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

  Cold sea temperatures brought enormous herring shoals southward from off the Norwegian coast into the North Sea, for they prefer water temperatures between 3 and 13°C. English and Dutch fishermen benefited from the herring surge, while the Norwegians suffered. This was not the first time the fish had come south. In 1588, in a previous cold snap, the great British geographer William Camden had remarked how "These herrings, which in the times of our grandfathers swarmed only about Norway, now in our times ... swim in great shoals round our coasts every year."' The revived fisheries brought a measure of prosperity to Holland, as the country fought for independence, as did the development of simple windmills for draining low-lying fields. But repeated storms and sea surges overthrew many coastal defenses and inundated agricultural land. In Norway, the shortened growing season was even more marked than further south, at a time when mountain glaciers were advancing everywhere. The Norwegians turned the cold weather to their benefit. Many coastal villages abandoned their fields and began building ships to export the timber from nearby forests. Between 1680 and 1720, Norway developed a major merchant fleet based on the timber trade, transforming the economy of the southern part of the country.

  The cold polar water spread southward toward the British Isles. The cod fishery off the Faeroe Islands failed completely, as the sea surface temperature of the surrounding ocean became 5'C cooler than today. Just as it had in the I 580s, a steep thermal gradient developed between latitudes 50' and 61-65' north, which fostered occasional cyclonic wind storms far stronger than those experienced in northern Europe today. The effects of colder Little Ice Age climate were felt over enormous areas, not only of Europe but the world.

  The retreat of the San Josef Glacier, South Island, New Zealand, 1865-1965. The glacier face has retreated even farther since the 1960s. Redrawn from New Zealand Government sources; see also jean Grove, The Little Ice Age

  The Franz Josef glacier in New Zealand's Southern Alps thrusts down a deep valley backed by mountains that rise to the precipitous heights of Mount Tasman, 3,494 meters above sea level.3 The path to the ice face winds through a barren valley floor, across fast-running streams fed by the melting glacier. As you walk up to the ice, you wend your way through massive blocks of hard rock polished into humps by the abrasive debris collected by the ice as it advanced and retreated along the valley. When you reach the face, you gaze up at a pale green river of ice glistening in the sun, a microcosm of the glacial fluctuations of the Little Ice Age.

  Franz Josef is a glacier on the move. Nine centuries ago, it was a mere pocket of ice on a frozen snowfield. Then Little Ice Age cooling began and the glacier thrust downslope into the valley below, smashing into the great rain forests that flourished there. The ice crushed everything in its path, felling giant trees like matchsticks. By the early eighteenth century, Franz Josef's face was within three kilometers of the Pacific Ocean, a river of aggressive ice pointing like an arrow toward the coast.

  Today, Franz Josef, like other New Zealand glaciers, is in retreat. Thousands of tourists walk up to the face every year, lingering at sunset to enjoy the sight of the mountain peaks bathed in rosy hues while the lower slopes lie in deep, purple shadow. Their pilgrimage takes them through rocky terrain that was completely covered with ice during the eighteenth and early nineteenth centuries. They can see how the glacier is a barometer of the greater cold of two centuries ago, followed by modern-day warming. Signs along the access path mark the spots where the end moraines halted at their maximum extent, then document the spectacular retreats and glacial fluctuations since 1850. The glacier retreated steadily until about 1893, when a sudden forward thrust destroyed the tourist trail to the face. In 1909, advances of up to fifty meters a month were reported. Franz Josef then retreated again before recovering about half the ground lost earlier in the 1920s. By 1946, the glacier was at least a kilometer shorter than it had been three-quarters of a century before. The pattern of advance and retreat continues to this day, with the retreats more prolonged than the advances.

  The New Zealand Alps are one of the few places in the world where glaciers thrust into rain forest. It was here, at the foot of Franz Josef, that I realized the Little Ice Age at its apogee was a truly global phenomenon, not just something of concern to Alpine villagers on the other side of the world.

