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Arctic Sea Ice Hockey Stick: Melt Unprecedented in Last 1,450 years

Posted on 24 November 2011 by Rob Painting

Many climate change "skeptics" obsess over the 'hockey stick', and their discussion inevitably leads back to 1998, when climate scientist Michael Mann first published his paper indicating that current global warming was anomalous in the last 1000 years or so. In plain language, Mann's work suggested that current warming was likely due to mankind's carbon dioxide pollution, not any as-yet-unidentified, or yet-to-be-discovered or observed natural phenomenon.

Despite the "skeptics" cherry-picked focus on a  peer-reviewed paper more than a decade old, the science has moved on considerably since then. Paper after paper has basically affirmed that current warming is outside the bounds of natural variation, and therefore likely due to human activities. For example we have seen a sea level hockey stick, an underwater hockey stick, a South American hockey stick, an Arctic summer temperature hockey stick, a tropical glacier hockey stick, a North American mountain snowpack hockey stick, a glacier length hockey stick, and warming of Atlantic water into the Arctic hockey stick

Into this league of hockey sticks, we have a just published scientific paper, (Kinnard [2011]), which shows that the Arctic sea ice retreat is also a hockey stick, and that the present rate of melt in the Arctic summer is unprecedented in the last 1,450 years. See figure 1. (Note that the hockey stick blade is facing down in this reconstruction).

Building a hockey stick

Because Arctic sea ice is influenced by both air and water temperatures, the study authors use a combination of Arctic ice core, tree-ring and lake sediments to reconstruct Arctic conditions over the last 2,000 years. As is often the case with these proxy reconstructions, the authors found the error bars in the reconstruction (the uncertainty) increased further back in time, due to a decreasing number of proxy records, and was not useful past 1,450 years ago. 

When compared (validated) against historical sea ice observations it was found that the reconstruction not only had a dominant temperature-related signal, but that the proxy-based reconstruction also had a second signal which corresponded with variations in sea ice cover (extent), therefore confirming the 2nd network signal was a proxy for Arctic sea ice cover (as shown in figure 1).  

Clearly there are periods in the reconstruction where rapid rates of ice loss occurred, but what stands out is that the length and rate of present day melt is unprecedented in the entire 1,450 year-long reconstruction. This is consistent with the Arctic summer temperature hockey stick (Kaufman [2009]) and warming of Atlantic water into the Arctic hockey stick (Spielhagen [2011]).

Arctic summer sea ice: going, going............ 

2011 saw the 2nd lowest summer sea ice extent on record (after 2007), and even more dramatically,  this year saw the lowest ever recorded volume of Arctic summer sea ice. 

This latest 'hockey stick' not only reinforces that current conditions in the Arctic are much warmer than the so-called Medieval Warm Period, but that sea ice is currently disappearing at a sustained speed that is unmatched in the last 1,450 years. 

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Comments 1 to 50 out of 59:

  1. The "Ice Hockey Stick." Startling stuff but are we truly surprised?
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  2. The BEST confirmations, Climategate 2.0 looking like a squib, and now yet another bloody Hockey Stick!

    Not looking to be such a festive season for some, is it? ;-)
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  3. WUWT claims that "during the peak of MWP glaciers were smaller than today" found here does not apply to arctic with very high certainty.
    Interesting to note, that on the graph above, arctic ice looks on average larger during peak WMP (1000-1300AD) rather than for LIA (1550-1850AD), although probably not statistically signifficant. Still, from that observation with counter-intuitive outcome, we can say that both MWP and LIA were local events while arctic ice could have enjoyed different conditions.
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  4. Yes, I was surprised. I had it in my head that there was real evidence of Greenland being significantly warmer at some point during the MCA, although the effect was localised. Does this mean that it was sufficiently localised not to cover the arctic too, or is my recollection wrong?
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  5. Kevin C - This global map is from Mann (2009) and is compared to a 1961-1990 baseline.



    Much of the present summer sea ice retreat seems to be from warm Atlantic water moving into the Arctic and getting at the ice from below. There's simply much, much more warm water available in the Atlantic today. Both Kinnard (2011) and Spielhagen (2011) show this anomalous ocean warming.
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  6. As usual: "shortcuts" (even for the post - definitely “too big”).

