Brian Fagan’s The Great Warming: Climate Change and the Rise and Fall of Civilizations contributes another fine book to the growing library of the history of climate change and human life.   Fagan here concentrates primarily on the Medieval Warm Period from about 800 to 1300 CE.   Jared Diamond’s Collapse: How Societies Choose to Fail or Succeed, is perhaps the best known climate history with some 10 examples of societies — many of them in the Medieval Warm Period– which failed, or succeded for a while.  Diamond’s focus, as seen in the titles,  is different than Fagan’s, less a history of climate and its influence on people and more on the decisions societies make, or fail to make, when confronted with great changes in circumstances. Other recent books on the general theme are Catastophe: An Investigation into the Origins of Modern Civilization, by David Keys, which covers some of the same events as Fagan,  and Late Victorian Holocausts: El Nino Famines and the Making of the Third World, by Mike Davis, which looks at climate history much nearer to the present time. Fagan himself, emeritus professor of anthropology at the University of Santa Barbara, has several related titles, including The Little Ice Age: How Climate Made History 1300-1850,  the centuries that followed the Medieval Warm Period, and The Long Summer: How Climate Changed Civilization,  which might be better called “How Climate Made Civilization,” as it looks at the years of pre-history, from about 15,000 BCE to the beginning of the Little Ice Age, about 13,500 CE.  Knowledge about climate and human habitation in these long ago centuries has increased greatly in recent years due to new and more subtle technologies, and the marvelous ability of serious science to take what is understood, create new theories which can be tested with new devices and knowledge cross fertilized between archeology, anthropology, climatology, and all of these with the paleo- prefix before them.  The Great Warming is a great place to begin.

Fagan picks the Medieval Warm Period for examination in part because it is continuously cited by climate change deniers as proof, they say, that the earth has warmed up before and it’s part of the natural cycle of things. The conclusions of 99% of climate scientists who say today’s climate is on track to warm to catastophic levels is so much bunkum. The other reason to focus on this period is because the recent surge of data-based evidence from all around the world has given us a much clearer picture of conditions we could only guess at a few years ago: carbon-dated trees long buried below the water of Mono and Walker Lakes in California, measurable titanium content in layered sequences of deep sea core, reflecting heavy and light run-off during precipitation, more and deeper ice-core samples showing carbonate levels connecting long droughts in the Tibetan plateau with droughts in the southern Andes.

The evidence of history, Fagan finds, is that while there were large, positive effects of the  Medieval Warm Period, they were largely confined to northern and western Europe. Looking further afield, the warmth that brought longer growing seasons to France and Germany, and made England a wine exporting country, brought devestating drought to the Eurasian steppes and almost certainly drove Ghenghis Khan and his sons west, destroying Baghdad, the center of the Islamic world, and into Vienna, poised to drive into Europe.

In the American southwest, similar decades long droughts, again during the Medieval Warm Period finished the Chaco Canyon pre-Pueblo civiliation. Multiple three and 6 year droughts sapped the Mayan empire until its collapse in the early 10th century.  In China, the warm period was associated with violent swings between extremes:

The droughts were not continuous but cyclical, which would have had dangerous shock effects on the loess lands where the northern borderlands lay.   When a sudden wet year followed a long drought cycle, , floods would have inundated the arid fields and disused irrigation works in short order.   The centuries of the Medieval Warm Period were climactically extremely volatile in this region of dramatic rainfall shifts, perhaps even more so than anywhere else on earth.

In Europe, where the increased warmth laid the basis for moden life, he cites crop productivity before the warm period then shows how it grew as the summers lengthened, rainfall became more regular, predictability was more accurate. As crops increased in size and food was above bare survival amounts, life span increased, family size got bigger.  As families got bigger more land was needed. Marginal land was converted and could be plowed with the advent of the moldboard plow which could turn over clayey ground as the earlier ard plow could not. Deforestestation began apace. In 500 CE over 3/4 of temperate western and central Europe was forest or swampland. By the early 1300s, the end of the warm period, over half of that was gone. As early as 1322 in England, villagers complained about deforestation. As crop-based wealth grew and supported more people, skilled trades advanced, capital was accumulated and such monuments as the Cathedral of Notre Dame could be built…

The chapter about the Mongol raiders is very interesting, though he spends too much time, in my opinion, on their “interesting” ways of killing, and the fear they sowed everywhere they went, and too little on the climate connection. He does say:

The prolonged warm period detected in the Mongolian tree rings coincides with Ginghis Khan’s savage conquests: hotter and drier conditions would have mean a surge in warfare at a time of potential hunger and rising unrest.

and follows Batu Khan’s withdrawal from Vienna by saying that the wetter, better conditions in Bulgaria and the Cuman steppes took away the incentive to drive on into Europe’s heartland.

He also has interesting, more speculative chapters about the Inuit in the Yukon and how warmer seasons allowed them to push east, how the gold trade between western Africa and Egypt was dried up as the sahara grew southward.

To Fagan’s own surprise, after synthesizing all the material available, “as my research progressed away from Europe, I realized that drought was the hidden villain in the the Medieval Warm Period.” And not only then:

In a telling analysis of ninteenth century droughts, the historian Mike Davis has estimated, conservatively, that at least 20 million to 30 million people, and probably many more, most of them tropical farmers, persihed as the consquence of harsh droughts caused by El Niño and monsoon failures during the nineteenth century, more people than in virtually all the wars of the century.

Fagan has an important story to tell, and by and large he tells it well.  The cut-outs with explanations of El Niño and the Southern Oscillation or Pacific Decadal Oscillation are helpful, as are the many maps, illustrating the regions under discussion.  Less successful for me are the periodic present tense narratives of peoples thousands of years ago:

The gray light of a clear sky before dawn spreads across a dry lake bed.  The men crouch low among the shrubs on the dry floor of a huge, rapidly shrinking lake in what is now California  This is the driest year they can remember…

For some readers, these portions may humanize the larger systems histories.  For me, they are a different register, and interrupt my otherwise pleasurable, and informative reading.

His fear is great.  Those societies that managed to survive calamitous droughts and other forms of climate chanage were those which were most adaptable, typically associated with smaller and well connected communities.  The larger, and less flexible cities or societies became, the less able they were to adapt.  He hold out some hope, however small.

The people of a thousand years ago remind us that our greatest asset is our opportunism and endless capacity to adapt to new circumstances.  Let us think of ourselves as partners with rather than potential masters of the changing natural world around us.

 The Great Warming is certainly worth reading, as it look like, are those others listed above.  For a more general view on climate change, the events and science of today, my preferred book is Tim Flannery’s The Weather Makers: A History of Climate Change.  It’s a series of essays, engaged in climate science and detailing the trouble spots on the globe today, examples of what we are facing.  Another excellent primer is Joe Romm’s [of Climate ProgressHell and High Water: The Global Warming Solution.

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