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536 AD and all that

Filed under: — gavin @ 2 March 2008 - (Deutsch) (Español)

“during this year a most dread portent took place. For the sun gave forth its light without brightness… and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear.”

This quote from Procopius of Caesarea is matched by other sources from around the world pointing to something – often described as a ‘dry fog’ – and accompanied by a cold summer, crop failures and a host of other problems. There’s been a TV special, books and much newsprint speculating on its cause – volcanoes, comets and other catastrophes have been suggested. But this week there comes a new paper in GRL (Larsen et al, 2008) which may provide a definitive answer….

It’s long been known that tree-rings (such as the one pictured from Arizona) often show an extremely small growth ring for AD 536 (you can count back from the marked AD 550 ring). In fact, if you look at the mean anomaly in a whole range of tree ring constructions, this event stands out along with 1601 and 1815 (known volcanic events) as being exceptional over the last 2000 years.

Average of the high-frequency components of 7 northern European tree ring reconstructions from Larsen et al, 2008. The filtering ensures that uncertainties in long term trends (which are not important in this context) don’t confuse the issue.

These data match the written sources quite well. However, tying it to a cause has always been plagued with problems of chronology. An initial attempt to tie this event to a volcanic pulse in the Dye3 ice core in Greenland foundered when the chronology was revised to put it 20 years earlier. However, there has recently been a concerted effort to place all the Greenland ice cores on a common timescale based on annual layer counts (Vintner et al, 2006). Because all the cores are being counted together, ambiguities in one can be corrected by reference to the others. Once the dates have been better established, the sulphate records (which generally show the impact of volcanic aerosols) can be examined to see if they line up. And low and behold, they do:

The second peak in the picture is dated at 534 AD which is close enough to 536 AD given the one or two year uncertainty in counting. Note that the 534 AD peak is actually smaller than the one a few years earlier. In assessing the importance of an eruption though, it isn’t enough to have just a peak in Greenland. That could simply signify an eruption that was close by. Instead, people look for a matching peak in Antarctica. This signifies that the eruption was likely tropical and the aerosols were carried into both hemispheres by the stratospheric circulation. Here is where previous attempts often faltered. The dating of ice cores in Antarctica is less exact than in Greenland because the accumulation is slower (it doesn’t snow as much). However, the relatively new Dronning Maud Land (DML) core has comparable resolution to the Greenland ones, and this one does have a clear sulphate peak at about 542 +/- 17 years. That is good enough to be a match to the 536 AD peak in Greenland. The correction you’d need to make to align them exactly would also fix some other apparent offsets for smaller events in the subsequent 100 years.

So it probably was a volcano, somewhere in the tropics, and it was likely the size of Tambora in 1815. There has been some speculation that it was an earlier eruption of Krakatoa (which went off again in 1883), but that is uncertain, as are the numerous consequences such as the fall of the Rome or the rise of Islam which have been attributed to this event. While not exploring that too deeply, this quote from Michael the Syrian indicates dramatically the potential for climate events like this one to really spoil your day:

“The sun was dark and its darkness lasted for eighteen months; each day it shone for about four hours; and still this light was only a feeble shadow … the fruits did not ripen and the wine tasted like sour grapes.”

160 Responses to “536 AD and all that”

  1. 151
    Les Porter says:

    # 147 David — see below. Thanks!
    # 149 Hank — thanks.

    Hank, also see:
    The Lovelock Interview:

    And from 1998, ten years earlier, in “Essays on Science and Society,”
    Science Essay:
    “a book for all seasons.”

    # 147, David B.Benson took me rightly to task, read on. . .

    David B. Benson,

    I just now scanned Archer/Ganopolski’s paper, and am printing it out for leisurely reference and to chase references, etc.

    What little I have digested in the last few minutes makes me wonder which plants survive the temperatures that will/would be forthcoming with another 5000 Gt C in the air.

    I will read the paper completely but 5 trillion tons C combines with O2 to make 44/12’s times that much CO2, such that we add another 18.3 trillion tons or 18,300 Gt CO2 to the atmosphere. It takes a fire (combustion) to join the C to the O2, and it gives off some chemical reaction heat, which I will ignore for this back of the envelope approach.

