During this last glacial period there were alternating episodes
of glacier advance and retreat. Within the last glacial period the Last Glacial Maximum
was approximately 22,000 years ago. While the general pattern of global
cooling and glacier advance was similar, local differences in the
development of glacier advance and retreat make it difficult to compare
the details from continent to continent (see picture of ice core data
below for differences). Approximately 12,800 years ago, the Younger Dryas,
the most recent glacial epoch, began, a coda to the preceding 100,000
year glacial period. Its end about 11,550 years ago marked the beginning
of the Holocene, the current geologicalepoch.
From the point of view of human archaeology, the last glacial period falls in the Paleolithic and early Mesolithic periods. When the glaciation event started, Homo sapiens were confined to lower latitudes and used tools comparable to those used by Neanderthals in western and central Eurasia and by Denisovans and Homo erectus in Asia. Near the end of the event, Homo sapiens
migrated into Eurasia and Australia. Archaeological and genetic data
suggest that the source populations of Paleolithic humans survived the
last glacial period in sparsely wooded areas and dispersed through areas
of high primary productivity while avoiding dense forest cover.
Artist's impression of the last glacial period at glacial maximum
Origin and definition
The last glacial period is often colloquially referred to as the "last ice age", though the term ice age
is not strictly defined, and on a longer geological perspective the
last few million years could be termed a single ice age given the
continual presence of ice sheets
near both poles. Glacials are somewhat better defined, as colder phases
during which glaciers advance, separated by relatively warm interglacials.
The end of the last glacial period, which was about 10,000 years ago,
is often called the end of the ice age, although extensive year-round
ice persists in Antarctica and Greenland.
Over the past few million years the glacial-interglacial cycles have
been "paced" by periodic variations in the Earth's orbit via Milankovitch cycles.
The last glacial period has been intensively studied in North America, northern Eurasia, the Himalaya
and other formerly glaciated regions around the world. The glaciations
that occurred during this glacial period covered many areas, mainly in
the Northern Hemisphere and to a lesser extent in the Southern
Hemisphere. They have different names, historically developed and
depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale (in the Central Rocky Mountains), Wisconsinan or Wisconsin (in central North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), Mérida (in Venezuela), Weichselian or Vistulian (in Northern Europe and northern Central Europe), Valdai in Russia and Zyryanka in Siberia, Llanquihue in Chile, and Otira in New Zealand. The geochronological Late Pleistocene includes the late glacial (Weichselian) and the immediately preceding penultimate interglacial (Eemian) period.
Last glacial period, as seen in ice core data from Antarctica and Greenland
Northern Hemisphere
Canada was nearly completely covered by ice, as well as the northern part of the United States, both blanketed by the huge Laurentide Ice Sheet. Alaska remained mostly ice free due to arid climate conditions. Local glaciations existed in the Rocky Mountains and the Cordilleran Ice Sheet and as ice fields and ice caps in the Sierra Nevada in northern California. In Britain, mainland Europe, and northwestern Asia, the Scandinavian ice sheet once again reached the northern parts of the British Isles, Germany, Poland, and Russia, extending as far east as the Taymyr Peninsula in western Siberia.
The maximum extent of western Siberian glaciation was reached by
approximately 18,000 to 17,000 BP and thus later than in Europe
(22,000–18,000 BP) Northeastern Siberia was not covered by a continental-scale ice sheet.
Instead, large, but restricted, icefield complexes covered mountain
ranges within northeast Siberia, including the Kamchatka-Koryak
Mountains.
The Arctic Ocean between the huge ice sheets of America and
Eurasia was not frozen throughout, but like today probably was only
covered by relatively shallow ice, subject to seasonal changes and
riddled with icebergscalving from the surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores there must even have been times of seasonally open waters.
Outside the main ice sheets, widespread glaciation occurred on the highest mountains of the Alps−Himalayamountain chain.
In contrast to the earlier glacial stages, the Würm glaciation was
composed of smaller ice caps and mostly confined to valley glaciers,
sending glacial lobes into the Alpine foreland. The Pyrenees, the highest massifs of the Carpathian Mountains and the Balkanic peninsula mountains and to the east the Caucasus and the mountains of Turkey and Iran were capped by local ice fields or small ice sheets.
In the Himalaya and the Tibetan Plateau, glaciers advanced considerably, particularly between 47,000 and 27,000 BP, but these datings are controversial. The formation of a contiguous ice sheet on the Tibetan Plateau is controversial.
Other areas of the Northern Hemisphere did not bear extensive ice sheets, but local glaciers in high areas. Parts of Taiwan, for example, were repeatedly glaciated between 44,250 and 10,680 BP as well as the Japanese Alps. In both areas maximum glacier advance occurred between 60,000 and 30,000 BP. To a still lesser extent glaciers existed in Africa, for example in the High Atlas, the mountains of Morocco, the Mount Atakor massif in southern Algeria, and several mountains in Ethiopia. In the Southern Hemisphere, an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro massif, Mount Kenya and the Rwenzori Mountains, still bearing remnants of glaciers today.
Southern Hemisphere
Glaciation of the Southern Hemisphere was less extensive. Ice sheets existed in the Andes (Patagonian Ice Sheet), where six glacier advances between 33,500 and 13,900 BP in the Chilean Andes have been reported.
Antarctica was entirely glaciated, much like today, but unlike today
the ice sheet left no uncovered area. In mainland Australia only a very
small area in the vicinity of Mount Kosciuszko was glaciated, whereas in Tasmania glaciation was more widespread.
An ice sheet formed in New Zealand, covering all of the Southern Alps,
where at least three glacial advances can be distinguished. Local ice caps existed in Western New Guinea, Indonesia, where in three ice areas remnants of the Pleistocene glaciers are still preserved today.
