This is a follow up posting to Younger Dryas -The Rest of the Story!
Guest post by Don J. Easterbrook
Dept. of Geology, Western Washington University.
The Younger Dryas was a period of rapid cooling in the late Pleistocene 12,800 to 11,500 calendar years ago. It followed closely on the heels of a dramatically abrupt warming that brought the last Ice Age to a close (17,500 calendar years ago), lasted for about 1,300 years, then ended as abruptly as it started. The cause of these remarkably sudden climate changes has puzzled geologists and climatologists for decades and despite much effort to find the answer, can still only be considered enigmatic.
The Younger Dryas interruption of the global warming that resulted in the abrupt, wholesale melting of the huge late Pleistocene ice sheets was first discovered in European pollen studies about 75 years ago. Terrestrial plants and pollen indicate that arboreal forests were replaced by tundra vegetation during a cool climate. This cool period was named after the pale yellow flower Dryas octopetella, an arctic wildflower typical of cold, open, Arctic environments. The Younger Dryas return to a cold, glacial climate was first considered to be a regional event restricted to Europe, but later studies have shown that it was a world-wide event. The problem became even more complicated when oxygen isotope data from ice cores in Antarctica and Greenland showed not only the Younger Dryas cooling, but several other shorter cooling/warming events, now known as Dansgaard-Oerscher events.
The Younger Dryas is the longest and coldest of several very abrupt climatic changes that took place near the end of the late Pleistocene. Among these abrupt changes in climate were: (1) sudden global warming 14,500 years ago (Fig. 1) that sent the immense Pleistocene ice sheets into rapid retreat, (2) several episodes of climatic warming and cooling between ~14,400 and 12,800 years ago, (3) sudden cooling 12,800 years ago at the beginning of the Younger Dryas, and (4) ~11,500 years ago, abrupt climatic warming of up to 10º C in just a few decades. Perhaps the most precise record of late Pleistocene climate changes is found in the ice core stratigraphy of the Greenland Ice Sheet Project (GISP) and the Greenland Ice Core Project (GRIP). The GRIP ice core is especially important because the ages of the ice at various levels in the core has been determined by the counting down of annual layers in the ice, giving a very accurate chronolgoy, and climatic fluctuations have been determined by measurement of oxygen isotope ratios. Isotope data from the GISP2 Greenland ice core suggests that Greenland was more than~10°C colder during the Younger Dryas and that the sudden warming of 10° ±4°C that ended the Younger Dryas occurred in only about 40 to 50. years.
Figure 1. Temperature fluctuations over the past 17,000 years showing the abrupt cooling during the Younger Dryas. The late Pleistocene cold glacial climate that built immense ice sheets terminated suddenly about 14,500 years ago (1), causing glaciers to melt dramatically. About 12,800 years ago, after about 2000 years of fluctuating climate (2-4), temperatures plunged suddenly (5) and remained cool for 1300 years (6). About 11,500 years ago, the climate again warmed suddenly and the Younger Dryas ended (7).
Radiocarbon and cosmogenic dating of glacial moraines in regions all over the world and abrupt changes in oxygen isotope ratios in ice cores indicate that the Younger Dryas cooling was globally synchronous. Evidence of Younger Dryas advance of continental ice sheets is reported from the Scandinavian ice sheet, the Laurentide ice sheet in eastern North America, the Cordilleran ice sheet in western North America, and the Siberian ice sheet in Russia. Alpine and ice cap glaciers also responded to the abrupt Younger Dryas cooling in both the Northern and Southern hemispheres, e.g., many places in the Rocky Mts. of the U.S. and Canada, the Cascade Mts. of Washington, the European Alps, the Southern Alps of New Zealand, and the Andes Mts. in Patagonia of South America.
Figure 2. Temperature fluctuations over the past 15,000 years showing the abrupt cooling during the Younger Dryas and other warming and cooling periods, the Oldest Dryas (cool), Bölllng (warm), Older Dryas (cool), Allerød (warm), InterAllerød (cool), and Younger Dryas (cool).
Figure 3. Oxygen isotope record from the Greenland ice core showing an abrupt temperature drop 12,800 years ago, 1300 years of cool climate, and sudden warming 11,500 years ago.
