c. 2600000 BCE - c. 12000 BCE
The Pleistocene epoch, ranging from c. 2,6 million years ago until c. 12,000 years ago. It is characterised by repeated cycles of glacials and interglacials.
c. 26500 BCE - c. 19000 BCE
Last Glacial Maximum - the time during which the ice sheets reached peak growth within the most recent glacial.
c. 11700 BCE
End of the most recent glacial episode within the current Quaternary Ice Age.
First description of an Ice Age by Louis Agassiz.
What Was the Little Ice Age?
When most people think of ice ages, or “glacial ages,” they often envision cavemen, woolly mammoths, and vast plains of ice—such as those that occurred during the Pleistocene (about 2.6 million to 11,700 years ago) or the late Carboniferous and early Permian periods (about 300 million years ago). During these parts of Earth’s past, mile-high ice sheets covered large parts of continents, and their presence affected the weather and climate throughout the world. In fact, during one prehistoric period, the Cryogenian (which spanned roughly 720 million to 635 million years ago), there is evidence to support the notion that the whole planet was either locked in ice or possibly covered in ice with only a thin film of slush near the Equator. Think present-day Europa or Enceladus. What about the relatively recent “Little Ice Age”? Was it a true glacial age? Yes and no.
Of course, the severity of the Little Ice Age, which lasted from the early 14th century through the mid-19th century, was not a deep freeze like the long ice ages of the ancient past. After all, human civilization thrived and expanded during the Little Ice Age, as several civilizations sent ships to explore, colonize, and exploit new lands.
Nevertheless, images depicted in paintings, data from ships’ logs and scientific reports of the time, and other historical writings have shown that many parts of Europe experienced cooler than normal conditions during this time. Since the people of the time did not keep accurate weather records (to the extent that we do now), present-day scientists looking to understand the climate of the Little Ice Age have relied on proxy records—that is, indirect sources of climatic information (such as coral growth, cores of lake sediments, ice cores, and annual rings in trees)—to better understand the regional and global climates of the time. Proxy records showed that mountain glaciers grew during the Little Ice Age at several locations—including the European Alps, New Zealand, Alaska, and the southern Andes—and mean annual temperatures across the Northern Hemisphere fell by 0.6 °C (1.1 °F) relative to the average temperature between 1000 and 2000 CE. Proxy records collected from western Greenland, Scandinavia, the British Isles, and western North America point to several cool episodes, lasting several decades each, when temperatures dropped 1 to 2 °C (1.8 to 3.6 °F) below the thousand-year averages for those areas. These regional temperature declines, however, rarely occurred at the same time. In addition, temperatures of other regions (such as in eastern China and in the Andes Mountains of South America) were fairly stable, while still other regions (such as southern Europe, North America’s Mississippi Valley, and parts of Africa and Asia) became drier, with droughts lasting several years at a time.
So what caused the Little Ice Age? It was likely a combination of factors that included long periods of low sunspot activity (which reduced the amount of solar energy that reached Earth), the effects of explosive volcanic eruptions, and drastic changes in the North Atlantic Oscillation (the irregular fluctuation of atmospheric pressure over the North Atlantic Ocean).
Although the Little Ice Age was not a formal ice age, one could certainly argue that it was a significant phenomenon associated with a variety of climatic changes affecting many disparate parts of the world. Earth’s climate changes often through time, so this cool 450-year slice of Earth’s history was not the only one of its kind. There have been warm intervals too. One example is the recent warming (caused by a mix of natural factors and human activities) that began after the Little Ice Age ended and continues to this day. Another example is the highly controversial medieval warm period—another time of relative warmth—which, according to some scientists, lasted from 900 to 1300 CE. Unlike the Little Ice Age and the recent period of warming, however, there is a great deal of disagreement with respect to the reach of the medieval warm period or whether it even happened at all.
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."
Why do glacial periods end abruptly?
Notice the asymmetric shape of the Antarctic temperature record (black line), with abrupt warmings shown in yellow preceding more gradual coolings (Kawamura et al. 2007 Jouzel et al. 2007). Warming at the end of glacial periods tends to happen more abruptly than the increase in solar insolation. Several positive feedbacks are responsible for this. One is the ice-albedo feedback. A second feedback involves atmospheric CO2. Direct measurement of past CO2 trapped in ice core bubbles shows that the amount of atmospheric CO2 decreased during glacial periods (Kawamura et al. 2007 Siegenthaler et al. 2005 Bereiter et al. 2015), in part because the deep ocean stored more CO2 due to changes in either ocean mixing or biological activity. Lower CO2 levels weakened the atmosphere's greenhouse effect and helped to maintain lower temperatures. Warming at the end of the glacial periods liberated CO2 from the ocean, which strengthened the atmosphere's greenhouse effect and contributed to further warming.
