The Great Warming Read online

  The Great Warming

  CLIMATE CHANGE AND THE

  RISE AND FALL OF CIVILIZATIONS

  Brian Fagan

  BLOOMSBURY PRESS

  NEW YORK • BERLIN • LONDON

  To

  the Great Cat of Ra and the Venerable Bede

  Black-and-whites extraordinary

  __________________

  “All right,” said the Cheshire Cat; and this time it vanished slowly, beginning with the end of the tail, and ending with the grin, which remained some time after the rest of it had gone.

  —Lewis Carroll, Alice’s Adventures in Wonderland (1865)

  Contents

  Preface

  Author’s Note

  1. A Time of Warming

  2. “The Mantle of the Poor”

  3. The Flail of God

  4. The Golden Trade of the Moors

  5. Inuit and Qadlunaat

  6. The Megadrought Epoch

  7. Acorns and Pueblos

  8. Lords of the Water Mountains

  9. The Lords of Chimor

  10. Bucking the Trades

  11. The Flying Fish Ocean

  12. China’s Sorrow

  13. The Silent Elephant

  Acknowledgments

  Notes

  Preface

  “My name is Ozymandias, King of Kings,

  Look on my works, ye Mighty, and despair!”

  Nothing beside remains. Beyond the decay

  Of that colossal wreck, boundless and bare,

  The lone and level sands stretch far away.

  —Percy Bysshe Shelley, “Ozymandias” (1812)

  THE GREAT HOUSE, PUEBLO BONITO, stands gaunt and silent, nestling under the precipitous cliff, the serried rooms open to the gray sky. A chill wind scatters dead leaves and delicate snowflakes across the empty plaza on this bleak winter day. Clouds hang low over the cliffs of Chaco Canyon, New Mexico, swirling in the gusts of the January storm. The silence is complete.

  A thousand years ago, Pueblo Bonito was a sacred place, which echoed to spectacular dances at the summer solstice. Visitors from miles around flocked to this, perhaps the greatest of all southwestern pueblos. Then, in A.D. 1130, fifty years of drought sank over Chaco Canyon. Maize yields plummeted. Within a few years, Pueblo Bonito emptied. Half a century later, Chaco Canyon was virtually deserted. After many centuries within the canyon walls, the Ancestral Pueblo had moved away and settled with relatives living in better-watered areas.

  This winter day, no ghosts of a thousand years ago rise to haunt my imagination and excite my consciousness. The past is dead, long vanished into oblivion. I’m reminded of Shelley’s Ozymandias, King of Kings, his deeds forgotten, his palaces reduced to crumbling ruins.

  In A.D. 1118, a decade before the great drought arrived at Chaco, the Khmer god-king Suryavarman II ascended to the throne of Angkor on Cambodia’s Tonle Sap in Southeast Asia. Almost immediately, he began building his masterpiece, Angkor Wat. Thousands of his subjects labored on his palace and temple, a vast replica of the Hindu universe, complete with sacred mountains. Nothing mattered but to serve the god-king. Suryavarman and his successors created a centripetal religious utopia erected on a foundation of intensive rice cultivation, irrigated with canals, reservoirs, and flooded paddies nourished by the summer flood.

  Angkor Wat no longer boasts gilded towers and brilliantly painted temples. But it still mesmerizes, with its maze of stairways and long, echoing galleries adorned with yard upon yard of royal processions, armies on the march, and sinuous dancing girls promising the delights of paradise. Then you realize that the place is lifeless, a moment frozen in time, abandoned by its builders when in full magnificence, partly because drought dried up their rice paddies and they went hungry.

  Again, Ozymandias comes to mind. Angkor Wat leaves you with a sense of futility and despair.

  Chaco Canyon and Angkor Wat are silent testimony to the power of climate to affect human society, for better or worse.

