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The reconstructed depth of the Little Ice Age varies between different studies (anomalies shown are from the 1950-80 reference period).

The Little Ice Age (LIA) was a period of cooling that occurred after a warmer era known as the Medieval Warm Period. While not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939.[1] It is conventionally defined as a period extending from the 16th to the 19th centuries[2][3][4] though climatologists and historians working with local records no longer expect to agree on either the start or end dates of this period, which varied according to local conditions. It is generally agreed that there were three minima, beginning about 1650, about 1770, and 1850, each separated by intervals of slight warming.[5] The Intergovernmental Panel on Climate Change (IPCC) describes areas affected by the LIA:

Evidence from mountain glaciers does suggest increased glaciation in a number of widely spread regions outside Europe prior to the 20th 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 20th century levels.[6]

There is more recent evidence that cold periods in the time frame of the LIA occurred at several locations in the Southern Hemisphere.[7]

Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the flow of ocean currents, an inherent variability in global climate, and decreased human populations due to the Black Death and the Columbian Exchange.

Contents

Dating of the Little Ice Age

There is no agreed beginning year to the Little Ice Age, although there is a frequently referenced series of events preceding the known climatic minima. Starting in the 13th century, pack ice began advancing southwards in the North Atlantic, as did glaciers in Greenland. The three years of torrential rains beginning in 1315 ushered in an era of unpredictable weather in Northern Europe which did not lift until the 19th century. There is anecdotal evidence of expanding glaciers almost worldwide. In contrast, a climate reconstruction based on glacial length[8][9] 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
  • 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.

In contrast to its uncertain beginning, there is a consensus that the Little Ice Age ended in the mid-19th century.

Northern hemisphere

The Frozen Thames, 1677
Winter Landscape with a Bird Trap, 1565, Pieter Bruegel the Elder.
The Hunters in the Snow by Pieter Brueghel the Elder, 1565
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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-17th century.[10] Canals and rivers in Great Britain and the Netherlands were frequently frozen deeply enough to support ice skating and festivals.[10] The first River Thames frost fair was in 1607; the last in 1814, although changes to the bridges and the addition of an embankment affected the river flow and depth, hence diminishing the possibility of freezes. The freeze 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 Denmark to invade Copenhagen. The Baltic Sea froze over, enabling sledge rides from Poland to Sweden, with seasonal inns built on the way.[11] 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 that island's harbors to shipping.

The last written records of the Norse Greenlanders are from a 1408 marriage in the church of Hvalsey — today the best-preserved of the Norse ruins.

The severe winters affected human life in ways large and small. The population of Iceland fell by half, but this was perhaps also due to fluorosis caused by the eruption of the volcano Laki in 1783.[12] Iceland also suffered failures of cereal crops and people moved away from a grain-based diet.[13] The Norse colonies in Greenland starved and vanished (by the 15th century) as crops failed and livestock could not be maintained through increasingly harsh winters, though Jared Diamond noted that they had exceeded the agricultural carrying capacity before then. In North America, American Indians formed leagues in response to food shortages.[14] In Southern Europe, in Portugal, snow storms were much more frequent while today they are rare. There are reports of heavy snowfalls in the winters of 1665, 1744 and 1886.[15]

Winter skating on the main canal of Pompenburg, Rotterdam in 1825, shortly before the minimum, by Bartholomeus Johannes van Hove

In 1995, Herbert Lamb said that, in many years, "snowfall was much heavier than recorded before or since, and the snow lay on the ground for many months longer than it does today."[16] Many springs and summers were outstandingly cold and wet, although there was great variability between years and groups of years. Crop practices throughout Europe had to be altered to adapt to the shortened, less reliable growing season, and there were many years of death and famine (such as the Great Famine of 1315–1317, although this may have been before the LIA proper). Viticulture entirely disappeared from some northern regions. Violent storms caused massive flooding and loss of life. Some of these resulted in permanent losses of large tracts of land from the Danish, German, and Dutch coasts.[16]

The extent of mountain glaciers had been mapped by the late 19th 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.[17] In Glacier National Park, the last episode of glacier advance came in the late 18th and early 19th century.[18] In Chesapeake Bay, Maryland, large temperature excursions during the Little Ice Age (~1400–1900 AD) and the Medieval Warm Period (~800–1300 AD) were possibly related to changes in the strength of North Atlantic thermohaline circulation.[19]

