Open Mind

Younger Dryas Impact Event

January 3, 2009 · 118 Comments

Not too long ago Firestone et al. (2008) reported considerable evidence for the impact of some object from space in northern North America about 12,900 years ago. Now, yet another report emerges showing the existence of “nanodiamonds” in sedimentary layers from that time, further evidence of an impact event which could have had important consequences for the environment at that time. In fact, there’s speculation (and in my opinion, well founded) that the impact event may have been the “trigger” which caused a climate event known as the Younger Dryas (”YD”).


The Younger Dryas was a rapid climate change during the last deglaciation, which is most pronounced in high latitudes of the northern hemisphere. It’s well recorded, for example, in \delta18O data (a proxy for temperature) from the GRIP (Greenland) ice core (the double-ended arrow marks the time span of the YD; the time axis is years BP = “before present”):

grip

Lower (more negative) \delta18O values indicate colder temperature, so the YD was a period of extreme cold in Greenland. Note that it was preceded by a period of extreme warmth in Greenland, the Bolling warm period, and that this graph starts with Greenland at temperatures typical of an ice age, but ends with Greenland temperature near typical interglacial values (the graph ends 10,000 years ago, not too far from the beginning of the modern “holocene” epoch).

From the Bolling warm to the YD cold period, the temperature change in Greenland is extreme, almost as much change as the transition from full glacial to full interglacial conditions. But that much temperature change (full glacial to full interglacial) did not occur worldwide. We can compare, e.g., the GRIP ice core \delta18O data to that from ice cores taken at Byrd station in Antarctica:

gripbyrd

These particular ice cores are selected because they have been accurately synchronized, using methane concentration data to align the time scales. Two things are obvious: first, that Greenland temperature is far more volatile than Antarctic temperature, showing many very large swings while Antarctic temperature is much more stable; second, that the YD cooling shown in Greenland does not show in Antarctica. We can see this more plainly if we take a closer look at the time span 20,000 to 10,000 years before present:

gripbyrd2

Antarctic data show a much more steady progression from glacial to interglacial conditions. There is a slight cooling indicated by the Antarctic \delta18O data, but it happens about a thousand years before the YD. Nonetheless, the YD does represent temperature decrease over much of the far northern latitudes, with signs of glacial advance in Europe, changes in food supply for early human populations, even evidence that the cooling extended to western North America and the north Pacific. But while YD cooling covered a vast area of the far north, it certainly does not represent as much global temperature change as the transition from full glacial to full interglacial conditions.

For a long time, the prevailing theory of the cause of the YD was the release of a vast quantity of fresh water into the north Atlantic ocean, probably from some giant freshwater lake held in place by glacial ice. The melting of glacial ice spilled this fresh water into the ocean, decreasing the salinity of the surface waters in the north Atlantic. This decreased the density of surface waters sufficiently to prevent their sinking to the deep ocean, driving the thermohaline circulation whose currents transport tremendous quantities of heat from the tropics to the poles — in this case, the far north. Robbed of ocean current heat transport, the far north turned back toward the deep freeze of glacial conditions for over 1,000 years following the onset of the YD.

But the new evidence strongly suggests that it was the impact event 12,900 years ago which triggered the YD. The evidence for the event (and its timing) is considerable, including not just nanodiamonds, but enrichment in Iridium (to 5,000 times background crust levels) and Nickel, and extraterrestrial Helium. Furthermore, the impactor probably exploded in the atmosphere, releasing tremendous quantities of heat which ignited forest fires over much of North America. The signs of massive burning are also numerous, including charcoal, soot, PAHs (polycyclic aromatic hydrocarbons), carbon spherules, glass-like carbon, and fullerenes.

As fascinating as is the climate impact of such an event, the effects on living things are equally thought-provoking. The Clovis people of prehistoric North America (known for the use of the “Clovis point” to tip their spears) declined quickly after the event, and the YD impact is suggested as a trigger; Clovis artifacts are plentiful in sediments below the layer containing the evidence of impact, but practically absent from layers above it. In fact the YD impact is suggested as the root cause of the extinction of megafauna like Mammoths and Mastodons, which would have suffered greatly from destruction of their ecosystem by wildfires, and reduced food supply due to other ecological changes. Hence their eradication may have had nothing to do with overhunting by early humans, but been due to destruction wrought by the impact of an extraterrestrial object.

Numerous factors could have caused the climate change associated with the YD. These include the injection of massive quantities of dust and soot into the air, resulting from both the impact itself and the wildfires which it ignited. In addition, there’s no candidate crater for the impact; Firestone et al. suggest that if the object had exploded in the atmosphere, and was on a low-angle trajectory over an ice sheet (the Laurentide ice sheet) at least a km. thick, then the absence of an impact site is not unexpected. But a huge thermal blast over an ice sheet may have been exactly the event leading to rapid melting and a large freshwater pulse into the north Atlantic ocean — exactly the condition which could shut down the thermohaline circulation and block heat transport from the tropics to the poles.

All told, the impact theory of the trigger of the YD is well supported by the evidence, and the number and ubiquity of markers for the impact event itself is considerable. This extraterrestrial object appears to have had a considerable influence on northern-hemisphere climate and on the progression of life, both for the megafauna of North America, and for human populations.

Categories: Global Warming
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118 responses so far ↓

  • Kipp Alpert // January 3, 2009 at 11:52 pm

    Tamino: Could Global Warming be sufficient to cause the thermohaline circulation decrease in density, and have a colder Europe.Also, if the circulation pattern stopped could this effect the Americas as well. KIPP

    [Response: I'm certainly not expert in these issues, I can only offer speculation and 2nd-hand opinions. There is of course the possibility that the Atlantic thermohaline could be affected by freshwater injection (from melting icecaps), but the opinions I've seen (from IPCC and the U.S. Climate Change Science Program) are that shutdown is unlikely to happen any time soon.

    If the thermohaline did shut down, it would surely affect Europe and probably N. America as well.]

  • Kipp Alpert // January 4, 2009 at 1:45 am

    Tamino: Thanks Sir; I was talking about in one hundred years or more. A recent article I read said that the Arctic and greenland Ice sheets were melting more than models expected, due to DRAMATIC CHANGES IN THE NORTH ATLANTIC—Subpolar seas bordering the North Atlantic have become noticeably less salty since the mid-1960s, especially in the last decade. This is the largest and most dramatic oceanic change ever measured in the era of modern instruments. This has resulted in a freshening of the deep ocean in the North Atlantic, which in the past disrupted the Ocean Conveyor and caused abrupt climate changes. From waht I can find there is low probability according to Hadley.http://homologa.ambiente.sp.gov.br/proclima/artigos_dissertacoes/artigos_ingles/globalwarmingandthemohalinecirculationstability.pdf

  • TCOisbanned? // January 4, 2009 at 2:20 am

    Is the post 10,00o data not displayed or not available. Not making any point, but just want to see the refernce level of current temps. Even just as a horizontal line.

    [Response: The available data which has been "synchronized" with Byrd station data does not include the post-10000yrBP time span. But the GRIP data after that are available, and indicate very little change relative to the 10,000 yrBP level (compared to the changes before that).]

  • Ray Ladbury // January 4, 2009 at 2:27 am

    Kipp, I haven’t heard anybody suggest a thermohaline shutdown is likely. The meltwater being injected, while fresh, will still be cold, and it would take a lot of fresh water to shut things down. It is not impossible, particularly if we were to see much faster melting in Greenland than we expected, but it’s one threat that doesn’t keep me awake at night.

    Tamino, nice summary. Iridium is a pretty good indicator of the sort of body that impacted, too–iron-nickel and sufficiently small that it never differentiated. Iridium is a strong siderophile and most of Earth’s went to the core dissolved in molten iron–makes for a pretty good signature for an extra-terrestrial impact.

    [Response: If I recall correctly, the Ir and Ni levels were unambiguously much higher than earth-crust levels, but not big enough to indicate meteoritic origin, so the authors hypothesize that the impactor was a small comet rather than meteor.]

  • Ray Ladbury // January 4, 2009 at 3:12 am

    Hmm, must have been a pretty dusty comet.

  • Hank Roberts // January 4, 2009 at 3:35 am

    http://ocw.mit.edu/OcwWeb/Earth–Atmospheric–and-Planetary-Sciences/12-091January–IAP–2008/CourseHome/index.htm

  • dhogaza // January 4, 2009 at 4:12 am

    Hey, TCO, any particular reason you haven’t tried to defend your position that you know more about the effect of pace on climate change on ecosystems than professionals in the field do?

    Just a couple of days ago you were, after all, totally self-assured that rate of change of climate vs. “landing point” was meaningless.

    Don’t disappoint us … defend your science denialist belief, please!

  • Tom G // January 4, 2009 at 5:32 am

    The CNN.com site is stating that the melt water from the air-burst rushed down the Mississippi River and went into the Gulf of Mexico.
    Where did they get that from?

  • Richard Steckis // January 4, 2009 at 6:51 am

    From Wikipedia:

    “An airburst would have been similar to but many orders of magnitude larger than the Tunguska event of 1908″

    Looking at the stable isotope data for Greenland, one can see a distinct decline in delta18O from 1909 to 1925 (with the exception of 1916). This could be a response to the 1908 Tunguska event (not confirmed though). That response was not evident for delta18O from Antarctica even though weather stations around the world recorded a temperature decline following Tunguska.

    The Tunguska impact yealded an explosive power of 10-15 megatons. The dryas event was said to be many orders of magnitude greater in explosive power. Just three orders of magnitude would give an explosive power equivalent to nearly the total nuclear arsenal on earth. And yet there was no evidence of the event in Antarctica. This intrigues me.

    If a 15 gigaton explosion (hypothetical) will not produce a response in Antarctica then what will? It should. No matter where on earth that explosion took place. Such a catastrophic event could not be confined to just the Northern Hemisphere.

