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What Causes Ice Ages?

  1. Mar 3, 2007 #1
    There is recent research that supports the assertion that the start of an ice age epoch is initiated by an increase in Galactic Cosmic Rays (GCR) and that the ice age glacial/interglacial cycle is controlled by processes that periodically modulate the amount of GCR that penetrates the solar large scale magnetic field and the geomagnetic field, and hence penetrates the earth's atmosphere.


    The following is a link to a paper that provides data and an explanation for the mechanisms, to support that GCR hypothesis.

    From Kirby, Mangini, and Muller's 2004 Paper "The Glacial Cycles and Cosmic Rays"

    "The cause of the glacial cycles remains a mystery. The origins is widely accepted to be astronomical ...(however) ... high precision paleoclimatic data revealed serious discrepancies with the Milankovitch model that fundamental challenges its validity and re-open the question of what causes the glacial cycles. We propose that the ice ages are not driven by insolation cycles but by cosmic ray changes ..."

    The Glacial Cycles and Cosmic Rays

    http://arxiv.org/pdf/physics/0407005

    Comment:
    GCR creates ions in the atmosphere which recent papers show affects the amount of low level cloud cover. The data shows a decrease in GCR results in a decrease in low level clouds which will warm the planet and an increase in GCR results in an increase in low level clouds. See the thread Clouds and Albedo for details.
     
  2. jcsd
  3. Mar 3, 2007 #2
    Hi William,

    Thanks for your posts and most welcome here. That's indeed an excellent paper, not entirely unexpected. But very helpful to convincing others that our current explanation for ice ages is a mess. I glanced over it and will study more in detail later. So the next comments are not very well founded and I may be forced to withdraw them but anyway.

    I know about the struggle of Rich Muller to solve the ice ages (inclination cycle and dustband). But the more ideas you have the more you risk of getting falsified. It doesn't seem to harm him.

    The idea appears to be that long term cosmic ray activity perhaps regulated by the magnetic field causes the dramatic climate changes. The sun rather than the earth being the driver of the geo magnetic field

    First of all, the overwhelming preassumption of ice ages is the warm - cold waxing/ waning ice sheet idea. Considering the "warm" mammoth steppe in Siberia (>3 degrees warmer than today) during the Last Glacial Maximum, any 'solution' that ignores this, cannot be a solution. To me it appears that the ice ages is much more about arid - moist due to a certain pet idea,

    I would think that the registration of the paleo magnetic field in benthic stacks at the sea floor would register the Earth generated part of the magnetic field, rather than the solar part. This would suggest that the main driver might be terra firma itself. Years ago I discussed the apparant ~30-50ka lag of glacial terminations to paleomagnetic excursions with Prof Langereis, who supervised Sint800. result: could be, could not be.

    Moreover, comparing the frequency bands of 10Be with Karners Benthic stack (deep ocean foraminifera) one should still wonder why the stacks don't show any inertia or millenium scale delay due to water mixing between surface events and deep ocean events.

    BTW, Karners stack is outdated, they should have used Lisiecky and Raymo's LR05 stack but of course it's tempting to stick with own work.

    Oh sorry this is not a peer review of course.
     
    Last edited: Mar 3, 2007
  4. Mar 3, 2007 #3
    Unstable Geomagnetic Field? Affects on Climate.

    Hi Andre,

    In reply to this excerpt from your comment:

    "The idea (my comment, Kirby's paper Glacial Cycles and Ice Ages, see above for details) is that the Ice age appears to be driven by changes in the cosmic ray activity which are regulated by the geomagnetic field. The large changes in the GCR flux it is hypothesized causes the observed dramatic climate changes, that are observed (glacial/interglacial cycle.) The sun rather than the earth being the driver of the geo magnetic field."

    Yes, something certainly is triggering a massive drop in the geomagnetic field. There is new data that indicates that the geomagnetic field, spends 20% of its time in a low state (5 to 10 times less than the current geomagnetic field intensity and unstable.) The question is what causes the geomagnetic field to drop and to become unstable? Changes happen for a reason.

