The Great Warming

by Brian Fagan

  In an attempt to understand these changes, the climatologist Sharon Nicholson has analyzed colonial meteorological records throughout tropical Africa and identified six different rainfall patterns, or climatic modes, through which African climate has cycled over and over again since the nineteenth century.3 These modes alternate at random from extreme aridity at one end of the spectrum, characteristic of the Sahel in the 1890s and in the 1960s, through various intermediate and related stages, to disastrous wet shifts, when herds multiplied and overgrazed a new green landscape on the margins of the desert. Today, climate in the Sahel leaps abruptly and without warning from one mode to another in a completely unpredictable manner. It is likely that exactly the same kinds of abrupt shifts occurred during the Medieval Warm Period, creating extraordinary challenges for people engaged in cattle herding, subsistence agriculture, and long-distance trade.

  Looking at these changes on a more global scale, we know that a dry year in the Sahel coincides with high pressure over the Azores and low pressure over Iceland. The northeast trades speed up and the Intertropical Convergence Zone stays well south.4 Southwesterly winds bring less moisture to West Africa. When the sea surface temperature between 10 and 25 degrees north is 3.6 to 7.2 degrees F (2 to 4 degrees C) colder, and the Gulf of Guinea’s waters are unusually warm, then the effect of the Intertropical Convergence Zone weakens. The deep-sea cores also show that the thresholds of many of the mode shifts are marked by very violent transitions in the interior, some of them preceded by extreme cooling spikes. One of these occurred in about A.D. 900, with another at the beginning of the eleventh century. Such unstable phases, with often prolonged droughts—and one stresses the word “prolonged”—would have been periods of remarkable difficulty and change for the Sahelians who experienced them.

  The Intertropical Convergence Zone (ITCZ)

  The northeast and southeast trade winds meet near the equator, forming an area of low pressure. The winds converge and force moister air upward. As the air rises and cools, the water vapor condenses. A band of heavy rain forms, which moves seasonally toward areas where solar heating is most intense, places with the warmest surface temperatures. From September to February, the ITCZ moves toward the southern hemisphere, reversing direction for the northern summer. While the ITCZ moves over land, it shifts much less than over open water, maintaining a near-stationary position just north of the equator. Here rainfall intensifies as solar heating increases, diminishes as the sun moves away. As temperatures warm up, so rainfall increases, diminishing with cooling. El Niño events (see chapter 9 sidebar) have a major effect on the ITCZ, deflecting it toward unusually warm sea surface temperatures in the tropical Pacific and bringing less rainfall to the Atlantic and to the Sahara Desert’s margins.

  The Intertropical Convergence Zone and its range.

  WHAT EFFECTS, THEN, did the warmer temperatures and droughts of the Medieval Warm Period have on the Saharan gold trade and on the peoples of the Sahel? As far as the Saharan caravans were concerned, the effects were remarkably small because of the camel, or, more accurately, because of the saddles on camels’ backs.

  On the Eurasian steppes, life depended on cattle and horses, on good pastureland. When higher temperatures and drought descended on the grasslands, the nomads moved out in search of pastureland and water. The desolate plains and highlands of the Sahara were not a place where cattle and horses could thrive a thousand years ago, even if the rainfall increased slightly. In classical times, the desert was a fearful wilderness. Herodotus remarked that Libya on the Mediterranean coast was “infested by wild animals. Further inland from the part full of animals Libya is sandy desert, totally waterless, and completely uninhabited by anyone or anything.”5 Only a scattering of pastoral nomads survived near oases, and for them the margin between survival and starvation was always razor thin. Anyone who lived here was tough, resourceful, and constantly on the move.

  The Romans turned North Africa into a prosperous granary, but never crossed the desert to the tropical lands to the south.6 They lacked the pack animals that would allow them to travel for days at a time without water. To cross the Sahara with laden beasts on a regular basis meant combining highly adaptable behavior with an animal capable of going for up to ten days without water. That animal was the camel. And the camel was remarkably immune to severe drought.

