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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. 51
    Hank Roberts says:

    Robin, I think — I’m not an expert, I just did a quick browse of what Google Scholar offers — that the distinction is based on the quantity of sulfur. I can’t think of any source that would produce a really large amount from a meteor or from a biological source hit by one.

    Just a quick look found me this quantity estimate for example:

    “During the steady-state period of activity of La Soufriere Volcano in 1979, the mass emissions of sulfur dioxide into the troposphere amounted to a mean value of 339 ± 126 metric tons per day. This value is similar to the sulfur dioxide emissions of other Central American volcanoes but less than those measured at Mount Etna, an exceptionally strong volcanic source of sulfur dioxide.”

    I don’t know how many days those volcanos were in steady-state activity, but the total adds up fast.

  2. 52
    Ike Solem says:

    RE#48 “We cant go cold turkey anyway..the infrastructure just isn’t there and wont be for decades.”

    “Car-Free, Solar City in Gulf Could Set a New Standard for Green Design.”

    “Renewable Energy: Desert Dreams”

    Thus, the time required to transition to a renewable energy basis could be measured in years rather than decades – it’s all a matter of how many resources are devoted to it.

  3. 53
    Slioch says:

    #29 # Pierre Gosselin asked

    “How do you explain Jan 08’s massive global temperature drop?”

    Firstly, remember that January 2007 was the warmest January on record (anomaly 0.87C NASA GISS), so that obviously amplifies the current fall. (Jan 2008 0.12C)

    Secondly, there is presently a strong La Nina (negative temperature anomaly) in the Pacific (caused by an upwelling of colder water from the depths). The cooler waters of the Pacific absorb large amounts of heat from the atmosphere and are probably (partly) responsible for the cold events witnessed recently in many parts of the world.
    La Nina events are the flip side of El Nino: during the latter the Pacific surface waters become abnormally warm. An El Nino event was responsible for the positive spike in global temperatures in 1998, and we appear at present to be getting a negative spike from this La Nina in 2008.

    Here are graphs of sea surface temperatures in the Pacific for Feb. 7th 2007 and Feb. 8th 2008. The lower graph in each set is the interesting one since it shows the anomaly relative to 1971-2000:

    Feb. 7th 2007:

    Feb. 6th 2008:

    If you doubt the cooling effect of La Nina, try taking a hot-water bottle filled with cold water to bed with you!

    Finally, Tamino’s articles (linked to in #31 above) should settle any remaining doubts you may have about if we are now experiencing global cooling: we are not.

  4. 54
    Ian Perrin says:

    James Lovelock is being more visionary than scientist in the quoted interview. When asked

    if he attributes the conflicting predictions to differences in scientific understanding or personality, he says: ‘Personality’.

    Put the 2020 and 2040 dates on one side and his views on the possibility of future disaster are not substantially different from James Hansen. The difficulty is that he has a track record of being on the mark with earlier, seemingly wild forecasts. Perhaps we should file these predictions but not forget them.

    The interviewer tells us

    He fears we won’t invent the necessary technologies in time, and expects ‘about 80%’ of the world’s population to be wiped out by 2100.


    Eventually we’ll have a human on the planet that really does understand it and can live with it properly.

    Even if he’s right then to fulfil his hope, we will need renewable sources of power. Nuclear can only be a temporary expedient in his scenario.

  5. 55
    Nigel Williams says:

    From the reports from Rome on the 535 event it would appear fairly certain that the present food supplies would fail totally with anything like that scale of impact on insolation. An aggressive natural disaster of the cataclysmic kind we don’t need right now. There are quite enough convergences in the pipeline.

    The recent cold snap at ground level will play havoc on food production. What is the impact of the southern USA weather on corn production? With USA producing about 8% of its fuel from corn and with the now-solid relationship between food and fuel any reduction in the corn harvest will increase the stress between food and fuel supplies – the oil shock of a few decades ago was only a 5% dip in supply.

    I think Lovelock is right in his general view. I admire the way Hansen et al say that everything will be sort of OK if only we can do X, Y and Z. But we wont and it is becoming increasingly clear that we cannot. So while Hansen et al are correct in their estimate of what is needed to keep us safe; their comments about “all we have to do is…” are simply to keep them in the loop as part of a socially acceptable run at the solution.

    I agree that we might as well stop messing about with mitigation. For example we have no idea how to sequester CO2 at any sort of commercial scale that would make a difference. There will be twice the volume of liquid CO2 as there is oil and handling that amount of CO2 product is impossible. The infrastructure will never be built, and if it does it would require twice the energy input to the system to get both the current energy output and the CO2 sequestered. Biofuels don’t add up – or rather they do:– to more CO2 than fossil fuels. Carbon taxes wont be spent anywhere useful, etc etc… Its all rubbish.

    But like Lovelock I think there is hope for a great adventure. Like the start of war there will be the opportunity for euphoric pursuit of new goals and new systems that will – to a degree – see the survival of some of us. We wont be building tanks or fighters – we will be building sustainable power supplies, local MASH units, self contained farms and running railways around the 100m above sea level contour to provide a simple old-world transport route that will last past the time the seas stop rising.

