115-595: The Huronian glaciation (or Makganyene glaciation ) was a period where at least three ice ages occurred during the deposition of the Huronian Supergroup . Deposition of this largely sedimentary succession extended from approximately 2.5 to 2.2 billion years ago ( Gya ), during the Siderian and Rhyacian periods of the Paleoproterozoic era. Evidence for glaciation is mainly based on
230-454: A proglacial lake above the valley created by an ice dam as a result of the 1815 eruption of Mount Tambora , which threatened to cause a catastrophic flood when the dam broke. Perraudin attempted unsuccessfully to convert his companions to his theory, but when the dam finally broke, there were only minor erratics and no striations, and Venetz concluded that Perraudin was right and that only ice could have caused such major results. In 1821 he read
345-596: A "lower Huronian ice age" from analysis of a geological formation near Lake Huron in Ontario. In his honour, the lower (glacial) member of the Gowganda Formation is referred to as the Coleman member. These rocks have been studied in detail by numerous geologists and are considered to represent the type example of a Paleoproterozoic glaciation. The confusion of the terms glaciation and ice age has led to
460-526: A fertilizer that causes massive algal blooms that pulls large amounts of CO 2 out of the atmosphere. This in turn makes it even colder and causes the glaciers to grow more. In 1956, Ewing and Donn hypothesized that an ice-free Arctic Ocean leads to increased snowfall at high latitudes. When low-temperature ice covers the Arctic Ocean there is little evaporation or sublimation and the polar regions are quite dry in terms of precipitation, comparable to
575-570: 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 the polar ice caps once reaching as far as the temperate zones of the globe. In Val de Bagnes , a valley in the Swiss Alps , there was a long-held local belief that the valley had once been covered deep in ice, and in 1815
690-408: A local chamois hunter called Jean-Pierre Perraudin attempted to convert the geologist Jean de Charpentier to the idea, pointing to deep striations in the rocks and giant erratic boulders as evidence. Charpentier held the general view that these signs were caused by vast floods, and he rejected Perraudin's theory as absurd. In 1818 the engineer Ignatz Venetz joined Perraudin and Charpentier to examine
805-467: A molten globe. In order to persuade the skeptics, Agassiz embarked on geological fieldwork. He published his book Study on Glaciers ("Études sur les glaciers") in 1840. Charpentier was put out by this, as he had also been preparing a book about the glaciation of the Alps. Charpentier felt that Agassiz should have given him precedence as it was he who had introduced Agassiz to in-depth glacial research. As
920-544: A prize-winning paper on the theory to the Swiss Society, but it was not published until Charpentier, who had also become converted, published it with his own more widely read paper in 1834. In the meantime, the German botanist 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
1035-462: A rate that is directly proportional to the fourth power of its temperature . Some of the radiation emitted by the Earth's surface is absorbed by greenhouse gases and clouds. Without this absorption, Earth's surface would have an average temperature of −18 °C (−0.4 °F). However, because some of the radiation is absorbed, Earth's average surface temperature is around 15 °C (59 °F). Thus,
1150-499: A result of personal quarrels, Agassiz had also omitted any mention of Schimper in his book. It took several decades before 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
1265-569: A result, global warming of about 1.2 °C (2.2 °F) has occurred since the Industrial Revolution , with the global average surface temperature increasing at a rate of 0.18 °C (0.32 °F) per decade since 1981. All objects with a temperature above absolute zero emit thermal radiation . The wavelengths of thermal radiation emitted by the Sun and Earth differ because their surface temperatures are different. The Sun has
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#17327654175621380-411: A significant causal factor of the 40 million year Cenozoic Cooling trend. They further claim that approximately half of their uplift (and CO 2 "scrubbing" capacity) occurred in the past 10 million years. 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
1495-434: A state of radiative equilibrium , in which the power of outgoing radiation equals the power of absorbed incoming radiation. Earth's energy imbalance is the amount by which the power of incoming sunlight absorbed by Earth's surface or atmosphere exceeds the power of outgoing longwave radiation emitted to space. Energy imbalance is the fundamental measurement that drives surface temperature. A UN presentation says "The EEI
1610-448: A surface temperature of 5,500 °C (9,900 °F), so it emits most of its energy as shortwave radiation in near-infrared and visible wavelengths (as sunlight). In contrast, Earth's surface has a much lower temperature, so it emits longwave radiation at mid- and far- infrared wavelengths. A gas is a greenhouse gas if it absorbs longwave radiation . Earth's atmosphere absorbs only 23% of incoming shortwave radiation, but absorbs 90% of
