Ice Age

#redirect Talk:Ice Age (movie)

Ice Age

#REDIRECT Ice age

Ice age

Vostok,_Antarctica_ice_core_over_the_last_400_000_years">Image:Vostok-ice-core-petit.png|thumb|right|Variations in CO2, temperature and dust from the Vostok, Antarctica ice core over the last 400 000 years An ice age is a period of long-term downturn in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers ("glaciation"). Glaciology, ''ice age'' is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist). More colloquially, when speaking of the last few million years, ''ice age'' is used to refer to colder periods with extensive ice sheets over the North American and European continents: in this sense, the last ice age ended about 10,000 years ago. This article will use the term ''ice age'' in the former, glaciological, sense; and use the term 'glacial periods' for colder periods during ice ages and 'interglacial' for the warmer periods. During the last few million years there have been many glacial periods, occurring at 40–100,000 year frequencies. These are the best studied. There have been four major ice ages in the further past. == Origin of ice age theory == The idea that, in the past, glaciers had been far more extensive was folk knowledge in some alpine regions of Europe (Imbrie and Imbrie, p25, quote a woodcutter telling de Charpentier of the former extent of the Switzerland Grimsel glacier). No single person invented the idea [http://academic.emporia.edu/aberjame/histgeol/agassiz/glacial.htm]. Between 1825 and 1833 Jean de Charpentier assembled evidence in support of this idea. In 1836 Charpentier convinced Jean Louis Rodolphe Agassiz of the theory, and Agassiz published it in his book ''�tude sur les glaciers'' of 1840. At this early stage of knowledge what were being studied were the glacial periods within the past few hundred thousand years, during the current ice age. The far earlier ice ages were unsuspected. == Major ice ages == There have been at least four major ice ages in the Earth's past. The earliest hypothesized ice age is believed to have occurred around 2700 to 2300 million years ago during the early Proterozoic Age. The earliest well-documented ice age, and probably the most severe of the last 1000 million years, occurred from 800 to 600 million years ago (the Cryogenian period) and it has been suggested that it produced a Snowball Earth in which permanent sea ice extended to or very near the equator. It has been suggested that the end of this ice age was responsible for the subsequent Cambrian Explosion, though this theory is recent and controversial. A minor ice age occurred from 460 to 430 million years ago. There was an extensive ice age from 350 to 260 million years ago. The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica, but intensified during the Pleistocene (starting around 3 million years ago) with the spread of ice sheets in the Northern Hemisphere. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000 and 100,000 year time scales. The last glacial period ended about 10,000 years ago. A [http://www.scotese.com/lastice.htm map is available] showing estimated ice extent and coastline changes during the last glacial period. The timing of ice ages throughout geologic history is in part controlled by the position of the continental plates on the surface of the Earth. When landmasses are concentrated near the polar regions, there is an increased chance for snow and ice to accumulate. Small changes in solar energy can tip the balance between summers in which the winter snow mass completely melts and summers in which the winter snow persists until the following winter. See the web site [http://www.scotese.com/earth.htm Paleomap Project] for images of the polar landmass distributions through time. Due to the positions of Greenland, Antarctica, and the northern portions of Europe, Asia, and North America in polar regions, the Earth today is considered to be prone to ice age glaciations. 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. It took some time for the current theory to be worked out. Analyses of ice cores and ocean sediment cores unambiguously show the record of glacials and interglacials over the past few million years. == Interglacials == In between ice ages, there are multi-million year periods of more temperate climate, but also within the ice ages (or at least within the last one), temperate and severe periods occur. The colder periods are called 'glacial periods', the warmer periods 'interglacials', such as the Eemian interglacial era. We are in an interglacial period now, the last retreat ending about 10,000 years ago. There appears to be a folk wisdom that "the typical interglacial period lasts ~12,000 years" but this is hard to substantiate from the evidence of ice core records. For example, an article in Nature [http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v429/n6992/abs/nature02599_fs.html] argues