Fagan: The Long Summer

From Scienticity

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Current revision as of 02:54, 15 May 2009

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Brian Fagan, The Long Summer : How Climate Changed Civilization. New York : Basic Books, 2004. xvii + 284 pages; illustrated with line drawings and maps; includes notes and index.

Sometime about 10,000 years ago human civilization underwent a profound change. Bands of hunter-gatherer people gave up their nomadic habits in favor of settling in communities. Humans began to domesticate plants and animals. The big question is why? What could cause such a sudden and drastic change in social human behavior?

Also about 10,000 years ago a major climatic shift took place leading to a warm period on the Earth that ended the last major Ice Age, a warm period that persists until today. This is the "long summer" Fagan refers to in his title, and he wants to consider the role that such a climatic shift could have had in changing the course of human civilization.

It's a great story and one that covers times and events that don't get much coverage in the history of civilization, largely because it mostly takes place before recorded history began. This book, whose first chapter is "The Late Ice Age Orchestra: 18,000 B.C. to 13,500 B.C.", is four-fifths done before we even reach "Celts and Romans: 1200 B.C. to 900 A.D."

It is relatively recently that we—the scientific "we" of knowledge shared by all—have had more than a very superficial picture of climatic shifts during deep time, the eons over which average temperatures change, oceans rise or fall by 60 meters, and ice caps, glaciers, and deserts come and go. Our current understanding comes from piecing together records from many different source, but the backbone has come from deep ice cores from which we can get very detailed information with great precision in dating the results. (For an excellent account, see Richard B. Alley, The Two-Mile Time Machine : Ice Cores, Abrupt Climate Change, and Our Future.)

In providing a detailed record of the beginnings and endings of all the glacial periods of the past 420,000 years, the Vostok [ice core, taken in Antarctica ]core shows us that the world's climate has almost always been in a state of change over these 420 millennia. But until the Holocene it has always oscillated. The Holocene climate breaks through these boundaries. In duration, stability, degree of warming, and concentration of greenhouse gases, the warming of the past fifteen millennia exceeds any in the Vostok record. Civilization arose during a remarkably long summer. We still have no idea when, or how, that summer may end. [p. 25]

Imagining what havoc big climatic shifts could wreak on small groups of subsistence farmers is difficult, let alone trying to imagine what it was like when the sea-levels were 90 meters lower than today. Fagan certainly can be accused of over dramatizing his narrative—his is a relatively straightforward style—but I still found his recounting of events, and their causes and consequences, vivid and fascinating. Sometimes he found just the right comparison to bring forward a small detail; this sentence caught my eye:

Fifteen thousand years ago, perhaps 40,000 Cro-Magnons lived in central and western Europe, well under half the number of people who pass through London's Heathrow Airport in a day. [p. 63]

Life is different when the population is so sparse, but Fagan did a good job helping me grasp what it was like while keeping the story alive and interesting with explanatory asides.

In 1892, a Peruvian sea captain, Camilo Carrillo, published a short paper in the Bulletin of the Lima Geographical Society, in which he drew attention to a warm, anomalous coastal climate that flowed along the Pacific coast, disrupting the rich anchovy fisheries close inshore. He wrote: "The Paita sailors, who frequently navigate along the coast in small craft ... name this counter-current the current of El Nino (the Child Jesus) because it has been observed to appear immediately after Christmas."

At the time, El Nino seemed like a merely local curiosity that disrupted fisheries and lowered the natural production of sea bird guano, a major Peruvian export of the day. A century of research by scientists all over the world has elevated the Christmas Child to the status of a global phenomenon, a seesaw of atmospheric pressure called the Southern Oscillation that affects the lives of millions—and has for thousands of years. The seesaw emanates from an east-west circulation in the eastern Pacific and a huge pool of warm water in the west. Dry air sinks gently over the cold eastern ocean, and flows westward on the southeasterly trade winds. When warming occurs in the eastern Pacific, the sea surface temperature gradient between east and west decreases, the trade wind flow weakens, and pressure changes between the eastern and equatorial Pacific follow, acting just like a seesaw—the Southern Oscillation.

The climatologist George Philander calls El Nino a dance between the atmosphere and the ocean. The dancers, gyrating unpredictably to a music that only they hear, make an ill-matched pair. The atmosphere is agile and quick to respond to prompts from its cumbersome partner. But their fandango triggers the eastward surge of warm water from the southwestern Pacific that starts an El Nino event. In the planet's catalogue of short-term climate changes, El Nino-Southern Oscillation (ENSO) events exercise an influence second only to the passing seasons. [p. 169—170]

Here, one more vivid example of how different and harsh life was for most of human history and pre-history.

Even in good years, the farmer [of 500 BC] endured the constant specter of winter famine. All it took to make people go hungry was too much or to little rainfall, an early or late frost, or an epidemic of cattle disease that decimated breeding stock and draught animals. Only the ancient ties of kin, social reciprocity, and a diminishing stock of wild plant foods and game kept every household from hunger. The threat of starvation always hung over the north, where centuries of good harvests had increased agricultural productivity, village populations rose in response, and expanding communities took up additional woodland and grazing range. People consistently underestimate how marginal subsistence agriculture is. Inevitably, farmers in growing villages take up more land, and as the best soils come under cultivation, they turn to more marginal fields, many of them on easily erodable hillsides. There is a subtle and invisible equation between population growth, good harvests, and the carrying capacity of the land. Almost invariably people farmed close to the limit, and sometimes beyond. many winters, villagers were hungry and people died. [pp. 195—196]

I didn't find this book quite so immediately satisfying as his The Little Ice Age : How Climate Made History 1300 – 1850, but I suspect that's only because the time periods are so much more distant and unfamiliar. Regardless, I thoroughly enjoyed reading it and learning from it.

-- Notes by JNS