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Will there ever be a 2nd ice age?

by Kutt
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Kutt
#1
Jan7-13, 11:13 PM
P: 236
Is the ace age ever expected to return at any point in the distant future?

Human beings survived the first ice age, so hypothetically speaking, what effect would it have on modern civilization if it occurred today?
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russ_watters
#2
Jan7-13, 11:20 PM
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Second? http://en.wikipedia.org/wiki/Ice_age#Major_ice_ages
Kutt
#3
Jan8-13, 01:58 AM
P: 236
Excuse me, will there be another ice age?

Travis_King
#4
Jan8-13, 09:57 AM
P: 841
Will there ever be a 2nd ice age?

You should read the wiki article...It discusses this very point.

Just a snippet:
The Earth has been in an interglacial period known as the Holocene for more than 11,000 years. It was conventional wisdom that the typical interglacial period lasts about 12,000 years, but this has been called into question recently. For example, an article in Nature[34] argues that the current interglacial might be most analogous to a previous interglacial that lasted 28,000 years. Predicted changes in orbital forcing suggest that the next glacial period would begin at least 50,000 years from now, even in absence of human-made global warming[35] (see Milankovitch cycles). Moreover, anthropogenic forcing from increased greenhouse gases might outweigh orbital forcing for as long as intensive use of fossil fuels continues.[36]
tadchem
#5
Jan9-13, 12:56 PM
P: 70
In other words, "we don't know." It could start tomorrow, it may not start for another 50,000 years. If the Yellowstone caldera erupts or some other VERY large volcanic event blows, we could have a mini-ice age precipitated by the volcanic dust, ash, and sulfur injected into the stratosphere. Pinatubo chilled the earth for a year.
Thermodynamics tells us the sun's heat cannot last forever.
10GYr from now?
BenG549
#6
Jan13-13, 08:51 PM
P: 70
Quote Quote by Kutt View Post
Is the ace age ever expected to return at any point in the distant future? Human beings survived the first ice age, so hypothetically speaking, what effect would it have on modern civilization if it occurred today?
According to my open university module on exploring science, technically speaking we are still in an ice age but currently we are in an interglacial period - http://en.wikipedia.org/wiki/Interglacial
MPKU
#7
Jan13-13, 08:53 PM
P: 50
Sure, we may not know, but as the way of the magic eight-ball, "All signs point to 'Yes'". I'd be willing to bet my life that there will be another one. When? That's a different question.
Drakkith
#8
Jan15-13, 01:05 AM
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FYI for those who didn't read the linked article in post #2, but we are STILL IN AN ICE AGE.

An ice age, or more precisely, a glacial age, is a period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual pulses of cold climate are termed "glacial periods" (or alternatively "glacials" or "glaciations" or colloquially as "ice age"), and intermittent warm periods are called "interglacials". Glaciologically, ice age implies the presence of extensive ice sheets in the northern and southern hemispheres.[1] By this definition, we are still in the ice age that began 2.6 million years ago at the start of the Pleistocene epoch, because the Greenland and Antarctic ice sheets still exist.[2]
SpaceDreamer
#9
Jan25-13, 08:14 PM
P: 46
The earth seems to go through periods of warming and cooling and those periods of cooling can bring an ice age depending on the temperature change. We will go into another ice age, the correct answer is we don't know as we cannot predict the future but the most likely explanation is yes but the real question is when.
jduster
#10
Feb4-13, 10:35 AM
P: 46
Considering the volatile history of Earth, it's all but certain that the Earth will have many more ice ages long after we're dead.
betzalel
#11
Feb15-13, 09:53 PM
P: 40
There have been 22 glacial/interglacial cycles. For the last 1.2 million years, the warm interglacial periods have a duration of roughly 10,000 to 12,000 years and the glacial periods have a duration of 90,000 years.

Based on what has happened in the past the current interglacial period will end. As climatologists do not understand what causes the glacial/interglacial cycle and what causes the past abrupt climate change events in the climate record, the "predictions" of when the current interglacial period will end are fiction, media discussions.

The last glacial period is called the Wisconsin glacial period as all of Canada and the Northern US states was covered by a 2 mile thick sheet of ice. Northern Europe has also covered by a massive ice sheet for roughly 90,000 years.

