The Great Warming

by Brian Fagan

  The growth of cities had lasting political and economic consequences. In England alone, there were at least sixteen cities with ten thousand or more inhabitants by 1300; these large and ever growing numbers of people depended on others to feed them. Medieval cities became magnets not only for artisans and well-connected merchants, but also for the poor and the landless, who lived in crowded tenements and hovels either inside or outside the city walls. Like towns, the new cities were busy, crowded places, teeming with the destitute and the merely poor, with all the volatile potential for social unrest that this implied. In times of famine, hunger fueled anger in congested slums, where violence lurked close below the surface. The warm centuries enjoyed generally plentiful harvests, but the cities that mushroomed in their train were increasingly vulnerable to poor harvests. In later times, the greatest fear of England’s Tudor monarchs was urban unrest caused by grain shortages.

  The population changed rapidly through the Medieval Warm Period. At its end, London had perhaps 80,000 to 100,000 people, a population that made it second only to Paris among cities north of the Alps. A major sea and river port, the city drew on an irregular area of about 4,000 square miles (10,350 square kilometers) for its grain supplies, some of it from estates more than 100 miles (160 kilometers) away. Growing cities with burgeoning populations depended on reliable food supplies. When serious famine descended on England in 1315–17, the king ordered his sheriffs to procure essential provisions and hay for his household from as far away as Sussex, Cambridgeshire, Norfolk, and Gloucestershire, as much as 150 miles (240 kilometers) away. London’s hinterland expanded and contracted with climatic conditions and the harvests that resulted from them. During the best decades of the warm centuries, the capital drew on perhaps a fifth of England’s total arable land, of which less than half provided grain regularly. Cities like Winchester had much smaller hinterlands, in the case of the latter possibly extending no more than 12 miles (19 kilometers) away. In a world where perhaps 10.5 percent of England’s population dwelled in towns and cities—that is, some 420,000 people—the agricultural requirements of urban markets were still restricted and selective. But this was to change in the future, as cities grew and climatic conditions became more unpredictable.

  The real impact of more favorable agricultural conditions and longer growing seasons was in the countryside. And there, as villages grew and lighter soils were taken up, food shortages became a reality. The logical solution was to take up more land, acreage hitherto off limits because of heavier soils, marshes, hillsides, and higher ground, some of it marginal because it was subject to erosion in heavy rainstorms. But most of the new arable came from clearing a landscape covered by forest since the Ice Age.

  THE SCALE OF deforestation during the warm centuries is mind-boggling.9 In A.D. 500, perhaps four fifths of temperate western and central Europe lay under forests and swamps. Half or even less of that coverage remained by 1200, and most of that clearing took place during the Medieval Warm Period in a massive onslaught on the environment. In the Netherlands, farmers reclaimed land from the North Sea by what has been called “offensive dyking,” which turned small islands in the coastal archipelagoes into larger ones.10 Huge areas of peat moor behind the coast were drained with ditches, then reclaimed laboriously in a cat-and-mouse battle with the water as the peat subsided. At first the reclaimers depended on ever deeper ditches; later, they relied on pumps and wind or water mills. The labor involved was enormous and continued for many generations, but, in the end, the moors became pastureland for sheep and cattle and arable for crops.

  Stripping Europe of its primordial forest was an act thick with cultural, economic, and political overtones. The farmers who cleared the forest deprived themselves of the safety net that a Scandinavian proverb called “the mantle of the poor.”11 Forests provided building materials, timber, firewood and game, medicinal plants and food, and browse and grazing for farm animals. The medieval farmer used more iron than ever before for axes, plows, and weapons—the metal smelted with charcoal from the forest. Great trees provided timber for cathedrals and palaces, for ships and humble structures like mills. Water mills were the new machinery of the age, as were windmills constructed almost entirely of wood. There was so much demand for timber for windmill vanes in Northamptonshire, England, in 1322 that complaints arose about deforestation. By the twelfth century, forest use was subject to intricate regulations that covered everything from grazing rights to firewood collection. Many different stakeholders, including the crown and the nobility, as well as humble folk, had rights in the forest, such as the right to hunt, to graze animals, and to use clearings. For example, many English peasants had the right to acquire construction timber, and firewood, deadwood that was knocked or pulled off trees, “by hook or by crook.” The dense trees and undergrowth were a means for survival. Increasingly complex regulations surrounded the forest and the right to use and clear it, which involved balancing royal privileges and landowners’ rights against the long-established economic needs of peasants.

