Do Climate Changes Mean Anything?

Thomas Gale Moore
Hoover Institution
Stanford University

"As you can see from this sweltering heat," President Clinton asserted July 20 in New Orleans, "the climate of our country and our globe is changing." Preaching the same message, Al Gore claimed, "The evidence of global warming keeps piling up, month after month, week after week."

But as most people realize, one hot spell does not a climate change make. Moreover, even if the climate were changing, it is likely that the change would be natural. Climate fluctuates!

In Climate of Fear: Why We Shouldn’t Worry about Global Warming, I devote one chapter to changes in the world’s climate over the last 10 to 12 millennia. Part of that material was drawn from the writings of H.H. Lamb, currently Emeritus Professor in the School of Environmental Science and founder of the Climatic Research Unit at the University of East Anglia in England. Recently he published a second edition of his work, Climate History and the Modern World, an updated version of his 1982 study, which includes new findings and treats global warming and other putative environmental issues.

After explaining how climate works, Lamb describes the fluctuations in temperature, rainfall, and storm patterns since the end of the last Ice Age. Throughout history natural cycles, together with such events as volcanic eruptions, oceanic changes, and variations in heating patterns have led to noticeable climate changes. His work details the ways in which he and others have reconstructed the climate over the past 12 thousand years.

The Big Thaw

As the world warmed with the ending of the Ice Age, people began to shift from a nomadic hunter-gatherer existence to a more settled life style. The warmer, wetter weather allowed early Stone Age hunters in the Middle East to move from the mountains to the valleys, which were more suitable for farming. As wild game migrated to the lowlands as well, humans took the novel step of domesticating animals and plants. The result was a more plentiful and reliable supply of food that led in turn to a population explosion. The improvement in food production freed some people from the chore of securing their own food directly and fostered, first, agricultural villages, then larger towns functioning as trading centers, and finally large cities with inhabitants who specialized in trade and crafts.

Lamb considers in detail the era 5,000 to 7,000 years before the present (YBP) when the climate was about 1 to 3 degrees Celsius warmer than today, close to what the IPCC is predicting for the end of the next century. In North America, the time necessary to melt the huge ice sheets that had covered much of the region delayed this warm period until around 4,000 years ago. Lamb reports that Europe experienced "mild winters and warm summers and with the storm belt far away to the north," and that the average temperature was some "2 degrees [Celsius] higher than in recent times." Forests extended much farther north into areas that are now permafrost. Both the Orkney Islands and Iceland, currently without trees, nurtured forests.

Trading, travel, and local cultures flourished. Snow and ice no longer blocked travel through the Alps and these Neolithic people mined gold high up in the mountains. Seafarers traded tin from Cornwall for bronze goods from the Mediterranean. Megalithic monuments from this period, such as Stonehenge, are spread from the Mediterranean to Britanny, Cornwall, Wales, the Outer Hebrides to Orkney. That many of these structures were astronomical observatories suggests that the skies were less cloudy than today.

During that temperate period, rain watered many areas which are now major deserts. In the Sahara, for example, archaeologists have found cave drawings and paintings, dating from around 7,000 to 5,000 YBP, of elephants, rhinoceroses, buffalo, hippopotami, crocodiles, antelopes, giraffes, and deer. Lamb estimates that in what are now the driest regions of the desert, those sectors which rarely see rain, rainfall 8,000 YBP was typically 8 to 15 inches a year.

In the Indus valley, Lamb reports that major cities flourished from around 4500 to 3700 YBP in areas now desert. The local farmers grew wheat, barley, melons, dates and perhaps cotton. Between 15 inches and 30 inches of rain fell yearly, allowing rhinoceroses, elephants, and water buffalo to flourish. Lamb attributes this fertile period to the warmer climate, which led the monsoon rains to spread farther north.

In China as well temperatures during this early warm period averaged about 2 degrees Celsius above current levels. That part of the world was apparently one of the warmest areas on the globe. In central China snow was rare and bamboo grew about 3 degrees latitude farther north than it does at present.

The warmth was worldwide and so were the benefits. In Australia, before the cooling at about 4500 YBP, much of that dry continent was much wetter than today. Both the tropics and the temperate regions, according to Lamb, enjoyed more rainfall.

