Ice Age

Ice Age


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From 18,000 to 10,000 years ago, the last Ice Age (or Pleistocene Epoch) occurred. This led to glacial growth and cold climates.The formation of glaciers lowered sea levels and exposed land masses that had previously rested underwater. Ice sheets covered North America, Antarctica, and Europe, profoundly affecting the geography of these continents.North American Ice Age mammals included woolly mammoths, mastodons, and giant ground sloths that weighed more than three tons and stood almost 20 feet tall. The Ice Age menagerie also included the usual assortment of sabertooth cats, giant lions, and gargantuan bears.Despite such formidable conditions, Asiatic peoples gradually began to venture across the Bering Strait. Using such techniques as Radiocarbon Dating, scientists have gradually narrowed their views to two theories—the Clovis-First Model and the Early-Entry Model.


History of ICE

Despite U.S. Immigration and Customs Enforcement’s relatively young age, its functional history – encompassing the broad roles, responsibilities and federal statutes now carried out and enforced by the men and women of ICE – predates the modern birth of the agency by more than 200 years.

This informative video describes the conditions that gave rise to legislation authorizing the collection of import taxes and customs fees first envisioned by founding father Alexander Hamilton, the nation’s first secretary of the Treasury. It traces the remarkable development of the country throughout the 19th and 20th centuries, including the essential role of immigration and the evolving laws and regulations that governed it through a period of rapid growth and expansion.

In March 2003, the Homeland Security Act set into motion what would be the single-largest government reorganization since the creation of the Department of Defense. One of the agencies in the new Department of Homeland Security was the Bureau of Immigration and Customs Enforcement, now known as U.S. Immigration and Customs Enforcement, or ICE.

Congress granted ICE a unique combination of civil and criminal authorities to better protect national security and public safety in answer to the tragic events on 9/11. Leveraging those authorities, ICE's primary mission is to promote homeland security and public safety through the criminal and civil enforcement of federal laws governing border control, customs, trade and immigration.

ICE now has more than 20,000 law enforcement and support personnel in more than 400 offices in the United States and around the world. The agency has an annual budget of approximately $8 billion, primarily devoted to three operational directorates – Homeland Security Investigations (HSI), Enforcement and Removal Operations (ERO) and Office of the Principal Legal Advisor (OPLA). A fourth directorate – Management and Administration – supports the three operational branches to advance the ICE mission.


Why an ice age occurs every 100,000 years: Climate and feedback effects explained

Science has struggled to explain fully why an ice age occurs every 100,000 years. As researchers now demonstrate based on a computer simulation, not only do variations in insolation play a key role, but also the mutual influence of glaciated continents and climate.

Ice ages and warm periods have alternated fairly regularly in Earth's history: Earth's climate cools roughly every 100,000 years, with vast areas of North America, Europe and Asia being buried under thick ice sheets. Eventually, the pendulum swings back: it gets warmer and the ice masses melt. While geologists and climate physicists found solid evidence of this 100,000-year cycle in glacial moraines, marine sediments and arctic ice, until now they were unable to find a plausible explanation for it.

Using computer simulations, a Japanese, Swiss and American team including Heinz Blatter, an emeritus professor of physical climatology at ETH Zurich, has now managed to demonstrate that the ice-age/warm-period interchange depends heavily on the alternating influence of continental ice sheets and climate.

"If an entire continent is covered in a layer of ice that is 2,000 to 3,000 metres thick, the topography is completely different," says Blatter, explaining this feedback effect. "This and the different albedo of glacial ice compared to ice-free earth lead to considerable changes in the surface temperature and the air circulation in the atmosphere." Moreover, large-scale glaciation also alters the sea level and therefore the ocean currents, which also affects the climate.

Weak effect with a strong impact

As the scientists from Tokyo University, ETH Zurich and Columbia University demonstrated in their paper published in the journal Nature, these feedback effects between Earth and the climate occur on top of other known mechanisms. It has long been clear that the climate is greatly influenced by insolation on long-term time scales. Because Earth's rotation and its orbit around the sun periodically change slightly, the insolation also varies. If you examine this variation in detail, different overlapping cycles of around 20,000, 40,000 and 100,000 years are recognisable.

Given the fact that the 100,000-year insolation cycle is comparatively weak, scientists could not easily explain the prominent 100,000-year-cycle of the ice ages with this information alone. With the aid of the feedback effects, however, this is now possible.

