Warmer Days and Longer Lives

Thomas Gale Moore
Senior Fellow
Hoover Institution
Stanford University

History demonstrates that warmer is healthier. Since the end of the last Ice Age, the earth has enjoyed two periods that were warmer than the twentieth century. Archaeological evidence shows that people lived longer, enjoyed better nutrition, and multiplied more rapidly than during epochs of cold.

That Ice Age ended about 12,000 to 10,000 years ago when the glaciers covering much of North America, Scandinavia and northern Asia began to retreat to approximately their current positions. In North America the glacial covering lasted longer than in Eurasia because of topographical features that delayed the warming. Throughout history warming and cooling in different regions of the world have not correlated exactly because of the influence of such factors as oceans, mountains, and prevailing winds.

As the earth warmed with the waning of the Ice Age, the sea level rose as much as 300 feet; hunters in Europe roamed through modern Norway; agriculture developed in the Middle East, the Far East and the Americas. By 7,000 years ago and lasting for about four millenniums, the earth was more clement than today, perhaps by 4deg. Fahrenheit, about the average of the various predictions for global warming from a doubling of CO2. Although the climate cooled a bit after 3000 B.C., it stayed relatively warmer than the modern world until sometime after 1000 B.C., when chilly temperatures became more common. During the four thousand warmest years, Europe enjoyed mild winters and warm summers with a storm belt far to the north. Rainfall may have been 10 to 15 percent greater than now. Not only was the country less subject to severe storms, but the skies were less cloudy and the days, sunnier.

From around 800 A.D. to 1200 or 1300, the globe warmed again considerably and civilization prospered. This warm era displays, although less distinctly, many of the same characteristics as the earlier period of clement weather. Virtually all of northern Europe, the British Isles, Scandinavia, Greenland, and Iceland were considerably warmer than at present. The Mediterranean, the Near East, and North Africa, including the Sahara, received more rainfall than they do today. During this period of the High Middle Ages, most of North America also enjoyed better weather. In the early centuries of the epoch, China experienced higher temperatures and a more clement climate. From Western Europe to China, East Asia, India, and the Americas, mankind flourished as never before.

This prosperous period collapsed at the end of the thirteenth century with the advent of the "Mini Ice Age" which, at its most frigid, produced temperatures in central England for January about 4.5deg.F colder than today. Although the climate fluctuated, periods of cold damp weather lasted until the early part of the nineteenth century. During the chilliest decades, 5 to 15 percent less rain fell in Europe than does normally today; but, due to less evaporation because of the low temperatures, swampy conditions were more prevalent. As a result, in the fourteenth century the population explosion came to an abrupt halt; economic activity slowed; lives shortened as disease spread and diets deteriorated.

Although the influence of climate on human activities has declined with the growth in wealth and resources, climate still has a significant effect on disease and health. A cold wet climate can confine people to close quarters, abetting contagion. In the past, a shift towards a poorer climate has led to hunger and famine, making disease more virulent. Before the industrial revolution and improved technology, a series of bad years could be devastating. If transportation were costly and slow, as was typical until very recently, even a regionalized drought or an excess of rain might lead to disaster, even though crops might be plentiful a short distance away.

For people in pre-modern times, perhaps the single best measure of their health and well-being is the growth rate of the population. 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 numbered only about 3 million. Fifteen thousand years later, around 8,000 B.C., the total had probably grown by one-third to 4 million. It took 5,000 more years to jump one more million; but, in the 1,000 years after 5000 B.C., it added another million. Except for a few periods of disaster, 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.

Another measure of the well-being of humans is their life span. The life of the hunter-gatherer was less rosy than some have contended. Life was short -- skeletal remains from before 8000 B.C. show that the average age of death for men was about 33 and that for women, 28. Death for men was frequently violent while many women must have died in childbirth.

Chart 2 below shows that the warmest periods -- the Neolithic and Bronze Ages and England in the thirteenth century -- enjoyed the longest life spans of the entire record. The rise in life expectancies during the latter warm period easily explains the population explosion that took place during the High Middle Ages. In contrast, the shortening of lives from the late thirteenth to the late fourteenth centuries with the advent of much cooler weather is particularly notable.

Good childhood nutrition is reflected in taller adults. As Chart 3 indicates Icelanders must have suffered from lack of food during the Mini Ice Age: their average stature fell by 2 inches. Only in the modern world, with greatly improved food supplies and medicines, has their height risen to levels exceeding those enjoyed in the Medieval period.

In summary, the evidence supports overwhelmingly the proposition that, during warm periods, humans have prospered. They multiplied more rapidly; they lived longer; and they were healthier. If the IPCC is right and the globe does warm, history suggests that human health is likely to improve.


Boserup, Ester. Population and Technological Change: A Study of Long-Term Trends, Chicago: University of Chicago (1981).

Kremer, Michael "Population growth and Technological Change: One Million B.C. to 1990," The Quarterly Journal of Economics, 108(3) (August 1993).

Lamb, Hubert H. The Changing Climate, London: Methuen (1968).

Lamb, Hubert H. [1977]. Climatic History and the Future, Princeton: Princeton University Press, Vol. 2 (1985).

Lamb, Hubert H. Weather, Climate & Human Affairs: A Book of Essays and Other Papers, London and New York: Routledge (1988).

Moore, Thomas G. "Why Global Warming Would Be Good for You" The Public Interest, (Winter 1995): 83-99.

Difference in Percentage Growth Rate of Population from the Expected

Period Climate Difference in Growth Rate 5000BC-1000BC Warmest Period +5deg.F +0.050% 500BC-600AD Cooling Period -0.011% 800AD-1200 Medieval Warm Period +0.001% +3deg.F 1300-1800 Mini Ice Age -0.034%
Source: Kremer 1993, table 1 and the author.


Life Expectancy at Various Periods

Mesolithic People in Europe -- Ice 32 Age Neolithic, Anatolia -- Warm Period 38 Bronze Age, Austria -- Warm Period 38 Classical Greece -- Cooler 35 Classical Rome -- Cooler 32 England 1276 a.d. -- Warm Period 48 England 1376-1400 -- Mini Ice Age 38 Source: Lamb [1977]: 264.


Average Height of Icelandic Males

Period (a.d.) Mean Height Medieval Warmth 874-1100 68" Mini Ice Age 1650-1800 66" Modern World 1952-1954 70" Source: Lamb [1977]: 264.