Early human migrations

Earliest human migrations and expansions of archaic and modern humans across continents began 2 million years ago with the migration out of Africa of Homo erectus. This was followed by the migrations of other pre-modern humans including H. heidelbergensis, the likely ancestor of both modern humans and Neanderthals. Finally, Homo sapiens ventured out of Africa around 100,000 years ago, spread across Asia around 60,000 years ago and arrived on new continents and islands since then.

Knowledge of early human migrations, a major topic of archeology, has been achieved by the study of human fossils, occasionally by stone-age artifacts and more recently has been assisted by archaeogenetics. Cultural and ethnic migrations are estimated by combining archaeogenetics and comparative linguistics.

Early humans (before Homo sapiens)

A reconstruction of Homo erectus. Anthropologists believe that H. erectus was the first hominid to control fire (reconstruction shown in Westfälisches Landesmuseum, Herne, Germany, in a 2006 exhibition).

Homo erectus migrated from out of Africa via the Levantine corridor and Horn of Africa to Eurasia during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 1.9 million years ago, and dispersed throughout most of the Old World, reaching as far as Southeast Asia. The date of original dispersal beyond Africa virtually coincides with the appearance of Homo ergaster in the fossil record, and about half a million years after the appearance of the Homo genus itself and the first stone tools of the Oldowan industry. Key sites for this early migration out of Africa are Riwat in Pakistan (~2 Ma?^[1]), Ubeidiya in the Levant (1.5 Ma) and Dmanisi in the Caucasus (1.81 ± 0.03 Ma, p = 0.05^[2]).

China was populated as early as 1.66 Mya based on stone artifacts found in the Nihewan Basin.^[3] The archaeological site of Xihoudu (西侯渡) in Shanxi Province is the earliest recorded use of fire by Homo erectus, which is dated 1.27 million years ago.^[4]

Southeast Asia (Java) was reached about 1.7 million years ago (Meganthropus). Western Europe was first populated around 1.2 million years ago (Atapuerca).^[5]

Robert G. Bednarik has suggested that Homo erectus may have built rafts and sailed oceans, a theory that has raised some controversy.^[6]

The expansion of H. erectus was followed by the arrival of H. antecessor in Europe around 800,000 years ago, which was in turn followed by migration from Africa to Europe of H. heidelbergensis, the likely ancestor of both modern humans and Neanderthals, around 600,000 years ago.^[7]

Homo sapiens migrations

Map of Y-chromosome haplogroups.

Homo sapiens seems to have appeared in East Africa around 200,000 years ago. The oldest individuals found left their marks in the Omo remains (195,000 years ago) and the Homo sapiens idaltu (160,000 years ago), that was found at the Middle Awash site in Ethiopia.^[8]

When modern humans reached the Near East 125,000 years ago, evidence suggests they retreated back to Africa, as their settlements were replaced by Neanderthals^{[citation needed][9]}. It is now believed that the first modern humans to spread east across Asia left Africa about 75,000 years ago across the Bab el Mandib connecting Ethiopia and Yemen.^[10] From the Near East, some of these people went east to South Asia by 50,000 years ago, and on to Australia by 46,000 years ago at the latest,^[11] when for the first time H. sapiens reached territory never reached by H. erectus. H. sapiens reached Europe around 43,000 years ago,^[12] eventually replacing the Neanderthal population by 40,000 years ago.^[13] East Asia was reached by 30,000 years ago. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover.^[14] The date of migration to North America, and whether humans had previously inhabited the Americas is disputed; it may have taken place around 30 thousand years ago, or considerably later, around 14 thousand years ago. The oldest radiocarbon dated carbonized plant remains were determined to be 50,300 years old and were discovered at the Topper site in Allendale South Carolina in May 2004 alongside stone tools similar to those of pre-Clovis era humans.^[15] The oldest DNA evidence of human habitation in North America however, has been radiocarbon dated to 14,300 years ago, and was found in fossilized human coprolites uncovered in the Paisley Five Mile Point Caves in south-central Oregon.^[16] Colonization of the Pacific islands of Polynesia began around 1300 BC, and was completed by 1280 AD (New Zealand). The ancestors of Polynesians left Taiwan around 5,200 years ago.

More recent migrations of language and culture groups within the modern species are also studied and hypothetised. The African Epipaleolithic Kebaran culture is believed to have reached Eurasia about 18,000 years ago, introducing the bow and arrow to the Middle East, and may have been responsible for the spread of the Nostratic languages. The people of the Afro-Asiatic language family seem to have reached Africa in 6,200 BC, introducing the Semitic languages to the Middle East.

