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Volcanic Influence on the Little Ice Age

Posted on 8 February 2012 by dana1981

The causes and even start and duration of the Little Ice Age (LIA), a global cooling event of approximately 0.5°C over several centuries ending in the late 19th Century, has been a challenge for climate scientists to pin down, with many possible contributing factors.  A very interesting new paper by Miller et al. (2012) seeks to answer these questions by simulating the climate response to a number of large volcanic eruptions during the LIA timeframe.  As the authors note, the challenge lies not only in determining the cause of the LIA, but when the event even started:

"...the natural radiative forcings are either weak or, in the case of explosive volcanism, shortlived [Robock, 2000], thus requiring substantial internal feedback. The LIA is particularly enigmatic. Despite extensive historical documentation and a wide array of proxy records that define climate change during the past millennium [Mann et al., 2008], there is no clear consensus on the timing, duration, or controlling mechanisms of the LIA."

A similar paper, Anderson et al. (2008), was previously discussed here.

The Data

Miller et al. used precisely-dated records of ice-cap growth from Arctic Canada and Iceland in their attempt to assess the timing and duration of the LIA.  The ice caps exhibit little or no flow, and thus preserve rooted tundra vegetation that was alive at the time of ice-cap expansion.  This enabled the scientists to use carbon dating on the vegetation.  This process accurately dates the time when snowline dropped below the vegetation altitude, killing the plants, and remained on average below that site until the summer warmth of recent decades.  The locations from which Miller et al. gathered vegetation samples are illustrated in Figure 1.

Figure 1

Figure 1: Arctic Canada sites with recently exposed entombed plants dated younger than 800 AD (circles) and older than 800 AD (triangles); Hvítárvatn, Iceland (square); Greenland temperature borehole site and sea ice record on the North Iceland shelf (round).

LIA Begins

The Miller et al. probability distribution function (PDF) and large number of vegetation klll dates toward the end of the 13th Century suggest that the LIA may have been triggered at this time, which is generally earlier than the LIA was previously thought to have begun.

"Discrete peaks in the composite PDF define widespread abrupt summer cooling events that resulted in a persistent snowline depression, allowing the expansion of ice caps over sites that did not subsequently become ice-free until the most recent decade. The cluster of kill-dates between 1275 and 1300 AD, following 300 years with few kill dates, defines an abrupt summer temperature decrease in the late 13th Century."

Figure 2, particularly frames b and c, illustrate the ice-cap growth at the end of the 13th Century, coinciding with an increase in atmospheric aerosols due to a period of high volcanic activity caused by four closely-spaced volcanic eruptions.

"The PDF [probability distribution function] peak defining abrupt LIA cooling 1275–1300 AD coincides with an interval of four large stratospheric sulfur loadings from explosive volcanism following a multi-centennial warm interval, during which complete revegetation of deglaciated sites would have fully reset the radiocarbon clock (Figure 2c)."

Fig 2

Figure 2: (a) Total solar irradiance (VSK [Schmidt et al., 2011]). (b) Global stratospheric sulfate aerosol loadings [Gao et al., 2008]. (c) Ice cap expansion dates based on a composite of 94 Arctic Canada calibrated 14C PDFs. (d) 30-year running mean varve thickness in Hvítárvatn sediment core HVT03-2 [Larsen et al., 2011]. (e) Arctic Ocean sea ice recorded in a sediment core on the north Iceland shelf [Massé et al., 2008]; heavy sea ice years correlate with anomalously cold summers across Iceland. (f) Temperature anomalies over southern Greenland (wrt 1881–1980 AD mean) from the borehole temperature inversion at DYE-3 [Dahl-Jensen et al., 1998].

The peaks shown in Figure 2c define widespread abrupt summer cooling events that resulted in a persistent snowline depression, allowing the expansion of ice caps over sites that did not subsequently become ice-free until recent years.