    From Zang and Gubbin's attached paper "Is the geodynamo Unstable?"

    http://eprints.whiterose.ac.uk/archive/00000416/01/gubbinsd4.pdf

    Recent palaemagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops by a factor of 5-10... The 'normal' state of the geomagnetic field dominated by an axial dipole, seems to interrupted every 30-100 kyrs: it may not be as stable as we once thought."

    "These important results paint a rather different picture of the long term behavior of the field from the conventional one of a steady dipole reversing at random intervals; instead, the field appears to spend up to 20% of its time in a weak, non-dipole state (Lund et al 1998). ... This raises a number of important but difficult questions for geodynamo theory. How can the geomagnetic field change, so rapidly and dramatically? Can slight variations of the geomagnetic field affect the dynamics of core convection significantly? If so, is the geomagnetic process intrinsically unstable?
     
  5. Mar 4, 2007 #4
    problem here is that the paper ignores Earth orbital pertubations. Earth precession does have a big impact on Earth Core dynamics (see Jim Vanyo). Aparantly, this is not recognised by Gubbins.

    I'm time pressed, Sorry, more later.
     
  6. Mar 5, 2007 #5
    When did Ice Sheets Start to Form In North America?

    For those who are not familiar with the glacial/interglacial cycle, attached is a link to a lecture that provides planetary temperature temperatures over the last 100 kyrs.

    John Stone, Climatic Record the Last 100,000 years

    http://www.washington.edu/research/or/symposium/stone.pdf


    A couple of comments concerning this ice age epoch.

    The ice sheets started to form in the Northern Hemisphere roughly 2.5Ma years ago. The Quaternary Ice Age has a cyclic pattern. Ice sheets have formed and then retreated, roughly 25 times, in the last 2.5 Ma. At the beginning of the Quaternary ice age 2.5 Ma yrs ago, the glacial/interglacial cycle period was 41kyr. 700 kyrs ago the glacial/interglacial cycle changed to a 100 kyr cycle, where the interglacial period is less than 20 kyrs and the glacial cycle is roughly 80 kyrs. Specifically why the glacial/interglacial cycle changed from a 41kyr cycle to a 100 kyr cycle is not known.

    The last glacial period is known as the Wisconsin Glacial period. During the coldest period of the last glacial period, all of Canada, portions of the Northern USA States, and large portions of Europe and Russia were covered with a ice sheet that was 3000 Meters to 4000 Meters thick. (Roughly 2 miles thick).

    Attached is a paper by Raymo that discusses the scientific problems with explaining the 41 kyr cycle, using an insolation based theory. As Raymo notes in the paper, the 21th century climate models cannot model the 41 kyr pattern.

    The 41 kyr World: Milankovitch’s Other Unsolved Mystery

    http://www.agu.org/pubs/sample_articles/cr/2002PA000791/2002PA000791.pdf

    Comment:
    Proxy evidence shows that the geomagnetic field changes with a 41 ky and 100 kyr cycle. An increase in the geomagnetic field reduces Galactic Cosmic Rays (GCR) that strike the atmosphere. GCR atmosphere strikes, is inversally correlated with low level cloud cover. An increase in GCR cause a decrease in low level clouds and vice versa. As the noted in the paper linked above, cyclic changes in amount of planetary low level clouds is hypothesized to be the cause of ice ages and the glacial/interglacial cycle.
     
  7. Mar 16, 2007 #6
    Abrupt Climate Change

    From Broecker’s famous Angry Beast article (see attached link for details) in which he discussions macroclimate models and extreme climate changes:

    The current climate models do not explain and cannot reproduce the sever and abrupt climate changes in the proxy climatic record.

    Comments:
    1) In the Angry Beast article Broecker postulates that the Younger Dryas (Youger Dryas is the name for the sever cooling event that occur during the start of this interglacial) was caused by a fresh water pulse, from Lake Agassiz (Lake Agassiz was a massive glacial lake in the Province of Manitoba) Subsequent data has shown that the fresh water pulse hypothesis is likely not correct, as the fresh water pulse occurred a 1000 years before the Younger Dryas. See attached paper below for the data and another hypothesis.

