Guest post by Dr. David Archibald
The Earth is currently in an interglacial period of an ice age that started about two and a half million years ago. The Earth’s current ice age is primarily caused by Antarctica drifting over the South Pole 30 million years ago. This meant that a large area of the Earth’s surface changed from being very low-albedo ocean to highly reflective ice and snow. The first small glaciers were formed in Antarctica perhaps as long ago as 40 million years. They expanded gradually until, about 20 million years ago, a permanent ice sheet covered the whole Antarctic continent. About 10 million years later, glaciers appeared on the high mountains of Alaska, and about 3 million years ago, ice sheets developed on lower ground in high northerly latitudes.
Pacific Ocean bottom water temperatures started declining 40 million years ago, falling 10° C to the current 3° C. The band of high ocean temperatures (above 25° C) also contracted towards the equator, from 45° latitude to 20°. Eventually the oceans lost enough heat that the Earth’s orbital parameters started causing surges in ice formation. There are three orbital parameters: eccentricity, precession and obliquity, shown in Figure 1.
Figure 1: Orbital Parameters: Eccentricity, Precession and Obliquity- click for larger image
This figure is developed from A.L.Berger, 1978, Long Term Variations of Daily Insolation and Quaternary Climatic Changes, Journal of the Atmospheric Sciences, volume 35 (12), 2362-2367.
Eccentricity is caused by changes in the shape of the Earth’s orbit due to the gravitational attraction of other planets. Precession is the change of direction of rotation. Obliquity is the tilt of the axis. When these effects aligned, their effect is reinforced. From three million years ago to about 800,000 years ago, the dominant pattern of glaciation corresponded to the 41,000 year period of changes in the Earth’s obliquity. Since then, a 100,000 year cycle has been dominant.
Ice ages occur because the summer sun in the northern hemisphere does not get hot enough to melt all the ice that accumulates over winter. Ice has a much higher reflectivity than rocks or vegetation, and so reflects more sunlight into space and the cooling is reinforced. Eventually the orbital parameters change back and warming occurs. Glacial periods tend to cool slowly and warm abruptly. Because the Earth’s orbital parameters can be calculated, the amount of sunlight in high northern latitudes can be calculated.
Figure 2: June Mid-Month Insolation at 65° North – click for larger image
This figure is derived from M.F.Loutre and A.Berger, 2000, Future Climate Changes: Are we entering an exceptionally long interglacial?, Climatic Change 46, 61-90
Figure 2 shows how that translates to insolation (sunshine) at 65° North. The recent peak in insolation was 11,000 years ago at the end of the last glacial period. It has since declined by about 10% to 476 watts per square metre. Insolation will rise from here for the next 30,000 years, but it will still be low enough for the next glaciation to form. This is shown by Figure 3 of Northern Hemisphere ice volume for the last 200,000 years and a projection for the next 130,000 years. According to these calculations, the Earth is at the beginning of a 20,000 year plunge into the next ice age.
The reason why the Earth doesn’t respond more rapidly to changes in insolation is due to the retained heat in the oceans, which smoothes the whole process over thousands of years. Over the short term, the oceans are very responsive to changes in solar activity. Figure 5 shows the very strong correlation between the annual rate of sea level rise and solar cycles over the 20th century. The sea level rise of the 20th century can largely be attributed to a more active Sun relative to the 19th century. About 70% of the sea level rise of the 20th century was due to thermal expansion of the oceans, with the rest due to melting glaciers.
Figure 3: Future Glaciation – click for larger image
This figure is derived from M.F.Loutre and A.Berger, 2000, Future Climate Changes: Are we entering an exceptionally long interglacial?, Climatic Change 46, 61-90
Figure 4: The Correlation between Sea Level Rise and Solar Cycles over the 20th Century. – click for larger image
The sea level data is derived from S.Holgate, Decadal rates of sea level change during the twentieth century, Proudman Oceanic Laboratory, Liverpool, UK.
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Way OT, but Anthony maybe you know what is going on with the Cannonball River at Breien ND? The river gauge has gone from 2.5′ at 7:30am to 31.05′ at 11:00am today. Could an ice dam cause this type of rise on a river? Reported on http://weather.hamweather.com/rivers/gauge/BREN8.html, and NOAA reports same level.