Small glaciers developed in a few favorable places in Southern Africa during the last glacial period. These small glaciers would have developed in the Lesotho Highlands and parts of the Drakensberg. The development of glaciers was likely aided by localized cooling indebted to shading by adjacent cliffs. Various moraines and former glacial niches have been identified in the eastern Lesotho Highlands, above 3,000 m.a.s.l. and on south-facing slopes, a few kilometres west of the Great Escarpment.
Studies suggest the mountains of Southern Africa were mostly subject to
mild periglaciation during the last glacial cycle and the annual
average temperatures were about 6 °C colder than at present. The
estimated 6 °C temperature drop for Southern Africa is in line with
temperature drops estimated for Tasmania and southern Patagonia during the same time. The environment of the Lesotho Highlands during the Last Glacial Maximum was one of a relatively arid periglaciation without permafrost
but with deep seasonal freezing on south-facing slopes. Periglaciation
in the Eastern Drakensberg and Lesotho Highlands produced solifluction deposits, blockfields and blockstreams, and stone garlands.
Deglaciation
Scientists from the Center for Arctic Gas Hydrate, Environment (CAGE) and Climate at the University of Tromsø, published a study in June 2017
describing over a hundred ocean sediment craters, some 3,000 meters wide and up to 300 meters deep, formed by explosive eruptions of methane from destabilized methane hydrates, following ice-sheet retreat during the last glacial period, around 12,000 years ago. These areas around the Barents Sea still seep methane today. The study hypothesized that existing bulges containing methane reservoirs could eventually have the same fate.
Named local glaciations
Antarctica glaciation
During
the last glacial period Antarctica was blanketed by a massive ice
sheet, much as it is today. The ice covered all land areas and extended
into the ocean onto the middle and outer continental shelf. According to ice modelling, ice over central East Antarctica was generally thinner than today.
Europe
Devensian and Midlandian glaciation (Britain and Ireland)
British geologists refer to the last glacial period as the Devensian. Irish geologists, geographers, and archaeologists refer to the Midlandian glaciation as its effects in Ireland are largely visible in the Irish Midlands. The name Devensian is derived from the LatinDēvenses, people living by the Dee (Dēva in Latin), a river on the Welsh border near which deposits from the period are particularly well represented.
The effects of this glaciation can be seen in many geological features of England, Wales, Scotland, and Northern Ireland. Its deposits have been found overlying material from the preceding Ipswichian stage and lying beneath those from the following Holocene, which is the stage we are living in today. This is sometimes called the Flandrian interglacial in Britain.
Weichselian glaciation (Scandinavia and northern Europe)
Europe during the last glacial period
Alternative names include: Weichsel glaciation or Vistulian glaciation (referring to the Polish river Vistula or its German name Weichsel). Evidence suggests that the ice sheets were at their maximum size for only a short period, between 25,000 and 13,000 BP. Eight interstadials
have been recognized in the Weichselian, including: the Oerel, Glinde,
Moershoofd, Hengelo and Denekamp; however correlation with isotope stages is still in process. During the glacial maximum in Scandinavia, only the western parts of Jutland were ice-free, and a large part of what is today the North Sea was dry land connecting Jutland with Britain.
The Baltic Sea, with its unique brackish water,
is a result of meltwater from the Weichsel glaciation combining with
saltwater from the North Sea when the straits between Sweden and Denmark
opened. Initially, when the ice began melting about 10,300 BP, seawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea. Then, as post-glacial isostatic rebound
lifted the region about 9500 BP, the deepest basin of the Baltic became
a freshwater lake, in palaeological contexts referred to as Ancylus Lake,
which is identifiable in the freshwater fauna found in sediment cores.
The lake was filled by glacial runoff, but as worldwide sea level
continued rising, saltwater again breached the sill about 8000 BP,
forming a marine Littorina Sea
which was followed by another freshwater phase before the present
brackish marine system was established. "At its present state of
development, the marine life of the Baltic Sea is less than about 4000
years old", Drs. Thulin and Andrushaitis remarked when reviewing these
sequences in 2003.
Overlying ice had exerted pressure on the Earth's surface. As a
result of melting ice, the land has continued to rise yearly in
Scandinavia, mostly in northern Sweden and Finland where the land is
rising at a rate of as much as 8–9 mm per year, or 1 meter in 100 years.
This is important for archaeologists since a site that was coastal in
the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.
Würm glaciation (Alps)
Violet: extent of the Alpine ice sheet in the Würm glaciation. Blue: extent in earlier ice ages.
The term Würm
is derived from a river in the Alpine foreland, approximately marking
the maximum glacier advance of this particular glacial period. The Alps
were where the first systematic scientific research on ice ages was
conducted by Louis Agassiz at the beginning of the 19th century. Here the Würm glaciation of the last glacial period was intensively studied. Pollen analysis, the statistical analyses of microfossilized
plant pollens found in geological deposits, chronicled the dramatic
changes in the European environment during the Würm glaciation. During
the height of Würm glaciation, c. 24,000 – c. 10,000 BP, most of western and central Europe and Eurasia was open steppe-tundra, while the Alps presented solid ice fields and montane glaciers. Scandinavia and much of Britain were under ice.
During the Würm, the Rhône Glacier
covered the whole western Swiss plateau, reaching today's regions of
Solothurn and Aarau. In the region of Bern it merged with the Aar
glacier. The Rhine Glacier
is currently the subject of the most detailed studies. Glaciers of the
Reuss and the Limmat advanced sometimes as far as the Jura. Montane and
piedmont glaciers formed the land by grinding away virtually all traces
of the older Günz and Mindel glaciation, by depositing base moraines and
terminal moraines of different retraction phases and loess
deposits, and by the pro-glacial rivers' shifting and redepositing
gravels. Beneath the surface, they had profound and lasting influence on
geothermal heat and the patterns of deep groundwater flow.
