Exploring abrupt climate change induced by comets and asteroids during human history

Broecker to Kunzig: This Deal is Real

Restored from the library fire 1/11/20

fixing climate

Readers will recall the awkwardly titled September post, “NatGeo actually calls Wally Broecker to discuss evidence for cosmic impact at Younger Dryas start.” The Tusk was trying to convey there my astonishment that a thoughtful and thorough article was written on recent advances in the study of the Younger Dryas Boundary. Only later, with very little digging, did I realize this was not simply a case of a reporter stumbling on to illuminating facts — but likely a “tell” of greater significance.

It turns out that eminent ancient climate scientist Broecker and reporter Robert Kunzig are hardly strangers. In fact, they share a deep and productive relationship pre-dating this particular National Geographic article on the Younger Dryas Boundary Hypothesis.


Interesting photo of Robert Kunzig

In 2009 Broecker and Kunzig co-authored a fine book, “Fixing Climate,” which the Tusk just finished reading. Fixing Climate is recommended to anyone who enjoys biography in the service of telling a good scientific tale. Nearly all of the book is the personal story of Wallace Broecker and his discovery and explanation of abrupt changes in climate, in particular our favorite period, the Younger Dryas. Broecker’s story is the story of Younger Dryas science in large measure, and a narrative of his life is a wonderful and exciting way to tell the story of the YD.

Wally Broecker and George HowardFat Tusk and Wally

Which brings me to what I find most interesting about their relationship in the context of our subject. It seems to me the article from September was no accident. The Tusk is supposing that Wally was tipping his writer buddy off to what he knew was building evidence for something extraordinary — and cosmic — having initiated his signature climate period. (Recall that Paetev et. al., discovered a 1000 fold increase in Platinum at the YDB, gives first credit to Broecker (for obtaining access to the Greenland ice core from what I understand)).

Screen Shot 2013-12-14 at 6.41.07 PM

As Wally is clearly coming around to the reality of the YD team’s claim, it seems obvious Kunzig was the recipient of a friendly tip from his pal that something big may be on the horizon.

“Most people were trying to disprove this,” said Wallace Broecker, a geochemist and climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Now they’re going to have to realize there’s some truth to it”

Broecker to Kunzig — “Did a Comet Really Kill the Mammoths 12,900 Years Ago?” NatGeo, September 2013


24 Responses

  1. If Broeker is going to sign onto the YDB, he is going to have a very big loose end to deal with – his oceanic conveyor shutdown.

    Rodney Chilton and others have noted that the ice dam break at Lake Agassiz came too late, because outlet via the St Lawrence River was still covered with a km or so of ice.

    Asserting a MacKenzie River outlet into the western Arctic Ocean does not suffice as a replacement for a climate cooling event, because such outlet water would dump into the already freezing or near freezing waters and would have no effect. PLUS, its outlet waters would have to travel at least 4,000km through narrow straights to reach the Labrador Sea and open ocean, and another 3,000km to reach the area east of Iceland where the Gulf Stream ostensibly ends and the resulting cold water sinks. So that is a non-starter. They might as well be talking of an outlet into the Pacific Ocean – which also wouldn’t work. But the MacKenzie is the only alternative they have to the St Lawrence, so they keep pushing it.

    The bottom line is that no Lake Agassiz fed oceanic conveyor failure could have produced the climate change that began the Younger Dryas. This oceanic conveyor and its threatening of a shutdown is the big thing in Wally Broeker’s career, as far as I know. (A Wiki review credits him with inventing the term “global warming” – which, in the face of ever mounting skepticism, has been all but abandoned now in favor of other terms such as “climate change.” I know. I am one of those skeptics, and I keep up with such things.)

    I am in favor of Wally joining our ranks, if he does, because of his prestige. I just hope he shouts it from the rooftops.

  2. No mystery, George

    “Columbia University’s Lamont-Doherty Earth Observatory”

    the same place Dallas Abbott works. See her plug for my book here at the Tusk.

    I am also very sure that most of the scientists there are familiar with the phytolith sequences for both North America and Europe.

  3. I’m pretty sure that the volcanologist folks will tell you that Krakatoa did indeed erupt that year. And that it was a much much bigger event than the one back in 1883. So maybe we’re looking at a double whammy.

    At the very least it’s one hell of a coincidence if a major impact event happened at the same time.

  4. Yes at the VERY least a major concidence, since major oceanic impacts are directly correlated to hot spot vulcanism, I think it would be safe to assume that a strike on a tectonicaly active region could cause a ready to blow volcano to blow.
    And krakatoa did indeed erupt that year, and various contemporary sources put the eruption in late spring or early summer. The Japanese note that snow falls in the summer of that year and the rice crop fails.
    A Chinese chronicler yellow of a noxious vapor that take hold of the land, and in Byzantium a writer comments,” the sun has dimmed to such a degree, that we are truely living in a dark age”.

  5. The trouble though as I understand it, is that the 535 date for a super eruption at Krakatoa is still just a very strong theory. It remains to be solidly confirmed.

  6. The thing that made the article interesting to me is that they found non-volcanic dust along with the volcanic dust associated with whatever happened in 535 AD, which tends to support an impact event.