The Younger Dryas had multiple glacial advances and retreats
The Younger Dryas was not just a single climatic event. Late Pleistocene climatic warming and cooling not only occurred before and after the YD, but also within it. All three major Pleistocene ice sheets, the Scandinavian, Laurentide, and Cordilleran, experienced double moraine-building episodes, as did a large number of alpine glaciers. Multiple YD moraines of the Scandinavian Ice Sheet have long been documented and a vast literature exists. The Scandinavian Ice Sheet readvanced during the YD and built two extensive end moraines across southern Finland, the central Swedish moraines, and the Ra moraines of southwestern Norway(Fig. 4). 14C dates indicate they were separated by about 500 years.
Figure 4. Double Younger Dryas moraines of the Scandinavian Ice Sheet.
Among the first multiple YD moraines to be recognized were the Loch Lomond moraines of the Scotish Highlands. Alpine glaciers and icefields in Britain readvanced or re-formed during the YD and built extensive moraines at the glacier margins. The largest YD icefield at this time was the Scotish Highland glacier complex, but smaller alpine glaciers occurred in the Hebrides and Cairngorms of Scotland, in the English Lake District, and in Ireland. The Loch Lomond moraines consist of multiple moraines. Radiocarbon dates constrain the age of the Loch Lomond moraines between 12.9 and 11.5 calendar years ago.
Multiple Younger Dryas moraines of alpine glaciers also occur throughout the world, e.g., the European Alps, the Rocky Mts., Alaska, the Cascade Range, the Andes, the New Zealand Alps, and elsewhere.
Figure 5. Double Younger Dryas moraines at Titcomb Lakes in the Wind River Range of Wyoming.
Implications
The multiple nature of YD moraines in widely separated areas of the world and in both hemispheres indicates that the YD consisted of more than a single climatic event and these occurred virtually simultaneously worldwide. Both ice sheets and alpine glaciers were sensitive to the multiple YD phases. The GISP2 ice core shows two peaks within the YD that match the glacial record. The absence of a time lag between the N and S Hemispheres glacial fluctuations precludes an ocean cause and is not consistent with the North Atlantic Deep Ocean Water hypothesis for the cause of the Younger Dryas, nor with a cosmic impact or volcanic origin.
Both 14C and 10Be production rates in the upper atmosphere changed during the YD. 14C and 10Be are isotopes produced by collision of incoming radiation with atoms in the upper atmosphere. The change in their production rates means that the Younger Dryas was associated with changes in the amount of radiation entering the Earth’s atmosphere, leading to the intriguing possibility that the YD was caused by solar fluctuations.
Why the Younger Dryas is important
What can we learn from all this? The ice core isotope data were hugely significant because they showed that the Younger Dryas, as well as the other late Pleistocene warming and cooling events could not possibly have been caused by slow, Croll-Milankovitch orbital forcing, which occurs over many tens of thousands of years. The ice core isotope data thus essentially killed the Croll-Milankovitch theory as the cause of the Ice Ages.
In an attempt to save the Croll-Milankovitch theory, Broecker and Dention (1990) published a paper postulating that large amounts of fresh water discharged into the north Atlantic about 12,800 years ago when retreat of the Laurentide ice sheet allowed drainage of glacial Lake Agassiz to spill eastward into the Atlantic Ocean. They proposed that this large influx of fresh water might have stopped the formation of descending, higher-density water in the North Atlantic, thereby interrupting deep-water currents that distribute large amounts of heat globally and initiating a short-term return to glacial conditions. If indeed that was the case, then the Younger Dryas would have been initiated in the North Atlantic and propagated from there to the Southern Hemisphere and the rest of the world. Since that would take time, it means that the YD should be 400-1000 years younger in the Southern Hemisphere and Pacific areas than in the Northern Hemisphere. However, numerous radiocarbon and cosmogenic dates of the Younger Dryas all over the world indicate the cooling was globally synchronous. Thus, the North Atlantic deep current theory is not consistent with the chronology of the Younger Dryas.
The climatic fluctuations before and after the Younger Dryas, as well as the fluctuations within it, and the duration of these changes are not consistent with a single event cause of the YD. Neither cosmic impact or volcanic eruptions could produce the abrupt, multiple climatic changes that occurred during the late Pleistocene.