The Pinedale (central Rocky Mountains) or Fraser (Cordilleran Ice Sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains
in the United States. The Pinedale lasted from approximately 30,000 to
10,000 years ago and was at its greatest extent between 23,500 and
21,000 years ago.
This glaciation was somewhat distinct from the main Wisconsin
glaciation as it was only loosely related to the giant ice sheets and
was instead composed of mountain glaciers, merging into the Cordilleran Ice Sheet. The Cordilleran Ice Sheet produced features such as glacial Lake Missoula, which would break free from its ice dam causing the massive Missoula Floods. USGS
geologists estimate that the cycle of flooding and reformation of the
lake lasted an average of 55 years and that the floods occurred
approximately 40 times over the 2,000 year period between 15,000 and
13,000 years ago. Glacial lake outburst floods such as these are not uncommon today in Iceland and other places.
It radically altered the geography of North America north of the Ohio River. At the height of the Wisconsin Episode glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelleys Island in Lake Erie or in New York's Central Park, the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleranice sheets formed the Cypress Hills, which is the northernmost point in North America that remained south of the continental ice sheets.
The Great Lakes
are the result of glacial scour and pooling of meltwater at the rim of
the receding ice. When the enormous mass of the continental ice sheet
retreated, the Great Lakes began gradually moving south due to isostatic
rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River.
With the assistance of several very broad glacial lakes, it released floods through the gorge of the Upper Mississippi River, which in turn was formed during an earlier glacial period.
In the Sierra Nevada, there are three named stages of glacial maxima (sometimes incorrectly called ice ages) separated by warmer periods. These glacial maxima are called, from oldest to youngest, Tahoe, Tenaya, and Tioga.
The Tahoe reached its maximum extent perhaps about 70,000 years ago.
Little is known about the Tenaya. The Tioga was the least severe and
last of the Wisconsin Episode. It began about 30,000 years ago, reached
its greatest advance 21,000 years ago, and ended about 10,000 years ago.
Greenland glaciation
In
Northwest Greenland, ice coverage attained a very early maximum in the
last glacial period around 114,000. After this early maximum, the ice
coverage was similar to today until the end of the last glacial period.
Towards the end, glaciers readvanced once more before retreating to
their present extent.
According to ice core data, the Greenland climate was dry during the
last glacial period, precipitation reaching perhaps only 20% of today's
value.
Map showing the extent of the glaciated area in Venezuelan Andes during the Mérida glaciation
The name Mérida Glaciation is proposed to designate the alpine glaciation which affected the central Venezuelan Andes
during the Late Pleistocene. Two main moraine levels have been
recognized: one with an elevation of 2,600–2,700 m (8,500–8,900 ft), and
another with an elevation of 3,000–3,500 m (9,800–11,500 ft). The snow
line during the last glacial advance was lowered approximately 1,200 m
(3,900 ft) below the present snow line, which is 3,700 m (12,100 ft).
The glaciated area in the Cordillera de Mérida was approximately 600 km2 (230 sq mi);
this included the following high areas from southwest to northeast:
Páramo de Tamá, Páramo Batallón, Páramo Los Conejos, Páramo Piedras
Blancas, and Teta de Niquitao. Approximately 200 km2 (77 sq mi) of the total glaciated area was in the Sierra Nevada de Mérida, and of that amount, the largest concentration, 50 km2 (19 sq mi), was in the areas of Pico Bolívar, Pico Humboldt [4,942 m (16,214 ft)], and Pico Bonpland
[4,983 m (16,348 ft)]. Radiocarbon dating indicates that the moraines
are older than 10,000 BP, and probably older than 13,000 BP. The lower
moraine level probably corresponds to the main Wisconsin glacial
advance. The upper level probably represents the last glacial advance
(Late Wisconsin).
Llanquihue glaciation (Southern Andes)
Map showing the extent of the Patagonian Ice Sheet in the Strait of Magellan area during the last glacial period. Selected modern settlements are shown with yellow dots.
The Llanquihue glaciation takes its name from Llanquihue Lake in southern Chile which is a fan-shaped piedmontglacial lake.
On the lake's western shores there are large moraine systems of which
the innermost belong to the last glacial period. Llanquihue Lake's varves are a node point in southern Chile's varve geochronology. During the last glacial maximum the Patagonian Ice Sheet extended over the Andes from about 35°S to Tierra del Fuego
at 55°S. The western part appears to have been very active, with wet
basal conditions, while the eastern part was cold based. Cryogenic
features like ice wedges, patterned ground, pingos, rock glaciers, palsas, soil cryoturbation, solifluction
deposits developed in unglaciated extra-Andean Patagonia during the
Last Glaciation. However, not all these reported features have been
verified. The area west of Llanquihue Lake was ice-free during the LGM, and had sparsely distributed vegetation dominated by Nothofagus. Valdivian temperate rain forest was reduced to scattered remnants in the western side of the Andes.
Global
average temperatures show that the Little Ice Age was not a distinct
planet-wide time period, but the end of a long temperature decline that
preceded recent global warming.
The Little Ice Age (LIA) was a period of regional cooling that occurred after the Medieval Warm Period. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. The time period has been conventionally defined as extending from the 16th to the 19th centuries, but some experts prefer an alternative timespan from about 1300 to about 1850.
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. The Intergovernmental Panel on Climate ChangeThird Assessment Report
considered that 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.
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.
The IPCC Fourth Assessment Report (AR4) of 2007 discusses more recent research, giving particular attention to the Medieval Warm Period:
...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.
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, 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)
state that cold summers and ice growth began abruptly between 1275 and
1300, followed by "a substantial intensification" from 1430 to 1455.
In contrast, a climate reconstruction based on glacial length 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:
1560 to 1630 for beginning of worldwide glacial expansion known as the Grindelwald Fluctuation
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.