    If the authors in the abstract of their work they put such a statement : „... although extensive uncertainties remain, especially before the sixteenth century ...” It is worth mentioning … although.

    Of course, the authors mainly say that: „...both the duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years.” but they add that there are doubts - the margin of error.

    “... and may result from nonlinear feedbacks between sea ice and the Atlantic meridional overturning circulation. These results reinforce the assertion that sea ice is an active component of Arctic climate variability and that the recent decrease in summer Arctic sea ice is consistent with anthropogenically forced warming.” - write Kinnard et al. 2011. Granted, with the addition that this is not limited to: „recent decrease” and „anthropogenically forced warming.”

    Kaufman et al., 2009 argued that: in the period between 5600 and 3600 years BP (0 BP = calendar year 1950) energy flows in summer (JJA) at 65°N was reduced by 7.1 W • m-2 - demonstrating the fundamental role orbital factor in creating the natural decreasing trend in Arctic temperatures. The Earth now began to "orbit" closest to the Sun during the year in January - instead of in September as it did 7 thousand. years ago ... So for the past thousands of years in the summer months, gradually decreased the intensity of sunlight “arriving” at the Arctic. Summer Arctic became cooler at a rate of 0.2°C per thousand years.

    It should be noted however that this trend was many times interrupted for 200 years and even 400 years (by the trend positive) just through: „... nonlinear feedbacks between sea ice and the Atlantic meridional overturning circulation ...” - changes in amount of heat transported to the Arctic along Atlantic waters. We do not know precisely reasons for these historic natural disturbances. Spielhagen et al., 2011.: “Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years.”

    "Disturbances" trend can be so natural, and the current unprecedented "disturbance" questionable. The Kaufman “unprecedented” - it was one of the biggest disputes in science in recent years.
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    Response:

    [DB] The prudent reader will note that in this discussion of Arctic Sea Ice (being by definition at sea level) Arkadiusz introduces a common "skeptic trick"/technique of introducing data from a local ice core in Greenland to "muddy the waters".  The issue, beyond the core data representing but a single geospacial location and thus by itself not representative of the whole (and much larger) region in which it resides, is that the core is near the Greenland summit (in order to get the deepest profile of the ice possible) and therefore at an elevation of over 2 miles above sea level.

    Permissum lector caveo (let the reader beware)...

  7. Kevin C - I suspect that your recollection is wrong, or, at least, misleading.

    The narrative we remember for the Viking Greenland settlements goes "The Vikings farmed Greenland, therefore it must have been much warmer. Later the settlements got buried under glaciers."

    The first part of that is correct, but the rest of the narrative is wrong.

    They did farm, but they farmed in two settlements in limited coastal fringes, and it was worse-than-subsistence farming (because the farming and building eroded the fragile top-soil). The same sort of farming seems to have been possible for much of the intervening time, therefore the farming cannot be taken as direct evidence of warmer conditions.
    The Viking settlements did not get buried under glaciers (google Hvalsey Church). One got burried under wind-blown sand. Thus the failure of the settlements cannot be taken as direct evidence of cooler conditions.
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  8. Arkadiusz Semczyszak - I know it's the language barrier, but I always find it hard to figure out what you're on about. But I'll have a stab at it.

    - Error bars. That's the large guava-coloured area in figure 1. Notice how it enlarges the further back in time one goes?

    - Kinnard (2011) state: "These results reinforce the assertion that sea ice is an active component of Arctic climate variability and that the recent decrease in summer Arctic sea ice is consistent with anthropogenically (human-caused) forced warming"

    - Kaufman (2009). Yup, orbital factors saw a decline in Arctic summer temperatures from the Holocene Climatic Optimum onwards, until humans started burning fossil fuels like crazy.

    Spielhagen (2011) state: "We find that early–21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming."
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  9. Thanks Rob: That was the information I was after.