  Soon after Suryavarman’s loyal subjects labored on Angkor Wat, the cathedral of Notre Dame de Chartres rose in northern France. Built in a mere sixty-six years after A.D. 1195, this Gothic cathedral was the sixth church on the site, a miracle in stone and glass. Like Angkor Wat, Chartres is a masterpiece, but this one’s still part of the fabric of human life, a place where masses are celebrated and psalms chanted. Here the infinite becomes a miracle in stone and glass. Chartres is all windows, set among soaring beams and graceful arches. Gemlike sunlight shines through them, creating transcendental effects. The setting still brings heaven to earth and links the secular and the spiritual, just as it did a thousand years ago. Here the past is still alive.

  Chartres was built at a time when Europe basked in a warmer climate and enjoyed a long series of good harvests. Those who benefited thanked God and the unknown powers of the cosmos for their bounty. They built a cathedral in gratitude.

  The world of a thousand years ago was a vibrant, diverse place, much of it a tapestry of volatile civilizations, great lords, and endemic warfare. Camel caravans, the Great Silk Road, and monsoon winds connected much of the Old World in the first iteration of a truly global economy. However, most humans still lived in small hunting bands or as subsistence farmers, surviving from harvest to harvest, eking out a living from the soil. We have long known of this world from archaeology, from excavations into great cities, into caves and humble shell mounds, and from scatters of Norse iron nails in the High Arctic, from historical documents and oral traditions. But it’s only now that we’re learning just how profoundly the warmer climate of the day affected humanity.1 This book is the story of five centuries of changing climate—in fact, of a global warming—between A.D. 800 and 1300, and of the changes’ impact on the world of a millennium ago. As in our own time, climate change did not plot a straight line from year to year, and varied from place to place. But its peaks and valleys followed a trend that we can clearly make out in retrospect. We have much to learn from this story about the power of climate change to affect our own future.

  THE MEDIEVAL WARM Period was named half a century ago by a British meteorologist, Hubert Lamb.2 He wrote of an era from about A.D. 800 to 1200 that he pieced together from a jigsaw of climatological and historical clues: four or five centuries of relatively amiable climate that brought good harvests to Europe and permitted the Norse to land in Greenland and North America. The Medieval Warm Period gave way to six centuries of highly unsettled climate and cooler conditions: the Little Ice Age.

  We have long known many details of the better-documented Little Ice Age, when, famously, the Thames River froze over.3 There were famines and severe tempests, occasional winters of exceptional cold. But the Medieval Warm Period was, until recently, a climatological mystery. Lamb wrote at a time when paleoclimatology, the study of ancient climate, was in its infancy, and long before humanly caused global warming was on the scientific radar. Today, we know a lot more about the Medieval Warm Period than he did. Thanks to tree-ring research, we now have detailed information on seasonal rainfall and temperatures in Europe and in the North American Southwest going back at least a millennium. In the chapters that follow, sidebars will discuss some of the methods we use to study prehistoric climate. Ice cores from Greenland, also from high in the Andes and elsewhere, provide important data on cooler and warmer cycles over the past two thousand years. Growth layers in tropical coral from small Pacific atolls also document climatic shifts over many centuries. And tree-ring sequences from around the world are slowly putting flesh on the Medieval Warm Period’s still-shadowy skeleton.

  Europeans built cathedrals and the Norse sailed to North America during the Medieval Warm Period, but the picture of the warm centuries that’s emerging from the new research depic
ts a climatic villain as much as a hero. There was indeed warming, in most places reflected in milder winters and longer summers, but the temperature differences never amounted to more than a few degrees. Nor was everywhere necessarily warmer. In the eastern Pacific, the same centuries were cool and dry. These were times of sudden, unpredictable climatic swings, and, above all, of drought. Extended medieval dry cycles helped topple Chaco Canyon and Angkor Wat, contributed to the partial collapse of Maya civilization, and starved tens of thousands of northern Chinese farmers.

  Much of this aridity can be attributed to persistent La Niña conditions in the Pacific, especially around 1100 to 1200, but climate change was not the only villain. (See the sidebar in chapter 9 for a discussion of La Niñas.) No one in their right mind would argue that climate “caused” all the economic, political, and social changes described in these pages. 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. The effects of climatic shifts were usually far more indirect.