  • Richard Steckis // January 4, 2009 at 6:52 am

    sorry. I meant yielded.

  • Richard Steckis // January 4, 2009 at 7:17 am

    What I am asking here is: Is there something unique about Antarctica that causes it not to reflect what are quite obviously events that should have a global impact?

  • TCOisbanned? // January 4, 2009 at 8:25 am

    dhog:

    1. you are mischaracterizing my position. I do not claim ecology expertise. (you have a tendancy to do that…I think you jump too fast.) I think trying to shut down the discussion by some claim of expertise when they’re not here (or are they?) and they have not endorsed the position either is pretty asinine.

    2. I don’t have to have expertise overall to ask an intersting question. For instance if the temp rate is 1 degC/century in 20th century, but year to year difference can be a couple degrees

    3. Recall that Hank raised the temp issue in regard to rice growing (which is huiman cultivation, btw, similar to your garden), but has not cited any works to show that rate hurt the plants more than level of excursion.

    4. With all due respect, I did not stop discussing because of being routed or scared or anything. but because there was little interesting response. Hank cited a non-responsive paper (after first sentence, rest of paper is about different issue, measuring rate…not the impact of the rate.) and you resorted to telling me I couldn’t ask questions in church.

    5. But anyway, on the off chance that you want to actually hav e a discussion, perhaps explain to me how a 3 deg/century change would differ from an immediate 3 deg change, would differ from a 1 deg/Century rate, but wait 300 years.

  • Tom Woods // January 4, 2009 at 1:32 pm

    Perhaps a large impulse of fresh water caused a shut down of the thermohaline circulation, or perhaps not…

    If it was the dust from the impactor itself that caused the dramatic drop in temperatures then the theory of a shut down of this circulation may be lost to new science. This may also quiet some arguments that a melting Greenland ice cap will shut down the thermohaline circulation and end the global warming leads to cooling argument.

  • dhogaza // January 4, 2009 at 5:33 pm

    But anyway, on the off chance that you want to actually hav e a discussion, perhaps explain to me how a 3 deg/century change would differ from an immediate 3 deg change, would differ from a 1 deg/Century rate, but wait 300 years.

    Or perhaps you could put some effort into trying to learn what scientists, say those at The Nature Conservancy who are working hard to try to figure out what various rates of change will do to the ecosystems on their landholdings, know.

    You’ve claimed that rate of change is unimportant. You’ve been informed that those best equipped to determine whether or not this statement is true have reached the opposite conclusion. You ask us for a “discussion” to prove that your uninformed opinion is wrong. Sorry, I think it’s up to you to convince us that your uninformed opinion is more likely to be right than that of professionals who work in relevant fields.

    It’s sort of like the entire contra-climate science effort, isn’t it? You argue from essentially a position of personal incredulity, and aren’t really changing that position. After all, you’re still convinced that climate science has got it all wrong … wouldn’t expect you to accept that biologists and ecologists know anything interesting.

  • TCOisbanned? // January 4, 2009 at 5:56 pm

    dhog:

    First you say we shouldn’t have a discussion, because the experts have spoken.

    Then, you come back and ask me why I’m not talking about?

    *loco smilie*

    I totally think we can talk about these things and am all up for it and for learning something. To start with we need to define terms and such. I mean when I saw Hank cite a paper that was about MEASURING rates as an example of a paper describing EFFECTS of rates, it was clear that issue analysis could help.

  • mauri pelto // January 4, 2009 at 6:35 pm

    Tamino your line of reasoning on this is not as strong as usual. This is not to say you are not correct but I find little evidence of stratigraphy that is compelling here. We have a fantastic amount (thousands literally) of stratigraphic records from this period due to close examination of many end moraines, loess deposits, pollen records and varves from the last ice age. These have not shown an evident impact layer. An impact sufficient to cool off the climate of Greenland substantially could not be confined to a hemisphere. This is documented by eruptions such as Pinatubo. Our atmospheric system is too good at mixing to allow such large regional temperature change in the absence of others. Also the delta O18 values depend on the source of the ppt. If the source changes this can alter the signal. We do not need as large a temp change as is indicated. This is because it is transport distance that leads to enrichment of O18. thus, a longer path from evaporation to snowfall can lead to an enrichment without a temp. change. This does not of course influence the O18 values in the ocean cores themselves, which do reflect the ocean temperature.

    [Response: First of all, the reasoning isn't mine, but that of the authors. If you want to review the details of their stratigraphic evidence you can find it in the article (which is linked). I found it compelling, especially the enrichment of Ir and extraterrestrial He.

    I don't think anyone has suggested that the impact alone was the cause of Greenland (or far-northern latitude) cooling, rather that it was the *trigger*, probably for a temporary shutdown of the thermohaline circulation. Certainly *something* caused cooling in the far north (as indicated by glacial advance and other evidences, not just 18O abundances) which is not indicated in the southern hemisphere.]

  • Hank Roberts // January 4, 2009 at 7:40 pm

    TCO, I gave you a couple of places to start, this is a broad area well studied. I don’t claim any one paper will educate or convince a skeptic. But the study of how rates of change affect populations — not just contemporary — are there to find and read.

    The contemporary papers mostly focus on pointing out how much faster the current rate of change is than anything in the past. The context is the many studies documenting how ecology changes as the environment changes.

    Some 800 papers have cited this one, it’s a place to start:

    Fingerprints of global warming on wild animals and plants
    Root, TL | Price, JT | Hall, KR | Schneider, SH | Rosenzweig, C | Pounds, JA
    Nature [Nature]. Vol. 421, no. 6918, pp. 57-60. 2 Jan 2003.

    “Over the past 100 years, the global average temperature has increased by approximately 0.6 degree C and is projected to continue to rise at a rapid rate. Although species have responded to climatic changes throughout their evolutionary history, a primary concern for wild species and their ecosystems is this rapid rate of change. We gathered information on species and global warming from 143 studies for our meta-analyses. These analyses reveal a consistent temperature-related shift, or ‘fingerprint’, in species ranging from molluscs to mammals and from grasses to trees. Indeed, more than 80% of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species. Consequently, the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations. The synergism of rapid temperature rise and other stresses, in particular habitat destruction, could easily disrupt the connectedness among species and lead to a reformulation of species communities, reflecting differential changes in species, and to numerous extirpations and possibly extinctions. ”

    If your next question is going to be to ask me to explain why it’s a problem to “disrupt the connectedness” then I suggest considering this:

    http://abstrusegoose.com/strips/computer_programming_101.JPG

  • Hank Roberts // January 4, 2009 at 7:46 pm

    See, e.g.,
    BioScience
    Volume 55, Issue 9 (September 2005)
    Article: pp. 749–759

    Forecasting Regional to Global Plant Migration in Response to Climate Change

    The rate of future climate change is likely to exceed the migration rates of most plant species. The replacement of dominant species by locally rare species may require decades, and extinctions may occur when plant species cannot migrate fast enough to escape the consequences of climate change. Such lags may impair ecosystem services, such as carbon sequestration and clean water production. Thus, to assess global change, simulation of plant migration and local vegetation change by dynamic global vegetation models (DGVMs) is critical, yet fraught with challenges. Global vegetation models cannot simulate all species, necessitating their aggregation into plant functional types (PFTs). Yet most PFTs encompass the full spectrum of migration rates. Migration processes span scales of time and space far beyond what can be confidently simulated in DGVMs. Theories about climate change and migration are limited by inadequate data for key processes at short and long time scales and at small and large spatial scales. These theories must be enhanced to incorporate species-level migration and succession processes into a more comprehensive definition of PFTs.

    Keywords: climate change, dispersal, migration, long-distance dispersal, dynamic global vegetation models

    DOI: 10.1641/0006-3568(2005)055[0749:FRTGPM]2.0.CO;2

  • Hank Roberts // January 4, 2009 at 7:56 pm

    See also:

    http://web.mac.com/ventana121/Bruno_lab/Publications_files/Duarte%202007.pdf

    http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2486.2006.01180.x

    Point is, some guys on a blog are not going to manage to teach Ecology 101.

    Without learning at least that much, you won’t understand what people are talking about or why they’re worried about the rate of change.

    Slow change is basically not comprehended at human generation times — nobody believes great-grandpa’s memories of how it used to be.
    Science is the only tool we have to improve on that lack of ability to see what’s happening.

    But change at those rates is devastating

  • P. Lewis // January 4, 2009 at 8:01 pm

    Katabatic winds whipping freshly deposited, δ18O-depleted snow out to sea might be one mechanism.

    And Tungusaka seems unlikely to be of bolide origin, whether impact or air burst, according to many who know about these things.

    Extracted from the NS, which can probably be found online if so desired:

    To others, these arguments illustrate a basic problem with the bolide hypothesis. “There is no evidence of any extraterrestrial material,” says Wolfgang Kundt, a physicist at the University of Bonn in Germany. “It can’t be a meteorite impact. That means there’s got to be a terrestrial explanation.”

    Kundt believes that the explosion was the result of a massive escape of high-pressure gas from deep within Earth’s crust. His calculations suggest that the sudden release of 10 million tonnes of methane-rich natural gas would create the devastation seen at Tunguska. There is evidence of similar releases of methane on the seabed off Norway, where one crater or “pockmark” on the Blake Ridge covers 700 square kilometres.

  • Gerda // January 4, 2009 at 8:22 pm

    kipp, check out this;
    http://www.climatescience.gov/Library/sap/sap3-4/final-report/default.htm#finalreport
    especially section 4 ‘The Potential for Abrupt Change in the Atlantic Meridional Overturning Circulation’ for all you ever wanted to know about ocean circulation.