Feedbacks

A difficulty in attributing the LIA cooling to volcanic eruptions is that aerosols have a short residence time in the atmosphere, generally being washed out after just a year or two.  If spaced relatively close together, volcanic eruptions can have a cooling effect over the span of a few decades, but the LIA was a much longer event.

"Decadally paced eruptions may produce greater cooling than a single large eruption if the recurrence interval is shorter than the upper ocean temperature relaxation time of decades [Schneider et al., 2009]. This may explain multidecadal cold episodes, but many Canadian sites that became ice-covered ~1275 AD and ~1450 AD, following episodes of strong explosive volcanism, remained continuously ice-covered until the most recent decade (Figure 2c)."

Thus in order to explain a long-term cooling like the LIA, the volcanic eruptions must trigger certain feedback effects in order to extend their impact on the climate.  Miller et al. ran transient climate model simulations and believe they have identified some of these possible feedbacks.

First, the reduced incoming solar radiation due to the volcanic aerosols blocking sunlight allowed Arctic ice to expand.  The Arctic ice expansion increases the overall reflectivity (albedo) of the Earth, causing it to cool further.  The increase in Arctic sea ice in the north Atlantic Ocean also bring more cold and fresh water to the region, impacting the ocean circulation.

"...increased southward sea ice export following the eruptions led to freshening and vertical stratification of the North Atlantic subpolar gyre, reducing open ocean convection and thus weakening the Atlantic meridional overturning circulation."

Miller et al. concluded that these feedbacks were sufficient to sustain a LIA cooling for centuries.  Their theory is supported by reconstructions of sea ice around Iceland, where sea ice does not form, and only appears when there is a large export of sea ice from the Arctic Ocean. 

"Sea ice was rarely present on the North Iceland shelf from 800 AD until the late 13th Century, when an abrupt rise in sea-ice proxies suggests a rapid increase in Arctic Ocean sea ice export, followed by another increase ~1450 AD, after which sea ice was continuously present until the 20th Century [Massé et al., 2008] (Figures 1 and 2e).  The increase in sea ice north of Iceland at the start of the LIA, and its persistence throughout the LIA, supports our modeling experiments suggesting explosive volcanism and associated feedbacks resulted in a self-sustaining expanded sea-ice state beginning 1275–1300 AD."

Summary

Miller et al. suggest that a period of anomalously high volcanic activity at the end of the 13th Century could have triggered Arctic sea ice and ocean circulation feedbacks sufficient to cause the centuries-long cooling associated with the LIA.  The authors conclude by noting that while the decline in solar activity associated with the Maunder Minimum in the 17th Century contributed to the LIA cooling, a decline in solar irradiance is not necessary to explain the initial triggering of the LIA cooling.

"The coincidence of repeated explosive volcanism with centuries of lower-than-modern solar irradiance (Figure 2a) [Schmidt et al., 2011] indicates that volcanic impacts were likely reinforced by external forcing [Mann et al., 2009], but that an explanation of the LIA does not require a solar trigger."

However, it's also worth noting that it took four closely-spaced large volcanic eruptions to trigger these feedbacks and LIA cooling.  In most cases, the effects of volcanic eruptions on the global temperature are limited to a timespan of a few years. 

Additionally, while the data supporting the volcanic trigger of the LIA in the paper are fairly convincing, the modeling suggesting that the associated feedbacks are sufficient to sustain cold temperatures for several centuries is less conclusive.  In another paper, Zhang et al. (2011), only two simulations out of four show the proposed feedback.  In an interview with Science magainze regarding this paper, NASA climate scientist Gavin Schmidt agreed that too few model runs have been performed to conclusively demonstrate that the cooling feedbacks sustained the LIA by themselves.

"I think it is likely that the abrupt start to the Little Ice Age in the late 13th century is volcanic in origin...I'm far less convinced that this is the cause of the subsequent centuries of climate change."

