The Great Warming

by Brian Fagan

  Chan Chan was an enormous city, one of the largest in the world in its heyday, rivaling London, Paris, and highland Mexico’s Teotihuacán of centuries earlier. By 1200, Chan Chan’s urban sprawl covered 7.7 miles (20 square kilometers), with only nobles, artisans, and other skilled workers living within the city core. No one knows the size of Chan Chan’s population, but a staggering number of artisans lived in humble mud and cane huts along the southern and western edges of the central precincts—some 26,000 of them, including metalsmiths, weavers, and other specialists.15 Another 3,000 lived close to the royal compounds; some 6,000 nobles and officials occupied detached adobe enclosures nearby. The city was apparently planning further expansion, for much of the land between Chan Chan and the Pacific remained open. How many people lived within the Chimu kingdom is unknown, but a figure in the 250,000 range would probably be a plausible estimate.

  From their secluded compounds in the heart of the city, the lords of Chimor presided over an expanding but highly structured state. Egyptologists sometimes refer to the Nile Valley as an “organized oasis.” The same term could be applied to the Chimor domains, centered as they were on coastal river valleys. We know little of the rulers or their system of governance, but Spanish accounts suggest that they governed by granting considerable, if carefully supervised, authority to local nobles. If the later Inca are any guide, then the lords of Chimor sent officials throughout their domains to inventory and supervise the activities of every household, and especially their fishing or agricultural production. The lords maintained their growing state by a combination of military force and tribute, helped by an efficient communication system. Everything flowed to the center, to major centers like Chan Chan, where artisans labored over fine gold and silver ornaments, feather headdresses, and other artifacts that denoted the prestige and power of their owners. Just like any other preindustrial civilization, the lords were careful to reward loyalty and prowess in battle with insignia and prestigious gifts. They were also well aware that their entire state rested on food supplies that could not be acquired by force or tribute. Without a stable agricultural basis, Chimor was very vulnerable indeed.

  The Chimu capital was always at risk from El Niño floods and especially from lengthy droughts. Adding to the risk was a huge population of nonfarmers within the city. Apart from a small nobility and numerous artisans, numerous officials would have been required to administer the city, its markets, and its food supplies in a society where most authority was highly centralized. Fortunately, its rulers could draw on centuries of experience with irrigation, soil conservation, and water management. Their pragmatic strategies for survival were remarkably effective.

  JEQUETEPEQUE VALLEY, A.D. 1200. Patchworks of green fields in a large, dry riverbed: the routine has varied little for generations. About every ten days, the farmers gather by the sluices that control water flow from the canal at the side of the valley. As a village official watches closely, the stone gates are opened. Precious water gushes from the canal and cascades through narrow channels into the fields. The meticulous irrigation work takes all day, with narrow defiles being opened and closed until the crops are watered evenly and fairly and each farmer has received the same allocation. Few words are exchanged as the hours pass, for everyone knows the routine well. They know the water is available, even if there has been no rain for months.

  How did Chimor survive the jolting droughts between 1245 and 1310, at a time when El Niños arrived in unexpected waves?16 Batán Grande’s fate alone must have given Chimor’s leaders ample grounds for worrying about food supplies for their growing city. For centuries, coastal farmers such as Moche villagers had used highly flexible agricultural systems, cultivating fertile plots on a small scale, laying them out along coastal hills where they could maximize runoff from springs and the occasional rainstorm. Such small-scale farming systems, which utilized as much land as possible consistent with available water supplies, worked well when population densities were considerably lower. The Moche strategy had the advantage of requiring relatively small-scale labor investment and no elaborate irrigation technologies, but there were now simply too many people, especially nonfarmers, for small-scale agriculture to support. In stark contrast, and confronted with rapidly growing cities and a burgeoning population, the lords of Chimor invested massively in closely organized, highly diversified agriculture. To do so, they relied on an ancient system of tribute by labor, known as mi’ta, which required annual labor by everyone to build major buildings and other public works.