  • David B. Benson // January 4, 2009 at 8:38 pm

    Richard Steckis // January 4, 2009 at 7:17 am — Yes, Antarctica is quite special. Begin with orbital forcing. When warming the far north, it is cooling Antarctica; there is a definite so-called see-saw effect between the two polar regions found in synchronized ice core records. Ending a stade (massive ice sheets) via a transition to an interglacial requires just the right ‘cooperation’ of this effect.

    A much smaller see-saw is observed during MWP; the northern hemisphere was warmer but Patagonia followed the Antarctic so-called cold reversal. I do not see how this is related to orbital forcing and find it still rather mysterious.

    Meteologically, the polar regions are from close to 60 degrees of latitude to the pole in question. Check in an atlas for where this lies in the far south. In effect, Antarctica is (partially) isolated from the rest of the atmosphere. Indeed I believe I am correct in stating that it is the driest continent, even drier than Australia. I think this helps explain Antarctica’s special role, but I am no meteorologist, so am unready to say more.

    [Response: Among Milankovitch forcings, precession does affect the two hemispheres oppositely, but inclination affects the two hemispheres in synchronization.]

  • dhogaza // January 4, 2009 at 9:07 pm

    I totally think we can talk about these things and am all up for it and for learning something.

    Hank’s given you some help, above, but the take-home point is this:

    Point is, some guys on a blog are not going to manage to teach Ecology 101.

    Without learning at least that much, you won’t understand what people are talking about or why they’re worried about the rate of change.

    It is not our job to educate you.

    Personally, I don’t really care if you parade your ignorance in public. At least at this point you’ve admitted that you don’t know WTF you’re talking about and that your claim that “rate of change is meaningless” to ecological systems is a statement of faith, not rooted in fact.

    Seems like a good place to leave it.

  • TCOisbanned? // January 4, 2009 at 9:47 pm

    Hank, I’m well aware that there is a lot of writing on the rate of warming and it’s statistical relevance. Have read 2 VS papers on it. I was reacting more to the, the rate’s the problem statement in your comment a long time ago, as that is a different concept and I was worried you are confusing the two. Your first citation gave that impression.

    What I’m looking for is some sort of “rate versus damage” correlation. If we double the rate (and the period) how much worse or better would things be? The opposite? What about a step change?

    Note that yty variation is a couple orders of magnitude greater than the trend line itself, so plants and animals have some periodic exposure to conditions more extreme than average plus trend.

    I’m actually quite sympathetic to the idea that adaption can’t keep up with the temp change (after all adapation and competition has already chosen certain creatures to best inhabit certain climes). My point is more that the rate is irrelevant since we are so far past any adaption point. Intuitively above a certain threshold of rate, it’s not the rate that matters but the level excursion. As such, plants and animals would be just as fucked with a one degree rise immediately or over 100 years (at the end of the 100 years).

    Thank you very kindly for those other cited papers, I will look at them as well. I really do appreciate that you do a little more than the average poster in terms of just checking google scholar or webofscience. That said, if we are discussing a spoecific logical issue, just citing long papers and not skimming them yourself to make sure that they are relevant is not so helpful.

    P.s. One nit, you said you cited a couple places (earlier), but I only saw one, which I commented on. What was the other? I clicked on a link that you had put with no explanation, but it seemed directed to a different poster/differnet debate.

    P.s.s. Dhog: Give me a little while to respond. Want to look at Hank’s papers. You haven’t “beaten me” if there is not a fast response. you’ve beaten me when I admit it (and I will, if so).

  • TCOisbanned? // January 4, 2009 at 10:02 pm

    (goofing off, not reading papers yet)

    Mauri:

    That is really cool that we have such a luminary in the field viusiting and chatting with us. I find the glacier retreats as some of the best evidence of a change in surface temperature in 20th century (contra UHI worriers).

    I wonder how you have such an effort on Cascade phenomenology given that Nichols is not a research school and not in the Cascades. Would think that TPTB would fund someone in the region at a state school. Do you have funding worries? And what’s your secret?

    I wonder what your take is on statistical capability of earth science researchers. I remember Fritts making comments that he is not a statistician. Also, Dano (an AGWer) making statement that field guys live for getting out in the field, not for data analysis. Yet many of the arguments/inferences turn on statistical (even sampling) issues. So does the field need more math smart feild guys? Or more collaboration? Or is everything fine? And if you do have collaboration with a data porcessor type, are you confident they’re doing it right or is there some concern that you don’t understand all their work?

  • Dave A // January 4, 2009 at 10:06 pm

    Tamino,

    On the basis of two papers published a few months apart and involving some of the same personnel you can say “the evidence is well founded”?

    Give us a break!

    [Response: I read the paper, I found the evidence to be compelling. It's outside my field, so there may be a lot I don't know which bears on its likelihood.

    But the evidence itself is sound. There *is* a dramatic cooling in Greenland ice core data, it's quite sudden, it'a corroborated in other regions of the far northern hemisphere, and it's not indicated globally. There *is* material in sediments from that time which shows powerful signs of extraterrestrial origin. There *is* even more material which shows powerful signs of being the result of massive biosphere burning.

    Read the paper, form your own opinion.]

  • David B. Benson // January 4, 2009 at 10:21 pm

    As best I can remember the book I read years ago, an earlier proglacial lake drainage was south down the Mississippi; the proglacial lake drainage at Younger Dryas was down the St. Lawrence, but I could have these two reversed I suppose.

    A later release, during the 8.2 kya event, was via Hudson’s Bay.

  • Kipp Alpert // January 4, 2009 at 10:32 pm

    Gerda:Thanks,very good site.I’ve got to start organizing my own computer, for some rapid climate education! KIPP

  • Kipp Alpert // January 4, 2009 at 11:33 pm

    TCO:You Ask–But anyway, on the off chance that you want to actually have a discussion, perhaps explain to me how a 3 deg/century change would differ from an immediate 3 deg change, would differ from a 1 deg/Century rate, but wait 300 years.
    This is easy,if you think about it. You see, man left nature and became more or less civilized.All other species can’t just up and leave their environment.Most ecosystems are dependent, on most of the other parts of that system to exist. If rapid climate change interferes with an environment,habitat, or area, the faster an environment changes, the more destruction will take place. Even glaciers grow over thousands of years,only to watch them melt,in 200 years.
    The Arctic is a poster child for the effects of rapid climate change,and Global Warming. The Antarctic is higher, therefore colder,but a one Celsius change could bring the predators in,like sharks,that would feast if it was just slightly warmer. The antarctic cyclone(vortex) is now spinning quite well and the fast running sea around Antarctica, keeps other weather from, entering it’s desert like conditions. Since natural systems take hundreds to many thousands of years to grow adapt etc., the faster the environment changes, the more destruction would occur. When it rains you have a river,when it pours you have a flood. Now if you think about it, Global Warming is a scary scenario.Is that why your a skeptic. KIPP

  • TCOisbanned? // January 4, 2009 at 11:55 pm

    Kipp, if the one degree change in the Antarctic happened twice as slowly (say 100 years instead of 50), would the entry of the feasting sharks differ, once the change had occurred? Note that as you made your comment you lapsed from the effects of rate in the beginning to the effects of level in the end. I absolutely understand that climate change will change the flora and fauna. That should be obvious by just driving in a car from north to south. You don’t need to convince me of that.

  • Kipp Alpert // January 5, 2009 at 12:21 am

    TCO: You understand that the time an animal has to adapt, is based on each specie and other considerations.Obviously, any thing that needs to adapt more slowly, then it’s environment will allow, should die. Seriously, I don’t understand the point of your comment. Where is this conversation leading us?KIPP

  • TCOisbanned? // January 5, 2009 at 12:54 am

    Yeah, I got that. Did you read any of my comments where I took things further? Where I asked at what point the rate is irrelevant (versus a step change)? Where I discussed how speciation had already occurred to give benefits in certain regions such that competition of organisms adapted to said environment is more likely to occur than evolution of the organism on site? Where I talked about the much larger dimension of inherent variability (yty) versus the trend per year?

    Seriously, I’m two steps aheada ya. Let me talk it out with Hank. You go deal with some lightweights.

  • Hank Roberts // January 5, 2009 at 1:44 am

    > at what point the rate is irrelevant

    You can’t answer this for a single species; you can’t answer it for an ecosystem. We simply don’t know.

    What we know: the longer you leave an area to nature the more complicated the ecology gets, at least up to centuries if not longer.

    Have you taken an ecology class? Would you work through one online, if say MIT or Berkeley or one of the other universities has made online coursework available free?

    Or can you focus on any particular example well enough to read on it for a few weeks?

    I’d suggest off hand the British “hedgerow” — these have been studied about as long as anything; they’re in many cases still in the same place as they were when first studied. I know there are papers counting up the number of species living in hedgerows and describing how they add more species over time. The older a hedgerow is, the more species have come to live in it. It’s a miniature ecosystem.

    Take any one of those. Work out how each individual species in it will respond to changing climate. Ask how removing any one of those changes the interaction among the rest (and the interaction with the farm fields on either side).

    This sort of paper is worth reading. What we know is that various plants move successfully with changing climate because pollen can be found identifying when they lived where. It’s a huge field in itself. We know the pollinators’ timing of their life cycles matches the plants. The pollinators can move rather faster across the ground over time. We know how fast they moved as the last ice age came and went.

    We know none of them can outrun a bulldozer — although most of them can survive a patchy forest fire either underground or by infill from undamaged areas around.

    We know a bit about recovery (Surtsey, Mt. St. Helens, other areas wiped clean).

    In between, we’re figuring it out.

    Will you get upset if I mention airframes, rivets, and ecosystems? It’s an apt comparison.

    Seriously — how much ecology are you willing to study? Somewhere there must be a blog addressing it more in detail. We can hunt for it and find a teacher willing to help talk through ecology and climate change.