Simulating the ice and climate

The researchers obtained their results from a comprehensive computer model, where they combined an ice-sheet simulation with an existing climate model, which enabled them to calculate the glaciation of the northern hemisphere for the last 400,000 years. The model not only takes the astronomical parameter values, ground topography and the physical flow properties of glacial ice into account but also especially the climate and feedback effects. "It's the first time that the glaciation of the entire northern hemisphere has been simulated with a climate model that includes all the major aspects," says Blatter.

Using the model, the researchers were also able to explain why ice ages always begin slowly and end relatively quickly. The ice-age ice masses accumulate over tens of thousands of years and recede within the space of a few thousand years. Now we know why: it is not only the surface temperature and precipitation that determine whether an ice sheet grows or shrinks. Due to the aforementioned feedback effects, its fate also depends on its size. "The larger the ice sheet, the colder the climate has to be to preserve it," says Blatter. In the case of smaller continental ice sheets that are still forming, periods with a warmer climate are less likely to melt them. It is a different story with a large ice sheet that stretches into lower geographic latitudes: a comparatively brief warm spell of a few thousand years can be enough to cause an ice sheet to melt and herald the end of an ice age.

The Milankovitch cycles

The explanation for the cyclical alternation of ice and warm periods stems from Serbian mathematician Milutin Milankovitch (1879-1958), who calculated the changes in Earth's orbit and the resulting insolation on Earth, thus becoming the first to describe that the cyclical changes in insolation are the result of an overlapping of a whole series of cycles: the tilt of Earth's axis fluctuates by around two degrees in a 41,000-year cycle. Moreover, Earth's axis gyrates in a cycle of 26,000 years, much like a spinning top. Finally, Earth's elliptical orbit around the sun changes in a cycle of around 100,000 years in two respects: on the one hand, it changes from a weaker elliptical (circular) form into a stronger one. On the other hand, the axis of this ellipsis turns in the plane of Earth's orbit. The spinning of Earth's axis and the elliptical rotation of the axes cause the day on which Earth is closest to the sun (perihelion) to migrate through the calendar year in a cycle of around 20,000 years: currently, it is at the beginning of January in around 10,000 years, however, it will be at the beginning of July.

Based on his calculations, in 1941 Milankovitch postulated that insolation in the summer characterises the ice and warm periods at sixty-five degrees north, a theory that was rejected by the science community during his lifetime. From the 1970s, however, it gradually became clearer that it essentially coincides with the climate archives in marine sediments and ice cores. Nowadays, Milankovitch's theory is widely accepted. "Milankovitch's idea that insolation determines the ice ages was right in principle," says Blatter. "However, science soon recognised that additional feedback effects in the climate system were necessary to explain ice ages. We are now able to name and identify these effects accurately."


Karoo

The Karoo Ice Age took place sometime between 360 and 260 million years ago and was initially recorded during the 1800’s. During the earliest part of this ice age, scientists believe that ice sheets grew from the southern region of both present-day Africa and present-day South America. Most theories of how this ice age was first created are primarily rooted in the knowledge that plants on land began to undergo significant evolutionary changes during this time. As these plants grew to immense sizes, they worked to reduce the levels of carbon dioxide and increase the levels of oxygen in the atmosphere. As these changes occurred, the summers were not warm enough to melt the ever-increasing ice sheets around the world.

The major effect of the Karoo Ice Age is often cited as the increased evolution of plants and animals during this time. As oxygen levels increased, animals began to experience changes to their metabolic systems. As a result, large vertebrate (both land roaming and flying species) were able to evolve.


Lags and leads

A lot of discussion online about the role of CO2 in ice ages – and associated arguments by those sceptical of climate change – has focused on the fact that CO2 lags behind temperatures during “deglaciation” at the end of ice ages.

In some ways, however, this is exactly what we would expect there were no humans burning fossil fuels during the end of the last ice age, so CO2 served more as a feedback to orbital changes rather than the climate forcing that it is today.

As Alley tells Carbon Brief:

“There is no way for the orbits to directly change CO2 – a bit more sun in the northern summer melts ice, but doesn’t immediately cause CO2 to change. So, CO2 must be a feedback. Because the amount of sunshine – and the amount of ice – have direct and immediate effects on temperature, there should be places on Earth in which any change in CO2 lags rather than leads the orbital cause and the temperature change.

This should not bother anyone. It often does, but it shouldn’t. The analogy I sometimes use is that, if I overspend my credit card and go into debt, interest will kick in and make my debt bigger. The interest lags debt – first I go into debt, then I pay interest, then I go further into debt. Pretty much everyone understands that this is a sensible, if unpleasant situation. When the orbits affect ice and temperature, this changes other things that, in turn, affect CO2, which, in turn, affects temperature some more – similarly sensible if the full story is understood.”