The Climate Cools

The downturn in temperatures and the drying of the climate led to the disappearance of several civilizations and great disturbances in many. The earlier period of fine warm weather, Lamb hypothesizes, may be the origin of Golden Ages’ tales, such as the Garden of Eden. After the warmest period, the earth seems to have cooled. By 2500 YBP, the long-term average temperature had declined about one degree in Europe, leaving it still about one degree higher than the twentieth century average.

In North America, with a cooling and drying around 5000 YBP, the first agriculture, which had originated in New Mexico and Arizona around 6500 YBP, disappeared. About four thousand years ago, the ancient Egyptians recorded several severe droughts lasting 50 or more years brought on by the cooling. An invasion by people from the East, no doubt displaced by the drier weather, ended the Old and Middle Kingdoms of Egypt.

After a further cooling from 3000 to 2500 YBP, the climate during most of the Roman period apparently warmed, at least in Europe. Italians were able to cultivate both vines and olives much farther north than in earlier centuries. From 150 BC to 300 AD, caravans traveled along the Great Silk Road to trade with Asia. Subsequent cooling and drought brought commerce to a halt. Coincident with the fall of the Roman Empire, the climate deteriorated. As Lamb points out, some historians have attributed the invasion of barbarian tribes from central Asia to the drying of their pastures. From approximately 400 AD to around 900, the climate became much colder. The winters of 763-4 and 859-60 were extraordinarily cold, with the ice so thick in the Adriatic near Venice that it could hold up heavily loaded wagons. There was ice even on the Nile.

Return of the Prodigal Sun

The Dark Ages in Europe ended with a return to warmer weather on the Continent and in North America at the start of this last millennium. The capacity of English vineyards to rival the French indicates that summers were 0.7 to 1 degree Celsius warmer then than now. Lamb asserts that it was even warmer in central Europe. This warm interlude produced a period of great prosperity, leading to the construction of great cathedrals, a flourishing of trade, and a population explosion.

The weather in North America followed the pattern in Europe, warmer and wetter. Farming flourished in northwestern Iowa, a region in which rainfall is currently marginal for growing corn. A thriving culture existed in the Mississippi valley until the weather turned colder and drier between 1200 and 1300.

See Chart of summer warmth and/or seasonal duration in California, 3500 BC to the present.

With the return of colder times, starting around 1200 in the Arctic regions, spreading south to Europe by 1300, and becoming acute during the Little Ice Age of the sixteenth and seventeenth centuries, the economic and cultural progress of the warmer period ceased for awhile. Greenland was abandoned; Iceland declined; Scotland suffered. Periodically famine took a terrible toll throughout the continent. Great storms wracked Europe. In 1421, 1446, and 1570, gales killed 100,000 or more as a result of coastal flooding off the North Sea. Lamb reports that the mortality from the sixteenth century tempest was about 400,000! The winters of 1407-8 and 1422-3 were so cold that the Baltic froze, permitting traffic across the sea and allowing wolves to pass from Norway to Denmark. Disease, particularly but not solely, the Black Death, stalked Europe. The average life expectancy fell by 10 years over the fourteenth century. Farms, villages, and whole regions were abandoned.

After a generally warmer interlude between 1500 and 1550, northern Europe turned much colder. The Little Ice Age, which reached a peak in the sixteenth and seventeenth centuries, experienced temperatures that were as much as 1.5 degrees Celsius colder than the twentieth century. Great hurricanes, exceeding in severity the worst storms of modern times, savaged the North Atlantic. A gale whose winds exceeded the speeds of any modern tempest destroyed the Spanish Armada and changed history. Traces of this era of cold persisted until the mid-nineteenth century.

How's the Weather?

That depends. Lamb’s great work documents overwhelmingly that climate varies. The Earth has known shifts from colder to warmer and back a number of times since the end of the last Ice Age. No one contends that mankind had anything to do with those changes. The warmth of the twentieth century appears to be normal; it is exceeded by the warmth of the Medieval period and by the era 4000 to 8000 YBP. Viewed in its historical context, the warming of the last century is most easily explained by a return to more normal temperatures after the cold of the Little Ice Age. Attributing that change in weather to man may be exaggerating human influence on this globe.

As history demonstrates, warmer is better, colder is worse.


H.H. Lamb. Climate History and the Modern World, Second Edition, London and New York: Routledge, 1995.

Thomas Gale Moore. Climate of Fear: Why We Shouldn’t Worry about Global Warming, Washington, DC: Cato Institute, 1998.