1725-662: Is a long period of reduction in the temperature of Earth 's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers . Earth's climate alternates between ice ages, and greenhouse periods during which there are no glaciers on the planet. Earth is currently in the ice age called Quaternary glaciation . Individual pulses of cold climate within an ice age are termed glacial periods ( glacials, glaciations, glacial stages, stadials, stades , or colloquially, ice ages ), and intermittent warm periods within an ice age are called interglacials or interstadials . In glaciology ,
1840-478: Is an associated effective emission temperature (or brightness temperature ). A given wavelength of radiation may also be said to have an effective emission altitude , which is a weighted average of the altitudes within the radiating layer. The effective emission temperature and altitude vary by wavelength (or frequency). This phenomenon may be seen by examining plots of radiation emitted to space. Earth's surface radiates longwave radiation with wavelengths in
1955-440: Is because their molecules are symmetrical and so do not have a dipole moment.) Such gases make up more than 99% of the dry atmosphere. Greenhouse gases absorb and emit longwave radiation within specific ranges of wavelengths (organized as spectral lines or bands ). When greenhouse gases absorb radiation, they distribute the acquired energy to the surrounding air as thermal energy (i.e., kinetic energy of gas molecules). Energy
2070-465: Is because when these molecules vibrate , those vibrations modify the molecular dipole moment , or asymmetry in the distribution of electrical charge. See Infrared spectroscopy .) Gases with only one atom (such as argon, Ar) or with two identical atoms (such as nitrogen, N 2 , and oxygen, O 2 ) are not infrared active. They are transparent to longwave radiation, and, for practical purposes, do not absorb or emit longwave radiation. (This
2185-454: Is being measured. Strengthening of the greenhouse effect through additional greenhouse gases from human activities is known as the enhanced greenhouse effect . As well as being inferred from measurements by ARGO , CERES and other instruments throughout the 21st century, this increase in radiative forcing from human activity has been observed directly, and is attributable mainly to increased atmospheric carbon dioxide levels. CO 2
2300-435: Is essential to the greenhouse effect. If the lapse rate was zero (so that the atmospheric temperature did not vary with altitude and was the same as the surface temperature) then there would be no greenhouse effect (i.e., its value would be zero). Greenhouse gases make the atmosphere near Earth's surface mostly opaque to longwave radiation. The atmosphere only becomes transparent to longwave radiation at higher altitudes, where
2415-578: Is estimated to potentially outweigh the orbital forcing of the Milankovitch cycles for hundreds of thousands of years. 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. An important form of feedback is provided by Earth's albedo , which is how much of the sun's energy is reflected rather than absorbed by Earth. Ice and snow increase Earth's albedo, while forests reduce its albedo. When
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#17327654175622530-422: Is expressed in units of W/m , which is the number of joules of energy that pass through a square meter each second. Most fluxes quoted in high-level discussions of climate are global values, which means they are the total flow of energy over the entire globe, divided by the surface area of the Earth, 5.1 × 10 m (5.1 × 10 km ; 2.0 × 10 sq mi). The fluxes of radiation arriving at and leaving
2645-491: Is produced by fossil fuel burning and other activities such as cement production and tropical deforestation . Measurements of CO 2 from the Mauna Loa Observatory show that concentrations have increased from about 313 parts per million (ppm) in 1960, passing the 400 ppm milestone in 2013. The current observed amount of CO 2 exceeds the geological record maxima (≈300 ppm) from ice core data. Over
2760-445: Is sometimes called thermal radiation . Outgoing longwave radiation (OLR) is the radiation from Earth and its atmosphere that passes through the atmosphere and into space. The greenhouse effect can be directly seen in graphs of Earth's outgoing longwave radiation as a function of frequency (or wavelength). The area between the curve for longwave radiation emitted by Earth's surface and the curve for outgoing longwave radiation indicates
2875-597: 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 the European Project for Ice Coring in Antarctica (EPICA) Dome C in Antarctica over the past 800,000 years); changes in Earth's orbit around the Sun known as Milankovitch cycles ;
2990-516: 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 (CO 2 ) will defer the next glacial period. Researchers used data on Earth's orbit to find
3105-424: Is the most critical number defining the prospects for continued global warming and climate change." One study argues, "The absolute value of EEI represents the most fundamental metric defining the status of global climate change." Earth's energy imbalance (EEI) was about 0.7 W/m as of around 2015, indicating that Earth as a whole is accumulating thermal energy and is in a process of becoming warmer. Over 90% of