  The high tide of glacial advance at Franz Josef came between the late seventeenth and early nineteenth centuries, just as it did in the European Alps. Glaciers in the Alps advanced significantly around 1600 to 1610, again from 1690 to 1700, in the 1770s, and around 1820 and 1850. Ice sheets in Alaska, the Canadian Rockies and Mount Rainier in the northwestern United States moved forward simultaneously. Glaciers expanded at the same times during the nineteenth century in the Caucasus, the Hi malayas, and China. The Qualccaya ice core in Peru's southern Andes provides evidence of frequent intense cold from A.D. 1500 to 1720, with prolonged droughts and cold cycles from 1720 to 1860.

  As Franz Josef shows, the cycles of glacial advance and retreat were never clear-cut, often rapid, and always irregular in duration. Nor did the maximum advances coincide from one region to the next. The northern glaciers in both Europe and North America advanced late in the Little Ice Age and retreated early. (Iceland is an exception: its glaciers reached their greatest extent in the late nineteenth century.) In contrast, the more southerly glaciers, like those in the New Zealand Alps, advanced early, retreated and advanced again and again to the same extended positions before shrinking decisively in the late nineteenth and early twentieth centuries.

  The increasing cold affected not only glaciers but mountain snow levels, which extended lower than today. Snow cover lasted longer into the spring. High mountains in the Andes of Ecuador were perennially snowcapped until at least the late nineteenth century. Travelers in Scotland reported permanent snow cover on the Cairngorm Hills at about 1,200 to 1,500 meters, which would require temperatures 2 to 2.5°C cooler than those of the mid-twentieth century. Wrote traveler John Taylor of the Deeside area in about 1610: "the oldest men alive never saw but snow on the tops of divers of these hills, both in summer as well as in winter."4 A temperature drop of only 1.YC (about that recorded in central England at the time) would have been sufficient to bring the snowline down to about 1,200 meters in the Scottish mountains and would have allowed glacier ice to form in some shaded gullies.5

  The colder conditions had striking biological consequences that we can only extrapolate from modern plant, tree, and animal movements. Trees like birch and pine extended into new territory when conditions became warmer near the northern forest line, then retreated as conditions grew colder, a process that was not necessarily instantaneous. Between 1890 and the 1940s, the North Atlantic Oscillation was in a high mode, bringing milder weather and a constant flow of depressions across northern Europe. During these warmer years, many European birds extended their ranges northward, for they are highly sensitive to the depth and duration of snow cover, the length and warmth of summers, and the harshness of winters. Animal distributions can also reflect the availability of their favorite foods. For example, puffins declined sharply around Britain between 1920 and 1950 because the fish species they ate preferred colder water. When sea temperatures dropped after the 1950s, the sand eels returned, and northern puffin colonies increased again.

  Iceland welcomed all manner of European bird species during the first half of the twentieth century, among them breeding pairs of blackheaded gulls, swallows, starlings, and fieldfare. Even more striking is the distribution of the serin, a bird that flourished among the sunny borders of woodlands throughout the western Mediterranean during the eighteenth century. By 1876, serins had colonized much of central Europe; they now breed as far north as the Low Countries, northern France, and Scandinavia. When northern latitudes cooled slightly in the 1960s, species like the snowy owl moved southward to nest in Shetland, and great northern divers returned to Scotland from the north.

  All these changes, like those of moths and butterflies, are minor co
mpared with the shifts in animal distributions that must have taken place during the coldest episodes of the Little Ice Age. Were these shifts noticed at the time? Except for economically important species like the herring and cod, any such observations were not written down-at least, they are unknown to modern scholars. But if people noticed a slow change in their local animals and plants, surely few of them knew of the remarkable lack of sunspots between 1645 and 1715.

  Sunspots are familiar phenomena. Today, the regular cycle of solar activity waxes and wanes about every eleven years. No one has yet fully explained the intricate processes that fashion sunspot cycles, nor their maxima and minima. A typical minimum in the eleven-year cycle is about six sunspots, with some days, even weeks, passing without sunspot activity. Monthly readings of zero are very rare. Over the past two centuries, only the year 1810 has passed without any sunspot activity whatsoever. By any measure, the lack of sunspot activity during the height of the Little Ice Age was remarkable.