Geophysical and social impact by region
Europe
The Frozen Thames, 1677
The Baltic Sea
froze over twice, 1303 and 1306–07; years followed of "unseasonable
cold, storms and rains, and a rise in the level of the Caspian Sea.” 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. Canals and rivers in Great Britain and the Netherlands were frequently frozen deeply enough to support ice skating and winter festivals. The first River Thames frost fair was in 1608 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. 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 locked 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. Iceland also suffered failures of cereal crops and people moved away from a grain-based diet. 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.
Greenland was largely cut off by ice from 1410 to the 1720s.
Winter skating on the main canal of Pompenburg, Rotterdam in 1825, shortly before the minimum, by Bartholomeus Johannes van Hove
In his 1995 book the early 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." In Lisbon, Portugal, snowstorms were much more frequent than today; one winter in the 17th century produced eight snowstorms.
Many springs and summers were cold and wet but with great variability
between years and groups of years. This was particularly evident during
the 'Grindelwald Fluctuation' (1560-1630): a rapid cooling phase that
was associated with more erratic weather - including increased
storminess, unseasonal snow storms and droughts.
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).
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." 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.
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. According to the science historian James Burke,
the period inspired such novelties in everyday life as the widespread
use of buttons and button-holes, and knitting of custom-made
undergarments to better cover and insulate the body. Chimneys were
invented to replace open fires in the centre of communal halls, so
allowing houses with multiple rooms, separation of masters from
servants.
The Little Ice Age, by anthropologist 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." Historian Wolfgang Behringer has linked intensive witch-hunting episodes in Europe to agricultural failures during the Little Ice Age.
The Frigid Golden Age, by environmental historian Dagomar Degroot of Georgetown University,
by contrast, reveals that some societies thrived while others faltered
during the Little Ice Age. In particular, the Little Ice Age transformed
environments around the Dutch Republic — the precursor to the
present-day Netherlands — so that they were easier to exploit in
commerce and conflict. The Dutch were resilient, even adaptive, in the
face of weather that devastated neighboring countries. Merchants
exploited harvest failures, military commanders took advantage of
shifting wind patterns, and inventors developed technologies that helped
them profit from the cold. The 17th-century "Golden Age" of the
Republic therefore owed much to the flexibility of the Dutch in coping
with a changing climate.
Cultural responses
Historians
have argued that cultural responses to the consequences of the Little
Ice Age in Europe consisted of violent scapegoating.
The prolonged cold, dry periods brought drought upon many European
communities, resulting in poor crop growth, poor livestock survival, and
increased activity of pathogens and disease vectors.
Disease tends to intensify under the same conditions that unemployment
and economic difficulties arise: prolonged, cold, dry seasons. Both of
these outcomes – disease and unemployment – enhance each other,
generating a lethal positive feedback loop.
Although these communities had some contingency plans, such as better
crop mixes, emergency grain stocks, and international food trade, these
did not always prove effective.
Communities often lashed out via violent crimes, including robbery and
murder; sexual offense accusations increased as well, such as adultery, bestiality, and rape.
Europeans sought explanations for the famine, disease, and social
unrest that they were experiencing, and blamed the innocent. Evidence
from several studies indicate that increases in violent actions against
marginalized groups that were held responsible for the Little Ice Age
overlap with years of particularly cold, dry weather.
One example of the violent scapegoating occurring during the Little Ice Age was the resurgence of witchcraft trials,
as argued by Oster (2004) and Behringer (1999). Oster and Behringer
argue that this resurgence was brought upon by the climatic decline.
Prior to the Little Ice Age, "witchcraft" was considered an
insignificant crime and victims were rarely accused. But beginning in the 1380s, just as the Little Ice Age began, European populations began to link magic and weather-making.
The first systematic witch hunts began in the 1430s, and by the 1480s
it was widely believed that witches should be held accountable for poor
weather.
Witches were blamed for direct and indirect consequences of the Little
Ice Age: livestock epidemics, cows that gave too little milk, late
frosts, and unknown diseases. In general, as the temperature dropped, the number of witchcraft trials rose, and trials decreased when temperature increased. The peaks of witchcraft persecutions overlap with hunger crises that occurred in 1570 and 1580, the latter lasting a decade. These trials primarily targeted poor women, many of whom were widows.
Not everybody agreed that witches should be persecuted for
weather-making, but such arguments primarily focused not upon whether
witches existed, but upon whether witches had the capability to control
the weather. The Catholic Church in the Early Middle Ages
argued that witches could not control the weather because they were
mortals, not God, but by the mid-13th-century most populations agreed
with the idea that witches could control natural forces.
Historians have argued that Jewish populations were also blamed for climatic deterioration during the Little Ice Age. Christianity was the official religion of Western Europe, and within these populations there was a great degree of anti-Semitism.
There was no direct link made between Jews and weather conditions,
they were only blamed for indirect consequences such as disease. For example, outbreaks of the plague were often blamed on Jews; in Western European cities during the 1300s Jewish populations were murdered in an attempt to stop the spread of the plague. Rumors were spread that either Jews were poisoning wells themselves, or conspiring against Christians by telling those with leprosy to poison the wells. As a response to such violent scapegoating, Jewish communities sometimes converted to Christianity or migrated to the Ottoman Empire, Italy, or to territories of the Holy Roman Empire.
Some populations blamed the cold periods and the resulting famine
and disease during the Little Ice Age on general divine displeasure. Particular groups, however, took the brunt of the burden in attempts to cure it. For example, in Germany, regulations were imposed upon activities such as gambling and drinking, which disproportionately affected the lower class, and women were forbidden from showing their knees. Other regulations affected the wider population, such as prohibiting dancing and sexual activities, as well as moderating food and drink intake.
In Ireland, Catholics blamed the Reformation for the bad weather. The Annals of Loch Cé,
in its entry for the year 1588, describes a midsummer snowstorm: "a
wild apple was not larger than each stone of it," blaming it on the
presence of a "wicked, heretical, bishop in Oilfinn"; that is, the
Protestant Bishop of Elphin, John Lynch.