    . . . .[Come on! Imagine — Air/ fuel explosive! Finely powder 5,000 Gt C spread it as a powder in the appropriate volume of air, throw in a match or spark and . . . locally that is quite an explosion, and changes a lot of carbon dust to CO2. . . Slow burn also produces some BTUs. . . or maybe CH4 . . .( Filmmaker’s, we’ll get back to “The Day The Arctic Burned” (Sensational!-low-budget climate-change-film in the spirit of The Day After Tomorr . . . ). . .methane rises, bubbles to the surface, froths the Arctic Ocean, Shiphand Seaman First Class Jureska Novograd, who’s still trying to quit smoking, stands in the almost chilly arctic summer air on the bow of the Progresso an open Arctic Ocean-crossing ice-breaker-freighter, bound for Portugal, sees ahead where the ocean looks like it has a new layer of ice, but as the freighter gets closer, Jureska sees the white color is the Arctic Ocean boiling bubbling, seething — and light’s his last smoke. . . .and finally quits smoking. . . but the Arctic Ocean’s surface burns and flashes for weeks and months as the methane rises. . . the Arctic Communities are heavily. . .] . . .

    Back to the Earth-CO2, on the recovery track. . .

    5.0 x1012 x 44.01/12.01 = 18,322 billion tons CO2 That’s what 5000 Gt C + 02 weighs as CO2.

    The atmosphere weighs 5135.2 trillion tons (NCAR before Bushed)

    44.01/28.96 = 1.5197 (how heavy CO2 is WRT “average” air.)

    So we take 5,000 billion tons C combined with O2 for 18,322 billion tons CO2, and add it to the current (385ppmv) 3004.53 Gt CO2 in air “now” to yield a total of 21,327 Gt CO2 in air, and what would that do to the Model Temperatures and length of time to remove from the air?

    I’ve done this below showing that the extra 5000 Gt C as C02 corresponds to a value of approximately 2,733 ppmv, or 7 times the current concentration of CO2. That is a possibility (my low budget film above) and no matter how long algae that survive a hot ocean take — we lose a lot of land plants.

    (I believe Land plants are perhaps more efficiently exposed to CO2 quantities via immersion in air with the available CO2 than plants in the top couple of meters water — and can capture larger quantities of CO2 on land than plants in water. I grant that some mosses do really well, and will check this assertion (My Act of Faith assertion) out, but for the moment. . .)


    Ice age CO2 x ratio x weight of atmosphere = weight of CO2 in atmosphere.
    0.000280 x 1.5197 x 5,135.2 x 1012 = 2,185.11 billion tons CO2 ice age
    0.000385 x 1.5197 x 5,135.2 x 1012 = 3,004.53 billion tons CO2 now
    0.002733 x 1.5917 x 5,135.2 x 1012 = 21,326.76 billion tons CO2 (5000 Gt C new)


    My remarks, Off the Cuff. . .since I have not delved into the full set of references and am only “remarking” on the “conservative approach . . .”

    Archer and Ganopolski, in their results section, pgs 4, 5, 6, have serious fun and do not stretch the modeling at all. (Now these models have not at microtime scales real accurately reflected the current arctic sea ice situation.) And I therefore question the average 4.7o C positive perturbation for 500 kyr . [-15] (i think it might be over 8o C).

    I realize the Delta T for a CO2 doubling giving 3o C is used, but point out that 2733 ppm is a lot more than doubling-and-a-half and corresponds to more than 7 times the current 385 ppm for which we have no easily antecedent proxy for temperature and near current solar constant.

    (We ain’t been here before, exactly. . .just do the best we can from the past record to turn it ahead like a mirror, using our rearview mirror to drive this unknown road; yeah we stumble a lot.)

    Karen Bice, et al, (Woods Hole) with the hot tub ocean from 91o to 107o F. 33o to 42o C from foraminifera, and proxy CO2 values from 1300 to 2300 ppmv in the 80 — 100 Mya range (before K/T) had solar constants logically in the ~1356 range. (Solar Constant just whipped out here as a linear function from Earth current to 4.5 Gya at ~970 W/m2, then back to 100 Mya.)

