Publisher’s Comments
“Climate has been making history for a very long time, though historians have rarely paid much attention to it. But as it turns out, a few less inches of rain, a change in temperature of just a degree or two can make all the difference in how human events unfold. The Great Warming demonstrates that although human beings made history, they very definitely do not make it under circumstances of their own choosing.”
— Ted Steinberg, author of Down to Earth: Nature's Role in American History and American Green: The Obsessive Quest for the Perfect Lawn.

Book Reviews

The Great Warming
“This is not only World History at its best, sweeping across all of humankind with a coherent vision, but also a feat of imagination and massive research. If Fagan has given the medieval period throughout the globe a new dimension, he has at the same time issued an irrefutable warning about climate change that is deeply troubling.
— Professor Theodore Raab, Princeton University

Climate Change? Been There, Done That
New York Times, by William Grimes
Published: March 21, 2008
If you don’t think climate change produces winners as well as losers, consider this: In the 12th and 13th centuries England exported wine to France. Vineyards also flourished in improbable regions like southern Norway and eastern Prussia. A centuries-long spell of mild, predictable weather blessed Western Europe with abundant crops, healthy populations and budget surpluses sufficient to finance projects like Chartres Cathedral.
       This is the credit side of a global balance sheet carefully itemized by Brian Fagan in “The Great Warming,” his fascinating account of shifting climatic conditions and their consequences from about A.D. 800 to 1300, often referred to as the Medieval Warm Period. The debit side is appalling: widespread drought, catastrophic rainfall, toppled dynasties, ruined civilizations. Abandoned Maya temples in the Yucatan and the desolation of Angkor Wat, supreme achievement of the Khmer empire, bear witness to climatic change against which royal power and priestly magic proved impotent.
      Mr. Fagan, an anthropologist who has written on climate change in “The Long Summer” and “The Little Ice Age,” proceeds methodically, working his way across the globe and reading the evidence provided by tree rings, deep-sea cores, coral samples, computer weather models and satellite photos. The picture that emerges remains blurry — scientists still understand little about such weather-changers as El Niño and La Niña — but it has sharpened considerably over the past 40 years, enough for Mr. Fagan to present a coherent account of profound changes in human societies from the American Southwest to the Huang He River basin in China.
      Longer summers and milder winters in Europe, especially stable from 1100 to 1300, allowed Norse explorers to range as far as Greenland and Labrador. At the same time a population boom in the rest of Europe led to radical deforestation, as trees were cleared to create farmland. By the end of the Medieval Warm Period half the forests that covered four-fifths of Western and Central Europe in A.D. 500 had disappeared.
      Across vast swaths of the globe, however, severe, persistent droughts lasted not just for years but for generations. The Sierras of modern-day California experienced the severest droughts of the past 4,000 to 7,000 years. Acorn trees died, and along with them peoples largely dependent on acorns for food. Although data remain sketchy, it seems probable that extended droughts dried up pastureland on the Central Asian steppe, propelling the armies of Genghis Khan westward.
      In the southern Yucatan arid conditions proved too much for the elaborate reservoirs, called “water mountains,” that the Maya used to irrigate their fields. Mr. Fagan permits himself an ominous aside: “The analogies to modern-day California, with its aqueducts for water-hungry Los Angeles, or to cities such as Tucson, Ariz., with its shrinking aquifers and falling water table, are irresistible.”
      Mr. Fagan is as interested in human adaptation as he is in weather. While California’s acorn eaters suffered, peoples in the Southwestern deserts expanded their diet to include new edible plants. In the Sahara caravan organizers simply adjusted their routes according to changing rainfall patterns.
      “The camel and its load-carrying saddle proved an effective weapon against heat and drought even in the worst years, when extreme aridity affected cattle people living far south of the desert,” Mr. Fagan writes.
      Northern China got the worst of both worlds during the Medieval Warm Period: violent climatic swings that resulted in lengthy dry spells or torrential rainfall. Meanwhile, in the South Pacific, faltering trade winds allowed Polynesian voyagers to head east, eventually reaching Rapa Nui (Easter Island) around 1200.
      Mr. Fagan has a somewhat rigid, formulaic way of presenting his material. Well aware that the general reader can handle only limited amounts of ice-core data, he tries to generate period atmosphere by including present-tense “you are there” episodes. “The hushed crowd in the plaza gazes upward to the temple at the summit of the pyramid,” one section begins. A little drama certainly helps, but he overworks this device. The book is overpopulated with sweating plowmen and fishermen peering into the mist.
      The causes of the Medieval Warm Period remain unclear, and there is debate over what the actual temperatures were. Mr. Fagan draws one unambiguous conclusion from the evidence, however, in a final chapter on the present-day implications of the great warming of a thousand years ago. Drought is the great enemy, “the silent and insidious killer associated with global warming,” he writes.
      Population density has placed enormous pressure on increasingly scarce water resources. As a result modern droughts, brought on by El Niño events, have taken an enormous toll in lives and wreaked measureless economic devastation. Prepare for worse.
      “Judging from the arid cycles of a thousand years ago, the droughts of a warmer future will become more prolonged and harsher,” Mr. Fagan writes. “Even without greenhouse gases, the effects of prolonged droughts would be far more catastrophic today than they were even a century ago.”
      For a spark of hope Mr. Fagan offers the example of Chimor, a kingdom in coastal Peru tormented by El Niño flooding and severe droughts throughout the Medieval Warm Period. The Chimu people thrived nonetheless by diversifying their food supply and protecting their scarce water resources. In a historically arid region with uncertain food supplies, they successfully tapped their centuries of experience with irrigation, soil conservation and water management. Look no further for a global-warming role model.

