From the UNIVERSITY OF TEXAS AT AUSTIN
Researchers at The University of Texas at Austin have found that a well-known period of abrupt climate change 12,000 years ago occurred rapidly in northern latitudes but much more gradually in equatorial regions, a discovery that could prove important for understanding and responding to future climate change.
The research, published Sept. 2 in Nature Communications, focuses on the Younger Dryas, a cooling period that started when the North Atlantic Current, an ocean current, stopped circulating. The event caused Earth’s northern hemisphere to enter into a deep chill, with temperatures in Greenland dropping by approximately 18 degrees Fahrenheit in less than a decade.
The event also caused rainfall to decrease in places as far away as the Philippines. However, whereas temperatures in Greenland responded quickly to the ocean current shutdown and subsequent reboot 1,000 years later, it took hundreds of years for rainfall in the Philippines to be affected and to recover.
“We found that the temperature in Greenland is like a small ship that you can stop and turn quickly because of the influence of sea ice in the region, while rainfall in the tropics is like a big ship that takes a long time to course correct,” said Jud Partin, a research associate at the University of Texas Institute for Geophysics (UTIG) who led the study.
The changes in temperature and rainfall are linked to a common cause: the slowdown of the ocean currents in the North Atlantic, which affect climate and temperature as they move warm water from the Gulf of Mexico toward the Arctic. As the world warmed after the last ice age, glaciers melted and diluted northern seawater with freshwater. The resulting change in ocean water density disrupted the current and, in effect, the climate, causing a period of global cooling.
The event also inspired the premise of the 2004 disaster flick “The Day After Tomorrow,” which exaggerates the speed and strength of the cooling by depicting the planet entering an ice age in a matter of weeks after the ocean current collapses.
Although other studies well document the changes in temperature and precipitation around the world, this new study concludes that these changes do not occur or recover at the same rate, as had been previously assumed.
Understanding the relationship between temperature and precipitation in the wake of climate change is particularly important because it previews what could happen if the planet’s ice sheets continue to lose mass and add freshwater to the North Atlantic.
At a conference in Paris during July of more than 2,000 climate scientists, the potential collapse of the North Atlantic Current’s circulation was identified as a possible catastrophic consequence of climate change.
“A slowdown of the ocean circulation is a double-edged sword: If we see some temperature changes associated it … and somehow are quick to act and alleviate the change, then we have the potential to stop it before it impacts rainfall globally,” Partin said. “The longer the circulation event lasts means that it will take that much longer for rainfall to recover.”
The researchers discovered how rainfall in the Philippines was affected by the Younger Dryas event by analyzing minerals deposited in a stalagmite growing from the floor of a cave in Puerto Princesa Subterranean River National Park in Palawan. They found that it took more than 550 years for drought conditions to reach their full extent in the region, and about 450 years to return to pre-Younger Dryas levels after the North Atlantic Current began circulating again. The record suggests rainfall was about 25 percent lower than present levels during the cold snap.
They then compared these findings with previously published ice core data. According to these records, it took a decade or less for temperatures in Greenland to drop by approximately 18 degrees Fahrenheit once the current collapsed and about 40 years to rebound after it returned.
Partin conducted the work with UTIG Director Terry Quinn and collaborators from the National Taiwan University and the University of the Philippines-Diliman. UTIG is a research unit of The University of Texas at Austin Jackson School of Geosciences.
Computational models of the Younger Dryas temperature and precipitation also provided insight into the role of sea ice in Greenland’s abrupt temperature change.
“Sea ice around Greenland acts as a ‘switch,’ causing that region to respond more quickly than the rest of the planet does by insulating the air from heat stored in the deep ocean,” said Yuko Okumura, a UTIG research associate and a co-author on the study.
###
The study was funded by a grant from the National Science Foundation.
Do I need to make some popcorn? The 12,000 year figure should precipitate some interesting remarks.
Funny how one small item can be used to deduce global weather patterns.
By the way, no droughts so far in the West Coast have come even close to the Great Drought 500 years ago. Most of the native farming communities in Arizona perished and they left broken pottery all over the Tucson valley from Kitt Peak to Mount Lemmon.