I called the National Weather Service in Bismarck and was told the following two things:
1. North Dakota remains fully frozen — no flowing water anywhere.
2. They get noise from their instruments due to ice sometimes.
Thanks, the gauge went down right after I made the comment so I then suspected an instrument problem.
I think you misunderstood or I misunderstand
Steinar Midtskogen in his post said, “I was taught in elementary school” and then listed a fairly complex scientific concept.
I don’t understand what was objectionable about my jokingly asking where he attended elementary school since it was obviously a pretty advanced one.
Is it really a complex concept for kids that water at 4 degrees sinks to the bottom? No need to know exactly why. Anyway, my point was that I was surprised to see this 13 degrees figure mentioned without any explanation, since it seems to contradict a well known fact even by those who haven’t studied science.
The Pacific is deep and to have the bottom water at 13 degrees sounds as fantastic to me as if the Arctic ocean was frozen solid to the bottom during some ice age. So an explanation would be in place how this is possible, since, if it’s true, I must be missing something very important.
So much has been forgotten. A good study of the ice ages is a book written by Fred Hoyle entitled “Ice”. We know it is a good book because he dismisses CO2-related warming in about three lines of text. On pages 99 of that book is Figure 28 showing the bottom temperature of the Pacific Ocean over the last 40 million years, after from Emiliani, Scientific American, vol.198, 1958.
The references to ‘the bottom water of the Pacific’ might cover a wide range of situations. The depth of the Pacific bottom is highly (is that called a pun ?! – sorry-) variable. Perhaps the description just requires a more detailed explanation?
Water at 4C will sink to the bottom, yes, but I seriously doubt your conclusion that the bottom must therefore be at 4C. First, compression does not drive a fluid to its most compressed temperature. Adiabatic compression as in an air conditioner increases the temperature of a gas as it compresses, despite all gases expanding with temperature. Second, if you take a huge body of water, all of it hotter than 4C, then some of it must be at the bottom. If there is some process that drives the temperature from whatever it was to 4C, then heat would have to travel from cold water to hot, violating the second law of thermodynamics. I don’t guarantee this is correct, but my take on it says you are incorrect. If you see a flaw in my reasoning, I really want to have it explained to me.
Scientists capture dramatic footage of Arctic glaciers melting in hours
Scientists have captured dramatic footage of massive lakes in the Arctic melting away in a matter of hours.
http://www.telegraph.co.uk/earth/environment/climatechange/4734859/Scientists-capture-dramatic-footage-of–Arctic-glaciers-melting-in-hours.html
Glaciologist Jason Box has been testing a Moulin, a shaft that allows water to travel from the glacier’s surface to its bottom, in a glacier on the Greenland ice cap to find out how fast it is melting.
He said: “There’s no escape from a Moulin. It’s just got danger written all over it. But the information is so important that we actually had to take that risk.”
Dr Box said: “We’re in the midst of a climate catastrophe and glaciers are the epicentre of that problem.
“Glaciers around the planted are decanting into the oceans at shocking rates and I want to stop that.”
He then should “insert” himself into the glacier and verify his theory.
After all the glacier according to him will melt in a matter of hours so he will survive…
Wasn’t this the same experiment where they dropped little yellow bath duckies into the moulon expecting them to surface in the ocean but they have completely disappeared!!!!!
Also in that article: Greenland lost enough water in a year to cover Germany with 1 meter water. Since Greenland is 6 times the size of Germany, this implies that per unit area Greenland loses 17cm of water, i.e. 20 cm of ice per year. 20 cm in about 2000 meter ice (if not more) , 1 in 10000. So what’s the problem? One winter’s snowfall and it’s all back again.
Dr Box’s “shocking rates” are actually pretty modest, but even so I am very curious how he intends to “stop that”. By shouting at the Sun, I guess.
In the article it says he wants to stop glacial melting by covering glaciers in blankets.
I lol’d
I wonder if Jason Box is aware of the real global ice mass balance?
I wonder if Jason Box realizes that if the fresh water influx to the oceans increase so does precipitation. A reduction in influx results in a reduction in evaportation and precipitation thus an increase in drought? Why does he want to increase drought?