Warm Memories, An illuminating account of how global warming changed medieval history offers
disturbing lessons for today
Financial Times magazine, by Andrew Robinson
March 15/16, 2008
Now that global warming and climate change are established facts, however inconvenient, we are all starting to ponder what will happen to our particular corner of the planet in the next few decades. One approach is through the computer models used by the Intergovernmental Panel on Climate Change (IPCC) in their influential scientific reports. Another is to consider how conditions changed in warmer historical periods, notably AD800-1300, often known as the Medieval Warm Period.
      This is what the prolific writer and archaeologist Brian Fagan does in The Great Warming, a follow-up to his earlier study, The Little Ice Age, covering the global cooling from about 1430 to 1850.
      In Europe, there can be no doubt of the existence of the medieval warming, even though we lack reliable temperature
records predating 1850. In the 12th and 13th centuries, so temperate was England that merchants exported wine to France, to the consternation of French growers; wine was also produced in southern Norway.
       At the same time, following the Norse settlement of Greenland in the AD980s, that inhospitable place had a flourishing economy for three centuries until it was abandoned to the ice around 1450.
      Elsewhere the record is less clear-cut, as Fagan is acutely aware. “The Medieval Warm Period was not a discrete episode when climate was distinctly different from what came before,” he cautions. Nevertheless, on the basis of various clues, he detects the fingerprints of the warming on many key events worldwide.
       The collapse of the Classic Maya civilisation in Central America in the ninth century was probably precipitated by successive droughts in a land where water supplies were always under stress. The settlement of remote Easter Island (Rapanui) around 1200 by canoeists heading east from Polynesia with westerly winds may have been made feasible by the faltering of the usual northeasterly Pacific trade winds during El Niño events connected with warmer sea-surface
temperatures.
      Genghis Khan’s Mongol invasions in the early 13th century could have been prompted partly by drought wreaking havoc on the pastures of the steppes. This possibility is supported by the withdrawal of his grandson Batu Khan and the Golden Horde in the 1240s at the height of their military success with the return of cooler, wetter conditions.
      These are not mere conjectures. They are based on climatological studies of recent vintage, using ice-cores, deep-sea and lake cores, coral records and tree rings, supplemented by historical documents such as the reports of the flowering of cherry trees in Japan and Korea that date back a thousand years. Five-hundredyear- old pines from the mountains of Mongolia have allowed experts to construct a climatic sequence back to AD850.
      “The prolonged warm period detected in the Mongolian tree rings coincides with Genghis Khan’s savage conquests,” Fagan writes. Also important is the variation in solar irradiance caused by small tilts in earth’s orbit, sunspots and major volcanic eruptions – the eruption of Mount Pinatubo in the Philippines in 1991, for example, counteracted current global warming for several years.
      His conclusion is that the medieval warming was generally good for Europe, but it produced prolonged droughts in many parts of the world, including the Sahara, Peru, India and northern China, each of which gets a chapter.
      The droughts were especially severe in the American west, Fagan’s home for decades (in Santa Barbara, California) after he emigrated from England. Tree rings from multiple western locations agree that the four driest periods centred on AD935, 1034, 1150 and 1253, followed by an extended wetter period from 1300-1900, then a return to droughts.
      Thinking of the fate of the profligate Maya rulers, Fagan remarks ominously: “The analogies to modern-day California, with its aqueducts for waterhungry Los Angeles, or cities such as Tucson, Arizona, with its shrinking aquifers and falling water-table, are irresistible.”
      The Great Warming is a thought-provoking read, which marshals a remarkable range of learning, not least its author’s experience of sailing and the oceans. According to him, today humankind is more, not less, vulnerable to climate change than it was a thousand years ago – because today so many more millions are living at a subsistence
level. Moreover, the global temperature predicted for 2050 by the IPCC is substantially higher than in medieval times.
      If Fagan is right, within a decade or two I predict that Hollywood producers will decamp from drought-ridden
Los Angeles for cooler climes.

