neolithic, Bro
nze 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 particularl
y notable. Moreover, the rise in life expectancies during the warm period coul
d easily explain the population explosion that took place during that period.

Good childhood nutrition is reflected in taller adults. Skeleton remains colle
cted 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 ce
ntimeters (two inches).56  The shorter stature came at the end of the Ice Age w
hen large animals were disappearing. Some archaeologists have found that averag
e age of death for adults also declined during this transitionary period.57 Stu
dies of bone chemistry from Middle Eastern skeletons indicate a reduction in me
at consumption. The new diet although more dependent on grains, fruits, and veg
etables must have been less nutritious than the old. As large game animals disa
ppeared with the end of the Ice Age, humans widened the variety of plants in th
eir diet, increasingly consuming vegetable matter that they had ignored for tho
usands 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 dec
line 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 tho
se of North American aborigines it seems safe to conclude that health and nutri
tion were declining before the advent of agriculture and that it may be that ag
riculture 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 skel
eton 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 agricul
ture led to shorter people, a few have found the reverse. In Israel, for exampl
e, 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 nutr
itious with the shift from large animal hunting to food production but that its
 quality initially exceeded that of medieval Europe. Table 2 on heights, howeve
r, 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 wa
rm 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
¡F hotter, about the average of the various predictions for global warming afte
r a doubling of CO2.61 Although the climate cooled a bit after 3000 b.c., it st
ayed relatively warmer than the modern world until sometime after 1000 b.c., wh
en 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 le
ss cloudy and the days sunnier.

Notwithstanding the less stormy weather, rainfall was more than adequate to pro
duce widespread forests. Western Europe, including parts of Iceland and the Hig
hlands of Scotland, was mantled by great woods.62 The timber, until average tem
peratures 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 Amer
ica and oak and hazel in Europe. These species have never regained their once d
ominant position in Europe and America. Not only did Europe enjoy a benign clim
ate with adequate rainfall, but the Mediterranean littoral, including the Middl
e East, apparently received considerably more moisture than it does today.63 Th
e Indian subcontinent and China were also much wetter during this Optimal perio
d.64

As a Senator, Al Gore, writing on the prospect of further global warming and it
s 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: fo
r most of that period the earth was cooling, not warming! His chart actually im
plies that further cooling would be undesirable. In fact, history demonstrates
and climatology attests that warming should drive the monsoon rains that origin
ate 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.6
7 The water level in Lake Chad about 14¡ north of the equator in central Africa
 was some 30 to 40 meters, that is, 90 to 125 feet higher, than it is today, in
dicating much greater precipitation. Ruins of ancient irrigation channels in Ar
abia, probably from the warmest millennia, derived their water from sources wel
l 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 abunda
nce of life disappeared.

Research has shown, however, that some portions of the globe did suffer from dr
ier conditions. The Caspian Sea may have been at its lowest level in over 80,00
0 years during the warmest recent period Ñ 4,000 to 6,000 years ago Ñ when it w
as some 20 to 22 meters Ñ 66 to 72 feet Ñ below its modern height.69

The Southern Hemisphere seems to have flourished as well during the warm millen
nia after the most recent Ice Age. Professor Lamb reports that the southern tem
perate zone enjoyed both warmer weather and more moisture than it does currentl
y.70 Scholars have found that Australia was consistently wetter than today in b
oth the tropical and temperate regions.71 Since the end of that epoch, the grea
t 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 subt
ropical 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 t
wentieth century.73 Even Antarctica enjoyed warmer weather, about 4¡ to 5¡F hig
her, 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 Neverth
eless, the basic ice sheet remained intact.

As already mentioned, the invention of agriculture coincided with the end of th
e last Ice Age and the melting of the glaciers. Archaeologists have found the e
arliest evidence for husbandry and farming in Mesopotamia around 9000 b.c.75  A
s the earth warmed, the Middle East became wetter and the Iranian plateau shift
ed from an open dry plain with roving bands of game to a more wooded environmen
t 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 coincid
ence in time and the forcing nature of climate change suggest that the warmer w
etter weather, especially in the mountains, may have encouraged new techniques.


The transition from the Ice Age to a warmer climate that led eventually to agri
culture is best documented in Europe. During the cold period, most of Europe wa
s 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. Tho
se located near the seas or large rivers found seafood a plentiful source of su
bstance. On the other hand, people who made their living at the edge of the oce
an faced seas that were rising about 3 feet each century and which often drowne
d 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 emp
loyment of agriculture arose in the Middle East. Planting of wheat and barley b
egan in southwest Asia between 8000 b.c. and 7000 b.c. In north ChinaÕs 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 t
he 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 docum
ented 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 spec
ies 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 im
plies the cultivation of plants after 3500 b.c. Domestication of cattle occurre
d in the Sahara about 8,000 years before the present.77