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Comments

Comments 1 to 27:

  1. This theory that effects of the volcanic eruptions lingered for centuries after the events themselves seems like a new sort of 'tipping point' argument. That is, volcanic aerosols usually fall out of the atmosphere within a few years and have no significant long term effects... but this study is suggesting that a large enough set of volcanic events could introduce sudden sharp cooling which then becomes self-sustaining for hundreds of years. If that eventually proves out it would indicate that there are some major climate feedbacks that can be triggered on very short timescales... Arctic ice and ocean circulation for the study in question. There has long been concern about potential tipping points in these same areas with the gradual GHG warming we have been seeing, but this suggests it is possible that an otherwise temporary warming spike (e.g. El Nino) could result in a similar self-sustaining change.
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  2. IIRC that region in Canada has been invoked as a likely key to triggering glacial periods, as snow lies on the Canadian archipelago and around Hudson Bay later during the summer as the summer sun weakens it reinforces the cooling trend allowing Hudson Bay to remain frozen all year round. This allows a very slow southward creep of summer snow which forms the begining of the glaciers. Norwegian Mountains and then the Scottish Highlands also play a role.

    That is that they are very close to the point where all summer snow can lie with a small amount of cooling.

    It is possible these volcanos did not cause the little ice age but their impact was enough to allow the build up of cold summers with snow all year round to drop the temperaturtes that was not able to clear fully before a slight drop in solar output refinforced the millenia long dropping solar energy in mid summer at high nothern latitudes.

    It is far from a done deal with this at the minute but it is a very interesting study and seems to just catch a point where the climate is valnrable to reinforcing changes.
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  3. Mann has a new paper out which discusses volcanic eruptions in the 13th Century too. RealClimate discussion here.
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  4. @CBDunerson - the paper's thesis in no way suggests the volcanic effects lingered for centuries. Nor does it in any suggest that the long-term effect was "self-sustaining". There is an event co-incidence of volcanic activity, aerosols, and a temperature drop in the Alantic northern border. The LIA was global, long-term, and uneven in its onset. And the recap notes that the timeframe is not only localized, but earlier than usual dates associated with onset.

    A problem with the paper is identifying the volcano. It isn't huge (the 1258 super-eruption is still unsolved). But if the source is actually close to the coast of Iceland, the grouping of proxies could limit bigger implications.

    @Dana - that Mann link is a subtle game-changer. He forwards a very tentative case for missing rings, ... the disclaimers Mann himself puts into the article is a warning flag.
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  5. It's troubling that neither the Miller (paper discussed here) nor Gao et al 2008 say which volcano was the likely source of these eruptions. Statements like Miller's "two of the most volcanically perturbed half centuries of the past millennium" are too vague even for geologists.

    Emile-Geay et al 2006 suggest that ... a tropical location is likely, given the
    worldwide presence of the ashes and simultaneous presence of its signal in ice cores from both poles.
    El Chicon is possible.

    However, Timmreck et al 2008 found that this eruption, wherever it was located, wasn't much of a cooler-offer:

    The large AD 1258 eruption had a stratospheric sulfate load approximately ten times greater than the 1991 Pinatubo eruption. Yet surface cooling was not substantially larger than for Pinatubo (∼0.4 K).

    Incredibly, Miller does not cite either of these papers, which are clearly relevant.

    Another relevant source is Environmental History resource page on the impacts of volcanoes on European climate history. Mention is made of severe climate change during the mid 6th century "dust veil event," but nothing about 1258.
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  6. Here is a large eruption database, from a comment by David Benson on the RC thread. There's only one VEI 6 volcano (Krakatoa class) in the 13th century.
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  7. owl905 - Mann's paper is about accounting for 'dropped years' from minimal/no growth at marginal tree environs. The trees chosen for tree-ring paleo data are deliberately in marginal regions so that they more clearly show the effects of temperature, rather than fertilizer, local bear populations, insect infestations, etc. In other words, the Mann paper is about improving the time accuracy of tree-ring data.