The current interglacial period, the Holecene, has interrupted by the Younger Dryas abrupt climate change event, 12,900 years ago, at which time the Northern Hemisphere changed from interglacial warm back to glacial cold, with 70% of the cooling occurring in 10 years and the glacial cold remaining for 1000 years. There is a massive change in cosmogenic isotopes that correlate with the Younger Dryas event which indicates that there was a significant solar magnetic cycle change and something that abruptly changed the geomagnetic field at that time.

The past interglacial periods ended abruptly. There is evidence in the paleoclimatic record of cyclic abrupt climate change (The large climate change events "Heinrich events" - 8000 to 10000 years, the Younger Dryas is an example of a Heinrich event - and the smaller climate change events the "Dansgaard–Oeschger" events which have a 1400 year period). There is evidence of solar changes at the time of the D-O cyclic changes and the Heinrich events, however, there is currently not consensus as to how a change to the sun could cause an abrupt climate change on the earth.

Based on solar physics it is believed the sun cannot get significantly warmer or colder in a short period, so the explanation is not a change in the TSI (Total Solar Irradiation). The explanation (if the sun is the cause of past abrupt climate change events) is therefore likely related to an unexplained change to the solar magnetic cycle.

http://nsidc.org/news/press/day_after/NRCabruptcc.pdf

Until the 1990s, the dominant view of climate change was that Earth’s climate system has changed gradually in response to both natural and human-induced processes. Evidence pieced together over the last few decades, however, shows that climate has changed much more rapidly—sometimes abruptly— in the past and therefore could do so again in the future.

http://www.esd.ornl.gov/projects/qen/transit.html
Abstract
The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on time scales of centuries to decades or even less. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11,500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well-studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (Interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries.

Various mechanisms, involving changes in ocean circulation, changes in atmospheric concentrations of greenhouse gases or haze particles, and changes in snow and ice cover, have been invoked to explain these sudden regional and global transitions. We do not know whether such changes could occur in the near future as a result of human effects on climate. Phenomena such as the Younger Dryas and Heinrich events might only occur in a 'glacial' world with much larger ice sheets and more extensive sea ice cover. However, a major sudden cold event did probably occur under global climate conditions similar to those of the present, during the Eemian interglacial, around 122,000 years ago. Less intensive, but significant rapid climate changes also occurred during the present (Holocene) interglacial, with cold and dry phases occurring on a 1500-year cycle, and with climate transitions on a decade-to-century timescale. In the past few centuries, smaller transitions (such as the ending of the Little Ice Age at about 1650 AD) probably occurred over only a few decades at most. All the evidence indicates that most long-term climate change occurs in sudden jumps rather than incremental changes.

According to the marine records, the Eemian interglacial ended with a rapid cooling event about 110,000 years ago (e.g., Imbrie et al., 1984; Martinson et al., 1987), which also shows up in ice cores and pollen records from across Eurasia. From a relatively high resolution core in the North Atlantic. Adkins et al. (1997) suggested that the final cooling event took less than 400 years, and it might have been much more rapid.
The event at 8200 ka is the most striking sudden cooling event during the Holocene, giving widespread cool, dry conditions lasting perhaps 200 years before a rapid return to climates warmer and generally moister than the present. This event is clearly detectable in the Greenland ice cores, where the cooling seems to have been about half-way as severe as the Younger Dryas-to-Holocene difference (Alley et al., 1997; Mayewski et al., 1997). No detailed assessment of the speed of change involved seems to have been made within the literature (though it should be possible to make such assessments from the ice core record), but the short duration of these events at least suggests changes that took only a few decades or less to occur.