    AnotherBee: Thanks for clarifying the distinction between the mythical warm Greenland and the real one. The version in my head was much closer to the real one, but given how these myths propogate I should have been more precise in my question. So your comment was well made.
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  10. For me, work Kinnard (2011) only authorizes them to this conclusion: “Our reconstructed warming of ~2°C since the LIA matches the reported temperature increase of the Arctic Atlantic Water Layer (AAWL), obtained from observational data of the past ~120 years (21) (Fig. 3C). At present, there are no subcentennial-scale open ocean proxy data series available to document the temperature evolution of AAWL in the Arctic Ocean proper in the preceding two millennia.” and: “Although we cannot quantify from our data the variability of previous AW inflow to the Arctic by volume, our temperature data series and the above observational link suggest that the modern warm AW inflow (averaged over two to three decades) is anomalous and unique in the past 2000 years and not just the latest in a series of natural multidecadal oscillations.”

    And what of the “millennium oscillations”?

    Without these data (first citation) - how can so much speculation:

    "We know that the Arctic is the most sensitive region on the Earth when it comes to warming, but there has been some question about how unusual the current Arctic warming is compared to the natural variability of the last thousand years," said Marchitto, also an associate professor in CU-Boulder's geological sciences department. "We found that modern Fram Strait water temperatures are well outside the natural bounds."

    I think I wrote a clear and without errors ...
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  11. Kevin C,

    It was warmer than present in Greenland during the MWP according to Kobashi et al. 2011 (includes Jason Box).

    Around 1100 AD it was warmer than present for most of a 50 year period and then around ~700 AD it was significantly warmer than present for ~100 years. (More than 1°C for most and 2°C warmer for a short period) (Nearly the difference from present to the LIA in Greenland).
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    Response:

    [DB] An open copy may be found here:

    http://www.leif.org/EOS/2011GL049444.pdf

    Section 5.3 is relevant to this discussion.

  12. I have a question - was the original figure in Monckton Pink or did you recreate it that way? ;)

    Happy Thanksgiving to all here who celebrate it.
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    Response: [JC] It's the original colour. So "Monckton pink" is the official term for it now, is it?
  13. That's some dramatic graph.
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  14. #11, Robert Way,

    The paper refers to snow temperature of Greenland only, not to the global average temperature.

    Unofortunately, the period you mention ~700 AD is outside the range generally considered to the be the Medieval Warm Period - that is taken to be 950-1150, a period when the snow temperature is shown to be about the same as the present. Viking settlement in Greenland began only after 900 AD, so these may not have had the advantage of a warmer climate usually assumed, and the "MWP" kinda vanishes.

    In fact, before the Vikings, Greenland had been settled by an Inuit-related people known as the Dorset people. Perhaps they left because of climate conditions, but that does not sound right for a Inuit-related better-adapted people than the Vikings.

    The paper is interesting and should repay further comparative study. However, it raises as many questions as it answers.
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  15. Concerning the Arctic zone, I recall some research suggested there could have been less or equivalent sea ice than now in the early Holocene, because of regional orbital forcing (for example this EOS 2006 paper ). But theses conditions have disappeared since mid-Holocene (for example Polyak 2010 conclusion : "This [recent modern period] ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities").

    Rob Painting #5 : the point is unclear for me. On this Mann MCA / present comparison, part of the North Atlantic basin seems warmer too during Medieval period, so isn't it sufficient for the advection of heat water you refer to?
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  16. Rob Painting : «In plain language, Mann's work suggested that current warming was likely due to mankind's carbon dioxide pollution, not any as-yet-unidentified, or yet-to-be-discovered or observed natural phenomenon»

    Beside the political hype, I suggest there are two debates in the Hockey Stick(s) : one is an immediate (often mediatic) interest for ‘record’, another is the scientific interest for natural variability (forced and unforced). That is to say : if you reconstruct a multicentennial variability in pre-industrial period with ±0,2K variation, it will not have the same implication for model that if you get a ±0,8 K variation (and that, whatever your variation for 1950-2010, very likely due to GHG). The second reconstruction would imply a higher sensitivity to forcings and/or a higher low frequency variation in the surface distribution of heat due to atmosphere-ocean coupling. I think modellers need to precise these points so as to refine detection-attribution studies or to better constrain their 'control runs' without anthropogenic forcing. At least, it is the way I interpret the most interesting part of this ‘controversy’... but maybe it is a bad interpretation!
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  17. Chriscoz @3,

