An ICE AGE is a period of long-term reduction in the temperature of
* 1 Origin of ice age theory * 2 Evidence for ice ages * 3 Major ice ages * 4 Glacials and interglacials
* 5 Positive and negative feedback in glacial periods
* 6 Causes of ice ages
* 6.1 Changes in Earth\'s atmosphere
* 6.1.1 Human-induced changes
* 6.2 Position of the continents * 6.3 Fluctuations in ocean currents * 6.4 Uplift of the Tibetan plateau and surrounding mountain areas above the snowline * 6.5 Variations in Earth\'s orbit (Milankovitch cycles) * 6.6 Variations in the Sun\'s energy output * 6.7 Volcanism
* 7 Recent glacial and interglacial phases
* 7.1 Glacial stages in North America * 7.2 Last Glacial Period in the semiarid Andes around Aconcagua and Tupungato
* 8 Effects of glaciation * 9 See also * 10 References * 11 External links
ORIGIN OF ICE AGE THEORY
Life timeline view • discuss • edit -4500 — – -4000 —
– -3500 — – -3000 — – -2500 — – -2000 — – -1500 —
– -1000 — – -500 — – 0 — _WATER _ Single-celled
life _PHOTOSYNTHESIS _ EUKARYOTES Multicellular
life LAND LIFE DINOSAURS MAMMALS FLOWERS ←
P r o t e r o z o i c
n Pongola Huronian
Cryogenian Andean Karoo Quaternary
Axis scale : millions of years .
Orange labels: known _ICE AGES_.
Also see: _
In 1742 Pierre Martel (1706–1767), an engineer and geographer
Meanwhile, European scholars had begun to wonder what had caused the
dispersal of erratic material. From the middle of the 18th century,
some discussed ice as a means of transport. The Swedish mining expert
Daniel Tilas (1712–1772) was, in 1742, the first person to suggest
drifting sea ice in order to explain the presence of erratic boulders
in the Scandinavian and Baltic regions. In 1795, the Scottish
philosopher and gentleman naturalist,
Only a few years later, the Danish-Norwegian geologist Jens Esmark (1762–1839) argued a sequence of worldwide ice ages. In a paper published in 1824, Esmark proposed changes in climate as the cause of those glaciations. He attempted to show that they originated from changes in Earth's orbit. During the following years, Esmark's ideas were discussed and taken over in parts by Swedish, Scottish and German scientists. At the University of Edinburgh Robert Jameson (1774–1854) seemed to be relatively open to Esmark's ideas, as reviewed by Norwegian professor of glaciology Bjørn G. Andersen (1992). Jameson's remarks about ancient glaciers in Scotland were most probably prompted by Esmark. In Germany, Albrecht Reinhard Bernhardi (1797–1849), a geologist and professor of forestry at an academy in Dreissigacker, since incorporated in the southern Thuringian city of Meiningen , adopted Esmark's theory. In a paper published in 1832, Bernhardi speculated about former polar ice caps reaching as far as the temperate zones of the globe.
In 1829, independently of these debates, the Swiss civil engineer
Ignaz Venetz (1788–1859) explained the dispersal of erratic boulders
in the Alps, the nearby Jura Mountains, and the North German Plain as
being due to huge glaciers. When he read his paper before the
Schweizerische Naturforschende Gesellschaft , most scientists remained
sceptical. Finally, Venetz convinced his friend Jean de Charpentier.
De Charpentier transformed Venetz's idea into a theory with a
glaciation limited to the Alps. His thoughts resembled Wahlenberg's
theory. In fact, both men shared the same volcanistic, or in de
Charpentier's case rather plutonistic assumptions, about the Earth's
history. In 1834, de Charpentier presented his paper before the
Schweizerische Naturforschende Gesellschaft. In the meantime, the
Karl Friedrich Schimper (1803–1867) was studying
mosses which were growing on erratic boulders in the alpine upland of
Bavaria. He began to wonder where such masses of stone had come from.
