Talk:Ice age

From Wikipedia, the free encyclopedia

Ice age is included in the 2006 Wikipedia CD Selection, or is a candidate for inclusion in the next version. Please maintain high quality standards and, if possible, stick to GFDL-compatible images.

Contents

[edit] Changes

I think the sentence in the 'variations in solar energy output' section should be changed... "rising temperatures produce more water vapour, water vapour is a greenhouse gas (much weaker than CO2, but there will eventually be vastly more water vapour), the temperature rises, more water vapour is produced, etc." This seems to imply that water vapor is only responsible for a small part of the greenhouse effect, and it also says that their will be vastly more water vapor, when in fact their already is in relation to CO2

Semantics are important, but shouldn't we adress the blatant vandalism found in the overview?

[edit] 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 come 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 [1]

[edit] 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.

[edit] 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. -- Modemac

[edit] 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. -- SEWilco 07:39, 13 Aug 2003 (UTC)


[edit] Orbital Obliquity additions

(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.

(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.
(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.
Ah, thats a bit more like it.
He doesn't seem to have been active recently. But thats OK.
Odd, why isn't that listed above?
Didn't find it but I assume you're correct.

(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. (SEWilco 12:23, 1 Feb 2004 (UTC))
(William M. Connolley 19:19, 1 Feb 2004 (UTC)) Yes yes but you miss my point. The article refed is garbled.
(SEWilco 18:25, 2 Feb 2004 (UTC)) Yes, that paper is not of top quality. The contrasts in it were useful.
I am the author of the paper in question. I was a college student when I wrote it, and any reasonably sophisticated analysis of the same papers I cited would be more helpful than my efforts, which were really only online so that I could turn in the paper without walking to the classroom.
FWIW, the sentence above labeled nonsense should have said "the narrowness of this peak" rather than "this narrow peak". Obviously, everyone has noticed the 100k-year cycle.
The paper is certainly "not of top quality". I have no training in environmental science (outside of a few undergrad classes). The paper should not be cited here. (it isn't now) Jim Apple 04:14, 23 January 2006 (UTC)
This is all moot anyway
But its certainly an interesting postscript! Thanks for the info William M. Connolley 09:48, 23 January 2006 (UTC).

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. (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.

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. (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. (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.

[edit] 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 (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[2] and others[3] have pointed out that changes in obliquity seem to be relevant.

[edit] Para modified

How does this look? (SEWilco 18:47, 2 Feb 2004 (UTC)) Again? (SEWilco 10:07, 4 Feb 2004 (UTC))

However, Milankovic cycles have periods of 95, 125, and 400 thousand years[4]. 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[5], Gordon J. MacDonald[6], 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[7] replies with more details for traditional explanations.


(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.
(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.
(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 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.
(William M. Connolley 17:36, 4 Feb 2004 (UTC)) Errm.


[edit] Another try

(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.

[edit] 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. - SamE 21:21, 3 May 2004 (UTC)

(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.
The only part of that comment that's correct is the last line. Scientifically, the earth is less than 10,000 years old. The Ice Age most likely occured a little over 4000 years ago, from the most modern scientific evidence. The only "pollution in science pages" I see is claiming that an archaic theory that rests upon the earth being far older than scientifically possible is fact. Evolution is the antithesis of science. - MarioFanaticXV

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).

[edit] 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 [8] 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 [9] 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[10] 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. Dragons flight 12:12, Jul 20, 2004 (UTC)

[edit] 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. Bryan 04:20, 26 Aug 2004 (UTC)

(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. Pollinator 11:35, Aug 26, 2004 (UTC)

(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.

[edit] 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. Logicnazi 05:18, 21 Dec 2004 (UTC)

(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.
In my experience, which includes some glaciology, Ice Age refers to periods such as Weichselian / Würm / Wisconsin, etc, and not the entire last 5 million years. It is synonymous to glaciation, and translates to Eiszeit in German and Istid in Swedish. If an author writes 'the last ice age', I would take for granted that he is writing about the last glaciation (i.e., Weichselian / Würm / Wisconsin / Valdaj, etc), and for all the glaciological literature I have read, I have never suspected anything else. If you want to refer to all of them together, the term Pleistocene can be used (the Pleistocene glaciations). I'm just afraid that trying to establish a definition that differs from regular usage will introduce confusion in the future, when articles written today may be misunderstood. --Lindorm 22:42, 19 July 2006 (UTC)

[edit] Edits by 131.172.4.45

I am reverting the edits by 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.