  The Golden Trade would never have thrived without the camel, but it was the development of a load-carrying saddle that made the camel the “ship of the desert.” Camels store fat in their humps; their long necks allow them to browse in trees and brush; and their padded feet allow them to walk on soft sand. They conserve water through an efficient kidney system and they absorb heat by allowing their body temperature to rise significantly without perspiring. The Romans knew all about camels. They used them in North Africa to pull carts, and even as defensive barriers to protect soldiers.7 They knew that these curmudgeonly beasts thrived in desert conditions. But these advantages were of limited value without an effective load-carrying saddle, which the Romans lacked.

  The Saharan camel saddle came into use during the early Christian era, perhaps around the Nile Valley in what is now the modern Sudan, not for fighting, but for cargo. The saddle lies on the beast’s shoulders forward of the hump, and so positioned it maximizes load-carrying capacity, endurance, and control. A Saharan camel driver steered his charge with a stick or with his toes. For the first time, camel caravans could now carry sufficient water and provisions (for the humans in the party) to cross long distances between oases from North Africa to the western Sudan.

  No one knows when the first camel caravans traversed the western Sahara, but it was well before Islamic armies conquered North Africa in the seventh century. They followed obscure tracks that soon became well-established trade routes controlled by Muslim traders who came from a culture with a far broader outlook on the world than their predecessors from North Africa.

  Saharan caravans followed a well-established routine. Heavily laden camels plodded southward from Sijilmassa each fall, south to Taghaza, where they picked up cake salt from nearby mines. Salt is a precious commodity for African farmers to this day, for they lack local supplies. From Taghaza they followed well-trodden paths to Walata, Ghana, and Jenne on the middle Niger River. The journey was hazardous under the most favorable circumstances. The desert was always hostile, even in times of slightly greater rainfall. Heat and dehydration were a constant threat. So were desert nomads, robed in blue burnooses, armed with gazelle-hide shields and spears, who would launch pitiless attacks without warning. Most caravan organizers negotiated agreements with nomad chiefs allowing them safe passage through the oases they controlled. The nomads also provided guides, who used rocky outcrops and the stars to navigate. They also provided camels to the merchants, who sold them back at the end of the journey.

  The caravans were well-organized convoys. The camels laden with merchandise were supported by numerous others carrying water and provisions, or serving as mounts. Safety came in numbers—safety from raiding nomads, in a larger number of beasts who carried water and food, in the ability to transport larger loads and to make a great profit. During the twelfth century, some caravans numbered as many as twelve hundred to two thousand beasts. The journey itself lasted between six weeks and two months, with departure in the autumn. Writes the contemporary Muslim geographer al-Idrisi: “The camels are loaded at a very early hour and one travels until the moment when the sun appears on the horizon and the heat generated on the earth is unsupportable.”8 The caravans would rest until late afternoon, then proceed silently through the night, guided by the stars, just as they still do today.

  Camel caravans made the long journey across the Sahara even during the driest years of the Medieval Warm Period. Those who traversed the desert spent a great deal of time acquiring intelligence about water supplies, for wells and oases were vital to a safe journey. Conditions were never the same from one year to the next. The cycles of wetter and drier conditions affected
the patterns of the trade. When conditions were wetter, large numbers of wells were dug in the aqueous gravels of the central Sahara, around the highlands of the Ahaggar and Adrar des Iforas. Many caravans then followed direct routes over the dunes of the central Sahara to Taghaza and the town of Awdaghust (in modern-day Mauretania) on the borders of the desert, an important salt-trading center. During dry cycles, the caravans would follow more roundabout routes far to the west, or, passing eastward and northward from the Bilad es-Soudan, they traveled to the Adrar des Iforas, then west, ending up ultimately in Sijilmassa. The versatility of the camel provided sufficient flexibility to ride the gyrations of the desert pump.9 The numbers of dead and exhausted beasts could be enormous; casualties were often in the hundreds from one caravan alone. The bleached skeletons of camels and their drivers littered the routes, but the Golden Trade never ceased. 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.