During the summer of 1835 he made some excursions to the Bavarian
Alps. Schimper came to the conclusion that ice must have been the
means of transport for the boulders in the alpine upland. In the
winter of 1835 to 1836 he held some lectures in Munich. Schimper then
assumed that there must have been global times of obliteration
("Verödungszeiten") with a cold climate and frozen water. Schimper
spent the summer months of 1836 at Devens, near Bex, in the Swiss Alps
with his former university friend
Louis Agassiz (1801–1873) and Jean
de Charpentier. Schimper, de Charpentier and possibly Venetz convinced
Agassiz that there had been a time of glaciation. During the winter of
1836/37, Agassiz and Schimper developed the theory of a sequence of
glaciations. They mainly drew upon the preceding works of Venetz, de
Charpentier and on their own fieldwork. Agassiz appears to have been
already familiar with Bernhardi's paper at that time. At the
beginning of 1837, Schimper coined the term "ice age" (_"Eiszeit"_)
for the period of the glaciers. In July 1837 Agassiz presented their
synthesis before the annual meeting of the Schweizerische
Naturforschende Gesellschaft at Neuchâtel. The audience was very
critical and some opposed to the new theory because it contradicted
the established opinions on climatic history. Most contemporary
scientists thought that the
In order to overcome this rejection, Agassiz embarked on geological fieldwork. He published his book _Study on Glaciers_ ("Études sur les glaciers") in 1840. De Charpentier was put out by this, as he had also been preparing a book about the glaciation of the Alps. De Charpentier felt that Agassiz should have given him precedence as it was he who had introduced Agassiz to in-depth glacial research. Besides that, Agassiz had, as a result of personal quarrels, omitted any mention of Schimper in his book.
All together, it took several decades until the ice age theory was fully accepted by scientists. This happened on an international scale in the second half of the 1870s following the work of James Croll , including the publication of _Climate and Time, in Their Geological Relations_ in 1875, which provided a credible explanation for the causes of ice ages.
EVIDENCE FOR ICE AGES
There are three main types of evidence for ice ages: geological, chemical, and paleontological.
GEOLOGICAL evidence for ice ages comes in various forms, including rock scouring and scratching, glacial moraines , drumlins , valley cutting, and the deposition of till or tillites and glacial erratics . Successive glaciations tend to distort and erase the geological evidence, making it difficult to interpret. Furthermore, this evidence was difficult to date exactly; early theories assumed that the glacials were short compared to the long interglacials. The advent of sediment and ice cores revealed the true situation: glacials are long, interglacials short. It took some time for the current theory to be worked out.
The CHEMICAL evidence mainly consists of variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks and ocean sediment cores. For the most recent glacial periods ice cores provide climate proxies from their ice, and atmospheric samples from included bubbles of air. Because water containing heavier isotopes has a higher heat of evaporation , its proportion decreases with colder conditions. This allows a temperature record to be constructed. However, this evidence can be confounded by other factors recorded by isotope ratios.
The PALEONTOLOGICAL evidence consists of changes in the geographical distribution of fossils. During a glacial period cold-adapted organisms spread into lower latitudes, and organisms that prefer warmer conditions become extinct or are squeezed into lower latitudes. This evidence is also difficult to interpret because it requires (1) sequences of sediments covering a long period of time, over a wide range of latitudes and which are easily correlated; (2) ancient organisms which survive for several million years without change and whose temperature preferences are easily diagnosed; and (3) the finding of the relevant fossils.
Despite the difficulties, analysis of ice core and ocean sediment cores has shown periods of glacials and interglacials over the past few million years. These also confirm the linkage between ice ages and continental crust phenomena such as glacial moraines, drumlins, and glacial erratics. Hence the continental crust phenomena are accepted as good evidence of earlier ice ages when they are found in layers created much earlier than the time range for which ice cores and ocean sediment cores are available.
MAJOR ICE AGES
Timeline of glaciations, shown in blue.
There have been at least five major ice ages in the earth's past (the
Karoo Ice Age and the
Rocks from the earliest well established ice age, called the Huronian
, formed around 2.4 to 2.1 Ga (billion years) ago during the early
Proterozoic Eon. Several hundreds of km of the
Huronian Supergroup are
exposed 10–100 km north of the north shore of Lake Huron extending
from near Sault Ste. Marie to Sudbury, northeast of Lake Huron, with
giant layers of now-lithified till beds, dropstones, varves, outwash,
and scoured basement rocks. Correlative
Huronian deposits have been
The next well-documented ice age, and probably the most severe of the
last billion years, occurred from 850 to 630 million years ago (the
Cryogenian period) and may have produced a Snowball
Andean-Saharan occurred from 460 to 420 million years ago, during
Late Ordovician and the
The evolution of land plants at the onset of the
caused a long term increase in planetary oxygen levels and reduction
of CO2 levels, which resulted in the
Karoo Ice Age . It is named after
the glacial tills found in the Karoo region of South Africa, where
evidence for this ice age was first clearly identified. There were
extensive polar ice caps at intervals from 360 to 260 million years
ago in South Africa during the
The current ice age , the Pliocene-Quaternary glaciation, started
about 2.58 million years ago during the late
Ice ages can be further divided by location and time; for example, the names _Riss_ (180,000–130,000 years bp ) and _Würm _ (70,000–10,000 years bp) refer specifically to glaciation in the Alpine region . The maximum extent of the ice is not maintained for the full interval. The scouring action of each glaciation tends to remove most of the evidence of prior ice sheets almost completely, except in regions where the later sheet does not achieve full coverage.
