The Little Ice Age: How Climate Made History 1300-1850 Read online

  In 1195, Notre Dame de Chartres cathedral rose in northern France on a sacred site occupied by six previous churches. Built in a mere quarter-century, Chartres is a masterpiece of Gothic architecture, where the Christian cosmos becomes a miracle in stone and glass. The cathedral is all windows, the great rose window of the western front symbolizing the Virgin Mary herself, evoking soul, eternity, the sun and cosmos. The other rose windows in the cathedral depict the Virgin and Child, the martyrs who spread the Word and the New Testament, and the wounded Christ at the center of the Last Judgment in the west window. Each window uses the same vocabulary of color, form, geometry and symbol. The gemlike transmutation of the light shining through Chartres's windows created transcendental effects that could heal and revivify the worshipers crowded in the soaring nave. On the floor of the nave, a circular tiled maze has a rose at the center, a labyrinth that depicts the path of the human soul through life on earth. There is only one maze path to the center. The confusion of the maze walker reflects the complex journey of life on earth, through the challenges of harvests good and bad, through war and pestilence, through youth, adulthood, and old age.

  Like other cathedrals, Chartres was a magnet of medieval life. Only about 1,500 people lived in Chartres, except at major festivals, when as many as 10,000 visitors crowded the cathedral. The great bells tolled in times of joy and mourning. They sounded warnings and rang out with exultation and in crisis. Every Easter, a New Light was kindled to celebrate the Resurrection and the new farming year. The faithful lit a thousand tapers and carried them from village to village, household to household, as life was renewed. Come autumn, hundreds of heavily laden carts brought the fruits of a warm, bountiful summer as offerings to God. Like the Norse conquests, cathedrals too are a consequence of a global climatic phenomenon, an enduring legacy of the Medieval Warm Period.

  For five centuries, Europe basked in warm, settled weather, with only the occasional bitter winters, cool summers and memorable storms, like the cold year of 1258 caused by a distant volcanic eruption that cooled the atmosphere with its fine dust. Summer after summer passed with long, dreamy days, golden sunlight, and bountiful harvests. Compared with what was to follow, these centuries were a climatic golden age. Local food shortages were not unknown, life expectancy in rural communities was short, and the routine of backbreaking labor never ended. Nevertheless, crop failures were sufficiently rare that peasant and lord alike might piously believe that God was smiling upon them.

  Nothing prepared them for the catastrophe ahead. As they labored through the warm summers of the thirteenth century, temperatures were already cooling rapidly on the outer frontiers of the medieval world.

  When the world was half a thousand years younger all events had much sharper outlines than now. The distance between sadness and joy, between good and bad fortune, seemed to be much greater than for us.... There was less relief available for misfortune and for sickness; they came in a more fearful and more painful way. Sickness contrasted more strongly with health. The cutting cold and the dreaded darkness of winter were more concrete evils....

  But one sound always rose above the clamor of busy life and, no matter how much of a tintinnabulation, was never confused with other noises, and for a moment, lifted everyone into an ordered sphere: that of the bells. The bells acted in daily life like concerned good spirits, who, with their familiar voices, proclaimed sadness or joy, calm or unrest, assembly or exhortation.

  -Johan Huizinga

  The Autumn of the Middle Ages

  omplex interactions between the atmosphere and the ocean govern Europe's climate. A constantly changing pressure gradient reigns over the northern Atlantic and much of Europe's climate, its influence as pervasive in the north as the celebrated Southern Oscillation of the southwestern Pacific, which governs El Ninos and much tropical weather. The North Atlantic Oscillation (NAO) is a seesaw of atmospheric pressure between a persistent high over the Azores and an equally prevalent low over Iceland. This seems like an arcane piece of scientific information until you understand that the NAO governs the position and strength of the North Atlantic storm track and thus the rain that falls on Europe, especially during winter.