That said, understanding of the interrelationship between CO2 and temperature at the end of ice ages has advanced in recent years with better reconstructions of both past temperature and CO2 levels in ice cores from Antarctica.

While scientists used to think that CO2 lagged temperatures by 600 to 1,000 years during deglaciation, a number of recent studies have suggested that the lag is considerably smaller or even too small to detect. It is challenging to precisely match up CO2 records and temperature records from ice cores as there is a delay between new snowfall on an ice sheet (that traps the air bubbles) and then that snow slowly compressing into ice.

The figure below shows Antarctic temperatures (red line) and CO2 from recent proxy reconstructions (blue line) during the end of the last ice age – from 23,000BC to 8,500BC. While some periods might experience lags of a few hundred years, the relationship appears much more tightly coupled than was suggested by earlier reconstructions with larger uncertainties.

Antarctic reconstructed air temperature (red line) at Dome Fuji site Antarctica using isotope modeling from Uemura et al 2018 and Antarctic composite ice core atmospheric CO2 data (blue line) from Bereiter et al 2014. Data spans the period from 23,000BC to 8,500BC. Chart by Carbon Brief using Highcharts.

In addition, looking at temperature data from Antarctica alone also obscures a more nuanced global picture.

A 2013 paper by Dr Jeremy Shakun of Boston College and colleagues examined a network of 80 climate proxy records around the world during the end of the last ice age. They found that while CO2 generally lagged temperatures in the southern hemisphere – consistent with Antarctic reconstructions – the same was not true for the rest of the world.

Both the northern hemisphere and overall global temperatures actually lagged CO2 in other words, for the world as a whole, warming happened after atmospheric CO2 concentrations increased. The reasons for this are complex and are driven in part by changes in ocean currents as ice ages end.

The figure below shows the results from the Shakun et al 2013 paper for different regions of the world, along with the uncertainties in their estimate across different climate proxy locations and time periods during the end of the last ice age. The orange values are for the southern hemisphere, the blue values show the northern hemisphere and the grey values show global temperature estimates. The count on the y-axis represents how many of the 1,000 simulations – which examined the sensitivity of the results to uncertainties in CO2 age datingand proxy temperature estimates – show a lag of that size.

The lags between increases in atmospheric CO2 concentrations and temperature for the global (grey), northern hemisphere (NH blue) and southern hemisphere (SH red) proxy stacks over the period from 20,000 to 10,000 years before present. Figure 2b in Shakun et al 2013.

Specifically, Shakun and colleagues argue that changes in orbital cycles triggered initial melting of ice sheets in the northern hemisphere. This caused large amounts of freshwater to pour into the oceans as ice sheets melted, disrupting the Atlantic Meridional Overturning Circulation (AMOC), which, in turn, cooled the northern hemisphere and warmed the southern hemisphere.

This southern hemisphere warming caused ocean releases of CO2, which, in turn, warmed the entire planet. Shakun et al suggest that the vast majority of the global warming at the end of the last ice age occurred after CO2 increased, though this warming was driven by a combination of albedo (reflectivity) changes and the greenhouse effect.


What are the Major Ice Ages of the Earth's History?

The Earth has experienced at least five major ice ages in its 4.57 billion year history: the Huronian glaciation (2.4 to 2.1 billion years ago), the Sturtian/Marinoan glaciation (710 to 640 mya), the Andean-Saharan glaciation (460 to 430 mya), the Karoo Ice Age (350 to 260 mya) and the most recent Ice Age, which is currently ongoing (40 to 0 mya). The definition of an Ice Age is a long-term drop in global temperatures from the historical norm, accompanied by an extension of continental ice sheets. Each Ice Age is cyclical, generally on timescales of 44,000 and 110,000 years, during which glacial ice rhythmically extends and recedes.

The precise causes of historical Ice Ages are unknown, but likely emerged due to a variety of factors, including: positions of the continents, atmospheric composition (greenhouse gases), volcanic activity, the Earth's albedo (reflectivity), variations in the Earth's distance from the Sun (Milankovitch cycles), variations in solar output, and asteroid impacts. When the right variables are in place, an Ice Age begins, and once it gets started, positive feedback effects come into play. The strongest is simply that ice is more reflective than land or forest, so large areas covered in ice sheets reflect away the Sun's rays, causing further drops in temperature and increased glaciation.

