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Climate Hustle

The Last Interglacial - An Analogue for the Future?

Posted on 24 June 2011 by Steve Brown

Many of the current predictions for future climate and environmental impacts have been made on the basis of complex computer models of the Earth's systems.  Though such models have been successful in many areas, and are improving in accuracy and fidelity with increasing computer power, they still carry large uncertainties and margins of error, especially the further into the future that models are run.  One way that such uncertainties might be reduced is by looking at the geological and fossil record for periods in Earth's history that were warmer than today and determine how the environment responded.  This may allow us to better estimate the effects of climate change that could face us.

The Last Interglacial, also known as the Eemian in Europe and broadly corresponding to the global  interglacial record of Marine Isotope Stage 5e (MIS 5e), was a period with significantly higher temperatures in many parts of the Northern Hemisphere compared to the the present day (IPCC AR4) and similar to some predictions for the next century by current research.  The Last Interglacial offers several benefits for comparison with the present day in that continental configuration, flora and fauna are near identical to today, as well as being a recent enough period to provide a range of high-resolution palaeoenvironmental proxy indicators.  The Last Interglacial was also a period with higher global sea-level and a corresponding reduction in ice sheet area and volume,  which are consistent with IPCC predictions for responses to future global warming.  The period also had an atmospheric CO2 level of up to 300 ppm; similar to the pre-industrial era.

Timeline of past 150 ky BP 

Figure 1: Timeline of past 150,000 years. (illustration by jg at brightstarswildomar)

In Europe, the early part of the Eemian, as it was in transition from the preceding glacial stage,  was distinguished by treeless, grassy plains that eventually gave way to pine forests and then extensive oak and hazel forests as the climate warmed.  Global sea-level was estimated to have been at least 5 metres higher, resulting from a reduction in size of the Greenland and Antarctic Ice Sheets.  Coniferous forests were widespread at high-latitudes; deciduous forests were widespread at mid-latitudes, with low-latitudes predominantly savannah with grass plains and sparse tree cover.  Northwestern Europe, with its crust being isostatically depressed from the the weight of ice cover from the previous glaciation, was flooded by the Eemian Sea which connected the Barents and North Seas, leaving Scandinavia as an island (Kukla et al., 2002).

Mean temperature peaked in the first 3000 years of the Eemian, while precipitation remained relatively low.  The Eemian then progressed from a seasonal continental climate to a more oceanic climate in Europe with higher precipitation.  This oceanic climate may have been made more pronounced due to the connection between the Arctic and Atlantic oceans via the Baltic / Eemian Sea that opened up as global sea-level rose in the early Eemian (Zagwijn, 1996).

In Arctic Canada, the mean summer temperature was estimated to be 4 to 5oC higher than today and had vegetation similar to modern southwest Greenland (Frechette et al., 2006); Kienast et al. (2007), produced a pollen based climate reconstruction from the East Siberian Arctic and found the mean temperature of the warmest month during the warmest interval of the Last Interglacial was around 9 to 14.5oC, compared to 2.8oC today.  These reconstructions also suggest that mean annual precipitation was up to 50 mm higher than today.  In Alaska, summer temperatures were 1 to 2oC higher than today, but winters were 1 to 3oC cooler; in Greenland, summers were up to 5oC warmer than present.     Animal fossils identified in a variety of localities around North America indicate a warmer climate than present and provide consistency with Last Interglacial climatic reconstructions from Europe, Japan and Australia (Muhs et al., 2002).   Though there were significantly higher temperatures in many regions, it seems unlikely that average global temperatures were higher than 1oC compared to today (Hansen & Sato, 2011)

Overall, the early Eemian climate in the North and Western Europe was characterised as being predominantly oceanic i.e. with relatively cool summers, comparatively warm winters and reliable precipitation, with a modern Mediterranean climate in Southern Europe, while other regions of the Northern Hemisphere maintained a more seasonal, continental climate with warmer summers and colder winters (Brewer et al., 2008; CAPE-Last Interglacial Project Members, 2006). 