Evidence of a recent, extreme ice age on
GLACIALS AND INTERGLACIALS
Glacial period and
Within the ice ages (or at least within the current one), more
temperate and more severe periods occur. The colder periods are called
_glacial periods_, the warmer periods _interglacials_, such as the
Glacials are characterized by cooler and drier climates over most of
the earth and large land and sea ice masses extending outward from the
poles. Mountain glaciers in otherwise unglaciated areas extend to
lower elevations due to a lower snow line . Sea levels drop due to the
removal of large volumes of water above sea level in the icecaps.
There is evidence that ocean circulation patterns are disrupted by
glaciations. Since the earth has significant continental glaciation in
The earth has been in an interglacial period known as the Holocene for around 11,700 years, and an article in _Nature_ in 2004 argues that it might be most analogous to a previous interglacial that lasted 28,000 years. Predicted changes in orbital forcing suggest that the next glacial period would begin at least 50,000 years from now, even in absence of human-made global warming (see Milankovitch cycles ). Moreover, anthropogenic forcing from increased greenhouse gases might outweigh orbital forcing for as long as intensive use of fossil fuels continues.
POSITIVE AND NEGATIVE FEEDBACK IN GLACIAL PERIODS
Each glacial period is subject to positive feedback which makes it more severe, and negative feedback which mitigates and (in all cases so far) eventually ends it.
POSITIVE FEEDBACK PROCESSES
Ice and snow increase Earth's albedo , i.e. they make it reflect more of the sun's energy and absorb less. Hence, when the air temperature decreases, ice and snow fields grow, and this continues until competition with a negative feedback mechanism forces the system to an equilibrium. Also, the reduction in forests caused by the ice's expansion increases albedo.
Another theory proposed by Ewing and Donn in 1956 hypothesized that
NEGATIVE FEEDBACK PROCESSES
Ice sheets that form during glaciations cause erosion of the land beneath them. After some time, this will reduce land above sea level and thus diminish the amount of space on which ice sheets can form. This mitigates the albedo feedback, as does the lowering in sea level that accompanies the formation of ice sheets.
Another factor is the increased aridity occurring with glacial maxima, which reduces the precipitation available to maintain glaciation. The glacial retreat induced by this or any other process can be amplified by similar inverse positive feedbacks as for glacial advances.
According to research published in _ Nature Geoscience _, human emissions of carbon dioxide (CO2) will defer the next ice age. Researchers used data on Earth's orbit to find the historical warm interglacial period that looks most like the current one and from this have predicted that the next ice age would usually begin within 1,500 years. They go on to say that emissions have been so high that it will not.
CAUSES OF ICE AGES
The causes of ice ages are not fully understood for either the
large-scale ice age periods or the smaller ebb and flow of
glacial–interglacial periods within an ice age. The consensus is
that several factors are important: atmospheric composition , such as
the concentrations of carbon dioxide and methane (the specific levels
of the previously mentioned gases are now able to be seen with the new
ice core samples from EPICA Dome C in
Some of these factors influence each other. For example, changes in Earth's atmospheric composition (especially the concentrations of greenhouse gases) may alter the climate, while climate change itself can change the atmospheric composition (for example by changing the rate at which weathering removes CO2).
Maureen Raymo , William Ruddiman and others propose that the Tibetan and Colorado Plateaus are immense CO2 "scrubbers" with a capacity to remove enough CO2 from the global atmosphere to be a significant causal factor of the 40 million year Cenozoic Cooling trend. They further claim that approximately half of their uplift (and CO2 "scrubbing" capacity) occurred in the past 10 million years.