  WE KNOW ENOUGH about climate change during the warm centuries to be virtually certain that they were a time of abrupt and sudden rainfall shifts. The Saharan pump would have moved into frenzied activity as the desert margins advanced and retreated even on a yearly basis. The Islamic discovery of the West African gold trade seems to have coincided with the end of a period of relatively stable conditions, with at least some more rainfall than today. Water holes would have been more plentiful, and desert travel by camels, while yet perilous, could be organized on a relatively large scale. Fortunately for the outside world, the adaptability of the camel and the skill of those who lived in the desert and on its edges gave the Saharan gold trade a considerable degree of immunity from climatic shifts.

  The human bridge was as important as the camel. Much of the trade depended on the nomadic Berbers, ancient inhabitants of the desert, who bred camels and also accompanied many of the caravans. They lived at both ends of the trade routes and served as the human link between north and south. The other connection was Islam, which was eventually to become the common religion of the North African merchants, Saharan nomads, and many African rulers and traders south of the desert.

  Gold was of profound importance in the Muslim world, which was a strong incentive for the trade to overcome the hazards of desert travel. The golden dinars minted by the caliph in Baghdad, and by the caliph alone, circulated throughout the Maghreb (northwestern Africa) and Spain. At first, gold supplies came from booty taken in Syria and Egypt, also from Christian treasuries and sources in upper Egypt and farther up the Nile. But by the eighth century, West African gold was already well known. The metal itself arrived as dust, traded from miners in the Bambuk region of the Senegal River, twenty days’ journey south of the kingdom of Ghana in the Sahel, then a major staging post for the gold trade. Enterprising merchants tried to gain control of the gold sources, but to no avail. The miners firmly maintained their independence and little was known about their operations. They extracted the ore from auriferous river gravels by digging numerous small pits. But the yield from these simple workings was enormous. The Baghdad astronomer al-Fazari, writing late in the eighth century, called Ghana the “land of gold.”

  In A.D. 804, the rulers of the Maghreb began using Sudanese gold to mint their own dinars. Sudanese gold financed wars of conquest and brought immense wealth to Islam. Until the twelfth century, most West African gold remained in the Muslim world. Western Europe had abandoned gold-based currency, partly because an adverse balance of trade with the east had drained its supplies with few means of replenishment. As Europe’s economies recovered and the Italian cities built powerful fleets to combat Arab piracy, a growing volume of trade in cloth and other commodities attracted increasing quantities of gold. By the end of the thirteenth century, European mints were making gold coins. Country after country returned to the gold standard. The demand for gold increased; prices rose, then stabilized. Most of late-fourteenth-century Europe’s gold came from the western Sudan. The relative immunity of the camel to the ravages of the desert pump ensured that the trade continued to help change history.

  No one knows exactly how much gold passed into the trans-Saharan trade from West Africa. Tax records levied on caravans at Sijilmassa during the tenth century and quoted by the author Ibn Haukal cover imports of some 9.4 tons (8.5 metric tons) of gold annually, perhaps half of an annual total of some 16.5 to 18.7 tons (15 to 17 metric tons), carried northward from West Africa. In 951, Ibn Haukal saw a promissory note for 42,000 dinars drawn on a merchant in the north, a measure of the staggering wealth of the trade in its heyday.10

  Where, then, did the gold come from? Before traveling farther south, the caravans stopped at Awdaghust at desert’s edge, a large and populous Berber town of flat-roofed mudbrick and stone houses overlooked by a high outcrop. In Awdaghust’s always crowded market, one could buy salt, sheep, honey from the Sahel, and food of all kinds—provided one paid in gold. The prosperous oasis town had good water and was home to merchants with a monopoly over the trans-Saharan trade. They organized their caravans under the auspices of the Sanhaja nomads of the desert. The Muslim geographer al-Bakri tells us that the nomadic Sanhaja ruler of the town’s domains extended over a distance of two months’ traveling. He was said to be able to field one hundred thousand camels. Gold and salt flowed through the town, whose leaders were careful to maintain good relations with powerful chiefs to the south, especially those presiding over a gold-rich kingdom named Ghana.