I spliced together some of John Cristy’s comments on Greenland made during his presentation while participating in debate with Schlesinger. (Global Warming Debate / William Schlesinger versus John Christy /John Locke Foundation / February 11, 2009)
http://s247.photobucket.com/albums/gg136/BigLee57/?action=view¤t=GreenlandMelt.flv
What a load of old cobblers!
This is pure gee whiz, boy’s own derring-do inconsequential rubbish.
The first clue comes when the voice over states in a quietly awed voice that the scientists are out to see if they can save the planet.
Then the talk is all of danger – ‘there’s no escape from a moulin’ etc etc.
Finally, after many dangerous adventures in his crampons, the actor (surely this is not for real) provides an accurate (about 5 and a half miles per hour -I forget the exact figure and cannot bring myself to go back and look at it again) measurement of the flow velocity.
Oh the precision! And then, without any measurement of the area of the flow, not even an estimate, we are told how many zillions of litres are going down the plug hole every day (or whatever). From the bare velocity information this clown (surely this is meant to be funny) can provide statements about volume rate of flow.
And then we are told that there are ‘hundreds’ of these over the Greenland ice-cap. Alas and alarum! Oh woe for the planet! (@ur momisugly#^&!!**)
And Dr Box wants to stop the glaciers decanting into the oceans at these ‘shocking rates’…….. For heaven sakes, why doesn’t he just jump in and block the plug-hole?
But worst of all, there is not one scene, not even a still shot of any Arctic glacier or lake melting away “in hours”.
Where do you get this unutterable rubbish?
It does seem as if the reporter/news outlet is unable to distinguish between the concept of “draining” and the of “melting”.
Greenland is losing enough water each year to cover Germany a metre deep.
Germany is losing enough water each year to cover Germany a metre deep (approximately). That’s how much precipitation it has.
What drivel.
I live 25km North of Hambur, Germany, It has rained, or snowed for 90% of the time I have lived here (5 years) a day of sun gets front page on the news! Contract about finish, moving to Italy, if that’s global warming.
“The Earth’s current ice age is primarily caused by Antarctica drifting over the South Pole 30 million years ago.”
So did it just drift there and stop or is it still moving. What happens when Antarctica moves off the south pole? Would the ice move back into the ocean like the north pole? Would that cause a rise in sea level or would the land rise as ice was removed and offset the weight of ice in water. Is anyone studying current continental drift. Seems to me there has been quite a bit of movement in the pacific and western united states plates lately, so hows Antartctica just sitting there?.
I apologise if I seem dumb, but an object in motion and all that.
Continental drift is alive, although a bit hungover.
Jeez; it’s carnaval
Atlantis (in Greek, Ἀτλαντὶς, “daughter of Atlas”) is a legendary island first mentioned in Plato’s dialogues Timaeus and Critias.
wiki
http://www.surfacestations.org project going
Reply: I couldn’t think of a better response to my post Fernando. I intentionally left Rio before it got so loud I wouldn’t be able to sleep for a week ~ charles the moderator aka jeez
Continents drift at about the rate your fingernails grow. It isn’t something to worry about in our lifetimes.
Heck, you could even make a case that we as a species evolve faster than the continents drift, so it isn’t an issue for our species… though it might be for what ever species we evolve into in a few more million years … 😉
BTW, there is a crack in Iceland where one can directly measure the rate of sea floor spreading and continental drift. One side is N. American plate, the other is Europe. It has ‘fresh’ rock in the bottom from old lava a few thousand years ago. I’ve seen film of a guy standing in the bottom of the crack describing the two sides…
Antarctica once was in the tropics, witnessed by its large coal reserves (in the places that have been explored). Yes, the Earth has iceages only if either one of the poles, or both, are occupied by a landmass. Indeed, they are shifted in and out of place by continental drift.
The reason is simple: if the poles were covered by oceans, any ice formed would float on the water. Not only would that mean high sealevels, but also, little ice because the ice would not grow thicker than a few tens of meters at most. This is what we observe now at the North Pole; the ice thickness is determined by the cooling at the surface being balanced by the “heat” from water underneath, constantly replenish by ocean currents from warmer places.