The Younger Dryas cold event at about 12,900-11,500 years ago seems to have had the general features of a Heinrich Event, and may in fact be regarded as the most recent of these (Severinghaus et al. 1998). The sudden onset and ending of the Younger Dryas has been studied in particular detail in the ice core and sediment records on land and in the sea (e.g., Bjoerck et al., 1996), and it might be representative of other Heinrich events.
http://en.wikipedia.org/wiki/Milankovitch_cycles

100,000-year problem

The 100,000-year problem is that the eccentricity variations have a significantly smaller impact on solar forcing than precession or obliquity and hence might be expected to produce the weakest effects. The greatest observed response is at the 100,000-year timescale, while the theoretical forcing is smaller at this scale, in regard to the ice ages.[10] However, observations show that during the last 1 million years, the strongest climate signal is the 100,000-year cycle. In addition, despite the relatively great 100,000-year cycle, some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.[11] Various explanations for this discrepancy have been proposed, including frequency modulation[12] or various feedbacks (from carbon dioxide, cosmic rays, or from ice sheet dynamics). Some models can reproduce the 100,000-year cycles as a result of non-linear interactions between small changes in the Earth's orbit and internal oscillations of the climate system.[13][14]

400,000-year problem

The 400,000-year problem is that the eccentricity variations have a strong 400,000-year cycle. That cycle is only clearly present in climate records older than the last million years. If the 100ka variations are having such a strong effect, the 400ka variations might also be expected to be apparent. This is also known as the stage 11 problem, after the interglacial in marine isotopic stage 11 that would be unexpected, if the 400,000-year cycle has an impact on climate. The relative absence of this periodicity in the marine isotopic record may be due, at least in part, to the response times of the climate system components involved—in particular, the carbon cycle.

Stage 5 problem

The stage 5 problem refers to the timing of the penultimate interglacial (in marine isotopic stage 5) that appears to have begun ten thousand years in advance of the solar forcing hypothesized to have caused it (the causality problem).

Effect exceeds cause
420,000 years of ice core data from Vostok, Antarctica research station.
The effects of these variations are primarily believed to be due to variations in the intensity of solar radiation upon various parts of the globe. Observations show climate behavior is much more intense than the calculated variations. Various internal characteristics of climate systems are believed to be sensitive to the insolation changes, causing amplification (positive feedback) and damping responses (negative feedback).

The unsplit peak problem
The unsplit peak problem refers to the fact that eccentricity has cleanly resolved variations at both the 95 and 125ka periods. A sufficiently long, well-dated record of climate change should be able to resolve both frequencies,[15] but some researchers interpret climate records of the last million years as showing only a single spectral peak at 100ka periodicity. It is debatable whether the quality of existing data ought to be sufficient to resolve both frequencies over the last million years.

The transition problem
Variations of Cycle Times, curves determined from ocean sediments
The transition problem refers to the switch in the frequency of climate variations 1 million years ago. From 1–3 million years, climate had a dominant mode matching the 41ka cycle in obliquity. After 1 million years ago, this switched to a 100ka variation matching eccentricity, for which no reason has been established.

Identifying dominant factor
Milankovitch believed that decreased summer insolation in northern high latitudes was the dominant factor leading to glaciation, which led him to (incorrectly) deduce an approximate 41ka period for ice ages.[16] Subsequent research has shown that the 100ka eccentricity cycle is more important, resulting in 100,000-year ice age cycles of the Quaternary glaciation over the last million years.
betzalel
#12
Feb16-13, 03:47 AM
P: 40
The following graph shows how planetary climate has changed over the last 5.5 million years, from the study of ocean sediments. As the graph shows the planet has gotten colder and colder.

As the planet cooled, the Antarctic Ice sheet formed (12 million years ago). As the planet cooled further, roughly 2.6 million years, ice sheets started to form in the Northern Hemisphere with a cycle of glacial/interglacial of 41,000 years.

As the planet cooled further, 1.6 million years ago the glacial/interglacial cycle changed from a 41,000 year cycle to a 100,000 year cycle.