    There will be opportunities for good old commercial interests to prevail in the production and operation of new systems. But the old systems will surely fail. Energy and food are now inextricably intertwined, and we will find – perhaps before the middle of this year – that the world will move into a hoarding phase where citizens and nations start building stores not as short term buffers against variations in commodity prices but as reserves for the long term future – until until.

    The variations in climate, the stagnation in oil production, the increased demand for food, the imposition of export levies in numerous countries to halt export of foodstuffs, droughts and climate extremes, trembling commodity markets, failing banks, collapsing ice sheets, melting glaciers and the increased rate of extinctions in amphibians, insects, sea life and small mammals (not to mention the coming demise of our primary predator the Polar Bear!) are all indicators of a convergence of forces against the survival of modern society in its present form.

    In the main any opportunity for useful control of these forces has already slipped beyond the control of any man or country.

    For those of us left standing these will definitely be exciting times! It will indeed be “…life Jim, but not as we know it!”

  6. 56
    Pete Best says:

    Re #49, Yellowstone is every 600,000 years and one is over due by 40,000 years I believe. As for Lovelock, I agree that his message appears very starck but he sees earth science differently to te majority. For one he is a true systemesist and laments the lack of the true complex modelling in terms of the biosphere as well as physical processes which he belieevs is sigificant.

    His predictions are based on additional factors which makes them more dire than the majority of climate scientists but who is to say that he is not right rather than misguided.

    Re. Re#13, Sorry RC. I i no way meant to associate James Hansen with RC, only with GISS.

  7. 57

    Pierre Gosselin writes:

    [[Going fossil fuel cold turkey would mean economic suicide.]]

    True. We’ll have to do it gradually, say, in a couple of decades.

    [[If you want to see misery, death and destruction, then implement the nonsense proposed by Gore and Co.]]

    What nonsense would that be?

    [[Fortunatelly, it won’t be allowed to go that far. When people start paying through the nose for this hysteria, they’ll use their votes run ya’ll out of town.]]

    The contraction is “y’all” from “you all.”

    [[Already with the high energy and food prices, we’re beginning to see social instability.]]

    We’ve seen social instability for a long, long time.

  8. 58
    Ray Ladbury says:

    Robin Johnson, Having been near both volcanos and forest fires, I can say without a doubt that forest fires cannot touch volcanos for production of sulfur. Sulfur melts at a relatively low temperature, and so will dissolve into the superheated water associated with a magma body. When pressure is released by the eruption, it will flash to vapor and react with the water to form sulfuric acid and other sulfates as it is dispersed at high altitudes–even into the stratosphere.
    Forest fires, because carbon is the dominant element, tend to form a lot of CO2 and ash. Not the same at all.

  9. 59
    Lawrence Coleman says:

    Re: 46. You’re wrong! Our Gov in australia has just been advised rather strongly by a leading and respected economist Prof. Ross Garnaut about the economic impact of global warming and he advocates just that. well..a 90% reduction in greenhouse gasses by 2050 anyway. More and more reports are coming in saying that the only way to stabilise climate and then reverse the damage done is by going almost completly carbon neutral ASAP. Sorry DBrown..get your facts straight first!

  10. 60
    Lawrence Coleman says:

    Just read a bio of James Lovelock’s life and achievements..what an incredible man!! His insights into life itself and the atmosphere as an extention of everything that has ever breathed to me were based on buddhism..well I’m buddhist so I’m biased..hehe! We wont destroy the earth..only us and virtually every animal and plant on this planet for a heck of a long time. The earth WILL recover maybe in a million years..but it will recover!
    Here’s the link of one of his bios…

  11. 61
    Robin Johnson says:

    Thanks Hank and Ray.

  12. 62

    On the subject of renewables:

    There really is very little reason we can’t do more to deploy renewable sources of energy. The incremental cost is measured in pennies per KWH, and the total cost differences in many instances is dollars per month. For some sources, such as wind, there is now a financial incentive to use wind rather than coal — the “all wind” electric plans here in Texas are fractionally cheaper than the mixed coal-nuke plans.

    I wish I could say my electric costs are going down, but at something like 300KWH for January (they misred my meter last month by 100KWH, so I’ve not updated the image the link off my name references, but last month was 408KWH or so according to them), that monthly customer service fee starts to show up in the cost of electricity as pennies per KWH.

    On the subject of distributed generation:

    Sorry, not a solution. I’d love it if it were, and the solar array on my roof would also love it if it were. But, alas, I have the graphs of power output to prove that distributed generation is a really BAD idea. What distributed generation is a good idea for is surviving the coming problems the electric grid is going to face as ever increasing amounts of load are shifted from carbon-based to electron-based sources. I’m not interested in being without electricity because 1/3rd of the population decides to plug their electric cars in on a Sunday night so they can drive the next day and the grid collapsed because the load exceeded that of the hottest summer afternoon.