This research shows the issue l have with claims that ocean currents are the leaders in climate change.
The claim been that the melting of the NA ice sheets were the cause of the cooling in the YD. Yet in order for the melting to cause the shut down of the North Atlantic drift then that would mean it must have been running during the ice age.So how could its shut down have caused cooling during YD and yet still there was a bitter cold climate in the NH for much longer during the ice age when the North Atlantic drift was up and running.
What is far less known is that there were two freshwater discharges at the end of the ice age. But only the first one caused a cooling event. The second one around 9500 years ago had little effect on the climate.
Why should that be? my guess is because by this time the weather patterns had become far to variable for it to have a lasting impact. Because when there a increase in the variation of the weather from year to year. lt blocks the formation of major climate change from happening.
Exactly, and the opening of the Bering Strait was the cause? Principal fresh water input to the Arctic is the Strait?
Hmmm…. they are sneaking in cooling! We will see more of this has bolder young scientists push back against near retirees of consensus climate. I laughed when they remarked that we had to do something to prevent the slowing of the Gulf Stream to prevent a 1000yrs drought in the Philipines, not thinking that other things might have slowed down the drip and maybe even sealed it off:
http://wattsupwiththat.com/2015/09/02/ancient-cold-period-could-provide-clues-about-future-climate-change/#comment-2019906
Where the drying up of aquifers could take hundreds of years to refill up again before the ‘drip’ in the caves could resume after the rains got started up and…
http://wattsupwiththat.com/2015/09/02/ancient-cold-period-could-provide-clues-about-future-climate-change/#comment-2019976
at the end of the drought the increasing salts in solution in the shrinking acquifers likely sealed off the ‘leaks’ to the cave delaying for a long time after the rains resumed the ‘drip’ on this single stalagmite.
But….what caused the slowdown?
Do the authors of the paper mention Bond Events?
and
There has been a lot of research on Bond Events; they seem like well accepted science. I haven’t seen the paper but it sounds like these guys are ignoring (or are ignorant of) them. Here’s a link to the paper: link
OK, I’ve seen it. I just haven’t read it thoroughly. 🙂
We appear to have two causes for the effect, cold. And no cause for the effect, warm.
I have never trusted using ice as a proxy for temperature… I just do not see how they can correct for certain events and conditions. Especially when they compare proxy readings using one approach (like O18) on Greenland ice versus proxies using another approach (like Deuterium) on Antarctic ice.
For example, if the water vapor in an air mass moves over some mountains (or other obstruction that causes air to lift) it should produce rain that contains O18 at a slightly elevated ratio. If that same air mass then moves north and produces say snow…It is missing some of the O18 it was “expected” to have, and the temperature record proxy will be moved to a colder reading. (Am I right?) Also, they may interpret this in conjunction with other proxies to mean there is more fresh water, therefore more rainfall, therefore warmer weather.
Opposite happens if the air mass take up water evaporated from water that is high in O18, the water vapor is now naturally rich on O18 and it will tend to have proxy readings showing warmer temperatures. So if the water vapor comes from fresh water or snow, it should have elevated O18.
If you “assume” all the water vapor came from the ocean, and that the ratio does not change over time, then you can assume the proxy readings work reasonably well – but how do you know?
By the time they add in all of their “adjustments”, they can make the proxies read just about anyway they want (kind of like the land temperature adjustments).
At least with cave formations, you can reasonably tell that the formation was dryer or wetter over time – as long as the acidic conditions don’t change of course (if something were to remove some acidity from ground water, it will dissolve less limestone and therefore deposit less limestone, so it will look dryer at that period).
So the finding that Greenland’s supposed temperature changes happened at a different speed then the supposed temperatures near the tropics doesn’t mean much – there are too many “assumptions” in proxy measurements.
The magnitude of the ice sheets melting at that time were far greater than what is left in the Northern Hemisphere currently. The icecap over Sweden alone back then likely matched Greenland’s now.
The oceans all over the entire planet were 400 feet lower. How much ice was that? Compare it with how much the the oceans would be expected to rise if Greenland melted in a hurry (which seems highly unlikely). As much as 30 feet?