Most of the time, the Earth is not in an Ice Age, and the average global temperature is about 22 °C (71 °F). Ice sheets are almost completely absent, found only at high altitudes (alpine glaciers). The poles are cold, but not covered in ice, and forests extend from pole to pole. Dinosaur fossils have been found at less that 10° latitude from the ancient South Pole. Only during about 15% of the Earth's history has there been an Ice Age.

The two most famous Ice Ages are probably the Sturtian/Marinoan glaciation and the most recent Ice Age. The Sturtian/Marinoan glaciation was so severe that evidence of continental glaciers have been found around the equator from this period. The average global temperature may have dropped lower than -30 °C (-22 °F), colder than present-day Antarctica. Some scientists even believe that the oceans froze from top to bottom during this time, resulting in a "Snowball Earth" scenario. Life would have survived in refugia such as deep-sea hydrothermal vents.

The most recent Ice Age is well-known because we humans have had our entire history within it. We think ice sheets covering Greenland and Antarctica are typical, even though they're not. More than about 10,000 years ago, there was a severe glacial period that covered the continents in glaciers as far south as Chicago and Paris. During this time period, humans had to mostly avoid colonizing Europe or northern Asia, as these areas were frozen solid. For this reason, human fossils predating the last glacial period are found only in Africa, the Middle East, China, Southeast Asia, Australia, and only small parts of Europe such as Spain and southern France.

Michael is a longtime InfoBloom contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

Michael is a longtime InfoBloom contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.


Contents

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. [11]

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. [13]

There is no consensus regarding the time when the Little Ice Age began, [14] [15] 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) [7] state that cold summers and ice growth began abruptly between 1275 and 1300, followed by "a substantial intensification" from 1430 to 1455. [7]

In contrast, a climate reconstruction based on glacial length [16] [17] 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 Atlanticpack ice began to grow cold period possibly triggered or enhanced by the massive eruption of Samalas volcano in 1257 [18]
  • 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
  • 1560 to 1630 for beginning of worldwide glacial expansion known as the Grindelwald Fluctuation [19]
  • 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. [20] [21] [22]

Europe Edit

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.” [23] 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. [24] Canals and rivers in Great Britain and the Netherlands were frequently frozen deeply enough to support ice skating and winter festivals. [24] 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. [25] 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. [26] Iceland also suffered failures of cereal crops and people moved away from a grain-based diet. [27] 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. [28]

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." [29] In Lisbon, Portugal, snowstorms were much more frequent than today one winter in the 17th century produced eight snowstorms. [30] 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. [31] 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). [32] 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." [33] 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. [29]

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. [34] 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. [35]

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." [36] Historian Wolfgang Behringer has linked intensive witch-hunting episodes in Europe to agricultural failures during the Little Ice Age. [37]

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. [38]

Cultural responses Edit

Historians have argued that cultural responses to the consequences of the Little Ice Age in Europe consisted of violent scapegoating. [39] [40] [41] [37] [42] 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. [43] 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. [43] 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. [39] Communities often lashed out via violent crimes, including robbery and murder sexual offense accusations increased as well, such as adultery, bestiality, and rape. [40] 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. [41] [37] [39]

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. [37] But beginning in the 1380s, just as the Little Ice Age began, European populations began to link magic and weather-making. [37] 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. [37] 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. [40] In general, as the temperature dropped, the number of witchcraft trials rose, and trials decreased when temperature increased. [39] [37] The peaks of witchcraft persecutions overlap with hunger crises that occurred in 1570 and 1580, the latter lasting a decade. [37] 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. [37] [39] 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. [39]

Historians have argued that Jewish populations were also blamed for climatic deterioration during the Little Ice Age. [40] [42] Christianity was the official religion of Western Europe, and within these populations there was a great degree of anti-Semitism. [40] There was no direct link made between Jews and weather conditions, they were only blamed for indirect consequences such as disease. [40] 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. [40] Rumors were spread that either Jews were poisoning wells themselves, or conspiring against Christians by telling those with leprosy to poison the wells. [40] 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. [40]

Some populations blamed the cold periods and the resulting famine and disease during the Little Ice Age on general divine displeasure. [41] Particular groups, however, took the brunt of the burden in attempts to cure it. [41] 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. [41] Other regulations affected the wider population, such as prohibiting dancing and sexual activities, as well as moderating food and drink intake. [41]

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. [44] [45]

Depictions of winter in European painting Edit

William James Burroughs analyses the depiction of winter in paintings, as does Hans Neuberger. [46] 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". [47] 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. [48]

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. ". [47] [49]

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. [47]