As noted in my above comment there is no explanation as to what causes the glacial/interglacial cycle (the timing of the glacial/interglacial cycle is related to the earth's orbital position, however detailed analysis shows that there is some cycle abrupt climate change event that is causing the glacial/interglacial and the mechanisms of that event is modulated by the earth's orbital configuration as opposed to the glacial/interglacial cycle being caused by amount of summer sunlight at N65) and what causes the cyclic abrupt climate change events - Heinrich events (6000 to 8000 year periodicity) and Dansgaard–Oeschger events (1400 year periodicity), however it appears based on observations that what ever causes the Heinrich events and the D-O events also causes the glacial/interglacial cycle.


http://upload.wikimedia.org/wikipedi...ate_Change.svg
Drakkith
#13
Feb16-13, 11:11 AM
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Betzalel, in your link in the post above this one, it appears the fluctuations in the temperature because drastically higher as we get closer to the present. Any idea why? Is it just due to the increased time each cycle takes?
betzalel
#14
Feb16-13, 01:28 PM
P: 40
Quote Quote by Drakkith View Post
Betzalel, in your link in the post above this one, it appears the fluctuations in the temperature because drastically higher as we get closer to the present. Any idea why? Is it just due to the increased time each cycle takes?
http://upload.wikimedia.org/wikipedi...ate_Change.svg

Your question is astute. You are looking at the paleo ocean sediment temperature data and asking for a physical explanation for what is observed. The analysis and research as to what has happened in the past has started to converge. There is general agreement among the specialists as to what has happened in the paleoclimatic past (certainly for the last 5 million years.)

What is missing is a physical explanation, a cause to explain the glacial/interglacial cycle, abrupt climate change, and other larger term changes.

The data shows the planet has been cooling for 20 million years. Differing to another thread what is causing the planet to gradually cool for 20 million years and also differing the question what controls the amount of CO2 in the atmosphere which is surprisingly difficult to explain.

When the planet was warmer there was no glacial/interglacial cycle. The planet’s internal systems (cloud cover) stabilizes planetary temperature when it is warmer. This statement is supported by recent top of the atmosphere analysis of radiation Vs ocean surface temperature which shows planetary clouds in the tropics increase or decrease to resist forcing changes by reflecting more or less sunlight off into space.

As the planet cools ice sheets start to form which upsets the planet’s temperature regulating systems as the ice sheets reflect sunlight off into space in summer and winter. Ice sheets take hundreds and thousands of years to melt and as they become thicker, it becomes more difficult for the ice sheet to melt, as their upper surface is colder due to the the higher elevation of the top of the ice sheet (there is cooling of roughly 3C for every 1000 feet gain in elevation).

A basic energy balance calculation indicates if the polar cap ice sheet’s lower latitude extent on the planet reaches around 30 degrees sufficient sunlight is reflected off into space to push the earth to full glaciation (oceans freeze). Also as the ice sheets move to lower latitudes there is more moisture to form snow in the winter, spring, and fall which accelerates the formation of the ice sheet.

As the planet continues to cool the glacial phase becomes more extreme, colder. As the extent of the ice sheet increases there are ice sheets at lower latitudes which reflects higher intensity sunlight (sunlight at lower latitudes off into space), which results in increased cooling.

It is interesting as you note, however, that as the planet has cooled, the short (10,000 to 12,000 year duration) interglacial periods have become warmer. To explain physically why that is the case it is necessary to have a strawman working hypothesis to explain what is causing the glacial/interglacial cycle and the cyclic abrupt climate change events (Heinrich and D-O) that are observed in the paleo climate record.

As noted above the cause of the glacial/interglacial cycle and the cause of abrupt climate change is not the varying amount of summer sunlight at 65N caused by orbital changes.
I have looked at this subject in detail and can provide a working hypothesis based on recent breakthroughs in geomagnetic research and paleoclimate analysis.

The geomagnetic researchers have found that there is a 3 to 5 times increase in the geomagnetic field intensity during the interglacial periods. A working explanation for why the planet is warmer when the geomagnetic field intensity is stronger is Svensmark’s ion mediated cloud formation theory (the amount of ions in the atmosphere particularly over the ocean which is particulate poor determines how clouds from, the lifetime of the cloud, and the albedo of the cloud. ) When the geomagnetic field strength is higher the geomagnetic field deflects more cosmic rays (cosmic rays are mostly high energy protons) which reduces the number of ions that are produced in the atmosphere. (Less cloud cover warmer planet).

The explanation for why the warm interglacial period is warmer even as the planet continues to cool can be explained by the physical reason for what is causing the cyclic abrupt changes to the geomagnetic field. (i.e. It has been found that geomagnetic field intensity is stronger during the interglacial period as the glacial periods became colder. There needs to be an explanation as to what is physically causing the cyclic geomagnetic field intensity changes.)