As Professors Ammerman and Cavalli-Sforza put it, ÒOne of the few variables tha
t would seem to be shared is timing: early experiments at plant domestication o
ccurred in southwest Asia, east Asia, and Central America during the period bet
ween 8000 b.c. and 5500 b.c.Ó78 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 manÕs in
volvement with nature. Prior to this humans simply took what nature offered. Pe
ople hunted or scavenged the local animals that happened their way. Women gathe
red fruits and vegetables that grew wild in their territory. With farming and h
erding, mankind, for the first time, began to modify his environment. Humans de
termined what would be grown, which plants would survive in their gardens, whic
h animals would be cultivated and bred, and which would be shunned or eliminate
d. 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 i
mportant innovation in human existence. Prior to this change, humans lived in s
mall 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 break
able, was not part of their culture. Any musical instruments must have been sma
ll and portable. Many small children would have been a hindrance as would elder
ly feeble individuals. Such small groups would have had little opportunity to d
evelop specialization. Virtually all males must have participated in the hunt w
hile all females, not giving birth or caring for infants, must have helped gath
er edibles. These tribal or family groups could not have supported elaborate pr
iesthoods, bureaucratic governmental structures, or even people who specialized
 in artistic, cultural or intellectual activities. As a consequence these socie
ties were probably quite egalitarian with only a few, such as the chief or elde
r and perhaps a medicine man, that stood out from the rest.

The development of agriculture and the establishment of fixed communities led t
o a population explosion and the founding of cities. Agricultural societies pro
duce enough surplus to support such urban developments, including the evolution
 of trades and new occupations. A large community could afford to have speciali
sts who made farm tools, crafted pots, and traded within the village and betwee
n the locals and outsiders. The people in today's Palestine established the fir
st known city, Jericho, and thus the first step towards specialization Ñ which
lies at the heart of economic advancement Ñ around 8000 b.c.79

Farming required the development of property rights in lands, although initiall
y pastures may have been held in common. Even though in the beginning farm hold
ings were probably fairly equally distributed, over time some families must hav
e acquired larger holdings than others. This increase in income inequality may
offend modern sensibilities, but it provided a major benefit. A wealthy class o
r a rich ruler could afford to maintain individuals who would create desirable
objects, such as art, elaborate pots, and musical instruments, and who could re
cord eclipses, star movements or trade with other centers.

ManÕs taming of animals and plants represents a movement towards establishing p
roperty rights. In a hunter-gathererÕs world no one owns the wild beasts or the
 fruit and grains until they are collected. This can work satisfactorily only a
s 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 Ñ
 privatization of animals and plants Ñ became the answer to over hunting and ov
er grazing.

In Europe, the Optimum period produced an expansion of civilization with the co
nstruction of cities and a technological revolution. The Bronze Age replaced th
e New Stone Age.80 The more benign climate with less severe storms encouraged t
ravel by sea.

Trade flourished during this warm period. People from ancient Denmark shipped a
mber 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 an
d southern Italy. Astrological monuments built around this time, such as Stoneh
enge, 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 Brenne
r Pass, the dominant link between northern and southern Europe. Northern Europe
ans exchanged tin for manufactured bronze from the south. Alpine people mined g
old and traded it for goods crafted around the Mediterranean. Baltic amber foun
d its way to Scotland.

During the warm period prior to 3000 b.c., China enjoyed much warmer temperatur
es. In particular midwinters were as much as 9¡F 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 nort
h Ñ about 3¡ in latitude Ñ than is now possible.83  Chinese archaeologists have
 found evidence in a district near Sian that the climate 5,000 to 6,000 years a
go was warmer and wetter than the present.

Prior to around 2500 to 1750 b.c., northwestern India, which is now very dry, e
njoyed greater rainfall than it does in the twentieth century.84  In the Indus
Valley, the Harappas created a thriving civilization that reached its apogee du
ring the warmest and wettest periods, when their farmers were growing cereals i
n what is now a desert.85 The area was well watered with many lakes. This civil
ization disappeared around 1500 b.c. at a time when the climate became distinct
ly 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 human
s 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 o
cean flooding of coastal communities. A few times each century, people were for
ced 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 worldÕs climate and, in particular, the European
 varied between periods of warmth and cold. Based on the height of the upper tr
ee lines in middle latitudesÕ mountains, the temperature record following the p
eak warm period around 5000 b.c. demonstrates a more or less steady decline rig
ht up to the 20th century.88  As mentioned above, tree ring data for New Zealan
d 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 prev
ious 4,500 years. However, the climate became more clement and somewhat more st
able 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 declin
ed; the Roman Empire spread its authority through much of what is now Europe, t
he 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 Archaeolo
gists have also found evidence that Greeks adopted warmer clothing after 1300 b
.c. The population living in the Alps diminished sharply with the cooler weathe
r and mining ceased. Classical historian Ray Carpenter attributes a depopulatio
n 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 fro
m remains of ancient harbors at Naples and in the Adriatic which are located ab
out one meter (three feet) below current water levels.93 Further support for lo
wer sea levels has been found on the North African coast, around the Aegean, th
e Crimea, and the eastern Mediterranean. Lower oceans imply a colder world lead
ing 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 a
bout three feet above current elevations. The ancient harbors of Rome and Raven
na from the time of the Roman Empire are now located about one kilometer from t
he 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, indic
ating a world-wide warming.