— Andrew Robinson is the author of “Earthshock” (Thames & Hudson), which won the Association of Earth Science Editors Outstanding Publication Award.

Drought and Famine — What the Past Teaches us to Fear most about Global Climate Change
Amercian Scholar
You can hear it under the breath of grudging half-converts now sighing about inconvenient truths. In response to reports from the Intergovernmental Panel on Climate Change and the National Academy of Sciences which confirm that humans are causing global climate to change, they concede this fact and yet mutter: so what? Most people recognize an unsettling future when they see it, but some still wonder if climate change will be that bad. A vocal minority even trumpets the potential benefits of longer corn-growing seasons in the temperate Great Plains. So long as subsidized ethanol keeps prices up, expect a rush on Canadian real estate. Brian Fagan, an emeritus professor of anthropology at the University of California, Santa Barbara, offers a unique contribution to this discussion. Dismissing the “chatterers and doomsday sayers,” Fagan notes that “almost none of these self-proclaimed prophets bother to look back at climate change in earlier centuries and millennia, except for politically charged discussions as to whether the world was warmer a thousand years ago than it is today.” The Great Warming escapes this tired debate. The globe is warming, Fagan assures us, and the primary cause of that warming is human activity. That settled, Fagan turns our attention back a full millennium to demonstrate historical climate data’s hidden potential as a source for highly plausible doomsday scenarios. The Great Warming explores the confluence of climate and culture during a period of global warming beginning around 800 A.D. and ending around 1300 A.D., dubbed the Medieval Warm Period. Fagan’s investigation highlights a little-discussed danger that we will have to face as we confront a warmed world: famine. Calling it “the silent elephant in the climatic room” of all global warming debates, Fagan finds famine brought on by sustained droughts almost everywhere in this past world, from the American West to Northern China to the Peruvian highlands. Sometimes famine caused (only!) prolonged suffering and mass death, while in a few cases, as with the Maya, it led to the downfall of great civilizations. Modern civilizations throughout the world today, with much higher population densities and limited mobility, would be alarmingly susceptible to generation-long droughts. Even more than rising sea levels or catastrophic storms, Fagan cautions, we should be wary of drought and famine: forces that would lay low even the confident. Despite this warning—amplified in a brief, closing chapter—Fagan’s passion lies beyond preaching doomsday. Readers should not underestimate this book, writing it off as another addition to a burgeoning genre: the travel guide to a torrid world. Fagan’s project is much bigger. He re-creates past societies in a lively and engaging manner, aided by his expert synthesis of obscure climatological data, much of which has only become available within the last 30 years. The reader witnesses: Europeans in the High Middle Ages, buoyed by good harvests and warmer temperatures; the Norse taking advantage of retreating glaciers to make their great northern sea voyages and their eventual commerce with people from as far away as the Bering Strait; the Mongols, conquering a great empire as they flee a harshening desert; and even Polynesian islanders making the most of changes in wind patterns to reach the impossibly small and distant Rapa Nui. Climate change contributed to these instances of cultural efflorescence and expansion. In his ability to bring nature into our global, historical narratives, Fagan rivals Alfred Crosby, William H. McNeill, and Jared Diamond, scholars who revealed to large audiences the explanatory power of microscopic biota or gross geography. Fagan promises to do the same for longterm climate dynamics. He proves that the regional volatility associated with climate change—best exemplified by the swings of El Niño/Southern Oscillation, which Fagan places second only to the seasons as a determinant of climatic variation — shaped societies. And he does this without succumbing to a reductive determinism. Take, for example, Fagan’s engaging story of the near