Greenland ice sheet (east coast) [image credit: Hannes Grobe @ Wikipedia]
Of course the other question about the start of an ice age still remains.
New University of Melbourne research has revealed that ice ages over the last million years ended when the tilt angle of the Earth’s axis was approaching higher values, reports Phys.org.
During these times, longer and stronger summers melted the large Northern Hemisphere ice sheets, propelling the Earth’s climate into a warm ‘interglacial’ state, like the one we’ve experienced over the last 11,000 years.
The study by Ph.D. candidate, Petra Bajo, and colleagues also showed that summer energy levels at the time these ‘ice-age terminations’ were triggered controlled how long it took for the ice sheets to collapse, with higher energy levels producing fast collapse.
Researchers are still trying to understand how often these periods happen and how soon we can expect another one.
Since the mid 1800s, scientists have long suspected that changes in the geometry of Earth’s orbit are responsible for the coming and going of ice ages—the uncertainty has been over which orbital property is most important.
Petra Bajo’s paper, “Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition,” published today in Science, moves closer to resolving some of the mystery of why ice ages end by establishing when they end.
The team combined data from Italian stalagmites with information from ocean sediments drilled off the coast of Portugal.
“Colleagues from the University of Cambridge and Portugal’s Instituto Português do Mar e da Atmosfera compiled detailed records of the North Atlantic’s response to ice-sheet collapse,” said Associate Professor Russell Drysdale, from the research team.
“We could identify in the stalagmite growth layers the same changes that were being recorded in the ocean sediments. This allowed us to apply the age information from the stalagmite to the ocean sediment record, which cannot be dated for this time period.”
Using the latest techniques in radiometric dating, the international team determined the age of two terminations that occurred about 960,000 and 875,000 years ago. The ages suggest that the initiation of both terminations is more consistent with increases in Earth’s tilt angle. These increases produce warmer summers over the regions where the Northern Hemisphere ice sheets are situated, causing melting.
Full report here.
Tallbloke's Talkshop 
They’re not going to live long enough to test their hypothesis. Neither will their 10th generation descendants. Besides, archaeological digs across Canada have shown there were no ice caps pre-Holocene, trashing the 200 year old notion the earth has gone through an “ice” age.
Um, er, maybe NOT SO MUCH as End of an Ice Age as simply a change in the Global Weather! Just look at it as on a Much larger Scale. Not quite like night follows day, but Cooling by / from what cause. Referring to AbsZero state may help in configuring the mind AWAY from +/- 0C
If there are Parallels in every other natural thing in the Universe, then it is “simply” just another natural progression in the Life on Earth, ( 4get abt D’atenboro)
Maybe time to be thinking OUTSIDE the box again. – Which Box? well of course the small box INSIDE the Larger Box!
How does this differ from the Milankovitch hypothesis?
Report: New University of Melbourne research has revealed that ice ages over the last million years ended when the tilt angle of the Earth’s axis was approaching higher values.
But this was ‘revealed’ – or at least recommended – 15 years ago, in line with Milankovitch.
The simplest inference, consistent with the observations, is that ice-sheets terminate every second (80ky) or third (120ky) obliquity cycle—at times of high obliquity—and similar to the original Milankovitch assumption.
. . .
Hypotheses not accounting for the obliquity pacing are unlikely to be correct.
Huybers, Peter J., and Carl Wunsch. 2005. Obliquity pacing of the late Pleistocene glacial terminations. Nature 434: 491-494.
Click to access Obliquity_HuybersWunsch.pdf
See also: Obliquity, inclination and eccentricity of Earth – a model: Part 1
The idea there is that the eccentricity period is the geometric mean of 2 and 3 obliquity cycles i.e. ~100,000 years average.
oldbrew: The period of a glacial cycle is not a constant time-wise and for the last 450kyrs has been increasing in length. Neither are the cycles the same, though similar. See here in figs https://wattsupwiththat.com/2017/08/04/paleoclimate-cycles-are-key-analogs-for-present-day-holocene-warm-period/
My conviction here – based on my reading of the value of obliquity between 6k2bce and 2k2bce, and the above link, – is that chaotic changes to obliquity are triggered by some planetary tick-tock, and when glacial loading reaches a point of instabillity (Iz versus Ix Iy), the switch occurs. Then there also is the ratcheting effect into a deep glacial, to be followed by abrupt change. The curves in the above link show such ratcheting, again triggered by – possibly- same tick-tock; the Eddy?.
See also https://phys.org/news/2017-06-collapse-european-ice-sheet-chaos.html
Glacial send and interglacials begin 6500 years after obliquity, eccentricity and precession all peak together. This happens every 2 or 3 obliquity peaks. The delay of 6500 is the time for raised insolation from the combined Milankovich peak to warm the oceans which are deep and big. Thanks to Javier for this graph:
Aslan
If ice becomes plastic under pressure once it attains a certain depth. How can large ice sheets form if not constrained by the valleys they are hypothesised to form?
‘The study by Ph.D. candidate’
Red flag. He is a graduate student. He has not earned the right to have Ph.D. associated with his name. This credential escalation is usually a sign of junk science.
phil salmon says: March 13, 2020 at 10:07 pm
Glacial send and interglacials begin 6500 years after obliquity, eccentricity and precession all peak together. This happens every 2 or 3 obliquity peaks.
– – –
From my earlier comment…
See also: Obliquity, inclination and eccentricity of Earth – a model: Part 1
The idea there is that the eccentricity period is the geometric mean of 2 and 3 obliquity cycles i.e. ~100,000 years average.
6500 years looks like 1/4 of the axial precession, currently estimated as ~25770 years. For a possible lunar element to that, see:
The key number there is 6441 tropical years = 339 Metonic cycles.
– – –
On Javier’s graph, reading from the left it looks like there are 3 breaches of the central line in every 5 obliquities, until the last 5 (most recent) with only 2 – but 2 consecutive breaches straight afterwards.
Re obliquity, and its extrapolation backwards, see Axel Wittmann “Obliquity of the Ecliptic” 1978.
http://adsabs.harvard.edu/full/1979A%26A….73..129W
Click to access nph-iarticle_query
The derived formulae do not agree with the measurements, nor with the trending, for the last 3k yrs. Also the as measured obliquity, between 5k2 – 2k2bce from man-made structures, there is no agreement at all. The abrupt changes are much larger. So that the obliquity curve as shown in phil salmon’s graph may be only a component from a minor signal signature.
Am I right in thinking that when obliquity causes warmer summers, it will also cause cooler winters?Raises a few questions about what is significant for the global impact.
Oldbrew
The key number there is 6441 tropical years = 339 Metonic cycles.
Yes that’s a more precise analysis. So that delay interval seems to make sense.
In general, ocean circulation changes especially in the deep ocean, drive both inception and termination of glacial periods.
This paper by Weaver et al shows deep ocean warming around Antarctica starting ~20,000 years ago leading to the Holocene inception:
Click to access deglaciation.pdf
Here are some thoughts about recent trends in the deep ocean:
Reblogged this on Utopia, you are standing in it!.
It is long established that Ice ages typically end at the height of obliquity around 24.2 degrees, however, not every time. The paper is just a rehash of what we already know.
HOWEVER, all ice ages start when obliquity drops below 23.5 degrees, NO EXCEPTIONS.
You will note that very little is published on this point. I call it scientific cowardice and those that do publish are promptly marginalized. It is the massive 800 lbs. gorilla in the room.
Reblogged this on Climate Collections.