From there they spread around the world. An initial venture out of Africa 125,000 years ago was followed by a flood out of Africa via the Arabian Peninsula into Eurasia around 60,000 years ago, with one group rapidly settling coastal areas around the Indian Ocean and one group migrating north to steppes of Central Asia.^[17]

There is evidence from mitochondrial DNA that modern humans have passed through at least one genetic bottleneck, in which genome diversity was drastically reduced. Henry Harpending has proposed that humans spread from a geographically restricted area about 100,000 years ago, the passage through the geographic bottleneck and then with a dramatic growth amongst geographically dispersed populations about 50,000 years ago, beginning first in Africa and thence spreading elsewhere.^[18] Climatological and geological evidence suggests evidence for the bottleneck. The explosion of Lake Toba created a 1,000 year cold period, as a result of the largest volcanic eruption of the Quaternary, potentially reducing human populations to a few tropical refugia. It has been estimated that as few as 15,000 humans survived. In such circumstances genetic drift and founder effects may have been maximised. The greater diversity amongst African genomes may be in part due to the greater prevalence of African refugia during the Toba incident.^[19]

Within Africa

The most recent common ancestor shared by all living human beings, dubbed Mitochondrial Eve, probably lived roughly 120–150 millennia ago,^[20] the time of Homo sapiens idaltu, probably in East Africa.^{[citation needed]}

The broad study of African genetic diversity headed by Dr. Sarah Tishkoff found the San people to express the greatest genetic diversity among the 113 distinct populations sampled, making them one of 14 "ancestral population clusters." The research also located the origin of modern human migration in south-western Africa, near the coastal border of Namibia and Angola.^[21]

Around 100,000-80,000 years ago, three main lines of Homo sapiens diverged. Bearers of mitochondrial haplogroup L0 (mtDNA) / A (Y-DNA) colonized Southern Africa (the ancestors of the Khoisan ( peoples), bearers of haplogroup L1 (mtDNA) / B (Y-DNA) settled Central and West Africa (the ancestors of western pygmies), and bearers of haplogroups L2, L3, and others mtDNA remained in East Africa (the ancestors of Niger–Congo- and Nilo-Saharan-speaking peoples).

Exodus from Africa

Red sea crossing.

There is some evidence for the argument that modern humans left Africa at least 125,000 years ago using two different routes: the Nile Valley heading to the Middle East, at least into modern Israel (Qafzeh: 120,000–100,000 years ago); and a second one through the present-day Bab-el-Mandeb Strait on the Red Sea (at that time, with a much lower sea level and narrower extension), crossing it into the Arabian Peninsula, settling in places like the present-day United Arab Emirates (125,000 years ago)^[22] and Oman (106,000 years ago)^[23] and then possibly going into the Indian Subcontinent (Jwalapuram: 75,000 years ago). Despite the fact that no human remains have yet been found in these three places, the apparent similarities between the stone tools found at Jebel Faya, the ones from Jwalapuram and some African ones suggest that their creators were all modern humans.^[24] These findings might give some support to the claim that modern humans from Africa arrived at southern China about 100,000 years ago (Zhiren Cave, Zhirendong, Chongzuo City: 100,000 years ago;^[25] and the Liujiang hominid (Liujiang County): controversially dated at 139,000–111,000 years ago ^[26]). Dating results of the Lunadong (Bubing Basin, Guangxi, southern China) teeth, which include a right upper second molar and a left lower second molar, indicate that the molars may be as old as 126,000 years.^[27]

Since these previous exits from Africa did not leave traces in the results of genetic analyses based on the Y chromosome and on MtDNA (which represent only a small part of the human genetic material), it seems that those modern humans did not survive or survived in small numbers and were assimilated by our major antecessors. An explanation for their extinction (or small genetic imprint) may be the Toba catastrophe theory (74,000 years ago). However, some argue that its impact on human population was not dramatic.^[28]

According to the Recent African Origin theory a small group of the L3 Haplogroup bearers living in East Africa migrated north east, possibly searching for food or escaping adverse conditions, crossing the Red Sea about 70 millennia ago, and in the process going on to populate the rest of the world. According to some authors, based in the fact that only descents of L3 are found outside Africa, only a few people left Africa in a single migration to a settlement in the Arabian peninsula.^[29] From that settlement, some others point to the possibility of several waves of expansion close in time.