CHANGES IN EARTH\'S ATMOSPHERE
There is evidence that greenhouse gas levels fell at the start of ice
ages and rose during the retreat of the ice sheets, but it is
difficult to establish cause and effect (see the notes above on the
role of weathering).
In 2009, further evidence was provided that changes in solar insolation provide the initial trigger for the earth to warm after an Ice Age, with secondary factors like increases in greenhouse gases accounting for the magnitude of the change.
There is considerable evidence that over the very recent period of the last 100–1000 years, the sharp increases in human activity, especially the burning of fossil fuels , has caused the parallel sharp and accelerating increase in atmospheric greenhouse gases which trap the sun's heat. The consensus theory of the scientific community is that the resulting greenhouse effect is a principal cause of the increase in global warming which has occurred over the same period, and a chief contributor to the accelerated melting of the remaining glaciers and polar ice . A 2012 investigation finds that dinosaurs released methane through digestion in a similar amount to humanity's current methane release, which "could have been a key factor" to the very warm climate 150 million years ago.
William Ruddiman has proposed the early anthropocene hypothesis, according to which the anthropocene era, as some people call the most recent period in the earth's history when the activities of the human species first began to have a significant global impact on the earth's climate and ecosystems, did not begin in the 18th century with the advent of the Industrial Era, but dates back to 8,000 years ago, due to intense farming activities of our early agrarian ancestors. It was at that time that atmospheric greenhouse gas concentrations stopped following the periodic pattern of the Milankovitch cycles . In his overdue-glaciation hypothesis Ruddiman states that an incipient glacial would probably have begun several thousand years ago, but the arrival of that scheduled glacial was forestalled by the activities of early farmers.
At a meeting of the American Geophysical Union (December 17, 2008), scientists detailed evidence in support of the controversial idea that the introduction of large-scale rice agriculture in Asia, coupled with extensive deforestation in Europe began to alter world climate by pumping significant amounts of greenhouse gases into the atmosphere over the last 1,000 years. In turn, a warmer atmosphere heated the oceans making them much less efficient storehouses of carbon dioxide and reinforcing global warming, possibly forestalling the onset of a new glacial age.
POSITION OF THE CONTINENTS
The geological record appears to show that ice ages start when the continents are in positions which block or reduce the flow of warm water from the equator to the poles and thus allow ice sheets to form. The ice sheets increase Earth's reflectivity and thus reduce the absorption of solar radiation. With less radiation absorbed the atmosphere cools; the cooling allows the ice sheets to grow, which further increases reflectivity in a positive feedback loop. The ice age continues until the reduction in weathering causes an increase in the greenhouse effect .
There are three known configurations of the continents which block or reduce the flow of warm water from the equator to the poles:
* A continent sits on top of a pole, as
Some scientists believe that the
FLUCTUATIONS IN OCEAN CURRENTS
Another important contribution to ancient climate regimes is the variation of OCEAN CURRENTS, which are modified by continent position, sea levels and salinity, as well as other factors. They have the ability to cool (e.g. aiding the creation of Antarctic ice) and the ability to warm (e.g. giving the British Isles a temperate as opposed to a boreal climate). The closing of the Isthmus of Panama about 3 million years ago may have ushered in the present period of strong glaciation over North America by ending the exchange of water between the tropical Atlantic and Pacific Oceans.
Analyses suggest that ocean current fluctuations can adequately account for recent glacial oscillations. During the last glacial period the sea-level has fluctuated 20–30 m as water was sequestered, primarily in the Northern Hemisphere ice sheets. When ice collected and the sea level dropped sufficiently, flow through the Bering Strait (the narrow strait between Siberia and Alaska is about 50 m deep today) was reduced, resulting in increased flow from the North Atlantic. This realigned the thermohaline circulation in the Atlantic, increasing heat transport into the Arctic, which melted the polar ice accumulation and reduced other continental ice sheets. The release of water raised sea levels again, restoring the ingress of colder water from the Pacific with an accompanying shift to northern hemisphere ice accumulation.