    2) An alternative hypothesis to Broecker’s non-linear knife edge hypothesis (Small natural or anthropogenic changes can force the macroclimate from one mode to another mode and hence create the massive ice sheets and so forth.) is the hypothesis there is a massive semi-periodic external forcing, that forces the macroclimate from one mode to another.

    Link: Reduced solar activity as a trigger for the start of the Younger Dryas?

    http://scholar.google.com/url?sa=U&...aphy/GEC/Reduced_solar_activity_as_a_trig.pdf
     
  8. Mar 18, 2007 #7
    That's a fairly general paradigm, but it's hard to see how a mouse can lead the charge of an angry herd of elephants.

    [edit: added:

    http://www.americanscientist.org/template/AssetDetail/assetid/51963?fulltext=true&print=yes#52137

    (the whole article is highly recommended reading but here the focus is on:

    Sorry William, if I'm disturbing your lesson material but the story seems to be completely different. In many proxies there is clear evidence that the average Younger Dryas temperature was not that low, although the seasonality extremes were much greater compared to the adjacent periods


    Now Am I insane or? Since textbook lesson one, A sub 1 about the Quartenary is that the Younger Dryas was a bitterly cold interval with massive glacier advance..NOT!

    So why that misconception? The main reason for this are the problems with carbon dating. In the early 70-80ies when carbon dating matured, little was known about the variability of Atmospheric delta14C. So they found a lot of glacial activity both around 11,000 and 10,000 carbon years ago, the Younger Dryas. Then the Greenland ice cores showed massive Younger dryas changes between 12,800 and 11,600 layer counted years and independetly from other proxies it became slowly clear that the carbon dating underestimated the age by 1000-2000 years in that range.

    Nowadays carbon dating and calibration is much more accurate and the glacial features are found to be typically something like 10,010 +/- 50 or 10,970 +/- 50 carbon years. These dates would calibrate to 11.500 +/- 100 calendar years and 12005 +/- 25, calendar years using the INTCAL04 conversion table:
    http://www.radiocarbon.org/IntCal04.htm

    But that's outside the Younger Dryas in the Greenland Summit ice cores, actually at its transitions. So there you are looking at the reason of the widespread misconception. The 'massive' glaciations took place just prior and after the Younger Dryas in outbursts of extremely wet climates of the Allerod and the Preboreal, not during the event itself.

    Then what was the Younger Dryas? A hyper arid period, likely due to a greatly reduced water cycle, due to very low sea surface temperatures. Note that the last Siberian refuge of Mammoths during the Younger Dryas was northernmost Taimyr Peninsula, currently high arctic tundra, then a productive grassy steppe with horses, reindeer, aurox etc.

    See also these thread for some substantiation:

    https://www.physicsforums.com/showthread.php?t=125669
    https://www.physicsforums.com/showthread.php?t=73130
     
    Last edited: Mar 18, 2007
  9. Mar 18, 2007 #8
    Effect of Stoppage of Gulf Stream?

    Hi Andre,

    I agree with your above comment “it's hard to see how a mouse can lead the charge of an angry herd of elephants.”

    Andre's above comment provides a link to Richard Seager’s article in American Scientist “Is the Gulf Stream responsible for Europe’s Warm Winters” which debunks the myth that a sudden stoppage of the Thermal Haline Conveyor (THC) for what ever reason, would result in a sudden drop in European temperatures.

    The Gulf Stream myth has been spread in the popular press, movies, and so forth. Seager’s paper also questions the assertion that THC stoppage could have been the forcing function for the multitude of sudden cooling events that occur in the proxy climate record.

    The following is an excerpt from Seager's article. (See the link for details and a graph that shows, based on analysis and data that is widely accepted, that the atmosphere rather than ocean currents is responsible for the majority of heat transfer equater to mid latitudes.)