3220-404: Is transferred from greenhouse gas molecules to other molecules via molecular collisions . Contrary to what is sometimes said, greenhouse gases do not "re-emit" photons after they are absorbed. Because each molecule experiences billions of collisions per second, any energy a greenhouse gas molecule receives by absorbing a photon will be redistributed to other molecules before there is a chance for
3335-473: The Alps of Savoy . Two years later he published an account of his journey. He reported that the inhabitants of that valley attributed the dispersal of erratic boulders to the glaciers, saying that they had once extended much farther. Later similar explanations were reported from other regions of the Alps. In 1815 the carpenter and chamois hunter Jean-Pierre Perraudin (1767–1858) explained erratic boulders in
3450-655: The Carboniferous and early Permian periods. Correlatives are known from Argentina, also in the center of the ancient supercontinent Gondwanaland . Although the Mesozoic Era retained a greenhouse climate over its timespan and was previously assumed to have been entirely glaciation-free, more recent studies suggest that brief periods of glaciation occurred in both hemispheres during the Early Cretaceous . Geologic and palaeoclimatological records suggest
3565-515: The Great Oxygenation Event , a time of increased atmospheric oxygen and decreased atmospheric methane . The oxygen reacted with the methane to form carbon dioxide and water, both much weaker greenhouse gases than methane, greatly reducing the efficacy of the greenhouse effect , especially as water vapor readily precipitated out of the air with dropping temperature. This caused an icehouse effect and, possibly compounded by
Huronian glaciation - Misplaced Pages Continue
3680-683: The Himalayas are a major factor in the current ice age, because these mountains have increased Earth's total rainfall and therefore the rate at which carbon dioxide is washed out of the atmosphere, decreasing the greenhouse effect. The Himalayas' formation started about 70 million years ago when the Indo-Australian Plate collided with the Eurasian Plate , and the Himalayas are still rising by about 5 mm per year because
3795-765: The Late Ordovician and the Silurian period. The evolution of land plants at the onset of the Devonian period caused a long term increase in planetary oxygen levels and reduction of CO 2 levels, which resulted in the late Paleozoic icehouse . Its former name, the Karoo glaciation, was named after the glacial tills found in the Karoo region of South Africa. There were extensive polar ice caps at intervals from 360 to 260 million years ago in South Africa during
3910-541: The Medicine Bow Mountains, Wyoming , Chibougamau , Quebec, and central Nunavut. Globally, they occur in the Griquatown Basin of South Africa, as well as India and Australia. The tectonic setting was one of a rifting continental margin . New continental crust would have resulted in chemical weathering . This weathering would pull CO 2 out of the atmosphere, cooling the planet through
4025-482: The Pleistocene Ice Age. Because this highland is at a subtropical latitude, with four to five times the insolation of high-latitude areas, what would be Earth's strongest heating surface has turned into a cooling surface. 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
4140-715: The Turonian , otherwise the warmest period of the Phanerozoic, are disputed), ice sheets and associated sea ice appear to have briefly returned to Antarctica near the very end of the Maastrichtian just prior to the Cretaceous-Paleogene extinction event . The Quaternary Glaciation / Quaternary Ice Age started about 2.58 million years ago at the beginning of the Quaternary Period when
4255-506: The cytoplasmic nucleic acids , allowing endosymbiosis with aerobic eubacteria (which eventually became ATP -producing mitochondria ), and this symbiogenesis contributed to the evolution of eukaryotic organisms during the Proterozoic . Hypothetical runaway greenhouse state Tropical temperatures may reach poles Global climate during an ice age Earth's surface entirely or nearly frozen over Ice age An ice age
4370-482: The ecological niches vacated by anaerobes in most environments. The surviving anaerobe colonies were forced to adapt a symbiotic living among aerobes, with the anaerobes contributing the organic materials that aerobes needed, and the aerobes consuming and "detoxing" the surrounding of oxygen molecules lethal to the anaerobes. This might have also caused some anaerobic archaea to begin invaginating their cell membranes into endomembranes in order to shield and protect
4485-452: The reduction by surface ferrous compounds, atmospheric methane and hydrogen sulfide . However, as the cyanobacterial photosynthesis continued, the cumulative oxygen oversaturated the reductive reservoir of the Earth's surface and spilt out as free oxygen that "polluted" the atmosphere, leading to a permanent change to the atmospheric chemistry known as the Great Oxygenation Event . The once- reducing atmosphere , now an oxidizing one,
4600-407: The thermal inertia of the climate system resists changes both day and night, as well as for longer periods. Diurnal temperature changes decrease with height in the atmosphere. In the lower portion of the atmosphere, the troposphere , the air temperature decreases (or "lapses") with increasing altitude. The rate at which temperature changes with altitude is called the lapse rate . On Earth,