  High North Atlantic Oscillation index

  The "NAO index" expresses the constant shifts in the oscillation from year to year and decade to decade. A high NAO index signals low pressure around Iceland and high pressure off Portugal and the Azores, a condition that gives rise to persistent westerly winds. These westerlies bring heat from the Atlantic's surface to the heart of Europe, together with powerful storms. The same winds keep winter temperatures mild, which makes northern European farmers happy and produces dry conditions in southern Europe. A low NAO index, in contrast, brings shallower pressure gradients, weaker westerlies, and much colder temperatures over Europe. Cold air from the north and east flows from the North Pole and Siberia, snow blankets Europe, and Alpine skiers have a wonderful time. NAO's winter oscillations account for about half the variability in winter temperatures in northern Europe and also exercise an important effect on summer rainfall. A high NAO index brings more rain in the summer, as it did after 1314.

  Low North Atlantic Oscillation index

  The seesaw swings unceasingly, in cycles that can last seven years or more, even decades, or sometimes much less. The swings are unpredictable and sudden. An extreme low NAO index causes a reversal of winter temperatures between Europe and Greenland. When pressure in Greenland is higher than in Europe-the "Greenland above" (GA) effect-persistent blocking high pressure systems form between Greenland and Scandinavia. Temperatures are above average in western Greenland and lower than usual in northwestern Europe (and also in eastern North America). Winter in western Europe is bitterly cold. When pressure over Greenland is lower than that in Europe-"Greenland below" (GB)then temperatures are reversed and the European winter is milder than normal.

  The extreme swings of the NAO are part of the complex atmospheric/ocean dynamics of the North Atlantic, which include sea-surface temperature anomalies, the strength of the Gulf Stream, atmospheric wave structure, and the distribution of sea ice and icebergs. These interactions are poorly understood, but there seems little doubt that many of the swings in the NAO result from changes in sea surface temperatures in the North Atlantic. One day, computer simulations of dynamic ocean temperatures and atmospheric relationships may allow meteorologists to predict winter rainfall in Europe several years in advance, a scientific breakthrough of momentous importance.

  Greenland below effect

  The chaotic atmosphere over the North Atlantic plays a major role in the NAO's unpredictable behavior. So do the mild waters of the Gulf Stream, which flow northeast off North America and then become the North Atlantic current, bringing warm water to the British Isles and adjacent coasts as far north as Iceland and Norway. The warmer surface waters of the north flush regularly, sinking toward the bottom, carrying atmospheric gases and excess salt. Two major downwelling sites are known, one just north of Iceland, the other in the Labrador Sea southwest of Greenland. At both these locations, vast quantities of heavier, salt-laden water sink far below the surface. Deep subsurface currents then carry the salt southward. So much salt sinks in the northern seas that a vast heat pump forms, caused by the constant influx of warmer water, which heats the ocean as much as 30 percent beyond the warmth provided by direct sunlight in the north. What happens if the flushing fails? The pump slows down, the warm North Atlantic current weakens, and temperatures fall rapidly in northwestern Europe. When downwelling resumes, the current accelerates and temperatures climb again. The effect is like a switch, triggered by the interaction of atmosphere and ocean. For example, in the early 1990s, the Labrador Sea experienced vigorous downwelling, which gave Europe mild winters. In 1995/96, the NAO index changed abruptly from high to low, bringing a cold winter in its wake.

  Greenland above effect

  The NAO has affected European climate for thousands of years. By piecing together information from
tree rings, ice cores, historical records, and modern-day meteorological observations we now have a record of the North Atlantic Oscillation going back to at least 1675. Low NAO indices seem to coincide with known cold snaps in the late seventeenth century. Over the past two centuries, NAO extremes have produced memorable weather like the very cold winters of Victorian England in the 1880s. An other low index cycle in the 1940s enveloped Europe in savage cold as Hitler invaded Russia. The 1950s were somewhat kinder, but the 1960s brought the coldest winters since the 1880s. Over the past quartercentury, high NAO indices have brought the most pronounced anomalies ever recorded and warmed the Northern Hemisphere significantly, perhaps as a result of humanly caused global warming.

