Paul Mitchinson is a part-time writer and a full-time father of two. He writes when he can. » more about me

Time’s Weather Vane

National Post, 4 April 2001

More than a few shivering Canadians must have been cheering on George W. Bush last week, as he announced the United States’ formal rejection of the 1997 Kyoto climate accord. After a gruelling winter, it’s tough to get worked up about global warming.

But climate change is beginning to worry growing numbers of archeologists and historians. Increasingly sophisticated scientific data are suggesting the rise and fall of civilizations have been influenced by weather fluctuations such as El Niño events and centuries-long droughts.

Climate is one of “dozens of factors” that archeologists have traditionally investigated, says Brian Fagan, anthropologist at the University of California, Santa Barbara. “But we’ve known very little about it until recently.” That began to change in the 1980s and 1990s, as concern over the effects of global warming grew. Then, in 1997-98, as monsoon rains pulverized California, heat waves swept across Australia and Brazil, and smoke from forest fires blanketed Indonesia, the public started paying attention. A T-shirt slogan urged people to “Blame it on El Niño.”

Fagan turned that slogan into the theme of his 1999 book Floods, Famines and Emperors. El Niño has delivered a “knockout blow” to many civilizations, he argues. He mentions not only the Classical Maya collapse of the 9th century, but also the destruction of the northern Peruvian Moche civilization two centuries earlier. Both cultures suffered repeated catastrophic droughts and floods, some of which were caused by El Niño.

Scientists are piecing together a global history of climate from a mass of new information about ancient weather patterns. Much of the data has come from studying tree rings, a science known as dendrochronology. By comparing these rings’ relative thicknesses, researchers have sketched the broad outlines of weather patterns going back centuries. One of the earliest discoveries explained the mysterious migration of Arizona’s Anasazi Indians in the 13th century. Their dispersal has been convincingly attributed to a sustained drought and cold temperatures lasting from 1276 to 1299.

But scientific testing has gone far beyond measuring tree rings. Chemical analyses of coral skeletons are helping to provide accurate readings of centuries of sea surface temperatures. Meteorological information dating back several millennia has been gathered from core samples of ice sheets and sea bottoms.

One such study seems to explain the origins of agriculture. Scientists measuring electrical conductivity in a Greenland ice sheet have been able to date the so-called Younger Dryas climate episode to 12,000 years ago.

That sudden onset of cool, dry conditions threatened the hunting and gathering of a people in Palestine and Syria we call Natufians. This induced them to abandon a subsistence strategy that had served human beings well for some 2.5 million years.

The Natufians began to cultivate plants, pioneering one of humanity’s most important advances. Recent archeological data has corroborated the theory that Natufian plant domestication began with the climatic crisis.

But sudden climate change rarely has such a happy ending. Last year, researchers analyzing a marine sediment core from the Gulf of Oman confirmed that massive droughts afflicted Mesopotamia around 2,200 BC and lasted for three centuries. This climatic crisis almost certainly contributed to the collapse of the powerful Akkadian empire.

Harvey Weiss, a Yale anthropologist, thinks these discoveries should serve as warnings. A paper he co-authored in the journal Science in January argued that climate was one of the primary agents in the collapse of prehistoric and early historical societies. “I think that improved research is driving the concern about global warming,” he says over the phone. The new data “indicate a pattern of incidents of century-scale drought that [led to] either social collapse or what we call ‘habitat-tracking’: moving elsewhere.” And he suggests climate change might cause “unprecedented social disruptions” in the present century.

Other researchers have been discovering similar lessons in modern history. Fagan has recently published a book on the impact of the “Little Ice Age,” a period of global cooling that lasted from about 1500 to 1850. And in an upcoming book, Geoffrey Parker, an Ohio State University historian, will be examining the influence of climate on the “17th-century crisis”: a series of interlocking economic, social and political upheavals that struck much of the world between 1635 and 1665. Recent climatological data has confirmed that drought and extreme cold afflicted many regions, from New England to Europe to Japan.

Richard Grove, an historian at the Australian National University in Canberra, draws even broader conclusions. Currently working on a book about the effect of El Niño throughout history, Grove suggests that European colonial expansion in Southeast Asia might have been facilitated by a series of droughts in the 17th and 18th centuries. “The Dutch found it easier [to expand their influence] in Southeast Asia,” he says, “because the people were weakened by a succession of huge El Niño events.” Even the French Revolution of 1789, he has recently pointed out, coincided with severe weather disturbances between 1788 and 1793.

Such explanations might raise the red flag of “environmental determinism,” a theory developed in the early 20th century by an American geographer, Ellsworth Huntington (1876-1947). Huntington believed that human culture was a product of climate and heredity, and that the heat of the tropics slowed the advance of civilization. Many have attacked his views as racist.

Historians have been careful to avoid such simplistic explanations. “Before you make any claims about the historical consequences of weather,” remarks Mike Davis, a historian at the State University of New York in Stony Brook, “you have to understand the transmission belt that turns climate shocks into significant human history.” For Davis, that means understanding how human beings responded to climate change through their political and economic institutions — the bread and butter of traditional historians.

Davis has just published Late Victorian Holocausts , a harrowing account of the catastrophic El Niño droughts of the 1870s and 1890s that took tens of millions of lives in northern Africa, India and China. The famines were “the greatest human tragedy since the Black Death,” he believes. But, he adds, colonial politics transformed what might have been a manageable drought into a human holocaust.

This is exactly the point that researchers such as Weiss hope to get across. Climate change will happen, either naturally or by human intervention. But whether human society will be up to the challenge is another matter altogether. “If we don’t look at the lessons of history,” reflects Fagan, “we’re done.”