In terms of magnitude, this is a case of comparing apples with watermelons.
Caleb
Did you know that they were two freshwater discharges at the end of the ice age.?
Which begs the question “why did the second event have no impact on the climate” if these events are such a strong cause of climate change.
That is an excellent question, and is one I’m sure the better minds are grappling with. Better minds are humble, and know we are very ignorant concerning the most basic plumbing of deep-sea currents, and how they are engineered, and better minds also know that if their study is to benefit mankind they should begin by being able to forecast what leads to what. It is the more puny minds that march off to Paris with some flimsy concept, dreaming they can control what we can’t even forecast.
I was under the impression that the YD came about because of a cosmic impact. How did that event turn off the conveyor?
I assume you’re being sarcastic.
The YD impact fantasy is entirely without evidence.
Richard Lindzen is not a fan of the Gulf Stream stalling due to ice melt theory either. Watch him debunk Bill Nye. (way back in 2007) https://www.youtube.com/watch?v=McsZ1U20W0M
“The longer the circulation event lasts means that it will take that much longer for rainfall to recover.”
I am going to hazard a guess that NASA will use the GPM Core spacecraft in tandem with some other satellite yet to be named to begin to detect this horrifying Circulation Event unfolding in the oceans below, right before our very eyes.
After reading the full paper and some its citations I conclude:
1. Their results are in full agreement with the Arctic Iris Effect that I cross-posted here at WUWT yesterday http://landscapesandcycles.net/arctic-iris-effect-and-dansgaard-oeschger-event.html
2. Suggestions that transition into and out of the Younger Dryas is based on previous assumptions that the AMOC turned off due to freshwater flooding. However they do not provide any new evidence to support that assertion. The turning on and off of the AMOC assumption has 2 problems. First that the AMOC is NOT driven by buoyancy the conveyor belt model assumes. The conveyor belt is rapidly being deconstructed. As Lozier 2010 wrote, ““the conveyor-belt model no longer serves the community well—not because it is a gross oversimplification but because it ignores crucial structure and mechanics of the ocean’s intricate global overturning.” Wunsch calls the conveyor a myth that has set back oceanography for decades.
Second even if freshwater flooding could shut down the AMOC, there is no consensus if flooding ever happened and a growing number of papers presenting contradictory evidence as discussed at WUWT here http://wattsupwiththat.com/2011/10/05/evaporation-not-outflow-drained-ancient-lake-agassiz-during-the-younger-dryas/
Finally the shutdown of the AMOC is based on proxies that measure Deep Water formation. A covering of ice will prevent water from contacting the freezing air temperatures and thus prevents formation of cold sinking water. However because Deep Water shuts off, the inflow of warm water does not! And water flowing into the Arctic simply exits at a different depth.
The 2 models in their paper had very different sub-models with different sea ice extent and changes. The rapid change happened in the model with greater changes in sea ice, but not in the other model without the sea ice change, even though both models were being hosed with ad hoc fresh water.
The Arctic Iris Effect readily explains the YD. Increased ice causes poor heat ventilation and rapid cooling, while reduced sea ice causes rapid warming. As in the rapid warming event of Dansgaard Oeschger events, Greenland and other ice caps experienced greater ice accumulation that was double the amount during the colder periods. That ice accumulation would readily cause rapid glacier expansion and calving that then traps sea ice preventing the ice from being flushed from Arctic and causing it to thicken.
This paper’s only addition to our knowledge of the YD was demonstrating very little tropical temperature changes and reinforcing expectations of changes in precipitation. Changes in the ITCZ that coincide with changes in ice cover are well established, their observations merely added to that understanding. The lack of temperature changes in tropical waters simply supports the notion that minor changes in ocean temperature can be amplified by the iris effect
Present day ice sheets melting into the North Atlantic? Who wrote this thing? There are only two ice sheets left, in Greenland and Antarctica. Jud Partin and his associates can’t possibly be suggesting that Antarctic melting adds freshwater to the North Atlantic.