4715-618: 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. According to a study published in Nature in 2021, all glacial periods of ice ages over
Huronian glaciation - Misplaced Pages Continue
4830-559: The Earth and its atmosphere emit longwave radiation . Sunlight includes ultraviolet , visible light , and near-infrared radiation. Sunlight is reflected and absorbed by the Earth and its atmosphere. The atmosphere and clouds reflect about 23% and absorb 23%. The surface reflects 7% and absorbs 48%. Overall, Earth reflects about 30% of the incoming sunlight, and absorbs the rest (240 W/m ). The Earth and its atmosphere emit longwave radiation , also known as thermal infrared or terrestrial radiation . Informally, longwave radiation
4945-420: The Earth are important because radiative transfer is the only process capable of exchanging energy between Earth and the rest of the universe. The temperature of a planet depends on the balance between incoming radiation and outgoing radiation. If incoming radiation exceeds outgoing radiation, a planet will warm. If outgoing radiation exceeds incoming radiation, a planet will cool. A planet will tend towards
5060-399: The Earth can cool off. Without the greenhouse effect, the Earth's average surface temperature would be as cold as −18 °C (−0.4 °F). This is of course much less than the 20th century average of about 14 °C (57 °F). In addition to naturally present greenhouse gases, burning of fossil fuels has increased amounts of carbon dioxide and methane in the atmosphere. As
5175-400: The Earth's greenhouse effect can also be measured as an energy flow change of 159 W/m . The greenhouse effect can be expressed as a fraction (0.40) or percentage (40%) of the longwave thermal radiation that leaves Earth's surface but does not reach space. Whether the greenhouse effect is expressed as a change in temperature or as a change in longwave thermal radiation, the same effect
5290-481: The Earth's greenhouse effect may be measured as a temperature change of 33 °C (59 °F). Thermal radiation is characterized by how much energy it carries, typically in watts per square meter (W/m ). Scientists also measure the greenhouse effect based on how much more longwave thermal radiation leaves the Earth's surface than reaches space. Currently, longwave radiation leaves the surface at an average rate of 398 W/m , but only 239 W/m reaches space. Thus,
5405-481: The Huronian Ice Age, most organisms were anaerobic , relying on chemosynthesis and retinal -based anoxygenic photosynthesis for production of biological energy and biocompounds . But around this time, cyanobacteria evolved porphyrin -based oxygenic photosynthesis , which produced dioxygen as a waste product. At first, most of this oxygen was dissolved in the ocean and afterwards absorbed through
5520-467: The Indo-Australian plate is still moving at 67 mm/year. The history of the Himalayas broadly fits the long-term decrease in Earth's average temperature since the mid-Eocene , 40 million years ago. 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
5635-579: The North Atlantic Ocean far enough to block the Gulf Stream. Ice sheets that form during glaciations erode the land beneath them. This can reduce the land area above sea level and thus diminish the amount of space on which ice sheets can form. This mitigates the albedo feedback, as does the rise in sea level that accompanies the reduced area of ice sheets, since open ocean has a lower albedo than land. Another negative feedback mechanism
5750-603: The North Atlantic during a warming cycle may also reduce the global ocean water circulation . Such a reduction (by reducing the effects of the Gulf Stream ) would have a cooling effect on northern Europe, which in turn would lead to increased low-latitude snow retention during the summer. It has also been suggested that during an extensive glacial, glaciers may move through the Gulf of Saint Lawrence , extending into
5865-827: The Scandinavian peninsula. He regarded glaciation as a regional phenomenon. Only a few years later, the Danish-Norwegian geologist Jens Esmark (1762–1839) argued for 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. Esmark discovered the similarity between moraines near Haukalivatnet lake near sea level in Rogaland and moraines at branches of Jostedalsbreen . Esmark's discovery were later attributed to or appropriated by Theodor Kjerulf and Louis Agassiz . During
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#17327654175625980-544: The Swiss Alps with his former university friend Louis Agassiz (1801–1873) and Jean de Charpentier. Schimper, 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, Charpentier and on their own fieldwork. Agassiz appears to have been already familiar with Bernhardi's paper at that time. At
6095-880: The Val de Bagnes in the Swiss canton of Valais as being due to glaciers previously extending further. An unknown woodcutter from Meiringen in the Bernese Oberland advocated a similar idea in a discussion with the Swiss-German geologist Jean de Charpentier (1786–1855) in 1834. Comparable explanations are also known from the Val de Ferret in the Valais and the Seeland in western Switzerland and in Goethe 's scientific work . Such explanations could also be found in other parts of
6210-621: 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