invasion of Europe by fiercely disciplined Mongol horsemen. Fagan argues that the Mongols, a nomadic people who lived on the Eurasian steppe, had long moved with the rhythms of the “desert pump” — the desert expanding with heat and drought, then contracting as cooler rains made way for resurgent vegetation. Based on the best records available — tree-ring sequences read from preserved Siberian pines—higher temperatures and drought on the Mongol’s home steppes coincided with the string of great victories that established Genghis Khan’s magnificent empire. Still thirsting for more fertile land, the Mongols made it to Europe in 1241 and defeated Henry the Bearded in Silesia. Two factors—one human and one climatic—intervened at this moment. Genghis’s successor as Great Khan, his son Ögötai, died. Batu Khan, who sought the office of Great Khan himself, abandoned his plans to invade Europe and returned to the steppes to press his claim to the throne. When he got there, he found vastly improved grazing conditions brought on by cooler, wetter weather. The new productivity of the land having muted Batu’s incentive to drive west, Europe remained barely touched by the Mongol Empire. On the opposite side of the world, Maya lords on the path to empire bound themselves to the rains and their ability to harvest them. In obeisance to their god-kings, Mayas constructed great Water Mountains: reservoirs that served the growing cities of the southern lowlands. The lords played out their divine claims in temple rituals — until the sustained and unprecedented droughts that arrived with the Medieval Warm Period undermined their political and religious legitimacy. The civilization, already stressed by war amongst local lords, was not prepared for multiyear droughts that could outlast even their advanced water technologies. With the simultaneous failure of the Water Mountains and the political structure, the great Maya cities collapsed in the early 10th century. In contrast, the Chimu, in what is now Peru, survived their droughts. Like the Maya, the Chimu had built a centralized society dependent on massive waterworks. But, unlike the Maya, the Chimu knew the sting of great droughts and had already adapted by building redundant irrigation systems to withstand the flooding that preceded Pacific-spanning La Niña droughts, by planting a wide variety of crops on intensively farmed fields, and by hedging their bets with a trade in anchovies from the coast. As Fagan puts it, “Chimor’s cities survived the Medieval Warm Period because its lords closely supervised a subsistence culture that revolved around insuring against drought, floods, and deprivation.” For those parts of the world that offer no tale of expansion or destruction, Fagan explains stability. The people of the Sahel — those responsible for the Sahara gold trade—barely felt the warm centuries. The gold trade was grueling, and camel drivers depended on constant reconnaissance to successfully navigate the expanding desert sea. But what was new about that? No drama animates Fagan’s chapters on the Sahara gold traders or the similarly mobile peoples who lived near Owens Lake in modern- day California. Yet drama seldom ends well: when it comes to climate change, we should prefer boring stories to exciting ones. The society that presents a boring story for future historians is one that remains flexible, and, in so doing, simply remains. Ultimately, writing climate change into history exposes the complex relationship of the historical enterprise to the past, present, and future. The Great Warming depends on information that scientists have only begun to mine from tree rings, ice and deep-sea cores, and coral records. Yet, despite Fagan’s complaint that past climate data has been tied up for too long in debates on anthropogenic global warming, such data often owes its existence to those debates. Present concerns motivated climate research, from which we now draw insight into history. Insight into the foreign past can be disorienting but also productive. In the case of The Great Warming, our gazing dizzily into the past for a few hundred pages has done us a great service. Fagan cannot prove that drought and famine will be key problems in our warming world. He is looking at the past and at vastly different societies from our own. We would be fools, though, to ignore his warnings
— Dan Bouk