In Ethiopia and Mauritania, permanent snow was reported on mountain peaks at levels where it does not occur today.[20] 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.[20] In China, warm weather crops, such as oranges, were abandoned in Jiangxi Province, where they had been grown for centuries.[20] 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).[21] In North America, the early European settlers also reported exceptionally severe winters. For example, in 1607-1608 ice persisted on Lake Superior until June.[16] 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.[22]

Antonio Stradivari, the famous violin maker, produced his instruments during the Little Ice Age. It has been proposed that the colder climate caused the wood used in his violins to be denser than in warmer periods, contributing to the tone of Stradivari's instruments.[23]

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 17th century, writes Fagan, agriculture had dropped off so dramatically that "Alpine villagers lived on bread made from ground nutshells mixed with barley and oat flour." Finland lost perhaps a third of its population to starvation and disease.[24] Historian Wolfgang Behringer has linked intensive witch-hunting episodes in Europe to agricultural failures during the Little Ice Age.[25]

The Reverend Robert Walker Skating on Duddingston Loch, attributed to Henry Raeburn, 1790s

Depictions of winter in European painting

Burroughs (Weather, 1981) analyses the depiction of winter in paintings, as does Hans Neuberger.[26] Burroughs asserts that this occurred almost entirely from 1565 to 1665, and was associated with the climatic decline from 1550 onwards. Before this there were almost no depictions of winter in art and he hypothesizes that the unusually harsh winter of 1565 inspired great artists to depict highly original images, and the decline in such paintings was a combination of the "theme" having been fully explored, and mild winters interrupting the flow of painting.

The famous winter paintings by Pieter Brueghel the Elder (e.g. Hunters in the Snow) all appear to have been painted in 1565. Snow also dominates many village-scapes by the Pieter Brueghel the Younger, who lived from 1564 to 1638. Burroughs states that Pieter Brueghel the Younger "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..."

Winter landscape with iceskaters, c. 1608, Hendrick Avercamp

Dutch painting of the theme appears to begin with Hendrick Avercamp after the winter of 1608. There is then an interruption of the theme between 1627 and 1640, with a sudden return thereafter; this hints at a milder interlude in the 1630s. The 1640s to the 1660s cover the major period of Dutch winter painting, which fits with the known proportion of cold winters then. The final decline in winter painting, around 1660, does not coincide with an amelioration of the climate; Burroughs therefore cautions against trying to read too much into artistic output, since fashion plays a part. He notes that winter painting recurs around the 1780s and 1810s, which again marked a colder period.

Neuberger analyzed 12,000 paintings, held in American and European museums and dated between 1400 and 1967, for cloudiness and darkness.[26] His 1970 publication shows an increase in such depictions that corresponds to the LIA,[26] peaking between 1600 and 1649.[27]

Scottish painting and contemporary records demonstrate that curling and skating were formerly popular outdoor winter sports,[28] but it is now seldom possible to curl outdoors in Scotland due to unreliable conditions.

Central America

An analysis of several proxies undertaken in Mexico's Yucatan Peninsula, linked by its authors to Mayan and Aztec chronicles relating periods of cold and drought, supports the existence of the LIA in the region.[29]

Southern hemisphere

The San Rafael Glacier in Southern Chile in 1990 & 2000. Compared with the current extent, in 1898 the glacier reached much further into the lagoon.

Since the discovery of the Little Ice Age, there have been doubts about whether it was a global phenomenon or a cold spell restricted to the Northern Hemisphere. In recent years, several scientific works have pointed out the existence of cold spells and climate changes in areas of the Southern Hemisphere, and their correlation to the Little Ice Age.

Africa

In Southern Africa, sediment cores retrieved from Lake Malawi show colder conditions between 1570 and 1820, suggesting the lake Malawi records "further support, and extend, the global expanse of the Little Ice Age."[30]

A novel 3000 year temperature reconstruction method based on the rate of stalagmite growth in a cold cave in South Africa suggest a cold period from 1500-1800 "characterizing the South African Little Ice age."[31]

Antarctica

Kreutz et al. (1997) compared results from studies of West Antarctic ice cores with the Greenland Ice Sheet Project Two (GISP2) and suggested a synchronous global Little Ice Age (LIA).[32]

An ocean sediment core from the eastern Bransfield Basin in the Antarctic Peninsula shows centennial events that the authors link to the Little Ice Age and Medieval Warm Period (MWP).[33] The authors note "other unexplained climatic events comparable in duration and amplitude to the LIA and MWP events also appear."

