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Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, an inherent variability in global climate, or decreases in the human population.
Contents
Areas involved
The Intergovernmental Panel on Climate Change Third Assessment Report (TAR) of 2001 describes areas affected by the LIA:The IPCC Fourth Assessment Report (AR4) of 2007 discusses more recent research, giving particular attention to the Medieval Warm Period. It states that "when viewed together, the currently available reconstructions indicate generally greater variability in centennial time scale trends over the last 1 kyr than was apparent in the TAR." Considering confidence limits, "The result is a picture of relatively cool conditions in the seventeenth and early nineteenth centuries and warmth in the eleventh and early fifteenth centuries, but the warmest conditions are apparent in the twentieth century. Given that the confidence levels surrounding all of the reconstructions are wide, virtually all reconstructions are effectively encompassed within the uncertainty previously indicated in the TAR. The major differences between the various proxy reconstructions relate to the magnitude of past cool excursions, principally during the twelfth to fourteenth, seventeenth and nineteenth centuries."[9]Evidence from mountain glaciers does suggest increased glaciation in a number of widely spread regions outside Europe prior to the twentieth century, including Alaska, New Zealand and Patagonia. However, the timing of maximum glacial advances in these regions differs considerably, suggesting that they may represent largely independent regional climate changes, not a globally-synchronous increased glaciation. Thus current evidence does not support globally synchronous periods of anomalous cold or warmth over this time frame, and the conventional terms of "Little Ice Age" and "Medieval Warm Period" appear to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries... [Viewed] hemispherically, the "Little Ice Age" can only be considered as a modest cooling of the Northern Hemisphere during this period of less than 1°C relative to late twentieth century levels.[8]
Dating
In contrast, a climate reconstruction based on glacial length[14][15] shows no great variation from 1600 to 1850, though it shows strong retreat thereafter.
For this reason, any of several dates ranging over 400 years may indicate the beginning of the Little Ice Age:
- 1250 for when Atlantic pack ice began to grow
- 1275 to 1300 based on radiocarbon dating of plants killed by glaciation
- 1300 for when warm summers stopped being dependable in Northern Europe
- 1315 for the rains and Great Famine of 1315–1317
- 1550 for theorized beginning of worldwide glacial expansion
- 1650 for the first climatic minimum.
Northern Hemisphere
Europe and North America
The Little Ice Age brought colder winters to parts of Europe and North America. Farms and villages in the Swiss Alps were destroyed by encroaching glaciers during the mid-seventeenth century.[19] Canals and rivers in Great Britain and the Netherlands were frequently frozen deeply enough to support ice skating and winter festivals.[19] The first River Thames frost fair was in 1607 and the last in 1814; changes to the bridges and the addition of an embankment affected the river flow and depth, hence diminishing the possibility of freezes. Freezing of the Golden Horn and the southern section of the Bosphorus took place in 1622. In 1658, a Swedish army marched across the Great Belt to Zealand to invade Copenhagen. The winter of 1794-1795 was particularly harsh, when the French invasion army under Pichegru could march on the frozen rivers of the Netherlands, while the Dutch fleet was fixed in the ice in Den Helder harbour. In the winter of 1780, New York Harbor froze, allowing people to walk from Manhattan to Staten Island. Sea ice surrounding Iceland extended for miles in every direction, closing harbors to shipping.The population of Iceland fell by half, but this was perhaps caused by fluorosis after the eruption of the volcano Laki in 1783.[20] Iceland also suffered failures of cereal crops, and people moved away from a grain-based diet.[21] The Norse colonies in Greenland starved and vanished (by the early fifteenth century), as crops failed and livestock could not be maintained through increasingly harsh winters, though Jared Diamond noted they had exceeded the agricultural carrying capacity before then. In North America, American Indians formed leagues in response to food shortages.[22] In Lisbon, Portugal, snowstorms were much more frequent than today. Heavy snowfalls in the winters of 1665, 1744 and 1886 were reported.[23]
The extent of mountain glaciers had been mapped by the late nineteenth century. In both the north and the south temperate zones, snowlines (the boundaries separating zones of net accumulation from those of net ablation) were about 100 m lower than they were in 1975.[27] In Glacier National Park, the last episode of glacier advance came in the late 18th and early nineteenth centuries.[28] In Chesapeake Bay, Maryland, large temperature excursions were possibly related to changes in the strength of North Atlantic thermohaline circulation.[29]