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Related articles
- Younger Dryas -The Rest of the Story! (wattsupwiththat.com)
- New evidence of Younger Dryas extraterrestrial impact (wattsupwiththat.com)
- Catching up with the Younger Dryas: do mass-extinctions always need impacts? (skepticalscience.com)
- Study Finds New Evidence Supporting Theory of Extraterrestrial Impact (sott.net)
- The Great Ice Meltdown and Rising Seas: Lessons for Tomorrow (giss.nasa.gov)
IT IS NOT A METEOR, IT I S NOT A COMET AND IT IS NOT AN ASTEROID THAT CAUSED THE YOUNGA DRYAS. END OF STORY. THAT IS PURE NONSENSE..
Without shouting, I mostly agree. For one thing, there would be a signature in the dust layer associated with the event that I recall is lacking to ambiguous. There were — as I also recall — a number of other features to the YD — a prolonged drought in the US, dust storms hundreds of years long — it seemed to be a rather violent event with some very odd climate features. Well worth studying, well worth not drawing premature conclusions from as one studies.
rgb
the Gothenburg geomagnetic field excursion (13 000–12 000 years ago) http://www.sciencedirect.com/science/article/pii/003358947790031X
may also be of interest
It is, although paywalled. I will use my superhuman magic powers to get it for free shortly. Difficult to try to form a hypothesis linking the two events, but the timing is certainly interesting.
rgb
salvatore del prete says:
June 20, 2012 at 12:16 pm
The reason for the YD cold period and the 8200 years ago cool period and all other cool periods and warming periods is due to VARIATIONS in solar activity. The sun drives the earth’s climatic /oceanic systems, therefore any change it may undergo will have an impact on those systems.
I will follow with a more detail explanation of how this may all come about…..
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Perhaps Anthony can post it as a separate thread. You can submit it here: http://wattsupwiththat.com/submit-story/
Dennis Cox says:
June 20, 2012 at 3:27 pm
DC refuses to answer some very basic questions (I guess he never thought about them). Does any other catastrophist care to explain why the mammoths survived on northern islands? –AGF
rgbatduke says:
June 20, 2012 at 3:29 pm
……There were — as I also recall — a number of other features to the YD — a prolonged drought in the US, dust storms hundreds of years long…..
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And those hundreds of years long droughts and dust storms , not to mention the increase in fires, could easily wipe out the mega-fauna. What was not wiped out by starvation could have been hunted to death by predators including humans. Humans, having the ability to think and adapt survived, where as the mega-predators who were too specialized died out. However agfosterjr, insistence on blaming humans exclusively is typical of the “mankind hating” types who can never see anything but “evil humans” as the cause for every ill.
Does any other catastrophist care to explain why the mammoths survived on northern islands
Sure, while I don’t consider myself a catastrophist, whatever that is, I do acknowledge that catastrophes do occur on an almost regular if unpredictable basis. Remote outlier populations were isolated for the most part from human predation and far removed from the mostly continental and hemispheric effects of the Younger Dryas chronozone, and adapted to their dwindling range and food supply by a great reduction in size. It happened to humans as well.
Seriously, this is one of the best understood aspects of all of this. I’m wondering why you and you alone seem to be having a problem with this particular aspect of the megafaunal extinctions, completely independently of the causation. If you have anything lucid to contribute, please do so.
Thomas Lee Elifritz,
May I give you a shoutout for your blog? I notice there are no comments. That’s a shame.
Dennis Cox Nails it. The grey area is the exact dating and I believe that has been marked and should be looked at for confirmation/adjustment.
Wrangle Island Mammoths. That is easy to explain. Siberia is huge, a few specimens to the south survived the onslaught. As conditions improved they moved north. During the Holocene warm period, the tree line was much further north, and they roamed over ranges that included wrangle Island. Then as temps fell and food supply dwindled, they got smaller and they then ran out of habitat and died. This rapid dwafism process is well known
In the USA, the resultant firestorm was not universal, pockets were left intact and thats were smaller species survived. Luck playing a part. Also the Southern boundary is more constrained than that in Siberia with a vastly different natural climate. Thus the different survival profile.
The mythological 40 days and 40 nights of rain is a recorded reference to the vast amounts of ice sheet vaporized and returning to earth. That alone would have had massive impacts, including washing away a lot of evidence.
Off topic, I know, but mentioned above in other comments:
Re the shrinking human brain capacity: with the recent knowledge that some caucasians and asians have about 4% neanderthal genes, (and some denisovian genes), is there a possibility that as we ‘dilute out’ that proportion by interbreeding …. we lose brain capacity (neanderthals had bigger brains….)…??
Cannot for the life of me see how it could relate to global warming – (do the Inuit have really big heads?)