CO2 mixing ratios at Law Dome

The Siple Dome (SD) has a climate event with an onset time that is coincident with that of the LIA in the North Atlantic based on a correlation with the GISP2 record. This event is the most dramatic climate event seen in the SD Holocene glaciochemical record.[34] The Siple Dome ice core also contained its highest rate of melt layers (up to 8%) between 1550 and 1700, most likely due to warm summers during the LIA.[35]

Law Dome ice cores show lower levels of CO2 mixing ratios during 1550-1800 AD, leading investigators Etheridge and Steele to conjecture "probably as a result of colder global climate".[36]

Sediment cores (Gebra-1 and Gebra-2) in Bransfield Basin, Antarctic Peninsula, have neoglacial indicators by diatom and sea-ice taxa variations during the period of the LIA.[37]

Australia, New Zealand and Pacific Islands

There is limited evidence about conditions in Australia, though lake records in Victoria suggest that conditions, at least in the south of the state, were wet and/or unusually cool.[citation needed] In the north of the continent the limited evidence suggests fairly dry conditions, while coral cores from the Great Barrier Reef show similar rainfall today but with less variability.[citation needed] A study that analyzed isotopes in Great Barrier Reef corals suggested that increased water vapor transport from southern tropical oceans to the poles contributed to the LIA.[38]

Paleosea-level data for the Pacific Islands suggest that sea level in the region fell, possibly in two stages, between AD 1270-1475. This was associated with a 1.5°C fall in temperature (determined from oxygen-isotope analysis) and an observed increase in El Niño frequency.[39]

Borehole reconstructions from Australia suggest that, over the last 500 years, the 17th century was the coldest in that continent, although the borehole temperature reconstruction method does not show good agreement between the northern and southern hemispheres.[40]

In the Southern Alps of New Zealand, the Franz Josef glacier advanced rapidly during the Little Ice Age, reaching its maximum extent in the early 18th century, in one of the few places where a glacier thrust into rain forest.[24]

South America

Tree ring data from Patagonia show cold episodes between 1270 and 1380 and from 1520 to 1670; periods contemporary with LIA events in the Northern Hemisphere.[41][42] Eight sediment cores taken from Puyehue Lake have been interpreted as showing a humid period from 1470-1700, which the authors describe as a regional marker of LIA onset.[43] A 2009 paper found cooler and wetter conditions in southeastern South America between 1550 and 1800 AD, citing evidence obtained via several proxies and models.[44]

Although it only provides anecdotal evidence, in 1675 the Spanish explorer Antonio de Vea entered San Rafael Lagoon through Río Témpanos (Spanish for Ice Floe River), without mentioning any ice floe, and stated that the San Rafael Glacier did not reach far into the lagoon. In 1766 another expedition noticed that the glacier did reach the lagoon and calved into large icebergs. Hans Steffen visited the area in 1898, noticing that the glacier penetrated far into the lagoon. Such historical records indicate a general cooling in the area between 1675 and 1898, and "The recognition of the LIA in Northern Patagonia, through the use of documentary sources, provides important, independent evidence for the occurrence of this phenomenon in the region.”[45] As of 2001, the border of the glacier has significantly retreated compared to the borders of 1675.[46]

Climate patterns

In the North Atlantic, sediments accumulated since the end of the last ice age, nearly 12,000 years ago, show regular increases in the amount of coarse sediment grains deposited from icebergs melting in the now open ocean, indicating a series of 1-2°C (2-4°F) cooling events recurring every 1,500 years or so (Bond et al., 1997). The most recent of these cooling events was the Little Ice Age. These same cooling events are detected in sediments accumulating off Africa, but the cooling events appear to be larger, ranging between 3-8°C (6-14°F).[47]

Causes

Scientists have tentatively identified these causes of the Little Ice Age: decreased solar activity, increased volcanic activity, altered ocean current flows, the inherent variability of global climate, and reforestation following decreases in the human population. One of the difficulties in identifying the causes of the Little Ice Age is the lack of consensus on what constitutes "normal" climate, or if one exists.