     
  10. Mar 18, 2007 #9
    In March 2004, a geological team from the University of Wisconsin found evidence of cyclical changes in cosmic ray bombardment of rocks. They didn't assume from that, that the rate of bombardment was cyclical. Since cosmic rays don't penetrate very far, they took it as evidence that the rocks were intermittently covered by ice. Their work showed that ice ages are globally simultaneous, rather than local, events.

    http://www.news.wisc.edu/9557.html

    I know you're familiar with the CHRONOS PROJECT:
    http://www.universetoday.com/am/publish/geologists_use_particles_earth_surface.html

    Kirkby and Mangini analyzed ocean sediments rather than surface rock. Is it possible that the variation they found is due to changes here on Earth, rather than in the rate of cosmic ray bombardment? i.e. changes in dust levels in the atmosphere, or in the rate of erosion by wind and/or water?
     
  11. Mar 19, 2007 #10
    Galactic Cosmic Rays

    Hi BillJx,

    In reply to your comments:

    A) Evidence that shows simultaneous planetary temperature changes glacial/interglacial. If the evidence which you provide a link to is correct, then there must be a mechanism that could cause simultaneous planetary temperature changes.

    B) Galactic Cosmic Rays
    Galactic Cosmic Rays (GCR), which are mostly protons, travel at about 150,000 km/s to just less than 300,000 km/s the speed of light. A portion of the GCR flux penetrates the sun’s and earth’s magnetic field, and through secondary reactions with molecules in the earth’s atmosphere, create charged nuclei, which affect cloud formation.

    GCR protons have a typical energy of range of 100 Mev to 10 Gev. The solar system is currently traveling through the spiral arms of the galaxy, a region where the GCR more than doubles in magnitude. It is hypothesized that the increase in GCR is the reason (trigger) why the earth is currently in an ice epoch.

    GCR is modulated by changes in the earth’s magnetic field and by changes in the sun’s large scale magnetic field. (Stronger field less GCR. Less GCR, less clouds and as clouds reflect the sun, less clouds would result in an increase in the planet's temperature.)

    B) Proxy Data to determine Past GCR Levels
    GCR create isotopes which do not occur naturally. The researchers can isolate the cosmogenic isotopes in sea floor sediment and in the ice cores. By measuring the relative abundance of the cosmogenic isotopes, researches can make determine an estimate of past GCR level.

    Attached is a link to Shaviv and Vezier’s paper that shows there is correlation between the start and end of the glacial epoch with increases and decreases of Galactic Cosmic Ray (GCR). Shaviv examines meteorites (GCR creates isotopes in the meteoriods) to find how the GCR varied over time, over 300 million years. Shaviv believes his analysis shows, that the increase and decrease of GCR correlates with the passage of the solar system through the spiral arms of the galaxy. GCR intensity is higher in the spiral arms as there is higher formation of stars in the arms.

    http://www.phys.huji.ac.il/~shaviv/Ice-ages/GSAToday.pdf

    Also attached is Shaviv and Vezier’s response to criticism concerning their paper.

    http://www.phys.huji.ac.il/~shaviv/ClimateDebate/RahmstorfDebate.pdf

    See the thread in this forum "Clouds and Reflectivity" for how it is hypothesized that GCR changes and solar changes affect low level cloud intensity.
     
  12. Mar 20, 2007 #11
    But don't forget that several mammoth mummies found(Jarkov, Fishhook, Yukagir, Mol et al 2006), dated around the onset of the Last Glacial Maximum, confirm that there was a productive (hence not too cold) grassy steppe in what is now the high arctic tundra of Siberia with very little grass. This disdains a global character of the cooling. Also there are good signs that there was no ice age going on in the lower lattitudes (Colinvaux et al 2000, Kastner & Goñi 2003,).

    That's why I invented the pulsating equator.