    Read the paper here:

    Or the easy version here:

    The Archer paper and Bice paper only intersect in my mind in the realm of comparative CO2 ppmv’s and terrestrial temperatures. I have recently counted on the ocean’s solubility and temperature as per solubility as a “place” for the CO2 to go, to save us from the death of land/food plants.

    Now, it doesn’t look that good. I don’t think the ocean is going to absorb this excess we have now, let alone what Archer and Ganopolski provide caveat to real disaster — which is only cacti and far north phytoplankton as means of re-capturing the CO2 we’ve exhaled to the air. Karen Bice’s 42o C ocean provides one example of past high temperatures and proxied high ppmvs CO2. Oceans don’t get that warm now, according to NASA, NOAA, and I reference this:

    Also relevant:

    (from work of Maura Rabbette)

    If the “Day the Arctic Burned” (5000 Gt C) arises as a punctuating step with methane release, the temperatures ought to be scaled up to a Delta T (for CO2) of 7.13x instead of 2x, or 4x. Which is a criticism of Carl Johnson’s simplistic linear approach as well. (Not Archer, et al)

    Carl Johnson does not really address the ocean contribution, except obliquely. Why, for example, do the ocean depths stay so cool when it is obvious that the ocean basin basalts should be conducting some of the earth’s geothermal through the ocean basins to warm the oceans. Yet Carl only wants to use the top 3000 feet of continental rock to equilibrate with 390 ppmv CO2 temperatures. (Don’t think about this unless you just can’t help it.)

    But it does not look good ahead of us.

    David B. Benson, I won’t pick on you for “not reading the thread posts” — or thinking you haven’t — ever again! Also want to thank you for the head’s up for the two papers, and I will look for Jim Hansen’s 1500 year extrapolation.

    I really really enjoyed the Archer and Ganopolski paper, think they are conservatives, and will dig through the paper again.

    I find that I started out totally downplaying the “sulfate aerosol shield” a few months ago — and still do not like it for all the obvious reasons, the main one being that it will be funded by Big Carbon Inc, and possibly be used to extend the use of Fossil C for everything but lubricants, and transportation. Now I am starting to feel P. Crutzen and others have a piece of our only salvation with the way this planetary emergency is playing out.

    Huge “moving/running” plants, like the Trifids (original written) version trained genetically to gorge on CO2 in un-ending quantities to their own extinction might be better. . . we could do the same on fossil carbon, huh?

    What plants are going to save all creatures, great and small?


  2. 152
    David B. Benson says:

    Les Porter (151) — You are welcome. See also my comment #150.

    In figuring these out, please take into account that Peak Oil, followed not long thereafter by Peak Oil, will limit the ability to attempt to exploit deep ocean methane (strictly natural gas) hydrates. So it is probably more sensible to calculate with smaller figures than 5000 GtC. Use the Peak Oil+Coal figures plus whatever CO2 equivalent for the methane being expressed from bogs and tundra appears to be a sensible estimate as temperatures rise.

    You might also wish to study more about PETM. The Wikipedia page provides a starting point and you can also use the search feature at the top of the Real Climate page.

  3. 153
    Les Porter says:

    Minor note: the 280 ppm is end of Ice age, beginning of the warm. You can plug in 0.000188 to get the tons of CO2 airborne in a full fledged Ice Age. I meant to put that in there. It is 1466.29 Gt C.

    That is what keeps the planet from a snowball with recent insolation. My Quick and Dirty, taken back to say 700 Mya changes the Solar Constant to ~1305 W/m2, which to me is in equatorial wet fluctuating snowy ball range, but obviously with also the possibility of a band of tropical or equatorial zone oceans — where large areas either side of the equator are fluctuating sea ice. That is a while back, the linear extrapolation is from ~1368 “now” to solar ignition ~960 W/m2 4.5 Gyr back “then” in time.

    Sorry if I misled anyone. The table figure should have started off with the 188 ppm value, and the others are back of envelope despite the digits.

    The 536 AD event, unlike the K/T just cooled things down a little. Warming can also make it hard for crops to transpire and lots of water will be consumed to keep a plant alive in the heat. To exhaustion, demise, exceeding what it has adapted to.