Review from Booklist, December 15, 2007
A prequel to the author's fascinating The Little Ice Age (2001), a history of climate's influence on civilization from 1300 to 1850, Fagan's work queries the response of societies to the warm period of 800 to 1300. Encompassing the inhabited globe, Fagan's breadth balances with his power to synthesize a range of scientific and archaeological evidence with historical imagination, achieving a global perspective on the medieval warm period, as scholars title the time. Each chapter about a geographical area evocatively depicts its farmers or hunters in the backbreaking task of wresting food from their environment before presenting locally specific weather events of these centuries. (Sidebars explain how scientists determine ancient weather.) Stressing climatic volatility even within a planet-wide warm-up, Fagan delineates the precarious relationship between societies outgrowing their resources. Bountiful to Europe, the warm period was a disastrous drought to more southerly civilizations in Asia, Central America, and southwest North America. Superbly integrating the human and climatological past, Fagan's expertise wears easily in a fine popular treatment relevant to contemporary debate about climate.
— Gilbert Taylor

Kirkus review, December 2007
What happened when the world grew warmer from 800 to 1200 CE. Drawing on data gathered during the past 30 years by climatologists using such modern tools as deep-sea cores, ice borings, computer modeling, tree and coral rings, Fagan (Fish on Friday: Feasting, Fasting, and the Discovery of the New World, 2006, etc.) offers a tentative history of the “Medieval Warm Period,” when rising surface temperatures produced sudden, unpredictable climate swings throughout the world. Although much remains unknown, there is good evidence that there were winners and losers in this period of global warming. It was a time of abundant harvests and the cultural achievements of the High Middle Ages in Europe, while other areas from the Americas to China and Eastern Africa experienced long periods of drought and famine. “Farmers went hungry, civilizations collapsed, and cities imploded,” writes Fagan. Prolonged drought stalks these pages, a silent killer the author considers a harbinger of what could happen during our own time of global warming. Medieval droughts lasted for decades in California and the American Southwest, he notes. Even the lower Hudson River Valley experienced arid conditions that, if they occurred today, would endanger urban water supplies. Much of the book describes how the Medieval Warm Period affected trade, warfare and other aspects of life. In Central America, drought repeatedly disrupted the lives of the Mayans, who relied on unpredictable water sources. Elsewhere, many rural societies coped by building canals for irrigation, borrowing food from neighbors in times of need, maintaining kinship ties with distant communities and moving there when droughts came. Today’s more densely populated planet, notes the author, with 250 million people living on agriculturally marginal lands, is far more vulnerable to long periods of drought, especially the developing world and such populous areas as Arizona, California and southwestern Asia.

An alarm bell ringing out from a distant time. 

Publisher’s Weekly November 5 2007
Global warming is hardly new; in fact, the very long-term trend began about 12,000 years ago with the end of the Ice Age. Anthropologist Fagan (The Little Ice Age) focuses on the medieval warming period (ca. 800-1300), which helped Europe produce larger harvests; the surpluses helped fund the great cathedrals. But in many other parts of the world, says Fagan, changing water and air currents led to drought and malnutrition, for instance among the Native Americans of Northern California, whose key acorn harvests largely failed. Long-term drought contributed to the collapse of the Mayan civilization, and fluctuations in temperature contributed to, and inhibited, Mongol incursions into Europe. Fagan reveals how new research methods like ice borings, satellite observations and computer modeling have sharpened our understanding of meteorological trends in prehistorical times and preliterate cultures. Finally, he notes how times of intense, sustained global warming can have particularly dire consequences; for example, “by 2025, an estimated 2.8 billion of us will live in areas with increasingly scarce water resources.” Looking backward, Fagan presents a well-documented warning to those who choose to look forward. Illus., maps.

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