  For many centuries, Europe's weather has been at the mercy of capricious swings of the NAO Index and of downwelling changes in the Arctic. We do not know what causes high and low indices, nor can we yet predict the sudden reversals that trigger traumatic extremes. But we can be certain that the NAO was a major player in the unpredictable, often extremely cold, highly varied weather that descended on Europe after 1300.

  In the thirteenth century, Greenland and Iceland experienced increasing cold. Sea ice spread southward around Greenland and in the northernmost Atlantic, creating difficulties for Norse ships sailing from Iceland as early as 1203. Unusual cold brought early frosts and crop failures to Poland and the Russian plains in 1215, when famine caused people to sell their children and eat pine bark. During the thirteenth century, some Alpine glaciers advanced for the first time in centuries, destroying irrigation channels in high mountain valleys and overrunning larch forests.

  While colder temperatures afflicted the north, Europe as a whole benefited from the change. The downturn of temperatures in the Arctic caused a persistent trough of low pressure over Greenland and enduring ridges of high pressure over northwestern Europe. A period of unusually warm, mostly dry summers between 1284 and 1311, in which May frosts were virtually unknown, encouraged many farmers to experiment with vineyards in England. After the turn of the fourteenth century, however, the weather turned unpredictable.

  The year 1309/10 may have been a "Greenland above" year. The dry and exceptionally cold winter made the Thames ice over and disrupted shipping from the Baltic Sea to the English Channel. An anonymous chronicler wrote,

  In the same year at the feast of the Lord's Nativity, a great frost and ice was massed together in the Thames and elsewhere, so that poor people were oppressed by the frost, and bread wrapped in straw or other covering was frozen and could not be eaten unless it was warmed: and such masses of encrusted ice were on the Thames that men took their way thereon from Greenhithe in Southark, and from Westminster, into London; and it lasted so long that the people indulged in dancing in the midst of it near a certain fire made on the same, and hunted a hare with dogs in the midst of the Thames.I

  By 1312, the NAO Index was high, the Atlantic storm track shifted southward, and winters were mild again. Three years later, the rains began in earnest.

  The deluge began in 1315, seven weeks after Easter. "During this season [spring 1315] it rained most marvellously and for so long," wrote a contemporary observer, Jean Desnouelles. Across northern Europe, sheets of rain spread in waves over the sodden countryside, dripping from thatched eaves, flowing in endless rivulets down muddy country lanes. Wrote chronicler Bernardo Guidonis: "Exceedingly great rains descended from the heavens, and they made huge and deep mud-pools on the land." Freshly plowed fields turned into shallow lakes. City streets and narrow alleys became jostling, slippery quagmires. June passed, then July with little break in the weather. Only occasionally did a watery sun break through the clouds, before the rain started again. "Throughout nearly all of May, July, and August, the rains did not cease," complained one writer.z An unseasonably cold August became an equally chilly September. Such corn and oats as survived were beaten down to the ground, heavy with moisture, the ears still soft and unripened. Hay lay flat in the fields. Oxen stood knee deep in thick mud under sheltering trees, their heads turned away from the rain. Dykes were washed away, royal manors inundated. In central Europe, floods swept away entire villages, drowning hundreds at a time. Deep erosion gullies tore through hillside fields where shallow clay soils could not absorb the endless water. Harvests had been less than usual in previous years, causing prices to rise, but that of 1315 was a disaster. The author of the Chronicle of Malmesbury wondered, like many others, if divine vengeance had come upon the land: "Therefore is the anger of the Lord kindled against his people, and he hash stretched forth his hand against them, and hath smitten them."3 Tree rings from northern Ireland show that 1315 was a year of extraordinary growth for oak trees.