South Asia and Australia

Dating of teeth from China provides evidence of an early migration of modern humans from Africa into Southeast Asia before 80,000 - 120,000 years ago.^[30]
The later major migration from Africa traveled along the coast of Arabia and Persia to India and the rest of South Asia. Along the way H. sapiens interbred with Neanderthals and Denisovans,^[31] with Denisovan DNA making 0.2% of mainland Asian and Native American DNA.^[32] David Reich of Harvard University and Mark Stoneking of the Planck Institute team, found genetic evidence that Denisovan ancestry is shared by Melanesians, Australian Aborigines, and smaller scattered groups of people in Southeast Asia, such as the Mamanwa, a Negrito people in the Philippines suggesting the interbreeding took place in Eastern Asia where the Denisovans lived.^[33][34][35] Denisovans may have crossed the Wallace Line, with Wallacea serving as their last refugium.^[36][37] Homo erectus crossed the Lombok gap reaching as far as Flores, but never made it to Australia.^[38]

The map shows the probable extent of land and water at the time of the last glacial maximum, 20,000 yrs ago and when the sea level was probably more than 110m lower than today.

During this time sea level was much lower and most of Maritime Southeast Asia formed one land mass known as Sunda. Migration continued Southeast on the coastal route to the straits between Sunda and Sahul, the continental land mass of present-day Australia and New Guinea. The gaps on the Weber Line are up to 90 km wide,^[39] so the migration to Australia and New Guinea would have required seafaring skills. Migration also continued along the coast eventually turning northeast to China and finally reaching Japan before turning inland. This is evidenced by the pattern of mitochondrial haplogroups descended from haplogroup M, and in Y-chromosome haplogroup C.

Sequencing of one Aboriginal genome from an old hair sample in Western Australia, revealed that the individual was descended from people who migrated into East Asia between 62,000 and 75,000 years ago. This supports the theory of a single migration into Australia and New Guinea before the arrival of Modern Asians (between 25,000 to 38,000 years ago) and their later migration into North America.^[40] This migration is believed to have happened around 50,000 years ago, before Australia and New Guinea were separated by rising sea levels approximately 8,000 years ago.^[41][42] This is supported by a date of 50,000 - 60,000 years ago for the oldest evidence of settlement in Australia,^[11][43] around 40,000 years ago for the oldest human remains^[11] and the extinction Australian megafauna by humans between 46,000 and 15,000 years ago advocated by Tim Flannery,^[44] which is similar to what happened in the Americas. The continued use of stone age tools in Australia has been much debated.^[45]

Europe

Europe is thought to have been colonized by northwest-bound migrants from Central Asia and the Middle East, as a result of cultural adaption to big game hunting of sub-glacial steppe fauna.^[46] When the first anatomically modern humans entered Europe, Neanderthals were already settled there. Debate exists whether modern human populations interbred with Neanderthal populations, most of the evidence suggesting that it happened to a small degree rather than complete absorption. Populations of modern humans and Neanderthal overlapped in various regions such as in Iberian peninsula and in the Middle East. Interbreeding may have contributed Neanderthal genes to palaeolithic and ultimately modern Eurasians and Oceanians.

An important difference between Europe and other parts of the inhabited world was the northern latitude. Archaeological evidence suggests humans, whether Neanderthal or Cro-Magnon, reached sites in Arctic Russia by 40,000 years ago.^[47]

Around 20,000 BC, approximately 5,000 years after the Neanderthal extinction, the Last Glacial Maximum took place, forcing northern hemisphere inhabitants to migrate to several shelters (known as refugia) until the end of this period. The resulting populations, whether interbred with Neanderthals or not, are then presumed to have resided in those hypothetical refuges during the LGM to ultimately reoccupy Europe where archaic historical populations are considered their descendants. An alternate view is that modern European populations have descended from Neolithic populations in the Middle East that have been well documented in this area. The debate surrounding the origin of Europeans has been worded in terms of cultural diffusion versus demic diffusion.^{[citation needed]} Archeological evidence and genetic evidence strongly support demic diffusion, that a population spread from the Middle East over the last 12,000 years.^{[citation needed]} A scientific genetic concept called the Time to Most Recent Common Ancestor or TMRCA has been used to refute the demic diffusion in favour of cultural diffusion.^[48]