    We know plenty, in bits and pieces. Nobody can give you a broad gross generalization and say a 2 degree change in one year, permanently, is specifically different in a known way than a 2 degree change in a century or a millenium.

    People can look up for you how fast particular plant species moved as the ice age advanced, which ones survived and which were lost, and at how plants came back as the ice withdrew.

    You can look at the band along which the earthworms are working its way northward (because earthworms didn’t survive under the icecaps).

    Vast detail. Too new to be able to say with any certainty what we’re doing by upping CO2 so fast. Best we can say is it is 10x or 100x faster than what’s known to have been survived, and that we know some species in some areas didn’t survive the rates of change in the past.

  • Tom G // January 5, 2009 at 1:49 am

    Thanks David.
    I read Tamino’s links and didn’t see any mention of the Mississippi and I was puzzled where CNN got their information….I thought I might of missed something.
    I’ll look up the Mississippi drainage thing tomorrow when I get a chance….google is my friend…

  • Kipp Alpert // January 5, 2009 at 2:00 am

    TCO:The reason that you are beneath me,is that first,I didn’t know what conversations you had about these other points . The comment that I did refer to was badly written, and not thought out. I am above you as I don’t need to lesson you to bolster myself.If you need an intellectual outlet abnegate your high level of scientific dramatics and admit your an inferior denier, without the courtesy or wisdom to treat others as you would like to be treated yourself. You can go SUCK on your lollypop bottom feeder. Smuck. KIPP

  • Kipp Alpert // January 5, 2009 at 2:11 am

    David B.Benson:It has been noted that the YD, did flow out partially from the St. Lawrence River, but now with the information about the impact event, I have read that the impact lead to water flooding down the Mississippi.
    KIPP

  • Richard Steckis // January 5, 2009 at 2:58 am

    Tamino.

    “But the evidence itself is sound. There *is* a dramatic cooling in Greenland ice core data, it’s quite sudden, it’a corroborated in other regions of the far northern hemisphere, and it’s not indicated globally.”

    Perhaps you should also have a look at:

    http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_63494.htm

    I have not read the paper but will try to get it.

    By saying that the event is not evident from stable isotope records in Antarctica does not mean that the event did not have global reach. If it was an impact event of the magnitude impied in Wickipedia it could not but have global reach.

    [Response: This appears to be either an oral or poster presentation at a conference, hence it's not a peer-reviewed publication and unless the author makes it available (perhaps on a website) it may not be obtainable. Meetings generally publish only abstracts for such presentations.

    Others have argued for a global impact of the YD, many have argued against it, but nobody I know of has argued that the large sudden YD cooling was a global event, and the Antarctic ice core data flatly contradict that idea.]

  • TCOisbanned? // January 5, 2009 at 3:12 am

    Hank, let me check out those papers you mentioned. I have wide technical experience accross multiple fields and am familiar with jumping into new field’s literature. I’m not going to go take another ecology 101 class, when I’m asking a specific question. Yes, I agree the rate dependance would vary by species. But then how do you know that rate is the critical issue for your rice.

  • Richard Steckis // January 5, 2009 at 3:41 am

    An interesting article from 1994:

    Science 3 June 1994:
    Vol. 264. no. 5164, pp. 1434 - 1437
    DOI: 10.1126/science.264.5164.1434

    Younger Dryas Age Advance of Franz Josef Glacier in the Southern Alps of New Zealand
    G. H. Denton 1 and C. H. Hendy 2

    1 Department of Geological Sciences and Institute for Quaternary Studies, University of Maine, Orono, Maine 04469, USA.
    2 Department of Chemistry, University of Waikato, Hamilton, New Zealand

    A corrected radiocarbon age of 11,050 ± 14 years before present for an advance of the Franz Josef Glacier to the Waiho Loop terminal moraine on the western flank of New Zealand’s Southern Alps shows that glacier advance on a South Pacific island was synchronous with initiation of the Younger Dryas in the North Atlantic region. Hence, cooling at the beginning of the Younger Dryas probably reflects global rather than regional forcing. The source for Younger Dryas climatic cooling may thus lie in the atmosphere rather than in a North Atlantic thermohaline switch.
    Submitted on December 20, 1993
    Accepted on April 25, 1994

    [Response: 1994 is pretty old for research on this topic; Huybers argues more recently that there is fair confidence in the absence of the Younger Dryas in Antarctica, New Zealand and parts of Oceania. And even if cooling did occur simultaneously in the southern hemisphere, it wasn't of the magnitude observed in the far north.]

  • Richard Steckis // January 5, 2009 at 3:46 am

    Ray Ladbury.

    I came across this paper just today:

    http://www.sciencemag.org/cgi/content/abstract/260/5110/962

    I understand now what you meant by 14C/12C ratios. My aplogies for our previous exchange on this one.

  • Richard Steckis // January 5, 2009 at 3:59 am

    Last one for the moment:

    “Letters to Nature
    Nature 328, 609 - 611 (13 August 1987); doi:

    Cold climatic episode of Younger Dryas age in Tierra del Fuego

    C. J. Heusser* & J. Rabassa†

    * Department of Biology, New York University, 1009 Main, New York 10003, USA
    † Centre Austral de Investigaciones Científicas, C. C. 92, 9410 Ushuaia, Tierra del Fuego, Argentina

    Pronounced climatic change during the last glacial maximum is recognized as global in extent, and has been attributed to orbital forcing1. Not readily explained in a global context because of the equivocal nature of the evidence are the late-glacial climatic events of short (100–1,000-yr) duration. The cold climate of the Younger Dryas chron (approx11,000–10,000 yr BP), for example, is known to have been particularly pronounced over the North Atlantic and parts of Europe and North America2,3, whereas in the Southern Hemisphere, cold conditions for that time are not well established. Here we present evidence for late-glacial climatic cooling in southernmost South America from studies of radiocarbon-dated glacial and pollen stratigraphy at sites along the Beagle Channel in Tierra del Fuego, where a forest–tundra tension zone in the region is especially sensitive to shifting climate. We conclude that the cold episode corresponds with the time of the Younger Dryas in Europe, when a drop in temperature, ascribed most recently to colder sea surface temperatures and production rate of deep water in the North Atlantic4,5, apparently occurred worldwide.

    © 1987 Nature Publishing Group
    Privacy Policy”

    I think the Younger Dryas was global in extent.

  • dhogaza // January 5, 2009 at 4:06 am

    Where I asked at what point the rate is irrelevant (versus a step change)? Where I discussed how speciation had already occurred to give benefits in certain regions such that competition of organisms adapted to said environment is more likely to occur than evolution of the organism on site? Where I talked about the much larger dimension of inherent variability (yty) versus the trend per year?

    Well, no, actually you said “everyone is wrong except me!” with no backing data, and none of what you claim to have said above.

    So you’re back to lying again. A pity. I thought you were partially reformed this past year or so, and now I know you’re not.

    Seriously, I’m two steps aheada ya. Let me talk it out with Hank. You go deal with some lightweights.

    Seriously, “liar” is a fair indication of YOUR being a lightweight.

    I realize that the bottle(s) you endlessly suck have added to your delusions of grandeur but …

    If you think the rest of us will be fooled …

    We probably don’t care :)

  • dhogaza // January 5, 2009 at 4:13 am

    I’m two steps aheada ya.

    In the sense of being intellectually dishonest, you’re probably an infinite number of steps ahead of us who actually care about objective knowledge.

    You’re nothing more than a arrogant, semi-intelligent, partially-educated troll.

  • Hank Roberts // January 5, 2009 at 4:52 am

    TCO, I can’t tell you about rice. Try scholar for hedgerow +”climate change” or pick any other chunk of ecology that’s describable. Hedgerows have been studied since natural history began to be written down. Or search scholar for ecosystem disruption, or plant migration, or ecological succession +glaciation - you’ll pick up the search terms to use by poking at the papers.

    Start by finding the terms used to describe ecosystems and change from normal variations and then look for work talking about what happens as climate changes (e.g. ice age) changes. Look at the rate of change in the past and look at the rate of change now.

    A few that might produce more citing papers and search terms.

    And remember I’m some guy on a blog, and my last ecology course formally speaking was in the late 1960s. I keep reading, but I’m not going to be a teacher here. When you find an author who is making sense and has depth, look for more from that author. Read the “cited by” papers. Try the authors’ websites. This is an enormous area widely studied.

    http://www.sciencemag.org/cgi/content/abstract/sci;297/5585/1292
    Science 23 August 2002:
    Vol. 297. no. 5585, pp. 1292 - 1296
    DOI: 10.1126/science.1071281
    Ecological Effects of Climate Fluctuations
    Cited by 414:
    http://scholar.google.com/scholar?num=50&hl=en&lr=&newwindow=1&safe=off&cites=597292793303300043

    http://www.nature.com/nature/journal/v416/n6879/abs/416389a.html
    Review

    Nature 416, 389-395 (28 March 2002) | doi:10.1038/416389a
    Ecological responses to recent climate change

    There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.
    Cited by 1137:
    http://scholar.google.com/scholar?num=50&hl=en&lr=&newwindow=1&safe=off&cites=2430527888090798281

  • dhogaza // January 5, 2009 at 5:03 am

    My aplogies for our previous exchange on this one.

    Kudos for Steckis for apologizing. A few dozen posts of this sort might actually cause folks to treat him seriously as someone who wants to learn, rather than being simply a knee-jerk denialist.

    Of course, the process could’ve been shortened considerably if he hadn’t started out by spewing knee-jerk denialist arguments and arguing that his experience as a scientist with an advanced degree qualified him to declare that all of climate science is fraudulent …

  • TCOisbanned? // January 5, 2009 at 5:30 am

    I’m going to read the Hank stuff and then come back. dhog, you live in your own world where you mischaracterize what I say and OFTEN misassume what I’m referring to. go sit in the corner, son.