In Ethiopia and Mauritania, permanent snow was reported on mountain peaks at levels where it does not occur today.[30] Timbuktu, an important city on the trans-Saharan caravan route, was flooded at least 13 times by the Niger River; there are no records of similar flooding before or since.[30] In China, warm-weather crops, such as oranges, were abandoned in Jiangxi Province, where they had been grown for centuries.[30] Also, two periods of most frequent typhoon strikes in Guangdong coincide with two of the coldest and driest periods in northern and central China (AD 1660-1680, 1850–1880).[31] In North America, the early European settlers reported exceptionally severe winters. For example, in 1607-1608, ice persisted on Lake Superior until June.[24] The journal of Pierre de Troyes, Chevalier de Troyes, who led an expedition to James Bay in 1686, recorded that James Bay was still littered with so much floating ice that he could hide behind it in his canoe on July 1.[32]
Antonio Stradivari, the famous violin maker, produced his instruments during the Little Ice Age. The colder climate is proposed to have caused the wood used in his violins to be denser than in warmer periods, contributing to the tone of Stradivari's instruments.[33] According to the science historian James Burke the period inspired such innovations in everyday life as the widespread use of buttons and button holes, knitting of custom-made undergarments to better cover and insulate the human body, and installation of fireplace hoods to make more efficient use of fires for indoor heating,[34] as well as the development of the enclosed stove, in early versions often covered with ceramic tiles.
The Little Ice Age by anthropology professor Brian Fagan of the University of California at Santa Barbara tells of the plight of European peasants during the 1300 to 1850 chill: famines, hypothermia, bread riots, and the rise of despotic leaders brutalizing an increasingly dispirited peasantry. In the late seventeenth century, writes Fagan, agriculture had dropped off so dramatically, "Alpine villagers lived on bread made from ground nutshells mixed with barley and oat flour." [35] Historian Wolfgang Behringer has linked intensive witch-hunting episodes in Europe to agricultural failures during the Little Ice Age.[36]
Depictions of winter in European painting
William James Burroughs analyzes the depiction of winter in paintings, as does Hans Neuberger.[37] Burroughs asserts that this occurred almost entirely from 1565 to 1665 and was associated with the climatic decline from 1550 onwards. Burrough claims that before this, there were almost no depictions of winter in art, and "hypothesizes that the unusually harsh winter of 1565 inspired great artists to depict highly original images and that the decline in such paintings was a combination of the "theme" having been fully explored and mild winters interrupting the flow of painting".[38] In fact wintery scenes, which have technical difficulties in painting, had been regularly and very well handled since the early fifteenth century by artists in illuminated manuscript cycles showing the Labours of the Months, typically placed on the calendar pages of books of hours. January and February are typically shown as snowy, as in February in the famous cycle in the Les Très Riches Heures du duc de Berry, painted 1412-1416 and illustrated below. At this period independent landscape subjects had not developed as a genre in art, so the absence of other winter scenes is not remarkable.The famous winter landscape paintings by Pieter Brueghel the Elder, most famously The Hunters in the Snow, are all thought to have been painted in 1565. His son Pieter Brueghel the Younger (1564-1638) also painted many snowy landscapes, though according to Burroughs as he "slavishly copied his father's designs. The derivative nature of so much of this work makes it difficult to draw any definite conclusions about the influence of the winters between 1570 and 1600...".[39]
Neuberger analyzed 12,000 paintings, held in American and European museums and dated between 1400 and 1967, for cloudiness and darkness.[37] His 1970 publication shows an increase in such depictions that corresponds to the LIA,[37] peaking between 1600 and 1649.[40]
Paintings and contemporary records in Scotland demonstrate that curling and ice skating were popular outdoor winter sports, with curling dating back to the sixteenth century and becoming widely popular in the mid-nineteenth century.[41] As an example, an outdoor curling pond constructed in Gourock in the 1860s remained in use for almost a century, but increasing use of indoor facilities, problems of vandalism, and milder winters led to the pond being abandoned in 1963.[42]
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