    The Miller et al paper discussed in this thread, on the other hand, is about considering an ocean circulation tipping point caused by a series of strong volcanic eruptions, leading to the LIA period lasting hundreds of years. That's a different question entirely, and quite frankly (aside from year-resolution of tree-ring data) unrelated. Identifying the volcano(s) would be very interesting, although they did not show much data for that other than the near-equatorial location due to both hemispheres being affected.

    The Mann paper is quite interesting - and the language you seem concerned about (your "...warning flag" comment) is entirely reasonable for an initial effort that should be followed up with additional work.
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  8. @KR-No idea what your response is about - dropped years is years without rings = missing rings (Mann even uses the term p.3). Your statement about tree-line is straight off both RealClimate and the Mann paper.

    Dana introduced the Mann paper, so it is part of this thread. And no, it's not "quite frankly unrelated". Both papers focus on different aspects of the forcing effect and timing of volcanic events. Miller's case is boosted if Mann's suggestion of a stronger forcing effect is true.

    As for the "language you seemed concerned about", no again. It's Mann that's putting up the warning flags not too leap too far too fast with the suggestion. Part of Mann's requirement is to find other tree-types in the same region as controls.
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  9. If the LIA was caused by erupting volcanoes and we could cancel out the LIA, is possible that the current warming is just one long continuation of the Medieval Warming Period, Roman Warming Period, all the way back to ..... ?
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  10. owl905, I don't know if we are having some sort of semantic breakdown or if you really believe things to be exactly the opposite of my understanding.

    The Miller 2012 paper absolutely does suggest that volcanic eruptions caused cooling, which in turn was amplified by climate feedbacks, which resulted in the centuries of cooler temperatures generally known as the LIA. I mean, the bloody title of the paper is, "Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks".

    If you disagree with the above then you are going to need to explain what you think the Miller paper is about. If you don't have some radically different understanding of the paper then you must somehow be reading my original post to mean something other than what I said above. At which point I'd suggest that, as a general principal, it would be wise to consider all possible meanings of words and phrases you read and then not assume that interpretations which conflict with reality were the ones intended.
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  11. Mango#9: No and no.

    It's still not established that the LIA was caused by volcanic eruption - especially if no one can point to which volcano erupted at what time. Nor can we suddenly leave out the Maunder minimum entirely.

    As for 'we could cancel the LIA,' what do you mean? The very existence of the LIA, whatever its causes, shows there is not just one long warming. Even if that were so, why would the modern warming be at a more rapid pace?
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  12. @muoncounter #11

    If volcanic eruptions were the start of the LIA, as has been suggested, wouldn't the Maunder Minimum, which occurred midway through the LIA, just have exasperated the cold period started by erupting volcanoes?
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  13. Yes, the Maunder Minimum would have effectively amplified the volcano and feedback-caused cooling, if this theory is correct. However, the notion that we're just 'recovering' from the LIA is faulty, because we're currently warming much faster than the MWP warming or LIA cooling, and volcanoes and solar activity have had little influence over that warming, especially over the past ~50 years, as we showed here.
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  14. @dana1981 #13

    Thank you dana, this is as I thought and I agree "if this theory is correct".
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  15. A new discussion of the 'missing' volcano just popped up. Well-illustrated and sourced, including a figure from the new Mann paper.



    It sure looks like these coolings are short-lived transients.
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  16. @CB - your response doesn't match your original claim. And your response indicating that I either agree or disagree with Miller is untrue - I disagreed with your statement that the volcanic effect lingered for centuries.

    As for evidence that supports a better interpretation, read Mann - "does not require a solar trigger", but probably still requires that notorious weaker solar source. And that is not a feedback. And it makes a mess of the 'self-sustaining' phrase.