I recently saw pictures of the USA dust bowl event. Horrendous. Imagine something ten times worse( and it has happened many times before). Suggest somebody who knows about it posts a picture collage. That will provide sobering images.
It’s off topic. But I’m sorry, I jus’ gotta respond to this one.
On the subject of brain capacity: We have an African Grey parrot here with a brain that’s smaller than a peach pit. And some great big dogs with brains that weigh more than that whole damn bird. Yet the bird is infinitely more inteligent than any of the dogs. And she has a vocabulary.
Moral of the story: Brain structure is more important than brain size. And brain size is no indicator of brain “capacity”.
Dennis Cox says:June 20, 2012 at 7:56 pm
“…the bird is infinitely more intelligent than any of the dogs. And she has a vocabulary…”
I think you may be correct there … I saw a documentary on a parrot study… it could count up to five and combine its vocabulary to describe things, usually food. The trick dogs have is to understand human body language, and know where we are looking, and what our gestures mean.
Re human brains, probably we need to redefine our terminology; I guess I was shortcutting….
I suspect it is correct to say, in relation to humans, that there may be little connection between brain size (cranial capacity) and cognitive ability.
But really, I was not entering into that discussion, I was only commenting on the fact that there are reports that the ‘cranial capacity’ of the modern human is about 150 cc LESS than that of humans of 20,000 years ago. (and that some have proposed it may be linked to AGW).
I find it difficult to envisage a mechanism…..
http://discovermagazine.com/2010/sep/25-modern-humans-smart-why-brain-shrinking/article_view?b_start:int=2&-C=
salvatore del prete says
Mainstream has their heads in the sand, and the SETUP is in place and has been in place for at least 3 years to cause this climate regime we are currently in, to finally change into another climate regime. Now when I say change into another climate regime ,that does not necessarily mean a drastic drop in temperatures, but what it means is the temperatures will decline ,and it won’t be gradual, it will be in quick jerks and these jerks could be as small as .2C to as much as 2.0 C, but the jerks themselves will be fast,although the magnitude of jerks in temp. will depend on how the items that control the climate phase in with one another, with solar activity leading the way.
Henry says
we are agreed on that it is cooling, but according to my latest apparent mathematics the rate of cooling is very predictable and slowly on parabolic curves…..polynominals of the 2nd order.
http://www.letterdash.com/henryp/global-cooling-is-here
You can calculate exactly at what rate we are cooling. Currently it is -0.08 K per annum (on the Means).
no jerks and jumps – I can calculate exactly at what rate each year we are cooling .
However, it seems that everyone here and everywhere else seem to be in denial that it is cooling since 1994, so obviously one day they might pick on the ways of their errors (in global temp. measurement) in which case it might look like there are big jumps…..
Otherwise I note that you do not show us any measurements or any analysis of data that would seem to support the things that you claim.
Dennis Cox says:
June 20, 2012 at 11:22 am
Some of the denials of the YD impact event are getting ludicrous.
…
One can explain the extermination of the giant animals by recognizing what effect the event must have had on the food supply.
Much of the edible biomass of North America would have been burned away down to the last blade of grass.
The bigger you are, the more you need to eat every day. The animals that survived the impact event and didn’t face extinction were simply those that didn’t need to eat so much.
Most of the Mega fauna that went extinct after the event probably just starved. And with them went any specialist predators that depended on them for food.
The biggest NH megafauna extinctions (e.g. wooly rhino, N American wild horses) took place 30,000-40,000 years ago, well before the YD.
The reason for the YD cold period and the 8200 years ago cool period and all other cool periods and warming periods is due to VARIATIONS in solar activity. The sun drives the earth’s climatic /oceanic systems, therefore any change it may undergo will have an impact on those systems.
Evidence? This is an open question today, let alone then. I don’t disagree, mind you, I just don’t agree either until there is convincing evidence. I end up 2/3 or 3/4 convinced from time to time (because there is some evidence) but then somebody like Lief comes along and points out that the evidence is not consistent and hence might be coincident, and then there is the pesky problem of the mechanism(s).