William James Burroughs analyses the depiction of winter in paintings, as does Hans Neuberger.
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".
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 an independent genre in art, the absence of other
winter scenes is not remarkable. On the other hand, snowy winter
landscapes and stormy seascapes in particular became artistic genres in
the Dutch Republic during the coldest and stormiest decades of the
Little Ice Age. At the time when the Little Ice Age was at its height,
Dutch observations and reconstructions of similar weather in the past
caused artists to consciously paint local manifestations of a cooler,
stormier climate. This was a break from European conventions as Dutch
paintings and realistic landscapes depicted scenes from everyday life,
which most modern scholars believe that were full of symbolic messages
and metaphors that would have been clear to contemporary customers.
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...".
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.
Neuberger analysed 12,000 paintings, held in American and
European museums and dated between 1400 and 1967, for cloudiness and
darkness. His 1970 publication shows an increase in such depictions that corresponds to the Little Ice Age, peaking between 1600 and 1649.
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. 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.
General Crisis of the Seventeenth Century
The General Crisis of the Seventeenth Century
in Europe was a period of inclement weather, crop failure, economic
hardship, extreme inter-group violence, and high mortality causally
linked to the Little Ice Age. Episodes of social instability track the
cooling with a time lapse of up to 15 years, and many developed into
armed conflicts, such as the Thirty Years' War (1618–1648).
It started as a war of succession to the Bohemian throne. Animosity
between Protestants and Catholics in the Holy Roman Empire (Germany
today) added fuel to the fire. Soon, it escalated to a huge conflict
involving all major European powers that devastated much of Germany. By
the war's end, some regions of the Holy Roman Empire saw their
population drop by as much as 70%.
But as global temperatures started to rise, the ecological stress faced
by Europeans also began to fade. Mortality rates dropped and the level
of violence fell, paving the way for a period known as Pax Britannica,
which witnessed the emergence of a variety of innovations in technology
(which enabled industrialization), medicine (which improved hygiene),
and social welfare (such as the world's first welfare programs in
Germany), making life even more comfortable.
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. Native Americans formed leagues in response to food shortages. 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. 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, Equilibrium Line
Altitude (the boundaries separating zones of net accumulation from those
of net ablation) were about 100 metres (330 ft) lower than they were in
1975. In Glacier National Park, the last episode of glacier advance came in the late 18th and the early 19th centuries. In 1879, famed naturalist John Muir found that Glacier Bay ice had retreated 48 miles. In Chesapeake Bay, Maryland, large temperature excursions were possibly related to changes in the strength of North Atlantic thermohaline circulation.
Because the Little Ice Age took place during the European
colonization of the Americas, it threw off a lot of the early
colonizers. The colonizers had expected the climate of North America to
be similar to the climate of Europe at similar latitudes, however the
climate of North America had hotter summers and colder winters than were
expected by the Europeans. This was an effect aggravated by the Little
Ice Age. This unpreparedness led to the collapse of many early European
settlements in North America.
When colonizers settled at Jamestown, in modern day Virginia,
historians agree it was one of the coldest time periods in the last 1000
years. Droughts were also a huge problem in North America during the
Little Ice Age, settlers arriving in Roanoke were in the largest drought
of the past 800 years. Tree ring studies done by the University of
Arkansas discovered that many colonists arrived at the beginning of a
seven year drought. These times of drought also decreased Native
American populations and led to conflict due to food scarcity. English
colonists at Roanoke forced Native Americans of Ossomocomuck to share
their depleted supplies with them. This led to warfare between the two
groups and Native American cities were destroyed. That cycle would
repeat itself many times at Jamestown. The combination of fighting and
cold weather led to the spread of diseases as well. The colder weather
brought on by the Little Ice Age helped the Malaria parasites brought by
Europeans in mosquitoes develop faster. This in turn led to many deaths
among Native American populations.
Cold winters made worse by the Little Ice Age were also an issue
in North America for colonists. Anecdotal evidence shows that people who
lived in North America suffered during this time. John Smith, who
established Jamestown, Virginia, wrote of a winter so cold, not even the
dogs could bear it. Another colonist, Francis Perkins, wrote in the
Winter of 1607 that it got so cold that the river at his fort froze due
to extremely cold weather. In 1642, Thomas Gorges wrote that between
1637 and 1645, colonists in Maine in Massachusetts had horrendous
weather conditions. June of 1637 was so hot that European newcomers were
dying in the heat and travelers had to travel at night to stay cool
enough. He also wrote that the winter of 1641-1642 was “piercingly
Intolerable” and that no Englishman nor Native American had ever seen
anything like it. Stating that the Massachusetts bay had frozen as far
as one could see and that horse carriages now roamed where ships used to
be. The summers of 1638 and 1639 were very short, cold, and wet
according to Gorges and this led to compounding food scarcity for a few
years. To make matters worse, creatures like caterpillars and pigeons
were feeding on crops and devastating harvests. Every year that Gorges
writes about, he notes unusual weather patterns that include high
precipitation, drought, and extreme cold or extreme heat. These all are
byproducts of the Little Ice Age.
While the Little Ice Age dropped global temperatures by an
estimated 0.1 degrees celsius, it increased global weirding all over
North America and the world. Summers got hotter and winters got colder.
Floods ensued and so did droughts. The Little Ice age didn’t just cool
places off a bit, it threw the climate into a weird unpredictable beast
that made living in North America significantly harder for all of its
inhabitants.
While nobody knows exactly what caused the Little Ice Age, one
theory from Warren Ruddimen states that approximately 50% of the Little
Ice Age originated in North America. This theory states that when
European diseases wiped out 95 percent of Native Americans, the
resulting effects led to global cooling. Approximately 55 million Native
Americans died due to those diseases and the theory is that as a result
of those deaths, 56 million hectares of land was abandoned and
reforested. Ruddimen believes that this caused more oxygen to enter the
air and then created a global cooling effect.