    Distributed generation is needed so we can survive the end of the oil era, not so we can cut carbon emissions at the coal-fired plants. ERCOT, the grid where I live, produces somewhere around 35GW on a day like today — maybe a bit higher if we dip below freezing tonight. But 35GW is a whopping 18 nuclear plants at 2GW each. Toss in some landfill natural gas or landfill reclaimed biomass powered generators for frequency and voltage regulation and all of Texas is off the carbon addiction for electric generation. Time to realize that? Ten or 15 years. Doubt my math? You can check the ERCOT load / generation numbers at . Current generation — 39,400MW.

    The solution isn’t distributed generation, which has to be the dumbest idea anyone ever dreamt up (yes, really — managing ERCOT is no simple feat. Imagine all 17 million or so Texans all poking their fingers in ERCOT’s interconnect), it’s large scale storage technologies such as compressed air and pumped hydro. Several more GW of wind out in West and North Texas, pump the Lower Colorado back into the Highland Lakes during the periods of high wind, or air into salt dome down south, and we’ve got our regulation abilities from wind sources.

    The main obstacles are not the techology. The entire automobile fleet is already being replaced on a shorter timescale than we have to end our oil addiction (I’m a “we can’t cause global warming because we can’t afford the price of fossil fuels” skeptic, for those of you who don’t know me). We know how to build electric motors. We know how to build batteries. Toyota’s system (Hybrid Synergy Drive) is now very well proven and leds itself to conversion to plug-in hybrid. All that remains is the will to pull the trigger, and people don’t want to give up their giant oil swilling SUVs or their cutsie dimmable lights to avert what, for themselves, is going to be a financial disaster.

  13. 63
    d. beck says:

    George Monbiot has got it in the best perspective. He says small is not beautiful anymore. It will take a gargantuan effort such as Iceland developing enough thermal generating facilities to power nearly the whole of Europe. Do-able but far off.

    Think of how much electricity Yellowstone could produce (don’t think too much about that super eruption though, cause no one knows how to avoid that. In my dreams I see Bill Gates buying a hundred automatic drilling machines placed 20 miles away drilling a low angle to intersect the magma chamber well below center, and slowly venting it). Sorry for getting off topic.

    Here is Monbiot’s speech in Aug. ’07 at the Camp for Climate Change in London. He is the second speaker in at approx. 15 minutes. Best keep the volume down. It was recorded from the audience and their applause is quite loud.

  14. 64
    Nick Gotts says:

    I’m not sure what James Lovelock’s doing in this thread, but since he does not appear to be going away, I fear I must dissent from the general tone of reverence. There’s no doubt Lovelock has considerable achievements to his credit, but he’s far from infallible in his judgements on environmental matters – as he, again to his credit, recognises (in “Homage to Gaia”, 2000). A pioneer of measuring trace atmospheric gases, in 1974 he declared that the CFCs in the atmosphere posed “no conceivable hazard” (Lovelock, J.E., Maggs, R.J. and Wade, R.J. (1973). Halogenated Hydrocarbons in and over the Atlantic. Nature ’241, 194-196). More generally, he was for a long time very confident of “Gaia’s” ability to deal with human-caused pollution – a confidence which I am sure was quite sincere, but was very convenient to the large companies, such as Shell, who financed his work. The “Gaia Hypothesis” is certainly brilliant, if only as a “meme” extraordinarily well adapted to its cultural environment. Aitkenhead’s interview says Gaia theory “forms the basis of almost all climate science”. I do not know whether Aitkenhead acquired this view from Lovelock, but I would be interested in the contributors’ views on the statement itself. The interview also makes clear that Lovelock makes absolutely no effort to limit his own GHG emissions or other impacts on the environment.

  15. 65
    cce says:

    A smart grid ensures that people don’t overload the grid at any particular time. Set the price high enough, and people will find different times to charge their cars.

  16. 66

    RE #48 “what’s the point of maintaining a robust economy if the world’s dying”

    That got me thinking, we really don’t have a robust economy, if we’re consuming & destroying the capital. It’s like selling the building and machines of a factory part by part. On the books it looks like we’re making a good profit, but once the capital is all gone, there will be a collapse. And I’m just speaking of using up and polluting finite resources, on which economies ultimately depend. If you include the effects of GW, the situation is even more dire… you sell the roof of your factory, which makes your books look great for the moment, then the next moment a flood and hurricane strike and destroy an even greater portion of your capital, plus killing some of your workers. Then you have to sell all the more capital to cover up the losses.

    We’re in the midst of a close-out fire sale, which simply gives the illusion of a robust economy.

  17. 67
    Nick O. says:

    Re. #58 (Ray L.) Ray, do we have any data on comets releasing SO2, just pursuing the air burst (as opposed to full impact) idea? Or would they produce other volatiles that might have the same climate effect as that indicated in the c. 536 AD data?