It appears an abrupt change to the solar magnetic cycle (there are cosmogenic isotope changes that correlate with the geomagnetic excursion and there are smaller geomagnetic field changes (archeomagnetic jerks) where the geomagnetic field’s tilt abruptly changes by 10 to 15 degrees which also correlates with solar magnetic field changes. There are burn marks on the surface of the earth that coincide with the timing of the Younger Dryas abrupt climate change event. There is a geomagnetic excursion that correlates in time with Younger Dryas abrupt cooling event) causes the small and large abrupt changes to the geomagnetic field.

The modulation of the geomagnetic field by a rare, cyclic solar event, explains how a short duration solar event say over a number of months, can cause an abrupt cooling event such as the Younger Dryas where the planet when from interglacial warm to glacial cold with 70% of the cooling occurring in 10 years and remaining cold for 1000 years. As the geomagnetic field takes hundreds and thousands of years to equalize after the abrupt solar forcing event alters geomagnetic field on the surface of the planet, as the field in the liquid core reaches a minimal energy state which is a simple polar field aligned with the earth’s axis of rotation.

The solar forcing mechanism also explains why orbital eccentricity, the tilt of the planet, and the seasonal timing of perihelion correlate with the glacial/interglacial cycle. Following the logic of the hypothesized mechanism, the largest magnitude solar magnetic cycle restart would need to occur with a periodicity of 8000 to 10000 years to explain the periodicity of the Heinrich events. The affect of the solar magnetic cycle restart on the geomagnetic field strength is depend on the orbit configuration at the time of the solar magnetic restart and dependent on whether there is insulating ice sheets covering the earth at the time of restart.

Assuming that is what is forcing the geomagnetic field (i.e. following the logic of the assumed mechanism) then the extent of the ice sheets at the time of the abrupt change to solar magnetic cycle (it appears the solar magnetic cycle is interrupted and when it restarts what happens can cause a geomagnetic excursion.) determines how that solar abrupt change modulates the geomagnetic field as does the orbital configuration at the time when the solar magnetic cycle restarts.

Recent geomagnetic field analysis has found geomagnetic excursions (excursion is the name for a failed geomagnetic reversal at which time the geomagnetic field intensity drops by a factor of 7 to 10 times) occur during the Heinrich events and during interglacial termination.

http://sciences.blogs.liberation.fr/...llot07EPSL.pdf


Are there connections between the Earth's magnetic field and climate?

We review evidence for correlations which could suggest such (causal or non-causal) connections at various time scales (recent secular variation approx 10–100 yr, historical and archeomagnetic change appox. 100–5000 yr, and excursions and reversals approx. 10^3–10^6 yr), and attempt to suggest mechanisms. Evidence for correlations, which invoke Milankovic forcing in the core, either directly or through changes in ice distribution and moments of inertia of the Earth, is still tenuous. Correlation between decadal changes in amplitude of geomagnetic variations of external origin, solar irradiance and global temperature is stronger. It suggests that solar irradiance could have been a major forcing function of climate until the mid-1980s, when “anomalous” warming becomes apparent. The most intriguing feature may be the recently proposed archeomagnetic jerks, i.e. fairly abrupt (approx. 100 yr long) geomagnetic field variations found at irregular intervals over the past few millennia, using the archeological record from Europe to the Middle East. These seem to correlate with significant climatic events in the eastern North Atlantic region. A proposed mechanism involves variations in the geometry of the geomagnetic field (f.i. tilt of the dipole to lower latitudes), resulting in enhanced cosmic-ray induced nucleation of clouds. No forcing factor, be it changes in CO2 concentration in the atmosphere or changes in cosmic ray flux modulated by solar activity and geomagnetism, or possibly other factors, can at present be neglected or shown to be the overwhelming single driver of climate change in past centuries. Intensive data acquisition is required to further probe indications that the Earth's and Sun's magnetic fields may have significant bearing on climate change at certain time scales.
http://eprints.whiterose.ac.uk/416/
Is the geodynamo process intrinsically unstable?

Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal' state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30 to 100 kyr; it may not therefore be as stable as we thought.

Recent studies suggest that the Earth's magnetic field has fallen dramatically in magnitude and changed direction repeatedly since the last reversal 700 kyr ago (Langereis et al. 1997; Lund et al. 1998). These important results paint a rather different picture of the long-term behaviour of the field from the conventional one of a steady dipole reversing at random intervals: instead, the field appears to spend up to 20 per cent of its time in a weak, non-dipole state (Lund et al. 1998).
http://www.mendeley.com/research/pal...nce-geodynamo/

Paleoclimatic context of geomagnetic dipole lows and excursions in the Brunhes, clue
for an orbital influence on the geodynamo?

The hypothesis of an influence of the astronomical precession on the geodynamo energy budget was recently reappraised by theoreticians. Paleomagnetic indications of such an influence remain controversial because reconstructions of paleointensity variations from sediments are suspected to be contaminated by lithological, paleoclimatically induced influences. Three sets of complementary indicators are however available: 1) records of the direction of magnetization in sediments, 2) records of magnetic anomalies of the deep sea floor basalts and 3) records of production variations of cosmogenic isotopes from sediment and ice cores. These records confirm the genuine geomagnetic origin of paleointensity lows and their narrow link with excursions or short reversals recorded in various materials and often dated by radiometric methods. The analysis of these time series and their comparison with δ18O records of the paleoclimate suggest that such globally recorded geomagnetic dipole lows have preferentially occurred in the context of interglacial or transitional paleoclimates at the time of low or decreasing obliquity. The dominant periods, extracted with the complex continuous wavelet transform technique, range from 40 to 125 ka, further suggesting a link with orbital parameters. These results encourage future efforts of research to improve the precision, the resolution and the dating of the time series of geomagnetic dipole low, in order to better decipher orbital signatures and understand their origin. An important implication of this topic is that the next geomagnetic dipole low should be related with the present interglacial.
Drakkith
#15
Feb16-13, 03:10 PM
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Interesting. Thanks!
klimatos
#16
May21-13, 01:28 AM
P: 412
The explanation for the periodicity of the ice ages during the Pleistocene is probably the best known and most widely accepted of all the climate-forcing hypotheses. It involves orbital-forcing (the Milankovich Theory). I refer you to this excellent NASA online explanation: http://earthobservatory.nasa.gov/Features/Milankovitch/

Over the last approximately 1.2 million years of the Pleistocene, there have been roughly 102 ice ages, each occurring at roughly 100,000-year intervals. We are currently some 20,000 years into the 50,000-year very irregular warming portion of the current cycle. This will be followed by some 50,000 years of equally irregular cooling and another onset of continental glaciation.

Homo sapiens first appeared during the last interglacial, and withstood the last continental glaciation. It might be interesting to note that during this last interglacial, surface temperature are estimated to have been from 0°C (Equator) to 10°C (about 65°N) warmer than at present. Sea levels were some seven meters higher than at present.

Both the Antarctic and Greenland icecaps continued through all of these interglacial periods, although obviously somewhat reduced.

It is hypothesized that ice ages occurred during geological eras other than the Pleistocene, but the evidence is weak.
SteamKing
#17
May21-13, 02:58 AM
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"Over the last approximately 1.2 million years of the Pleistocene, there have been roughly 102 ice ages, each occurring at roughly 100,000-year intervals.", quoted from klimatos

102 * 100,000 = 10,200,000 years

Can you provide a reference for the 102 ice ages figure?
klimatos
#18
May22-13, 02:40 PM
P: 412
SteamKing,

The 1.2 million year span of the Pleistocene was a simple, late-night brain fart. The current estimated span of the Pleistocene is, of course, roughly 2.5 million years. I have no excuse. I should have caught it before I posted.

The "102" number can be found in http://en.wikipedia.org/wiki/Pleistocene . Look under "Oxygen isotope ratios".
Whether you count all 102 advances as true "ice ages", of course, will depend upon your definition of that term. I should also have mentioned that the 100,00 year interval only applies to the most recent series of glacial episodes, as betzalal did in post 12. The earlier episodes had shorter cycles.


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