6325-471: The air is less dense, there is less water vapor, and reduced pressure broadening of absorption lines limits the wavelengths that gas molecules can absorb. For any given wavelength, the longwave radiation that reaches space is emitted by a particular radiating layer of the atmosphere. The intensity of the emitted radiation is determined by the weighted average air temperature within that layer. So, for any given wavelength of radiation emitted to space, there
6440-416: The air temperature decreases by about 6.5 °C/km (3.6 °F per 1000 ft), on average, although this varies. The temperature lapse is caused by convection . Air warmed by the surface rises. As it rises, air expands and cools . Simultaneously, other air descends, compresses, and warms. This process creates a vertical temperature gradient within the atmosphere. This vertical temperature gradient
6555-402: The air temperature decreases, ice and snow fields grow, and they reduce forest cover. This continues until competition with a negative feedback mechanism forces the system to an equilibrium. One theory is that when glaciers form, two things happen: the ice grinds rocks into dust, and the land becomes dry and arid. This allows winds to transport iron rich dust into the open ocean, where it acts as
6670-424: The amount found in mid-latitude deserts . This low precipitation allows high-latitude snowfalls to melt during the summer. An ice-free Arctic Ocean absorbs solar radiation during the long summer days, and evaporates more water into the Arctic atmosphere. With higher precipitation, portions of this snow may not melt during the summer and so glacial ice can form at lower altitudes and more southerly latitudes, reducing
6785-410: The amount of longwave radiation emitted by the surface: Earth's surface temperature is often reported in terms of the average near-surface air temperature. This is about 15 °C (59 °F), a bit lower than the effective surface temperature. This value is 33 °C (59 °F) warmer than Earth's overall effective temperature. Energy flux is the rate of energy flow per unit area. Energy flux
6900-448: The atmosphere with greenhouse gases absorbs some of the longwave radiation being radiated upwards from lower layers. It also emits longwave radiation in all directions, both upwards and downwards, in equilibrium with the amount it has absorbed. This results in less radiative heat loss and more warmth below. Increasing the concentration of the gases increases the amount of absorption and emission, and thereby causing more heat to be retained at
7015-500: The atmosphere, with the main gases having no effect, and was largely due to water vapor, though small percentages of hydrocarbons and carbon dioxide had a significant effect. The effect was more fully quantified by Svante Arrhenius in 1896, who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901. Matter emits thermal radiation at
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#17327654175627130-492: The atmosphere." The enhanced greenhouse effect describes the fact that by increasing the concentration of GHGs in the atmosphere (due to human action), the natural greenhouse effect is increased. The term greenhouse effect comes from an analogy to greenhouses . Both greenhouses and the greenhouse effect work by retaining heat from sunlight, but the way they retain heat differs. Greenhouses retain heat mainly by blocking convection (the movement of air). In contrast,
7245-474: 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 Swiss Society for Natural Research at Neuchâtel. The audience was very critical, and some were opposed to the new theory because it contradicted the established opinions on climatic history. Most contemporary scientists thought that Earth had been gradually cooling down since its birth as
7360-467: The case of Jupiter , or from its host star as in the case of the Earth . In the case of Earth, the Sun emits shortwave radiation ( sunlight ) that passes through greenhouse gases to heat the Earth's surface. In response, the Earth's surface emits longwave radiation that is mostly absorbed by greenhouse gases. The absorption of longwave radiation prevents it from reaching space, reducing the rate at which
7475-495: The causes of 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 for earlier glaciations, making it difficult to interpret. Furthermore, this evidence
7590-463: 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 CO 2 ). Maureen Raymo , William Ruddiman and others propose that the Tibetan and Colorado Plateaus are immense CO 2 "scrubbers" with a capacity to remove enough CO 2 from the global atmosphere to be
7705-710: The continental ice sheets are the Greenland and Antarctic ice sheets and smaller glaciers such as on Baffin Island . The definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap . The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid- Cenozoic ( Eocene-Oligocene Boundary ). The term Late Cenozoic Ice Age is used to include this early phase. Ice ages can be further divided by location and time; for example,
7820-405: The continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis , which are the two major sinks for CO 2 at present." It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian explosion , though this model is recent and controversial. The Andean-Saharan occurred from 460 to 420 million years ago, during
7935-431: 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