UPLIFT OF THE TIBETAN PLATEAU AND SURROUNDING MOUNTAIN AREAS ABOVE THE SNOWLINE
Matthias Kuhle 's geological theory of Ice Age development was
suggested by the existence of an ice sheet covering the Tibetan
Plateau during the Ice Ages (
Last Glacial Maximum ?). According to
Kuhle, the plate-tectonic uplift of Tibet past the snow-line has led
to a surface of c. 2,400,000 square kilometres (930,000 sq mi)
changing from bare land to ice with a 70% greater albedo . The
reflection of energy into space resulted in a global cooling,
Kuhle explains the interglacial periods by the 100,000-year cycle of radiation changes due to variations in Earth's orbit. This comparatively insignificant warming, when combined with the lowering of the Nordic inland ice areas and Tibet due to the weight of the superimposed ice-load, has led to the repeated complete thawing of the inland ice areas.
VARIATIONS IN EARTH\'S ORBIT (MILANKOVITCH CYCLES)
The Milankovitch cycles are a set of cyclic variations in characteristics of the Earth's orbit around the Sun. Each cycle has a different length, so at some times their effects reinforce each other and at other times they (partially) cancel each other. Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65 N latitude.
There is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age. The present ice age is the most studied and best understood, particularly the last 400,000 years, since this is the period covered by ice cores that record atmospheric composition and proxies for temperature and ice volume. Within this period, the match of glacial/interglacial frequencies to the Milanković orbital forcing periods is so close that orbital forcing is generally accepted. The combined effects of the changing distance to the Sun, the precession of the Earth's axis , and the changing tilt of the Earth's axis redistribute the sunlight received by the Earth. Of particular importance are changes in the tilt of the Earth's axis, which affect the intensity of seasons. For example, the amount of solar influx in July at 65 degrees north latitude varies by as much as 22% (from 450 W/m² to 550 W/m²). It is widely believed that ice sheets advance when summers become too cool to melt all of the accumulated snowfall from the previous winter. Some believe that the strength of the orbital forcing is too small to trigger glaciations, but feedback mechanisms like CO2 may explain this mismatch.
While Milankovitch forcing predicts that cyclic changes in the Earth's orbital elements can be expressed in the glaciation record, additional explanations are necessary to explain which cycles are observed to be most important in the timing of glacial–interglacial periods. In particular, during the last 800,000 years, the dominant period of glacial–interglacial oscillation has been 100,000 years, which corresponds to changes in Earth's orbital eccentricity and orbital inclination . Yet this is by far the weakest of the three frequencies predicted by Milankovitch. During the period 3.0–0.8 million years ago, the dominant pattern of glaciation corresponded to the 41,000-year period of changes in Earth's obliquity (tilt of the axis). The reasons for dominance of one frequency versus another are poorly understood and an active area of current research, but the answer probably relates to some form of resonance in the Earth's climate system. Recent work suggests that the 100K year cycle dominates due to increased southern-pole sea-ice increasing total solar reflectivity.
The "traditional" Milankovitch explanation struggles to explain the
dominance of the 100,000-year cycle over the last 8 cycles. Richard A.
Gordon J. F. MacDonald , and others have pointed out that
those calculations are for a two-dimensional orbit of
William Ruddiman , has suggested a model that
explains the 100,000-year cycle by the modulating effect of
eccentricity (weak 100,000-year cycle) on precession (26,000-year
cycle) combined with greenhouse gas feedbacks in the 41,000- and
26,000-year cycles. Yet another theory has been advanced by Peter
Huybers who argued that the 41,000-year cycle has always been
dominant, but that the
VARIATIONS IN THE SUN\'S ENERGY OUTPUT
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There are at least two types of variation in the Sun's energy output
* In the very long term, astrophysicists believe that the Sun's output increases by about 7% every one billion (109) years. * Shorter-term variations such as sunspot cycles , and longer episodes such as the Maunder Minimum , which occurred during the coldest part of the Little Ice Age .
The long-term increase in the Sun's output cannot be a cause of ice ages.
Volcanic eruptions may have contributed to the inception and/or the
end of ice age periods. At times during the paleoclimate, carbon
dioxide levels were two or three times greater than today. Volcanoes
and movements in continental plates contributed to high amounts of CO2
in the atmosphere.
RECENT GLACIAL AND INTERGLACIAL PHASES
_ Northern hemisphere glaciation during the last ice ages. The setup of 3 to 4 kilometer thick ice sheets caused a sea level lowering of about 120 m. Main article: Timeline of glaciation
THIS SECTION NEEDS EXPANSION with: Recent glacial and interglacial phases in other areas outside North America. You can help by adding to it . (March 2008)_
GLACIAL STAGES IN NORTH AMERICA
The major glacial stages of the current ice age in North America are
the Illinoian ,
During the most recent North American glaciation, during the latter part of the Last Glacial Maximum (26,000 to 13,300 years ago), ice sheets extended to about 45th parallel north . These sheets were 3 to 4 kilometres (1.9 to 2.5 mi) thick.