If, however, there is a landmass at the pole, much largere quantities of ice will accumulate and form gletchers at first and a thick ice shield eventually, containing
much more ice than otherwise without land. Hence a lowering of sealevel.
It’s more complicated than just having Antarctica at the South Pole. The Antarctic continent drifted to the antarctic circle and South Pole more than 20 million years before the latest great glaciatons commenced about 30 million years ago. Consequently, it was a combination of events including the location of Antarctica which caused the latest ice ages. Likewise, Antarctica will still be present at the South Pole when the ice ages decline during the next 50 million years. Yet, the glaciations will wane and wax on the Antarctic continent as the Atlantic Ocean basin stops expanding and begins to re-close following the subduction of the mid-Atlantic Ridge, bringing Australasia back into contact with Antarctica. Greenland and the North Pole will be free of glaciation, while the Antarctic retains lesser and greater glaciations as the continental configurations continue to shift and shift oceanic circulation patterns.
Continents move in response to plate tectonics, caused by convection in the mantle. Typical rates are on the order of a few (1-6) centimeters a year. Now assuming there is some mantle convection current impelling the Antarctic as a whole, it will take millions of years to move it substantially away from its present location.
Ed,
Perhaps Jason Box and his team could wedge themselves into the top of the moulin and stop some of the decanting, or go looking for epicentres at earthquakes 🙂
common cause
As Mr. Svalgaard has kindly calculated the total tidal pull on the Sun’s surface is of order of 2mm. The graphic showing apparent correlation of see level and sunspot cycle shows tides of 2 to 3 mm around the central value. Therefore, it can be concluded that the sea level (even sometimes precedes the solar cycle) has noting to do with solar cycle but with planets’ tidal pull on the oceans volume.
The apparent correlation (although not perfect) may lead us to conclude that planet’s influence is the common cause to both, the rise in sea level and the sunspot cycle, this Mr. Svalgaard bitterly opposes.
Not from the coincidence of sizes. The 2 mm is for a body the size of the Sun. For the Earth the bulge due to Jupiter would be 0.0021 mm.
which for the metric challenged is 1/50th of the width of a human hair.
I do not bitterly oppose anything. I explain patiently from elementary physics how things are and what does or does not work.
And I thank you very much for that
If Hansen gets fired, would you consider his job?
No Pamela, I’m beholden to no-one now
Does anyone know if they use Chlorine36 to map sea water exchange? Looks like it ought to work…
From the wiki:
http://en.wikipedia.org/wiki/Chlorine-36
“Additionally, large amounts of 36Cl were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of 36Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, 36Cl is also useful for dating waters less than 50 years before the present. 36Cl has seen use in other areas of the geological sciences, including dating ice and sediments.”
So, Cl36 enters seawater at the surface, floats to poles, enters the THC plunge to the bottom … Or do you need the hydrophobic decay products to make this work?
I don’t think a correlation between sea level rise and sunspot number necessarily suggest that the sea levels would not be rising without the current level of solar activity. Note that even weak cycles like solar cycle 16 coincided with an increase in sea levels. How small would the cycles have to be to not cause an increase in sea level? I’d think that the oceans would have caught up with the current level of solar radiation by now, and that sea level rising rates would vary around 0. The radiative imbalance in the system likely arrives from cloud cover changes.
Ed, Reference to Glaciologist Jason Box and his Moulin suggest (?) something
new about this. Not so. Lakes on glacier surfaces and their rapid disappearances, along with disappearing streams, through open shafts in the ice are as old as glaciers. The topography created underneath reveals, when the glacier is gone, where these flows once were. A Moulin makes a roar as did old grinding mills; thus, sounds like a mill = Moulin.
OT here but it looks like the OSPDP seem to be ‘losing’ sea ice around the Arctic. Compare the current SST anomoly map http://www.osdpd.noaa.gov/PSB/EPS/SST/data/anomnight.2.23.2009.gif with the last one 4 days ago http://www.osdpd.noaa.gov/PSB/EPS/SST/data/anomnight.2.19.2009.gif
The Antactic sea ice seems to be acting normally so the glitch seems to be just around the Arctic circle.
We have recently discovered Antarctica isn’t a contiguous continent. Its more of an archipaeligo.