Solar activity

Solar activity events recorded in radiocarbon.

During the period 1645–1715, in the middle of the Little Ice Age, there was a period of low solar activity known as the Maunder Minimum. There is a still very poor understanding of the correlation between low sunspot activity and cooling temperatures.[48][49] The Spörer Minimum has also been identified with a significant cooling period between 1460 and 1550.[50] Other indicators of low solar activity during this period are levels of the isotopes carbon-14 and beryllium-10.[51]

Volcanic activity

Throughout the Little Ice Age, the world also experienced heightened volcanic activity.[52] When a volcano erupts, its ash reaches high into the atmosphere and can spread to cover the whole Earth. This ash cloud blocks out some of the incoming solar radiation, leading to worldwide cooling that can last up to two years after an eruption. Also emitted by eruptions is sulfur in the form of SO2 gas. When this gas reaches the stratosphere, it turns into sulfuric acid particles, which reflect the sun's rays, further reducing the amount of radiation reaching Earth's surface. The 1815 eruption of Tambora in Indonesia blanketed the atmosphere with ash; the following year, 1816, came to be known as the Year Without a Summer, when frost and snow were reported in June and July in both New England and Northern Europe. Other volcanoes that erupted during the era and may have contributed to the cooling include Billy Mitchell (ca. 1580 ± 20 ), Mount Parker (1641), Long Island (Papua New Guinea) (ca. 1660), and Huaynaputina (1600).[10]

Ocean Conveyor slowdown

Another possibility is that there was a slowing of thermohaline circulation.[53][54][55] The circulation could have been interrupted by the introduction of a large amount of fresh water to the North Atlantic, possibly caused by a period of warming before the Little Ice Age known as the Medieval Warm Period.[56][57][58] There is some concern that shutdown of thermohaline circulation could happen again as a result of the present warming period.[59][60]

Decreased human populations

Some reseachers have proposed that human influences on climate began earlier than is normally supposed and that major population declines in Eurasia and the Americas reduced this impact, leading to a cooling trend. William Ruddiman has proposed that somewhat reduced populations of Europe, East Asia, and the Middle East during and after the Black Death caused a decrease in agricultural activity. He suggests reforestation took place, allowing more carbon dioxide uptake from the atmosphere, which may have been a factor in the cooling noted during the Little Ice Age. Ruddiman further hypothesizes that a reduced population in the Americas after European contact in the early 1500s could have had similar effect.[61][62] A 2008 study of sediment cores and soil samples further suggests that carbon-dioxide uptake via reforestation in the Americas could have contributed to the Little Ice Age.[63] Faust, Gnecco, Mannstein and Stamm (2005) supported depopulation in the Americas as a factor, asserting that humans had cleared considerable amounts of forests to support agriculture in the Americas before the arrival of Europeans brought on a population collapse.[64] The authors link the subsequent depopulation to a drop in carbon dioxide levels observed at Law Dome, Antarctica.[64] This hypothesis has not gained widespread scientific support.

Inherent variability of climate

Spontaneous fluctuations in global climate might explain past variability. However, it is very difficult to know what the true level of variability from only internal causes might be, since other forcings, as noted above, exist; and their magnitude may not be known either. One approach to evaluating internal variability is to use long integrations of coupled ocean-atmosphere global climate models. These have the advantage that the external forcing is known to be zero; but the disadvantage that they may not fully reflect reality. These variations may result from chaos-driven changes in the oceans, the atmosphere, or interactions between the two.[65] Two studies have concluded that the demonstrated inherent variability is not great enough to account for the Little Ice Age.[65][66]

End of Little Ice Age

Beginning around 1850, the climate began warming and the Little Ice Age ended. Some global warming critics believe that Earth's climate is still recovering from the Little Ice Age and that human activity is not the decisive factor in present temperature trends,[67][68] but this idea is not widely accepted. Mainstream scientific opinion on climate change is that warming over the last 50 years is caused primarily by the increased proportion of CO2 in the atmosphere caused by human activity. There is less agreement over the warming from 1850 to 1950.