There are theories — with some corroborating evidence — that the sun is long period variable with a periodicity of 300 or 600 My and that this drives ice ages. There are other theories — with some corroborating evidence — that the sun bobs up and down and passes through both the galactic plane and spiral arms and that this modulates the GCR rate which in turn modulates the climate, e.g. —
http://www.sciencebits.com/ice-ages
There are verified physical mechanism whereby GCRs “can” modulate albedo, and these mechanisms may or may not feed back on top of more mundane feedback mechansims such as the vastly simpler one Willis is proposing, that when it gets warmer the tropics respond with more thunderstorms which increase the cooling rate both by transporting moist heat up to where it is more efficiently lost and by reflecting incoming sunlight, for a net negative feedback to any forcing. Then there is the aforementioned possibility that both the Sun’s brightness and the chemistry of the Earth’s atmosphere could be modulated by means of passage of the solar system through the interstellar medium, which is not uniform in density (and whose local density is basically unmapped AFAIK). There are seriously unknown phenomena, such as the effect of a large CME that hits the Earth, or a series of such CMEs.
As Lief I think just obliquely pointed out, there is the Earth’s magnetic field itself! As it wanders around it alters the geographical pattern of cosmic ray protection and might well nonlinearly feed back into climate. This got me thinking about pole strength variation as well, but attendez — the northern magnetic pole has been moving steadily north across Canada since the early 1800s!:
http://science.nasa.gov/science-news/science-at-nasa/2003/29dec_magneticfield/
The field has also weakened by 10% or so over that time (according to this article). We are thus left with yet another thing that is strongly correlated with the Earth’s temperature increase over the same time — one could try to construct a model where strong fields are net cooling, and where net cooling is globally more efficient the closer the poles are to the equator. Hence moving the north pole further north is net warming. Weakening the global field strength is net warming. Both of these together could — note that I say could, I haven’t constructed a plausible mechanism and am not asserting that there is one, we are still at the correlation stage searching for causality — be responsible for some fraction of the observed warming since the early 19th century.
The problem isn’t with finding correlations between cosmic, solar, and geological phenomena that could be responsible for some fraction or even “all” of the observed fluctuation in global temperature. Such correlated phenomena abound! Worse, there is absolutely nothing that prevents them all from affecting global climate, in a nonlinear and coupled way!
This latter easily explains why there is no perfectly correlated “signal” between e.g. solar state and temperature, between CO_2 and temperature, between ENSO and temperature, between anything and temperature. A solar maximum is net warming, except when it’s not because some magnetic, aerosol, decadal oscillation, thermohaline, or greenhouse gas (in any combination!) trump it. So we are constantly trying to resolve signal from not-quite-noise, resolve a one-to-one causal relation when in reality that is as difficult as detecting the true killer of Julius Caesar (which knife was it that did the job, when there were so many at work?).
We are constantly looking for a smoking gun. What if there are smoking guns, in the hands of demented dwarves that roll dice before firing in nearly random directions?
I will follow with a more detail explanation of how this may all come about…..
And I eagerly await it, but bear in mind that it will just have to stand in line with all of the other postulated causes and observed near-coincidences in the data. People on list hate models, but in the end one really does need a highly multivariate model that can manage all of this even to test a complex set of hypotheses. The human brain wants it all to be simple: “The Sun modulates the Earth’s Global Temperature” or “CO_2 modulates the Earth’s Global Temperature”. But what if it is the Sun, CO_2, the Sun’s magnetic field, the Earth’s magnetic field, the state of the ocean, the phase of the decadal oscillations, the particular positioning of the continents as they drift about, the phase of the Earth in a complex dance of axial tilt, orbital eccentricity, and axial precession, the location of the solar system as it plows through an unmeasured interstellar medium, the number of active volcanoes and the number of those volcanoes that explode (or worse, just erupt for a few tens or hundreds of thousands of years a la supervolcanos like Yellowstone) with Gt+ energy release per century, deforestation, and let’s not forget asteroids and Dr. Evil’s diabolical device (a.k.a. the great unknown). All of these could be significant contributors, and they could be intertwined and could reinforce or partially cancel one another, depending on their nearly completely independent or even random periods or phases.
People just don’t get it. This is a hard problem. One simply cannot solve it by looking at a window 100 years, 200 years, or 500 years long. Bob Carter has the right of it — one needs to start by looking at global climate over geological time to start to understand what the range of natural variation is, and frankly, until one can understand the longest time scale variations first and systematically working one’s way down to mundane timescales one hasn’t a friggin’ prayer of understanding the shortest time scale variations. We know this because we have clear evidence, unexplained, of enormously rapid changes in global temperature that have nothing to do with anthropogenic CO_2, at least. How can we possibly exclude the possibility that the mechanism responsible for those rapid changes isn’t alive and well and working today, and is responsible for the not even particularly rapid changes we observe today, especially when the geological evidence is such that not one person on Earth would look at the geological variation of global temperature, point to the end, and say “Oh my, look at the runaway warming!”