    Refs:

    Colinvaux P.A., P.E. De Oliveira, M.B. Bush, 2000, Amazonian and neotropical plant communities on glacial time-scales: The failure of the aridity and refuge hypotheses, Quaternary Science Reviews 19 (2000) pp 141-169

    Kastner, TP., Goñi, MA 2003 Constancy in the vegetation of the Amazon Basin during the late Pleistocene: Evidence from the organic matter composition of Amazon deep sea fan sediments, Geology,Volume: 31 Issue: 4 Pages: 291-294

    Mol, D., Tikhonov A., van der Plicht J., Kahlke R-D., Debruyne R., van Geel B., van Reenen G., Pals J. P., de Marliave C., Reumer J.W.F., 2006. Results of the CERPOLEX/Mammuthus Expeditions on the Taimyr Peninsula, Arctic Siberia. Russian Federation Quaternary International, January volumes 142-143 pp. 186-202.
     
    Last edited: Mar 20, 2007
  13. Mar 21, 2007 #12
    Pulsating Equator Hypothesis

    Hi Andre:

    Re: "This disdains a global character of the cooling. Also there are good signs that there was no ice age going on in the lower lattitudes (Colinvaux et al 2000, Kastner & Goñi 2003,). That's why I invented the pulsating equator."

    Why don't you start a new thread, to discuss the Pulsating Equator Hypothesis hypothesis. I would be interested to discuss, but I need a better base from which to start the discussion. What is the hypothesized mechanism? What drives it? Is it periodic?

    As to significantly warmer temperatures, at LGM. Does the sea level reflect higher or lower temperatures, at the LGM? i.e. Is there data that does not support significantly warmer temperatures? Does other data support the hypthosis? If not why not?

    See the attached link to a paper that discusses sea level last 350 kyrs.

    http://www.geol.ucsb.edu/faculty/lea/pdfs/Lea QSR 2002.pdf

    As to the high latitudes being warm during the LGM, can you provide a link to a full paper rather than to an abstract? Without data and analysis there is nothing to discuss.
     
  14. Mar 22, 2007 #13
    Dear William, thanks for your interest, lets go over all this.

    We could revive this thread:

    https://www.physicsforums.com/showthread.php?t=153634

    I know the part of the scientific method saying that the hypothesis requires a physically sound mechanism. We know that the Earth has a pulsating equator now, albeit in millimeters. Why can't it be ~100 meters order of magnitude on a millenium time scale on an equatorial bulge of 21 km. But a mechanism, is far from understood. To explain the ice ages it would have to be the cause of the 100,000 years cycle, which cannot be explained as a Milankovitch wobble.

    Since the milankovitch cycles are fairly stable on a multi million years time scale and the 100,000 years cycle emerged only 900,000 years ago, the only factor I can think of such a behavior, is the solid inner core of the earth, which is assumed to be growing under the pressure and the cooling. 900,000 years ago it may have exceeded a critical size to break the physical stability of the core spin axis. The resultant misaligment of core and mantle spin axis would have caused turbulence, excess heat, which reduced the core size again, which could have permitted the spin axes to realign eventually, starting a new cycle of cooling and core growing. I know there is an old publication that assumes that the size of the equatorial bulge is also a function of the total fluidity of planet (haven't found it back yet). Perhaps it is. But surely that's all highly speculative.

    Point is that it seems physically not impossible to have a pulsating equator and we have one now.

    http://www.space.com/scienceastronomy/equator_bulge_020801.html

    Others have thought about it:
    http://adsabs.harvard.edu/abs/1982Prir........46M

    There is an abundance of proxy data considering paleo sea surface temperatures (Mg/Ca Ca/Sr, d18O, alkenones etc). The problem is however the dependence of those data on assumed chemical conditions. Ion ratios and biota activity are sentitive to pH, the biota producing the proxies may have reacted on changing conditions and you bet that the oceans reacted vigourously on the moving of the ocean bottom, amplified by massive methane hydrate decomposition events on record (Bryn et al 2005, Evans et al 2005, Maslin et al 2005, Mienert et al 2005) Refs here:

    http://home.wanadoo.nl/bijkerk/ext-refs-new.pdf

    Perhaps have a look at that ref list and realize that there must be a common denominator that fits for all of those phenomenons. There is the puzzle of the Pleistocene.