Dragons flight 14:22, Mar 18, 2005 (UTC)

[edit] TOCright

Can anybody justify the use of TOCright on an eight item table of contents? This template has only survived deletion on the grounds that it is used sparingly and it really doesn't seem to me to improve the layout of this article at all. Joe D (t) 8 July 2005 23:52 (UTC)

As I said in my edit comment, I think that on most screens the TOC fits next to the introductory paragraph nicely, and placing it there makes it not interrupt the text. (SEWilco 9 July 2005 01:03 (UTC))
That's not what it's for though, it's for preventing very long TOCs from creating excessive whitespace etc. An eight item TOC doesn't cause a problematic interruption of the text, but does look ugly when floating right. Joe D (t) 9 July 2005 13:05 (UTC)
TOCright can be used to good effect in some articles, but I don't think it is necessary for this one. violet/riga (t) 9 July 2005 13:15 (UTC)

[edit] periodicity

"During the last few million years there have been many glacial periods, occurring at 40–100,000 year frequencies..."

If this statement is meant to say 40,000 to 100,000 years between glacial periods, this is not the way to write it -- it's too open to confusion, and omitting extra zeroes is not important enough to risk complete misunderstanding. Common sense tells me it's ridiculous to think they can happen every 40 years.DavidH 00:36, July 28, 2005 (UTC)–

I've "fixed" this. 40 - 100 was ambiguous for another reason, ie it imples that 80 kyr is also possible, whereas the periods are 40 *or* 100 kyr. William M. Connolley 09:07:12, 2005-07-28 (UTC).

[edit] other continents?

Just wondering, why do we have a special section on glaciation in North America, but not for any other continent? Perhaps knowledgeable folks could add sections for each other continent. This would be a bit of a feather in Wikipedia's cap, since most other resources seem to include a bit about North America and a little about Europe, but very little about South America, Asia, Australia, or Africa. -- Securiger 09:10, 17 February 2006 (UTC)

Not totally sure, but the N A (Laurentide) ice sheet was very big and important. By contrast, the European one doesn't do much. William M. Connolley 09:34, 17 February 2006 (UTC).
The European ice sheets were actually quite large, as was that of Chilean Patagonia and the Altiplano and are of similar significance. It would also be worthwhile to have an article on glaciation in Asia, though the purpose should be to illustrate why it was so limited in extent compared to that of Europe and North America.

[edit] Another Cause offered

03-28-2006

I had a dream last night. I don't recall it's parameters. But I was suddenly jolted out of bed at 3 a.m. with a thought that just has to be written down and sent to a few people for their perusal.

Once or twice (or more) in the earth's history a huge rock fell on the earth which devastated life forms at the time. Many species went extinct. This theory has a very solid scientific foundation and is understood by geologists and planetary sciences as THE explanation for the end of the dinosaurs.

My theory of the Ice Ages also involves a very large meteor. But it didn't hit the earth. It actually hit the earth's moon. The massive explosion as the meteor plowed into the moon (this probably happened several times over the millennia) ejected many, many tons of dust and debris into near earth orbit. The dust cloud encapsulated the earth. Direct sunlight was cut off by a huge percentage by the dust cloud that encased the earth. Temperatures plunged. Ice Ages resulted. Over thousands of years the dust and debris were swept up by the moon or simply fell to earth and temperatures moderated.

To test this new theory I suggest that geologists analyze the dust and debris of the period for similarities with the "moon rocks" that NASA recovered . Some large chunks must have been transferred here from an explosion that large.