  18. 68
  19. 69
    Ray Ladbury says:

    Nick O., We have to ask where the sulfur would come from. There is no process I can think of for a comet to be particularly enriched in sulfur. So, it would have to be a direct hit on a site on Earth where sulfur was enriched. You might have a somewhat high sulfur content in a bog, but there would be lots of organic matter to burn along with it–not the sort of event we’re looking for. For high-sulfur/low-organic, you are looking at a geologically active area with lots of hyhdrothermal activity (e.g. Rotorua in N. Zealand or Yellowstone in the US). Such sites are a lot more likely to supply their own explosive potential rather than requiring a cometary impact.

  20. 70
    Lawrence Brown says:

    This topic ought to make anyone thinking of the global engineering strategy of injecting aerosols into the stratosphere, to mitigate the effects of AGW, give it another look and go back to the drawing board.
    If we overshoot the planned upon levels of sulfates and the fruits and other food products don’t ripen, at our current levels of population, for a season or two, we’re in big trouble.

  21. 71
    Harold Pierce Jr says:

    RE: Age of Fossil Fuels Will Last Forever!

    I have said this many times here and elsewhere, I will say this once again here, and I will say this at RC for the very last time. We will always use increasing amounts of fossils fuels because there are no subsitutes with the requisite chemical and physical properties, and there never ever will be any reduction in the emission of carbon dioxide.

    For example, boats, planes, freight trains and trucks, construction, mining and agricultural machines, most cars and light trucks, motorcycles, snowmobiles, ATV’s, all military vehicles, go-carts, golf course and sports field grass mowers, etc will require and use liquid fossils fuels becasue these fuels have high energy density and are easily prepared from crude oil by fractional distillation and blending, low energy processes that do not require the breaking of chemical bonds. Even catalytic cracking of heavier distillate fractions is a low energy process.

    The “Fuels of Freedom” are chemically inert (except to reaction with oxygen. halogens and several highly reactive chemicals such as singlet oxygen) noncorrosive, highly portable, and can be stored indefinitely in sealed containers (e.g., steel drums) and under an inert atmosphere (e.g., nitrogen) in large tanks.

    Fossils fuels will always be required for lime and cement kilns, metal smelters, steel mills, foundries and metal casting plants, metal cutting and braising torches, all factories that make ceramics (e.g., bricks, tiles, china, glass, etc), all food production, processing and distribution, space and water heating, cooking and baking, BBQ’s, manufacture of porcelain-coated metals, harvesting of wood and lumber manufacture, isolation of essential oils by steam distillation for prepartion of fragrances and flavors, etc.

    The reasons we use thermal plants for generating electricity is that these plants have a small footprint, can be located close to consumers, and produce electricity reliably and at very high energy-densities.

    Fossils are the feedstock for the petrochemical
    industries (sometimes called the chemical process industries), which manufacture everything from A to Z, such as synthetic fibers. There is not enough suitable land for growing cotton, flax and sheep to meet world demand.

    If you guys have any schemes that will replace fossil fuels for the above applications and uses, I’m quite sure the engineers will glady welcome your suggestions.

    We will always have lots of fossil fuels because we can always use coal for manufacture of synthetic hydrocarbons. Germany did this on amassive scale during WW II and South Africa use the process and it supplies about 40% of liquid hydrocarbons which can be
    manufactured into a wide range of useful materials.

    Google “SASOL” for more info.

  22. 72
    Paul says:

    Well, I have no doubt that every last barrel of oil, ton of coal, and cubic meter of gas will be extracted as soon as commercially feasible, no matter the harm to the environment, but…”always” ? That’s hard to picture.Always is such a long time.

  23. 73
    Bruce Tabor says:

    Re 60 Lawrence Coleman,
    My understanding is that going “cold turkey” means you immediately stop doing something, in this case using carbon based fuel sources.

    A reduction or 90% in the per-capita CO2 emissions over the 42 years between now and 2050 proposed by the Garnaut Review here in Australia is not the same as “going cold turkey”.

    Yes it’s a rapid transition, but the idea is to use our current sources of wealth and energy (fossil fuels) to leverage us into new sources of wealth and energy, just as has happened whenever the form of energy that underpins society has changed.

  24. 74
    Jim Eager says:

    Re Harold Pierce @ 71: “I will say this once again here, and I will say this at RC for the very last time. ”

    Is that a promise?

  25. 75
    Bruce Tabor says:

    Re 64 Nick Gotts.
    I agree on Lovelock. His recent book “The Revenge of Gaia” was probably the most unscientific book on global warming I’ve ever read, with the possible exception of Michael Crichton’s State of Fear. The books are from opposite ends of the spectrum, but only one pretends it is not fiction.

    He is justly famous for the Gaia Hypothesis, which has led to Earth Systems Science. But he continues to encourage the religious overtones of the concept, that Gaia is somehow teleological or purposful. And the concept that Gaia is a homeostatic organism, striving to maintain a constant environment is over the top. A better concept might be a broad scale corollary of Le Chatelier’s Principle: that when an equilibrium is disturbed the equilibrium shifts to partially counteract the change. There is nothing unique to living systems about this behaviour.