  While I was writing this preface, I went for a walk along the shores of a nearby slough. I picked up a small pebble and threw it into the mirror-still water. A plop and the stone disappeared, but the concentric ripples from the point of impact radiated outward toward the banks. A surprisingly long time passed before the last ripple vanished. So it was with ancient climate change. It was not so much the immediate impact of a major shift like drought, a flood cycle, or an El Niño that caused political or social change. Rather, the subtle consequences that rippled through society made the difference: new strategies for storing water; the planting of more drought-resistant cereals; the development of new institutions such as secret societies that collected information for predicting rainfall. This book is as much about how the human societies of a thousand years ago coped with climate change as it is about the warming and other climatic phenomena themselves.

  Humans have always lived in unpredictable environments, in a state of flux that requires them to adapt constantly and opportunistically to short- and long-term climate change. What is fascinating about the world of a thousand years ago is that we now have just enough climatological information to look behind the scenes, as it were, to examine the inconspicuous undercurrents of climate that helped push Angkor to collapse or forced Mongolian horse nomads to search for new pasture. These undercurrents are now part of the meat and drink of history. A generation ago, they would have been ignored.

  THE GREAT WARMING explores societies both historically obscure and well known. We cannot understand the significance of the Medieval Warm Period without traveling far beyond Europe, where the effects of the warmer centuries were strongly positive and the continent saw the cultural flowering we now call the High Middle Ages. The higher temperatures and accompanying shifts in rainfall patterns rippled across the globe, bringing both opportunity and catastrophe.

  One consequence was greater interconnectedness between radically different societies living long distances apart. The Norse took advantage of favorable ice conditions in the north to journey to Iceland, Greenland, and beyond, where they came in contact with Inuit hunter-gatherers in Baffin-land. El Niño activity in the Pacific occasionally reduced the strength of prevailing northeasterly trade winds. Polynesian sailors sailed north and eastward to colonize some of the remotest islands on earth. During the warm centuries, more and more of Europe’s gold crossed the Sahara on camels from West Africa. Strong southwesterly monsoons fostered nonstop voyages across the Indian Ocean from the Red Sea, Arabia, and East Africa to India and beyond. All these long-distance connections changed history, as did many other interconnections that ebbed and flowed with the changing political fortunes of human societies and climatic shifts.

  Some Major Historical Events

  This is a selective listing in chronological order. For clarity, many major events and developments are omitted.

  A.D. 570 Birth of Mohammed

  600 Classic Maya civilization in full swing

  618 T'ang dynasty begins in northern China

  710 Islamic conquest of Spain (al-Andalus)

  750 Abbasids assume power in Baghdad, ushering in a great era of

  Islamic rule and scholarship

  793 Norse raid on Lindisfarne, England

  802 Jayavarman II founds the Angkor state, Cambodia

  814 Death of King Charlemagne of France (742-814)

  874 Norse settlement of Iceland

  900 Sicán lords dominate Peru's north coast;

  Collapse of Maya civilization in southern lowlands

  907 T'ang dynasty falls in northern China;

  Period of Khitan conquests begins in Manchuria and

  Mongolia

  971 Mahmud, a Ghazi ruler from Afghanistan, raids India for

  sixty years

  980s Eirik the Red colonizes Greenland

  990s Norse discovery of North America; sporadic trade with Inuit

  groups in the Baffinland area

  1000 Thule population movements from the Bering Strait eastward

  across the High Arctic and to Greenland

  1066 William the Conqueror invades England: the Norman

  Conquest

  1100 Gradual abandonment of Chaco Canyon, New Mexico

  1113 Suryavarman II starts building Angkor Wat, Cambodia

  1181 Jayavarman VII builds Angkor Thom, Cambia

  1200 Chimor controls Peru's North Coast;

  First settlement of Rapa Nui (Easter Island);