Neuberger analysed 12,000 paintings, held in American and European museums and dated between 1400 and 1967, for cloudiness and darkness. [46] His 1970 publication shows an increase in such depictions that corresponds to the Little Ice Age, [46] peaking between 1600 and 1649. [50]

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. [51] 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. [52]

General Crisis of the Seventeenth Century Edit

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). [53] 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%. [54] 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. [55]

North America Edit

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. [29] Native Americans formed leagues in response to food shortages. [28] 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. [56] 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. [57] In Glacier National Park, the last episode of glacier advance came in the late 18th and the early 19th centuries. [58] In 1879, famed naturalist John Muir found that Glacier Bay ice had retreated 48 miles. [59] In Chesapeake Bay, Maryland, large temperature excursions were possibly related to changes in the strength of North Atlantic thermohaline circulation. [60]

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. [61]

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. [62]

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. [63]

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. [64]

Mesoamerica Edit

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. [65]

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. [66]

Atlantic Ocean Edit

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. [67] 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). [68]

Asia Edit

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: [4]

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. [69] 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). [70] 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. [71]

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. [72] 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. [73]

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. [74] 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. [75]

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. [76]

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. [77]

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. [78]

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. [79]

Africa Edit

The influence of the Little Ice Age on African climate has been clearly demonstrated throughout the 14th-19th century. [80] Despite variances throughout the continent, a general trend of declining temperatures led to an average cooling of 1 °C in the continent. [81]

In Ethiopia and North Africa, permanent snow was reported on mountain peaks at levels where it does not occur today. [69] 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. [69]

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." [82] 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." [83] 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. [84] 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. [85] 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. [86]

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. [87] 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.

Antarctica Edit

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. [88] 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. [89] 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. [90] 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. [91] 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." [92]

Sediment cores in Bransfield Basin, Antarctic Peninsula, have neoglacial indicators by diatom and sea-ice taxa variations during the Little Ice Age. [93] 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. [94]

Australia and New Zealand Edit

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. [95]

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. [95] 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. [96] 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. [95] 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.

Over the next century, such deforestation led to biodiversity loss, wind and water-based soil erosion, and soil salinity. [97] 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. [98] 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. [99] Borehole reconstructions from Australia suggest that over the last 500 years, the 17th century was the coldest on the continent. [100] 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. [101] 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. [102] 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. [103]

Pacific Islands Edit

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. [104] Tropical Pacific coral records indicate the most frequent, intense El Niño-Southern Oscillation activity in the mid-seventeenth century. [105] 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. [106] 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. [107] 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. [108] 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. [109]

South America Edit

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. [110] [111] 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. [112] A 2009 paper details cooler and wetter conditions in southeastern South America between 1550 and 1800, citing evidence obtained via several proxies and models. [113] 18 O records from three Andean ice cores show a cool period from 1600 to 1800. [114]

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." [115] As of 2001, the border of the glacier had significantly retreated as compared to the borders of 1675. [115]

Scientists have tentatively identified seven possible causes of the Little Ice Age: orbital cycles decreased solar activity increased volcanic activity altered ocean current flows [116] fluctuations in the human population in different parts of the world causing reforestation, or deforestation and the inherent variability of global climate.

Orbital cycles Edit

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. [117] 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. [117]

Solar activity Edit

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%. [ citation needed ] 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. [118]

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. [119]

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.

Volcanic activity Edit

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." [7]

Throughout the Little Ice Age, the world experienced heightened volcanic activity. [120] 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. [7] 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). [24] 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, [121] when frost and snow were reported in June and July in both New England and Northern Europe.

Ocean circulation Edit

Another possibility is that there was a slowing of thermohaline circulation. [57] [116] [122] [123] 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. [36] [124] [125] There is some concern that a shutdown of thermohaline circulation could happen again as a result of the present warming period. [126] [127]

Decreased human populations Edit

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. [128] In total, the plague may have reduced the world population from an estimated 475 million to 350–375 million in the 14th century. [129] It took 200 years for the world population to recover to its previous level. [130] 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. [131] [132] 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. [133] [134] 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. [135] [136] [137] 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. [136] 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. [12] 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. [138] The depopulation is linked to a drop in carbon dioxide levels observed at Law Dome, Antarctica. [133] 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. [139] [140]

Population increases at mid- to high-latitudes Edit

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. [141]

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. [142] 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. [143] 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 Edit

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. [144] Two studies have concluded that the demonstrated inherent variability is not great enough to account for the Little Ice Age. [144] [145] The severe winters of 1770 to 1772 in Europe, however, have been attributed to an anomaly in the North Atlantic oscillation. [146]


What Causes Ice Ages?