So here we have a warmer, wetter world than today's, with higher sea-levels, smaller ice-sheets, but a level of atmospheric CO2 much lower than today.  Does this mean that increasing levels of CO2 do not cause global warming after all? Climate always changes and we have nothing to worry about, right?  We'll explore the answers to these questions and more in this continuing series of posts.

This is Part 1 of an anticipated five part series of posts on the Last Interglacial climate.  Next post in the series: The Last Interglacial - Why was it so warm?

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Comments 1 to 37:

  1. One degree C higher than today and sea levels were 5 meters higher. How much warming did you say was already in the pipeline? Too bad for the people of Bangladesh (and Florida where I live).
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  2. To a so-called skeptic, the immediate reaction will be :

    "See, temperatures have been higher in the past - where were the SUVs ? That 'proves' that it's not us."

    Or :

    "See, things weren't that bad - 'we' got through it then, we'll get through it now."

    Or :

    "All that lovely warmth. Cold kills, you know."
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  3. I'm interested to see where you are going with this. Mainly from a communication perspective, although the style is engaging enough to have me interested in the material too.
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  4. Kevin,

    Not everything needs to be about skeptics. Some people are actually interested in the science of climate :-)
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  5. "Today" what do you mean when you say today? Which baseline? 1950-1980 or 1980-2010?
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  6. Kevin C - as well as serving the genuinely curious, the series will be a useful rebuttal to drive-by skeptics who claim the Earth was warmer back then - insinuating current warming is a natural cycle.
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  7. References to temperature relative to today are generally relative to global temp at year 2000.
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  8. 2000 is now 11 years ago. I suppose it is today for 'large enough values of today'.
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  9. If you like, you could average the last 11 years. That would be close enough to today.
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  10. In paleoclimate literature "today" often means 1950, sometimes something else (just look at the papers). It's worth keeping in mind but it's really not worth fussing about the baseline as long as everyone understands it. Especially for the "larger" climate changes of the past, whether anomaly is computed relative to 2000 or 2011 makes virtually no difference, and is within reconstruction uncertanties anyway.
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  11. That's the problem, Chris, not everyone understands what the baseline is. How much warming have we had since 1950? It's 0.79ºC, according to GISS J-D averages.

    That's quite significant, if you're referring to temperatures about a degree warmer than "today".
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  12. Note: I just picked the January-December anomalies for 1950 & 2010 from the GISS data - obviously, you need to look at a longer-term average to make it meaningful...
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  13. This will be an interesting series to follow.

    A few thoughts:

    While it is interesting to compare two different interglacials, and certainly both can be traced back ultimately to Milankovitch cycles, I would think that comparing CO2 levels and anticipated effects might yield some very sketchy projections. Rising temps during interglacials probably begin a positive feedback process with outgassing of CO2 from the oceans leading to more warming etc., but the sudden anthropogenic burst of CO2 during this interglacial to far higher levels than the past several interglacials should create a completely different dynamic, as the ocean themselves have not warmed enough to have released a similar amount of CO2...i.e. we are heading closer to what we saw in CO2 levels during the PETM but ocean temps are currently cooler. So, as oceans warm and begin to become net producers of CO2 from outgasssing rather than the large CO2 sink they been, it's possible we could see a sudden jump in the annual rate of CO2 growth, far larger than the annual increase from anthropogenic sources alone. This would be a far different dynamic than the last interglacial and would likely lead to all sorts of other very different climate dynamics.

    I certainly look forward to the rest of this series...
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  14. Hello.

    Sorry if this is a double post, the board software seems to have eaten my last one.

    I'm curious about something regarding the Eemian as an analogy to a future warmer world. The Eemian was a period of the Green Sahara.

    "Approx. 125,000 - 120,000 y.a., moistest phase of the Eemian Interglacial (Isotope Stage 5e). Rainforest occupied a far greater area than at present, and rainfall was generally higher over north Africa. Data are sparse, mainly coming from long cores recording pollen and dust flux off the west coast of Africa. From these indicators, it seems that the situation generally resembled that of the early Holocene, around 8,000 14C y.a. General Eemian 'optimum' conditions in north Africa are summarized in map form by Frenzel et al. (1992) and by van Andel & Tzedakis (1996)."