24.56.162.170 16:23, 31 March 2006 (UTC)

Nice dream :-) - now if you can find a published account of it in a peer reviewed journal, we can include it in the article. Cheers! Vsmith 16:30, 31 March 2006 (UTC)
When they say "the impact of relatively large meteorites", I have thought they were referring to the possibility that their impact would be capable of reducing the Earth's axial tilt. The effect of meteorites is believed to account for the anomalous axial tilt of some other planets in our solar system. Modern computer models demonstrate reduced mean axial tilt (i.e. independent of variation brought about by Milankovitch cycles, which are assumed to be the same) would lower temperatures if all other boundary conditions are equal and continents in their current positions.
The thing here is that there seems little information on whether (and) what changes in the Earth's mean axial tilt have occurred in the past. In the article History of the Earth's Obliquity in Earth-science reviews (volume 34, issue 1, pages 1-45) it is suggested that the Earth's axial tilt has remained stable over Phanerozoic time but was much greater over the Precambrian. However, smaller variations in mean axial tilt brought about by asteroidal or meteoritic collisions could easily cause or end ice ages and are not discussed. Yet, according to the axial tilt article, the level of variation in the Earth's axial tilt is decreasing. This suggests alterations in mean axial tilt must be followed by higher variation that gradually falls as the new tilt stabilises.
If it does not refer to changes in mean axial tilt, what does the phrase "the impact of relatively large meteorites" refer to that would cause ice ages?

luokehao 17:25, 21 December 2006 (UTC)

[edit] Causes

I was under the impression that one of the contending theories for ice age causes was related to a cyclic interaction between atmospheric conditions and ocean currents. My understanding was to this effect: the warming of the atmosphere (via heightened carbon dioxide levels or methane, etc.--not sure how this part is explained; possibly by geological activity?) leads to the melting of polar freshwater ice, which in turn disturbs the currents of the saltwater oceans (which are responsible for the distribution of temperate and warm air currents), causing a calming of the oceans and consummate cooling of the atmosphere, thereby lowering the overall temperature and inducing the freezing of an ice age. Is this not a widely held hypothesis, or should it receive mention in the article? --5-23-06

[edit] So, has no one seen this research?

http://www.livescience.com/forcesofnature/050330_earth_tilt.html

As far as I can tell, the theory explained at the above link isn't mentioned here. In fact, I don't see any mention of the idea that the 100,000-yr "cycle" is actually just a mixture of 80,000- and 120,000-yr periods (is it really true?). I don't know the subject very well, so maybe I misunderstand, or maybe the stuff in the above article is unworthy of mention. But if so, I would like to know. Thanks. Xezlec 03:27, 10 June 2006 (UTC)


[edit] Terminology

What does "the forcing" mean? HMAccount 22:32, 25 June 2006 (UTC)

[edit] Contributing cause

Since Milankovitch cycles are inadequate to explain an ice age, there must be additional contributing cause. The following, which I believe is consistant with observations, describes how conditions can be brought about by which Milankovitch could then cause the climate to toggle to the opposite climate trend. The strong effect of the incident angle of light on the reflectance of water does not appear to be widely considered in ice age study.

The strong effect of the incident angle of light on the reflectance of water does not appear to be widely considered in ice age study - ah, there you have a problem. Wikipedia does not encourage independent research - in fact it forbids it (WP:OR). If people haven't proposed this mechanism, it doesn't go into the article even if you and I are sure its correct. However, I'm not sure its correct, the most obvious problem being that the sfc area involved is small. But... you don't need to answer that point. You need to find a reputable source making your argument. Note that a series of reputable sources making a chain of arguments that you think you can connect together is not good enough William M. Connolley 20:29, 6 August 2006 (UTC)
sfc area?? == surface area

During the current interglacial period, sea level has risen about 120 meters and water area increased accordingly covering the continental shelves which were exposed at the peak of the last glacial. Water responds differently than land to incident solar radiation. That part of incident solar radiation that is reflected from a body of water is specular and is calculated by the Fresnel equations. A graph showing the reflectivity of water vs. incident angle of light can be seen at[11]. Fresnel reflection is directional and therefore does not contribute significantly to albedo which is primarily diffuse reflection. Therefore, added water area always reduces earth’s albedo but may actually decrease the heat added to the planet.