  4. 154
    Nick Gotts says:

    OT, posted here because the original article is by Gavin, to whom this is relevant. In New Scientist for 22 March, p.11, there is an article “Rising Temperatures bring their own CO2”. Fine, you might think, we all know about this feedback. However, in the contents page, the article is pointed to using the words “Climate sceptics may have a point”, and in the article itself, Fred Pearce begins:
    “Climate sceptics are right. Temperature increases do precede rises in atmospheric carbon dioxide – the opposite of what you would expect if changes in CO2 were really driving climate change. That’s the verdict of leading atmospheric modeller Peter Cox, a climate expert at the University of Exeter.”
    Pearce does go on to say Cox stresses this does not mean we do not have to worry about GHGs, but quotes him as saying:
    “People on both sides want a one-way link, but the historical record shows the causality goes both ways”.
    No papers by Cox are cited – the most recent relevant one I can find is “Positive feedback between global warming and atmospheric CO2
    concentration inferred from past climate change” by
    Marten Scheffer, Victor Brovkin and Peter Cox, published in Geophysical Research Letters in 2006 (I can’t find an exact reference). This paper stresses that the historical work on the Little Ice Age agrees with climate model results.
    Is Cox given to saying stupid things for publicity, or is this (as I suspect) a misquotation or out-of-context quote by Pearce? (At the end of the article, Gavin is quoted as saying “We are headed into unknown territory and the only things we have to guide us are physics and our knowledge of the past.”) I intend to complain to NS about this irresponsible rubbish, which we are bound to see cited by denialists for the indefinite future, but it would be useful to know who is at fault.

  5. 155
    john lagace says:

    Lawrence Coleman is a pompous ass! There are as many learned neurons on both sides of the AGW or ACC or whatever you wish to call it argument. The IPCC is political and deserving of immense skepticism.

    Admit that you will apologize and quit science if you are wrong and only then will you have shown the humanity to be believed by others just as intelligent as you are.

    To believe you alone have wrested sense from chaos is laughable. You invite argument by your impudent denunciation of opposing voices.

    You are a fool.

    John lagace


  6. 156
    Ray Ladbury says:

    John Lagace, OK, so you are skeptical of the IPCC. Fine. So start with the peer-reviewed scientific literature. The number of published studies is a pretty good metric. The number of studies that support anthropogenic causation of climate change outnumber those that do not by roughly 2 orders of magnitude–a pretty good sign of consensus. But don’t stop there. Look at how often the papers are cited once they are published. Here the consensus for anthropogenic causation is even more stark–nearly every study that questions anthropogenic causation pretty much falls flat. They simply do not point to fruitful new avenues of inquiry–being cited only by refutations or when the authors subsequently “update” the cycle a few years hence. Look into the backgrounds of those publishing the “dissenting” studies–virtually none of them are actual climate scientists. Finally, look at the position statements taken by professinal organizations of scientists. Not one actually dissents from an anthropogenic mechanism for climate change. To make the claim that there are “as many learned neurons” on either side of the question of anthropogenic causation is sheer ignorance–the neurons that claim we aren’t behind the changes have never studied climate change.
    Finally, might I suggest that you will get much further on this site of you confine yourself to the details of your opponents’ arguments rather than launching ad homenim attacks.

  7. 157
    Doug Weller says:

    I’m not sure how much to rely on Keys. Reviewing Keys’ book in British Archaeology, the British archaeologist Ken Dark commented that “much of the apparent evidence presented in the book is highly debatable, based on poor sources or simply incorrect” and that “Nonetheless, both the global scope and the emphasis on the 6th century AD as a time of wide-ranging change are commendable, and the book contains some fascinating and obscure information which will be new to many. However, it fails to demonstrate its central thesis and does not offer a convincing explanation for the many changes discussed.

  8. 158
    David B. Benson says:

    Somewhere I read of a claim that a meteorite impact in northwestern Australia gave rise to 536 AD and all that.

  9. 159
    Hank Roberts says:

    David, you may be thinking of Plimmer? Odd duck. Google for +536 “dust veil” “cometary dust” — lots of stuff out there.

    “… 535 AD Krakatoa exploded, as did Rabaul in 536 AD. The Earth passed through cometary dust in 536 AD. The dusty atmosphere reflected heat and darkness prevailed and, as a result, the climate cooled….”

  10. 160
    David B. Benson says:

    Hank Roberts (159) — Definitely not Plimmer.