Freshwater Arctic ice melt is an effect, not a cause, of ocean driven climate change.
(Confusion of cause and effect effect is a universal feature of the political narrative of self justification of totalitarian regimes, according to historian Anthony Beevor.)
There is a fundamental difference between millenial scale ocean oscillations in the north and south hemispheres.
In the NH changes between cold and warm periods are abrupt and more frequent.
In the SH, changes are smooth, gradual and less frequent.
This is explained by the chaotic nonlinear (Lyapunov) stability of the oceans in both hemispheres.
The Atlantic Meridional Overturning Circulation (AMOC) contains a positive feedback between North Atlantic Deep Water (NADW) formation in the Norwegian Sea, and salinity arising from the Gulf Stream.
And as we all know, a positive feedback within a dissipative oscillatory system will introduce chaotic fluctuation, sure as night follows day.
This was well described in this paper by Weaver et al 2003:
http://home.sandiego.edu/~sgray/MARS350/deglaciation.pdf
This constitutes a positive feedback between the overturning circulation and the salinity in the North Atlantic first described by Stommel (33). Specifically, the intensified formation of NADW advects more saline subtropical waters to the northern North Atlantic, which increases surface density there and further intensifies the overturning circulation.
This positive feedback between the Gulf stream, which carries saline water to the North Atlantic, and NADW, drives the chaotic fluctuation of the AMOC and (consequently) NH temperatures, which contrast with the slow smooth and serene ocean temperature oscillations in the SH. This contrast is what makes oceanography on our planet interesting – at least in our current continental configuration.
Everything but the science is settled. Summary report: We don’t now what we think we know. Some of us knew that.
There are piles and piles of Zombie theories associated with: the Younger Dryas, what causes cyclic abrupt climate change, what is the effect of changes in atmospheric CO2 on planetary climate, and related to what causes the glacial/interglacial cycle. Zombie theories fill the void when the true cause of what is observed is not known. The big barrier to solving the climate puzzle is the sun is significantly different than the standard model. There are piles and piles of astronomical anomalies and paradoxes that support that assertion.
Back to the Zombie theories.
As noted in the next linked paper, the melt pulse occurred a 1000 years prior to the Younger Dryas event which has been known for at least a decade. No cooling at that time. There is not even correlation in time with the melt pulse and the abrupt onset of cooling in North America and Europe. There is no discrete conveyor to interrupt. Regardless modeling indicates a complete interruption to the North Atlantic drift current would only cool Europe and North America a couple of degrees.
https://www.rug.nl/research/portal/files/6661387/2000QuatIntRenssen.pdf
It is interesting that the YD 1200 year cooling occurred when summer insolation at 65N was maximum. The theory that summer solar insolation at 65N controls the glacial/interglacial cycle is also a Zombie theory.
There is the largest C14 change in the Holocene during the Younger Dryas. The cause of the largest C14 change in the Holocence is the cause of the YD. The cause of cyclic abrupt climate change is the sun which causes abrupt changes to the geomagnetic field. During a geomagnetic excursion multiple poles appear on the earth, include a low latitude geomagnetic pole which cause a more than doubling of GCR in the vicinity of the pole which explains the low latitude cooling. There is a delay in the change in low latitude magnetic pole occurrence due to the back emf that is generated to resist the change in the liquid core. The first change in the field occurs at the site of massive change in the field which is where the burn marks are. The burn marks are caused by a massive movement of electrical charge from the ionosphere to the surface of the planet. That creates the high temperature debris with no impact and no iridium.