  • Kipp Alpert // January 5, 2009 at 6:36 am

    DHOGAZA: Thanks for noting my TCO conversation.I was trying to figure out what Tco was saying.His next blog completely threw me for a surprise. Kipp said:”You understand that the time an animal has to adapt, is based on each specie and other considerations.Obviously, any thing that needs to adapt more slowly, then it’s environment will allow, should die. Seriously, I don’t understand the point of your comment. Where is this conversation leading us?”
    Tco said:”But anyway, on the off chance that you want to actually have a discussion, perhaps explain to me how a 3 deg/century change would differ from an immediate 3 deg change, would differ from a 1 deg/Century rate, but wait 300 years”. As they say,this guy is picking up again,for sure.No class bitch. Look forward to joining your team and slaughtering DENIERS.
    Really stupid questions that any person could answer on their own. Then a very insulting remark. I think he has been sucking on something. I was in the rooms,a friend of Bills,23 years ago. Is TCO picking up.He should try some Hydroponic and chill, then go into this good night.Thanks for covering my back.I shall reciprocate for sure.TCO has just made a bad adversary. You have made a real friend.KIPP

  • Hank Roberts // January 5, 2009 at 6:36 am

    May I suggest a brief pause to consider
    http://davidbrin.blogspot.com/

    Friday, January 02, 2009
    Suggestion #20: Seek ways to end Culture War

    Let’s finish this series of “unusual suggestions for America and the Obama Administration.)? with the one that is simplest and most basic. Something that seems so easy and wise, you really have got to wonder why it hasn’t already been done. Or at least tried.

    Let me lay it on the line. We have one priority, above all others, because solving it will unleash our native aptitude at fixing every other problem. That priority is to cure the sickness that is eating away at the guts and marrow of the greatest nation in history. The nation that Jean Francois Revel called the “best hope? for the “best kind of human revolution.? The kind of revolution that leads us to far higher horizons and to becoming better people, all around the world.

    That priority is to put a stop to the treason that is called “culture war? and get us back to talking to one another again, as grownups…..
    ———————————————

    Remember, don’t feed the trolls. Not the external ones and most certainly not the one that lives inside each of us waiting to get out.

  • Richard Steckis // January 5, 2009 at 9:43 am

    Tamino.

    “Response: 1994 is pretty old for research on this topic; Huybers argues more recently that there is fair confidence in the absence of the Younger Dryas in Antarctica, New Zealand and parts of Oceania. And even if cooling did occur simultaneously in the southern hemisphere, it wasn’t of the magnitude observed in the far north.”

    1994 is not that old. Science is not necessarily negated by the passing of 12 years. I would like a ref to the Huybers paper you refer to.

    No one is suggesting that the magnitude would be anything like that of the Northern Hemisphere. The impact event was in the Northern Hemisphere and therefore it stands to reason that the changes were of greater magnitude there. The question is: “Was there a global reach to the impact event?”

    I think any impact event of the magnitude attributed to the one that precipitated the Younger Dryas would most definitely have global reach.

    Antarctica is unique. Just because the delta18O results do not show the YD event does not mean it did not reach the Southern Hemisphere. I would have to look into the behaviour of 18O at extremes of temperature and chemistry. For instance, I know that in marine environments with hypersalinity (e.g. Shark Bay in Western Australia) the delta18O changes can depart from expected and theoretical values.

    [Response: Are we arguing over something? Because I didn't even come close to claiming that the YD was absolutely positively not global. I said that it "is most pronounced in high latitudes of the northern hemisphere" and "that much temperature change (full glacial to full interglacial) did not occur worldwide" and "the YD cooling shown in Greenland does not show in Antarctica." You seem to agree with all of that.

    I sometimes get the impression you want to turn things into an argument, just to be contentious.]

  • stephan harrison // January 5, 2009 at 11:44 am

    Re David Benson’s message. The MWP doesn’t correlate with ACR. The ACR is a problem when trying to isolate a Younger Dryas signal in Patagonia. We have dated moraines to the period of the YD but this could also be an ACR signal. Dating is not conclusive. We have lake sediment records now which may be able to distinguish these events.

    Overall, I still think the YD is elusive in Patagonia….and probably also in New Zealand.

  • dko // January 5, 2009 at 12:47 pm

    I was pretty much with ya down to this point:

    “But a huge thermal blast over an ice sheet may have been exactly the event leading to rapid melting and a large freshwater pulse into the north Atlantic ocean — exactly the condition which could shut down the thermohaline circulation and block heat transport from the tropics to the poles.”

    Turn a blowtorch on a block of ice and it takes a long time to melt. If an air burst had the atmosphere hot enough to ignite trees for a few hours, that still wouldn’t melt an ice sheet one km thick.

    [Response: I didn't say that it melted an ice sheet one km. thick. Does the blowtorch melt *none* of the ice?]

  • Ray Ladbury // January 5, 2009 at 1:56 pm

    Steckis, Apology accepted. Incident forgotten. And apologies for my somewhat sharp tongue/typing fingers.

  • Richard Steckis // January 5, 2009 at 2:16 pm

    Tamino:

    “Response: Are we arguing over something? ”

    No. But I do love to debate.

    “I sometimes get the impression you want to turn things into an argument, just to be contentious.”

    I guess I can get a little carried away with the latitude you give me (unlike Real Climate).

  • Richard Steckis // January 5, 2009 at 2:16 pm

    Thanks Ray.

  • blue // January 5, 2009 at 3:07 pm

    Kipp, you may already have come across him but here’s anyway - Stefan Rahmstorf is working on thermohaline circulation and climate: publications
    At a minimum this gives you a starting point for digging deeper.

    Here’s a short 2003 article, which near the end summarizes simulations, where heat transport by the circulation were switched on and off: nature_concept_03.pdf

  • Hank Roberts // January 5, 2009 at 3:21 pm

    DKO, I think a continental glacier sized lake dammed up by ice and moraine, full to the brim, could easily start to break down the dam with just the sloshing, let alone the heating, of an impact or airburst of the magnitude described.

  • bigcitylib // January 5, 2009 at 5:53 pm

    I’ve only seen the abstract, but

    http://www.pnas.org/content/105/33/11651.abstract

    …suggests that Clovis numbers did not decline at the appropriate moment.

    The latest version of the theory also requires an “airburst” of the object in question (no crater has been found), and there is some doubt as to whether the physics of this will work .

    http://bigcitylib.blogspot.com/2009/01/killer-comet-theory-crosses-important.html#links

  • mauri pelto // January 5, 2009 at 6:04 pm

    I agree with DKO on this one. All you have to do is visit an active volcano with glaciers. It is amazing to see thermal vent steaming surrounded by glacier ice. We have seen that glaciers actually survive major eruptions. The LIS was destabilized before the YD, we do not need a special event to do so. The paper presents some interesting stratigraphic data, but then offers some rather large conclusions such as destabilizing the LIS that are simply not backed up by any evidence. I believe that such evidence would have been noted already if this impact was a key to further destabilization. Glacier dammed lakes do not drain over, but under a glacier, so sloshing is not important. they do this typically be floating the ice a bit until additional outflow can . If we had enough heat to melt significant ice it would have done a lot worse to vegetation and water temperatures in lakes, ponds and shallow seas. I had a chance to observe the weakness of heat at alleviating ice the other night too, I was in a hot tub at 39C while the air temp was -15 C. My beard 5 cm above the waterline froze.

  • Kipp Alpert // January 5, 2009 at 8:17 pm

    Blue:Thanks a lot.KIPP

  • Kipp Alpert // January 5, 2009 at 8:22 pm

    Hank Roberts: Remember, don’t feed the trolls. Not the external ones and most certainly not the one that lives inside each of us waiting to get out.
    Hank:
    That’s a very insightful remark. Have you had scientific training,our are you a learned amateur.If so how long did it take for you to become so scientifically wisdomic. KIPP

  • Dave A // January 5, 2009 at 10:59 pm

    dhogaza

    “I realize that the bottle(s) you endlessly suck have added to your delusions of grandeur but …”

    “You’re nothing more than a arrogant, semi-intelligent, partially-educated troll.”

    What an unpleasant personality you have. Do you think remarks like this achieve anything other than turning people away from all you say?

  • Hank Roberts // January 5, 2009 at 11:10 pm

    No wisdom here, Kipp, just the habit of using the library, for decades. I’ve completed college and a few years post-college, but I learned the habit of looking things up by growing up around biologists at various university and field station sites. Best advice I can give, get to where the reference librarians near you know your face when you walk in, and smile. Ask them “what else can I find through the library that I can’t find from home with Google.” There’s far more information available than we can see online.

  • Hank Roberts // January 5, 2009 at 11:28 pm

    Mauri, is this sort of picture still considered likely for some glacial lakes? Do we have sediment cores for example that can say when an area was under ice, vs. under open water? Is the thinking now that the lakes were mostly under ice not behind ice/gravel dams?
    http://www.eos.ubc.ca/research/glaciology/
    How do we know?