Changes in the climate in Eurasia appear to have played a major role in the wav
es 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 beg
an to warm and conditions in central Asia improved apparently leading to a popu
lation explosion.95 These people, needing room to expand and a way to make a li
ving, invaded the more civilized societies of China and the West. The medieval
warmth from around 1000 a.d. to 1300 also seems to have also triggered an expan
sion from that area. During this second optimum period, the homeland of the Kha
zars 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 invad
e 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 we
re often crippled with arthritis while their predecessors during the warmer Bro
nze Age period suffered little from such an affliction. Although some archaeolo
gists have attributed the difficulties of the dark age people to harder work, t
he cold wet climate between 600 and 1000 a.d. may have fostered such ailments.9
8

During the centuries after the fall of the Roman empire and with the deteriorat
ion of the climate, Greece languished. In 542 a.d., the population was decimate
d by the plague, aggravated by cold damp conditions; the Black Death struck aga
in between 744 and 747.99 As a consequence the number of people was sharply red
uced. Greece was partially re-populated in the ninth and tenth centuries when t
he Byzantine Emperors brought Greek settlers from Asia Minor back into the area
. For the first time in centuries Greek commerce and prosperity returned Ñ prob
ably 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 wa
s 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 Mediterr
anean.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 whol
e of the midlands Ñ all of which became a Danish overseas kingdom by the mid-te
nth century. At the same time, they stormed France and the king had to cede the
m 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 civiliz
ation prospered. This Little Climate Optimum generally displays, although less
distinctly, many of the same characteristics as the first climate optimum.102 V
irtually 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. C
hina 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 A
mericas, 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, fro
m 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 geographe
rs 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 t
oday carry too little water to turn them attest to greater rainfall. Although E
ngland 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 ce
ntral Europe comes from the period in which German colonists founded villages.
As average temperatures rose people established towns at higher elevations. Ear
ly 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 abo
ve 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 o
f 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 centur
y but the population enjoyed mild wet winters. In the Mediterranean it was mois
t as well with summer thunderstorms frequently reported.108

Studies have shown that some areas became drier during these centuries. In part
icular, the Caspian Sea was apparently four meters Ñ over 13 feet Ñ 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 ÒGolden StateÓ suffered from extreme droughts from around 900 to 1100 and a
gain from 1210 to 1350 while the tip of South America during the first 200 year
s 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 p
arts 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 cli
mate was somewhat warmer than normal in the ninth, tenth, and eleventh centurie
s, 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 o
f the thirteenth century was quite clement and very cold weather returned in th
e fourteenth century.115  Another historian found on the basis of records of ma
jor floods and droughts that between the ninth and eleventh century China suffe
red much fewer of these calamities than during the fourteenth through the seven
teenth.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 reco
rd, the tenth century springs were warmer than normal; in the eleventh century
they were cooler; the twelfth century experienced the latest springs; the thirt
eenth 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 e
ighth or ninth centuries and continued into the eleventh. The warm climate move
d 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 s
pread 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 Òdark agesÓ
 the population of Europe had been relatively stagnant. Towns shrank to a few h
ouses clustered behind city walls. Although we lack census data, the figures fr
om 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 populati
on soared. It might be more enlightening to ask why the population remained sta
gnant for so long. As John Keegan, the eminent military historian put it: ÒThe
mysterious revival of trade between 1100 and 1300, itself perhaps due to an equ
ally 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 mo
ney economy won the funds to protect themselves from dangers beyond the wallsÓ.
119

Although it is impossible to document it, the change in the climate from a cold
, wet one to a warm, drier climate Ñ it had more rainfall, but more evaporation
 reduced bogs and marshy areas Ñ 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 undo
ubtedly took many small children and the elderly Ñ 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 i
n 1189 that Òbecause their own marsh had dried up, they converted them into goo
d and fertile ploughland.Ó120 Moreover, prior to the twelfth century German set
tlers on the east side of the Elbe frequently named their towns with mar, which
 meant marsh, but later colonists did not use that suffix. BartlettÕs explanati
on is that the term had gone out of use, but an alternative one is that the war
mer climate had dried up the marshes.121

With a more pleasant climate people spent longer periods outdoors; food supplie
s were more reliable. Even the homes of the peasants would have become warmer a
nd less damp. The draining or drying up of marshes and wetlands reduced the bre
eding grounds for mosquitoes that brought malaria. In all the infant and childh
ood mortality rate must have fallen spawning an explosion in population.

>From the ninth century, with a climate still quite cool, to the eleventh, medie
val Europe was almost totally agricultural. The few cities that existed consist
ed 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.1
22 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 w
hat 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 a
lmost entirely self-sufficient. The serfs that tilled the land had inherited ri
ghts to enough land to sustain a family. Typically the older son would follow h
is father. Any other sons either joined the priesthood, became monks, vagabonds
, or in later centuries, mercenaries. Given the cold climate before the elevent
h century, the lack of medical care, and a restricted diet fostering poor nutri
tion, few babies lived to adulthood. The problem of an excess of labor was, the
refore, nonexistent. The truth is that the population was growing so slowly tha
t a labor shortage persisted and the feudal nobility established laws prohibiti
ng 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 wit
h 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 mouth
s exceeded farm output: food prices rose while real wages fell. Farmers, howeve
r, did well with more ground under cultivation and low wages payable to farm ha
nds.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 li
fe expectancy required parents to be flexible in designating their heirs. Rober
t 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 c
hildren, especially the men, had to find new opportunities. The crusades furnis
hed an occasion for both the sons of serfs and of the nobility to enrich themse
lves and even to find new land to cultivate. Others moved to virgin territory i
n eastern Europe, Scandinavia or previously forested or swampy areas.126  The F
ranks and Normans launched invasions of England, southern Italy, Byzantine Gree
ce, and the eastern Mediterranean. In 1130 the Tancred de Hauteville clan, a no
table example, founded the Kingdom of Sicily. This family, a classic case of an
 Òover-breeding, land-hungry lesser nobility,Ó consisted of 12 sons from two mo
thers who, recognizing that their Norman property was inadequate, invaded south
ern 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 Europ
e than in southern. The rapid rise in numbers north of the Alps fits the improv
ed 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 lan
ds typically flocked to towns and urban centers, becoming laborers, artisans, o
r traders. Both those who moved to the new cities and those who founded colonie
s were legally freed of feudal obligations. This new liberty, making risk takin
g and innovation possible, was essential for those in commerce.