  Europe was a continent of constant turmoil and minor wars, of endless killings, raids, and military expeditions. Many conflicts stemmed from succession disputes and personal rivalries, from sheer greed and reckless ambition. The wars continued whatever the weather, in blazing sunshine or torrential rain, armies feeding off villages, leaving empty granaries and despoiled crops in their train. War merely increased the suffering of the peasants, who lived close enough to the edge as it was. But the rains of 1315 stopped military campaigning in its tracks.

  Trade and geography made Flanders one of the leading commercial centers of fourteenth-century Europe. Italian merchant bankers and moneylenders made their northern headquarters here, attracted by the great wealth of the Flemish weaving industry. Technically a fief of France, the country and its prosperous towns were more closely tied to England, whose wool formed the cloth woven across the North Sea. The quality and fine colors of Flemish fabrics were prized throughout Europe and as far afield as Constantinople, creating prosperity but a volatile political situation. Both England and France vied for control of the region. While the Flemish nobility kept French political interests and cultural ties dominant, the merchants and working classes favored England out of self-interest. In 1302, Flemish workers had risen in rebellion against their wealthy masters. The flower of French knighthood, riding north to crush the rebellion, had fallen victim to the swampy terrain, crisscrossed with canals, where bowmen and pikemen could pick off horsemen like helpless fish. Seven hundred knights perished in the Battle of Courtai and the defeat was not avenged for a quarter-century. The inevitable retaliation might have come much earlier had not the rain of 1315 intervened.

  In early August of that year, French king Louis X planned a military campaign into Flanders, to isolate the rebellious Flemings from their North Sea ports and lucrative export trade. His invasion force was poised at the border before the Flemish army, ready to advance in the heavy rain. But as the French cavalry trotted onto the saturated plain, their horses sank into the ground up to their saddle girths. Wagons bogged down in the mire so deeply that even seven horses could not move them. The infantry stood knee-deep in boggy fields and shivered in their rain-flooded tents. Food ran short, so Louis X retreated ignominiously. The thankful Flemings wondered if the floods were a divine miracle. Their thankfulness did not last long, for famine soon proved more deadly than the French.

  The catastrophic rains affected an enormous area of northern Europe, from Ireland to Germany and north into Scandinavia. Incessant rain drenched farmlands long cleared of woods or reclaimed from marsh by countless small villages. The farmers had plowed heavy soils with long furrows, creating fields that absorbed many millimeters of rain without serious drainage problems. Now they became muddy wildernesses, the crops flattened where they grew. Clayey subsoils became so waterlogged in many areas that the fertility of the topsoil was reduced drastically for years afterward.

  As rural populations grew during the thirteenth century, many communities had moved onto lighter, often sandy soils, more marginal farming land that was incapable of absorbing sustained rainfall. Deep erosion gullies channeled running water through ravaged fields, leaving little more than patches of cultivable land. In parts of southern Yorkshire in northern England, thousands of acres of arable land lost their thin topsoil t
o deep gullies, leaving the underlying rock exposed. As much as half the arable land vanished in some places. Inevitably, crop yields plummeted. Such grain as could be harvested was soft and had to be dried before it could be ground into flour. The cold weather and torrential rains of late summer 1315 prevented thousands of hectares of cereals from ripening fully. Fall plantings of wheat and rye failed completely. Hay could not be cured properly.

  Hunger began within months. "There began a dearness of wheat. ... From day to day the price increased," lamented a chronicler in Flanders.4 By Christmas 1315, many communities throughout northwestern Europe were already desperate.

  Few people understood how extensive the famine was until pilgrims, traders, and government messengers brought tales of similar misfortune from all parts. "The whole world was troubled," wrote a chronicler at Salzburg, which lay at the southern margins of the affected region.5 King Edward II of England attempted to impose price controls on livestock, but without success. After the hunger grew worse, he tried again, placing restrictions on the manufacture of ale and other products made from grain. The king urged his bishops to exhort hoarders to offer their surplus grain for sale "with efficacious words" and also offered incentives for the importation of grain. At a time when no one had enough to eat, none of these measures worked.