  • Kipp Alpert // January 6, 2009 at 2:29 am

    Dave A:Dhogaza:As a fairly new blogger here I was slammed from behind pretty hard by TCO.
    I was just trying to answer his question, and be decent.Dhogaza reiterated TCO’s comments, with a few choice words of his own. I really appreciated that, and he knows his science too. I have been dealing with some pretty crude skeptics over at Accuweather for a year now, and can ultimately handle this, but I nevertheless, appreciated a sign of equanimity.
    No harm,No foul

  • Kipp Alpert // January 6, 2009 at 2:34 am

    Blue:Stefan Rahmstorf is a great find. Many good articles to read.Thanks Again,KIPP

  • Kipp Alpert // January 6, 2009 at 2:45 am

    Hank Roberts:
    Well I grew up with a well known Jazz musician,Trigger Alpert,my Dad was with Glenn Miller,Frank Sinatra,Barbara Striesand.I,m a commercial Portrait photgrapher, some stuff you have seen. I don’t no much about science but I’m learning and reading as fast as I can. After a year, this stuff just blows my mind! You open a door, and enter a new world.Amazing. I know that you have to study a lot on your own, as this is the one of the best ways to learn, short of working around Scientists. Librarys around here, Maybe Stamford Ct.UCONN branch. Pretty near for me. Thanks,KIPP

  • Kipp Alpert // January 6, 2009 at 3:56 am

    How can you reconcile the Clovis Scenario, with this study.
    Following recent studies [e.g., Gamble C, Davies W, Pettitt P, Hazelwood L, Richards M Camb Archaeol J 15:193–223), the summed probability distribution of the calibrated dates was used to identify probable changes in human population size between 15,000 and 9,000 calBP. Subsequently, potential biases were evaluated by modeling and spatial analysis of the dated occupations. The results of the analyses were not consistent with the predictions of extraterrestrial impact hypothesis. No evidence of a population decline among the Paleoindians at 12,900 ± 100 calBP was found. Thus, minimally, the study suggests the extraterrestrial impact hypothesis should be amended.

  • Kipp Alpert // January 6, 2009 at 7:02 am

    Last post is April 08.I though I leave it there to learn how you Aproach a sientific point.See a little critical epmperical thinking at work.If that is what it is.Justa feelin my way……///KIPP

    Falsifiable/ Oxford 1908 addition/Def.Popper,
    1.critical thinking,as a way to prove nothing.
    2.Faifiable:Albert Camus;”you don,t exist”
    3.Falsifiable:Rodney Dangerfield”Take my wife please! KIPP

  • Hank Roberts // January 6, 2009 at 9:04 am

    that’s from: http://www.pnas.org/content/105/33/11651.abstract
    Paleoindian demography and the extraterrestrial impact hypothesis
    http://www.pnas.org/cgi/crossref-forward-links/105/33/11651

  • Richard Steckis // January 6, 2009 at 9:51 am

    Kipp:

    “I,m a commercial Portrait photgrapher, some stuff you have seen.”

    Do you have a website for your photography?

    Mine is http://www.zone4photo.com.au

    Nowhere near complete yet.

  • ChrisC // January 6, 2009 at 11:13 am

    With regard to the melting of glacial ice during an impact event, my guess is that the heat release from such an impact (the explosion itself) would have a limited effect on glaciers not in the immediate impact region.

    More likely, the forcing of dust into the atmosphere, along with large forest fires could have deposited large amounts of soot/black carbon ect… in high precipitation regions (where glaciers are often located). This could have the effect of changing the albedo of the ice sheet itself, resulting in a fast melting of the ice sheets. Just pontificating.

    However, the stability of ice sheets near an active volcano vent has very little to do with the ability of the ice to “withstand” the heat released. Given time, the vent would quite happily melt all the ice.

    Ice sheets are maintained on volcanic cones primarily due to two factors:

    1) Precipitation is generally higher over these areas due to orographic uplift;
    2) Temperatures are generally lower at high elevations due, resulting in more precip falling as snow and freezing rain.

    The result of this is that the volcano still happily melts the ice. However, on average, the loss of ice is balanced by more falling snow and ice. This is called glacial mass balance.

    Changes in atmospheric temperature (from an impact or whatever) have the capability to alter the amount of precipitation that falls, whether it falls as snow or rain and the rate of glacial melt. These factors in combination could result in the loss of ice sheets rapidly, rather than simply an explosion itself.

  • mauri pelto // January 6, 2009 at 12:48 pm

    The large lakes that were impounded by the Laurentide or Cordilleran Ice Sheet were not subglacial or supraglacial, but proglacial. That is beyond the ice margin. They were dammed in general by the ice. The natural drainage path for them, traveled beneath the ice. As the ice thinned and the lake grew, a point is reached where the ice can be lifted off its bed and flow begins, the flow than can actually erode the ice dam a bit. A good example graphically is Lake Agassiz. Take a look at the paper linked here, look at the figures 30-41 first to provide a visual. The supraglacial lakes-on a glacier surface are never very large, note Greenland today. The issue is that wherever you have sufficient melting to create a lake, you also have a drainage system that develops for the meltwater to drain from the ice sheet-glacier. The largest lake I have observed was on the Jakobshavns in 1985 and it was 3 km across at its widest and not very deep.

  • mauri pelto // January 6, 2009 at 1:12 pm

    The information for the occurrence of the impact is compelling Tamino, but for the affects at this point, I have to admit it provokes more laughter than anything. I like the line by Schulz “Schultz admits that there is little decisive evidence about the actual details about the impact and its effects. Scientists suspect that a carbon-rich asteroid or comets were the culprits. The objects would have exploded over North America or slammed into it, or both, shattering and melting ice sheets” - so it slammed into the ice sheets and melted them. Ice sheets are not glass, small glaciers have withstood volcanic eruptions, massive earthquakes and landslides triggered by said avalanches. Think back to Denali a few years ago. The ice sheets that melted and shattered have well dated chronologies of advance and retreat, and after this shattering experience managed to advance. This is a good example of why you need to stick to your field. When I complete a paper on glacier rettreat or dynamics I then do not extrapolate to other fields such as in my case isostatic rebound that I am not an expert in.

    [Response: We agree that the evidence for the impact event is compelling. It seems to me that the evidence for extensive biomass burning is also compelling. I don't see how such an extensive event could fail to have some impact on regional climate (admittedly, it's not my field), and the simultaneity of the event with the onset of the YD is suggestive that they are related. Your incredulity has modified my opinion of the likelihood of the extent of the impact's events -- but I suggest that "implausible" is a far more realistic description of the speculation than "laughable."]

  • Hank Roberts // January 6, 2009 at 4:36 pm

    Has anyone compared large impacts to earthquakes as initiators of large waves? My guess is not melting ice or breaking ice up, it’s that a big excursion could do enough damage at a choke point/moraine/ice dam to start water moving. After that happens water makes its own channel.

    How big a whack does an impact make, what kind of wave does it make?

    Thinking of the many contemporary earthen dam failures that begin with overtopping or a small fissure, and the observation that Antarctic ice shelves can be fractured by unusually large waves from distant storms (I’ll hunt for that, it was a surprising one).

  • Joel Shore // January 6, 2009 at 4:44 pm

    By the way, when I look at the GRIP data, I notice that even proceeding the Y-D event, there was a more gradual cooling from ~14300 years ago until the Y-D event onset at ~12900 years ago (admittedly with some notable ups and downs…but the general trend was down over that period). Is there any understanding as to why Greenland had already been generally cooling over that ~1500 year period during which the general trend was a transition between glacial and interglacial conditions?

  • luminous beauty // January 6, 2009 at 7:00 pm

    Mauri,

    You’re not inferring that volcanic activity cannot trigger jökulhlaups, I trust.

    That would be big news to the population of Iceland.

    [Response: For those (like me) who had no idea what the word means, apparently

    A jökulhlaup (or glacier burst) is a subglacial outburst flood. It is an Icelandic term that has been adapted into the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, which are triggered by a volcanic subglacial eruption, but now is accepted to describe any abrupt and large release of water from a subglacial lake.

    ]

  • mauri pelto // January 6, 2009 at 7:43 pm

    I am only finding the shattering and melting of the ice sheet laughable, the rest is hard to judge. Hank is right there is so much to be gained at the Library. A book like Late Quaternary environments of North America has numerous stratigraphic diagrams and pollen records that do not show the obvious black mat layer. Remember this is just what they were looking for. So I am perplexed that we have a clear layer in some places and not others. I must in equal fairness point out that though it is clear that a large freshwater pulse entered the North Atlantic its source is not known. Lake Agassiz has often been the suggested source, but it is pretty well dated and drained fairly late. We do have tremendous amounts of information gathered from former lake shorelines and moraines in the midwest in an attempt to piece this together. The link here illustrates that the answer is not in for the source of the meltwater pulse. That is what makes the Younger Dryas fascinating, its origin remains uncertain. This is from someone I was in grad school with, and is not a band wagon jumper. and has spent alot of time digging in the midwest. http://www.eeescience.utoledo.edu/Faculty/Fisher/Lowell_etal_EOS05.pdf

  • Phil. // January 6, 2009 at 9:07 pm

    [Response: For those (like me) who had no idea what the word means, apparently

    A jökulhlaup (or glacier burst) is a subglacial outburst flood.

    There was a spectacular one in 96, here’s some dramatic pictures of it, the road bridge shown across the middle of the first photo didn’t make it!

    http://www.wdcgc.spri.cam.ac.uk/news/jokulhlaup/

  • Hank Roberts // January 6, 2009 at 9:47 pm

    One other thought — a big widespread airburst might have evaporated enough water to create massive rainfall, and so produce a rush of fresh water.

    One of the ways of “weeding” in native plant restoration and wineries is to use a propane torch and wave the flame over the plants, just briefly. Not enough to burn anything, but like blanching in cookery.

    So the flame leaves the plant, and about half a second afterward, the plant puffs a cloud of steam and turns bright, bright green. All its cells broke open, exposing all its chlorophyll to oxygen. A few hours later the plant falls over. An airburst from a cloud of meteors or a disintegrated comet need not even burn or char a huge area, if it’s hot enough just to “blanch” all the lightweight thin leafy plant material on the surface, and put most all of that water into the air.

    I’ve seen the same effect after forest fires where hot air or fire swept across an area killing all the leaves but not burning them — the leaves are bright yellow and almost weightless, far lighter than typical fall colored leaves. Dessicated.