  Chan Chan depended on large, step-down wells for its domestic water supplies. The earliest public structures lay near to the ocean, where the water table was close to the surface. East of the city, low-lying terrain with a high water table allowed an elaborate complex of sunken gardens that extended 3 miles (5 kilometers) upstream from the Pacific. By 1100, Chimor’s mi’ta laborers had also dug an enormous network of canals that watered the flatlands to the north and west of the city. Here irrigation water also replenished the urban aquifer. When a massive El Niño in that year devastated the irrigation system upstream of Chan Chan and altered the course of the Moche River, the ever persistent rulers commissioned the digging of a 43-mile (70-kilometer) intervalley canal to irrigate the land above the city with water from the neighboring Rio Chicama to the north. This expensive project was never completed, and the maintenance of water supplies required ever greater labor as the city expanded upstream into areas where wells had to be much deeper. The city eventually contracted toward the Pacific where the water table was shallower.

  The Chimu created elaborate, redundant irrigation canals throughout their domains that supplied water to different parts of river valleys. Some of these canals were 18 to 25 miles (30 to 40 kilometers) long. The north side of the Jequetepeque Valley alone still features at least 250 miles (400 kilometers) of such canals built over many centuries. This vast canal system was never in use all at one time, for there was insufficient water to fill its entire length. The communities that depended upon it must have developed a carefully managed timetable of water delivery to everyone at different times. Today, local farmers water their crops about every ten days, and this was probably the practice in Chimu times as well. Those relying upon the network could bring different parts of the system online if some segments were destroyed by flooding or springs ran dry in drought cycles. The Chimu canal systems provided a practical way of mitigating extreme climatic uncertainty.

  The Chimu also developed technologies that were designed to handle extremes of rainfall. The rulers of Farfán Sur, Cañoncillo, and other major centers in their domains constructed elaborate overflow weirs as part of their irrigation canals, especially for the aqueducts that bridged large canyons. When a major flood occurred, such overflows could slow turbulent water and prevent erosion. The same aqueducts boasted stone-lined conduits that allowed water to flow through the base of the structure without damaging it. Such measures were not totally successful, for there are many signs of rebuilding, but they certainly provided some protection against catastrophic surges.

  The farmers also constructed crescent-shaped stone sand breaks in areas near the coast. These had the effect of slowing the flow of dune sand into irrigation canals and fields. Judging from abandoned breaks, this defensive strategy was apparently less effectual than their flood control measures.

  In earlier centuries, the Moche had defended themselves against drought and flood by relying on extensive field systems that lay in different settings and could be maintained with relatively little labor. When El Niños brought floods, or during dry cycles, entire communities moved to different locations; field systems were rebuilt by each village. There was intense competition for fertile land from one valley to the next, with little attempt at centralized management of agriculture. The Chimu responded very differently, for they lived in a more densely populated world. Whereas their predecessors had lived in dispersed settlements across valley landscapes, they developed large towns and cities and practiced
agriculture on a regional scale. Unlike the Moche, who developed flexible, less labor-intensive farming, the Chimu invested in entire agricultural landscapes created with enormous labor. For instance, Chimu lords built large storage reservoirs and terraced steep hills to control the flow of water down the slopes. Even in extreme droughts, their canals carried water from deep-cut riverbeds to terraces long distances away. With this infrastructure, the Chimu created thousands of acres of new fields; they brought water from great distances to harvest two or three crops a year where only one harvest had been possible before, and that at the time of the annual flood.

  When reclamation became uneconomic, the lords of Chimor acquired land by conquest instead. As rulers often do, they rationalized this conquest, in this case developing an institution known to anthropologists as split inheritance. A lord would die and be buried in his compound. His mummified body would preside over his court as if he were still alive. Courtiers would attend him, talk to him as if he were alive, parade his body at public ceremonies. Meanwhile, his successor came to power with neither any possessions whatsoever nor a tax base in labor to support his establishment. His only option was to conquer new lands and their inhabitants. The constant military campaigns that resulted expanded Chimor from the Rio Santa to the Rio Jequetepeque, then to the Lambayeque and beyond, until the lords of Chan Chan ruled more than 700 miles (1,126 kilometers) of the coast. In agricultural terms, the strategy worked. At the height of their power, the Chimu controlled more than twelve river valleys with at least 125,000 cultivable acres (50,590 hectares), all farmed with hoes or digging sticks.