Migration of the Cro-Magnons into Europe

Cro-Magnon are considered the first anatomically modern humans in Europe. They entered Eurasia by the Zagros Mountains (near present-day Iran and eastern Turkey) around 50,000 years ago, with one group rapidly settling coastal areas around the Indian Ocean and one group migrating north to steppes of Central Asia.^[17] Modern human remains dating to 43-45,000 years ago have been discovered in Italy^[49] and Britain,^[50] with the remains found of those that reached the European Russian Arctic 40,000 years ago.^[51][52]
Humans colonised the environment west of the Urals, hunting reindeer especially,^[53] but were faced with adaptive challenges; winter temperatures averaged from −20 to −30 °C (−4 to −22 °F) while fuel and shelter were scarce. They travelled on foot and relied on hunting highly mobile herds for food. These challenges were overcome through technological innovations: production of tailored clothing from the pelts of fur-bearing animals; construction of shelters with hearths using bones as fuel; and digging of “ice cellars” into the permafrost for storing meat and bones.^[53][54]

A mitochondrial DNA sequence of two Cro-Magnons from the Paglicci Cave in Italy, dated to 23,000 and 24,000 years old (Paglicci 52 and 12), identified the mtDNA as Haplogroup N, typical of the latter group.^[55] The inland group is the founder of both North- and East Asians, Caucasoids and large sections of the Middle East population. Migration from the Black Sea area into Europe started sometime around 45,000 years ago, probably across the Bosphorus and along the Danubian corridor. By 20,000 years ago, the whole of Continental Europe had been settled.

Migration of modern humans into Europe, based on simulation by Currat & Excoffier (2004)^[56] (YBP=Years before present)

Up to 37,500 YBP

Up to 35,000 YBP

Up to 32,500 YBP

Up to 30,000 YBP

 

Competition with Neanderthals

The expansion of modern human population is thought to have begun 45,000 years ago, and may have taken 15,000-20,000 years for Europe to be colonized.^[57][58]
During this time the Neanderthals were slowly being displaced. Because it took so long for Europe to be occupied, it appears that humans and Neanderthals may have been constantly competing for territory. The Neanderthals had larger brains, and were larger overall, with a more robust or heavily built frame, which suggests that they were physically stronger than modern Homo sapiens. Having lived in Europe for 200,000 years, they would have been better adapted to the cold weather. The anatomically modern humans known as the Cro-Magnons, with widespread trade networks, superior technology and bodies likely better suited to running, would eventually completely displace the Neanderthals, whose last refuge was in the Iberian peninsula. After about 25,000 years ago the fossil record of the Neanderthals ends, indicating that they had become extinct. The last known population lived around a cave system on the remote south-facing coast of Gibraltar from 30,000 to 24,000 years ago.

A 2010 study of Neanderthal genes and modern human genes concluded that interbreeding took place between Neanderthals and Homo sapiens sapiens between roughly 80,000 to 50,000 years ago in the Middle East, resulting in Europeans and Asians having between 1% and 4% Neanderthal DNA, while sub-Saharan Africans do not have Neanderthal DNA.^[59] Comparison of remnant Neanderthal DNA has shown that this 4% is not consistent, suggesting that there was not one, but several cases of interbreeding between the two species, with Caucasian and Balkan DNA contributing more to the Eurasian human lineage than the Altaic groups.

Three-part origin of modern Europeans

Evidence published in 2014 from genome analysis of ancient human remains suggests that the modern native populations of Europe largely descend from three distinct lines: Hunter-gatherers who lived 45,000 years ago and most probably originated in the second human migration out of Africa into Europe, early agriculturists who moved into Europe about 9,000 years ago and mixed in, and finally a population of pontic-caspian steppe nomads who contributed DNA (and Indo-European languages) to a wide range of modern humans including native Americans.^[60]

Central and Northern Asia

Mitochondrial haplogroups A, B and G originated about 50,000 years ago, and bearers subsequently colonized Siberia, Korea and Japan, by about 35,000 years ago. Parts of these populations migrated to North America.