P.S. The paleo data supports the assertion that Interglacial periods end abruptly not gradually. There is a new computer model run that has published in Nature by the cult of CAGW to push the Zombie theory that interglacial periods end gradually.
http://cdiac.ornl.gov/trends/temp/vostok/graphics/tempplot5.gif
This is the Greenland Ice sheet temperature data for the last 100,000 years. Can you see the cyclic abrupt changes?
http://oceanservice.noaa.gov/education/pd/tidescurrents/media/effect_influences_3.gif
ClimateMyth/Zombie Theory 1- An interruption to the discrete Gulf Stream (a discrete deep water return for the North Atlantic Drift Current (aka The ‘Gulf Stream’) does not exist, see below, but even if it did so a melt pulse could interrupt it) would not result in significant cooling of Europe or America. The Gulf stream myth has been perpetuated for almost 20 years.
http://www.atmos.washington.edu/~david/Gulf.pdf
http://www.americanscientist.org/issues/feature/2006/4/the-source-of-europes-mild-climate
The comet/asteroid impact theory is a zombie theory. As noted by an astrophysicist who commented on a NOVA program. He noted also that no one asked the astrophysics community for their input on the YD impact theory. It is physically impossible for a single comet/asteroid to cause ten burn marks with observed pattern. It would take eight to nine separate comets and/or asteroids which is ridiculous as the burn marks occurred almost simultaneously.
There are ten burn mark sites (nine in the North America and one in Europe).
http://www.pnas.org/content/suppl/2007/09/20/0706977104.DC1
It is not possible for a single object to ‘break up’ to cause the burn marks. Look at the locations where the burn marks were found.
Greenland temperatures from the ice cores during the last ice age above.
First issue is that the temperature change is miscalibrated by the use of faulty borehole models. The temperature change was not 20C but more like 8C to 10C. The correct formulae for the oxygen isotopes are only 8C of temperature change, 3C in the Younger Dryas.
Second, the Younger Dryas is a very small part of the downspike in temperatures during the period. Temperatures started crashing at 14,300 years ago, well before the Younger Dryas period which started at 12,800 years ago. Why are they so fixated on the Younger, when the change in the climate started about 3,000 years earlier when there was rapid warming followed by rapid cooling and then there was another period of cooling called the Younger Dryas.
Third, the entire ice core record shows extreme variability. There were more 30 Younger Dryas-type events in the 100,000 years of the ice age. Why is the Younger Dryas so special. What about the Older Dryas. Why is there no papers about it. If one is going to try to explain the Younger Dryas, maybe one should start with explaining the 30 similar events which happened during the whole ice age.
Climate science is focused on cash and splash; not true understanding.
+1
Really nothing much new in this paper. Problem is that Greenland is and always has been a “regional” teleconnection point. Opposite phase downstream(and upstream).
“As the world warmed after the last ice age, glaciers melted and diluted northern seawater with freshwater. The resulting change in ocean water density disrupted the current and, in effect, the climate, causing a period of global cooling.”
I assume that the glaciers melt at the end of every “ice age”
Is there evidence for a Younger Dryas type event at the end of each glacial period???
M,
Yes. Not just the YD but all such rapid cooling events. The YD is not unusual.
Seems to me, I recall something of a theory that the YD was due to a “sudden” release of fresh water.
I don’t see that happening to day. The ice is already melted considerably in the NH.
I still await an EXPLANATION – not a description – of what CAUSED the warming that ended the ice ages.
Was it elevated levels of CO2??
If so, from where did this CO2 come?
It was the same cause as the ends of the previous ice ages. CO2 had nothing to do with it. A warmer world meant more CO2 in the air. The raised concentration was a result of warming, not the cause.
Milankovitch Cycles, ie orbital and rotational mechanics, cause the cyclic ice ages, ie NH glaciations. The key factor is insolation at 75 degrees N.
I couldn’t tell if there was conclusive physical evidence or whether this is just more theory based on computer models.
This is my thought about the bigger picture of why the climate changes. D/O events and the Arctic Iris theory which I sent in an earlier post simply being superimposed on this bigger picture and adding to the climate instability y during glacial times all though this Arctic Iris Effect is always in operation but not as dramatic during inter- glacial periods of time.
Below are my thoughts about how the climatic system may work. It starts with interesting observations made by Don Easterbrook. I then reply and ask some intriguing questions at the end which I hope might generate some feedback responses. I then conclude with my own thoughts to the questions I pose.