    "WUWT claims that "during the peak of MWP glaciers were smaller than today""

    Well of course they would float that red herring. I'm not sure to which glaciers they are referring to. But as you say it does not apply to the Arctic. A new paper has also just been published on the Canadian Arctic glaciers by Fisher et al. (2011). They conclude:

    "Arctic ice core melt series (latitude range of 67 to 81 N) show the last quarter century has seen the highest melt in two millennia and The Holocene-long Agassiz melt record shows the last 25 years has the highest melt in 4200 years. The Agassiz melt rates since the middle 1990s resemble those of the early Holocene thermal maximum over 9000 years ago."

    Add to that the rapid loss of ice shelves in the Canadian Arctic that were buttressing glaciers, and we have quite the spate of bad news, and this is relatively early days of the Anthropocene.
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  18. "Unprecedented melting in 1450 years--" am I the only one who recalls the 1500-year warming-cycle?

    http://www.ncpa.org/pub/st279

    "The Earth currently is experiencing a warming trend, but there is scientific evidence that human activities have little to do with it. Instead, the warming seems to be part of a 1,500-year cycle (plus or minus 500 years) of moderate temperature swings."
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    Response:

    [DB] "am I the only one who recalls the 1500-year warming-cycle?"

    Apparently you're one who doesn't remember the debunking of that particular meme, here:

    It's a 1500 year cycle

    The prudent reader will take note of the source of "Truth"AtLast's linked blog piece, the National Center for Policy analysis, a Washington, DC-based "think tank", has produced such memorable pieces as:

    How the Rise of Trendy Environmentalism is Harming the Environment

    A Rough Week for Climate Change Myths

    U.S. Press AWOL on Climate Skepticism

    Climate Models Fail, AGAIN!

    The spin is palpable; the "truth", lacking.

  19. Here is a nice story from Hubert Lamb's ”Climate, History and the Modern World” (2nd ed 1995):
    ”For it is recorded in the Landnámabók, a book written in Iceland about 1125 cataloguing the settlement of Iceland a couple of centuries earlier and describing the Old Norse settlement of Greenland between AD 985 and 1000, that one of the first Greenland settlers, Thorkel Farserk, a cousin of Erik the Red who founded the colony, having no serviceable boat at hand, swam out across Hvalseyjarfjord to fetch a full-grown sheep from the island of Hvalsey and carry it home to entertain his cousin. The distance was well over two miles. Dr L.G.C.E.Pugh of the Medical Research Laboratories, Hampstead, has given his opinion, from studies of the endurance of Channel swimmers and others undertaking similar exploits, that 10 °C would be about the lowest temperature at which a strong person, even if fat, not specially trained for long-distance swimming, could swim the distance mentioned. As the average temperatures in the fjords of that coast in August in modern times have seldom exceeded 6 °C (+3 to +6 °C being more typical), it seems that the water must have been at least 4 °C warmer than this limit in the year in which Thorkel swam it and brought home his sheep.”
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  20. Lars#19: "it seems that the water must have been at least 4 °C warmer than this limit in the year in which Thorkel swam it"

    Yes, it would seem that particular day must have been unusually warm. Why would that one anecdotal incident have any bearing on annual averages and climate change?
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  21. Lars,

    Interesting story, however I don't think historical anecdotal evidence and opinion is proof that the seas around Greenland were 4oC warmer than today. I think I'll stick to getting my information from Scientists.

    Also I think this guy might disagree with DR Pugh Ice Man.
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  22. TruthAtLast, why would you get your information from a political advocacy think tank?

    Singer and Avery are making a rather strained attempt at using D.O. events to try exculpate CO2, which is the only thing they ever try to do, in spite of all scientific evidence against the gas. I'm not sure what exactly the content of the whole book is and I will not waste my time on it. This has been discussed many times on SkS. There has not been a D.O. event in over 20K years. Their modern equivalent, Bond events show only loose correlation with climate changes; the last known Bond even is believed to have occurred approximately 1400 years ago. Since the postulated periodicity of the oscillation is 1470 yrs we should be due for one now. Note that these are Northern hemisphere cold events.