A Paleolithic site on the Yana River, Siberia, at 71°N, lies well above the Arctic circle and dates to 27,000 radiocarbon years before present, during glacial times. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought.^[61]

Americas

Paleo-Indians originated from Central Asia, crossing the Beringia land bridge between eastern Siberia and present-day Alaska.^[62] Humans lived throughout the Americas by the end of the last glacial period, or more specifically what is known as the late glacial maximum, no earlier than 23,000 years before present.^{[62][63][64][65]} The details of Paleo-Indian migration to and throughout the American continent, including the dates and the routes traveled, are subject to ongoing research and discussion.^[66]
Dates for Paleo-Indian migration out of Beringia are a matter of current debate. Estimates range from 40,000 to around 16,500 years ago.^[67][68][69]

The routes of migration are also debated. The traditional theory is that these early migrants moved when sea levels were significantly lowered due to the Quaternary glaciation,^[63][66] following herds of now-extinct pleistocene megafauna along ice-free corridors that stretched between the Laurentide and Cordilleran ice sheets.^[70] Another route proposed is that, either on foot or using primitive boats, they migrated down the Pacific coast to South America as far as Chile.^[71] Any archaeological evidence of coastal occupation during the last Ice Age would now have been covered by the sea level rise, up to a hundred metres since then.^[72] The recent finding of Australoid genetic markers in Amazonia supports the coastal route hypothesis.^[73][74]

Little Ice Age

From Wikipedia, the free encyclopedia

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 the Medieval Warm Period.^[1] Although it was not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939.^[2] It has been conventionally defined as a period extending from the 16th to the 19th centuries,^[3][4][5] but some experts prefer an alternative timespan from about 1300^[6] to about 1850.^[7][8][9] Climatologists and historians working with local records no longer expect to agree on either the start or end dates of the period, which varied according to local conditions.

The NASA Earth Observatory notes three particularly cold intervals: one beginning about 1650, another about 1770, and the last in 1850, all separated by intervals of slight warming.^[5] The Intergovernmental Panel on Climate Change Third Assessment Report considered the timing and areas affected by the Little Ice Age suggested largely-independent regional climate changes rather than a globally-synchronous increased glaciation. At most, there was modest cooling of the Northern Hemisphere during the period.^[10]

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.

Areas involved

The Intergovernmental Panel on Climate Change Third Assessment Report (TAR) of 2001 described the areas affected:

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 interval, 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.^[10]

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.... 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."^[11]

Dating

The last written records of the Norse Greenlanders are from a 1408 marriage at Hvalsey Church, now the best-preserved of the Norse ruins.

There is no consensus regarding the time when the Little Ice Age began,^[12][13] but a series of events before the known climatic minima has often been referenced. In the 13th century, pack ice began advancing southwards in the North Atlantic, as did glaciers in Greenland. Anecdotal evidence suggests expanding glaciers almost worldwide. Based on radiocarbon dating of roughly 150 samples of dead plant material with roots intact, collected from beneath ice caps on Baffin Island and Iceland, Miller et al. (2012)^[6] state that cold summers and ice growth began abruptly between 1275 and 1300, followed by "a substantial intensification" from 1430 to 1455.^[14]

In contrast, a climate reconstruction based on glacial length^[15][16] shows no great variation from 1600 to 1850 but strong retreat thereafter.

Therefore, 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 the 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.

The Little Ice Age ended in the latter half of the 19th century or early in the 20th century.^[17][18][19]

Northern Hemisphere

Europe

The Frozen Thames, 1677

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.^[20] Canals and rivers in Great Britain and the Netherlands were frequently frozen deeply enough to support ice skating and winter festivals.^[20] The first River Thames frost fair was in 1607 and the last in 1814; changes to the bridges and the addition of the Thames Embankment affected the river flow and depth, greatly diminishing the possibility of further 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 Denmark to attack Copenhagen. The winter of 1794–1795 was particularly harsh: the French invasion army under Pichegru was able to march on the frozen rivers of the Netherlands, and the Dutch fleet was fixed in the ice in Den Helder harbour.

Sea ice surrounding Iceland extended for miles in every direction, closing harbors to shipping. The population of Iceland fell by half, but that may have been caused by skeletal fluorosis after the eruption of Laki in 1783.^[21] Iceland also suffered failures of cereal crops and people moved away from a grain-based diet.^[22] The Norse colonies in Greenland starved and vanished by the early 15th century, as crops failed and livestock could not be maintained through increasingly harsh winters, but Jared Diamond has suggested they had exceeded the agricultural carrying capacity before then. Greenland was largely cut off by ice from 1410 to the 1720s.^[23]