  First settlement of New Zealand occurred at an unknown

  date around this time

  1206 Ginghis Khan elected Great Khan of the Mongols;

  Muslim dynasties assume power in Delhi, India

  1207 Mongolian campaigns against the Chin of northern China

  begin

  1215 Ginghis Khan captures Beijing

  1220 Ginghis Khan smashes the Khwarezmed empire

  1227 Death of Ginghis Khan

  1230 Major El Niño event devastates Peru's north coast

  1241 Mongol general Subutai defeats Henry the Bearded at Legnica,

  Silesia, then retreats to the steppes

  1258 Mongols capture Baghdad

  1276 Great drought in American Southwest lasts a quarter century;

  Mesa Verde is abandoned

  1279 Kubilai Khan becomes emperor of China and rules until 1294

  1315 Seven-year famine begins in western Europe

  1324 Mansa Musa of Mali visits Cairo on his pilgrimage to Mecca

  1348- The Black Death devastates medieval Europe

  1398 Timur attacks and overruns Delhi, India

  1431 Angkor state collapses

  1470 Chimor falls to the Inca

  1492 Spanish monarchy conquers Islamic Spain;

  Christopher Columbus sails to the Indies

  1519 Hernán Cortés lands in the Aztec empire

  1532 Francisco Pizarro advances on the Inca

  Opportunity went hand in hand with misfortune. When we move beyond Europe and the North Atlantic into drier environments and lands with unpredictable rainfall, we enter a medieval world where drought cycles and even a few inches of rain could make all the difference between life and death. While Europe basked in summer warmth and the Norse sailed far west, much of humanity suffered through heat and prolonged droughts. A huge swath of the world, from much of North America through Central and South America, and far across the Pacific to northern China, experienced long periods of severe aridity. Drought cycles settled over the Saharan Sahel, the Nile Valley, and eastern Africa, creating havoc. Farmers went hungry, civilizations collapsed, and cities imploded. Archaeology and climatology tell us that drought was the silent killer of the Medieval Warm Period, a harsh reality that challenged human ingenuity to the limit.

  Most societies on earth were affected by medieval warming, many of them for the worse.

  TODAY, PERHAPS EVEN, more than a millennium ago, we live in climatically dramati
c times: we have seen a steady rise in global temperatures accompanied by weather-related disasters from tsunamis to hurricanes. While the scientists quietly labor in the background, the chatterers and doomsday sayers are vociferous in their predictions of disaster triggered by anthropogenic global warming. Yet 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. It wasn’t; we’ve entered a time of sustained warming, which dates back to at least 1860, propelled in large part by human activity—by the greenhouse gases from fossil fuels.

  The prolonged debate over anthropogenic global warming is over, for the scientific evidence documenting our contributions to a much warmer world of the future is now beyond the stage of controversy. Now the discussions are changing focus, as we grapple with the long-term problems of reducing pollutants and living with the consequences of a world where ice sheets are melting and sea levels rising. Most of the passionate debate about contemporary climate change revolves around extreme weather events and sea level rises. The melting of ice caps and the increased danger of flooding are no trivial matter. But the experience of the Medieval Warm Period tells us that the silent and oft-ignored killer is drought, even during a period of mild warming. The computer projections for drought in an anthropogenically warmed world, described in chapter 13, are frightening. We already know that some 20 million to 30 million tropical farmers perished as a result of droughts during the nineteenth century, when there were far fewer people on earth.4 Now we are entering a period of sustained warming with millions of people already at risk, living as they do on agriculturally marginal lands, or, in the case of Arizona and California, in huge cities looting water from aquifers and rivers.

  The Medieval Warm Period tells us much about how humans adapt to climatic crisis, and offers forewarning of lengthy droughts when warming occurs. We’re entering an era when extreme aridity will affect a large portion of the world’s now much higher population, where the challenges of adapting to water shortages and crop failures are infinitely more complex. One can only hope that our uniquely human qualities of adaptiveness, ingenuity, and opportunism will carry us through an uncertain and challenging future.