Many of the people living in North America had their own theories
as to why the weather was so poor. Colonist Ferdinando Gorges blamed
the cold weather on cold ocean winds. Humphrey Gilbert tried to explain
the extremely cold and foggy weather of Newfoundland by saying the earth
drew cold vapors from the ocean and drew them west. Dozens of others
had their own theories as to why North America was so much colder than
Europe. But because of their observations and hypotheses, we know a lot
about the Little Ice Age’s effect on North America.
Mesoamerica
An analysis of several climate proxies undertaken in Mexico's Yucatán 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.
Another study conducted in several sites in Mesoamerica such as
Los Tuxtlas and Lake Pompal in Veracruz, Mexico demonstrate a decrease
in human activity in the area during the Little Ice Age. This was proven
by studying charcoal fragments and the amount of maize pollen taken
from sedimentary samples using a nonrotatory piston corer. The samples
also showed volcanic activity which caused forest regeneration between
650 and 800 A.D. The instances of volcanic activity near Lake Pompal
indicate varying temperatures, not a continuous coldness, during the
Little Ice Age in Mesoamerica.
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.
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).
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:
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. 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). Scholars have argued that the fall of the Ming dynasty may have been partially caused by the droughts and famines caused by the Little Ice Age.
There are debates on the start date and time periods of Little
Ice Age's effects. Most scholars agree on categorizing the Little Ice
Age period into 3 distinct cold periods. 1458-1552, 1600-1720, and
1840-1880. According to data from the National Oceanic and Atmospheric Administration, the Eastern Monsoon
area of China was the earliest to experience the effects of Little Ice
Age from 1560-1709. In the Western region of China surrounding the Tibetan Plateau, the effects of Little Ice Age lagged behind the Eastern region, with significant cold periods between 1620 and 1749.
The temperature changes was unprecedented for the farming communities in China. According to Dr. Coching Chu's
1972 study, the Little Ice Age during the end of Ming Dynasty and start
of Qing Dynasty (1650-1700) was one of the coldest periods in recorded
Chinese history.
Many major droughts during summer months were recorded while
significant freezing events occurred in Winter months, hurting the food
supply significantly during Ming Dynasty.
This period of Little Ice Age would correspond to major historical events of the period. The Jurchen people resided in Northern China and formed a tributary state to the Ming government and Wanli Emperor.
From 1573 to 1620, the Manchurian land experienced famine experienced
extreme snowfall, which depleted agriculture production and decimated
the livestock population. Scholars argued that this was caused by the
temperature drops during Little Ice Age. Despite the lack of food
production, Wanli Emperor ordered the Jurchens to pay the same amount of
tribute each year. This led to anger and sowed seeds to the rebellion
against Ming China. In 1616, Jurchens established the Later Jin dynasty. Led by Hong Taiji and Nurhaci, the Later Jin dynasty moved South and achieved decisive victories in battles against the Ming military such as the Battle of Fushun in 1618.
Following the earlier defeats and the death of Wanli Emperor, Chongzhen Emperor
took the reign of China and continued the war effort. From 1632 to
1641, the Little Ice Age climate began to cause drastic climate changes
in Ming territories. For example, rainfall in Huabei region dropped by 11% ~ 47% compared to historical average. Meanwhile, the Shaanbei region along the Yellow River experienced six major floods that ruined cities such as Yan’an. The climate factored heavily in weakening the Imperial government’s control over China and accelerated the fall of Ming dynasty. In 1644, Li Zicheng led Later Jin forces into Beijing, overthrowing the Ming Dynasty, and establishing the Qing Dynasty.
During the early years of the Qing Dynasty, the little ice age
continued to have a significant impact on Chinese society. During the
rule of Kangxi Emperor
(1661-1722), majority of the Qing territories were still much colder
than the historical average. However, Kangxi Emperor pushed reforms and
managed to increase socioeconomic recovery from the natural disasters,
partially benefiting from the peacefulness of the early Qing dynasty.
This essentially marked the end of the Little Ice Age in China and led
to a more affluent era of Chinese monarchial history known as the High Qing era.
In the Himalayas,
the general assumption is that the cooling events in the Himalayas were
synchronous with cooling events in Europe during the Little Ice Age
based on the characteristics of moraines. However, applications of
Quaternary dating methods such as surface exposure dating
demonstrated that glacial maxima occurred between 1300 and 1600 CE,
which was slightly earlier than the recorded coldest period in Northern
Hemisphere. Many large Himalayan glacial debris remained close to their
limits from the Little Ice Age to present. The Himalayas also
experienced increase in snowfall at higher altitudes, resulting in a
southward shift in the Indian summer monsoon and an increase in
precipitation. Overall, the increase in winter precipitation may have
caused some glacial movements.
The influence of the Little Ice Age on African climate has been clearly demonstrated throughout the 14th-19th century.
Despite variances throughout the continent, a general trend of
declining temperatures led to an average cooling of 1 °C in the
continent.
In Ethiopia and North Africa, permanent snow was reported on mountain peaks at levels where it does not occur today. 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.
Several paleoclimatic studies of Southern Africa have suggested
significant changes in relative changes in climate and environmental
conditions. 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." 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."
This δ18O stalagmite record temperature reconstruction over a 350-year
period (1690-1740) suggests that South Africa may have been the coldest
region in Africa, cooling as much as 1.4 °C in the Summer.
Further, solar magnetic and Niño-Southern Oscillation cycle may have
been key drivers of climate variability in the subtropical region. Periglacial features in the eastern Lesotho Highlands might have been reactivated by the Little Ice Age.
Another archaeological reconstruction of South Africa reveals the
rise of the Great Zimbabwe people society due to ecological advantages
due to increased rainfall over other competitor societies’ such as the
Mupungubwe people.