From Don Easterbrook – Aside from the statistical analyses, there are very serious problems with the Milankovitch theory. For example, (1) as John Mercer pointed out decades ago, the synchronicity of glaciations in both hemispheres is ‘’a fly in the Malankovitch soup,’ (2) glaciations typically end very abruptly, not slowly, (3) the Dansgaard-Oeschger events are so abrupt that they could not possibility be caused by Milankovitch changes (this is why the YD is so significant), and (4) since the magnitude of the Younger Dryas changes were from full non-glacial to full glacial temperatures for 1000+ years and back to full non-glacial temperatures (20+ degrees in a century), it is clear that something other than Milankovitch cycles can cause full Pleistocene glaciations. Until we more clearly understand abrupt climate changes that are simultaneous in both hemispheres we will not understand the cause of glaciations and climate changes.
My explanation:
I agree that the data does give rise to the questions/thoughts Don Easterbrook, presents in the above. That data in turn leads me to believe along with the questions I pose at the end of this article, that a climatic variable force which changes often which is superimposed upon the climate trend has to be at play in the changing climatic scheme of things. The most likely candidate for that climatic variable force that comes to mind is solar variability (because I can think of no other force that can change or reverse in a different trend often enough, and quick enough to account for the historical climatic record, and can perhaps result in primary and secondary climatic effects due to this solar variability, which I feel are a significant player in glacial/inter-glacial cycles, counter climatic trends when taken into consideration with these factors which are , land/ocean arrangements , mean land elevation ,mean magnetic field strength of the earth(magnetic excursions), the mean state of the climate (average global temperature gradient equator to pole), the initial state of the earth’s climate(how close to interglacial-glacial threshold condition it is the ice dynamic/ average global temperature) the state of random terrestrial(violent volcanic eruption, or a random atmospheric circulation/oceanic pattern that feeds upon itself possibly) /extra terrestrial events (super-nova in vicinity of earth or a random impact) along with Milankovitch Cycles, and maybe a roll for Lunar Effects.
What I think happens is land /ocean arrangements, mean land elevation, mean magnetic field strength of the earth, the mean state of the climate, the initial state of the climate, and Milankovitch Cycles, keep the climate of the earth moving in a general trend toward either cooling or warming on a very loose cyclic or semi cyclic beat(1470 years or so) but get consistently interrupted by solar variability and the associated primary and secondary effects associated with this solar variability, and on occasion from random terrestrial/extra terrestrial events, which brings about at times counter trends in the climate of the earth within the overall trend. While at other times when the factors I have mentioned setting the gradual background for the climate trend for either cooling or warming, those being land/ocean arrangements, mean land elevation, mean state of the climate, initial state of the climate, Milankovitch Cycles , then drive the climate of the earth gradually into a cooler/warmer trend(unless interrupted by a random terrestrial or extra terrestrial event in which case it would drive the climate to a different state much more rapidly even if the climate initially was far from the glacial /inter-glacial threshold, or whatever general trend it may have been in ) UNTIL it is near that inter- glacial/glacial threshold or climate intersection at which time allows any solar variability and the associated secondary effects, and or other forcing no matter how SLIGHT at that point to be enough to not only promote a counter trend to the climate, but cascade the climate into an abrupt climatic change. The back ground for the abrupt climatic change being in the making all along until the threshold glacial/inter-glacial intersection for the climate is reached ,which then gives rise to the abrupt climatic changes that occur and possibly feed upon themselves while the climate is around that glacial/inter-glacial threshold resulting in dramatic semi cyclic constant swings in the climate from glacial to inter-glacial while factors allow such an occurrence to take place. Which was the case 20000 years ago to 10000 years ago.
The climatic back ground factors (those factors being previously mentioned) driving the climate gradually toward or away from the climate intersection or threshold of glacial versus interglacial. However when the climate is at the intersection the climate gets wild and abrupt, while once away from that intersection the climate is more stable.
Although random terrestrial events and extra terrestrial events could be involved some times to account for some of the dramatic swings in the climatic history of the earth( perhaps to the tune of 10% ) at any time , while solar variability and the associated secondary effects are superimposed upon the otherwise gradual climatic trend, resulting in counter climatic trends, no matter where the initial state of the climate is although the further from the glacial/inter-glacial threshold the climate is the less dramatic the overall climatic change should be, all other items being equal.