  The seventeenth and early eighteenth centuries were times of great scientific advances and intense astronomical activity. The same astronomers who observed the sun discovered the first division in Saturn's ring and five of the planet's satellites. They observed transits of Venus and Mercury, recorded eclipses of the sun, and determined the velocity of light by observing the precise orbits of Jupiter's satellites. Seventeenth-century scholars published the first detailed studies of the sun and sunspots. In 1711, English astronomer William Derham commented on "great intervals" when no sunspots were observed between 1660 and 1684. He remarked rather charmingly: "Spots could hardly escape the sight of so many Observers of the Sun, as were then perpetually peeping upon him with their Telescopes ... all the world over."6 Unfortunately for modern scientists, sunspots were considered clouds on the sun until 1774 and deemed of little importance, so we have no means of knowing how continuously they were observed.

  The period between 1645 and 1715 was remarkable for the rarity of aurora borealis and aurora australis, which were reported far less frequently than either before or afterward. Between 1645 and 1708, not a single aurora was observed in London's skies. When one appeared on March 15, 1716, none other than Astronomer Royal Edmund Halley wrote a paper about it, for he had never seen one in all his years as a scientist-and he was sixty years old at the time. On the other side of the world, naked eye sightings of sunspots from China, Korea, and Japan between 28 B.C. and A.D. 1743 provide an average of six sightings per century, presumably coinciding with solar maxima. There are no observations whatsoever between 1639 and 1700, nor were any aurora reported.

  In the 1890s, astronomers F. W. G. Sporer and E. W. Maunder drew attention to this long sunspot-free period in the late seventeenth and early eighteenth centuries. If seventeenth-century observers were to be believed, almost all sunspot activity ceased for seventy years, a dramatic departure from the modern sun's behavior. This lacuna in sunspot activity has since been known as the "Maunder Minimum."

  In later papers, Maunder made some striking assertions. First, very few sunspots were seen over the seventy years between 1645 and 1715. Second, for nearly half this time (1672-1704) no sunspots were observed on the northern hemisphere of the sun whatsoever. Only one sunspot group at a time was seen on the sun between 1645 and 1705. Last, the total number of sunspots throughout the seventy years was less than the number that occur in a single active year today. Maunder quoted extensively from contemporary observations, among them that of the French astronomer Picard in 1671, who "was pleased at the discovery of a sunspot since it was ten whole years since he had seen one, no matter how great the care which he had taken from time to time to watch for them." 7 Maunder himself pointed out that this apparent anomaly in the sun's history might have had important consequences for terrestrial weather, perhaps far more important than the regular eleven-year cycles of solar activity in normal times.

  Better catalogs of historical solar aurorae, hitherto unknown sunspot observations by early Asian scholars and new tree-ring data have all upheld the validity of the Maunder Minimum. Radiocarbon-dated tree rings are a valuable source of information on fluctuations in solar radiation. Carbon 14 is formed in the atmosphere through the action of cosmic rays, which are in turn affected by solar activity. When the sun is active and sunspot cycles are at their maximum, some of the incoming galactic rays are prevented from reaching the earth, resulting in less 14C in the tree rings of the day. When the cycle is low, terrestrial bombardment by cosmic rays increases and 14C levels rise. The dated tree-ring sequences document a well-defined fall in 14C levels and a peak in solar activity between about A.D. 1100 and 1250, the height of Europe's Medieval Warm Period. Carbon 14 levels rose significantly as solar activity slowed between 1460 and 1550 (the Sporer Minimum), then fell for a short time before rising again sharply between A.D. 1645 and 1710, peaking in about 1690, an anomaly so marked that it is named the De Vries Fluctuation, after the Dutch scientist who first identified it. This anomaly coincides almost exactly with the Maunder Minimum.

  Was there a relationship between solar activity and the Little Ice Age? There is certainly a nearly perfect coincidence between major fluctuations in global temperature over the past 1,000 years and the changes in 14C levels identified in tree rings. This implies that long-term changes in solar radiation may have had a profound effect on terrestrial climate over decades, even centuries. Certainly the sun has never been constant, and over the past 1,000 years it has shone with periods of greater and lesser activity far more extreme than the levels of today.8 We may never be able to decipher the direct linkages between sun and short-term climatic change, but there are compelling connections between the prolonged periods of low solar activity and the maxima of the Little Ice Age.