Quite the contrary. They’d go to sleep, because the present isn’t even close to being extreme. It is boringly normal.
rgb
rgb says:
http://wattsupwiththat.com/2012/06/19/the-intriguing-problem-of-the-younger-dryaswhat-does-it-mean-and-what-caused-it/#comment-1014565
Henry says:
You say a lot of things but you do not bring anything to the table. All is speculation.
I say:
http://www.letterdash.com/henryp/global-cooling-is-here
from where you should be able to understand from all three curves, for maxima, means and minima, that warming is long gone. In fact it stopped in 1994/5.
That being the case (for me it is fact)
brings us all back to the Orssengo Curve
http://wattsupwiththat.files.wordpress.com/2010/04/orssengo3.png
His actuals also show a marked cooling from 1994. If you want to know where that graph came from, look here:
http://wattsupwiththat.com/2010/04/25/predictions-of-global-mean-temperatures-ipcc-projections/
The only thing about the Orssengo graph that seems a bit wrong to me is that he thought the maximum of warming would be around 2000. I see it a bit earlier. So the graph may have to be shifted a little to the left. However, either way, I don’t see anything disastrous yet on the horison although I did buy some extra warm cloths. Making wars and exploding (atomic) bombs does seem to be a cause for extra cooling. (note the blue areas in the graph and the one simple error on the scale)
rgb,
All reasonable points but whatever the factors affecting the Earth’s energy budget at any given moment the netted out effect at that moment is represented in the average sizes, positions and intensities of the established permanent climate zones.
Look to them to see what is going on.
Poleward / zonal jets and widened Hadley cells occur when the troposphere is warming.
Equatorward / meridional jets and smaller Hadley cells occur when the troposphere is cooling.
Lots of varied evidence supports that simple proposition.
Then rank the potential factors in order of scale and it is clear that sun and oceans are magnitudes ahead of everything else with all the other factors usually cancelling each other out most of the time.
We need to establish the characteristics of the air circulation at the point where warming switches to cooling and vice versa.
There was such an inflection point in the mid 70s and I aver there was another around 2000.
Gail Combs says:
June 20, 2012 at 4:11 pm
” However agfosterjr, insistence on blaming humans exclusively is typical of the “mankind hating” types who can never see anything but “evil humans” as the cause for every ill.”
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On the contrary, absolution of human involvement in “overkill” is simply a perpetuation of the “noble savage” ideology: the ancients were worthy caretakers while we moderns destroy all. Moreover early humans possibly contributed to massive deforestation by accidental or intentional fire setting. The literature is replete with stacked decks favoring the innocent hunters; e.g., that a small fraction of remains contain a spearheads, when of course those animals that were killed by Clovis hunters were dismembered, and spearheads removed.
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Grey Lensman says:
June 20, 2012 at 7:14 pm
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You explain nothing. The island dwellers are the most vulnerable of all, having no place to escape or migrate to. And it was impossible for mainland beasts to escape to the islands after the sea rose; the “dwarf” mammoths were there before and after YD. Whatever one’s explanation for megafauna extinctions, island extinctions generally are those most certainly attributable to human causes–not necessarily through hunting, but also by introduction of dogs, pigs, agriculture, fire and disease.
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phlogiston says:
June 21, 2012 at 5:07 am
“The biggest NH megafauna extinctions (e.g. wooly rhino, N American wild horses) took place 30,000-40,000 years ago, well before the YD.”
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Not sure where you get that–the horses lasted till about 12kya, and probably the rhinos too.
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It’s bad enough blaming the climate when the ice ages were 3 million years old. It’s reasonable and necessary to take tectonics into account, and many early migrations and extinctions are attributable to the appearance of the Panama and Bering Strait bridges. Even if humans crossed much earlier, their Arctic technology was lacking, but they and their dogs were probably responsible for some of the earlier extinctions. But the appearance of Clovis hunters spelled doom for the mainland mammoths and a host of other species. Climate cycles make for a very poor excuse, and meteors make a very poor excuse for climate change. So meteors are improbable times improbable as extinction causes. It’s not just island mammoths, it’s South American giant armadillos, ground sloths, etc.