    Nice story Lars, how can we tell whether it's true? I tend to be skeptical by nature, especially of people bragging.
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  23. Truth @18,

    Hang on, I though it was a 60 year cycle? Or is that an 11 year cycle? Those who deny the reality and theory of AGW and try to wish away reality love to talk about cycles. In my post @17 I link to work by Fisher et al. (2011) that shows the ice caps in the Canadian Arctic are at their lowest levels in at least 4200 years. Is there a 4200 year cycle? I'm sure one could ferrit one out with enough curve fitting.

    Polyak et al. (2010) found that the sea ice extent in the Arctic basin is currently at its lowest levels in 2000 years. Is there a 2000 year cycle?

    And if these cycles are true, then the Arctic sea ice should start recovering any year now. but that is not what the data show, they show an accelerating rate of loss.


    [Source]
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  24. TruthAtLast #18, Watch this, and try to pay attention.
    http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=385x275077
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  25. "WUWT claims that "during the peak of MWP glaciers were smaller than today""

    Wouldnt apply to any Southern Hemisphere glacier that I am aware of. Of course LIA wasnt particularly pronounced in SH.
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  26. skept.fr @ 15 - "Rob Painting #5 : the point is unclear for me. On this Mann MCA / present comparison, part of the North Atlantic basin seems warmer too during Medieval period, so isn't it sufficient for the advection of heat water you refer to?"

    I think you will notice that the reconstruction in Mann (2009) reveals a very localized patch of ocean warming in the North Atlantic. The overwhelming majority of the ocean during medieval times was cooler than the 1961-1990 baseline, especially the rest of the Atlantic.

    This is just consequence of the two very different processes operating between the two intervals. We know elevated CO2 levels were not responsible for the medieval climate, but today we have levels of atmospheric CO2 not seen for perhaps as long as 20 million years. This is crucial because elevated greenhouse gases, such as CO2, trap more heat in the ocean on a global scale. Therefore ocean heat content today is much higher than medieval times - there is simply more of it in the Atlantic today to melt the Arctic sea ice.

    Take a gander at Lee (2011) - What caused the significant increase in Atlantic Ocean heat content since the mid‐20th century?, particularly figure 1(a) and (b).

    As discussed in an earlier SkS post, the MWP seems to have been a re-organization of the global climate. Despite the localized warming aroung Greenland, the global mean background state was much cooler than today.
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  27. Lars #19 : Interesting. As you know, Lamb coined the terme ‘medieval warm period’ in his famous 1965 paper. Historical climatology, that is reconstruction of past climates by historical archives rather than physical or chemical proxy-based analysis, has known many evolution since the founding works in the 1960s, 1970s and 1980s. In particular, Lamb has been criticized by some researchers because of the scarcity of records, the poorness of their historiographic interpretation and the inherent difficulty of statistic extrapolations to large area. (A French book from a PhD thesis had been devoted to that re-evaluation of Lamb’s work, Alexandre P, 1987, Le climat au Moyen Âge, EHESS ; see also Hughes et Diaz 1994 for the re-analysis of previous MWP studies.) The story of Thorkel Farserk, cousin of Erik the Red, is typical of these uncertain records used in the first generation of historical climatology : one event in one season in one year, a possibly ‘pretyffied’ story (it has been suggested by Viking specialists that Erik the Red an co-founders were good propagandists for settlement in the new and ‘green’ land), etc. All that is too imprecise to infer a mean seasonal or annual temperature for whole Greenland, and of course for the whole Arctic circle (recall that we are speaking of sea-ice extent, not the Southern coast of Greenland).