  Average Europeans would have complained about the cold winters and sudden heat waves of their day, especially if they were farmers at the mercy of the capricious weather, but their sufferings paled beside the anxiety of those who lived in the shadow of the Alps.

  The threat of advancing ice had been around for a long time. The superstitious shook their heads when Saint Petronella's chapel succumbed to the ice. The cult of Saint Petronella was popular in the Alps as early as the eleventh century, for she was believed to cure fever. Her chapel lay at Grindelwald at the foot of the Eiger, in the shadow of a glacier, presided over by a single monk as recently as 1520. A generation later, Hans Rebmann, prior of the monastery at Thun, wrote: "On the side of the mountain [the Eiger], at Sainte- Petronelle, there was once a chapel, a place of pilgrimage. But a great glacier now hangs there and has entirely covered the site."9 Local legend claimed that on a clear day one could even see the chapel door through the ice.

  Alpine glaciers, which had already advanced steadily between 1546 and 1590, moved aggressively forward again between 1600 and 1616. Villages that had flourished since medieval times were in danger or already destroyed. Land values in the threatened areas fell. So did tithe receipts. During the long period of glacial retreat and relative quiet in earlier times, opportunistic farmers had cleared land within a kilometer of what seemed to them to be stationary ice sheets. Now their descendants paid the price of opportunism. Their villages and livelihoods were threatened.10

  The glacial thrust continued inexorably. The Vernagt glacier in the eastern Alps advanced vigorously in 1599 and 1600, forming a large lake behind a huge ice barrier. When the dike burst on July 10, 1600, a tidal wave of glacial melt inundated fields, bridges, and cart tracks, causing 20,000 florins worth of damage. The glacier continued to grow the following winter, again forming a lake. Fortunately the water seeped away during the warm months.

  Between 1627 and 1633, seven cold and wet summers led to aggressive advances along ice fronts throughout the Alps, causing large rock falls and floods, and destroying trees, farmsteads, and bridges. Between 1628 and 1630, Chamonix lost a third of its land through avalanches, snow, glaciers, and flooding, and the remaining hectares were under constant threat. In 1642, the Des Bois glacier advanced "over a mu
sket shot every day, even in the month of August." The people at Rogationtide marched in solemn procession to implore God's protection against the ice. In 1648, the inhabitants of the village begged the local tax collector to take account of the "other losses, damage, and floods recently caused in the said parish." By this time, people near the ice front were planting only oats and a little barley in fields that were under snow for most of the year. Their forefathers had paid their tithes in wheat. Now they obtained but one harvest in three, and even then the grain rotted after harvesting. "The people here are so badly fed they are dark and wretched and seem only half

  Inevitably, the scourge of advancing ice was seen as divine vengeance. When the Des Bois glacier threatened to block the Arve River, the inhabitants of Chamonix sent community leaders to brief the Bishop of Geneva on their plight. They told him of the constant threat posed by ice and wondered whether they were being punished for their sins. In early June 1644, the bishop himself led a procession of about three hundred people to the place where the "great and horrible glacier" threatened the village of Les Bois. The prelate blessed the menacing ice sheet, then repeated the ritual at another glacier near the village of Largentiere, at one poised above Le Tour, and at a fourth ice sheet at Les Bosson. The villages were literally hemmed in by moving ice, which lies a good kilometer away today. Fortunately, the blessings worked. The glaciers slowly retreated until 1663, but they left the land so scarred and barren that nothing would grow.

  The Aletsch glaciers advanced somewhat later than those around Chamonix. In 1653, the alarmed villagers of Naterser sent a deputation to the Jesuit community at Siders, asking for assistance, saying they were ready to do penance and to undertake other "good Christian works." Fathers Charpentier and Thomas spent a week at Nater, preaching, then leading a procession to the glacier four hours' walk away. The people plodded along, bareheaded in the rain, singing psalms and hymns every step of the way. At the glacier front, the Jesuits celebrated mass and preached a sermon at the glacier: "The most important exorcisms were used." They sprinkled the terminus with holy water and set up an effigy of Saint Ignatius nearby. "It looked like an image of Jupiter, ordering an armistice not to his routed troops, but to the hungry glacier itself" 12 The Jesuit disputation worked. We are told that Saint Ignatius "caused the glacier to be still."