The real water surface is wavy so reflectance assuming a flat surface as given by the Fresnel equations must be adjusted for waviness. A formula and graph for correction for waviness for two different wave energy spectrum definitions has been published. [1] With the average adjustment for the two spectrums applied for an assumed average wind speed of 5 m/s, the reflectivity of wavy water to unpolarized light increases progressively from 5% at an angle of 49.5 degrees to 20% at 72.8 deg and 50% at 83 deg. The rate of increase of reflectivity with angle then declines rapidly so that the reflectivity of wavy water is 67% at 90 deg (light parallel to surface) where it would be 100% if the water were smooth.

Reflectivity of land and various coverings is also given at [12] and does not vary significantly with the incident angle of sunlight. The reflectivity of land varies substantially depending on cover but appears to average about 0.15. Thus at incident solar radiation angles more than about 69 degrees from nadir, water absorbs less heat from the sun than does land. The effective angle for determining water reflectivity is the compound angle accounting for both latitude and time of day. Accounting for the specular reflection of wavy water and the compound angle of the added water surface to the direction of the sun, added water surface area that is further than about 60 degrees north or south latitude results in reduced heat to the planet. Closer to the equator, low reflectance of water during the day more than offsets the high reflectance near dawn and dusk so there is a net gain of heat at these locations. Thus the change in water surface area as the sea level rises provides either positive or negative feedback to ice age climate change depending on the latitude of the added water surface area.

Added water surface area towards the poles that is exposed late in an interglacial period reduces the heat added to the planet and, in concert with other factors, contributes to the toggle from interglacial to glacial. As a glacial period proceeds, lower temperatures and less exposed water area lead to less evaporation and a dryer climate with less cloudiness. The decline in cloud cover allows more solar energy to reach and be absorbed by all surfaces. The largest increase in the heat being absorbed takes place at ocean areas remote from the poles. Water areas at the equator with no cloud cover absorb about 95% of incident solar energy. The resulting net heat gain by the planet, in concert with other factors, may cause the climate to toggle from glacial to interglacial.

[edit] Acceptance of Milanković

I think it would be an interesting (and cautionary) point to mention that the Milanković theory was dismissed as "pseudoscience" until being proven likely in recent years (and we still find some people downplaying it if I'm not mistaken?).

[edit] Glaciation other than in N. America

Obviously a section on the extent of glaciation in Europe is needed alongside the N. American treatment -- mentioning the interesting connection of Britain to continent.

Also the general issue of sea level change doesn't seem to have been dealt with in depth if I'm not forgetting something I just read. Map of coastlines at glacial maximum would be great with features like Sundaland pointed out.

The articles on sea level change and continental shelf address this. I suggest a new section as follows:

[edit] Sea Level Change

Glaciation moves water from ocean to glacier resulting in sea level decline. Glacial melt during an intergalcial period moves water to the oceans producing sea level rise that covers the continental shelf. 4.232.0.79 18:53, 16 August 2006 (UTC)

[edit] Context with Great Flood and Atlantis myths

I've just added a huge section discussing the Ice Ages and the myths of the Great Flood and Atlantis. I'm not really sure how to handle inclusion of this into Wikipedia, but since this is the scientific view of the myths it seems more appropriate for this to be attached to this article. I ask the more experienced editors... would this be more appropriate as a separate article?

Rursus 21:17, 27 December 2006 (UTC) says from here:

I opinionate thusly: it would be more appropriate as a separate article, since the text is off-topic from Ice Age and far too long - however: making a short 'Myth interpretation section linking from Ice Age to that article may be OK. You may do it by the following steps:
1. add a link text to the section just below the heading, such as for example:
Main Article: Ice Age Myth Interpretations,
2. create a new web browser window/tab, and there go to wikipedia:Ice Age,
3. edit Ice Age Myth Interpretations in the old window by looking up Ice Age Myth Interpretations and creating it when reaching the page "No page with that title exists."
4. in the other window edit Ice Age,
5. cut and paste as you feel is appropriate.

Rursus 21:17, 27 December 2006 (UTC) said to here. STOP.