    Anyway, it seems that Europe, and particularly Northern Europe, have known warm summer conditions one millenia ago. For example this work of Goosse et el 2006 ('al' including M. Mann) : ‘Proxy records and results of a three dimensional climate model show that European summer temperatures roughly a millennium ago were comparable to those of the last 25 years of the 20th century, supporting the existence of a summer “Medieval Warm Period” in Europe.’
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  28. Rob Painting : thanks for explanations, but '404 Error File Not Found' for the Lee 2011 reference.
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  29. Skep @28,

    Here you go.
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  30. Bugger, left out a quotation mark. Now fixed.
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  31. @18 TruthAtLast:

    Nope, the 1500 year (+/- 500 years!) only holds in ice cores from the Northern Hemisphere, while the opposite pattern is seen in the Southern Hemisphere. In other words, it's a polar see-saw, not global warming. They're called Dansgaard-Oeschger events.
    Today, both hemispheres are warming.
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  32. Lars #19, I'd be very careful about quoting events from Landnamabok or other Icelandic sagas as if they are perfect historical records. Undoubtedly they often contain a grain of truth, and many events, such as the settlement of Greenland clearly happened much as weere told, but individual events may have some storytelling alteration. Add to that, in this case, the story was written down a century after it was supposed to have happened. Fancy trusting exactly what happened in a single event to your great-great-grandfather around the death of Queen Victoria?

    There's a story from the sagas, which I'll paraphrase, of two wizards who lived on the south coast of Iceland and lived on opposite sides of a river coming down from the mountain. They have a dispute, and one, who is blind, is told by his servant that the other wizard has sent the sea rising in flood across his land. He asks his servant to bring him a cup of the water - it is not salty - so the wizard realises the flood is from the mountain, not the sea. He goes and commands the floodwaters to leave his lands and flow down onto his enemy's lands. Their dispute continues, each sending floods down from the mountain onto each other.

    The place in south Iceland really exists, there are deep jökulhlaup flood channels in the mountain-side either side of the Sólheimá river, and there are well-dated flood deposits of about the right age (soon after Settlement of Iceland) that spread into the fields of the early farms. The mountain is the volcano Katla, covered by the Mýrdalsjökull ice cap, which has erupted on average every 50 years throughout Icelandic history. But do you literally believe that wizards moved the waters about? Of course not! Maybe the guy did swim the fjord to get his sheep - there's video of the 'ice man' swimming in the glacier lagoon Jokulsarlón too - or maybe the story got altered a bit in the retelling a century later. I certainly would not want to estimate a water temperature from a single story 1000 years ago written down 100 years after it was told!
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  33. Not to be pedant skept.fr but I believe that the quality of being poor, outside of the financial sense, is called paucity (not poorness). Also I'm not so sure about the historiographic adjective. Not trying to diminish your post but, although I'm sure everyone got your point, good language does help comprehension. Interesting references.
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  34. Philippe : oh yes, sorry, not an English-native, I'm confused! For 'historiographic', it refers of course to historiography as methodological discussion about the validity of sources. Historical records nead a special treatment from comparatists (historians) so as to evaluate their quality, ie their level of 'truth' and 'alteration' as skywatcher noted it. But Lamb was a climatologist, not an historian, so he tended to use unselectively the historical records. This point has been criticized by Emmanuel Le Roy Ladurie (French historian of climate, not climatologist) and Philippe Alexandre. This is the birth context of the 'Medieval Warm Period' context, in the 1960s.
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  35. Hem, not better (!), read for the last sentence : "This is the birth context of the 'Medieval Warm Period' context concept, in the 1960s".
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  36. Actually, on reading my copy of Jared Diamond's book "collapse", there is very strong evidence to suggest that the Greenland Colony was always close to collapse, with supplies from Norway being frequently required to keep it going. Of course, once the LIA hit, said supplies could no longer arrive as frequently-which caused the colony to finally collapse.
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  37. As someone whose background is both historiography and history I'm surprised that Viking colonisation of Greenland is considerred to in any way significant to climate history.
    Eric the Red chose the name "Greenland" for marketing purposes in order to attract settlers rather than as an accurate description of the place he had spent three years exploring.
    The failure of the Viking settlement on Iceland is held as an example of how failure to adapt agricultural practices to suit local conditions will doom colonists to failure.

    Similar examples of such failure to plan a colony and fail to adapt to local conditions can be found in British and French colonial failures in continental North America. Again, climate change is not a factor in these failures.