8050-540: The current glaciation, more temperate and more severe periods have occurred. The colder periods are called glacial periods , the warmer periods interglacials , such as the Eemian Stage . There is evidence that similar glacial cycles occurred in previous glaciations, including the Andean-Saharan and the late Paleozoic ice house. The glacial cycles of the late Paleozoic ice house are likely responsible for
8165-410: The decreasing concentration of water vapor, an important greenhouse gas. Rather than thinking of longwave radiation headed to space as coming from the surface itself, it is more realistic to think of this outgoing radiation as being emitted by a layer in the mid- troposphere , which is effectively coupled to the surface by a lapse rate . The difference in temperature between these two locations explains
8280-617: The deposition of cyclothems . Glacials are characterized by cooler and drier climates over most of 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. The glacials and interglacials coincide with changes in orbital forcing of climate due to Milankovitch cycles , which are periodic changes in Earth's orbit and
8395-689: The difference between surface emissions and emissions to space, i.e., it explains the greenhouse effect. A greenhouse gas (GHG) is a gas which contributes to the trapping of heat by impeding the flow of longwave radiation out of a planet's atmosphere. Greenhouse gases contribute most of the greenhouse effect in Earth's energy budget . Gases which can absorb and emit longwave radiation are said to be infrared active and act as greenhouse gases. Most gases whose molecules have two different atoms (such as carbon monoxide, CO ), and all gases with three or more atoms (including H 2 O and CO 2 ), are infrared active and act as greenhouse gases. (Technically, this
8510-552: The early Proterozoic Eon. Several hundreds of kilometers of the Huronian Supergroup are exposed 10 to 100 kilometers (6 to 62 mi) 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 found near Marquette, Michigan , and correlation has been made with Paleoproterozoic glacial deposits from Western Australia. The Huronian ice age
8625-466: The effect is even greater with carbon dioxide. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901. The greenhouse effect on Earth is defined as: "The infrared radiative effect of all infrared absorbing constituents in the atmosphere. Greenhouse gases (GHGs), clouds , and some aerosols absorb terrestrial radiation emitted by the Earth’s surface and elsewhere in
8740-728: The existence of glacial periods during the Valanginian , Hauterivian , and Aptian stages of the Early Cretaceous. Ice-rafted glacial dropstones indicate that in the Northern Hemisphere , ice sheets may have extended as far south as the Iberian Peninsula during the Hauterivian and Aptian. Although ice sheets largely disappeared from Earth for the rest of the period (potential reports from
8855-519: The first person to suggest drifting sea ice was a cause of the presence of erratic boulders in the Scandinavian and Baltic regions. In 1795, the Scottish philosopher and gentleman naturalist, James Hutton (1726–1797), explained erratic boulders in the Alps by the action of glaciers. Two decades later, in 1818, the Swedish botanist Göran Wahlenberg (1780–1851) published his theory of a glaciation of
8970-565: 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),
9085-417: 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 retreat into lower latitudes. This evidence is also difficult to interpret because it requires: Despite the difficulties, analysis of ice core and ocean sediment cores has provided a credible record of glacials and interglacials over
9200-421: The greenhouse effect retains heat by restricting radiative transfer through the air and reducing the rate at which thermal radiation is emitted into space. The existence of the greenhouse effect, while not named as such, was proposed as early as 1824 by Joseph Fourier . The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that
9315-434: The historical warm interglacial period that looks most like the current one and from this have predicted that the next glacial period would usually begin within 1,500 years. They go on to predict that emissions have been so high that it will not. 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
9430-503: The last 1.5 million years were associated with northward shifts of melting Antarctic icebergs which changed ocean circulation patterns, leading to more CO 2 being pulled out of the atmosphere . The authors suggest that this process may be disrupted in the future as the Southern Ocean will become too warm for the icebergs to travel far enough to trigger these changes. Matthias Kuhle 's geological theory of Ice Age development
9545-484: The last glacial period the sea-level 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
9660-512: The latest Quaternary Ice Age ). Outside these ages, Earth was previously thought to have been ice-free even in high latitudes; such periods are known as greenhouse periods . However, other studies dispute this, finding evidence of occasional glaciations at high latitudes even during apparent greenhouse periods. Rocks from the earliest well-established ice age, called the Huronian , have been dated to around 2.4 to 2.1 billion years ago during