  26. 76
    Bruce Tabor says:

    Re 71 Harold Pierce,
    I could go through and refute your argument case by case, but ultimately what you have said is a statement of religious belief, and one that is demonstrably a mathematical impossibility. On a planet where we “will always use increasing amounts of fossil fuels” the “Age of Fossil Fuels” cannot possibly last forever, as the reserves of fossil fuels are finite – even coal, oil shales, tar sands etc. This is even more the case when you consider EROI – energy return on investment. The only fossil fuels that are worth recovering are ones that ultimately yield more energy than they cost to recover and process for their ultimate purpose.

  27. 77
    Ray Ladbury says:

    Harold Pierce, Jr., According to the World Coal Institute: “At current production levels, proven coal reserves are estimated to last 147 years.”

    That assumes current production levels, but of course energy demand will continue to grow. I had hoped that forever would be further off than 1.5 centuries. So, when the coal runs out, do you propose to mine Titan?

    Fossil fuels are finite. They threaten the continued viability of civilization. Accept it and let’s find a way to cope without them.

  28. 78
    Bruce Tabor says:

    Re 55 Nigel Williams,
    I largely agree. You have the optimists view of what I view with great pessimism. To me “interesting times” – war, famine, depression, genocide – are better read about in books or perhaps seen from afar. Unfortunately we will be building tanks and fighters as this is an inevitable response in times of stress like this, along with the rise of tyrants and demagogues. A world population crash to around 1 billion, which is a realistic worst case, will not be pleasant for the 6-7 billion “missing”. Will the survivours consider they have lived through “interesting times” or a holocaust, as that is the only comparable magnitude of loss – the almost complete loss of European Jewry.

    On a minor point, I think you’ll find that 65-70 metres is the highest retreat needed and quite possibly only 12-25 metres will be required, but picking where sea level will stabilise will be difficult.

  29. 79
    Fernando Magyar says:

    Harold, Re 71,

    Google “SASOL” for more info.

    Just for sh*ts and giggles try googling Peak Oil and Peak Coal.

  30. 80
    Ellis says:

    As stated in Hansen 1981, and elsewhere, one of the main tenents of AGW is that as the atmosphere becomes more opaque the effective radiating level will rise and that because of the lapse rate will emit at a lower temperature, I suppose assuming that that level stays within the troposphere. In 1981 Dr. Hansen put the height at 6.5km/5.5km for tropics/poles. First, I would like to know where he got this number, was it by calculation or observation. And secondly, it has been 25 years, has that level moved higher? Or if that is an ill formed question, at what height did the earth emit from before we perturbed the natural order?
    Thank you for any insight.

    [Response: It's based on the mean emitting temperature (i.e. the T at which SB emission would equal absorbed solar) which is around 255 K. If the mean surface temperature is 288 K and the lapse rate is around 6 K/km then you end up with a mean emitting height of 5 to 6 km. This does not mean that this is where all outgoing LW comes from - you can see from the spectra that for different wavelengths the emissions come from different temperatures (heights) - that is of course how satellites can sense different parts of the atmosphere. Since it is a little bit of a convenient fiction, changes in this height are more useful as a pedagogic device than as a tool for diagnosing climate change. - gavin]

  31. 81
    J.Hansford. says:

    It would be nice if the AGW Catastrophists could actually measure some observations that give credence to the Hypothesis of Anthropogenic Global Warming…. That shows it has a SIGNIFICANT effect and affects climate. To the extent that it is clearly visible beyond the background noise of natural variation…. they can’t.

    So… Ten years now, there has been no warming trend. Despite the Hypothosis that Increasing CO2 drives warming… Now we have a cooling…. No mechanisms explained… Nor for the 40′s until 70′s cooling period either…

    We also just happen to have the lowest activity of sunspots…

    Sunspot activity makes a better fit than does Athropogenic CO2.

    Trying to fit Volcanoes into your bits and pieces here is not going to help… We’ve had large modern eruptions and a heap of data from them… The effects don’t stay in the atmosphere for any significant period.. The affects would not last centuries… What about St Helens and Pinotubo…

  32. 82

    Re #75 Bruce Tabor

    He is justly famous for the Gaia Hypothesis, which has led to Earth Systems Science. But he continues to encourage the religious overtones of the concept, that Gaia is somehow teleological or purposful. And the concept that Gaia is a homeostatic organism, striving to maintain a constant environment is over the top.

    My suspicion is that the Gaia Hypothesis is just a special case of the Anthropic Principle: the Earth appears to have all these self-restoring tendencies because we are around to talk about it :-)

    That doesn’t guarantee that it will last though, does it. A world population crash due to a sudden collapse of the agricultural production base, somewhere in the 2030-2060 time frame, is a worst case scenario, but unfortunately not one that seems entirely over the top — most people have no idea of the fragility of the ecological base of our production system.