See also

References

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  46. ^ http://hol.sagepub.com/cgi/reprint/17/7/987
  47. ^ USGCRP Seminar: Abrupt Climate Changes Revisited: How Serious and How Likely?
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  49. ^ Sunspot Activity at 8,000-Year High Space.com Astronomy October 27, 2004
  50. ^ Geoffrey Parker, Lesley M. Smith (1997). The general crisis of the seventeenth century. Routledge. pp. 287,288. ISBN 9780415165181. http://books.google.com/books?id=HGLs23umDXAC&pg=PA287&dq=Sp%C3%B6rer+Minimum+little+ice+age&as_brr=3&cd=4#v=onepage&q=&f=false. 
  51. ^ Crowley, Thomas J. (2000-07-14). "Causes of Climate Change Over the Past 1000 Years". Science 289 (5477): 270–277. doi:10.1126/science.289.5477.270. PMID 10894770. http://www.sciencemag.org/cgi/content/abstract/289/5477/270. 
  52. ^ Robock, Alan (1979-12-21). "The "Little Ice Age": Northern Hemisphere Average Observations and Model Calculations". Science 206 (4425): 1402–1404. doi:10.1126/science.206.4425.1402. PMID 17739301. 
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Further reading

  • Brian Fagan, 2000, The Little Ice Age: How Climate Made History, 1300-1850. Basic Books. ISBN 0-465-02272-3.

External links


Simple English


The Little Ice Age (LIA) was a period of cooling after a warmer era that is known as the Medieval Warm Period.

Climatologists and historians find it difficult to agree on either the start or end dates of this period. Some confine the Little Ice Age to approximately the 16th century to the mid 19th century. It is generally agreed that there were three minima, beginning about 1650, about 1770, and 1850, each separated by slight warming intervals.[1] It was initially believed that the LIA was a global phenomenon; it is now less clear if this is true.

Contents

=Solar activity

=

During the period 1645–1715, in the middle of the Little Ice Age, there was a period of low solar activity known as the Maunder Minimum. The physical link between low sunspot activity and cooling temperatures has not been established, but the coincidence of the Maunder Minimum with the deepest trough of the Little Ice Age is suggestive of such a connection.[2] The Spörer Minimum has also been identified with a significant cooling period near the beginning of the Little Ice Age. Other indicators of low solar activity during this period are levels of the isotopes carbon-14 and beryllium-10.[3]

Volcanic activity

Throughout the Little Ice Age, the world also experienced heightened volcanic activity.[4] When a volcano erupts, its ash reaches high into the atmosphere and can spread to cover the whole of Earth. This ash cloud blocks out some of the incoming solar radiation, leading to worldwide cooling that can last up to two years after an eruption.

Ocean Conveyor Shutdown

Another possibility is that there was a shutdown or slowing of Thermohaline circulation, also known as the "great ocean conveyor" or "meridional overturning circulation". The Gulf Stream could have been interrupted by the introduction of a large amount of fresh water to the North Atlantic, possibly caused by a period of warming before the little ice age. There is some concern that shutdown of thermohaline circulation could happen again as a result of global warming [5].

End of Little Ice Age

Beginning around 1850, the climate began warming and the Little Ice Age ended. Some global warming critics believe that Earth's climate is still recovering from the Little Ice Age and that human activity is not the decisive factor in present temperature trends,[6][7] but this idea is not widely accepted.

References

  1. "Little Ice Age definition". Earth Observatory. http://eobglossary.gsfc.nasa.gov/Library/glossary.php3?xref=Little%20Ice%20Age. Retrieved 2007-08-02. 
  2. Changing Sun, Changing Climate
  3. Crowley, Thomas J. (2000-07-14). "Causes of Climate Change Over the Past 1000 Years". Science 289 (5477): 270–277. http://www.sciencemag.org/cgi/content/abstract/289/5477/270. 
  4. Robock, Alan (1979-12-21). [Expression error: Unexpected < operator "The "Little Ice Age": Northern Hemisphere Average Observations and Model Calculations"]. Science 206 (4425): 1402–1404. doi:10.1126/science.206.4425.1402. 
  5. A Chilling Possibility
  6. Steigerwald, Bill (2007-02-10). "The politics of global warming". Pittsburgh Tribune-Review. http://www.pittsburghlive.com/x/pittsburghtrib/news/mostread/s_492572.html. 
  7. Solomon, Lawrence (2007-03-30). "Little Ice Age is still with us". National Post. http://www.canada.com/nationalpost/news/story.html?id=94b7d021-c5da-4e82-b37f-53d338709fb1. 

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