The Great Warming: Climate Change and the Rise and fall of Civilizations

May 25, 2009 5:23 am

Brian Fagan, Bloomsbury Press, 2008, 282pp.

Brian Fagan cannot be counted among those who dismiss the threat of global warming. He understands better than most that warming periods have occurred and that their effects on human societies can be drastic and severe. In his book The Great Warming: Climate Change and the Rise and Fall of Civilizations Fagan examines what historians and archeologists refer to as the medieval warming period, occurring approximately from 800 – 1300 A.D. By examining the relationship between climate and the respective fates of various civilizations, Fagan produces a compelling case for climate change as a vital force in history. His analysis is at once sweeping, subtle and beautifully descriptive. Fagan showcases an encyclopedic knowledge of the relationship between climate and civilizations as disparate as the Mongolian Empire in the Eurasia Steppe, the Maya Empire based in the Yucatan Peninsula and the Inuit based in the Canadian Artic, but draws firm conclusions only where warranted. Otherwise much of his analysis is well reasoned but necessarily speculative. Nevertheless, Fagan demonstrates that slight changes in temperature and rainfall patterns during the centuries in question produced subtle but vitally important changes to climate. More interesting is how climate change up ended apparently stable societies. For this reason, The Great Warming is also a grim warning about the potential consequences of climate change for our own civilization.

Fagan makes clear the effects of the medieval warming period were varied and depended on other climatic factors. In Europe the warming period was characterized by a 10% decline in rainfall and a temperature increase of 0.9 – 1.8 degrees Fahrenheit. The seemingly minor changes had far reaching effects on the overall climate and agricultural production. In Europe, the period was characterized by relatively stable harvests and slightly warmer winters. This combination was conducive to a period of population growth and the accelerated formation and expansion of towns and cities. As populations increased, more people were engaged in activities other than agriculture. Thus despite the relative stability of the climate, agricultural production was under increasing stress: there were more mouths to feed and yet fewer people engaged in agricultural production. Food shortages remained a constant threat, as well as the social unrest that would inevitably accompany them.

In explaining the interaction between climate and human communities, Fagan introduces the metaphor of the ‘desert pump,’ which refers to the desert’s capacity to draw in animals, plants and peoples during periods of rainfall. The effect of the precipitation is to shrink the desert: plants take root where rainfall occurs, prompting the eventual migration of nomadic populations and their animals. Once the rainfall ceases, the desert conditions return and the nomadic populations are forced to migrate once again. This is why the Eurasia steppe was comprised of populations who were perpetually on the move and perpetually at war with each other over scarce resources. Survival in such unforgiving lands was precarious at any time, let alone during a period of intensified warming.

Indeed, the effects of the medieval warming period were more dramatic in climates of either extreme heat or cold. To take one example, the collapse of the Maya Civilization highlights the vital relationship between climate patterns and cultural and political instability. The Maya civilization was located in the Yucatan Peninsula. Like other civilizations, the Maya were very much attuned to subtle climatic shifts and were thus adept at developing water management strategies conducive to agricultural production. Over the centuries, agricultural production was elaborate and sophisticated enough to help the Maya Civilization build Tikala and other great cities, the eventual effect of which was to expand their population base. Nevertheless, sustained warming eventually produced drought conditions, from which the Maya did not recover. By early in the 12th century most remaining Maya communities were scattered.

By contrast, the warming period created important opportunities for peoples living in the bitterly cold and harsh climates in and around the Artic circle. Evidence suggests that the warming period produced slightly warmer summers in areas as far north as the Beaufort Sea and east through the Canadian Archipelago and Baffin Bay. Water was consequently easier to navigate during the short summers, making possible encounters between different civilizations. Fagan relates how the Inuit came into contact with the Norseman, a people who migrated from Norway down to the Shetland Islands and eventually west to Baffin Bay before settling in Greenland. The Inuit had established trading relations with other peoples and were less insular then other groups inhabiting the harsh landscapes of the Canadian north. Indeed both the Inuit and the Norsemen craved what turned out to be a mutually beneficial trading relationship. The Inuit possessed ivory and the Norsemen iron. The Norsemen needed narwhal and walrus ivory to pay as tithe to the Norwegian Church. But a prolonged period of intensely cold winters and summers in the mid 14th century served to sever the connection between the Norsemen and Norway. The Norsemen migrated to the south of Greenland and the trading relationship with the Inuit collapsed. It is one among many fascinating stories of climate change Fagan tells in this remarkable book.

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