The climate is chaotic, random, and non linear, but in addition it is never in the same mean state or initial state which gives rise to given forcing to the climatic system always resulting in a different climatic out-come although the semi cyclic nature of the climate can still be derived to a degree amongst all the noise and counter trends within the main trend.
QUESTIONS: The Arctic Iris Effect goes to some degree in answering some of these questions combined with my other thoughts for the bigger picture in my opinion.
Why is it when ever the climate changes the climate does not stray indefinitely from it’s mean in either a positive or negative direction? Why or rather what ALWAYS brings the climate back toward it’s mean value ? Why does the climate never go in the same direction once it heads in that direction?
Along those lines ,why is it that when the ice sheets expand the higher albedo /lower temperature more ice expansion positive feedback cycle does not keep going on once it is set into motion? What causes it not only to stop but reverse?
Vice Versa why is it when the Paleocene – Eocene Thermal Maximum once set into motion, that being an increase in CO2/higher temperature positive feedback cycle did not feed upon itself? Again it did not only stop but reversed?
My conclusion is the climate system is always in a general gradual trend toward a warmer or cooler climate in a semi cyclic fashion which at times brings the climate system toward thresholds which make it subject to dramatic change with the slightest change of force superimposed upon the general trend and applied to it. While at other times the climate is subject to randomness being brought about from terrestrial /extra terrestrial events which can set up a rapid counter trend within the general slow moving climatic trend.
.
Despite this ,if enough time goes by (much time) the same factors that drive the climate toward a general gradual warming trend or cooling trend will prevail bringing the climate away from glacial/inter-glacial threshold conditions it had once brought the climate toward ending abrupt climatic change periods eventually, or reversing over time dramatic climate changes from randomness, because the climate is always under a semi extra terrestrial cyclic beat which stops the climate from going in one direction for eternity.
Savlatore,
“From Don Easterbrook – Aside from the statistical analyses, there are very serious problems with the Milankovitch theory. For example, (1) as John Mercer pointed out decades ago, the synchronicity of glaciations in both hemispheres is ‘’a fly in the Malankovitch soup,’ (2) glaciations typically end very abruptly, not slowly, (3) the Dansgaard-Oeschger events are so abrupt that they could not possibility be caused by Milankovitch changes (this is why the YD is so significant), and (4) since the magnitude of the Younger Dryas changes were from full non-glacial to full glacial temperatures for 1000+ years and back to full non-glacial temperatures (20+ degrees in a century), it is clear that something other than Milankovitch cycles can cause full Pleistocene glaciations. Until we more clearly understand abrupt climate changes that are simultaneous in both hemispheres we will not understand the cause of glaciations and climate changes.”
I see no problems.
1) Why is synchronicity a problem? The orbital mechanics affect both hemispheres. Perhaps you’re concerned about rotational mechanical effects, such as axial tilt. Both hemispheres are affect equally by insolation, but just at different times of the year. What controls the Pleistocene glaciations however is indeed the Northern Hemisphere, since the SH has been covered by ice sheets of varying extent since the Oligocene.
2) Glaciations most certainly do not end abruptly. From the depths of the LGM to the onset of the Holocene took about 9000 years (20 Ka to 11 Ka), and to continued deglaciation down to today’s levels thousands of years more. Even the period of most rapid deglaciation took thousands of years, with interrupted by cold snaps like the Dryases.
3) Why do D/O events have to be controlled by orbital mechanics? They occur throughout glacial epochs, not just during deglaciations. Celestial mechanics might contribute to them, but they well could have other causes.
4) Sorry, but “since the magnitude of the Younger Dryas changes were from full non-glacial to full glacial temperatures for 1000+ years and back to full non-glacial temperatures (20+ degrees in a century), it is clear that something other than Milankovitch cycles can cause full Pleistocene glaciations” makes no sense. The YD was during a deglaciation, not during a glaciation, ie ice sheet build up. Whatever caused the Dryas and other rapid cooling episodes is associated with deglaciation, not glaciation. That should be obvious.
Gloria good points.
Thanks and for your valuable comments here.