that the current interglacial might be most analogous to a previous interglacial that lasted 28,000 years. Nonetheless, fear of a new glacial period starting soon does exist (See: global cooling). However, many now believe that anthropogenic (i.e. manmade) forcing from increased "greenhouse gases" would outweigh any Milankovitch cycles (orbital) forcing; and some recent considerations of the orbital forcing have even argued that in the absence of human perturbations the present interglacial could potentially last 50,000 years. == Causes of ice ages == The cause of ice ages remain controversial, both for the large-scale ''ice age'' periods and the smaller ebb and flow of ''glacial/interglacial'' periods within an ice age. The general consensus is that it is a combination of up to three different factors: atmospheric composition (particularly the fraction of carbon dioxide and methane), changes in the Earth's orbit around the Sun known as Milankovitch cycles (and possibly the Sun's orbit around the galaxy), and the arrangement of the continents. The first of these three factors is probably responsible for much of the change, especially for the first ice age. The "Snowball Earth" hypothesis maintains that the severe freezing in the late Proterozoic was both caused and ended by changes in CO₂ levels in the atmosphere. However, the other two factors do matter. An abundance of land within the arctic and antarctic circles appears to be a necessity for an ice age, probably because the land masses provide space on which snow and ice can accumulate during cooler times and thus trigger positive feedback processes like albedo changes. The Earth's orbit does not have a great effect on the long term causation of ice ages, but does seem to dictate the pattern of multiple freezings and thawings that take place within the current ice age. The complex pattern of changes in Earth's orbit and the change of albedo may influence the occurrence of glacial and interglacial phases — this was first explained by the theory of Milutin Milankovic. The present ice ages are 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 Milankovic orbital forcing periods is so good that orbital forcing is the generally accepted explanation. 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 can change and significantly redistribute the sunlight received by the Earth. Of particular importance are changes in the tilt of the Earth's axis, which impact the intensity of seasons. For example, the amount of solar influx in July at 65 degrees north latitude is calculated to vary by as much as 25% (from 400 watt/m² to 500 W/m², see graph at [http://www.museum.state.il.us/exhibits/ice_ages/insolation_graph.html]). It is widely believed that ice sheets advance when summers become too mild to melt all of the accumulated snowfall from the previous winter. Some workers believe that the strength of the orbital forcing appears to be too small to trigger glaciations, but feedback mechanisms like CO₂ may explain this mismatch. While Milankovic forcing predicts that cyclic changes in the Earth's Orbit#Orbital_parameters 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 thousand years the dominant inter/glacial oscillation has been 100 thousand years, which corresponds to changes in Earth's eccentricity (orbit) and orbital inclination, and yet is by far the weakest of the three frequencies predicted by Milankovic. During the period 3.0 — 0.8 million years ago the dominant pattern of glaciation corresponded to the 41 thousand year period of changes in Earth's obliquity (tilt of the axis). The reasons for preferring one frequency to 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. The "traditional" Milankovitch explanation struggles to explain the dominance of the 100,000 year cycle over the last 8 cycles. Richard A. Muller and Gordon J. MacDonald [http://www.pnas.org/cgi/content/full/94/16/8329] [http://muller.lbl.gov/pages/glacialmain.htm] [http://muller.lbl.gov/papers/sciencespectra.htm] and others have pointed out that those calculations are for a two-dimensional orbit of Earth but the three-dimensional orbit also has a 100 thousand year cycle of orbital inclination. They proposed that these variations in orbital inclination lead to variations in insolation, as the earth moves in and out of known dust bands in the solar system. Although this is a different mechanism to the traditional view, the "predicted" periods over the last 400,000 years are nearly the same. The Muller and MacDonald theory, in turn, has been challenged by Rial [http://pangea.stanford.edu/Oceans/GES290/Rial1999.pdf]. Another worker, Ruddiman has suggested a plausible model that explains the 100,000 cycle by the modulating effect of eccentricity (weak 100,000 year cycle) on precession (23,000 year cycle) combined with greenhouse gas feedbacks in the 41,000 and 23,000 year cycles. And