    Here’s a pretty good exploration of what may (or may not) have happened in 535 AD at Krakatau. No proof, but a pretty decent exploration.


    There was also a massive eruption out of El Salvador around 536 AD.


    Prevailing winds in the southern hemisphere as you approach the equator tend to be east to west. They only switch over to west to east when you get north of 30 deg N. I have run across some articles that claim that the dust seemed to come out of the east rolling across Europe. Along with it came the Black Death (bubonic plague).

    I am starting to think that life on earth is well adapted to volcanic eruptions, and that actual extinction events need an additional push. Examples include the Eocene event 33 MY ago; KT extinction 65 MY ago and even the Permian – Triassic event around 250 MY ago. All 3 events were extinction events. All 3 have some sort of massive volcanic component to them. And all 3 appear to have some sort of impact event associated (though the Permian – Triassic evidence is by far the weakest).

    Fun article out of the Large Igneous Province folks discussing relationships between LIP formations and extinction events. They do not necessarily correlate. Worth your time if for no other reason than to look at the first illustration.


    I tend to suspect impact(s) were involved with 535 AD, as we have have such a difficult time identifying fairly recent impact events and the dust has to come from somewhere. Obviously, need to prove it though. Don’t buy into the notion that the Plague came with the inbound body, which has been suggested by some of the more vigorous arm-wavers. Cheers –

  7. Agimarc,
    The plague did not blow in on dust, but the global cooling made it a deadly disease.
    The bubonic plague originates in tropical east Africa. When average temps are above 70 degF, bubonic plague is not transmitable.
    The bacteria lives in the gut of the flea, and is not passed to the host. But when the temps drop below that, there is a change in the flea. A bacteria/blood clot forms at the entrance to the gut and blocks any blood that the flea feeds on from getting to the gut.So the flea is essentially starving to death, and jumps from host to host in an attempt to fees, thereby infecting each host until the flea does die of starvation.
    One must also note that the Byzantines had just started direct trade with east Africa at the begging of the decade, with Byzantine ships hauling cargo directly to Byzantium.
    Another aspect of all of this is how it affected western European history.
    This very same plague was carried to Britain by imperial traders. It decimates the British of the southern part of the island, and it figures heavily in the imagery of the Arthurian legend, where the kingdom is laid waste by “winter” and pestilence
    The Saxons/Angles/Jutes found whole districts empty of people, complete with villiages and towns. The plague did not affect them because they did not trade with the empire.

  8. I can at most see an impact triggering or contributing to the Younger Dryas cold reversal, but it’s going to take a lot more than a pulp novel by a known crank to invalidate a hydrological component. I’m really harsh when it comes to evidence, mathematics, hypotheses and theories. That goes with the territory I inhabit (physics, mathematics, chemistry, geology, engineering, etc.)

  9. Cevin Q – Was not trying to imply the plague came with the impact. Your explanation is in line with what I understand took place (though much better expounded). Was trying to pass along that the claim had been made in some of the wilder speculation fans. Cheers –

  10. agimarc: “There was also a massive eruption out of El Salvador around 536 AD.


    In reading that article it looks to me like a scientist doing two things: Jumping to conclusions and trying to get some attention. There is nothing in the article – other than assertion – that the eruption was anything more than a local event. The guy needs a LOT more evidence than he seems to have.

  11. Cevin Q –

    It looks from your comment that you read Keys’ book. I am reading it and REALLY not impressed. A whole LOT of speculation as to causes and correlations. His Krakatoa chapters are phenomenally weak. His only source is that one book of very questionable provenance written over 1,000 years after 535 AD. Take out the speculations and the weasel words (“maybe” “could have been”…) and there is nothing there.

    99% of all of this ties into volcanoes not one whit.

    His one scientist that says something happened at Krakatoa then is contradicted by another scientist who says it happened in El Salvador. Thanks for that, agimarc!

    And Keys’ scientist only pins it down to within a ~5000 year range.

    So, basically, the geologists are groping and floundering about volcanoes and can’t agree. And don’t know when or how big a volcanic event it was.

    The only NUMBER that Keys has is a date, and the date isn’t even 535 AD, it is 416 AD. And he blows that off conveniently by saying it was a screw up on the date. The one forensic type bit of data is a mistake – because he WANTS it to be 535 AD.

    Even if something big happened at Krakatoa then, so far I haven’t seen anything that says it was bigger than 1883.

    It is known that Krakatoa blows up every now and again. And it is very likely that, yes, it blew up and severed the land link between Sumatra and Java – but WHEN is the crux for us here. It might have been many centuries earlier.

    And it might have happened at a time reasonably close to 535 AD – but what does “close” mean in geological terms.

    Krakatoa = 535 AD is on less solid ground than, say, the YDB. The YDB has scads of forensic evidence.

    As to an impact, there is no reason to think a volcano was any more likely to have caused the plagues and collapses of empires.

    The socio-political shifts are all just circumstantial, pointing out the SOMETHING might have happened. Or, as others often throw out at us, it could all just be coincidence. Empires, after all, DO collapse for political or social reasons. Ours will, too, when the time comes.