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

The Twentieth Century climatologist Hubert 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."^[24] In Lisbon, Portugal, snowstorms were much more frequent than today; one winter in the 17th century produced eight snowstorms.^[25] Many springs and summers were cold and wet but with 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 dearth and famine (such as the Great Famine of 1315–1317, but that may have been before the Little Ice Age).^[26] According to Elizabeth Ewan and Janay Nugent, "Famines in France 1693–94, Norway 1695–96 and Sweden 1696–97 claimed roughly 10 percent of the population of each country. In Estonia and Finland in 1696–97, losses have been estimated at a fifth and a third of the national populations, respectively."^[27] Viticulture disappeared from some northern regions and storms caused serious flooding and loss of life. Some of them resulted in permanent loss of large areas of land from the Danish, German, and Dutch coasts.^[24]

The violin maker Antonio Stradivari 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 his instruments.^[28] According to the science historian James Burke, the period inspired such novelties in everyday life as the widespread use of buttons and button-holes, knitting of custom-made undergarments to better cover and insulate the body. Fireplace hoods were installed to make more efficient use of fires for indoor heating, and enclosed stoves were developed, with early versions often covered with ceramic tiles.^[29]

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, agriculture had dropped off dramatically: "Alpine villagers lived on bread made from ground nutshells mixed with barley and oat flour." ^[30] Historian Wolfgang Behringer has linked intensive witch-hunting episodes in Europe to agricultural failures during the Little Ice Age.^[31]

Depictions of winter in European painting

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

William James Burroughs analyses the depiction of winter in paintings, as does Hans Neuberger.^[32] Burroughs asserts that it occurred almost entirely from 1565 to 1665 and was associated with the climatic decline from 1550 onwards. Burroughs claims that there had been 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 that the decline in such paintings was a combination of the 'theme' having been fully explored and mild winters interrupting the flow of painting".^[33] Wintry scenes, which entail technical difficulties in painting, have been regularly and well handled since the early 15th 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. Since landscape painting had not yet developed as independent genre in art, the absence of other winter scenes is not remarkable.

The Hunters in the Snow by Pieter Brueghel the Elder, 1565

The famous winter landscape paintings by Pieter Brueghel the Elder, such as 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, but according to Burroughs, 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...".^[33][34]

Winter landscape with iceskaters, c. 1608, Hendrick Avercamp

Burroughs says that snowy subjects return to Dutch Golden Age painting with works by Hendrick Avercamp from 1609 onwards. There is then a hiatus between 1627 and 1640, before the main period of such subjects from the 1640s to the 1660s, which relates well with climate records for the later period. The subjects are less popular after about 1660, but that does not match any recorded reduction in severity of winters and may reflect only changes in taste or fashion. In the later period between the 1780s and 1810s, snowy subjects again became popular.^[33]

Neuberger analysed 12,000 paintings, held in American and European museums and dated between 1400 and 1967, for cloudiness and darkness.^[32] His 1970 publication shows an increase in such depictions that corresponds to the Little Ice Age,^[32] peaking between 1600 and 1649.^[35]
Paintings and contemporary records in Scotland demonstrate that curling and ice skating were popular outdoor winter sports, with curling dating back to the 16th century and becoming widely popular in the mid-19th century.^[36] 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.^[37]

North America

"February" from the calendar of Les Très Riches Heures du duc de Berry, 1412–1416

Early European explorers and settlers of North America reported exceptionally severe winters. For example, according to Lamb, Samuel Champlain reported bearing ice along the shores of Lake Superior in June 1608. Both Europeans and indigenous peoples suffered excess mortality in Maine during the winter of 1607–1608, and extreme frost was reported in the Jamestown, Virginia, settlement at the same time.^[24] Native Americans formed leagues in response to food shortages.^[23] The journal of Pierre de Troyes, Chevalier de Troyes, who led an expedition to James Bay in 1686, recorded that the bay was still littered with so much floating ice that he could hide behind it in his canoe on 1 July.^[38] In the winter of 1780, New York Harbor froze, allowing people to walk from Manhattan Island to Staten Island.