    Sea levels is perhaps the most important evidence. We know that there are many anomalies actually refuting the common paradigm. We also know that there was not nearly enough ice during the LGM (due to the alleged but missing ice on Siberia) to cause the 127 meters sea level rise for instance. We also know that there is no source for melt water pulse 1A. See:

    https://www.physicsforums.com/showthread.php?t=113807

    however a moving equatorial bulge would be a splendid explanation instead.

    As usual papers like that fill in the blanks with assumptions based on the current paradigms, ignoring the anomalies. There are only a few areas from where sea level proxies are used notably the corals of Barbados and the mangroves of the Indonesian Sunda shelf, both on rather low lattitudes. A pulsating equator is probably explaning the sea level changes much better.

    Interesting warm indicator are insect assemblages for instance in my ref list:
    Alfimov et al 2003, Kuzmuni 2001, Schirrmeister et al 2002, Sher et al 2002

    Most of the papers are behind bars and not directly assessable online. Sometimes reports of conferences help. Dig into this one for instance:

    http://www.yukonmuseums.ca/mammoth/progabst.htm

    Click the abstracts on the bottom of the page for a wealth of information, for instance:

    http://www.yukonmuseums.ca/mammoth/abstrmol-mor.htm containing basically the same information of Mol et al 2006.

    Furthermore, my pdf library is a few gigs, containing most, if not all of those listed publications. Not free papers have been accumulated by visiting homepages of authors, and/or mailing them with requests for papers (works very well. Sometimes, you get more than you ask for) or asking around. My study partner is very good at that. You could PM me an email address.
     
    Last edited: Mar 22, 2007
  15. Mar 24, 2007 #14
    Periodic Ocean Level Fluctuations - Heinrich Events

    Hi Andre,

    The Heinrich events are simultaneous ice sheet discharges from three ice sheets. The Laurentine, Greenland, and the Scandianvian ice sheets. As noted in the following review paper, there is a periodic rapid accumulation of ice (which is hypothesized to be due to a periodic increase in solar activity) that is followed by a very cold period, during which the ice sheets discharges ice into the ocean and stabilize.

    Review Article: "Sea Level Change through the Last Glacial Cycle" by Lambeck and Chappell

    http://geochemistry.usask.ca/bill/courses/International Field Studies/Sea level.pdf

     
  16. Mar 25, 2007 #15
    Thanks William, I included the Heinrich events in this little presentation here:

    http://home.wanadoo.nl/bijkerk/Pulsating-ice-age.pdf

    #17 on page 7.

    The article is a good example of filling in the wide wide gap between data and blanks with scholar assumptions. The most important is the oceanic isotope - ice sheet volume hypothesis of Rutherford I believe. However when you check the numbers and the calculations, you're short a massive Siberian ice sheet, which did not exist at all.

    Sea levels are much more complicated in the pulsating equator setting.
     
  17. Apr 9, 2007 #16
    Abrupt Planetary Cooling?

    Is the abrupt cooling event that occurred 8200 years ago, after a period of very high solar activity, an analogue for the current solar macro cycle changes? (See Astrophysics in this forum: Thread “Solar Cycle Changes” for details concerning recent anomalous solar changes.)

    The following is data and analysis that shows there was an abrupt planetary cooling event 8200 years ago, at a time when global temperatures were similar to or warmer than current temperatures. The paleo data indicates that the cooling event was wide spread; simultaneously affecting the Northern Hemisphere and tropical seas. The 8200 yr cooling event was the most sever temperature change in this interglacial period. There is also evidence of a concurrent drop in solar activity with the 8200 yr cooling event.

    http://www.geo.arizona.edu/palynology/geos462/8200yrevent.html

    Abrupt tropical cooling ~8,000 years ago
    M.K. Gagan, L.K. Ayliffe*, H. Scott-Gagan, W.S. Hantoro, B.W. Suwargadi, D. Prayudi, M.T. McCulloch


    http://wwwrses.anu.edu.au/enproc/EP/ep_annrep/gagan.html




    Comments:
    1) Recent changes in the Sun
    As noted in the astrophysics section of this forum (See thread: “Solar Cycle Changes”) the sun is currently spotless. Solar observers have noted a significant asymmetrical reduction in the solar meridian deep polar flow. The deep meridian flow is believed to control the solar magnetic cycle. There has been an abrupt drop in the velocity of the solar wind which is expected as the solar magnetic cycle appears to have been interrupted.