yet another theory has been advanced by Peter Huybers who argued that the 41,000 year cycle has always been dominant, but that the Earth has entered a mode of climate behavior where only the 2nd or 3rd cycle triggers an ice age. This would imply that the 100,000 year periodicity is really an illusion created by averaging together cycles lasting 80 and 120 thousand years. This theory is consistent with the existing uncertainties in dating, but not widely accepted at present (Nature 434, 2005, [http://web.mit.edu/~phuybers/www/Doc/Obliquity_HuybersWunsch.pdf]). == Recent glacial and interglacial phases == [[Image:Pleistocene north ice map.jpg|thumb|right|The maximum extent of glacial ice in the north polar area during Pleistocene time.]] The last glacial and interglacial phases of the Pleistocene are named, from most recent to most distant, as follows (names before the '/' are North America, names after it Northern European, dates in thousand years BCE. In the United Kingdom, Eastern Europe and the Alps yet other names are used; see Geology_of_the_United_Kingdom#Quaternary_Period for UK names): {| | Wisconsin glaciation | glacial period || 15 – 70 |- | Eemian interglacial era | interglacial || 70 – 130 |- | Illinoian glaciation | glacial || 130 – 180 |- | Yarmouth interglacial era | interglacial || 180 – 230 |- | Kansan glaciation | glacial || 230 – 300 |- | Aftonian interglacial era | interglacial || 300 – 330 |- | Nebraskan glaciation | glacial || 330 – 470 |- | Waalian interglacial era | interglacial || 470 – 540 |- | Donau II glaciation | glacial || 540 – 550 |- | Tiglian interglacial era | interglacial || 550 – 585 |- | Donau I glaciation | glacial || 585 – 600 |} The end of the last glacial also corresponds quite closely to the development of permanent human settlements and agriculture, and it is possible that there is a connection between the two events. == Glaciation in North America == The Wisconsinan glaciation has had a considerable effect on the landscape of the Northern Hemisphere. In North America the Great Lakes (North America) and the Finger Lakes were carved by ice deepening old valleys. The old Teays River drainage system was radically altered and largely reshaped into the Ohio River drainage system. Other rivers were dammed and diverted to new channels, such as the Niagara Falls, which formed a dramatic waterfall and gorge, when the waterflow encountered a limestone escarpment. Another similar waterfall near Syracuse, New York is now dry. Long Island was formed from glacial till, and the watersheds of Canada were so severely disrupted that they are still sorting themselves out — the plethora of lakes on the Canadian Shield in northern Canada can be almost entirely attributed to the action of the ice. As the ice retreated and the rock dust dried, winds carried the material hundreds of miles, forming beds of loess many dozens of feet thick in the Missouri River. Isostatic rebound continues to reshape the Great Lakes and other areas formerly under the weight of the ice sheets. ==Reference== *Imbrie, John and Katherine Palmer Imbrie. ''Ice ages: Solving the Mystery''. Cambridge, Massachusetts: Harvard University Press, 1979, 1986 (reprint). ISBN 089490020X; ISBN 0894900153; ISBN 0674440757. ==See also== * Geology * Timeline of glaciation *Varanger glaciation *Sturtian-Varangian *Glacial_erratic *Glacial Grooves *Glacier * Little Ice Age * Genesee River: Glacial Geology — Relief maps of some glacial landforms and drainage alterations in western NY. ==External links== *http://www.globalchange.umich.edu/globalchange1/current/lectures/samson/climate_patterns/ Glaciology History of climate ms:Zaman air batu

Ice age

= Still in a series of glaciations = 'A minor series of glaciations occurred from 460 to 430 million years ago. Two more extensive glaciations were from 350 million years before present to 250 million, and from 4 million years ago to about 10,000 years ago (the Pleistocene period).' Isn't there general agreement that we're still in a "series of gaciation" - that is, an Ice Age? Glaciations have gome and gone regularly for the last 4 million years, and we're in between two now. As long as we're talking about "series of glaciations", I think the "to about 10k years ago" is misleading. **I recently saw a show on the subject on the Discovery Channel. The theory is as follows; x number of million yrs ago, during continental shifting, the gap between North and South America was formed, essentially Central America. Until this time, the north pole was very cold but saw no precipitation due to the dry air. However, when Panama was formed, underwater oceanic currents could no longer flow from the Atlantic to the Pacific (or was it the Pac to the Atl?) ansd were thus subsequently diverted towards the North bringing along with it warm air, water and humidity. Only then did the North Pole see snow start to fall, eventually