The extent of mountain glaciers had been mapped by the late 19th century. In the north and the south temperate zones, snowlines (the boundaries separating zones of net accumulation from those of net ablation) were about 100 metres (330 ft) lower than they were in 1975.^[39] In Glacier National Park, the last episode of glacier advance came in the late 18th and the early 19th centuries.^[40] In Chesapeake Bay, Maryland, large temperature excursions were possibly related to changes in the strength of North Atlantic thermohaline circulation.^[41]

Mesoamerica

An analysis of several proxies undertaken in Mexico's Yucatan Peninsula, linked by its authors to Maya and Aztec chronicles relating periods of cold and drought, supports the existence of the Little Ice Age in the region.^[42]

Atlantic Ocean

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.^[43] 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).^[44]

Asia

Although the original designation of a Little Ice Age referred to reduced temperature of Europe and North America, there is some evidence of extended periods of cooling outside this region, but it is not clear whether they are related or independent events. Mann states:^[3]

While there is evidence that many other regions outside Europe exhibited periods of cooler conditions, expanded glaciation, and significantly altered climate conditions, the timing and nature of these variations are highly variable from region to region, and the notion of the Little Ice Age as a globally synchronous cold period has all but been dismissed.

In China, warm-weather crops such as oranges were abandoned in Jiangxi Province, where they had been grown for centuries.^[45] Also, the two periods of most frequent typhoon strikes in Guangdong coincide with two of the coldest and driest periods in northern and central China (1660–1680, 1850–1880).^[46]

In Pakistan, the Balochistan province became colder and the native Baloch people started mass migration and settled along the Indus River in Sindh and Punjab provinces.^[47]

Southern Hemisphere

Scientific works point out cold spells and climate changes in areas of the Southern Hemisphere and their correlation to the Little Ice Age.

Africa

In Ethiopia and Mauritania, permanent snow was reported on mountain peaks at levels where it does not occur today.^[45] 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.^[45]
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."^[48] A novel 3,000-year temperature reconstruction method, based on the rate of stalagmite growth in a cold cave in South Africa, further suggests a cold period from 1500 to 1800 "characterizing the South African Little Ice age."^[49]

Antarctica

CO₂ mixing ratios at Law Dome

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.^[50] 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.^[51] The authors note "other unexplained climatic events comparable in duration and amplitude to the LIA and MWP events also appear."

The Siple Dome (SD) had a climate event with an onset time that is coincident with that of the Little Ice Age in the North Atlantic based on a correlation with the GISP2 record. The event is the most dramatic climate event in the SD Holocene glaciochemical record.^[52] The Siple Dome ice core also contained its highest rate of melt layers (up to 8%) between 1550 and 1700, most likely because of warm summers.^[53] Law Dome ice cores show lower levels of CO₂ mixing ratios from 1550 to 1800, which Etheridge and Steele conjecture are "probably as a result of colder global climate."^[54]

Sediment cores in Bransfield Basin, Antarctic Peninsula, have neoglacial indicators by diatom and sea-ice taxa variations during the Little Ice Age.^[55] The MES stable isotope record suggests that the Ross Sea region experienced 1.6 ± 1.4 °C cooler average temperatures during the Little Ice Age, compared to the last 150 years to now.^[56]

Australia and New Zealand

Limited evidence describes conditions in Australia. Lake records in Victoria suggest that conditions, at least in the south of the state, were wet and/or unusually cool. In the north, evidence suggests fairly dry conditions, but coral cores from the Great Barrier Reef show similar rainfall as today but with less variability. 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 Little Ice Age.^[57] Borehole reconstructions from Australia suggest that over the last 500 years, the 17th century was the coldest on the continent, but the borehole temperature reconstruction method does not show good agreement between the Northern and Southern Hemispheres.^[58]

On the west coast of the Southern Alps of New Zealand, the Franz Josef glacier advanced rapidly during the Little Ice Age and reached its maximum extent in the early 18th century, in one of the few cases of a glacier thrusting into a rain forest.^[30] Based on dating of a yellow-green lichen of the Rhizocarpon subgenus, the Mueller Glacier, on the eastern flank of the Southern Alps within Aoraki/Mount Cook National Park, is considered to have been at its maximum extent between 1725 and 1730.^[59]

Pacific Islands

Sea-level data for the Pacific Islands suggest that sea level in the region fell, possibly in two stages, between 1270 and 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.^[60] Tropical Pacific coral records indicate the most frequent, intense El Niño-Southern Oscillation activity in the mid-seventeenth century.^[61]

South America

Tree-ring data from Patagonia show cold episodes between 1270 and 1380 and from 1520 to 1670, contemporary with the events in the Northern Hemisphere.^[62][63] Eight sediment cores taken from Puyehue Lake have been interpreted as showing a humid period from 1470 to 1700, which the authors describe as a regional marker of the onset of the Little Ice Age.^[64] A 2009 paper details cooler and wetter conditions in southeastern South America between 1550 and 1800, citing evidence obtained via several proxies and models.^{[65] 18}O records from three Andean ice cores show a cool period from 1600–1800 ^[66]

Although only 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 but stating that the San Rafael Glacier did not reach far into the lagoon. In 1766, another expedition noticed that the glacier reached 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: "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."^[67] As of 2001, the border of the glacier had significantly retreated as compared to the borders of 1675.^[67]

Possible causes

Scientists have tentatively identified these possible causes of the Little Ice Age: orbital cycles, decreased solar activity, increased volcanic activity, altered ocean current flows,^[68] the inherent variability of global climate, and reforestation following decreases in the human population.