    2) There is evidence that 20th century changes in solar wind caused the planet to warm and cool. See thread “Clouds and reflectivity”, for satellite data and earthshine data that shows there is direct correlation with 20th century changes in the solar wind and low level clouds. Also included in that thread is data that shows there is correlation with the solar parameter Ak (Ak is a measure of the solar parameters that affect the magnetic field about the earth) and the pattern of the 20th century temperature changes.

    3) An increase in the geomagnetic field reduces the amount of Galactic Cosmic Rays (GCR) that strike the earth's atmosphere. Satellite data and earthshine data shows that an decrease in GCR causes a decrease in low level clouds and an increase in GCR causes an increase low level clouds. Data also indicates that high speed solar winds causes an increase in the Global Electric Current, which through the process of "electroscavenging" removes cloud forming ions. From 1974 on, solar coronal holes started to appear at the end of the solar cycle which created very high speed solar winds. Through the process of electroscavenging it is believed that the high speed solar winds caused a significant reduction in low level clouds.
     
  18. Apr 12, 2007 #17
    Milankovitch 100k cycle

    I am mystified by the comments in earlier postings on this thread, that there was no known mechanism by which the Milankovitch 100k cycle can influence glacials/interglacials.

    Maybe I am simplistic (not maybe, I know I am!) but I have always understood the following to be the cause and mechanism.

    The cause is the orbital periodicities of Earth and the gas giant planets and resulting planetary positions relative to the Sun. These cause Earth's orbit to oscillate between circular and elliptic, with a period of between about 94,000 and 114,000 yrs and an amplitude of 5% to 7%, depending on the precise planetary configuration. The Sun, of course, stays at one focus of the ellipse of Earth's orbit.

    I have often read that this small change in eccentricity cannot explain ice ages, but to me, the opposite is very clear. It is easy to explain with a diagram, but I will try with words.

    First, although the eccentricity is low, the effect is large because of the inverse square law. With a minimum (circular) orbit radius of
    1.471 x 10e8 km, an eccentricity of 7% at max. aphelion gives max. radius of 1.574 x 10e8 km. The inverse square relationship results in Earth at max. aphelion receiving only 87.3% of the solar energy received at perihelon or circular orbit.

    A NASA website:

    http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch_2.html

    - says that Earth receives 20-30% less insolation at max. eccentricity, with no explanation, but I cannot see how that is worked out - if they are right, my point is more strongly made. If anyone can explain this conflict, I would be grateful.

    Now the tricky part. It takes 50,000yr to get from circular orbit to max. eccentricity. Therefore, for about 20,000yr (10,000 before and after max.), Earth receives only 90% of max. insolation for 3 months of every year. Both poles, by the way. And in that 20,000yr, almost a complete precession cycle occurs, so the effect is well distributed. That is surely an effective trigger for an ice age. As Earth approaches circular orbit, it heats rapidly as it increasingly gets almost maximum insolation all year round; as it leaves circular orbit and appoaches max. eccentricity, it radiates heat slowly; thus we get the sawtooth temperature profile seen in ice cores.

    In between these two extremes, the 21,000yr precession cycle can induce minor ice ages alternately between the two poles when orbital eccentriciy is high, but not when it is low or circular.

    This view also gives us a timing for peak of this interglacial. Orbital eccentricity is currently about 3%. Depending on the orbital eccentricity at the nadir of the last ice age (5% or 7%) we are just before or just after halfway to the peak of the interglacial - 30k or 20k yrs to go! Given the minimum temperature recorded in the Vostok core at 28k yrs ago, I would guess at 7% eccentricity at the last max. aphelion, about 20k years to go to mid-interglacial and crisping up nicely.

