Alex Mclane's Reviews > The Great Warming: Climate Change and the Rise and Fall of Civilizations

The Great Warming by Brian M. Fagan
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Dec 02, 10

Read in November, 2010

Fagan, Brian. “The Great Warming: Climate Change and the Rise and Fall of Civilizations” (Bloomsbury Press, New York 2008)

Fagan reveals a variety of effects on the global Medieval Warm Period from the abandonment of Pueblo Bonito and Angkor Wat structures due to drought to the increased farm yields in Europe due to predictable moderate weather patterns. Fagan navigates through a web of archeology and the latest climate based research to paint a picture of a time period where the entire world was effected by slightly higher global temperatures lasting for a few hundred years roughly from 950-1250 AD. The intended audience for this book is both the historical and scientific communities as well as anyone interested in global warming. Seeing the returns from the current climate trends being warmer than usual it seems a look back at past warming events like the Medieval Warm Period will help in preparing for the effects of current warming temperatures. Fagan’s concluding paragraph addresses the current situation with a stern warning of prolonged drought.
Fagan takes the reader on a trip around the world revealing the effects of climate change on human societies during the warm period in each chapter. Instead of moving geographically it might be better to review societies who benefited from the warming and those who were left wanting. Europe definitely benefited from the warm period. The warmer conditions provided calm “mirrorlike” seas that increased fishing production in Europe. Norse sailors established colonies in Greenland and traded iron for furs and ivory to Inuit hunters. The predictable weather allowed for budget surpluses, healthy populations, and abundant crops that helped finance some of the great cathedrals to be built in Western Europe. Also Europe got a break when Batu Khan withdrew from a Mongol planned Western European invasion because of improved pasturage in the Steppes that increased trade and provided vast conquered territory for grazing (p. 65). Though Fagan noted the increased temperatures and drier conditions might have been one of the major factors in the expansion of the Mongol Empire in the first place. Drought and shrinking pasturage usually coincided with unrest and military aggression among Steppe societies.
The settling of some of the most remote islands on Earth was brought about by changing weather patterns caused by warmer conditions. During major El Nino events easterly trade winds died down and westerlies become more common in January and February during the Medieval Warm Period. Fagan notes recent studies of the Pacific trade winds have shown a weakening of the Walker circulation in response to warming. Warmer sea surface temperatures during El Nino events slows down and could reverse the circulation from high pressure systems in the eastern Pacific Ocean to low pressure systems in Indonesia. The seesaw opposite of El Nino, the La Nina weather pattern, seems to have occurred during this time period as well bringing relatively cool and dry conditions to much of the Pacific (p. 181). The dry La Nina conditions possibly brought on by the weakening of the Walker circulation could have been the protagonist that fueled Polynesian sailors to find and settle new islands in the far reaches of the Pacific.
Although there were some victors in the “Great Warming” the idea of Fagan’s book and what he hit on with his warning for tomorrow is that increased global temperatures coincides with drought in many places on Earth. Those that suffered most during the Medieval Warm Period included the Native Americans in California who saw a failure in acorn harvests. A similar story occurred with Native Americans in the Great Basin where the bark beetle ravaged Piñón forests and caused harvests of their staple food the pine-nut to plummet. The warm period also coincided with the collapse of the Mayan Civilization in Central America. A multiyear drought that occurred in the Southern Yucatan overtaxed the water systems controlled by the nobility and citizens scattered and abandoned great cities.
There were some civilizations that rode out the storm of the great warming such as the Chimor who had adapted their irrigation strategies and diversified their food supply to prolonged droughts before the Medieval Warm Period. The Chimor lived next to one of the richest coastal fisheries in the world off the coast of Peru which allowed abundant anchovy harvests even when irrigation systems were low on water. The account of the Chimor civilization and its comparison to the Maya is one of the greatest strengths of Fagan’s book. It shows detailed research on Fagan’s part to locate a civilization that was well prepared for changing climate conditions and offer hope if future conditions get worse than they are presently.
Another strength of Fagan’s book is that he took the time explain the proxy evidence he used in the research for the book. This included measuring the titanium content in the Cariaco core sediment deposits from rivers flowing into the ocean in South America (p.140). High concentration of titanium reveals a greater amount of rainfall in the local watershed. There was less titanium found during the Medieval Warm Period timeframe. The unusually accurate annual growth rings in Palmyra coral samples reveal data in Australia’s Great Barrier Reef of cool and dry La Nina conditions during the Medieval Warm Period. Although fragile, coral can rival modern instrument records with its accuracy of oxygen isotope O-18 and O-16 indicating cool and warm water respectively (p. 179). Fagan noted bone fragments found in ancient rubbish heaps helped indicate high consumption rates of salt-water fish found even as far inland as Vienna, Austria during the Medieval Warm Period (p. 40). Proxy evidence of tree-ring data from old Siberian pines in Mongolia place Genghis Khan’s conquests within an extended warm period with frequent droughts. The site of analysis for the pines was chosen at Sol Dov for the ecological conditions were such that tree growth was influenced by temperature changes from one year to the next (p. 61).
Criticisms’ of Fagan’s book include an ambiguous reference that came in Fagan’s preface when he claimed “no one in their right mind would argue that climate ‘caused’ all the economic, political, and social changes described in these pages [p. xvi]. That kind of environmental determinism, the notion that climate caused the major developments of history, was discredited more than three quarters of a century ago [p. xii].” Having published this book in 2008 and looking back 75 years (three quarters of a century ago) would put the timeframe of Fagan’s reference to 1933 or the start of WWII. Most climates referred to in reference to the causes of WWII are human constructions such as political climates and economic climates but not actual weather climates. This was a main argument in Fagan’s book that there have been many social upheavals caused in part by a changed climate such as military upheaval with the Mongolian Empire. It would have been nice if he expanded on climate effects on major wars in history instead of just noted that not all wars have roots in climate conditions but perhaps there’s time for that issue in another book.
The greatest strength of Fagan’s book is his analysis of the effect of the Medieval Warm Period on prolonged droughts in many parts of the world. Fagan emphasized his argument with the word “prolonged” writing “the dry spells of a thousand years ago spanned not years, but generations (p. 229).” Environmental proxy evidence that has been researched around the world was painted a much broader picture of the effects of the Medieval Warm Period rather than just relying on European based sources such as artists’ renditions of landscapes at the time and wine production in England. I would recommend this book to the reader for many of the conclusions Fagan drew from the Medieval Warm Period have significant implications on how to prepare for present rising temperatures. Fagan’s cautious warning against the threat of prolonged drought should be taken seriously especially in geographical areas where it occurred in the past during the Medieval Warm Period.


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