    And when comparing with the Holocaust you’re missing three orders of magnitude.

  33. 83

    Nigel Williams writes:

    [[For those of us left standing these will definitely be exciting times! It will indeed be “…life Jim, but not as we know it!”]]

    What makes you think you or your descendants will be among those left standing?

  34. 84

    Harold Pierce Jr writes:

    [[We will always use increasing amounts of fossils fuels]]

    That’s physically impossible. There aren’t infinite amounts of fossil fuels. Using increasing amounts means the more we use, the faster we run out. Do you understand how a compound-interest expansion works?

    If the entire upper 10 kilometers of the Earth’s surface were pure anthracite, and use rises 2% per year compared to this year’s equivalent of about 3.9 x 1012 kilograms equivalent, we run completely out of fossil fuels in 688 years (and God knows what the surface temperature of the Earth would be like by then). If, a little more realistically, only one part in 1,000 is fossil fuels, we run out in 339 years. Either way, we run out.

  35. 85
    Jim Eager says:

    Re J.Hansford @ 81: “It would be nice if the AGW Catastrophists could actually measure some observations that give credence to the Hypothesis of Anthropogenic Global Warming….”

    Such measurements have been addressed here at RealClimate repeatedly, as has been your assertion that there has been no warming trend for ten years. Don’t blame others for your inability to pay attention.

    J.Hansford: “Sunspot activity makes a better fit than does Athropogenic CO2.”

    Then how, exactly, do you explain the divergence of sunspot activity from temperature rise after the late 1970s?

    What you fail to understand is that solar variation and greenhouse gases are entirely separate and independent phenomena that may offset or reinforce each other. Should solar activity lessen, cooling of Earth’s surface and atmosphere will result, but greenhouse gases will continue to make it warmer than it otherwise would be. Likewise, any increase in solar insolation will be amplified by greenhouse gases. Either way, adding more greenhouse gases will make it warmer yet.

  36. 86
    henry says:

    RE: 536 eruption

    “here are some suspects:

    PAGO New Britain C 530 AD ± 150 years 5
    VESUVIUS Italy 536 AD 4?
    RABAUL New Britain C 540 AD ± 100 years 6″

    Instead of a single, massive eruption, would a series of smaller, closely spaced eruptions have the same effect? Would all of the particulates from the first be cleared by the time any smaller “after-eruptions” came by?

    The list above shows two smaller eruptions within 10 yrs (I know, there’s a +/- 150 yrs). How much would have been in the air when the second one, IN THE SAME AREA, went off? Or a second one “down-wind” of the first?

    Speaking of the “dating”, would particulates from two, closely spaced (time and location) eruptions compound the dating errors?

    Just curious.

  37. 87
    Phil. Felton says:

    “Instead of a single, massive eruption, would a series of smaller, closely spaced eruptions have the same effect? Would all of the particulates from the first be cleared by the time any smaller “after-eruptions” came by?”

    I suspect that it needs a big one, sufficient to put a lot of particulates and water in the stratosphere where it will linger for years, small ones will wash out of the troposphere much more rapidly.

  38. 88
    Ray Ladbury says:

    Note: Volcanic eruptions of any type can be treated as Poisson events. The probability of having 2 in close succession will generally be small. Moreover, a large volcanic eruption is more efficient at throwing material high into the atmosphere, where it stays longer and has more effect.

  39. 89
    Harold Pierce Jr says:

    RE: #74

    Yep! I promise! And not only that, I’m not going to rebut my critics.

    I’m wasting too much time on these climate blogs. I still have to process about 100 temperature records from my favorite weather station and lightstation at Quatsino, BC. I just finished a multi-decadal analysis of the min temperature for Fall Equinox Interval (FEI, Sept 16-26) and have obtained some inexplicable results. Here is a brief synopsis. The data are reported for the mean min temp +/- AD, where AD is the classical average deviation. The results are: 1900-29, 280.5 +/- 1.5 K; 1930-89. 281.8 +/- 1.5 K; and 1990-2005, 283.1 +/- 1.5 K.

    The temperature jump of 1.3 K between the intervals is significantly different by the t-test (p less than 0.05). I compared the yearly means for each decadal interval on either side of the jump point using the t-test for unpaired data. I have no explanation for the long intervals of constant temperature for the 1900-29 and 1930-89 intervals. The total jump of 2.6 K applies only to this interval and not to the Spring, Summer and Winter intervals (i.e, 11 days centered on the soltice or equinox). I didn’t do a multi-decadal analysis on these intervals. However, I did compare the 1900-06 interval to the 2000-06 interval for min temperature for these four sampling intervals, but I still working on this for the max temp. I still have to do the multi-decadal analysis for the max temp for the FEI to see if the temp jumps occurs for this metric. So stayed tuned for more “hot” results from the Pierce Climate Research Center (aka the basement rec room!).

    Attn: Gavin! Is it OK to do a t-test on the yearly means for each decade when comparing two decades or do I have punch in 110 numbers (Groan!) for each data set? Please don’t say, “No!” BTW, I will send you hard copy when I get this project done.