Antarctica appears to be a contiguous continent because it’s icesheet is contiguous. I am unable to find an estimate of when that contiguous icesheet formed, but its creation would have had substantial effects on ocean currents and climate.
The land area of Antarctica at current sea levels is about half of what is shown on maps.
http://upload.wikimedia.org/wikipedia/commons/b/b7/AntarcticBedrock.jpg
I wonder how much the land would rise without the icecap, leaving it less like islands.
Prior to the ice depressing the land, the sea level would have been higher (the water having become the icecap). The text of the Wikipedia article suggests that isostatic rebound would be “hundreds of meters” which is probably greater than the sea level decline. I suspect that it is probable that more of the depressed area was above sea level than is now.
Sorry to be completely OT, but does anyone know what’s happened to ClimateAudit?
Thanks.
Look here.
See the WUWT home page article about the web server going down.
The formation of the Isthmus of Panama, about 3 million years ago, is one of the most important geologic events in the last 60 million years.It formation shut down the flow of water between the Atlantic and Pacific Oceans. Atlantic currents were forced northward, creating the Gulf Stream today. increasing the temperature of Europe by as much as 10 °C. The Atlantic, no longer mingling with the Pacific, grew saltier. This favors an ice free north pole.
Secondly, about the 4 °C temp for water under pressure. This is true for pure water, which is extensively hydrogen bonded. However, salts ruin the tight packing, as cations have an outer aqueous sphere, and so do anions to a lessor extent. The smallest degree of packing depends on what salts are present. The best way to drop volume is to get rid of the salts, the easyest way to do this is for the formation of precipitants. Expect some very funky mineralization reactions; using precipitation of minerals many endothermic reactions would be rendered thermodynamically viable.
Umm, they do still mingle, Cape Horn, Northwest Passage, water does flow under the ice.
The creation of the isthmus certainly altered important currents, and most likely affected global climate.
DocMartyn, are you suggesting precipitating minerals out of the oceans? Or are you just saying it’s ‘viable’?
I’m not a climate scientist, so I wouldn’t know if totally upsetting the oceans’ balance would be a problem or not… [/s]
If I take a purely empiral approach, isn’t the fact that the temperature of the deep ocean now is everywhere near 4C proof that it also applies to salt water?
Which still leaves me with the reported 10C.
Is anyone aware of a discussion/study regarding volume changes of the oceanic basins due to crustal rebound as the crust returns to its pre-ice age shape, and filling due to river silts and dust sedimentation ?
I would think that not only water volume due to temperature density changes, but the reductions in the volume of the container need to be considered, to evaluate the changes in sea level.
Take for example the 2004 Indian ocean Tsunami that involved uplift of the ocean floor over large areas. That obviously changed the volume of the ocean basin. Was there a world wide step change in mean sea level some time after December 2004? Was this a net gain or loss to ocean basin volume?
I can think of at least 5 mechanisms that should be constantly changing (reducing) the ocean basin volume.
– Crustal rebound and seismic uplift ( subduction would obviously subtract some volume)
– silt transport by major river deltas into the ocean basins.
– silt build up in the deep ocean due to dust and organic “snow” as organisms in the upper layers fix material and carry it to the ocean floor as they die.
– Volcanic intrusions due to undersea volcanic erruptioins.
– volcanic dust that settles in the ocean basins
I do not recall ever seeing any values being assigned to sea level change due to the volume of the container (the ocean basin) as it slowly fills up or changes shape due to these effects.
Something like 500 million metric tons of dust fall into the Atlantic basin each year from North Africa alone. You add to that Dust from the Gobi desert and silt from the major rivers you must have displaced a fair amount of water storage capacity in the basin.
http://www.space.com/scienceastronomy/planetearth/dust_storm_010514.html
Mt Pinatubo ejected approximately 10 cubic kilometers of dust, most of which most likely fell into the South China Sea for example. In other areas of the world like the Persian Gulf and the Red Sea you also have large deposition rates of dust into the oceans due to sand storms in the region.
So here is at least one other mechanism that should figure into world wide sea level change that is not driven by CO2 emissions. In fact warm most conditions might reduce the dust components, due to wind erosion.