  The King adorns himself like a woman wearing necklaces round his neck and bracelets on his forearms and he puts on a high cap decorated with gold and wrapped in a turban of fine cotton. He holds an audience in a domed pavilion around which stand ten horses covered with gold-embroidered materials . . . and on his right, are the sons of the vassal kings of his country, wearing splendid garments and their hair plaited with gold.

  At the door of the pavilion are dogs of excellent pedigree. Round their necks they wear collars of gold and silver, studded with a number of balls of the same metals.11

  Al-Bakri’s description of Ghana was the stuff of legend. He never visited the Sahel, but drew his account from sources in the Córdoba archives. His Ghana was a Mediterranean-style court deep in Africa, a capital with two towns, one with twelve mosques where Muslim merchants dwelled, the other the ruler’s compound, with sacred groves and royal tombs, nearly ten kilometers away. The royal treasure included a gold ingot said to weigh nearly 30 pounds (13.6 kilograms), so large that it became famous through the Christian and Muslim worlds.12

  This seemingly imposing capital, Koumbi Saleh, is commonly thought to have lain about 300 miles (480 kilometers) west-southwest of Timbuktu and the Niger River bend. There are indeed extensive stone ruins here, also Arabic inscriptions, but no traces of the royal quarter nor of the burial mounds said by Muslim travelers to lie close by. The ruins lie at the extreme northern limits of the Sahel, where agriculture would have been near impossible even in periods of higher rainfall.13 Maybe Koumbi was not Ghana’s capital at all, but a small trading community, part of an entirely different, more decentralized kingdom. For the moment, the kingdom of Ghana remains elusive, its capital peripatetic. Our only certainty is that it was not an Islamic polity, but an indigenous African domain, something very different from al-Bakri’s portrait, with roots deeper in West Africa, where the gold came from.

  For a long time, the gold sources were a mystery. Writing in A.D. 872, the historian al-Yaqubi repeated an oft-told tale about gold sprouting from the ground like carrots. As always happens with gold, the fables grew with the telling, until they produced an “Island of Gold” where gold was to be had for the taking.14 The miners were well aware of gold’s value and kept the locations of their ore deposits a close secret, lest outsiders try to take control of the supply. For this reason, they refused to trade face to face: the merchants piled their goods, mostly cake salt, on the riverbank and passed out of sight while the local people place
d heaps of gold alongside each pile. If the visitors were satisfied, they would take the gold and retreat, beating drums to signify the end of the transaction. On one occasion, they captured a miner in an attempt to find the source of the gold. He pined to death without revealing anything. The trade ceased altogether for three years before resuming.

  The miners of Bambuk and Buré, another area to the east, were timid, private people who jealously guarded their gold-mining activities, which is why they engaged in silent trade. No Berber merchant from the Sahara ever visited the goldfields, so the Island of Gold remained a mystery. It remains a geographical conundrum today. During the twelfth century, al-Idrisi described the island as an area nearly 300 miles long and 155 miles wide (500 by 250 kilometers) that flooded each year, where the local people “collected gold.” The position of the island on his map coincides with that of the seasonally flooded middle Niger delta, inhabited by Mande-speaking farmers and fisherfolk.

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  THE NIGER is one of Africa’s great rivers, rising in the mountains of Guinea near the Sierra Leone border, then flowing northeastward into a great inland delta, a patchwork of tributaries, channels, swamps and lakes. This interior floodplain is what the archaeologist Roderick McIntosh calls “a vast alluvial garden abutting the bleak Sahara.”15 Here, the desert caravan networks came in contact with much older riverine trade routes. The middle Niger floodplain was rich in grain and other basic commodities, including potting clay, but, like Mesopotamia, lacked stone, metal ores, and salt. Over many centuries the Mande farmers and fishers of the region developed a lattice of contacts with other peoples near and far to supply their needs. They were also active players in the Saharan gold trade.