The prehistoric reptiles known as dinosaurs arose during the Middle to Late Triassic Period of the Mesozoic Era, some 230 million years ago. They were members of a subclass of reptiles called the archosaurs (“ruling reptiles”), a group that also includes birds and crocodiles.
Scientists first began studying dinosaurs during the 1820s, when they discovered the bones of a large land reptile they dubbed a Megalosaurus (𠇋ig lizard”) buried in the English countryside. In 1842, Sir Richard Owen, Britain’s leading paleontologist, first coined the term 𠇍inosaur.” Owen had examined bones from three different creatures–Megalosaurus, Iguanadon (“iguana tooth”) and Hylaeosaurus (“woodland lizard”). Each of them lived on land, was larger than any living reptile, walked with their legs directly beneath their bodies instead of out to the sides and had three more vertebrae in their hips than other known reptiles. Using this information, Owen determined that the three formed a special group of reptiles, which he named Dinosauria. The word comes from the ancient Greek word deinos (“terrible”) and sauros (“lizard” or “reptile”).
Did you know? Despite the fact that dinosaurs no longer walk the Earth as they did during the Mesozoic Era, unmistakable traces of these enormous reptiles can be identified in their modern-day descendants: birds.
Since then, dinosaur fossils have been found all over the world and studied by paleontologists to find out more about the many different types of these creatures that existed. Scientists have traditionally divided the dinosaur group into two orders: the 𠇋ird-hipped” Ornithischia and the “lizard-hipped” Saurischia. From there, dinosaurs have been broken down into numerous genera (e.g. Tyrannosaurus or Triceratops) and each genus into one or more species. Some dinosaurs were bipedal, which means they walked on two legs. Some walked on four legs (quadrupedal), and some were able to switch between these two walking styles. Some dinosaurs were covered with a type of body armor, and some probably had feathers, like their modern bird relatives. Some moved quickly, while others were lumbering and slow. Most dinosaurs were herbivores, or plant-eaters, but some were carnivorous and hunted or scavenged other dinosaurs in order to survive.
At the time the dinosaurs arose, all of the Earth’s continents were connected together in one land mass, now known as Pangaea, and surrounded by one enormous ocean. Pangaea began to break apart into separate continents during the Early Jurassic Period (around 200 million years ago), and dinosaurs would have seen great changes in the world in which they lived over the course of their existence. Dinosaurs mysteriously disappeared at the end of the Cretaceous Period, around 65 million years ago. Many other types of animals, as well as many species of plants, died out around the same time, and numerous competing theories exist as to what caused this mass extinction. In addition to the great volcanic or tectonic activity that was occurring around that time, scientists have also discovered that a giant asteroid hit Earth about 65.5 million years ago, landing with the force of 180 trillion tons of TNT and spreading an enormous amount of ash all over the Earth’s surface. Deprived of water and sunlight, plants and algae would have died, killing off the planet’s herbivores after a period of surviving on the carcasses of these herbivores, carnivores would have died out as well.
Despite the fact that dinosaurs no longer walk the Earth as they did during the Mesozoic Era, unmistakable traces of these enormous reptiles can be identified in their modern-day descendants: birds. Dinosaurs also live on in the study of paleontology, and new information about them is constantly being uncovered. Finally, judging from their frequent appearances in the movies and on television, dinosaurs have a firm hold in the popular imagination, one realm in which they show no danger of becoming extinct.
Wrong Again: 50 Years of Failed Eco-pocalyptic Predictions
Thanks go to Tony Heller, who first collected many of these news clips and posted them on RealClimateScience.
Modern doomsayers have been predicting climate and environmental disaster since the 1960s. They continue to do so today.
None of the apocalyptic predictions with due dates as of today have come true.
What follows is a collection of notably wild predictions from notable people in government and science.
More than merely spotlighting the failed predictions, this collection shows that the makers of failed apocalyptic predictions often are individuals holding respected positions in government and science.
While such predictions have been and continue to be enthusiastically reported by a media eager for sensational headlines, the failures are typically not revisited.
1967: ‘Dire famine by 1975.’
1969: ‘Everyone will disappear in a cloud of blue steam by 1989.’