  40. 90

    Is there a reason why Europeans are so shy in declaring 2 consecutive none winters? Surely something which was read about the medieval warm period, from my Euro contacts it was/is quite astounding. What is remarkable about 536 AD event is that it was reported in Europe, also recorded by trees in Arizona, a truly world wide phenomenon, an easier to explain climate event. With retrospect this past winter shows climate in its true esoteric nature. , as some contrarians are celebrating what they call an extremely cold winter, an end of a long spell of NH warming. Climate is not so simple, does not turn on an impredictable dime, it has many 3 dimensional facets transposed in a time morass.

  41. 91
    Arch Stanton says:

    Re J Hansford @ 81 wrote: “…No mechanisms explained… Nor for the 40’s until 70’s cooling period either…”

    No mechanism only if you have blinders on or refuse to look for it. The mechanism is likely simple. 1998 was an anomalously warm year due to ENSO. This year is shaping up to be anomalously cool, also likely to ENSO. Reasons like these are why “climate” is averaged over many years, and is not based on a cherry picked start date. Weren’t you talking about background noise a moment ago? And then you go on to cite a short cycle! The 40’s-70’s were explained by increasing fossil fuel sulfates and other aerosol particles at that time.

    Re J Hansford @ 81 wrote: “…Sunspot activity makes a better fit than does Athropogenic CO2…”

    Then why don’t we see a significant trace of an 11 year periodicity in global temperatures? Check out what temps were doing 11 years ago when we were at a similar place in our solar cycle. Temps were rising. What happened to your imaginary sunspot correlation? If you knew much about sunspots and the current (semi-popular in skeptical circles) theory of GCRs you would know that Svensmark would expect the exact opposite correlation that you seem to from the sunspot cycles. Funny thing…his expectations don’t seem to correlate with measured temps either….

  42. 92
    David B. Benson says:

    henry (86) — Even the super-eruption of Mt. Toba about 74–71 kya left sulfates in the stratosphere for only about 3, perhaps 6 years. Tambora (VEI 7) produced a single year without a summer.

    So to obtain eighteen months of effects, the hypothesized two or more eruptions need to be one right after the other, so to speak. But yes, this might be the best accounting for the observations that we can have, baring more evidence. Nicely thought out, thank you.

    The dating is via radiocarbon. Unless one eruption causes fires in the forests of the other, I fail to see how the datings could be confused.

  43. 93

    RE #78 & “65-70 metres is the highest retreat needed”

    About how long (how many decades or centuries) would it take in a worse case scenario for the sea to rise 60 meters? I need this info for a story I’m writing.

  44. 94
    Chris Golledge says:

    What I got from this article is that it reinforces my belief that the primary threat from climate change is in our ability to produce food; sea level rise and other effects are merely add-ons.

    Most people in the developed world have no idea how sensitive farming is to weather patterns, because they aren’t farmers. Farmers are pretty good at optimizing what they can get from the land under the weather patterns they have adapted to locally. Almost any difference from ‘normal’ weather patterns will result in less food production. The devil in climate change is not the periods of equilibrium at either end; it’s the period of instability in the middle.

    We’ve all become concerned about the price of fuel; we’ve no idea what it will be like when the price of a loaf of bread becomes a significant portion of your income. If you are reading this, you are affluent enough to afford a computer and an internet connection and that pretty much means that getting enough food is not a daily struggle for you.

    From a very broad term perspective, fossil fuel energy is merely solar energy that has been stored. In the long run, the earth’s people are limited to the energy coming into the system, and that means solar, or its derivatives, wind and wave. (Or possibly geothermal or fusion, that would last a blessed long time if we can ever get it figured out, but then there would be only food production and living space to limit our population and the end result of that doesn’t have a good feel to it either.) Solar energy will not sustain the current world population at the level required by our industrialized societies. Eventually, something will have to give; either the world population decreases or our energy consumption dramatically drops. With current and foreseeable technology, a dramatic drop in energy use would mean a lot of people die; there is connectivity there. It’s very close to a catch 22.

    Paranoia warning, read on at your own risk.

    Do you think that the current administration is all stupid? I don’t think so. Do you think that they are power hungry? I think almost all people who seek positions of authority are. Do you think that they weren’t aware a few years ago that a continued military presence in the middle east would likely cost them the coming election? They must have been aware of the risk. So, what really motivated the war(s) and has kept us there? I don’t know, but it had to be more important than ensuring the politicians’ positions of power. It wasn’t WMD and it wasn’t bringing democracy to the region. My prediction is that whoever wins the election will have access to information they currently don’t, and we will stay. Best guess: Whatever nation has control over the most (energy) resources will be at a significant advantage in the coming decades.

    “May you live in interesting times.” is a curse, not a blessing. There will be tanks and planes. I fear for my children’s future.