Wikipedia logged me out because I took so long posting that. So no attribution and you don't know who to blame. Oh well. :) DMahalko 19:40, 23 December 2006 (UTC)

It should be a separate article, for the reasons already listed. Also the material must be supported with references - especially given that it all seems extraordinarily speculative. There are more widely-accepted explanations for the Great Flood myth (presumably you mean the Noah/Gilgamesh flood story). Raymond Arritt 22:13, 27 December 2006 (UTC)

[edit] List of doomsday scenarios

Could use votes to save this article, thanks MapleTree 22:28, 28 September 2006 (UTC)

[edit] Pleistocene

added section on T changes and an external link to more detailed discussion KonaScout 14:58, 16 November 2006 (UTC)

[edit] Vicious and virtuous cycles in ice ages

Can any one please explain why this was removed? It covered: (A) the increase in albedo initially accelerates the advance of the ice; (B) the advancing ice decreases weathering and thus causes an increase in the greenhouse effect, which brakes the advance of the ice; (C) during the Cryogenian Ice Age the unusual position of the continents (equatorial super-continent Rodinia) delayed the operation of mechanism (B) and therefore made both the ice age and the eventual increase in greenhouse effect much more severe than usual.Philcha 19:09, 5 December 2006 (UTC)

The only person who can say for certain why it was removed is the person who removed it (which was not me). But it's partially redundant with material that's already in the article. If you can find a way to weave it in so that it doesn't repeat what's already there, give it a shot. By the way, I suggest more specific terminology than "vicious and virtuous cycles" -- you probably want "positive and negative feedbacks." Raymond Arritt 01:36, 6 December 2006 (UTC)

[edit] Vulcanism

The author of this section seems to rule out the possibility that volcanoes can contribute to ice ages, yet there is some evidence that reflective aerosols cause a net cooling effect on the short term (eg. mt. pinatubo). Conflicting evidence (Tuba eruption 70ka) suggests that volcanism has nothing to do with it. I am not familiar with research into the effects of supervolcanoes on climate change, but there was supposedly a massive sea level fall associated with the siberian traps volcanism 251 million years ago that could indicate the initiation of an ice age. The long term net effect of volcanism may be heating, yet that doesn't rule out it's role in the initiation of an ice age. —The preceding unsigned comment was added by Luokehao (talk • contribs) 17:29, 21 December 2006.

If you can find a reference for it, go ahead and add a sentence or so. By the way, please sign your comments by putting four tildes at the end, like this: ~~~~ Thanks. Raymond Arritt 18:59, 21 December 2006 (UTC)
Ice ages are periodic - this is the main evidence linking them to orbital variations. Volcanoes, as far as we know, aren't. QED. You are talking about the current 100 kyr ice age cycle, aren't you? William M. Connolley 19:49, 21 December 2006 (UTC)

[edit] Better picture

I wish there was a better picture for this article. How about a map of the world showing the areas covered by ice? I couldn't find anything on Wikicommons. Steve Dufour 04:49, 14 March 2007 (UTC)

[edit] expanding/clarifying Evidence for Ice Age section

A little background on me: I'm not an expert or anything, but I love history and although I'm only a freshman in college I have read/studied alot of subjects on my own so I have a good base knoweldge of this subject. Even though I'm not able to contribute new evidence, material or studies I feel I can contribute by pointing out what I feel are weak points in the article, in hopes someone who really knows this stuff can come in and beef them up. Anyway, I was struck by a few key points while reading this section.


Three types of evidence were discussed: geological, chemical and paleontological. Evidence is intented to convince someone of a fact, but some of the phrasing within this section seemed self defeating and unnecessary to me.


For example at the end of the paragraph explaining the geological evidence it says "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." Is it necessary to add this? Seen from the view point of a student who is learning about ice ages for the first time, I would say this student would be confused somewhat because this statement seems to discredit the previously presented evidence.