Larry
Yes, the sizes of ocean basins have been studied.
http://www.google.com/search?q=volume+changes+of+the+oceanic+basins
And rebound after glacial events.
http://en.wikipedia.org/wiki/Post-glacial_rebound
You mentioned subduction, but omitted seafloor spreading. There are indeed many factors.
http://en.wikipedia.org/wiki/Sea_level
http://en.wikipedia.org/wiki/Sea_level_change
obviously I don’t know the orders of magnitude involved, but if you add dust you have to subtract all the fish we eat. No?
That was probably a stupid statement, but then I’m not shy nor afraid of saying something stupid to be corrected.
Hotrod.
I had wondered about the same thing, i.e. ocean basin volume. The Atlantic Ocean widens about 2-3 cm per year. Many other continental movements are even faster. Deep Ocean trenches get deeper or shallower depending on the rate of subduction of the ocean plate. Continental plates tilt one way or another.
With ocean level changes of .13 mm quoted for last year, just normal tectonic movement could easily account for that. Everyone always assumes that any and all ocean level change is due to water volume change. I’m with you. There are several things that could account for such a small change.
Bruce
hotrod: You mention a number of things that might affect ocean volumes. I can speak to some of them, and hazard an opinion at some others.
Isostatic rebound: Land areas that were covered by glaciers were, to some extent, depressed. Now that the ice is gone, they are rising (see: Isostasy for the principle). Areas in Maine, Norway, etc. have risen amounts measured in meters. However, glaciers gone to sea float sooner or later. The ocean floor is little affected by glaciers.
Seafloor spreading/subduction: The world is not, last I heard, increasing in diameter. Therefore, when new ocean seafloor is produced at the spreading ridges, seafloor somewhere else has to be consumed. This is “conservation of volume” (nothing is “new”, material is simply being recycled in the tectonic system). New seafloor material is relatively hot and so less dense, and stands up as a “ridge”. As it gets pushed away from the spreading ridge, it cools and becomes more dense and begins to sink (oceanic trenches result). Ultimately it is either subducted (taken back into the mantle) or obducted (thrust up onto the continental mass that it impinges on). Density – as a function of temperature and composition of rocks – more or less is the driver of the system.
Volcanic ash, etc. – In terms of Pompeii, this stuff was bad news. But x cubic kilometers spread over 75% of the earth’s surface (the oceans) is inconsequential. Over 4 billion years, it adds up of course, but most of that goop has been accreted to (added to, pasted on, or turned into lava/ash on) the continental masses/island arc systems through the subduction/obduction process. The oldest ocean deposits are some tens of millions year old; the earth > 5 BY.
River deltas: Some of these are big enough (Mississippi River, for one) to really affect local geology. They act like a glacier to some extent, depressing the materials beneath them or their own older deposits or finally the underlying mantle. As a result, older unconsolidated sediments are squeezed, forcing out water, shrinking open pore spaces, causing new denser minerals to form, etc. They are compacted and lose volume. In some cases (Miss. Delta for one), the underlying “rocks” are massive deposits of salt. These can flow like a magma under pressure, and rise to form salt domes (even occasionally “salt extrusions” like a lava flow). If finally the mantle is depressed, somewhere else something is pushed up (the mantle essentially is an incompressible material). The oldest ocean deposits are some tens of millions year old; the earth > 5 BY.
Same for the tsunami. I haven’t read that there was a big uplift of seafloor or continental mass, but something happened that shifted billions of tons of material rapidly one way or another, probably along a line of weakness (fault). Maybe something went up or down 5 or 20 meters over a large area. The main product was an enormous shock wave (tap your wine glass with a knife and watch the ripples). That shock wave was transmitted to the sea, which exercised it in a way that physics explains nicely and that was hugely destructive of human beings and their constructs.
Ultimately, we live in a very dangerous place. No one can guarantee our existence for the next five minutes, much less eons. Most of us don’t realize that, and so the AGW thing scares some badly. I am a geologist, so I realize (some of) the things that could happen. My retort to nature is: “Bring it on. We can handle it.” Man-made problems may however be a different ball of wax.
correction should read:
In fact warm moist conditions might reduce the dust components, due to wind erosion.
Larry
One thing to remember in talking about orbital cycles and changes in insolation is that the total amount of energy reaching the surface of the Earth over the period of a year does not change it is just distributed differently.