The warmth of the Little Climate Optimum made territory farther north cultivabl
e. 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 centu
ries. Greenland was 4¡ to 7¡F warmer than at present and settlers could bury th
eir dead in ground which is now permanently frozen. Scotland flourished during
this warm period with increased prosperity and construction.128 Greater crop pr
oduction 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 V
iking explorations and led to the foundation of colonies in Iceland and Greenla
nd.

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 wo
men from these areas to places east of the Elbe, into Wales, Ireland, and Scotl
and. Flemish dikes to hold back the sea date at least from the early eleventh c
entury. Although Pirenna and Bartlett attribute them to attempts to reclaim lan
d 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 ear
liest texts setting out rights on the reclaimed land fail to mention any obliga
tion to maintain the dikes, although later ones spell out the requirement, sugg
esting 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 cl
ose to the sea of the Britons, because the sea had taken and overwhelmed their
land É after they had failed to find a place to live in Ñ for the sea had overf
lowed the coast lands, and the mountains [sic] were full of people so that it w
as not possible for everyone to live together there because of the multitude of
 the people and the smallness of the land É131

In addition to the land north of the Alps, the warm rainier climate benefited s
outhern Europe, especially Greece, Sicily and southern Italy. All of the Mezzog
iorno in the Middle Ages did well.132 Nicolas Cheetham, a former British diplom
at who authored a recent book on Mediaeval Greece, reports that during the firs
t half of the thirteenth century, the plains and valleys of the Peloponnese wer
e fertile and planted with a wide variety of valuable crops and trees. They pro
duced wheat, olives, fruits, honey, cochineal for dyeing, flax for the linen in
dustry and, silk from the mulberry trees. The wealthy in Constantinople prized
highly the wines, olives, and fruit from Greece. ThessalyÕs grain fed the Byzan
tine Empire.133  Patras exported textiles and silk of very high quality. Extens
ive forests, which were full of game, supplied acorns for hordes of pigs. Herde
rs raised sheep and goats in the mountain pastures, while in  the valleys farme
rs 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 thri
ved, engendering great tolerance for contending religions.135 Christian communi
ties survived and prospered in Moslem Cairo and Cordova. The Rulers of Byzantin
e countenanced the Moslems and often preferred them to ÒbarbaricÓ Westerners.

In the West, Charlemagne, creator of the Holy Roman Empire, may have inaugurate
d the era of the High Middle Ages while Dante, writing The Divine Comedy, may h
ave closed it. In A History of Knowledge, Charles Van Doren contended that: Òth
e É three centuries, from about 1000 to about 1300, became one of the most opti
mistic, prosperous, and progressive periods in European history.Ó136 All across
 Europe, the population went on an unparalleled building spree erecting at huge
 cost spectacular cathedrals and public edifices. Byzantine churches gave way t
o Romanesque, to be replaced in the twelfth century by Gothic cathedrals. Durin
g this period construction began on the Abbey of Mont-St-Michel (1017), St. Mar
ks in Venice (1043), Westminster Abbey in London (1045), the Cathedral of our L
ady in Coutances (1056), the Leaning Tower at Pisa (1067), the Cathedral of San
tiago de Compostela in northern Spain (1078), the Cathedral of Modena (1099), V
Žzelay Abbey in France (1130), Notre-Dame in Paris (1163), Canterbury in Englan
d (1175), Chartres (1194), RouenÕs cathedral in France (1201), BurgosÕ cathedra
l 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 to
day were started by the optimistic populations of the eleventh through the thir
teenth centuries, although many were not finished for centuries. In southern Sp
ain, the Moors laid the cornerstone in 1248 for perhaps the worldÕs most beauti
ful fortress, the Alhambra. The Franks founded Mistra near ancient Sparta in th
e middle of the thirteenth century.

It took a prosperous society to launch such major architectural projects. In Eu
rope, building the cathedrals required a large and mostly experienced pool of l
abor. During the week of June 23 to June 29, 1253, the accounts of the construc
tion at Westminister Abbey, for example, showed 428 men on the job, including 5
3 stonecutters, 49 monumental masons, 28 carpenters, 14 glassmakers, 4 roofers,
 and 220 simple laborers.137  Nearly half of all workers were skilled specialis
ts. Even during the slowest season in November, the Abbey employed 100 workers,
 including 34 stonecutters. Masons and stonecutters earned the highest wages an
d usually hired a number of workers as assistants. Master craftsmen moved from
job to job around Europe without any concern about national borders Ñ the first
 truly European Community. Historians have found than only 5 to 10 percent of t
he masons and stonecutters were local people, but 85 percent of the men who qua
rried the stones Ñ an unhealthy and arduous job Ñ were from the vicinity.138 Th
us during these centuries a European-wide market flourished in skilled craftsme
n.

