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would boost productivity by 20 percent and that overall the harvest of timber in Canada would climb by about 7.5 percent. 11

Past Climate and Human Well-being Since statistics on the human condition are unavailable except for the most recent centuries, I have used indirect methods to demonstrate the influence of climate on man's well-being. A growth in the population, major construction projects, a significant expansion in arts and culture, all indicate that society is prosperous. If the population is expanding, food must be plentiful, disease cannot be overwhelming, and living standards must be satisfactory. In addition, if building, art, science, and literature are vigorous, the civilization must be producing enough goods and services to provide a surplus available for such activities. Renaissance Florence was rich; Shakespeare flourished in prosperous London; wealthy Vienna provided a welcome venue for Haydn, Schubert, Mozart, and Beethoven.

Clearly climate is far from the only influence on man's well-being. Governments that extort too much from their people impoverish their countries. A free open economy stimulates growth and prosperity. War and diseases can prove catastrophic. On the other hand, a change in climate has frequently been a cause of war or aided the spread of disease. A shift to more arid conditions, for example, impelled the Mongols to desert their traditional lands to invade richer areas. A cold wet climate can also confine people to close quarters, which can abet contagion. Moreover, a shift towards a poorer climate can lead to hunger and famine, which make disease more virulent.

The influence of climate on human activities has declined with the growth in wealth and resources. Primitive man and hunter-gatherer tribes were at the mercy of the weather, as are societies which are still almost totally bound to the soil. A series of bad years can be devastating. If, as was the usual case until very recently, transportation is costly and slow, even a regionalized drought or an excess of rain can lead to disaster, although crops may be plentiful a short distance away. Thus variation in the weather for early man had a more profound influence on his life and death than do fluctuations in temperature or rainfall in modern times when economies are more developed. Since the time of the Industrial Revolution, climate has basically been confined to a minor role in human activity.

History since the Last Ice Age The last Ice Age ended about 12,000 to 10,000 years ago when the glaciers covering much of North America, Scandinavia and northern Asia began to retreat to

Ilvan Kooten (1990): 704.

approximately their current positions. In North America the glacial covering lasted longer than in Eurasia because of topographic features that delayed the warming. Throughout history warming and cooling in different regions of the world have not been exactly correlated because of the influence of occans, mountains, prevailing winds, and numerous other factors. Nevertheless, across the Northern Hemisphere large temperature shifts have occurred roughly together — perhaps in some areas they have lagged other zones by a century or more.

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

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 modem Norway; agriculture developed in the Middle East. For about 3,000 to 4,000 years the globe enjoyed what historians of climate call the Climatic Optimum period a time when average world temperatures at least in the Northern Hemisphere — were significantly hotter than today, about 4° to 5° Fahrenheit warmer than the twentieth century. 12 During the relatively short period since the end of glaciation the climate has experienced periods of stability separated by “abrupt transition."13 During the Mini Ice Age, the temperature in central England for January was about 4.5°F colder than today. 14 In the central and northern latitudes of Euro during the warmest periods, rainfall may have been 10 to 15 percent greater than now and during the coldest periods of the Mini Ice Ages, 5 to 15 percent less. 15 On the other hand, cooler periods usually suffered from more swampy conditions because of less evaporation.

If modem humans originated 200,000 years ago, why did they not develop agriculture 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 - an innovation which yielded a more reliable and ample food supply. Farming developed first in the Middle East, right after the end of the last Ice Age a coincidence? The evidence suggests that from 11,000 to 9,000 years ago the climate became warmer and wetter in the Middle East shifting the ecology from steppe to open woodland. 16 This led to the

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12 Lamb (1968): 6. 13Wendland & Bryson (1974). 14 Lamb (1968): 12. 1S Lamb (1988): 30. 16 Ammerman & Cavalli-Sforza (1984): 28.

domestication of plants and animals, probably because the warmer, wetter weather made farming possible.

Although many people view the current world's huge population with alarm, most ecologists take the size of the population of a species as an indicator of its fitness. By this criterion, the domestication of plants and animals improved greatly Homo Sapiens fitness. This testimony is not the place to discuss the capacity of the globe to sustain the number of people expected to populate the world in the next century, but certainly anything that produced greater numbers of people thousands of years ago must have been beneficial for mankind.