Wisconsin glaciation left widespread impacts on the North
American landscape. The
The area from
Driftless Area , a portion of western and southwestern Wisconsin
along with parts of adjacent
LAST GLACIAL PERIOD IN THE SEMIARID ANDES AROUND ACONCAGUA AND TUPUNGATO
A specially interesting climatic change during glacial times has taken place in the semi-arid Andes. Beside the expected cooling down in comparison with the current climate, a significant precipitation change happened here. So, researches in the presently semiarid subtropic Aconcagua-massif (6,962 m) have shown an unexpectedly extensive glacial glaciation of the type "ice stream network". The connected valley glaciers exceeding 100 km in length, flowed down on the East-side of this section of the Andes at 32–34°S and 69–71°W as far as a height of 2,060 m and on the western luff-side still clearly deeper. Where current glaciers scarcely reach 10 km in length, the snowline (ELA) runs at a height of 4,600 m and at that time was lowered to 3,200 m asl , i.e. about 1,400 m. From this follows that—beside of an annual depression of temperature about c. 8.4 °C— here was an increase in precipitation. Accordingly, at glacial times the humid climatic belt that today is situated several latitude degrees further to the S, was shifted much further to the N.
EFFECTS OF GLACIATION
Although the last glacial period ended more than 8,000 years ago, its
effects can still be felt today. For example, the moving ice carved
out the landscape in Canada (See Canadian
The weight of the ice sheets was so great that they deformed the Earth's crust and mantle. After the ice sheets melted, the ice-covered land rebounded . Due to the high viscosity of the Earth\'s mantle , the flow of mantle rocks which controls the rebound process is very slow—at a rate of about 1 cm/year near the center of rebound area today.
During glaciation, water was taken from the oceans to form the ice at
high latitudes, thus global sea level dropped by about 110 meters,
exposing the continental shelves and forming land-bridges between
land-masses for animals to migrate. During deglaciation , the melted
ice-water returned to the oceans, causing sea level to rise. This
process can cause sudden shifts in coastlines and hydration systems
resulting in newly submerged lands, emerging lands, collapsed ice dams
resulting in salination of lakes, new ice dams creating vast areas of
freshwater, and a general alteration in regional weather patterns on a
large but temporary scale. It can even cause temporary reglaciation .
This type of chaotic pattern of rapidly changing land, ice, saltwater
and freshwater has been proposed as the likely model for the Baltic
and Scandinavian regions, as well as much of central North America at
the end of the last glacial maximum, with the present-day coastlines
only being achieved in the last few millennia of prehistory. Also, the
effect of elevation on
The redistribution of ice-water on the surface of the
The weight of the redistributed surface mass loaded the lithosphere ,
caused it to flex and also induced stress within the Earth. The
presence of the glaciers generally suppressed the movement of faults
below. However, during deglaciation , the faults experience
accelerated slip triggering earthquakes . Earthquakes triggered near
the ice margin may in turn accelerate ice calving and may account for
In Europe, glacial erosion and isostatic sinking from weight of ice
* ^ Imbrie, J.; Imbrie, K.P (1979). _Ice ages: solving the
mystery_. Short Hills NJ: Enslow Publishers. ISBN 978-0-89490-015-0 .
* ^ Gribbin, J.R. (1982). _Future Weather: Carbon Dioxide, Climate
and the Greenhouse Effect_. Penguin. ISBN 0-14-022459-9 .
* ^ Rémis, F.; Testus, L.; Testut (2006). "Mais comment s\'écoule
donc un glacier ? Aperçu historique" (PDF). _C. R. Geoscience_ (in
French). 338 (5): 368–385.
Bibcode :2006CRGeo.338..368R. doi
:10.1016/j.crte.2006.02.004 . CS1 maint: Multiple names: authors list
(link ) Note: p. 374
* ^ Montgomery 2010
* ^ Martel, Pierre (1898). "Appendix: Martel, P. (1744) An account
of the glacieres or ice alps in Savoy, in two letters, one from an
English gentleman to his friend at
* ^ Davies, Gordon L. (1969). _The
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* Cracking the Ice Age from PBS *