Economic activity blossomed throughout the continent. Banking, insurance, and f
inance developed; a money economy became well established; manufacturing of tex
tiles expanded to levels never seen before. Farmers were clearing forests, drai
ning swamps and expanding food production to new areas.139 The building spree m
entioned above was made possible by low wages resulting from a population explo
sion 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 w
ood were reconstructed in stone between the twelfth and fourteenth centuries.14
0 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 reli
gious 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 br
ought 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 f
acilitate the buying and selling of all types of goods but also functioned as m
ajor money markets and clearing houses for financial transactions. The fourteen
th century saw the waning of these enterprises probably because the weather bec
ame so unreliable and poor that transport to and from these locations with grea
t stocks of goods became impractical. Belgian historian Henri Pirenne attribute
s 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 diffic
ult.142 Wet roads were muddy rendering it arduous to transport heavy goods. Cro
p failures made for famines and more vagabonds who preyed on travelers.

During the High Middle Ages, technology grew rapidly. New techniques expanded t
he use of the water mill, the windmill, and coal for energy and heat. Sailing i
mproved 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 to
ols and weapons. The textile industry began employing wool, linen, cotton, and
silk and, in the thirteenth century, developed the spinning wheel. Soap, an ess
ential for hygiene, came into use in the twelfth century. Mining, which had dec
lined since the Romans, at least partly because the cold and snow made access t
o mountain areas difficult, revived after the tenth century.

Farmers and peasants in medieval England launched a thriving wine industry sout
h of Manchester. Good wines demand warm springs free of frosts, substantial sum
mer warmth and sunshine without too much rain, and sunny days in the  fall. Win
ters cannot be too cold Ñ 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 th
e Norman conquest, the French monarchy tried to prohibit British wine productio
n.143  Based on average and extreme temperatures in the most northern current w
ine growing regions of France and Germany compared to current temperatures in t
he 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 warme
r in the Middle Ages.144

Not only did the British produce wines during the Little Climate Optimum but fa
rmers grew grapes in East Prussia, Tilsit, and south Norway.145 Many areas cult
ivated in Europe were much further up mountains than is possible under the mode
rn climate. Together these factors suggest that the temperatures in central Eur
ope were about 1.8¡ to 2.5¡F higher than during the twentieth century.

EuropeÕs riches and a surplus of labor enabled and emboldened its rulers to tak
e on the conquest of the Holy Land through a series of Crusades starting in 109
6 and ending in 1291. The Crusades, stimulated at least in part by a mushroomin
g population and an economic surplus large enough to spare men to invade the Mu
slim empire, captured Jerusalem in 1099 Ñ a feat not equaled until the nineteen
th century. A major attraction of the first crusade was the promise of land in
a Òsouthern climate.Ó146

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 an
d culture flourished and all the world looked to Constantinople as its leader.1
48 Under the control of the Fatimid caliphate, Egypt cultivated a ÒHouse of Sci
ence,Ó where scholars worked on optics, compiled an encyclopedia of natural his
tory, with a depiction of the first known windmills, and described the circulat
ion of the blood. In Egypt block-printing appeared for the first time in the We
st.149 The caliphate turned Cairo into a brilliant center of Moslem culture. In
 Persia, Omar Khayyam published astronomical tables, a revision of the Muslim c
alendar, a treatise on algebra and his famous Rub‡iy‡t.150

As European commerce expanded, traders reached the Middle East, bringing back n
ot only exotic goods, but new ideas and information about classical times. Draw
ing on fresh information about Aristotelian logic, St. Thomas Aquinas defined m
edieval Christian doctrine in his Summa Theologica. Possibly the oldest continu
ous 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 gran
ted by the chancellor of Notre-Dame began to teach logic, thus inaugurating the
 University of Paris. Cambridge University traces its foundation to 1209 and Ox
ford 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 cent
ury 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 opt
imistic masterpiece, Aucassin et Nicolette. An anonymous Austrian wrote in Midd
le High German the Nibelungenlied.151

The Arctic
From the ninth through the thirteenth centuries agriculture spread into norther
n Europe and Russia where it had been too cold to produce food before. In the F
ar East, Chinese and Japanese farmers migrated north into Manchuria, the Amur V
alley and northern Japan.152  As mentioned above, the Vikings founded colonies
in Iceland and Greenland, a region that may have been more green than historian
s have claimed. It was also during this period that Scandinavian seafarers disc
overed ÒVinlandÓ Ñ somewhere along the East Coast of North America. The subsequ
ent Mini Ice Age cut off the colonies in Greenland from Europe, and they eventu
ally died off. Even today, during this warm period of the late twentieth centur
y, 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 t
heir culture spread from the Bering Sea into the Siberian Arctic. Two centuries
 later, these people migrated along the coast of Alaska and into Greenland. Dur
ing this period the EskimosÕ main source of food came from whaling, which had t
o be abandoned with the subsequent cooling. The Mini Ice Age forced the Thule E
skimos south out of northern Alaska and Greenland. These hardy aborigines had a
bandoned Ellesmere Land by the sixteenth century.