giving birth to the Ice Age. The theory was very well explained and illustrated, and I think it warrants further investigation as I see no mention of it here. - AL HERES THE LINK [http://dsc.discovery.com/convergence/iceworld/iceworld.html] ---- == Wait and see, but maybe humans preventing ice age == : I'm not sure - it may be impossible to say unless another one actually occured. It seems for the present we have emitted enough CO₂ to make it less likely. ---- == Warmed humidity can cause more snowfall == : A slight increase in temperature could make increased winter snowfall in colder regions. If temperature growth is then terminated this situation will continue indefinetely and thus theoretically hasten the arrival of a new ice age. : I remember reading a news story (I can't remember exactly where, though) that measurements of glaciers in the Alps in Europe have confirmed that we are in a "little Ice Age." ''However,'' this trend towards increased glacial action is being offset by the effects of global warming, which is causing many glaciers and much of the Antarctic ice floe to melt. -- User:Modemac ---- === Arctic Ocean thawing may cause snow bloom === : There also is concern that if the Arctic Ocean surface loses its ice, heating will occur for a few years due to the water absorbing much more heat than now. The exposed ocean would probably raise temperatures in this hemisphere. But much more water vapor would also be emitted, which during winter could cause a much larger snow cover than usual. A larger snow cover might not melt off as much as it presently does, causing a cooler summer and colder temperatures the following winter. This could cause feedback with increasingly colder or longer winters, as the glaciers begin to accumulate. : Back to the immediate subject -- It seems unlikely that whatever has been powerful enough to cause glaciations during 4my would happen to stop just when we arrive. It could have happened. Or we might warm our way out of the cycle. Or there is another glaciation in our future. : I think we need a few thousand more years before we have a trend which suggests the glaciation cycle has ended. Put on your calendar to update this article then. -- User:SEWilco 07:39, 13 Aug 2003 (UTC) ---- = Orbital Obliquity additions = (User:William M. Connolley 20:01, 20 Jan 2004 (UTC)) SEW added some stuff, including: "Han-Shou Liu[2] and others[3] have pointed out that changes in obliquity seem to be relevant", which are: : http://www.worldscinet.com/fnl/03/0301/S0219477503001099.html and : http://www.people.virginia.edu/~jba5b/c2.htm The first of these appears to be about "Orbital Noise of the Earth Causes Intensity Fluctuation in the Geomagnetic Field" and doesn't seem to have any relevance to climate/ice age. : (User:SEWilco 12:23, 1 Feb 2004 (UTC)) :* It's not a climate reference, it is a reference of obliquity periods: ''we show that noise spectrum of the obliquity frequency have revealed a series of frequency periods centered at 250-, 100-, 50-, 41-, 30-, and 26-ky''. I thought there was little enough text in that summary that it was apparent what is relevant to obliquity. There being many frequencies is of interest. :: (User:William M. Connolley 19:19, 1 Feb 2004 (UTC)) I still don't get it. "Han-Shou Liu[1] and others[2] have pointed out that changes in obliquity seem to be relevant.". Relevant to what? Not climate, you seem to be saying. :* I was trying to keep it brief, to point out the topic exists. I mentioned the full name of Liu for those wanting to get more information. Liu is referenced by many others, and the above is also of interest because it is recent work of his, and it shows some differences to his earlier work. :: I'm not a great historian of Liu's work, and I doubt many other people are. Could we try to keep things closish to Milankovitch/Ice Age stuff? "Han-Shou Liu[1] and others[2] have pointed out that changes in obliquity seem to be relevant." is brief to the point of incomprehensibility: you need to expand this if it is to make any sense. :: I point out that AFAIK there is no dispute about the various orbital periods of the earth. ::* http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v358/n6385/abs/358397a0.html ''Frequency variations of the Earth's obliquity and the 100-kyr ice-age cycles'' ::: Ah, thats a bit more like it. ::* http://denali.gsfc.nasa.gov/personal_pages/liu/liu.html Liu's NASA GSFC page ::: He doesn't seem to have been active recently. But thats OK. ::* http://www.umbrars.com/sr/1998/liu.htm ''WAVELET SPECTRAL ANALYSIS OF THE EARTHS ORBITAL VARIATIONS AND PALEOCLIMATIC CYCLES'' ::: Odd, why isn't that listed above? ::* http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.earth.28.1.419 ''New Perspectives on Orbitally Forced Stratigraphy'' (reference to Liu) :::Didn't find it but I assume you're correct. (User:William M. Connolley 19:19, 1 Feb 2004 (UTC)) From what I'm reading above, Liu seems to think there is a problem with the 100 kyr ecc cycle causing ice ages. Thats OK, because everyone knows that: the forcing is too weak. People invoke various geophysical explanations for this, e.g. response times for ice sheets. Jus to be clear: I've no objections to the article talking about Liu's work, but your one-sentence bit just didn't make sense to me. The second contains useful stuff but some nonsense ("Muller and MacDonald theorize that this narrow peak in this and other data implies an astronomical origin" is true but misleading, implying they originated the idea; "They further suggest that this narrow peak has been missed due to the spectral analysis methods used" is nonsense; the peak in question is the commonplace 100 kyr peak). :* There are problems with the ''commonplace 100 kyr peak''. Popularity does not determine correctness, particularly when there are oddities which may be major failures. (User:SEWilco 12:23, 1 Feb 2004 (UTC)) ::(User:William M. Connolley 19:19, 1 Feb 2004 (UTC)) Yes yes but you miss my point. The article refed is garbled. :::(User:SEWilco 18:25, 2 Feb 2004 (UTC)) Yes, that paper is not of top quality. The contrasts in it were useful. I think the Rial (the pretty colour pic) work *supports* the Milank stuff and opposes Muller etc. :* Yes, that is what Rial says. I included that link because it refers to several studies, which is useful for those needing more details. You mention *supports* as if only full support of an idea should be provided, but I'm sure you did not intend to imply that. (User:SEWilco 12:23, 1 Feb 2004 (UTC)) :: Rial opposing Muller etc is probably worth putting into the article. "However, Milankovic cycles predict an extremely cold period 400 thousand years ago which seems to have not happened." needs a ref. :* http://www.pnas.org/cgi/reprint/94/16/8329.pdf although I do not remember if that is one of the sources which I originally checked. Page 2, second column, first paragraph, refers to a review by Imbrie et al. (User:SEWilco 12:23, 1 Feb 2004 (UTC)) ::I think oyu've misunderstood this. It says stuff about the 400 kyr cycle. Not that Milank predicts cold 400 kyr ago. Could you quote more precisely if you want to support this point. ::: Yes, I did misunderstand. Theory indicates there is a 400 kyr cycle, which should have happened in the past 400 kyr. But records are not showing anything dramatically unusual in the past 400 kyr. There was an unusually long mild period 400 kyr ago ("Stage 11") which might have been due to the 400 kyr cycle, which implies the Holocene may be similar. (User:SEWilco 18:25, 2 Feb 2004 (UTC)) "Milankovic patterns also have two peaks near 100 thousand years but not at 100 thousand years." - not sure this is v important - peaks in spectral space don't nec correspond in real time. :* The issue is that the other methods included a process specifically to remove details. This has benefits, but might have hidden information relevant to the problem because the lost details fit in with other information. (User:SEWilco 12:23, 1 Feb 2004 (UTC)) ::Yes, but again: geophysically, there are mechanisms (ice sheet time constants for example) that might reasonably be expected to blur spectral peaks. I get the impression that some of these people are taking their time series a bit too seriously and not doing enough physics. ===Para removed to Talk for work=== Following the lack of reply to the above comments, the offending para is removed to here, and a v brief summary left behind (User:William M. Connolley 19:45, 25 Jan 2004 (UTC)). However, Milankovic cycles predict an extremely cold period 400 thousand years ago which seems to have not happened. Milankovic patterns also have two peaks near 100 thousand years but not at 100 thousand years. Richard A. Muller and Gordon J. MacDonald have pointed out that those calculations are for a two-dimensional orbit of Earth but the orbital inclination in the three-dimensional orbit has a 100 thousand year peak. Earth's movements through and out of the plane of the ecliptic of all planets match the temperature patterns of the past 1 million years. He suggests this might be due to an interstellar dust cloud or increased collisions in the Themis and Koronis asteroid families causing their dust band to increase. The sudden change 1 million years ago from 41 thousand year cycles to 100 thousand cycles is not explained by unchanging two-dimensional Milankovic cycles but is explained by a cause which is affected by the inclination cycle. Han-Shou Liu[http://www.worldscinet.com/fnl/03/0301/S0219477503001099.html] and others[http://www.people.virginia.edu/~jba5b/c2.htm] have pointed out that changes in obliquity seem to be relevant. === Para modified === How does this look? (User:SEWilco 18:47, 2 Feb 2004 (UTC)) Again? (User:SEWilco 10:07, 4 Feb 2004 (UTC)) However, Milankovic cycles have