  Dark forests were a complex presence in medieval life, with many uses and powerful symbolic importance, places where powerful forces lurked and great animals like the fierce aurochs, the long-horned wild ox, thrived. The forest was also the site of the royal and noble hunt, an activity reserved for the aristocracy that signified far more than the mere acquisition of meat. The hunt was a ritual display of courtly ceremony and power, even an enactment of the conquest of wilderness by the taming of wild beasts. The Metropolitan Museum of Art in New York owns seven medieval tapestries, The Hunt of the Unicorn, woven between 1495 and 1505, that commemorate centuries of hunting ritual. They show a symbolic medieval hunt: the hounds unleashed; the finding of the unicorn in its hiding place; the pursuit; the mythic beast at bay; and then the kill with the huntsman’s sword. The unicorn is an imaginary creature, and the tapestries show an idealized image of the hunt, but they convey its elaborate, ceremonial nature. The link between the royal presence and the overcoming of nature was irresistible, so inevitable conflicts arose between the nobility, who wanted to preserve the forests for hunting, and the rest of society, which valued the products of forested land. In the end, agriculture prevailed. The primordial forest shrank rapidly during the warm centuries in ferment of change and experimentation, and because of the intensified agriculture created by growing urban centers, higher population densities, and more mouths to feed.

  After the collapse of the Roman empire in the west in A.D. 476, Germanic tribes such as the Burgundians and Vandals from east of the Rhine overran most of what had been Gaul. The invaders arrived, perhaps eighty thousand of them, at a time when western Europe’s population had declined by some 40 percent, from a peak of about twenty-six million in Roman times, as a result of plague and famine during the sixth century. The newcomers simply filled out the existing cleared land, much of which had been abandoned. To the Germanic tribes, the forest, a sacred entity to be left alone, was impassable and protected. So the period of serious deforestation did not begin until the tenth century, when economic expansion and population growth in western Europe were compounded by migration from Scandinavia and central Europe.

  The surge in forest clearance came during the Medieval Warm Period, at a time when rainfall diminished by as much as 10 percent and temperatures rose between 0.9 and 1.8 degrees F (0.5 and 1 degree C). As local populations rose, so people took up abandoned or neglected lands. It is possible that the availability of new tracts that required only clearing led to earlier marriage, an increase in the birthrate, and perhaps larger families. Constant warfare entailed hungry armies, and the rising demands of a now more powerful church compounded the food supply problem. Confronted with potential shortages, growing families had two choices: they could lessen the number of years they allowed some of their fields to lie fallow (a dangerous practice in the long run, because of catastrophically lower crop yields from more readily exhausted land), or they could clear new fields. Fortunately, there was plenty of land t
o go around, so people often carved new acreage from the margins of the forest, a process known as assarting. (“Assart” comes from the French word essarter, “to clear.” It also implies the uprooting of stumps, an essential part of such clearing.)

  Day after day, men with axes would climb high in the trees, lopping off branches that were then piled up and burned. Sometimes a young man would lose his balance and fall, landing with a thud on the hard ground. Maybe he would be lucky and escape with bruises. More often, he would break an arm or leg and perhaps be crippled for life, or at best be one more mouth to feed until he could fend for himself again. Once the lopping was over, the tall trunks would stand bare and stark at the edge of the receding forest, to be chopped down by strong men working in unison, pausing frequently to sharpen their axes. Back at the nearby village, a blacksmith would be hard at work, hammering bent blades and forging new axes to keep up with demand. Slowly a new field would emerge from the forest, studded with large stumps. Once the trees were gone and the branches burned to fertilize the land with the ash, the villagers would move in and laboriously cut and pull the stumps from the ground, using oxen or horses to help them with stout ropes and iron chains.12

  Assarting was laborious and labor-intensive, usually a prolonged process. It began with periodic burning to clear brush, and heavier grazing of surrounding woodland. Eventually the forest deteriorated, at which point the assarters moved in, cleared the stumps, and founded new villages. Completely new settlements often rose in remote clearings in the forest, especially those of monastic houses that sought seclusion in the wilderness.