At the same time that the Eskimos were moving north, Viking explorers were vent
uring into Greenland, Vinland, and even the Canadian Arctic. Scandinavian sailo
rs 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 o
f Greenland may have been at least 7¡F 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 occu
rred as late as 1347, when a Greenland ship was blown off course.156 At the hei
ght of the warm period, Greenlanders were growing corn and a few cultivated gra
in. Some archaeologists have found evidence that Vikings from Greenland may hav
e 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 sout
h as the Gulf of California. At least one scientists believes that this visit i
s the origin of the Aztec belief in the visit of ÒfairÓ people from the East.15
7

The Far East
As noted above, the warming in the Far East seems to have preceded that in Euro
pe 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 d
uring the Northern Sung Dynasty (961 a.d. to 1127).158 This coincides with othe
r evidence of longer growing seasons and a warmer climate. He explains the fall
 in worker productivity after the twelfth century as stemming from population p
ressures, but a change in climate may have played a significant role. Chao repo
rts that the number of major floods averaged fewer than 4 per century in the wa
rm period of the ninth through the eleventh centuries while the average number
was more than double that figure in the fourteenth through the seventeenth cent
uries of the Mini Ice Age.159 Not only floods but droughts were less common dur
ing 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 s
cience. The Little Climate Optimum witnessed the highest rate of technological
advance in Chinese history. During the 300 years of the Sung Dynasty, farmers i
nvented 35 major farm implements Ñ that is, over 11 per century, a significantl
y higher rate of invention than in any other era.160 In the middle of the eleve
nth 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 o
f the Los Angeles County Museum of Natural History dates the earliest Chinese b
lue-and-white porcelain to the twelfth century.163 The Southern Sung produced p
ottery and porcelains unequaled in subtlety and sophistication. Literature, his
tory and scholarship flourished as well. Scholars prepared two great encycloped
ias, compiled a history of China, and composed essays and poems. Mathematicians
 developed the properties of the circle. Astronomers devised a number of techno
logical improvements to increase the accuracy of measuring the stars and the ye
ar.164

Chinese civilization has waned and waxed for about 3500 years, yet during all t
hose centuries only once has it ventured to spread its culture or its people be
yond its normal borders. Beginning with the twelfth century a.d., however, Chin
ese explorers and merchant ships plied the Indian Ocean and landed on the East
African coast.165 Although favorable weather may not have motivated these voyag
es, 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 incom
es in China. Certainly the more clement climate meant fewer storms and easier s
ea travel.

Japan also prospered during the Little Climate Optimum. In the Heian Period (79
4 a.d. to 1192) the arts thrived as emperors and empresses commissioned vast nu
mbers of Buddhist temples. Murasaki Shikibu, perhaps the worldÕs first female n
ovelist, composed JapanÕs most famous book, The  Tale of Genji. Other classical
 writers penned essays: Sei Shonagon Ñ another court lady Ñ wrote Makura-no-Sos
hi (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 India
n subcontinent prospered as well. Society was rich enough to produce colossal a
nd impressive temples, beautiful sculpture, elaborate carvings, many of which s
urvive to this day.166 The Lingaraja Temple, one of the finest Hindu shrines, a
s 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 e
rected the vast stupa of Borobudur; other temples Ñ the Medut, Pawon, Kelasan a
nd Prambanan Ñ originate in this era. In the early twelfth century, the predece
ssors of the Cambodians, the Khmers, built the magnificent temple of Angkor Wat
.168 In the eleventh century Burmese civilization reached a pinnacle. In or aro
und its capital, Pagan, between 931 and 1284, succeeding kings competed in cons
tructing 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 a
nd pagodas, built in a more hospitable era.

Archaeologists studying the compositions of forests in New Zealand have found t
hat 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 Mao
ris were settling in New Zealand.170  Partially confirming that warming are dat
a from Tasmania of tree rings which show a warm period from 940 to 1000 and ano
ther from 1100 to 1190.171

The Americas
Less is known about civilizations in the Americas during the Little Climate Opt
imum or even how the prevailing weather changed. Much of the currently arid are
as of North America were apparently wetter during this epoch. The Great Plains
areas east of the Rocky Mountains, the upper Mississippi Valley and the Southwe
st received more rainfall between 800 a.d. and 1200 than they do now.172 Radioc
arbon dating of tree rings indicates that warmth extended from New Mexico to no
rthern Canada. In Canada, forests extended about sixty miles north of their cur
rent limit.173

Starting around 800 to 900 a.d., the indigenous peoples of North America extend
ed their agriculture northward up the Mississippi, Missouri, and Illinois river
 basins. By 1000 they were farming in southwestern and western Wisconsin and ea
stern Minnesota.174 They grew corn in northwestern Iowa prior to 1200 in an are
a which is now marginal for rainfall.175 Indian settlements on the northern pla
ins 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 cold
er Arctic weather.

The Anasazi civilization of Mesa Verde flourished during the warm period, but t
he cooling of the climate at the end of the medieval warmth around 1280 probabl
y 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 Pu
eblo Indians to shift their farming to the edge of the Rio Grande River.