  45. 95
    Hank Roberts says:

    henry, I’m no expert, but looking quickly with terms I recall, there’s been a lot of work done identifying the chemicals and isotopes that can tell one layer of volcanic ash from another — they can be traced back to specific volcanos, by what’s in them, very often.

    This is quite an old cite but if you click the ‘citing sources’ link on the page it’ll lead you forward following other papers that referred to it, and you can see some of how this area of science developed:

  46. 96
    Jim Cross says:

    Volcanic Eruptions Cool the Earth – Yeah, We Knew That

    Regarding Henry’s post, I would be much more impressed if we could account for the Little Ice Age with volcanic events.

    This eruption I heard about through PBS (I think) a few years ago in a show on the Keys book. It’s nice the time scales on the ice cores can be lined up. Nevertheless, we are talking about a blip of few years of cooling.

    So this doesn’t amount to anything like disproving solar variation as a cause of some climate change as some posters have seemed to suggest.

  47. 97
    Cline Frasier says:

    The site is great and I enjoyed the post about the 534 anomaly. Unfortunately, the “(more)” link doesn’t work in Firefox 2. I was forced to use IE instead. For reasons I don’t understand, this comments feature doesn’t work in Firefox. My apologies for posting this here, but I couldn’t find anyplace else.

  48. 98
    Nigel Williams says:

    Lynn 93. Reading between the waves, Hansen is betting on multi-metre rise by 2100 – especially if we do BAU, and even if we do get back to 350ppm CO2 in the next few decades.

    I understand Greenland ice sheet is 8m of sea rise, West Antarctic is 7m rise gives a first round total of 15m. The other 55m comes from the rest of the Antarctic ice sheets plus glaciers etc. That gets us to around +70m above present high tide. After that there will be on-going thermal expansion of the ocean until we (oops we wont be here will we) until Mother Earth reaches thermal equilibrium. Probably (unless I am contradicted) +80m is a good number to look at for the new high tide mark. I believe if you are planning any sort of ‘sustainable’ structure you shouldn’t get closer than +100m, as the process of the coastal hills settling down to a natural angle of repose will take a while, and depending on slope will chew the cliff-edge back quite a way.

    How fast? Well emissions will slow a bit as we die off, but its unlikely we will get away with less than 450ppm CO2 as a peak because there will be a bit of a flurry of emission-related activity as we try and build our way to some sort of safe future using our existing infrastructure. Faint hope. But 450ppm and the combination of peak oil and peak food will see demand ease in say 50 years, and anything like BAU will see all the predicted social turmoil of climate and sea level rise refugees heading for the pie shop on the top of the hill. The rise will happen in a sine-wave style – slow at first (we’re seeing the beginning of the beginning now) increasing to a peak rate of change as we pass thru about +30 to +40m, and then slowing as the decreased volume of ice remaining contributes less per year.

    So if we get +5m by 2100 (perish the thought) then a sketch of 80m on a sine-like curve finds 5m at about 25% of the time (100 years), so peak at 50% (the next 100 years). So peak rate of rise is at around 2200CE, and then you are looking at maybe 5m in 20 years. Draw the curve yourself and see how it looks to you. If its less by 2100 (say only 2m) then that flattens and extends the whole thing. We hope. Since the tail will be due to the warming of the deep ocean the tail will be very long – millenia. So it will probably be C4000CE before coasts will start to settle down and develop, and once again shallow water shell fish, coastal spawning grounds and the like will begin to re-establish. In the intervening period the coastal waters will be a turgid mess of freshly eroded land swirling among rough bedrock and collapsing sea-cliffs. As the fishing reports say – it will definitely be ‘muddy and un-fishable’ for quite a while.

  49. 99
    Chris Colose says:


    As a follow up to Gavin’s response for further clarification, the tropopause has actually increased in height (See for example Santer et al, Science, 2003; 479-483). This reduces the stratosphere, and so you get much more cold air above you to radiate downward. If you did want to confine an “Effective radiating level” to a single altitude though, it would be much lower than the tropo-strato boundary anyway. If you increase the height of the effective radiating level, you extrapolate along a greater distance using the appropriate adiabiat and the surface is warmer.

  50. 100
    Meltwater says:

    in #93 Lynn Vincentnathan said:

    About how long (how many decades or centuries) would it take in a worse case scenario for the sea to rise 60 meters? I need this info for a story I’m writing.

    During the sort of interglacial period that we currently inhabit, if the Eemian example MIS-5e is any guide, 2°C suffices to raise global sea level for the next hundred years and many centuries to come by an average of 1.6 meters, or about 5 feet, per century. That may be the best case that we can, on average, expect. During MIS-5e, some centuries suffered a sea rise rate higher than average, others a lower; a few centuries knew some stability or even a sea level drop.

    The worst sea rise rate I can recall seeing in studies of paleoclimate is 5m per century but such a rapid rate has never been sustained for more than two centuries as far as I know. However, the worst-case total sea rise may be worse than you think, closer to 80 meters than 60. Either way, getting there at the 1.6m rate would obviously take a few thousand years. Hope that helps!

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