    Just pure speculation here. Whatever the cause of the water influx, it’d likely be some of all of the above. I’d like to see some idea of the impact physically — how much bigger than Tunguska for example?

  • David B. Benson // January 6, 2009 at 11:46 pm

    Joel Shore // January 6, 2009 at 4:44 pm — The Greenland ice core temperature proxies have ups and downs for several reasons. One is a reorganization of regional air flows, bringing precipitation from different parts of the ocean.

    mauri pelto // January 6, 2009 at 7:43 pm — Call the extraterrestiral impactor a bolide. Ordinarily such an airbrust leaves a central core; that for the 1908 CE event appears to finally have be located, magnetically, at the bottom of a lake. Similarly for the so-called Clovis comet a naturally place to look is the bottom of Lake Michigan. I doubt a proper magnetic survey has been done for any of the Great Lakes.

    Moreover, you oought to look at calculations for the speeds of the fragments from such an air burst to determine just how far into the Laurentide Ice Sheet such would penetrate. I’ll opine that (many) billions of tonnes of descending material might well rather ’swiss cheese’ the southern portions of the ice sheet, although the heating would certainly be (almost) completely negligible. In any case, I certainly find the idea that shattering a considerable portion of an ice dam would lead to failure shortly thereafter. This is a credible idea, not to be simply laughed at.

    Regarding a possible population collapse at the end of Clovis culture. Archaeologists love to argue and I haven’t followed all the lines of evidence. That said, Clovis culture came to a abrupt end and after a several hundred year hiatus there are signs of several distinct cultures, none obvious descendants of Clovis culture. The most similar might be Fulsom point culture. The prior assumption hass been that of a population decline, but the possiblity certainly exists that peoples living further to the south and west migrated to fill the vacuum, assuming (as is by far the most sensible) that Clovis culture left very few survivors of this bolide impact.

    Despite claims of YD in various locations in the southern hemisphere, here is the Wikipedia summary:

    “Huybers has argued that there is fair confidence in the absence of the Younger Dryas in Antarctica, New Zealand and parts of Oceania.”

    from

    http://en.wikipedia.org/wiki/Younger_Dryas

    The recent paper “Was the Younger Dryas Global?” by Thomas V. Lowell and Meredith A. Kelly

    http://www.sciencemag.org/cgi/content/full/321/5887/348

    suggests that it was not, but obviously more study is required. In any case, the impact in the southern hemisphere, if any, was distinctly muted in comparison to that in Europe.

  • David B. Benson // January 7, 2009 at 12:03 am

    Hank Roberts // January 6, 2009 at 9:47 pm — Vastly bigger than Tunguska. Stupendiously so. The tektities (nano-diamonds) have been found from Alberta in the west to alomst the east coast. The fires cover every Clovis site (that I know about) and evidence for these fires lies as far afield as Belgium.

    That was one big bolide and given that nickel appears to be associated with the event, I surmise there would be many nickel-iron fragments one to a few meters in diamater, with terminal speeds between 100 and 200 meters per second. Ice shattering indeed.

  • Kipp Alpert // January 7, 2009 at 12:17 am

    Hank Roberts:I can’t pinpoint where the Air burst originated.Also some say when all the water was unleashed,it went through the St.Lawrence and North Atlantic. Other articles talk about waves flowing through the Mississippi. Maybe the release of water went through all of these places. Your thoughts. KIPP

  • Kipp Alpert // January 7, 2009 at 12:25 am

    Richard Steckis:I have a guy that runs around with my books.Started at TimeLife.Eisenstat was nuts. What kind do you do. I went to your site and saw a beautiful white page.Need any Hasselblads?Tons of lenses.I actually liked the mimyaflexp330 twins lens,compur shutter,quiet and soft. KIPP

  • TCOisbanned? // January 7, 2009 at 12:47 am

    pelto, please respond to my previous questions.

  • dko // January 7, 2009 at 2:24 am

    For kicks and giggles, let’s assume an air burst of 100 megatons. (For perspective, the Tungaska event was equivalent to 10 to 15 Mt.) Let’s further assume that *all* of the energy was directed into ice that, conveniently, was right at the melting point. And, let’s figure the area affected at 10,000 km^2 (to Tungaska’s 2150 km^2).

    By my scratching, that is enough energy to melt 1.25 km^3 of the LIS. That’s a lot of water, but spread over the blast area it would average just 12.5 cm deep.

    Water’s heat of vaporization is much higher than its heat of fusion. So the same 100 Mt blast could, at most, evaporate 0.19 km^3 of open water. (The best analog I can think of would be the Pacific H-bomb tests.)

    Both scenarios assume that none of the blast energy was radiated into space, all the melt water ran off before it could refreeze, etc.

    The case for an impact around 12,900 years BP is gaining strength. To credit it for a major freshwater pulse, however, is a stretch. I would think a warm south wind would have melted more ice on a summer day.

  • Kipp Alpert // January 7, 2009 at 2:27 am

    YO!I have read that evidence of the Younger Dryas impact was found from New Zealand to
    Scotland.Would this bolster or help verify an extraterrestrial event due to it’s extent NH,then New Zealand. KIPP

  • Richard Steckis // January 7, 2009 at 3:30 am

    Kipp:

    “I went to your site and saw a beautiful white page”

    Your browser probably has an older version of the Flash reader. It is a Flash enabled site. I would loooove a Hasselblad but just can’t afford one.

    Regards

  • Kipp Alpert // January 7, 2009 at 5:17 am

    Richard Steckis:Seeing white.Hassy is to sharp.
    You shoot landscape.Use filters always.Tiltall Tri-pod(360×180 motion.),cablerelease.Sensors more important than pix.Above 8 pix is fine.Sensors take the place of silver halide reaction to light.More sensors more light to dark.Nikons are good.Never let someone know how tall you are, by the pictures you take. AKA.get best angle.Nver waste space.Use fill,strobe accent lights with slave,always shoot into sun for good bacKlight.Fill subject with white board or fill in flash.Use 130mm for portraits.Thin em out. Use light amber for people,polarizer and skylight for outdoors.81a blue fortungsten color temps.10- 20 magenta for flourescent. $100,000 please. KIPP

  • Steve Bloom // January 7, 2009 at 10:36 am

    On a semi-related subject, there was a report at AGU of results pinning the 536 AD climate event to comet fragment impacts. Others have been trying to blame it on an eruption (Tambora IIRC).

  • mauri pelto // January 7, 2009 at 12:48 pm

    We have plenty of moraines and varves to chronicle the retreat of the Laurentide ice Sheet. It was not shattered, or it could not have readvanced. We are not talking billions of tons of material are we? If we had all this material where are the big fragments? Do not let a good tale get in the way of a half century of field data, illustrating the retreat of the Laurentide ice sheet in the midwest and northeast being a slow process interrupted by several minor readvances, including after the advent of the Younger Dryas, how could this happen after it was shattered. Ice is also tougher than you think if any solid object is expected to penetrate to any depth. I do not know how to calculate this but I do know that a glacier has been bombed before and it accomplished nothing.

    TCOisbanned-the region I work in does not allow motorized access-Wilderness Area-this discourages most researchers from carrying everything in over hill and dale. I started 25 years ago while at U of Maine. No Govt. funding is used-those sources dry up with time. Field scientists are not the best with quantitative analysis, though we expend plenty of time learning it. I do not think we typically do not take full advantage of the data, thus better skills would tend to enhance our results. That is why Tamino has such interesting posts for me, good quant analysis. So we can always use better analyzers, however, without the fieldwork you cannot understand what is realistic and what is not, and that is what leads to problems. Such as a suggestion of shattering or melting an ice sheet via the YD impact. dko did a good job showing how it cannot melt. Volcanoes show the same thing, they melt lots of ice very locally that is all. The Grimsvotn in Iceland even in eruption does not make a dent in the volume of the Vatnojokull Ice Cap.

  • bigcitylib // January 7, 2009 at 3:01 pm

    For what its worth, this is how one of the paper’s authors (A.West) concieved of the impact about 6 months ago:

    The hypothesis is fairly complex. We believe the impact was a collision with a cloud of debris, much like Comet LINEAR [see above left]. The smaller objects would have detonated in the atmosphere, much like Tunguska. Depending on the angle of entry, the largest objects could have impacted the 3-km-thick ice sheet, creating ice-walled craters that left no lasting imprint on bedrock.

    There are multiple processes that could account for the diamonds: 1) some diamonds appear to have condensed inside burning biomass due to the heat and pressure of the impacts/airbursts; 2) diamonds are known form from shock impact upon terrestrial materials, such as coal, peat, carbonate rock, which would have been entrained as detritus in the ice sheet or would have been near the surface under the ice; 3) diamonds may have been formed by carbon vapor deposition (CVD) in the plasma of the fireball; 4) pre-existing kimberlite diamonds could have been ejected into the air along with other detritus entrained in the ice sheet; and 5) the impacts/airbursts most likely created immense meltwater surges both from above and below the ice and which would have carried pre-existing diamonds and other debris along with the meltwater.

  • John Mashey // January 7, 2009 at 3:46 pm

    This is in an interesting discussion, but it is instructive in another way.

    It is a good example of a *real* scientific controversy in progress, not a fake one.

  • Kipp Alpert // January 7, 2009 at 9:23 pm

    Help!Could Hank or anyone answer this or tellme where to look? I have read that evidence of the Younger Dryas impact was found from New Zealand to
    Scotland.Would this bolster or help verify an extraterrestrial event due to it’s extent NH,then New Zealand. KIPP
    Thanks KIPP

  • David B. Benson // January 7, 2009 at 9:52 pm

    mauri pelto // January 7, 2009 at 12:48 pm — The hypthesis is that just enough of the Laurentide was shattered to start the release of whatever proglacial lake existed at the time. Once the water ran out, surely the main mass of the Laurentide would re-advance.