Around 900, the Chimu Indians in South America developed an extensive irrigatio
n system on PeruÕs coast to feed their capital of between 100,000 to 200,000 so
uls Ñ a huge number for the era.177 The Toltec civilization, which occupied muc
h of Mexico, reached its apogee in the thirteenth century.178 By 1200, the Azte
cs had built the pyramid of Quetzalcoatl near modern Mexico City.179 The MayasÕ
 civilization, however, reached a peak somewhat earlier, before 1000, and decli
ned subsequently for reasons that remain unclear. It is possible that the warmi
ng 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 i
mproving agricultural conditions in the Mexican highlands and farther north int
o 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 n
ew ideas and new ways of coping with the world. Nevertheless, for most of the k
nown world, the Little Climate Optimum of the ninth through the thirteenth cent
uries 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. Cli
matologists are generally agreed that, at least for Europe, North America, New
Zealand and Greenland, temperatures fell after 1300 to around 1800 or 1850, alt
hough with many ups and downs. There was a cold period in the first decade of t
he fourteenth century, another around 1430 and again in 1560. The end of this p
eriod 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 bet
ween 1550 and 1700.180 One reasonable interpretation of the data is that the wo
rld 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¡F below those of the twentieth ce
ntury. This indicates that temperatures may have dipped by as much as 9¡F in th
e two hundred years from 1200 to 1400, a drop of about the same magnitude as th
e maximum rise forecast from a doubling of CO2. These frigid times did bring ha
rdships, and as the chart shows world population growth slowed. For much of the
se 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 av
erage temperatures from 1350 to about 1800, with the exception of a few small u
psurges and one strong temperature spike in the first half of the eighteenth ce
ntury.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 th
e 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, Òin most parts of the world the extent of s
now 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.Ó184

The Little Ice Age, especially the century and a half between 1550 and 1700 Ñ t
he exact timing varied around the globe Ñ produced low temperatures throughout
the year and considerable variation in weather from year to year and from decad
e 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 l
ower 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 line
s in the mountains of Europe, changes in oxygen isotope measurement, and advanc
es of the glaciers and of sea ice. This cooling diminished the abundance and qu
ality of wine production in France, Germany and Luxembourg as depicted in histo
rical documents such as weather diaries and farm records.186 The ocean, which h
ad reached relatively high levels both in the late Roman period and again durin
g the High Middle Ages, fell to lower elevations in the seventeenth and ninetee
nth centuries.187 As a result of an expanded ice cap, the circumpolar vortex, w
hich funnels weather around the globe, moved south and spawned increasingly col
d 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 w
orsening of the climate and disasters to people almost everywhere. During the c
oldest period of the seventeenth century, snow fell in the high mountains of Et
hiopia above 10,000 feet which today never see snow. The subtropical monsoon ra
ins 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 windstorm
s ever recorded in Europe. A terrible tempest destroyed the Spanish Armada in 1
588. 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 w
e lack any information, this may also, have enhanced tornado activity on the pl
ains 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 advance
d 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, intens
ified sharply; (7) harvests failed engendering famine and higher prices for bas
ic 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 na
vigation 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 out
posts of Scandinavia ceased. Based on the ratio of isotopes of oxygen in teeth
of ancient Norsemen, researchers have estimated that the climate in Greenland c
ooled by about 3¡ Fahrenheit between 1100 and 1450.193 For about 350 years, fro
m 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 o
f 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 mode
rn standards, worsened after the middle of the thirteenth century.196 One of th
e first severe bouts of cold wet weather afflicted Europe from 1310 to 1319, le
ading to large scale crop failures.197 Food supplies deteriorated sharply gener
ating famine for much of Europe in 1315-18 and again in 1321.198 Harvest defici
ts and hunger preceded the Black Death by 40 years.199 According to Lamb, for m
uch of the continent, Òthe poor were reduced to eating dogs, cats and even chil
dren.Ó200 This scanty food output contributed to a decline in population which
was aggravated by disease. The history of many villages shows that they were ab
andoned before the beginning of the plague not afterwards. By 1327, the populat
ion in parts of England Ñ especially those later devastated by the plague Ñ had
 fallen by 67 percent.201 People poorly nourished were quickly carried off by d
isease. Between 1693 and 1700 in Scotland, seven out of the eight harvests fail
ed and a larger percentage of the population starved than died in the Black Dea
th 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 lac
k of food.203 Bubonic plague spread across the Alps after 1348, killing in the
next two years about one-third of northern EuropeÕs people. Life expectancy fel
l 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 t
hat had been cultivated during the earlier warm epoch. Between 1300 and 1600 th
e growing season shrank by three to five weeks with a catastrophic impact on fa
rming.205  In Norway and Scotland, the population declined and villagers desert
ed 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 gre
atest disaster to ever befall Europe. The disease appears to have originated ar
ound 1333 in China, shortly after major rains and floods in 1332, which are rep
uted to have caused 7 million deaths, while disturbing wildlife and displacing
plague-carrying rats.207 The Black Death then spread to central Asia around 133
8-9, which, with the increased coldness, was also drying out. By 1348 rodents c
arrying 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 b
y dry hot ones. The unpleasant weather is likely to have confined people to the
ir homes where they were more likely to be exposed to the fleas that carried th
e disease. In addition the inclement weather may have induced rats to take shel
ter in human buildings, exposing their inhabitants to the bacillus.