  The warm centuries saw thousands of new settlements throughout western Europe. In France’s middle Yonne Valley, southeast of Paris, lords encouraged settlement and clearance by granting self-government to those who cleared new land and reducing or abolishing customary taxes on them. Payments in labor were waived: peasants were allowed by their controlling lords to marry outside their own community. As the French historian Marc Bloch once remarked, a kind of “megalomaniac intoxication” gripped many proprietors with grandiose visions of new landscapes where wastelands had become profitable acreage that would yield more wealth in kind and ease population pressure on farming land. In the east, German lords, both lay and ecclesiastical, encouraged colonizers to take up forested and swampy lands east of Berlin where small bands of elusive hunters lived. In the words of one appeal for recruits: “These pagans are the worst of men but their land is the best, with meat, honey, and flour. If it is cultivated the produce of the land will be such that none other can compare with it.”13

  One can argue for a direct connection between medieval warming, population growth, and farming innovation, but there were underlying social and religious factors as well. In earlier times, manor owners tried to keep peasants confined to their lands so they could control them and accumulate more rent. As the warming came, local rulers and church leaders in an increasingly pious age made constant efforts to consolidate their control for political gain and also to accumulate wealth. They gradually assumed the right to dispose of uncleared, unused land as if they were rulers, granting wilderness to groups of colonists who would clear and farm it, “bring it into the realm of human affairs.”14 People and their labor became a source of wealth for lords. These colonizers soon became free farmers, who owned land and could earn money for their crops. With the emancipation of the commoner and the widespread adoption of primogeniture, younger sons needed outlets—new land. Forest clearance was to them what the Crusades and wars of conquest were to the nobility.

  The religious played a huge role in forest clearance and the agricultural revolution. The Benedictines, in particular, considered manual labor as important as reading or prayer. Work had spiritual rewards. Saint Bernard wrote: “A wild spot, not hallowed by prayer and asceticism and which is not the scene of any spiritual life is, as it were, in a state of original sin. But once it has become fertile and purposeful, it takes on the utmost significance.”15 Benedictine communities did much to dispel the ancient dread of primordial forest among medieval peasants. The historian Michael Williams calls religious orders the “shock troops” of forest clearance. Numbers tell the story. Between 1098 and 1675, the Cistercians alone founded 742 communities, 95 percent of which were in existence by 1351. Each house engaged in intensive farming and forest clearance. Wrote Gerald of Barri: “Give these monks a naked moor or a wild wood, then let a few years pass away and you will find not only beautiful churches, but dwellings of men built around them.”16

  By any standards, the deforestation of Europe during the warm centuries ranks as one of the greatest such episodes in history. France’s forests were reduced from 74 million to 32 million acres (30 million to 13 million hectares) between about 800 and 1300, but a quarter of the country was still forested. Overall, perhaps more than half of Europe’s forests were cut down between 1100 and 1350. Clearance in Britain was more piecemeal, with less planned deforestation. Even so, the statistics of population increase are impressive by any standards. In just one tiny English parish, Hanbury in northeast Worcestershire, the population rose from 266 in 1086 to 725 by 1299.

  ALONGSIDE DEFORESTATION AND agricultural innovation came a dramatic growth in sea fishing, triggered by more favorable climatic conditions offshore, Christian doctrine, and a growing demand for military rations.17 Charlemagne and his successors had fostered maritime trade routes that connected the Baltic and North Sea coasts, partly because the Mediterranean was an Islamic sea. Most seafaring took place during the summer months, but even then the shallow waters and sluicing tides of eastern England and the Low Countries claimed many a slow-moving merchant vessel. The Medieval Warm Period brought slightly higher temperatures and longer summers to northern European waters. To judge from modern-day conditions, the warmer months would have witnessed periods of high temperatures and prolonged anticyclonic conditions when winds were calm and seas near mirrorlike. Compared with the Little Ice Age of later centuries, conditions were generally less stormy during the summer, although winter gales could still stream ashore and flood low-lying farmland, especially in the Low Countries. The warm centuries saw a rapid expansion of maritime trade that was in part a reflection of more benign conditions offshore. At the same time, sea fishing acquired growing importance, especially the traffic in salted herrings.