Also, in the paragraph concerning chemical evidence: Rather than information supporting ice ages and their documentation/dating (ice cores were mentioned) here it seems this paragraph actually presents negative evidence that is not expedient towards a credible base of pro-IA evidence. "This evidence is also difficult to interpret since other factors can change isotope ratios." It basically talks about how chemical evidence is unreliable because too many other factors affect the isotopes that are studied. We should replace this paragraph with firm evidence/statistics and studies from a credible source with citations. (I would if I had the knoweledge myself)


My tertiary quibble is this: The paragraph on paleontological evidence was just as disapointing as the paragraph about chemical evidence. This paragraph states what paleontological evidence is and how it relates to glacial periods but goes no farther. Instead of bolstering the argument with successive supporting material it is followed by material that once again explains how this particular evidence is not reliable!


The last paragraph goes on to say "Despite the difficulties, analyses of ice cores and ocean sediment cores unambiguously show the record of glacials and interglacials over the past few million years." As an impartial observer I would see that and say "Hey, they just talked about how all the evidence that is used to document ice ages/glacial periods is difficult to interpret or is potentially affected by other factors, but then they say they have unambiguous records? Since this is wikipedia I have to be mindful about the legitimacy of information I find, so I think this may be fake." Come on! Beef this thing up! I don't have the knoweledge to do it myself so like I said I'm pointing out what I think are weaknesses and points that should be expounded upon and added to in order to make this article better!

You seem to be asking for a simple straightforward story, irrespective of reality. The evidence *is* difficult to interpret. But nonetheless the evidence does "unambiguously show the record of glacials...". This is not to say that the article can't be improved William M. Connolley 10:13, 15 January 2007 (UTC)

Look this is a really disgraceful article in a number of ways. I've not read the discussion at all. But just reading the article its going well. And you are getting all this good technical information.... And then you get down to the section "INTERGLACIALS AND THE FUTURE" and thats where its evident that the communist-climate-hoax bully boys are there. And from there on in in the article it appears that these hard-leftist wankners have filibustered the article to get their tendentious bullshit through.

Its not the only filibuster these people are into. When it comes to EVIDENCE that the CO2 has as powerful effect as they say it does you will get no answer from these anti-science, unscientific wankers.

My suggestion is then that in all cases tone down the importance of CO2 in the article. It may have some effect sure. But it would be nice to have some evidence before they go dishonestly buggering the wiki with their make-beilieve.

The other suggestion I might make is in your POSITION-OF-THE-CONTINENTS section. I don't know if this is mainstream. Or whether it was me that made it up. But clearly the position of the continents as a major determinant of the climate follows directly from Stefan-Boltzmanns law. I don't have a reference for you because for all I know it might have been me that made this up. But I see this as self-evident.

http://forumserver.twoplustwo.com/showflat.php?Cat=0&Number=9246659&an=0&page=0&gonew=1

Actually its so obvious that I suspect me seeing the connection is a redundant achievement. But then you never know. If nobody mentioned this in wiki then it could have been me.

But for goodness sakes we can't have this excessive JIVE about CO2 in this article unless these HOAXERS turn honest on us and come up with some actual evidence for the effect being more then negligable. By the way, although the current global warming scare is clearly and without a doubt a total hoax put over by hard leftists.... nonetheless one is quite willing to believe that a sustained level of CO2 over many thousands of years could have a far more substantial effects.

But what I'm saying is that this dishonesty and tendentiousness has gotten so far out of hand that in the formulation of this article, people involved with the wiki ought to be totally biased against the protestations of the communists and they ought to try soften or nearly eliminate this rather obvious CO2 propaganda.

The speculative article that says that the current interglacial is going to last another 30 000 years or 50 000 years is totally out of place also. And its pretty obvious that some coterie of watermelon-commies slipped that one in, in their endless campaign against the science.

Please don't bother posting this SHIITE about there not being a conspiracy. Anybody that knows how these bully-boys work must realise that with a pack-instinct like that these guys need no conspiracy. And surely it was the leftists that brought this stupid rule to the wiki in the first place. Of course there is a conspiracy. These leftists are relentless liars. And they never seem to sleep.

Retrieved from "http://en.wikipedia.org../../../i/c/e/Talk%7EIce_age_ef92.html"