  Chimu society was based on large cities, situated on alluvial fans, with adjacent hillside populations and an empire connected by a sophisticated road network. Chimu rulers were ruthless in their administration. It could not have been otherwise, given the vast investment in managing water supplies. They forced their subjects into large cities and severely restricted individual mobility. With such centralized control, the Chimu rulers could respond to environmental uncertainty and events like El Niños on a regional scale, diverting crops from one area to another, bringing unscathed irrigation canals online, and deploying large numbers of mi’ta laborers to repair aqueducts and canals.

  Less than 10 percent of the coastal desert can be farmed, so Chimor also relied heavily on fishing. We learn from historical accounts that the fisherfolk of Chimor spoke their own dialects, married among themselves, and resided in separate communities under their own leaders. They were specialists, just like the farmers inland. They were largely self-sufficient, even growing reeds for their canoes in sunken gardens near the beach—also cotton for nets and lines, and gourds for floats. The fisher-folk traded their catches with farmers in exchange for produce. With a fishery at their doorstep that was accessible at least 280 days a year, Chimor’s shore dwellers were, to a considerable extent, immune from drought. During El Niños they could catch fish sufficient for their own use, but upwelling slowed and often ceased during such events, so much so that anchovy catches were drastically reduced. The commerce in fish meal would have withered during such times. In a society of specialists, each community faced its own risks and developed strategies for doing so.

  Unlike the Maya, whose civilization partially collapsed in the face of persistent arid cycles, Chimor, with its ruthless organization of valley landscapes, appears to have survived even prolonged droughts and exceptionally intense El Niños. With their growing cities and towns, the Chimu had no other option, faced as they were with the need to produce enormous food surpluses. Maya lords painted their commoners into an environmental corner, where a growing population, constant pressure to produce more food, and an overstressed rainforest environment were major factors in a political and social collapse. 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. To this end, they created an elaborate organized oasis based on massive human labor and on draconian control. They thrived by cultivating different microenvironments, just as the Maya did. Both the Chimu and the Maya managed scarce water supplies with basically simple technology but a heavy investment in human labor. Both depended on a rigid social order and on rituals involving mediation between the living and supernatural worlds. In the case of the Maya, an inflexible ideology and the demands of the nobility, with their constant preoccupation with warfare, served to hasten the implosion of elaborate cities and an entire society in the face of persistent drought. The Chimu faced droughts that were, if anything, even more persistent than those in the Maya lowlands. However, there was a profound difference. Like the Maya, the lords of Chimor presided over a hierarchical and rigid society. But they lived in one of the driest environments on earth, where rainfall was rare and water came from afar. These realities preadapted farmer and ruler alike to lengthy dry spells as something experienced in every lifetime, to the point that they had no option but to diversify their food supplies and use every drop of water with sedulous care. And unlike the Maya, they had one of the richest coastal fisheries in the world at their doorstep, which enabled them to diversify their food supplies through elaborate irrigation works and the anchovy fishery. This they did with opportunistic success. The Chimu succeeded where the Maya failed simply because they lived with drought every day of their lives and had the hardwon experience of their remote ancestors to draw upon.

  Chimor became a powerful force in the ever shifting political landscape of the Andes. Inevitably, formidable rivals rose in the highlands, who cast greedy eyes on the wealthy coastal state. The lords of Chimor controlled every aspect of their kingdom except one: the watersheds that provided mountain runoff to their valleys. In about 1470, ambitious Inca conquerors from the highlands gained control of these strategic water sources and conquered Chimor. The kingdom became part of Tawantinsuyu, “the Land of the Four Quarters,” and its artisans were relocated en masse to the Inca capital at Cuzco.