  Clupea harengus, the Atlantic herring, is among the most prolific of all fish, massing in the North Atlantic each spring, then passing southward into the Baltic and along the Scottish and English North Sea coasts in summer and early fall. No one knows whether herring are sensitive to sea surface temperatures, but it seems likely that they are, for there have been notable fluctuations in herring shoals over the centuries that were not wholly due to overfishing. Whatever their sensitivity to sea conditions, herrings were promiscuously abundant during the Medieval Warm Period, whereas relatively few people had eaten or fished for them in earlier times. Catching them required open boats and drift nets, also calm weather in the shallow waters of the North Sea. A combination of favorable weather conditions, especially in the early fall, and an inexorable demand for sea fish saw herring become a major international industry during the warm centuries.

  Herrings are fatty fleshed. Once caught, they decay within hours unless they are salted. Salting is an ancient technology dating far back into ancient times, but crude methods like placing the fish in piles of salt were ineffective with Clupea. Sometime in the ninth or tenth centuries, just as sea temperatures were warming slightly, Baltic fishers developed a method of salting herring in brine packed in sealed barrels, which allowed them to harvest migrating herring by the millions. The new methods soon spread to North Sea ports. For the first time, it was possible to transport salted fish long distances inland. Almost overnight, a huge industry came into being.

  Since the first days of Christianity, the devout had fasted and eaten meatless diets on holy days and during Lent. Most people ate a meatless diet of milk and grain anyhow, so the prohibition most st
rongly affected the noble and wealthy, as well as religious houses. The number of meatless days grew and grew. By 1200, effectively half the days of the year were classified as holy. Protein-rich fish were deemed acceptable food for such days, but there were not enough freshwater fish to go around, this despite an explosion in fish farming under the auspices of monasteries and lordly estates. Here, again, warmer conditions helped. The warm summers of the Medieval Warm Period provided ideal circumstances for farming such shallow-water fish as the carp. Cyprinus carpio flourishes in the wild in the muddy waters of the Danube and other southeastern European rivers. Between 1000 and 1300, carp spread rapidly across continental Europe as higher temperatures and long summers raised water temperatures in ponds and rivers. Cyprinus was relatively easy to farm, to the point that carp farming became a large industry in medieval Europe. But the fish were expensive. In 1356, a hundred carp served at a wedding in Namur cost twice as much as a cow. Religious houses and wealthy nobles were assiduous in cornering the market in farmed fish, rendering them effectively inaccessible to common folk.

  Fortunately for the devout and for those concerned with feeding the urban poor, a cheap substitute now appeared in the herring. There was a revolution in sea-fish-eating habits during the warm centuries. Between the seventh and tenth centuries, sea fish appear only in the middens (garbage deposits) of ports and estuary towns. Bone fragments found in such ancient rubbish heaps are a mine of information about ancient diets, giving us data on such esoterica as the weight of medieval cod and the ages at which butchers usually slaughtered oxen. By 1030, herring abounded at the coastal city of Hamwic (modern Southampton) and were traded far inland. During the late eleventh century, an estimated 3,298,000 herring were landed at English ports alone, this quite apart from landings on the Continent. By the twelfth century, herring were commonplace as far from the sea as Vienna. Fish became so important to Christian observance that Pope Alexander II even permitted Sunday fishing during herring season in 1170. For six weeks every fall, a huge herring fair at Yarmouth in eastern England supplied millions of barreled fish for people on both sides of the North Sea. The sales were enormous. Kings fed their armies on salted herring. Towns paid taxes in tens of thousands of Clupea. In 1390 the almoner to the king of France bought 78,000 herring on the Paris market for distribution to hospices and poor households.