Orbital cycles

Orbital forcing from cycles in the earth's orbit around the sun has, for the past 2,000 years, caused a long-term northern hemisphere cooling trend that continued through the Middle Ages and the Little Ice Age. The rate of Arctic cooling is roughly 0.02 °C per century.^[69] This trend could be extrapolated to continue into the future, possibly leading to a full ice age, but the twentieth-century instrumental temperature record shows a sudden reversal of this trend, with a rise in global temperatures attributed to greenhouse gas emissions.^[69]

Solar activity

Solar activity events recorded in radiocarbon

The Maunder minimum in a 400-year history of sunspot numbers

There is still a very poor understanding of the correlation between low sunspot activity and cooling temperatures.^[70][71] 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 Spörer Minimum has also been identified with a significant cooling period between 1460 and 1550.^[72] Other indicators of low solar activity during this period are levels of the isotopes carbon-14 and beryllium-10.^[73]

Volcanic activity

In a 2012 paper, Miller et al. link the Little Ice Age to an "unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg" and notes that "large changes in solar irradiance are not required."^[6]

Throughout the Little Ice Age, the world experienced heightened volcanic activity.^[74] When a volcano erupts, its ash reaches high into the atmosphere and can spread to cover the whole earth. The 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 sulfur dioxide gas. When it 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.

A recent study found that an especially massive tropical volcanic eruption in 1257, possibly of the now-extinct Mount Samalas near Mount Rinjani, both in Lombok, Indonesia, followed by three smaller eruptions in 1268, 1275, and 1284 did not allow the climate to recover. This may have caused the initial cooling, and the 1452–53 eruption of Kuwae in Vanuatu triggered a second pulse of cooling.^[6][14] The cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed.

Other volcanoes that erupted during the era and may have contributed to the cooling include Billy Mitchell (ca. 1580), Huaynaputina (1600), Mount Parker (1641), Long Island (Papua New Guinea) (ca. 1660), and Laki (1783).^[20] The 1815 eruption of Tambora, also 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.

Ocean circulation

Thermohaline circulation or Oceanic conveyor belt illustrated

Another possibility is that there was a slowing of thermohaline circulation.^{[39][68][75][76]} The circulation could have been interrupted by the introduction of a large amount of fresh water into the North Atlantic, possibly caused by a period of warming before the Little Ice Age known as the Medieval Warm Period.^[30][77][78] There is some concern that a shutdown of thermohaline circulation could happen again as a result of the present warming period.^[79][80]

Decreased human populations

Some researchers have proposed that human influences on climate began earlier than is normally supposed (see Early anthropocene for more details) 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 sixteenth century could have had a similar effect.^[81][82] Faust, Gnecco, Mannstein and Stamm (2005)^[83] and Nevle (2011)^[84] supported depopulation in the Americas as a factor, asserting that humans had cleared considerable amounts of forest to support agriculture in the Americas before the arrival of Europeans brought on a population collapse. 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.^[85] The depopulation is linked to a drop in carbon dioxide levels observed at Law Dome, Antarctica.^[83]

Increased human populations

It has been speculated that increased human populations living at high latitudes caused the Little Ice Age through deforestation. The increased albedo due to this deforestation (more reflection of solar rays from snow-covered ground than dark, tree-covered area) could have had a profound effect on global temperatures.^[86]

Inherent variability of climate

Spontaneous fluctuations in global climate might explain past variability. 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 whose magnitude may not be known either. One approach to evaluating internal variability is to use long integrations of coupled ocean-atmosphere global climate models. They have the advantage that the external forcing is known to be zero, but the disadvantage is that they may not fully reflect reality. The variations may result from chaos-driven changes in the oceans, the atmosphere, or interactions between the two.^[87] Two studies have concluded that the demonstrated inherent variability is not great enough to account for the Little Ice Age.^[87][88]