Aside from temperature variability, data from equatorial East
Africa suggests impacts to the hydrologic cycle in the late 1700s.
Historical data reconstructions from ten major African lakes indicate an
episode of “drought and desiccation” occurred throughout East Africa.
This period showed drastic reductions in lake depth as these were
transformed into desiccated puddles. It is very likely that locals could
traverse lake Chad, among others, and bouts of “intense droughts were
ubiquitous”. These predictors indicate local societies were probably
launched into long migrations and warfare with neighboring tribes as
agriculture was rendered virtually useless by the arid soil conditions.
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 cooling. 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.
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.
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. Law Dome ice cores show lower levels of CO 2 mixing ratios from 1550 to 1800, which Etheridge and Steele conjecture are "probably as a result of colder global climate."
Sediment cores in Bransfield Basin, Antarctic Peninsula, have neoglacial indicators by diatom and sea-ice taxa variations during the Little Ice Age.
Stable isotope records from the Mount Erebus Saddle ice core site
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.
Australia and New Zealand
Due
to its location in the Southern Hemisphere, Australia did not
experience a regional cooling as in Europe or North America. Instead,
the Australian Little Ice Age was characterized by humid, rainy climates
followed by drying and aridification in the nineteenth century.
As studied by Tibby et al. (2018), lake records from Victoria, New South Wales, and Queensland
suggest that conditions in the east and south-east of Australia were
wet and unusually cool from the sixteenth to early nineteenth centuries.
This corresponds with the “peak” of the global Little Ice Age from
1594-1722. For example, the Swallow Lagoon rainfall record indicates
that from circa 1500-1850, there was significant and consistent
rainfall, sometimes exceeding 300 millimeters. These rainfalls significantly reduced after circa 1890. Similarly, the hydrological records of Lake Surprise’s salinity
levels reveal high humidity levels from circa 1440-1880, while an
increase in salinity between 1860-1880 point to a negative change to the
once-humid climate. The mid-nineteenth century marked a notable change to east Australia’s rainfall and humidity patterns.
As Tibby et al. (2018) note, in eastern Australia, these
paleoclimatic changes of the Little Ice Age in the late 1800s coincided
with the agricultural changes resulting from European colonization.
Following the 1788 establishment of British colonies on the Australian
continent—primarily concentrated in eastern regions and cities like
Sydney, and later Melbourne and Brisbane—the British introduced new
agricultural practices such as pastoralism.
Practices such as these required widespread deforestation and
vegetation clearance. Pastoralism and land clearing is captured in works
of art such as prominent landscape artist John Glover’s 1833 painting, Patterdale Landscape with Cattle.
Patterdale Landscape with Cattle
(1833) by John Glover depicts agricultural practices like pastoralism,
which contributed to the aridification of Australia's late Little Ice
Age.
Over the next century, such deforestation led to biodiversity loss, wind and water-based soil erosion, and soil salinity.
Furthermore, as argued by Gordan et al. (2003), such land and
vegetation clearance in Australia resulted in a 10% reduction in water
vapor transport to the atmosphere. This occurred in western Australia as
well, in which nineteenth century land-clearing resulted in reduced
rainfall over the region.
By 1850-1890, these human agricultural practices, concentrated in the
eastern region of Australia, most likely amplified the drying and
aridification that marked the end of the Little Ice Age.
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. Borehole reconstructions from Australia suggest that over the last 500 years, the 17th century was the coldest on the continent.
The borehole temperature reconstruction method further indicates that
the warming of Australia over the past five centuries is only around
half that of the warming experienced by the Northern Hemisphere, further
proving that Australia did not reach the same depths of cooling as the
continents to the north.
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 rainforest.
Evidence suggests, corroborated by tree ring proxy data, that the
glacier contributed to a -0.56 °C temperature anomaly over the course of
the Little Ice Age in New Zealand. 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 1725-1730.
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. Tropical Pacific coral records indicate the most frequent, intense El Niño-Southern Oscillation activity in the mid-seventeenth century. Foraminiferald 18 O records indicate that the Indo-Pacific Warm Pool
was warm and saline between 1000 and 1400 CE, with temperatures
approximating current conditions, but cooled from 1400 CE onwards,
reaching its lowest temperatures in 1700, consistent with the transition
from mid-Holocene warming to the Little Ice Age.
The nearby Southwestern Pacific, however, experienced warmer than
average conditions over the course of the Little Ice Age, thought to be
due to increased trade winds causing increased evaporation and higher
salinity in the region, and that the dramatic temperature differences
between the higher latitudes and the equator resulted in drier
conditions in the subtropics.
Independent multiproxy analyses of Raraku Lake(sedimentology,
mineralology, organic and inorganic geochemistry, etc) indicate that Easter Island
was subject to two phases of arid climate leading to drought, with the
first occurring between 500 and 1200 CE, and second occurring during the
Little Ice Age, from 1570 to 1720.
In between these two arid phases, the island enjoyed a humid period,
extending from 1200 CE to 1570, coinciding with the maximum development
of the Rapanui civilization.
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. 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.
A 2009 paper details cooler and wetter conditions in southeastern South
America between 1550 and 1800, citing evidence obtained via several
proxies and models. 18O records from three Andean ice cores show a cool period from 1600 to 1800.
Although only anecdotal evidence, in 1675 the Spanish Antonio de Vea expedition 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." As of 2001, the border of the glacier had significantly retreated as compared to the borders of 1675.
Possible causes
Scientists have tentatively identified seven possible causes of the Little Ice Age: orbital cycles; decreased solar activity; increased volcanic activity; altered ocean current flows; fluctuations in the human population in different parts of the world causing reforestation, or deforestation; and the inherent variability of global climate.
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. 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.