periods of 95, 125, and 400 thousand years[http://muller.lbl.gov/papers/geology2.html]. Difficulties with Milankovic predictions include that the 400 kyr cycle is not detectable in most records, the major climate cycle has a sharp 100 thousand year peak (instead of 95 and 125 kyr), and some orbital changes which were expected to end an ice age actually took place after the ice age had already ended. Richard A. Muller[http://muller.lbl.gov/papers/nature.html], Gordon J. MacDonald[http://muller.lbl.gov/papers/sciencespectra.htm], and others have pointed out that those calculations are for a two-dimensional orbit of Earth but the three-dimensional orbit also has a 100 thousand year cycle of orbital inclination. Earth's movements through and out of the plane of the ecliptic of all planets match the temperature patterns of the past 1 million years. Being in the plane of Jupiter's orbit seems to have the greatest effect. Suspected causes include solar radiation or atmospheric effects due to an interstellar dust cloud or a dust band in our solar system. The change 1 million years ago, during the Middle Pleistocene Revolution, from 41 thousand year cycles to 100 thousand cycles is not explained by unchanging two-dimensional Milankovic cycles but is explained by a cause which is related to the orbital inclination cycle, such as increased collisions in the Themis and Koronis asteroid families. J.A. Rial[http://www.geosci.unc.edu/faculty/rial/Pacemaking.pdf] replies with more details for traditional explanations. :(User:William M. Connolley 21:17, 2 Feb 2004 (UTC)) I don't like the start. The basic point is trying to explain the competing mechanisms for causing the ice ages. Firstly, the 400 kyr stuff isn't very relevant: "tradiational" Milank doesn't predict a 400 kyr period, so the fact that its missing doesn't help much. Err, and then again Muller says: "''In contrast, spectral analysis of the coarse component fraction of the sediment (primarily foraminifera) shows a structure characteristic of standard Milankovitch theory, with a triplet of peaks with periods near those expected from the Earth's eccentricity: 95, 125, and 400 k.y.''", err, which seems to suggest that 400 kyr period *is* found in the record. The story needs to be straight. :: (User:SEWilco 10:07, 4 Feb 2004 (UTC)) Right, although the 400 ky being sometimes detectable is a confirmation that the 2-D orbital models do have some effect. Muller does say 400 is ''usually'' not detectable. ::: (User:William M. Connolley 17:36, 4 Feb 2004 (UTC)) This still isn't a straight story. Muller says "Although the spectra of eccentricity and inclination are quite different, they are remarkably easy to confuse for two reasons: First, it has become traditional to ignore the absence of the expected 400 k.y. eccentricity cycle since it is difficult to see in the short records and plausible effects have been postulated that could suppress it.". So I don't see concentrating on the 400 kyr cycle is a good idea. :(WMC) And I must have missed "and some warming changes happen before the orbital causes" as well. :: (SEW) Search for "causality" in Muller's [http://muller.lbl.gov/papers/nature.html Eccentricity is ruled out]. But I see my phrasing is not good. Maybe "and some orbital changes which were expected to end an ice age actually took place after the ice age had already ended". :::Um yes, its just about there, though not really: just references to other papers. So I don't see exactly what the problem is, just that M thinks there is one. :(WMC)The essential point of Muller, as I take it, is that the insolation modulation is *caused* by dust clouds (and the orbit of the earth carries it into and out of these) unlike the std Milank where the modulation comes directly from orbital variations. :: (SEW) Actually, Milank and Muller agree on orbital variations as being related to climate changes. :::Yes yes I understand that. The point is, that Milank and Muller predict essentially the same thing - 100 kyr cycles - but have different explanations: Milank is pure insolation (plus feedbacks) forced by orbital var, Muller is the same but orbital var leads to insol var via dust. :: Milank uses 2-D orbits and it has been believed that various effects upon solar warming caused climate alterations. Muller et al point out that the motion in the 3rd dimension seems to have a significant effect, but the reason for the effect is only speculation. Maybe Jupiter is dragging dust to form an ecliptic disk. Or maybe Jupiter is capturing incoming interstellar material, so it sometimes is shielding us. :(WMC)Where do you get the shift 1 Myr ago from? From http://muller.lbl.gov/papers/sciencespectra.htm ? In that case you need to omit "sudden", since the period from 1 Myr to 1.5 Myr ago seems to be missing. ::(SEW) 0.9 Myr Middle Pleistocene Revolution. Muller thinks an astronomical event caused the shift, while Rial