    From

    http://aa.usno.navy.mil/faq/docs/asteroid_masses

    we can assume that the specific density of the ‘bolide’ was 3.14; with an average radius of 1 km (for convenience) the total mass was about 4×10^9 tonnes.

    Using Barringer Crater

    http://en.wikipedia.org/wiki/Meteor_Crater

    as a rough guide, the more massive portiions of the ‘bolide’ would impact the Laurentide Ics Sheet at about 12,800 m/s. For the Barringer crater 50 meter diameter meterorite, the impact is thought to have released about 2.5 megatonnes TNT equivalent energy and dug itself about 400 meters into the impacted rock.

    Since rock has a specific gravity of around 3.3 g/cc^3, I suppose that a similar sized meteorite impacting ice would produce a crater three times the area and three times as deep; that is about 1200 meters down.

    I opine that enough of these, or larger fragments, would destabilize a proglacial lake ice dam, causing outflow to soon commence. By way of comparison, consder the well-researched

    http://en.wikipedia.org/wiki/Missoula_Floods

    with ice dams on the Clark Fork not more than 2 km high.

  • David B. Benson // January 7, 2009 at 9:59 pm

    Oops. 4x(3.14)^2 gigatonnes

  • David B. Benson // January 7, 2009 at 10:09 pm

    (Some days it just doesn’t work.) Assume a specific density so that the total maas, with average radius on 1 km, is about 12 gigatonnes.

  • David B. Benson // January 7, 2009 at 10:34 pm

    Kipp Alpert // January 7, 2009 at 9:23 pm — Younger Dryas was a climate event. Regarding its climate impact, the exact means by which a proglacial lake drained probably does not matter.

  • Kipp Alpert // January 7, 2009 at 10:35 pm

    TAMINOor RICHARD:Could you answer my last question. Overall Impact of YD.Mississippi and St.Lawrence.North Atlantic.I read artifacts found in New Zealand? KIPP

  • Hank Roberts // January 7, 2009 at 10:58 pm

    Sorry, Kipp, no clue, but if you find the source behind “I have read …” post that (or better yet, use Google Scholar, find that, then find the citing articles, the cited articles, and the related articles.
    You’ll need to sort out a lot of material.

  • Kipp Alpert // January 7, 2009 at 11:30 pm

    HanK:Thanks.Was your post finished or was something deleted. kipp

  • David B. Benson // January 8, 2009 at 1:08 am

    I found the following site:

    http://www.lpl.arizona.edu/impacteffects/

    and set the parameters to impact 2 km of ice. The results are:

    Projectile Diameter: 100.00 m = 328.00 ft = 0.06 miles
    Projectile Density: 3300 kg/m3
    Impact Velocity: 17.00 km/s = 10.56 miles/s
    Impact Angle: 45 degrees
    Target Density: 1000 kg/m3
    Target Type: Ice

    Atmospheric Entry:
    The projectile begins to breakup at an altitude of 51000 meters = 167000 ft
    The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 7.92 km/s = 4.92 miles/s
    The impact energy is 5.42 x 1016 Joules = 1.29 x 101MegaTons.
    The broken projectile fragments strike the ground in an ellipse of dimension 0.768 km by 0.543 km

    Crater Dimensions:
    Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

    Transient Crater Diameter: 1.76 km = 1.09 miles
    Transient Crater Depth: 0.622 km = 0.386 miles

    Final Crater Diameter: 2.2 km = 1.36 miles
    Final Crater Depth: 0.469 km = 0.291 miles

    The crater formed is a simple crater

    The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 217 m = 712 ft.
    At this impact velocity ( < 12 km/s), little shock melting of the target occurs.

    Thermal Radiation:
    At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.

  • TCOisbanned? // January 8, 2009 at 1:38 am

    It’s really a problem in impact mechanics folks. Not sure that Pelto is expert here or that thermal melting is appropriate calculation. And would remind that impacts are complicated events and at ballistic (supersonic) speeds especially so.

    Comparing to a rock impact is helpful, but also perhaps to a water impact.

    There may also be studies/data on the efficacy of ice as a ballistic armor material versus other materials. This could be helpful to examine for insights.

  • Kipp Alpert // January 8, 2009 at 2:17 am

    DavidB.Benson;I found that it drained into St.Lawrence,in Mississippi, and the Atlantic. I am trying to get an Idea of the magnitude. Without Imapct, it is From Europe and New Zealand. Looking for sedmintary evidence for extent and amount.KIPP

  • dko // January 8, 2009 at 2:33 am

    http://www.realclimate.org/index.php/archives/2009/01/the-younger-dryas-comet-impact-hypothesis-gem-of-an-idea-or-fools-gold/

  • Eric Steig // January 8, 2009 at 3:40 am

    For the RealClimate take on this — which agrees with Mauri’s — see:

    http://www.realclimate.org/index.php/archives/2009/01/the-younger-dryas-comet-impact-hypothesis-gem-of-an-idea-or-fools-gold

  • saltator // January 8, 2009 at 6:04 am

    Kipp:

    “$100,000 please.”

    Thanks for the advice but I am not paying! Try the website now. I mainly use a 4×5 Linhof with b&w film.

    Richard Steckis

  • mauri pelto // January 8, 2009 at 1:48 pm

    I agree I am no impact expert, not even a novice. But before we rush off to try to fit this idea applying also sorts of theory, first it must stand up to the scrutiny of other field work that has been published that does not see the impact in their stratigraphic work, or in the dating of ice sheets etc. At the moment the idea is in its infancy. Typically in science you publish only what your science backs up. In this case they have gone far beyond that with conjecture, that is not backed up. So let us give much scrutiny to this idea in light of all that we already know. Pay attention to the chronology that has been developed for the proglacial lakes Warren, Ojibway, Agasssiz. Pay attention to recession rates of various glacier lobes. Note the pollen diagrams that illustrate the progession of climate at the end of the last ice age. You will find lots of data that is not as intriguing but has at this point a sounder footing.

  • mauri pelto // January 8, 2009 at 7:24 pm

    Oh the link to 510 dated pollen diagrams in US and 335 for Canada are at http://www.ncdc.noaa.gov/paleo/ftp-pollen.html This paleoclimate database represents just one line of evidence that can be analyzed for potential effects of a YD impact. The effort was spearheaded by Eric Grimm and the U of Minnesota

  • chriscolose // January 9, 2009 at 6:48 am

    I just got back from a trip to Chicago (at least had a chance to meet Dr. Pierrehumbert and Dr. Archer) but I wish I got in on this topic sooner.

    Here is my impression :

    It is very much possible that an asteroid impact happened, but I don’t think it had much to do with the YD. Like mauri and others I am not in position to offer extensive insight on the geologic evidence, but I have seen nothing to support how such an impact would translate into a YD-like climate change. The popular ideas involve fresh water influx (the source of that influx has been debated), which doesn’t exclude an impact part, but there’s also little to support a significant impact influence. One of Ray Bradley’s ideas on discharging thick sea ice also has an interesting place in this which I elaborated on in my RC comment.

    There is a global YD signature though it appears more see-saw like between the North and South rather than a large global cooling (though probably some more ice growth in the North than decline in the South, some more dust, so a bit of extra albedo and some decline in methane, so likely a small net cooling). Dating has been an issue, since there was something called an “Antarctic cold Reversal” right before the YD. Keep in mind though that you can’t just do a direct correlation with Greenland and Antarctica ice cores… Antarctica is “farther from the action” when it comes to fresh water influx than Greenland, and the heat capacity of the Southern Ocean is important as well (the similar but weaker 8k event is not yet identified in southern records), so you do not anticipate to easily find a globally or see-saw like behavior just by plotting O18 records between the two sites.

  • Anders L., Sweden // January 9, 2009 at 10:19 am

    It came out of the sky? Again? Both the dinosaurs and the megafauna became extinct as a result of celestial objects falling down near or in North America? I think you have seen way too many disaster movies.

  • Barton Paul Levenson // January 9, 2009 at 7:16 pm

    Anders, do you know anything about celestial mechanics? Do you have any idea how many asteroids, comets, and meteors are orbiting in the solar system? Do you know the mean time between large impacts, or the statistical equations governing that figure?

    Over long periods of time, celestial objects do hit each other. In fact, that’s how the Earth originally formed. And all the other planets.

    That’s not science fiction. That’s science.

  • David B. Benson // January 9, 2009 at 7:50 pm

    Anders L., Sweden // January 9, 2009 at 10:19 am — There is now some serious doubt that the dinosaurs all went extinct at the K-T impact. Regarding North American large mammals, the importance of human causes versus impact causes will probably never be fully resolved; I opine some of both.

  • TCOisbanned? // January 9, 2009 at 11:34 pm

    I think the Indians ate the animals.

  • Hank Roberts // January 9, 2009 at 11:48 pm

    But after eating the megafauna, where did the Indians go?

  • David B. Benson // January 9, 2009 at 11:51 pm

    TCOisbanned? // January 9, 2009 at 11:34 pm — Think what you will. That does not change what actually occurred.

    My thoughts on the matter are infomed by conversations with research archaeologists and reading some of the literature on large mammal extinctions in North America versus Eurasia.

  • saltator // January 10, 2009 at 7:47 am

    But after eating the megafauna, where did the Indians go?

    They started eating fish!

  • Tara Preyer // January 10, 2009 at 6:32 pm

    Respected archaeologist Vance Haynes has a related article on the prevalence of “Black mats” at dated Clovis sites around the country. Make sure to see the photos in the supporting information: http://www.pnas.org/content/105/18/6520

  • David B. Benson // January 10, 2009 at 7:36 pm

    Just to correct my earlier mistake, tektities and nanodiamonds are different. Both implicate an extraterrestial object encounter.

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