    Also note that Mann's paper shows no 'four super-eruptions' in the 1375-1400 interval, and the graph posted by muoncounter properly shows a real possibility from the mystery 1458 timeframe.
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  17. owl905, you seem to be unable to differentiate between things that you (for whatever reason) assume I meant and what I actually meant (and/or said). This makes meaningful communication effectively impossible.
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  18. Oppenheimer 2003 on the 1258ish volcano.

    Palaeoclimate reconstructions indicate very cold austral and boreal summers in AD 1257–59, consistent with known patterns of continental summer cooling following tropical, sulphur-rich explosive eruptions. This suggests an eruption in AD 1257, producing a stronger climate forcing than hitherto recognized.

    A figure from a summary of Crowley 2000:



    Clearly these volcanic events were known; I'm still not seeing convincing evidence that they initiate cooling lasting hundreds of years.
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  19. If the freshening of the North Atlantic due to the export of ice from the Arctic ocean leads to the shutdown of the Gulf stream and therefore the extension of cold conditions in the North, the same effect could occur if the Arctic ocean becomes ice free. In this case, an accelerated melting of the Greenland ice sheet could occur as the now warm air from the ocean is sucked down katabatically over Greenland, melting the ice. We would possibly have a flickering back and forth between cold and warm periods, followed, when much of the ice is gone, to a very much warmer climate. This very cold winter in Europe may be a harbinger of things to come. How long does it take for the Gulf Stream to respond to a change in its driving force.
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  20. Until now I have understood that LIA and MWP are not global.

    Is this still correct ?
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  21. Neukom 2009 reports on southern South America:

    The reconstructed SSA mean summer temperatures between 900 and 1350 are mostly above the 1901–1995 climatology. After 1350, we reconstruct a sharp transition to colder conditions, which last until approximately 1700.

    MWP appears much more variable; hence the controversy over whether it really was a 'warm period' or just a 'climate anomaly.'
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  22. Typo: "ice caps exhibit little or now flow, " should read, "ice caps exhibit little or no flow, "
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    Moderator Response: [DB] Fixed; thanks!
  23. LIA appears to be global but much less pronounced in the Southern hemisphere than in NH (based on comparative glacial geomorphology). MWP varied globally in timing and strength as described in Mann et al, 2009
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  24. @Klaus 20 - Scaddenp quotes the best reconstruction. Add to that a Swedish study that highlights the disjoint between past northern and southern hemisphere trends.

    http://www.physorg.com/news/2011-10-simultaneous-northern-southern-hemispheres-result.html

    It's noteworthy for the current warming that the effect is ubiquitous. That's very different from the reconstructions that show both regional and hemisphere differences driven by natural variations.
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  25. For other reasons I just read this paper: Volcanic Ash as Fertilizer for the Surface Ocean (Langmann et al, 2010. Atmos. Chem. Phys. 3891-3899). At the end of the paper they mention Huaynaputina volcano in Peru in 1600 (cite de Silva and Zielinski 1998). They estimate that 9x10^15 g of Carbon were consumed by phytoplankton as a result, which they think reduced atmospheric CO2 by 10 ppm in Antarctic ice cores after 1600 (Meure et al 2006). It seems to me that a carbon pump effect (not to mention colder ocean surface absorbing more CO2) of volcanoes might help explain the persistence of the Little Ice Age. Is this already accounted for?
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  26. Large eruption database shows the 1600 Peru eruption at 3.0 x 1010 m3 of tephra, or 3x Pinatubo; this is 1.5x the 13th century eruption at Quilotoa.

    Buntgen et al 2006 show a glacial advance following the 1600 eruption.



    The upper curve is summer temperature from tree rings; the bottom curve is advance/retreat of the Great Aletsch glacier. At this level of resolution, the LIA splits into three mini-LIAs, making the 'recovering from LIA' meme even more of a stretch.
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  27. Thanks muoncounter -- SkS articles are fantastic and I always learn from the comments too.
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