Dr. Archibald,
Many thanks for taking the time and trouble to produce your “Ice Ages and Sea Levels” article, which I read with great interest. The article has prompted a few questions — and please forgive the absence of citations other than Wikepedia.. I am simply too ancient to want to learn how to handle that sort of informatin from my browsing of Google.
. Is the current series of glaciations the only known example of recurrent sequences of glaciation?
2 Wikipedia reports that ocean bottom drilling indicates that there have been about 80 glaciations thus far in the current series. You state that the last four glacial periods have run about 100,000 years, and prior to that the cucles covered 41,000 years. Dividing 41,000 into 1,700,000 gives 41 plus a tad, which of course doesn’t fit. I have come across a paleoclimate article which indicates that the initial glacian-interglaciation periods only lasted 25,000 years. If that were the case, it would easily be possible to strike a balance between the two that would work. Or could the Wiki information be that far off?
3. Do the orbital parameters provide an explanatory rationale for the 41,000 year long glacial cycles? My guess is that they don’t, and that they certainly wold not seem likely to explain 25,000 year cycles (assuming that they did occur).
4. Has anyone provided an explanation for the sudden shift from 41,000 year cycles to 100,000 year cycles? That is one robust climate change!
There is clearly a growing audience for reliable, unbiased information of the sort represented by your excellant and important article.
My 2c worth,
Indeed, the glacial/interglacial cycles have been getting longer over the current Ice Age, although not smoothly. It’s more like they have a sudden jump from one period to another, eg 41k years to 100k years.
Whatever the underlying cause of the glacial cycles, and my view is that it is currently unknown, is causing longer cycles. These cycles then synch with Milankovic cycles, which (by providing the insolation change) control the timing of the shift from warming to cooling and visaversa.
So the glacial cycles would happen anyway, but their timing is governed by the Milankovic cycle closest to the glacial cycle’s natural period.
C.Colenaty (20:48:30)
Yes, the orbital parameters provide an explanatory rationale for the 41,000 year glacial cycles. This arises from the axial obliquity of the Earth’s orbital variation which has a period of 41,000 years. A recent paper (abstract below) addresses your point about the switch in the glacial cycles from a dominant 41,000 year cycle to a 100,000 year “driver” (orbital eccentricity). It’s not “proven” but it does provide a rationale that is consistent with the evidence.
The idea seems to be that the 41kyr cycle was represented in the high Northern latitudes by the waxing (cooling phases) and waning (warming phases) of the Eurasian ice sheet, but as time progressed the N. American ice sheet became progressively more significant. At some point around the time of the switch from 41kyr to 100kyr the combined ice sheets became sufficiently large that they were able to survive the insolation changes on the timescales of the obliquity (41 kyr) and precession suppressing the 41 kyr transition to full interglacials. In other words the glacial cycles “missed the pulse” and interglacials were only realized in line with the eccentricity variations.
Bintanja R and van de Wal RSW (2008) North American ice-sheet dynamics and the onset of 100,000-year glacial cycles Nature 454 869-872
Abstract: The onset of major glaciations in the Northern Hemisphere about 2.7 million years ago(1) was most probably induced by climate cooling during the late Pliocene epoch(2,3). These glaciations, during which the Northern Hemisphere ice sheets successively expanded and retreated, are superimposed on this long-term climate trend, and have been linked to variations in the Earth’s orbital parameters(4). One intriguing problem associated with orbitally driven glacial cycles is the transition from 41,000-year to 100,000-year climatic cycles that occurred without an apparent change in insolation forcing(5). Several hypotheses have been proposed to explain the transition, both including and excluding ice-sheet dynamics(6-10). Difficulties in finding a conclusive answer to this palaeoclimatic problem are related to the lack of sufficiently long records of ice-sheet volume or sea level. Here we use a comprehensive ice-sheet model and a simple ocean-temperature model(11) to extract three-million-year mutually consistent records of surface air temperature, ice volume and sea level from marine benthic oxygen isotopes(12). Although these records and their relative phasings are subject to considerable uncertainty owing to limited availability of palaeoclimate constraints, the results suggest that the gradual emergence of the 100,000-year cycles can be attributed to the increased ability of the merged North American ice sheets to survive insolation maxima and reach continental-scale size. The oversized, wet-based ice sheet probably responded to the subsequent insolation maximum by rapid thinning through increased basal-sliding(13,14), thereby initiating a glacial termination. Based on our assessment of the temporal changes in air temperature and ice volume during individual glacials, we demonstrate the importance of ice dynamics and ice-climate interactions in establishing the 100,000-year glacial cycles, with enhanced North American ice-sheet growth and the subsequent merging of the ice sheets being key elements.
hotrod (18:46:16) :
In fact warm moist conditions might reduce the dust components, due to wind erosion.