Not only did the cold facilitate the spread of the plague, but it caused much o
ther 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 r
ye crop of Brittany and other parts of France. This blight caused hallucination
s, 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 live
d at the edge of habitable lands. For example, historians have estimated the po
pulation of Iceland at the end of the eleventh century at about 77,000, and ear
ly in the fourteenth it still numbered over 72,000. By the end of the eighteent
h century, after several hundred years of coolness and stormy weather, the numb
er 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 fo
r 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 cathedr
als halted.

The hardships of the fourteenth century induced a search for scapegoats. In 129
0 after some years of crop failures, the king of England expelled the Jewish po
pulation from the country. The French king followed this example in 1306 and ag
ain in 1393.213  In 1349, the Christians of Brabant massacred the local Jews an
d expelled the remainder twenty-one years later.

The Mini Ice Age at its coldest devastated the fishing industry. From 1570 to 1
640, during the most severe period, Icelandic documents record an exceptionally
 high number of weeks with coastal sea ice. Except for a few years, fishermen f
rom the Faeroe Islands suffered from a lack of cod from 1615 to 1828 Ñ cod need
s water warmer than 3.6¡ Fahrenheit to flourish. During the worst periods, 1685
 to 1704, fishing off south-west Iceland failed totally.214 In the very icy yea
r of 1695, Norwegian fishermen found no cod off their coast. Lamb calculates th
at the sea around the Faeroe Islands was probably 7¡ to 9¡F 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 Spa
in. The great variability in the weather made agricultural output quite uncerta
in and contributed to a farming crisis in the Iberian Peninsula. Although one c
annot know for sure that it was the weather, the whole of the Mediterranean lit
toral declined economically in the seventeenth century.216

The cold had devastating effects elsewhere in the world. In China, frosts kille
d the orange trees in Kiangsi province between 1646 and 1676.217  Per capita in
comes 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 f
arming in the upper middle west.

According to Nicolas Cheetham, in the second half of the thirteenth century war
fare in Greece and the necessity of keeping a large military establishment unde
r 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 Bri
el, a major figure in medieval Greece, died during a military campaign of dysen
tery, a disease often exacerbated by cold wet conditions.219

Notwithstanding the cooling climate and the ravages of disease after 1300, Euro
pean civilization recovered with the advent of the Renaissance in the fifteenth
 century. This burst of cultural activity represented a continuation, an expans
ion, and a deepening of the artistic and intellectual activity of the High Midd
le 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 EuropeÕs population caused by the Bla
ck Death, food supplies would have been too meager to support a large artistic
and cultured class that promoted and supported the arts. The reduced agricultur
al 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 r
esult 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 tempe
rature was 3¡F below the present. Grain prices increased sharply as crops faile
d. Famines were common. The Renaissance had ended; Europe was in turmoil. The C
ontinent suffered from cold and rain, which produced poor growing conditions, f
ood 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 winte
rs 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 Ñ up from two
 Ñ the population of China, as well as that of Korea and the Near East, decline
d for two centuries after 1200, undoubtedly reflecting a deteriorating climate.
223 The abandonment of sea trade by the Chinese most likely resulted from deter
iorating 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 oth
er animals and, after adjustment, most plants would be better off with higher t
emperatures. Not all animals or plants would prosper under these conditions; ma
ny are adapted to the current weather and might have difficulty making the tran
sition. 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 ha
s changed in the past and will no doubt continue to vary in the future. Human a
ctivity is likely to play only a small and uncertain role in climate change. Th
e burning of fossil fuel may generate an enhanced greenhouse effect or the rele
ase into the atmosphere of particulates may cause cooling. It may also be simpl
y hubris to believe that Homo Sapiens can affect temperatures, rainfall and win
ds.

As noted, not all regions or all peoples benefit from a shift to a warmer clima
te. Some locales may become too dry or too wet; others may become too warm. Cer
tain 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 gro
wing seasons, more rainfall overall, and fewer and less violent storms. The opt
imal 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 pe
ople 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 con
siderably more dependent on agriculture than the rich industrial nations. Such
populations lack the resources to aid their flora and fauna in adapting, and ma
ny of their farmers earn too little to survive a shift to new conditions. These
 agriculturally dependent societies could suffer real hardship if the climate s
hifts quickly. The best preventive would be a rise in incomes, which would dimi
nish their dependence on agriculture. Higher earnings would provide them with t
he resources to adjust.

The cost of trimming emissions of CO2 could be quite high. William Cline of the
 Institute for International Economics Ñ a proponent of major regulatory initia
tives to reduce the use of fossil fuels Ñ has calculated that the cost of cutti
ng 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 wor
ld outlays to slow warming would be considerably higher. In terms of the estima
ted level of world output in 1992, his estimate would amount to roughly $900 bi
llion annually, an amount that could slow growth and impoverish some who surviv
e 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 preventiv
e 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 p
romote plant growth that can sustain an expanding world population. Global chan
ge is inevitable; warmer is better; richer is healthier.


* A shorter version of this paper appeared as ÒWhy Global Warming would be Good
 for YouÓ in the Winter 1995 issue of The Public Interest.
1Mitchell [1991]:  70-71.
2Committee on Science, Engineering, and Public Policy [1991]. Policy Implicatio
ns 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.


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