1970: Ice age by 2000
1970: ‘America subject to water rationing by 1974 and food rationing by 1980.’
1971: ‘New Ice Age Coming’
1972: New ice age by 2070
1974: ‘New Ice Age Coming Fast’
1974: ‘Another Ice Age?’
1974: Ozone Depletion a ‘Great Peril to Life’
But no such ‘great peril to life’ has been observed as the so-called ‘ozone hole’ remains:
1976: ‘The Cooling’
1980: ‘Acid Rain Kills Life in Lakes’
But 10 years later, the US government program formed to study acid rain concluded:
1978: ‘No End in Sight’ to 30-Year Cooling Trend
But according to NASA satellite data there is a slight warming trend since 1979.
1988: James Hansen forecasts increase regional drought in 1990s
But the last really dry year in the Midwest was 1988, and recent years have been record wet.
1988: Washington DC days over 90F to from 35 to 85
But the number of hot days in the DC area peaked in 1911, and have been declining ever since.
1988: Maldives completely under water in 30 years
1989: Rising seas to ‘obliterate’ nations by 2000
1989: New York City’s West Side Highway underwater by 2019
1995 to Present: Climate Model Failure
2000: ‘Children won’t know what snow is.’
2002: Famine in 10 years
2004: Britain to have Siberian climate by 2020
2008: Arctic will be ice-free by 2018
2008: Al Gore warns of ice-free Arctic by 2013
2009: Prince Charles says only 8 years to save the planet
2009: UK prime minister says 50 days to ‘save the planet from catastrophe’
2009: Arctic ice-free by 2014
2013: Arctic ice-free by 2015
Gas hydrate dissociation off Svalbard induced by isostatic rebound rather than global warming
Methane seepage from the upper continental slopes of Western Svalbard has previously been attributed to gas hydrate dissociation induced by anthropogenic warming of ambient bottom waters. Here we show that sediment cores drilled off Prins Karls Foreland contain freshwater from dissociating hydrates. However, our modeling indicates that the observed pore water freshening began around 8 ka BP when the rate of isostatic uplift outpaced eustatic sea-level rise. The resultant local shallowing and lowering of hydrostatic pressure forced gas hydrate dissociation and dissolved chloride depletions consistent with our geochemical analysis. Hence, we propose that hydrate dissociation was triggered by postglacial isostatic rebound rather than anthropogenic warming. Furthermore, we show that methane fluxes from dissociating hydrates were considerably smaller than present methane seepage rates implying that gas hydrates were not a major source of methane to the oceans, but rather acted as a dynamic seal, regulating methane release from deep geological reservoirs.
There are several natural forces that together lead to an ice age on Earth.
The answer lies in how the orbit of the Earth around the sun changes. The average temperature on Earth depends on the Earth’s distance from the sun. If the Earth were closer to the sun, it would be hotter if the Earth were further away from the sun, it would be colder
A Yugoslav astronomer, Milutin Milankovitch, learned how changes in Earth’s orbit can changes in climate to cause ice ages. He studied three types of changes in Earth’s orbit: its shape, the tilt of the its axis, and the wobble of the its axis.
Shape of the Earth’s Orbit
If the Earth were the only planet orbiting the sun, its path would be circular. But there are other planets circling the sun too. Their gravity pulls slightly on the Earth as they pass nearby, causing the Earth’s orbit to change by a very small amount. The Earth’s orbit changes from circular to slightly elongate and back again about every 100,000 years.
When the orbit is circular, the distance between the sun and the Earth stays the same. But when the orbit is slightly elongate, the sun and Earth vary from being farther away from each other (making the climate colder) to being closer together (making the climate warmer).
The Earth is slightly tilted—that is what gives us our seasons.
Here’s how it works. On one side of its orbit around the sun, the Earth is tilted towards the sun. During this time, the northern hemisphere receives more heat so has higher temperatures—it is summer.
Six months later, the Earth is on the other side of its orbit, and the Earth is tilted away from the sun. Now, the northern hemisphere receives less heat so it is colder—it is winter.
However, the Earth’s tilt changes from 22° to 24° and back again about every 40,000 years. Right now, it is tilted at 23.5°. When the tilt is at its greatest, differences in temperatures between summer and winter will be greatest.
Like a spinning top as it is slowing down, the Earth’s axis wobbles in a circle every 23,000 years.