The pattern is clear: those animals with the longest history of familiarity with humans fared the mesolithic revolution the best. Those surprised by the upstarts fared worst. Those on the most remote and vulnerable islands lasted the longest, in spite of having nowhere to escape to. It took the humans a while to find them. –AGF
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rgbatduke says:
June 20, 2012 at 3:29 pm
IT IS NOT A METEOR, IT I S NOT A COMET AND IT IS NOT AN ASTEROID THAT CAUSED THE YOUNGA DRYAS. END OF STORY. THAT IS PURE NONSENSE..
Without shouting, I mostly agree. For one thing, there would be a signature in the dust layer associated with the event that I recall is lacking to ambiguous.
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Depends. If most or all of the proposed impacts were airbursts, especially if occurring over ice-sheets (and comets are mostly ices), there would be little dust. Most of the “debris” would be vaporized ice. The metallic remains of the impactors would be the only dust, and I think some of the proposed “sites” show traces of iridium, etc.
Stephen Wilde says
There was such an inflection point in the mid 70s and I aver (sic) there was another around 2000.
Henry says
Yes, looking at my curve for the means, it does look like things changed sign from cooling to warming around the beginning of the seventies (42 years ago) and again from warming to cooling 16.4 years ago, counted from before 2011 (the last complete record we have is from 2011)
But where did you get your information from?
You say a lot of things but you do not bring anything to the table. All is speculation.
I say:
http://www.letterdash.com/henryp/global-cooling-is-here
from where is sou should be able to understand from all three curves, for maxima, means and minima, that warming is long gone. In fact it stopped in 1994/5.
Dearest Henry,
You need to learn the difference between curve fitting and a theory, and the difficulty of extrapolating a fit curve as a predictive model. I am (I would humbly claim) a serious expert in modeling and fitting any smooth curve to a short trend in data and extrapolating it as if it is meaningful is an elementary mistake, one that will cost you your shirt if you use it either in climate science or the stock market.
If you want to actually understand something of the problem, read Koutsayannis paper: Nonstationarity versus scaling in hydrology
http://itia.ntua.gr/en/docinfo/673/
(Note well to everybody: This is an all time classic paper, and one that I strongly recommend that everybody grab and peruse. Figure 1 should be mandatory “reading” for every single person involved in climatology. It is also the original paper, as far as I can tell, on what will IMO end up being the most important contribution to statistical climatology of all time (so far) — the observation of a clear statistical scaling law in climate fluctuations and the consequent inference of Hurst-Kolmogorov dynamics. This might allow us to build working stochastic GCMs, or at least to clearly understand their mode of, failure, in the next decade. Other Koutsayannis papers and presentations are equally brilliant.)
So Henry, when you learn that there is more to predictive modelling than fitting smooth functions through data in some arbitrarily selected window and hoping/expecting it to extrapolate out of the window, I’d be happy to continue the converstation, but the Koutsayannis paper above, figure 1, illustrates better than any words why that approach, unsupported by an actual dynamical model that generates the supposed fit functions, is almost certainly mathematical nonsense with no real predictive value.
rgb
The Earth’s surface being 71% water, most impacts would be in or over the oceans, with perhaps titanic tsunamis following in their wake. It is thought that the Taurid complex was formed about 30,000 years ago from the break-up of a comet. Reasonably well-preserved mammoths have been turning up in the permafrost since antiquity, and some date to more than 40,000 years ago, while others are more recent. No doubt, a big enough flood can sweep all in its path, and there are other mechanisms for huge floods without considering impacts or tsunamis, but the problem of preservation remains, and such is showcased by Lyuba from c41,800 whose remains were found on the Yamal peninsula, of all places.
‘Not to discount the several other b’ars in the woods noted by RGB, above..
Depends. If most or all of the proposed impacts were airbursts, especially if occurring over ice-sheets (and comets are mostly ices), there would be little dust. Most of the “debris” would be vaporized ice. The metallic remains of the impactors would be the only dust, and I think some of the proposed “sites” show traces of iridium, etc.
I don’t disagree; this is the “ambiguous” part. The problem is that there is no “smoking gun” layer of iridium a la the Cretaceous extinction boundary, so there is little reason to infer a dino-killer scale asteroid as a cause. Also, much smaller asteroids could leave an ambiguous trace of iridium without actually affecting climate. Finally, see my discussion of energy — even a 2 kilometer wide asteroid (or an equivalent distribution of smaller asteroids) would be unlikely to have a greater impact than Tambora. Of course this doesn’t make the hypothesis untenable, because the climate is multvariate, we had just pulled out of the ice age, and the climate may have been unstable so that even a small perturbation triggered a cold transition then where Tambora failed to in 1815. But it does make it less plausible.