and Milank depend upon subtle orbital movements with a transition period. :::Please please get into the habit of quoting text for anything controversial, or interesting, like this. I still don't know where you get the "sudden" shift idea from. :(WMC) As near as I understand it, Liu's theory is not the same as Mullers. :: (SEW) Argh. Yeah, Liu was looking at the tilt of the polar axis, not the tilt of the orbital plane. Geology, not astronomy. An alteration of a Milank parameter, not an effect of the present patterns. ::: (User:William M. Connolley 17:36, 4 Feb 2004 (UTC)) Errm. === Another try === (User:William M. Connolley 18:24, 4 Feb 2004 (UTC)) OK, we're getting a bit bogged down in detail here. Instead of nit-picking yours, let me try mine again. But first, a couple of principles... * Milank *is* still the dominant explanation, perhaps (who knows) only for reasons of inertia, but nonetheless. So the article ought to reflect that, and not have much more text on competing explanations. * I don't think either of us has really read Muller, or Rial, or other literature, in enough detail to explain their ideas really well. * So we should avoid details, and mention the ideas, and provide links to the details. With that in mind, I propose: The "traditional" Milankovitch explanation struggles to explain the dominance of the 100 kyr cycle over the last 1 Myr. Richard A. Muller and Gordon J. MacDonald [2] [3] [4] and others have pointed out that those calculations are for a two-dimensional orbit of Earth but the three-dimensional orbit also has a 100 thousand year cycle of orbital inclination. They proposed that these variations in orbital inclination lead to variations in insolation, as the earth moves in and out of dust clouds. Although this is a different ''mechanism'' to the traditional view, the "predicted" periods over the last 400 kyr are nearly the same. The Muller and MacDonald theory, in turn, has been challenged by Rial [5]. (No room for Liu, because... I don't understand what he is saying). We also seem to be in some uncertainty as to what the ice age periodicities are, and when. So a list of, last 1 Myr: 100 kyr; 1.5-2.5 Myr: 41 kyr; or whatever; would be useful. Hmm, actually, thats in the article, but the break is set at 0.8 Myr. This should be ref'd. Meanwhile, I've re-arraned the paras in the Causes section to roughly chronological: ie first ice ages first, and ending with most recent, Milank. This stuff is a touch nusatisfactory at the moment as I think that 9without a good idea in your head already) you are likely to get confused by the article as to which causes fit which periods. ==Dates of Ice Ages== All of these dates assume an old earth, just as many pages assume evolution and take it as fact. I think we should get both sides of the issue. That's why I put the young earth stuff in there. Please consider it. - User:SamE 21:21, 3 May 2004 (UTC) : (User:William M. Connolley 21:56, 2004 May 3 (UTC)) I'm sure you like the young earth stuff but I have no sympathy with it. Its essentially pollution, when put into science pages. I've just been to a science conference, which discussed - amongst other things - ice cores and ocean sediment cores. No one proposed young earth stuff: there is no scientific support for the idea at all. Scientifically, there is only one side to this. If you want to put together a page entitled something like "ice cores interpreted from a young earth perspective" then feel free. That would be OK. But I very much doubt it can be done. The debate really belongs on the young earth pages, where it is occurring as we speak... (though of course as DJC commented on the talk pages, wiki is not a debating society). == Seems as though there IS enough of a variation in insolation on a 100KY and 400KY Cycle to expect climate change == The IPCC http://www.grida.no/climate/ipcc_tar/wg1/fig2-22.htm [http://www.grida.no/climate/ipcc_tar/wg1/fig2-22.htm] indicate that there has been a major interglacial period every 100ky, including one at 400ky. Is this an error? :Your link doesn't appear to be working at the moment, but this is basically correct. Some were a little earlier than expected, some were a little late, but basically every 100kyr for the last ~800kyr or so. This includes a major glaciation at 400 kyr that cannot be predicted by traditional orbital forcing arguments. This is known as the 400 kyr problem or the "stage-11" problem (in reference the marine isotopic stages). http://www.museum.state.il.us/exhibits/ice_ages/insolation_graph.html [http://www.museum.state.il.us/exhibits/ice_ages/insolation_graph.html] shows particularly strong 400 ky cyclicity and as much as a 25% difference in insolation during one precession cycle during the more high-amplitude 100ky cycles. I would think 25% less solar energy might make a difference. http://amper.ped.muni.cz/gw/articles/html.format/orb_forc.html[http://amper.ped.muni.cz/gw/articles/html.format/orb_forc.html] shows