    From an historian's perspective the failure of Viking settlement in Greenland is an entirely seperate subjuect to climate history.
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  38. Clarification to my last posting.
    The effect of climate change on the Norse Greenland colony may have been that expanding sea-ice made communication between Greenland and Scandinavia more difficult.
    However this has little if any bearing on the fact that the colony failed due using inappropriate agricultural practices for Greenland conditions.
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  39. Interestingly, in the Kinnard 2011 paper, there is nothing but a little uwpard trend of sea-ice extent during the usual core 'MWP' 900-1200. And the sharpest decline before the 1950-2010 condition occured... during the LIA. From the authors : 'The pronounced decrease in ice cover observed in both our terrestrial and oceanic proxy-based reconstructions between the late fifteenth and early seventeenth centuries occurred during the widespread cooling period known as the Little Ice Age (about ad 1450–1850 (ref. 18)). Reconstructed Arctic SATs show episodes of warming during this period (Fig. 3f), but according to our results the decrease in Arctic sea ice extent during the Little Ice Age was more pronounced than during the earlier Medieval Warm Optimum.'
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  40. Well, I must admit I had heard every denier argument, but Lars @ #19 has produced the best one ever!!

    So the cousin of Erik the Red swam over two miles through Greenland waters and then swam back, carrying a full grown sheep. And that's your argument against climate change and for the MWP?? What is this, Poe's Law?

    If you believe that either happened or is even possible, I have a nice bridge to sell you.
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  41. skept.fr @39 and mandas @40
    Agreed. Denialist arguments about the MWP consistantly fail upon examination and are greatly overstated in both extent and consequence.
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  42. Albatross @23

    If there was a climate cycle, there is no reason why we should be near the top of the climate cycle and about to go into a cooling phase any year. It could be a 4500 year climate cycle that we are 300 years away from peaking in.

    But it seems a curious element of 'skeptic' psychology that no matter what cycle is proposed we are always nearly at the peak of the cycle and it is always predicted that temperatures will cool any year, or have been cooling since 1998/2002/etc.
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  43. Marcus and Stevo #36-38, it's worth noting that the settlers on Greenland did very well for 400 years, and successfully adapted to climate change during their time there (onset of LIA). Their diet went from mostly terrestrial to 80% marine (Arneborg et al, you can tell from the isotopic composition of their bones) as they changed their diet to be mostly seals. So it wasn't a failure of their agriculture that killed them. It's fair to say it wasn't the cold alone that killed 'em (Diamond is out of date), could also be conflict with the Inuit, world economics and politics, disease, or some unholy mix of the lot. But failure to adapt is not something you can easily accuse them of, given what is now known from the archaeology.
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  44. skywatcher @43
    I concede to your point about surviving for about four centuries, but am not so sure I'd agree that they did "very well". We don't know how long they were in decline and thus we don't know how long they were hovering on or just below subsistance levels.
    True, the encroachment of the Inuit Thule culture was a major factor and one wonders whether competition for resources escalated to outright warfare. I expect the collapse of bow head whale resources was a result of increased competition for the same resource pool but admit that is just speculation.

    In any case, rather than lead this thread off topic, I see from your list of possible causes for the failure of the settlements we agree about what is relevant to AGW science. The failure of Norse Greenland cannot simply be sheeted home to MWP or LIA.
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  45. So far as I know, speculation about their level of subsistence prior to the eventual collapse is no more than speculation, and they were trading with Europe for a considerable portion of that time. They were there for a long time for the walrus ivory, not just to scratch out the barest existence imaginable, and lived in climate conditions comparable to some of those in parts of Iceland or Norway. But indeed that's for another day, we quite agree that it is utterly irrelevant for the topic and for AGW in general, despite skeptics suggesting otherwise!
    0 0
  46. Mandas and others, The silly story about Erik the Red came from Hubert Lamb, first director of CRU and the man behind the MWP concept. That Lamb used it shows the primitive state of temperature reconstructions just a generation ago.
    0 0
    Response:

    [DB] "The silly story about Erik the Red came from Hubert Lamb"

    Then you will certainly have no problem furnishing a link to support your Hubert Lamb claim.  If he did indeed use it, then you will have to furnish also the context in which he used it and then demonstrate why that is relevant to this thread.  Else you are being silly and off-topic and therefore this comment will be deleted.