Over history the number of humans has been expanding at ever more rapid rates. Around 25,000 years ago, the world's population may have measured only about 3 million. 17 Fifteen thousand years later, around 10,000 B.C., the total had grown by onethird to 4 million. It took 5,000 more years to jump one more million, but in the 1,000 years after 5000 B.C. it added another million. Except for a few disastrous periods, the number of men, women and children has mounted with increasing rapidity. Only in the last few decades of the twentieth century has the escalation slowed. Certainly there have been good times when man did better and poor times when people suffered — although in most cases these were regional problems. However, as the following chart shows, in propitious periods, that is, when the climate was warm, the population swelled faster than during less clement eras.

This chart is based on a paper by economist Michael Kremer who argues that, until the Industrial Revolution, existing technology limited the size of the population.18 As innovators discovered new techniques and invented new tools, more people could be fed and housed and the population expanded. Moreover, the greater the number of people, the more innovations would be hit upon. He assumed that every individual had an equal but very small probability of uncovering a new technique or device and that the probability of being an innovator was independent of the size of the population. Therefore the number of inventions would be proponional to the number of people. Thus as the world population expanded slowly at first the rate of technological innovation escalated and hence the rate of growth of the population that could be sustained. Only in recent times has technological change become so rapid that it has run ahead of population growth, leading to a rising standard of living, which in turn has reduced the birth rate.

17Kremer (1993): 683. 18Kremer (1993): 681-716.

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Kremer's hypothesis signifies that for most of history the rate of population growth should be proportional to the size of the population. To link his model and data with climate change, I started with his estimate of the world's people in 10,000 B.C. and calculated the rate of growth of the population over the next 5,000 years. For each subsequent period, I also computed the rate of increase in numbers of people. Comparing these expected rates with actual growth revealed eras in which the number of humans has expanded faster than predicted and periods during which the world's people has grown more slowly. The chart then shows the centuries in which the growth rate of the globe's populace has exceeded or fallen short of the rate expected under this simple model. As can be seen, warm periods have done considerably better than cold periods in terms of human expansion. The warmest period since the end of the last Ice Age produced the highest rate of population growth compared to what would have been expected — in this era agriculture was spreading. Moreover, the Mini Ice Age, which saw the coldest temperatures in the last 10,000 years, underwent the slowest relative population expansion. This chart demonstrates that mankind has prospered in warm periods and the hotter the better!

Another measure of the well-being of humans is how long they live. The life of the hunter-gatherer was not as rosy as some have contended. Life was short — skeleton remains from before 8000 B.C. show that the average age of death for men was about 33 and that of women 28.19 Death for men was frequently violent, while many women must have died in childbirth. Since women died so young, they had only around thirteen years in which to bear children. Anthropologists have estimated that on average they could have given birth to less than five live babies, assuming that they bore a child every 22 months. 20 An infant and childhood mortality rate of about 60 percent would have kept the population stagnant.

Table 1 below shows some relevant data. The warmest periods, the Neolithic, Bronze Ages and England in the thirteenth centuries enjoyed the longest life spans of the entire record. The shortening of lives from the late thirteenth to the late fourteenth centuries with the advent of much cooler weather is particularly notable. Moreover, the rise in life expectancies during the warm period could easily explain the population explosion that took place during that period.

Good childhood nutrition is reflected in taller adults. Skeleton remains collected over wide areas of Eurasia from the period when roving bands shifted from eating large animals and a few plants to smaller prey and a much wider variety of foods attest to a decline in height for both men and women of about five centimeters (two inches).21 The shorter stature came at the end of the Ice Age when large animals were disappearing. Some archaeologists have found that average age of death for adults also declined during this transitionary period.22 Studies of bone chemistry from Middle Eastern skeletons indicate a reduction in meat consumption. The new diet although more dependent on grains, fruits, and vegetables must have been less nutritious than the old. As large game animals disappeared with the end of the Ice Age, humans widened the variety of plants in their diet, increasingly consuming vegetable matter that they had ignored for thousands of years either because it was less nutritious, more difficult to secure

Table 1 and process, or less tasty. Table 2

Life Expectancy at Various Periods on heights, however, signifies that Mesolithic people in Europe, ca. 8000 B.C.

31.5 food was more plentiful and better Neolithic, Anatolia, ca. 6000 B.C.

38.2 during the medieval Period than Bronze Age, Austria, ca. 2000 B.C.

38 during the mini Ice Age. Classical Greece, ca. 500 B.C.

35 Classical Rome, 100 B.C.-A.D. 300

32 England 1276 A.D.

48 England 1376-1400

38 19Boserup (1981): 36-37. 20Boserup (1981): 38.

Source: Lamb (1977): 264 from Comfort (1969). 21 Cohen (1989): 112 2 Cohen (1989): 113.

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