Earth goes about its business in a pretty regular way, spinning on its axis and looping around and around the sun. But there are some variations in the pattern. Over time, the tilt of the Earth, its orbit, and its wobble change a bit. These very minor (and regular) adjustments in the angle of the Earth relative to the sun affects the amount of solar radiation, or insolation, that reaches Earth. “Even though the tilt changes by only one degree or two, that’s enough to change the angle at which the sun's energy hits,” explains Elizabeth Thomas, a paleoclimatologist at the University at Buffalo. And of course, less energy from the sun means colder temperatures.

During the colder winters, snow falls on the land. If the summers are cool enough, the snow lasts until the next winter. Eventually there will be more and more snow building up, and that will pack down into a glacier. The glacier will continue to grow until it’s a continent-sized ice sheet. Meanwhile, the Earth’s orbit changes enough from time to time to cause the ice sheets to retreat, a little or a lot, creating interglacial periods.


Ice Ages & Past Climates

Earth’s climate has undergone many changes over the course of geologic history, but the past one million years or so have been among the most dynamic. During that time, the planet has experienced repeated cycles of glacial (cold) and interglacial (warm) periods lasting about 80,000 years on average.

These were most likely driven by regular changes in Earth’s orbit and rotation known as the Milankovich Cycles that govern the seasonal timing and intensity of solar energy entering the atmosphere. Other factors that may have contributed to the formation and cessation of ice ages are the amount of greenhouse gases (mainly carbon dioxide, methane, and water vapor) in Earth’s atmosphere, the extent of sea and land-based ice across the northern hemisphere, and shifts in patterns of wind and ocean currents.

During ice ages, the most characteristic change to the planet has been the formation and spread large ice sheets and glaciers across much the Northern Hemisphere. The sheer weight of the ice at the height of the last ice age depressed Earth’s crust to such an extent that many areas are still slowly but noticeably rebounding to this day, 18,000 years after the retreat of the glaciers.

The formation of the ice also removed so much water from the global ocean that sea levels during ice ages were notably lower than interglacial periods such as the present day—as much as 400 feet lower during some periods. The movement of the ice across the surface of the planet also scoured deep valleys, created extensive chains of hills known as moraines, and created extensive lakes, including the Great Lakes.

Understanding the onset and termination of glacial and interglacial cycles is a key part of efforts to understand how Earth’s climate system works and how it responds to changes and disruptions. The steady rise of greenhouse gases in Earth’s atmosphere caused by human activity is a primary cause for concern because of its ability to potentially bring about additional, larger changes.

Scientists are also looking for ways to match changes in Earth’s past environmental conditions with the timing and speed of changes to past climate in order to understand how sensitive the climate system is to disruption and what chain of events might contribute to forcing large-scale changes or, conversely, to helping moderate changes.


How the Little Ice Age Changed History

It is easy to forget just how variable the climate of the earth has been, across the geologic time scale. That is partly because the extent of that variability is so difficult to imagine. A world entirely covered in ice, from pole to pole—the so-called snowball earth—is something we find it hard to get our heads around, even though the longest and oldest period of total or near-total glaciation, the Huronian glaciation, lasted for three hundred million years. A world without ice is also hard to visualize, though it is by comparison a much more recent phenomenon: perhaps only thirty-four million years ago, crocodiles swam in a freshwater lake we know as the North Pole, and palm trees grew in Antarctica. The reality is that our planet oscillates between phases with no ice, phases with all ice, and phases in the middle. The middle is where we happen to be right now—a fact that is responsible for our faulty perception of the earth’s climate as accommodating and stable.

In the roughly five thousand years of recorded human history, there has been one period in which we have had a real taste of our climate’s potential for moodiness, beginning around the start of the fourteenth century and lasting for hundreds of years. During this epoch, often known as the Little Ice Age, temperatures dropped by as much as two degrees Celsius, or 3.6 degrees Fahrenheit. Compared with the extremes of snowball earth, that might not sound like much, but for people who lived through it the change was intensely dramatic. This was also the period between the end of the Middle Ages and the birth of the modern world. In a new book, “Nature’s Mutiny: How the Little Ice Age of the Long Seventeenth Century Transformed the West and Shaped the Present” (Liveright), the German-born, Vienna-based historian Philipp Blom argues that this is no coincidence—that there is a complex relationship between the social, economic, and intellectual disruption caused by the changed climate and the emerging era of markets, exploration, and intellectual freedom which constituted the beginning of the Enlightenment.