  The great droughts that ravaged human societies from the Great Basin to South America resulted from still only dimly understood interactions between atmosphere and ocean in the tropical Pacific. We must now journey there to explore what little is known about the warm centuries in the waters where ENSO affected the climate like a colossus.

  CHAPTER 10

  Bucking the Trades

  I have heard from several sources, that the most sensitive balance was a man’s testicles, and that at night or when the horizon was obscured, or inside the cabin this was the method used to find the focus of the swells off an island.

  —Thomas Gladwin, East Is a Big Bird (1970)1

  A.D. 1200. Dawn in the South Pacific. The crews of the large double-hulled canoes are weary. They have been sailing for seventeen days before a fitful westerly, the sails slatting back and forth in the lumpy swell. As darkness gives way to a gray dawn, the stars fade from the heavens. The weathered navigator scans the far horizon, sees nothing, and then gazes at the flocks of seabirds wheeling overhead. He stands still, legs apart, eyes closed, feeling through his feet the subtle gyrations of the waves bouncing off an invisible island over the horizon. Minutes pass; the motionless pondering continues. Then the pilot looks toward the horizon and points off the bow slightly to the right. His helmsman alters course, bringing the wind slightly off his right shoulder; the other canoe follows suit.

  The sun climbs; the shadows on deck shorten. By noon, the wind has strengthened slightly. The canoes pick up speed, but the steersmen maintain the same angle to the swell. By now, the navigator has eaten some dried fish and drunk sparingly. He stands at the bow, looking into the far distance. Uneventful hours pass; the sun sinks to the west, casting the pilot’s figure across the bow wave. Then, as sunset approaches, he silently raises his arm and points straight ahead. A distant cluster of trees stands out against the hard line of the horizon, just visible as the canoes rise and fall in the jumbled swell.

  The canoes sail quietly through the night, aiming for the we
sterly end of the island, the crews ready to heave to if the land comes too close. At daybreak, huge palm trees stand tall on the low hills of the island. Everyone looks for signs of life, for village fires or signs of enemies. But the land is seemingly uninhabited. The pilot turns the canoes eastward, keeping a safe distance off, searching for a landing place. He spots a break in the cliffs, then a sandy beach. The sails are lowered, the canoes paddled to a safe berth in a place where high trees crowd on the landing place.

  Unbeknownst to them, the crews of the two canoes have just completed one of the boldest voyages of exploration in history. They had taken a gamble, sailing eastward from Mangareva Island in eastern Polynesia to a landfall on Rapa Nui (Easter Island), in a direction normally closed to them by prevailing northeasterly winds. Some weeks before, the trades had dropped gradually. Calm, humid weather ensued. Then light winds filled in from the west and persisted far longer than the usual few days. So the navigator had sailed, not knowing what lay over the horizon. Days after the canoes landed on their new homeland, the northeast trades returned.

  We think of Polynesia as a paradise world, a vast area of the central and southern Pacific encompassing a triangle whose points lie in Hawaii, New Zealand, and Rapa Nui and where life is little affected by climatic extremes and cycles of drought and flood. In fact, the South Pacific was at least as unpredictable climatically as other parts of the world, especially for canoe navigators and settlers on remote islands.

  Rapa Nui is the remotest of all inhabited Pacific Islands. This makes it a special case in terms of both navigation and its subsequent history. Just to reach the island required unusual climatic conditions, for it lies in the teeth of the prevailing trade winds. Oral traditions from the island tell of a leader named Hotu Matu’a, the Great Parent, who colonized the island with his extended family. He arrived without such staples as pigs or dogs, which were an important element in Polynesian subsistence, although, of course, these might have perished after landing. Nor do we know whether there were later voyages to the island. The chances are that there were not, partly because long periods of westerly winds were highly unusual. As far as we can tell, too, there were no return trips to Mangareva or elsewhere, perhaps because the colonists rapidly deforested their new homeland, making it impossible to build new oceangoing canoes.