Because of this wobble, the Earth moves just a little bit more than one complete orbit each year. So, for example, if the Earth is in one place its orbit on, say, 1 July, it will be just a little bit further around the orbit on 1 July of the following year. This is called “precession.”
If Earth’s orbit is slightly elongate, then the distance between the sun and Earth will be different each 1 July, making the summer either cooler or warmer.
When these three changes in Earth's orbit—its shape, the tilt of the Earth's axis, and the wobble of the Earth's axis—are combined, they can explain why we get glacial and interglacial periods.
Glacial periods occur when the Earth's orbit is elongate, when the Earth's axis has a low tilt, and when northern hemisphere summer occurs at a position on the orbit farther away from the sun so that it is cool.
A Changing Climate
At the start of the Quaternary, the continents were just about where they are today, slowing inching here and there as the forces of plate tectonics push and tug them about. But throughout the period, the planet has wobbled on its path around the sun. The slight shifts cause ice ages to come and go. By 800,000 years ago, a cyclical pattern had emerged: Ice ages last about 100,000 years followed by warmer interglacials of 10,000 to 15,000 years each. The last ice age ended about 10,000 years ago. Sea levels rose rapidly, and the continents achieved their present-day outline.
When the temperatures drop, ice sheets spread from the Poles and cover much of North America and Europe, parts of Asia and South America, and all of Antarctica. With so much water locked up as ice, sea levels fall. Land bridges form between the continents like the currently submerged connector across the Bering Strait between Asia and North America. The land bridges allow animals and humans to migrate from one landmass to another.
Maps of the extent of the Ice
My thanks to Thalion for bringing this source to my attention.
All three maps below come from an excellent source which is the printed version of the electronic journal:
Folklore Vol. 18&19
Editors Mare Kõiva & Andres Kuperjanov & Väino Poikalainen & Enn Ernits
Published by the Folk Belief and Media Group of ELM
PALAEOLITHIC ART FROM THE DANUBE TO LAKE BAIKAL
All three maps share the common legend:
1 - continental (a) and maritime (b) glaciers, 2 - open sea, 3 - lakes, 4 - elongated elevations, 5 - courses of waterways, 6 - primeval valleys (Grosvald 1983: 96- 97) and major sites of prehistoric art before (A) and after (B, C) the glacial maximum.
Map of the maximum extent of the ice during the last ice age, around 20 000 years ago.
Note in particular the extensive lakes ponded behind the ice, fed by the north flowing rivers.
Note also the increased size of the Caspian and Aral Seas, and the reduced size of the Black Sea.
Map of the extent of the ice during the last ice age 13000 years before the present.
Map of the extent of the ice during the last ice age 10500 years before the present, just before the final retreat of the ice.
Map of the extent of the ice during the last glacial maximum in northern Eurasia, showing the ice sheets, floating ice, and the ice-dammed lakes, as well as the margins of lakes such as Lake Black (the present Black Sea, much reduced in size), Lake Caspian, Lake Aral, and the huge Lake Mansi, as well as many smaller lakes.
Map: Adapted from Grosswald (1998)
- Burdukeiwicz, J., 1999: Late Palaeolithic Amber in Northern Europe, Investigations into Amber, Proceedings of the International Interdisciplinary Symposium, 2 - 6 September 1997 Gdansk, The Archaeological Museum Gdansk, Museum of Earth, Polish Academy of Sciences, Gdansk, 1999, pp 99-110.
- Grosswald, M., 1998, New approach to the Ice Age paleohydrology of northern Eurasia. In G. Benito,V. R. Baker, and K. J. Gregory (eds) in Palaeohydrology and Environmental Change, pp. 199–214. Chichester: John Wiley & Sons
- Svendsen, J. et al., 2004, Late Quaternary ice sheet history of Eurasia. Quaternary Science Reviews, doi:10.1016/j.quascirev.2003.12.008).
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Ice age, also called glacial age, any geologic period during which thick ice sheets cover vast areas of land. Such periods of large-scale glaciation may last several million years and drastically reshape surface features of entire continents. A number of major ice ages have occurred throughout Earth history. The earliest known took place during Precambrian time dating back more than 570 million years. The most recent periods of widespread glaciation occurred during the Pleistocene Epoch (2.6 million to 11,700 years ago).
A lesser, recent glacial stage called the Little Ice Age began in the 16th century and advanced and receded intermittently over three centuries in Europe and many other regions. Its maximum development was reached about 1750, at which time glaciers were more widespread on Earth than at any time since the last major ice age ended about 11,700 years ago.