The Little Ice Age is an example of how we so often find complete consensus around every aspect of climate change. Just kidding. We know for sure that the earth became cooler: the evidence can be found through a variety of techniques for assessing historical temperatures, such as the study of ice cores and tree rings. There are also extensive written accounts of the cold in the form of letters and diaries, sermons, the records of wine growers, and so on. The cooling happened in phases, with an initial drop beginning around 1300, and a sharper and more abrupt onset of cold starting in 1570 and lasting for about a hundred and ten years. It is the latter period that provides the focus for Blom’s book. Agreement about the fact that the cooling occurred, however, is not matched by an equivalent consensus about why.

There is evidence that the cooling may have been caused by a decrease in sunspot activity, and therefore in solar radiation, or by an increase in volcanic eruptions. (Though the seismic causality might be the other way around, as Blom explains: changes in oceanic currents could have altered pressures on the continental shelves, which “may in turn have contributed to the increase in volcanic eruptions and earthquakes reported during this period.”) There is evidence, too, that the cooling was to at least some extent man-made. So many people died of disease in the Americas after the arrival of Columbus—fifty-six million, according to the latest research in Quaternary Science Reviews—and so many areas of cleared, cultivated land were abandoned, and thus allowed to reforest, that CO2 levels were measurably reduced and the planet’s temperature lowered. Blom does the sensible thing and dodges a final verdict on what caused all those vicious winters.

“How can you look into those eyes and make her sleep outside?”

Whatever the cause, the effects were pronounced. Although Blom’s focus is Europe, the most densely settled northerly area of the planet, he makes it clear that the effects of the Little Ice Age were global in scale. In China, then as now the most populous country in the world, the Ming dynasty fell in 1644, undermined by, among other things, erratic harvests. In Europe, rivers and lakes and harbors froze, leading to phenomena such as the “frost fairs” on the River Thames—fairgrounds that spread across the river’s London tideway, which went from being a freakish rarity to a semi-regular event. (Virginia Woolf set a scene in “Orlando” at one.) Birds iced up and fell from the sky men and women died of hypothermia the King of France’s beard froze solid while he slept. Some of the central events of English history turn out to have been linked to the Little Ice Age: in 1588, the Spanish Armada was destroyed by an unprecedented Arctic hurricane, and a factor in the Great Fire of London, in 1666, was the ultra-dry summer that succeeded the previous, bitter winter. Fingerprints of the cold period can be found in surprising places. Why do the most admired violins in the history of music, made by Stradivarius and Guarneri, come from the middle of the Little Ice Age? Blom cites research arguing that trees took longer to mature in the cold, which resulted in a denser wood, with “better sound qualities and more intense resonance.”

The most consequential effect of the frigid weather, Blom argues convincingly, was to disrupt the harvest, especially the grain harvest. It led to a fundamental shift in the social order across Europe, and beyond. The Little Ice Age amounted to “a long-term, continent-wide agricultural crisis,” as Blom writes. Grain harvests did not return to their previous levels for a hundred and eighty years. That affected everything about how society worked. Before this moment in European history, society was largely organized along feudal lines. The bulk of the population consisted of peasants, living on land owned by a lordly overclass. Town life, meanwhile, was dominated by restrictive guilds, and, in Blom’s description, it “valued social capital—class and family standing, trustworthiness, competition—but did not encourage anyone to reach beyond his station.” This settled order, which had lasted for centuries, was overturned. At first, there were panics and uprisings, food riots and rebellions, and a spike in witch trials—because, in a pre-scientific world, the idea that witches were responsible for failing harvests made as much sense as any other explanation.

Over time, however, larger structural shifts emerged. In the basic bargain of feudal life, a peasant kept one part of his harvest for himself, put one part back into the ground for the next year’s harvest, and gave the last part to his feudal lord. When peasants had no surplus grain, this system collapsed. If local crops were failing, trading at a distance, to bring goods from farther afield, was critical. Money, and the ability to buy and sell with cash or its equivalent, took on a larger role. Cities with a culture of trade especially benefitted from this shift. The preëminent example in “Nature’s Mutiny” is Amsterdam, which went from being a sleepy backwater of the Habsburg Empire to a thriving, economically dynamic center of rapidly expanding commercial networks, with a population that grew tenfold in just over a century.