  12. Personally I rate Keys’ book at about 2.5 on a 1 to 10 scale. I couldn’t stomach all of his weasel words and his speculations. EVERY “maybe” was in the same direction – to help nudge the reader to his conclusion.

    If his conclusions were anything catastrophic he would be labeled an alternative researcher or a quack. Had it not had gradualism conclusions, he would never have gotten a scientist to check his stuff out.

    I’d be embarrassed to have such a book with my name on it.

  13. Steve –

    “In reading that article it looks to me like a scientist doing two things: Jumping to conclusions and trying to get some attention. There is nothing in the article – other than assertion – that the eruption was anything more than a local event. The guy needs a LOT more evidence than he seems to have.”

    Don’t substantially disagree with your observation, but it seems this is how the investigation begins.

    Am starting to wonder if volcanic eruptions are as hard to pin down as impact / airburst events – even relatively recent ones over the last several thousand years. We are still arguing about what happened at Krakatau in 535 and likely will for a long time to come. Source of the White River Ash in Alaska is suspected to be Mount Churchill, but so far not completely proven. Something big happened, but when and from where? Cheers –


  14. agimarc –

    What is there to pin down about volcanoes…

    Dates? Ash itself I don’t think is much help. But I could be wrong. 14C dates for what is immediately underneath. Older than about 40 kya gets pretty dicey, because of the asymptotic nature of half-lives; precision has to go all to hell. IntCal09 shows this in the width of its sigma bands. They go to great lengths to incorporate the latest – and MUCH vetted – data into their calibration curves. So, forensically, this is on pretty solid ground, and in the YDB time period it should be trusted.

    IntCal09: https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/3569/3082 – This is one we should all have bookmarked or saved to hard drive. it has ALL the latest graphs for >10,000 calibrated. The curves ALSO show ranges for each and every data point, from every study that is included, which is quite a few.

    Size? That has to be VERY unspecific in many cases, because ash gets spread over oceans and then lost (or at lest dispersed in the settling process, plus current erosion). Also, even ash on land becomes fertilizer for plants, and also gets washed into streams and rivers. Estimates done from what can be found after many millennia have to have a lot of assumptions built in, and every scientist is going to have a different set of assumptions. So area determinations – we should look at them with a jaundiced eye when we see numbers on size. They might be off by factors of 4 or 5 or more. Its forensic status is weak, IMHO.

    Chemistry? This should be on solid ground, tying deposits to specific volcanoes – as long as the magma was homogeneous, which as I understand is the assumption. If magma is anything like surface rocks, the chemistry often changes every few hundred meters or less. So what does that do to chemical matching? For now it is all we have. And at least it is forensic, as I see it.

    If anybody else wants to chime in, please do. My take is not the only one here.

  15. On the size thing for tephra, winds change, and it seems VERY difficult to map out the true extent of an ash fall from an earlier era. I have to think that hundreds and hundreds of samples would need to be taken AT THE PERIPHERY. But with the periphery unknown at the start, determining the periphery may mean taking samples inside and outside the periphery, too, to determine in a go/no-go sort of sensing of the edge. Thus, add many hundreds more samples. Why do I think such efforts are spotty? Or that interpolating is a common treatment? Interpolating is, by definition, an assumption of what goes on between sample points. Erosion also could/should make such efforts much less than precise.

  16. Steve – “What is there to pin down about volcanoes?”

    Maximum plume height.
    Total ejected mass of eruption.
    Duration of eruption.
    Location of eruption.
    Chemical breakdown of eruption.
    Time, date and duration of eruption including phases and pulses.

    Reasonably easy to characterize for effusive events (Columbia River Basalt Group). Really, really difficult to do for ash-rich / ignimbrite eruptions which dominate subduction boundaries.

    Problem with the grey eruptions is that while the pyroclastic density currents can be reasonable sized, dated and characterized, the simultaneous tephra / ash ejecta can’t. Additionally, this stuff is soft, subject to very quick weathering and erosion in the wetter parts of the world. The other problem is that vents that are active are will not puke out massive eruptions every single time they are active, making the problem of characterizing activity more difficult. In short, it is a mess. Cheers –

  17. Yes, nice comment, agimarc. I was getting at all of that, and you put the exclamation mark on it.

    Especially in my mind is the quick erosion factor in tropical areas in particular. Lying on top, much of it simply washes downstream in fairly short order. Over centuries it is amazing to me that any persists.

  18. George –

    Thank you for your kind words. I am a very poor amateur and know enough to be dangerous. Aero Engr by training. Interested in how things work, especially things that go boom. Live within dusting range of a bunch of active volcanoes here in AK. Self preservation kind of encourages me to know how things that can hurt me or make my life miserable work. I can’t stop them but may be able to be a little bit more ready next time around.

    Someone did a Thesis in 2008 taking cores from 27 lake bottoms on the Kenai Peninsula south of Anchorage. They were looking to match up banding of relatively recent ashfall events from local volcanoes. It was a mess and gives a small idea of the magnitude of the problem of characterizing output. Happy New Year to one and all. Cheers –


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