So I will have to stick with “I think I agree” that the cause of the YD isn’t likely to be meteors or falling asteroids because of a lack of convincing evidence, while acknowledging that an absence of evidence isn’t evidence of absence, and that even evidence of presence does not suffice to establish causation. I liked the freshwater interrupting thermohaline circulation argument because it was a good explanation of the timescale of the NH transition, and because the global thermohaline conveyor belt is one of the things that I do believe could even today quickly put the Arctic and Northern Europe into the deep freeze. The synchronicity of NH and SH cold transition argues against it, but it doesn’t necessarily argue for an asteroid either.
One of the very simplest hypotheses is a solar event, but corroborating evidence is tough to find. Another might be a truly massive volcano explosion, say 10-100 gt, with consequent global tsunamis (sinking of “Atlantis” sort of thing). But replacing the volcano with 4 km asteroid (about the right scale) would change little, except that in the case of an asteroid one would really expect the iridium signature to be consistent, clear, and global. That’s a lot of asteroid, after all. A volcanic explosion, OTOH, would have little in way of a global signature — a dust layer, which is at best what we’ve got, although resolving THAT is tough.
FWIW, it has its own wikipedia page — it can summarize the arguments better than any of us here on list (and includes the criticisms):
http://en.wikipedia.org/wiki/Younger_Dryas_impact_hypothesis
Basically, there is evidence of an impact in North America (in North Carolina where I live, actually, where the layer is clearly visible in eroded stream beds). The platinum group mineral content of the layer is inconsistent. The microdiamond content is consistent. The megafauna extinction pattern is inconsistent (and difficult to explain with any simple hypothesis). Overall, I think the inconsistents have it, although there may have been some other non-asteroidal major geological event that occurred at the same time as the YD and may or may not have triggered it. I just don’t know enough about the geology to know what is excluded.
rgb
Primitive man was mostly vegetarian and insectivorous, gradually becoming omnivorous. The further north they moved the more exclusively carnivorous they became, at least in winter. Those who crossed the Bering Strait were fishing and hunting specialists, having to turn almost exclusively to hunting at the expense of fishing as they moved inland, and having to learn vegetables from scratch as they moved southward. Feeding a clan required the most efficient hunting: the best hunters went for the biggest game, enabling the most rapid population growth. Clovis hunters increased at the expense of the mammoths, and when they were gone the Clovis hunters disappeared too.
Then the Folsom hunters flourished, going after the biggest game still left, the giant bison. It didn’t matter where a big game animal lived outside the tropics, if it was big it was in trouble. Giant wombats went extinct; little wombats didn’t.
Giant beaver went extinct; little beaver didn’t.
Giant ground sloths went extinct; little ones didn’t.
Giant bison went extinct; little ones didn’t.
Giant cameloids went extinct; little ones didn’t.
Gyptondon went extinct; little armadillos didn’t.
For totally unrelated reasons big mammoths went extinct and little ones didn’t–till later. Why was size a disadvantage? Because the hunters went for the biggest prey, the easiest meat for the most people. Big beaver have just as easy a time finding food as little beaver; big wombats as little wombats, big bison as little bison. Hunting preference is the deciding criterion. Climate hardly registers on the scale. Meteors don’t register at all. –AGF
HenryP asked:
“But where did you get your information from?”
In the 60s and 70s I kept my own records (long since disposed of) in anticipation of monitoring the expected cooling that everyone was banging on about back then.
Contrary to my expectations I saw more frequent southerly and westerly winds developing from the mid 70s onwards with a warming trend especially in the winters.
Many years later it was confirmed as the 1976 – 78 Climate shift which appears now to be well accepted..
Anyway, that led me to keep an eye on the warming trend but in a more informal fashion due to career and family committments and around 2000 I noted the whole thing going into reverse and that reversal continues to this day. I started talking about it on blogs some 4 years ago and have built a plausible climate theory on the basis of it.
To my mind all the new data is confirming my hypothesis but there has not yet been a long enough period of time to constitute proof.
Nonetheless I have put it out there and await developments with interest.