Here we see the birth of the idea that markets, and the rules of markets, have supremacy in human affairs we also see how the new dispensation offered opportunities to a new breed of ambitious, ruthless, commercially minded man. Amsterdam was the home of one of the world’s first big exploitative overseas businesses, the Dutch East India Company (Vereenigde Oostindische Compagnie), or V.O.C. Blom tells the story of Jan Pieterszoon Coen, a V.O.C. official who burned down the Indonesian city of Jakarta and then led an expedition to punish traders on nearby islands who had broken the V.O.C. monopoly on nutmeg by selling to English and Portuguese merchants. Coen executed the merchants, killed fifteen thousand islanders, and sold the survivors into slavery. His feats in Indonesia would not have been possible, he told the company directors, “had not the Almighty fought on our side and blessed us.” For true believers, God and the rules of markets were becoming inseparable—a conflation that, Blom argues, was taken to justify the exploitation of both people and natural resources and would lead us to our contemporary moment of environmental crisis.

This is a sweeping story, embracing developments in economics and science, philosophy and exploration, religion and politics. Blom delivers much of his argument through compressed, beautifully clear life sketches of prominent men. We meet the philosopher (and retired soldier) René Descartes, the mage and proto-scientist John Dee, the essayist Michel Montaigne, the Jesuit polymath Athanasius Kircher, the excommunicated Jewish philosopher Baruch de Spinoza, the encyclopedist Pierre Bayle, and the great painter Rembrandt van Rijn, who both depicted and embodied the new human landscape of Dutch economic transformation.

In the course of “Nature’s Mutiny,” therefore, we travel a considerable distance from the subject of unusually cold weather. Too far, a reader might think, for Blom’s argument to be regarded as a case conclusively settled. But it wouldn’t be fair to “Nature’s Mutiny” to see the issue of proof so starkly. It is a book about a new economic system and the philosophical and cultural trends that accompanied it climate is central to the story that it tells, but the connections don’t aim for the solidity of algebraic logic. Rather, Blom is seeking to give us a larger picture that is relevant to the current moment. His book is about links and associations rather than about definitive proof it is about networks and shifts in intellectual mood, about correlations as much as causes. Despite that, Blom’s hypothesis is forceful, and has the potential to be both frightening and, if you hold it up to the light at just the right angle, a little optimistic. The idea can be put like this: climate change changes everything. ♦


Post Ice Age History

By 13,000 years ago, retreating ice revealed a scoured landscape of rounded hills and deep, U-shaped valleys and fjords. The precipitous peaks in this landscape were taller than the glacier was deep and so the glacial ice flowed around them. Unlike the lower peaks rounded and eroded by the glacier's force, these taller peaks remained jagged in appearance. The land was swept clean of valley sediments.

During the Wisconsin Ice Age, the weight of the ice on the earth’s crust was so great it pushed the crust down several hundred feet into the semi-liquid mantle. As the ice melted and the weight relieved, the earth’s crust began to spring back in a phenomenon known as “isostatic rebound.”

A few species of plants and animals enduring frigid arctic conditions near the glaciers may have survived to recolonize the land as the ice retreated. For the most part, however, life had to return from afar. Plants and animals overcame physical barriers such as saltwater, mountains and the remaining ice fields to get here. It's believed mountain goats may have been the first land mammals to find their way into the bay by crossing the mountains from the Lynn Canal area.

All of Glacier Bay's new immigrants had to cope with ecological barriers such as cold temperatures, lack of water, inadequate food sources and poor soils. Living conditions in Glacier Bay continued to be harsh. Studies of pollen buried in lake sediments and bogs have provided a detailed record of the recovery of communities after the ice. For several thousand years, tundra and pine-alder scrub dominated the post-glacial landscape. By 9,000 years ago, spruce-hemlock forests had developed, suggesting that by then the climate was approaching the present wet and mild conditions. By 5,000 years ago, peat lands were forming along Icy Strait and glaciers were beginning to advance again into upper Glacier Bay.

All the while, the physical landscape was undergoing changes of its own. Post-Great Ice Age isostatic rebound, mountain-building and accumulation of sediments washed down from the uplands began extending valley bottoms, filling in fjords and connecting islands to the mainland. Where these sediments met the sea, waves and currents worked them into beaches and estuaries. It’s speculated that at this time it was getting easier for land animals to get into the area and survive here. Breeding sites for colonial birds and marine mammals probably became fewer. Thus, as forest species like deer and black bear became better established, puffins and sea lions diminished. Salmon began to find their way to the developing streams.

As of now, this story is very sketchily known, but deposits of animal bones in recently-discovered caves in southern Southeast Alaska have begun to provide a more detailed record of mammal and bird reoccupation of the land. This cave topography extends into the Glacier Bay area, but it remains almost totally unexplored at present.


Watch the video: MCND ICE AGE MV