In fact data supports this. Have a look at the icecore record as given in http://en.wikipedia.org/wiki/Ice_core ( not a hotbed of skeptics). The dust measures are high when it is very cold. This is explained as the result of most of the water tied up in ice and large areas open to wind erosion.
Paul Hildebrandt (12:13:33) :
Your Figure 7 goes back to 1750. Lee’s graph goes back to circa 1610. The portion of Lee’s graph from 1750 on is virtually identical to your Figure 7. Why is your graph correct and his wrong?
Because it is not identical. The correct [see below] sunspot numbers are higher than on his graph before 1945.
mikelorrey (13:04:50) :
“Except that the Sun was not more active during the 20th century.”
Actually, it was. The solar cycles of the 20th have had far higher peak sunspot counts and higher 11 year running average sunspot counts than previous centuries
Recent work [summarized in http://www.leif.org/research/Napa%20Solar%20Cycle%2024.pdf ] shows why I make the statement that activity in the 19th century [and 18th for that matter] was comparable to that in the 20th.
Thanks for the very interesting article about ice ages. It prompts a question which nobody here seems to be asking: shouldn’t we be more worried about the global cooling attendant upon returning to ice age conditions than about global warming? Or, isn’t concern about global warming short-term alarmism, and in the longer term our real problem is going to be global cooling?
That said, I’ve yet to read anything anywhere which says exactly when the next ice age is going to start. In part that may be because ice ages gradually deepen, and so the start of the next ice age will likely be one of a gradual cooling rather than a sudden, overnight (in geological terms) return of deep freeze conditions.
And if we’re currently thinking of ways of preventing AGW, shouldn’t we be thinking just as hard about ways of slowing or preventing a long cooling trend as a brief AGW warming trend? By adding CO2 to the atmosphere, for example. Assuming that CO2 does have some warming effect, might it not be argued that some global warming now will translate into a welcome delay in the start of the next ice age?
And if we’re going to be sceptical about AGW, shouldn’t we be equally sceptical about Milankovitch cycles? It’s another relatively new idea (I think Milankovitch figured it out in the 1920s). And I’ve read that it doesn’t explain everything.
Dr Archibald
You said “This meant that a large area of the Earth’s surface changed from being very low-albedo ocean to highly reflective ice and snow.”
Is that the case right up at the poles where angles of incidence are very shallow. Change of albedo should have only a marginal effect. If ice melt exposes open sea water, surely the incoming solar will still be largely reflected off the ocean surface at low angle of incidence?
Also, Kirchoff’s law tells us that a darker surface will be a more efficient radiator. So there should always be a counter-acting response to ice retreat at very high lattitude.
These should be good reasons to expect ice at the caps, regardless of the local topology. Just asking.
I believe Dr. Archibald’s arguments should be taken very, very seriously by people who really want to get to the bottom of the climate change mess. His reasoning is so simple and unbiased that the dogma gang should have a lot to learn from his way of approaching things.
My own pet theory is that the closing of the gap between the Americas stopped the direct oceanic connection between the Pacific and Atlantic oceans, forcing a long circuitous route for the deep ocean currents to transfer heat from the Pacific, which is low albedo water, to the Atlantic which is in the middle of the high albedo land hemisphere consisting of the americas and eurasian landmasses. Once the direct route was broken, most of the heat has to be transferred in deep ocean currents round Australia and Africa.
Both the ice ages and the joining of the Americas occurs 3 million years ago. Coincidence? I think not.
Thanks for the connection.
Dr. Roy Spencer has a new blog entry out about cloud feedbacks….very interesting.
http://www.drroyspencer.com/2009/02/what-about-the-clouds-andy/