9775-456: The longwave radiation emitted by the surface, thus accumulating energy and warming the Earth's surface. The existence of the greenhouse effect, while not named as such, was proposed as early as 1824 by Joseph Fourier . The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and
9890-467: The low solar irradiation at the time as well as reduced geothermal activities , the combination of increasing free oxygen (which causes oxidative damage to organic compounds ) and climatic stresses likely caused an extinction event , the first and longest lasting in the Earth's history, which wiped out most of the anaerobe -dominated microbial mats both on the Earth's surface and in shallow seas . In 1907, Arthur Philemon Coleman first inferred
10005-475: 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. Greenhouse effect The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source as in
10120-664: The more recent impression that the entire time period represents a single glacial event. The term Huronian is used to describe a lithostratigraphic supergroup and should not be used to describe glacial cycles, according to The North American Stratigraphic Code, which defines the proper naming of geologic physical and chrono units. Diachronic or geochronometric units should be used. The Gowganda Formation (2.3 Gya) contains "the most widespread and most convincing glaciogenic deposits of this era", according to Eyles and Young. In North America, similar-age deposits are exposed in Michigan,
10235-484: The most recent glacial periods, ice cores provide climate proxies , both from the ice itself and from atmospheric samples provided by included bubbles of air. Because water containing lighter isotopes has a lower heat of evaporation , its proportion decreases with warmer conditions. This allows a temperature record to be constructed. This evidence can be confounded, however, by other factors recorded by isotope ratios. The paleontological evidence consists of changes in
10350-526: The motion of tectonic plates resulting in changes in the relative location and amount of continental and oceanic crust on Earth's surface, which affect wind and ocean currents ; variations in solar output ; the orbital dynamics of the Earth–Moon system; the impact of relatively large meteorites and volcanism including eruptions of supervolcanoes . Some of these factors influence each other. For example, changes in Earth's atmospheric composition (especially
10465-459: 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. Within
10580-623: The oldest to youngest, the Ramsay Lake, Bruce, and Gowganda formations. Although there are other glacial deposits recognized throughout the world at this time, the Huronian is restricted to the region north of Lake Huron , between Sault Ste. Marie, Ontario , and Rouyn-Noranda , Quebec. Other similar deposits are known from elsewhere in North America, as well as Australia and South Africa. The Huronian glaciation broadly coincides with
10695-427: The past 800,000 years, ice core data shows that carbon dioxide has varied from values as low as 180 ppm to the pre-industrial level of 270 ppm. Paleoclimatologists consider variations in carbon dioxide concentration to be a fundamental factor influencing climate variations over this time scale. Hotter matter emits shorter wavelengths of radiation. As a result, the Sun emits shortwave radiation as sunlight while
10810-521: 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. There have been at least five major ice ages in Earth's history (the Huronian , Cryogenian , Andean-Saharan , late Paleozoic , and
10925-422: The range of 4–100 microns. Greenhouse gases that were largely transparent to incoming solar radiation are more absorbent for some wavelengths in this range. The atmosphere near the Earth's surface is largely opaque to longwave radiation and most heat loss from the surface is by evaporation and convection . However radiative energy losses become increasingly important higher in the atmosphere, largely because of
11040-400: The recognition of diamictite , that is interpreted to be of glacial origin. Deposition of the Huronian succession is interpreted to have occurred within a rift basin that evolved into a largely marine passive margin setting. The glacial diamictite deposits within the Huronian are on par in thickness with Quaternary analogs. The three glacial diamictite-bearing units of the Huronian are, from
11155-414: The reduced greenhouse effect and partly because solar luminosity and/or geothermal activities were also lower at that time, leading to an icehouse Earth . After the combined impact of oxidization and climate change devastated the anaerobic biosphere (then likely dominated by archaeal microbial mats ), aerobic organisms capable of oxygen respiration were able to proliferate rapidly and exploit
11270-502: The reduction in greenhouse effect . Popular perception is that one or more of the glaciations may have been snowball Earth events, when all or most of Earth's surface was covered in ice. However the palaeomagnetic evidence that suggests ice sheets were present at low latitudes is contested, and the glacial sediments (diamictites) are discontinuous, alternating with carbonate and other sedimentary rocks, indicating temperate climates, providing scant evidence for global glaciation. Before