    "That Lamb used it shows the primitive state of temperature reconstructions just a generation ago."

    This is certainly an unsupported, subjective and indeed off-topic comment.  Other comments exist here on models and their qualitative states.  The Search function will reveal many.  Continue this line of reasoning there, not here where it is off-topic.

  47. „... language barrier ...”

    ... of course yes - but only the “language of statistics”.

    The standard deviation is huge for the whole range of variation described by proxy - to the nineteenth century. For this we must add: „...extensive uncertainties remain, especially before the sixteenth century ...”

    For those who are “convinced” of the compatibility of temperature changes in the Arctic with the estimated GHGs forcing - in comparison - another forcing:
    Chung and Räisänen 2011 : Implications: “Since GHG forcing is well established, the problem is likely in how the models treat aerosol effects. In this scenario, the real aerosol forcing might be significantly positive in the Arctic and significantly negative outside of the Arctic, while the models miss this feature entirely.”
    0 0
    Response:

    [DB] And with this you are back to your long-established practice of cherry-picking quotes, as Tom notes below in comment 49.  The practice for which you have been cautioned and warned against ad nauseum.  And which you have ackowleged with the intent to do better.  Yet here we are.

    Language barriers are no longer an excuse, as this behavior is demonstrably willful.  No more.

  48. (-Snip-)

    None of the cited work does not settle here finally - objectively - last question - in this lengthy (sorry) quotation.
    My “alleged” - a typical “trick for skeptics” - "cherry picking" - use absolutely all the authors cited papers. Their subjective views on AGW have too much influence on the results - conclusions.
    0 0
    Response:

    [DB] Tom again deconstructs your continued cherry-picking in comment 50 and its irrelevance below.

    Extensive block-quoting (from the Kobashi paper discussed earlier in this thread) without appropriate context snipped.

  49. Arkadiuz Semczyszak @47, quotes from Chung and Räisänen 2011. However the full paragraph from which he quotes read:

    "If the models simulate climate feedbacks correctly, the indication is that models have significantly incorrect climate forcing. Since GHG forcing is well established, the problem is likely in how the models treat aerosol effects. In this scenario, the real aerosol forcing might be significantly positive in the Arctic and significantly negative outside of the Arctic, while the models miss this feature entirely."


    Clearly the conditional statement which Arkadiusz omitted is crucial to the meaning of the authors. In fact they are presenting one of three possibilities which their study is unable to distinguish between - the other two being that tropical feedbacks are overestimated, and that arctic feedbacks are underestimated. By omitting the conditional, Arkadiusz has quoted a conditional as a firm conclusion of the study.

    In fact, a recent study, Flanner et al, 2011, already finds evidence that the third option (which Arkudiusz misquotation conceals) of greater than predicted feedbacks is what is driving the unexpectedly rapid arctic melt:

    "Hemisphere forcing at −4.6 to −2.2 W m−2, with a peak in May of −9.0±2.7 W m−2. We find that cyrospheric cooling declined by 0.45 W m−2 from 1979 to 2008, with nearly equal contributions from changes in land snow cover and sea ice. On the basis of these observations, we conclude that the albedo feedback from the Northern Hemisphere cryosphere falls between 0.3 and 1.1 W m−2 K−1, substantially larger than comparable estimates obtained from 18 climate models."

    (My emphasis, see here for discussion on SkS)

    Taken together with Chung and Räisänen 2011, this suggests that models tend to underestimate climate sensitivity as Chung and Räisänen indicate.
    0 0
  50. With great irony, I have just finished a post that establishes yet another of Arkuiusz' frequent misquotations to find him claiming that he is falsely accused of cherry picking. Of course, deliberate misquotation is just another form of cherry picking (and a particularly deceitful form of it). So, having given us yet another example of cherry picking, he then denies that he practices that vise in the very next post.

    As I said, very ironic.

    More relevantly, Arkadiusz' 48 is in fact irrelevant to this topic, and he has kindly highlighted for us the reason why it is irrelevant.
    0 0

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