    I would be very interested to read any critique of this - always ready to learn.

    For some reason I cannot get this site to accept the full NASA website URL - after .gov/ it is Library/Giants/Milankovitch/milankovitch_2.html. See if this works!
     
  19. Apr 12, 2007 #18
    PS - I am not proposing this is the only forcing mechanism - only that it is mechanism behind the obvious approx. 100k cycle seen in ice cores, etc.

    There are many minor cyclic influences, many of which I suggest we know nothing about!
     
  20. Apr 12, 2007 #19
    You did quite some digging, Peter.

    First of all, the 8200years event as well as the Younger Dryas "cooling" etc is almost solely based on water isotopes, d18O, dD which has been declared temperature proxies in 1997 by Jouzel et al. They are NOT!

    d18O in precipitation is depending on temperature during consensation and rain out effect. If we assume the latter constant, then the condensation temperature is a measurement of the relative humidity of the air. Low when it is dry, high when it is humid. And that fits exactly with what we see in the ice cores and other proxies. Non calor sed umor.

    See also:
    http://home.wanadoo.nl/bijkerk/refuting the Greenland paleo thermometer1.pdf

    This would make the cold nature of the 8200y event suspect.

    The 100 ky cycle is indeed not related to Milankovitch and for two reasons it doesn't make sense. Why did it suddenly start about 900,000 years ago while the milankovitch cycles linger on for millions of years with only very small variation:

    http://home.wanadoo.nl/bijkerk/41-100k-world-milankovitch.GIF

    How could a Milankovitch minimum variation around 420,000 year ago trigger the largest "deglacitation spike"

    http://home.wanadoo.nl/bijkerk/milanko3.GIF

    See also some problems around 200,000 years ago.

    For a completely different idea, see the pulsating equator thread.
     
  21. Apr 14, 2007 #20
    Ice Age's and Milankovitch's 100k cycle.

    Hi Peter Lloyde

    In response to your comments.


    1. First the earth is currently at perihelion during the Northern Hemisphere winter (around December 25) and at aphelion during the Northern Hemisphere summer. Due to the seasonal difference, of the distance of the earth, from the sun, the Northern Hemisphere winters are roughly 4C warmer and the Northern Hemisphere summer's are roughly 4C colder due to the orbital effect. Note however that the opposite is true for the Southern Hemisphere. Cold Northern Hemisphere summers are according to the Milankovitch hypothesis, the reason why the glacial cycle begins.

    Comments:
    Another interesting question is why do the ice age epochs begin and end? This ice age epoch began roughly 17 MM years ago with ice sheets forming in the Antarctic. (The Antarctic has been polar centric for roughly 100 MM years. No ice sheets on the Antarctic continent prior to roughly 20 MM years and a climate warm enough to support reptiles.) Then roughly 1.7 MM years ago ice sheets began to form in the Northern Hemisphere. The general population is not concerned by the glacial period because they believe it be a gradual change.

    Some have stated that the next glacial period will not occur for 20 k years which is not correct, based on the proxy paleo climatic data and the competing hypothesis as to what causes the glacial/interglacial cycle. The past interglacial periods have all been shorter than the Holecene. Based on the pale data this interglacial period will end abruptly.

    It is interesting to note that the sun appears to be moving to a super Maunder type state in which the sun spot cycle stops. The Maunder minimum (Little Ice Age) lasted for 70 years.

    2. Northern hemisphere insolation is currently the same as during the last glacial maximum. Why are we not in an ice age? i.e. The opposite was true when the glacial period ended.

    3. When an ice age begins (based on the paleo data) the entire planet simultaneously cools, which does not make sense from the stand point of the insolation hypothesis. Also the cooling is very rapid. There is evidence of periodic abrupt climatic changes. Abrupt climate changes cannot be explained by the insolation hypothesis.

    4. The insolation hypothesis does not explain why the ice ages prior to 700 kyears ago followed a 41 k year cycle and then starting 700 k years started to follow a 100 kyear cycle.
     
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