Solar activity
Solar
activity includes any sun disturbances like sunspots, solar flares, or
prominences, and scientists can track these solar activities in the past
by analyzing both the carbon 14 or Beryllium 10 isotopes in items like
tree rings. These solar activities, while not the most common or
noticeable causes for the little ice age, provide considerable evidence
that they played a part in the formation of the little ice age and the
increase in temperature after the period. During the time of the little
ice age which ranged from 1450 to 1850, there were very low recorded
levels of solar activity in the Spörer, Maunder, and Dalton minima.
The Spörer minimum was between 1450-1550 AD, when the little ice
age started. A study by Dmitri Mauquoy and others found that at the
beginning of Spörer, the percentage of change of carbon-14 skyrocketed
to about 10%.
This percentage stayed pretty common along with the entire duration of
the Spörer minimum, then around 1600 dropped rapidly before the Maunder
(1645-1715) where it rose again to a little under 10% change. To put
this into perspective, during standard periods the percentage change in
carbon-14 idles between -5 to 5 percent so this is a considerable
change. At the end of the little ice age which is also the Dalton
minimum (1790-1830), the percentage change is normal around -1%. These
changes in the Carbon-14 have a strong relationship with the temperature
because during these three periods as an increase in the carbon-14 does
correlate with cold temperatures during the little ice age.
In a study by Judith Lean, where she talked about the sun and
climate relationships and the cause and effect relationship that helped
form the little ice age. In her research, she found that during a
certain time period there a .13% solar irradiance increased the
temperature of the earth by .3 degree Celsius. This was around 1650-1790
and this information can help you formulate another idea of what
happened during the little ice age. When they calculated correlation
coefficients of the global temperature response to solar forcing over
three different periods it comes out to an average coefficient of .79.
This shows a strong relationship between the two components and helps
the point that the little ice age was considerably cold with very low
solar activity. Lean and your team also formulated an equation where
Change in T is equal to -168.802+Sx0.123426. This equals turns out to a
.16 increase in temperature for every .1% increase in solar irradiance.
To summarize, the entire length of the little ice age had a high
percentage change in carbon-14 and low social irradiance. Both of these
show a strong relationship to the cold temperatures during the time and
while the changes of solar activity actually have on the temperature of
the earth compared to things like greenhouse gases is very minimal.
Solar activity is still important to the whole picture of climate change
and does affect the earth even if it’s just less than one Celsius over a
few hundred years.
Solar activity events recorded in radiocarbon
The Maunder minimum in a 400-year history of sunspot numbers
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."
Throughout the Little Ice Age, the world experienced heightened volcanic activity. 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. The cold summers can be maintained by sea-ice/ocean feedbacks long after volcanic aerosols are removed.
Thermohaline circulation or Oceanic conveyor belt illustrated
Another possibility is that there was a slowing of thermohaline circulation.
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. There is some concern that a shutdown of thermohaline circulation could happen again as a result of the present warming period.
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.
The Black Death is estimated to have killed 30% to 60% of Europe's population. In total, the plague may have reduced the world population from an estimated 475 million to 350–375 million in the 14th century. It took 200 years for the world population to recover to its previous level. William Ruddiman
proposed that these large population reductions in Europe, East Asia,
and the Middle East caused a decrease in agricultural activity. Ruddiman
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 hypothesized that a reduced population in the Americas after European contact in the 16th century could have had a similar effect.
Other researchers 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.
Richard Nevle, Robert Dull and colleagues further suggested that not
only anthropogenic forest clearance played a role in reducing the amount
of carbon sequestered in Neotropical
forests, but that human-set fires played a central role in reducing
biomass in Amazonian and Central American forests before the arrival of
Europeans and the concomitant spread of diseases during the Columbian exchange. Dull and Nevle calculated that reforestation in the tropical biomes of the Americas alone from 1500 to 1650 accounted for net carbon sequestration of 2-5 Pg.
Brierley conjectured that European arrival in the Americas caused mass
deaths from epidemic disease, which caused much abandonment of farmland,
which caused much return of forest, which sequestered greater levels of
carbon dioxide.
A 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. The depopulation is linked to a drop in carbon dioxide levels observed at Law Dome, Antarctica. A 2011 study by the Carnegie Institution's Department of Global Ecology asserts that the Mongol invasions and conquests,
which lasted almost two centuries, contributed to global cooling by
depopulating vast regions and allowing for the return of carbon
absorbing forest over cultivated land.
Population increases at mid- to high-latitudes
During the Little Ice Age period, it is suggested that increased deforestation had a significant enough effect on albedo
(reflectiveness of the Earth) to decrease regional and global
temperatures. Changes in albedo were caused by widespread deforestation
at high latitudes. In turn this exposed more snow cover to and increased
reflectiveness of the Earth's surface as land was cleared for
agricultural use. This theory implies that over the course of the Little
Ice Age land was cleared to an extent that warranted deforestation as a
cause for climate change.
It has been proposed that Land Use Intensification theory could
explain this phenomenon. This theory was originally proposed by Ester
Boserup and suggests that agriculture is only advanced as the population
demands it.
Furthermore, there is evidence of rapid population and agricultural
expansion that could warrant some of the changes observed in the climate
during this period.
This theory is still under speculation for multiple reasons.
Primarily, the difficulty of recreating climate simulations outside of a
narrow set of land in these regions. This has led to an inability to
rely on data to explain sweeping changes, or account for the wide
variety of other sources of climate change globally. As an extension of
the first reason climate models including this time period have shown
increases and decreases in temperature globally.
That is, climate models have not shown deforestation as a singular
cause for climate change, nor as a reliable cause for global temperature
decrease.
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 internal
causes might be given the existence of other forces, as noted above,
whose magnitude may not be known. 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. Two studies have concluded that the demonstrated inherent variability is not great enough to account for the Little Ice Age. The severe winters of 1770 to 1772 in Europe, however, have been attributed to an anomaly in the North Atlantic oscillation.
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