11385-567: The reduction in weathering causes an increase in the greenhouse effect . There are three main contributors from the layout of the continents that obstruct the movement of warm water to the poles: Since today's Earth has a continent over the South Pole and an almost land-locked ocean over the North Pole, geologists believe that Earth will continue to experience glacial periods in the geologically near future. Some scientists believe that
11500-408: The retained energy goes into warming the oceans, with much smaller amounts going into heating the land, atmosphere, and ice. A simple picture assumes a steady state, but in the real world, the day/night ( diurnal ) cycle, as well as the seasonal cycle and weather disturbances, complicate matters. Solar heating applies only during daytime. At night the atmosphere cools somewhat, but not greatly because
11615-469: The role of weathering). Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages, such as the movement of continents and volcanism. The Snowball Earth hypothesis maintains that the severe freezing in the late Proterozoic was ended by an increase in CO 2 levels in the atmosphere, mainly from volcanoes, and some supporters of Snowball Earth argue that it
11730-417: The size of the greenhouse effect. Different substances are responsible for reducing the radiation energy reaching space at different frequencies; for some frequencies, multiple substances play a role. Carbon dioxide is understood to be responsible for the dip in outgoing radiation (and associated rise in the greenhouse effect) at around 667 cm (equivalent to a wavelength of 15 microns). Each layer of
11845-500: The spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods , glacials or glacial advances, and interglacial periods, interglacials or glacial retreats. Earth is currently in an interglacial, and the last glacial period ended about 11,700 years ago. All that remains of
11960-557: 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 1835–36 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
12075-430: The surface and in the layers below. The power of outgoing longwave radiation emitted by a planet corresponds to the effective temperature of the planet. The effective temperature is the temperature that a planet radiating with a uniform temperature (a blackbody ) would need to have in order to radiate the same amount of energy. This concept may be used to compare the amount of longwave radiation emitted to space and
12190-481: The temperatures over land by increased albedo as noted above. Furthermore, under this hypothesis the lack of oceanic pack ice allows increased exchange of waters between the Arctic and the North Atlantic Oceans, warming the Arctic and cooling the North Atlantic. (Current projected consequences of global warming include a brief ice-free Arctic Ocean period by 2050 .) Additional fresh water flowing into
12305-477: The term ice age is defined by the presence of extensive ice sheets in the northern and southern hemispheres. By this definition, the current Holocene period is an interglacial period of an ice age. The accumulation of anthropogenic greenhouse gases is projected to delay the next glacial period. In 1742, Pierre Martel (1706–1767), an engineer and geographer living in Geneva , visited the valley of Chamonix in
12420-547: The tilt of Earth's rotational axis. 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. Moreover, anthropogenic forcing from increased greenhouse gases
12535-422: The warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide. She concluded that "An atmosphere of that gas would give to our earth a high temperature..." John Tyndall was the first to measure the infrared absorption and emission of various gases and vapors. From 1859 onwards, he showed that the effect was due to a very small proportion of
12650-552: The world. When the Bavarian naturalist Ernst von Bibra (1806–1878) visited the Chilean Andes in 1849–1850, the natives attributed fossil moraines to the former action of glaciers. 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,
12765-550: Was caused by the elimination of atmospheric methane , a greenhouse gas , during the Great Oxygenation Event . The next well-documented ice age, and probably the most severe of the last billion years, occurred from 720 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which glacial ice sheets reached the equator, possibly being ended by the accumulation of greenhouse gases such as CO 2 produced by volcanoes. "The presence of ice on
12880-429: Was caused in the first place by a reduction in atmospheric CO 2 . The hypothesis also warns of future Snowball Earths. In 2009, further evidence was provided that changes in solar insolation provide the initial trigger for Earth to warm after an Ice Age, with secondary factors like increases in greenhouse gases accounting for the magnitude of the change. The geological record appears to show that ice ages start when
12995-455: 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
13110-403: Was highly reactive and toxic to the anaerobic biosphere . Furthermore, atmospheric methane was depleted by oxygen and reduced to trace gas levels, and replaced by much less powerful greenhouse gases such as carbon dioxide and water vapor , the latter of which was also readily precipitated out of the air at low temperatures. Earth's surface temperature dropped significantly, partly because of
13225-526: 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, triggering
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