a similar pattern, though he assumes a different solar constant and therefore gets somewhat higher average fluxes, but the amplitude af the variations is on the order of 25%. :Greg, My comment that your statements were inaccurate was not because insolation changes of this magnitude don't occur, but because you didn't cite the season and the location, and in your first post you made it sound like the changing distance was the controlling factor in changing the insolation. The annual average change in isolation is near 0 (as changes in winter cancel changes in summer), so it is very important that this be referenced as a seasonal thing. Secondly, the main cause of these changes is the precession of the Earth's axis. Eccentricity sets the envelop, but the rapid change in the strength of seasons is basically controlled by precession. :Also, in this article, orbital variability is referenced extensively already. I really feel that the details, such as what you present, belong not here but on the page regarding Milankovitch cycles. Keep in mind that this is a page dealling with ice ages in general (i.e. both the recent ones and those in deep history), so I don't think it is appropriate to create too much detail regarding the recent ice ages. I should also say that I am inclined to move some of the already existing material off of this page as well. :Greg, I will let you have another go at the statements you are making before I make additional changes, but I still am not satisfied in the way you are representing the insolation chart. User:Dragons flight 12:12, Jul 20, 2004 (UTC) =Capitalization= This article just got moved from "ice age" to "Ice Age" and I don't think that's quite right. The article itself uses lower-case throughout. Furthermore this article is discussing ice ages in general, not a specific ice age which might have the proper name "Ice Age" (as the most recent glacial period is often called). I thought I'd bring it up here first, though, since I'm no expert. User:Bryan Derksen 04:20, 26 Aug 2004 (UTC) : (User:William M. Connolley 08:49, 26 Aug 2004 (UTC)) I can't see why either. Ice age is more obvious. I proposed the change a couple weeks ago, and there has been no comment on it, so regarded it as consensus. The talk on that got moved to talk at Ice Age (movie) if you want to see it. Capitalization is not the primary issue. The problem was that people looking for information on continental glaciation first got referred to a B movie about it. In this way the "main event" got the primary page. User:Pollinator 11:35, Aug 26, 2004 (UTC) : (User:William M. Connolley 11:57, 26 Aug 2004 (UTC)) Well, people watching Ice age (climate thingy) aren't watching Ice age (movie) so didn't see your note. There is no reason at all why the change in caps to the movie should affect the other page! So I've moved it back. == Ambiguity == The end of the paragraph defining ice ages and glacial ages is very confusing. You have used ice age in two differnt ways and then you try and clarify the issues by defining glacial in terms of ice ages. I'm still not quite sure what you meant so i can't fix it. User:Logicnazi 05:18, 21 Dec 2004 (UTC) : (User:William M. Connolley 10:39, 21 Dec 2004 (UTC)) Hmm, fair point. I have attepmted to resolve this ambiguity, which also involved a fair amount of changes-for-consistency elsewhere in the article. If there is a real glacio out there, do feel free to correct. == Edits by 131.172.4.45 == I am reverting the edits by User:131.172.4.45. The user gives no citations and the stated science appears to be wrong. Veizer et al.'s strontium isotope measurements do not support a long-term relationship between continental erosion and CO2 changes. The Sr measurements suggests that the Himilayan orogeny has been uniquely profound during the Phanerozoic in it's ability to increase continental erosion (and so might contribute to recent declines in CO2), but previous mountain building events have either been too extented in time or too randomly distributed through time to significantly perturb the continental erosion budget. And as far as I know, the weak perturbations that do occur during most of the record haven't been strongly tied to CO2 changes. Further, the CO2 declines during the Carboniferous are a biological effect (the result of the evolutionary invention of lignin bearing plants and excess carbon burial) not a geological effect. It is called the Carboniferous because so much carbon ended up in the rocks after all. Also, while I don't know what qualifies as "extensive" mountain building, there was significant mountain builing in the Rocky Mountain range and Eastern Alps during the Paleogene, which doesn't fit the notion of "absense" of mountain building. User:Dragons flight 14:22, Mar 18, 2005 (UTC)

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