    Africa during the early Holocene looked like this:

    A good deal wetter than present Africa, apparently. But the IPCC predicts drying in tropical regions in a warmer world, as I remember.

    Why is this? Is it because the tilt of Earth's axis, orbit etc. were different in the Eemian?

    I also notice that from looking at paleoclimates warmer periods tend to be wetter. As I remember the IPCC projections are a mixed bag here, with drying in tropical regions and moistening in temperate ones. There are exceptions to the first (e.g. Mousterian Pluvial, US Southwest was wetter than the ice age), but the ice age tropics had less forest, Eemian tropical Africa had less desert, and as I remember from a paper I read on the Pliocene warm period Pliocene warm period Africa also had less desert.

    I'm getting most of my information from here:

    I'm not saying the IPCC's wrong, I'm just curious about the percieved difference. This site seems to have many knowledgeable people so I thought this might be a good place to ask about it.

    Also I just want to clarify I'm not saying I think this would mean global warming is a good thing or shouldn't be prevented. I wouldn't mind living in the world of the Eemian, it looks quite pleasant to me and more inviting than our drier and colder world, but putting our planet through a rapid change from present world to Eemian world while our present civilization is living on it does not strike me as a prudent plan. If recreating the Eemian world is possible and a good idea I'd much rather it happen as part of a managed and responsible geoengineering project by a wealthy and responsible future, not an out of control side effect of energy generation by the poor present, allowed to happen because of short-sightedness and apathy.

    I'm just interested in why the apparent difference between paleoclimate data and the projections happens.

    An interested layman.
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  15. I should add, before anyone suggests I look at the "it's not so bad" page I did but I didn't see any discussion of this.
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  16. Having worked in climate science for some years (a physicist by profession), I learnt is that it is the rate of temperature that is far more important than the absolute value of the temperature. Earth may very well have experienced higher temperatures than today, but as far as I understand, the rate of increase in the last ~30 years has been totally unprecedented. This should speak volumes, and one does find references to rate of increase in published literature very often, but somehow while making the public aware of how much humans are altering the climate, the issue of rate of increase is often left out. I've always found that surprising...
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  17. Somes_J,

    You are correct in that warmer temperatures recent in wetter climates, and Africa is believed to have wetter during the two periods you described. Africa is also believed to have been drier during the last ice age.

    The desert areas are governed by the intertropical convergence zone (ITCZ), which follows the warmer temperatures, i.e. moves northward in the NH summer, and southward in the HN winter. Projections in a warmer world would cause an increase in the ITCZ, which would result in more rainfall in today's desert regions.

    Here is were the theories diverge. Some state that an expansion of the ITCZ will simply push the desert regions poleward, causing the semi-arid regions to dry into deserts. Others maintain that the deserts will shrink in size as the ITCZ expands, but the poleward side of the desert remain where htey are today.
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  18. @Somes_J - The key to the differences in environmental impacts between the Eemian and IPCC projections for the future will be due to the significant differences in forcings and feedbacks that are being observed and expected. For example, Eemian warming was mostly apparant at high northern latitudes due to the particular orbital configuration at the time and a correspondingly higher insolation. We currently have ~100 ppm more CO2 in the atmosphere and rising compared to the Eemian, which will contribute to enhanced greenhouse warming globally. Also, present day land use and deforestation will be contributing to different albedo feedbacks and differences to the hydrological cycle etc.

    The other key difference, as "LochNess" alludes to, is that the rate of change of warming and GHG increase going on today is unprecedented. The climatic changes during the Eemian happened over several thousand years and not in a few decades.
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  19. Somes_J - just expanding a bit more on Steve's comment: because Earth's orbit was more eccentric (elliptical) back then, it's obliquity (rotational tilt relative to its plane of orbit) greater and the northern hemisphere summer coincided with perihelion (closest part of Earth's orbit to the sun), it meant the NH summer received greater solar heating than today.

    By contrast the Eemian winter would have been much cooler, so there would have been a greater difference between summer and winter temperatures in the NH (seasonality) this would have had a marked effect of the hydrological cycle at that time, such as the African Monsoon. See Herold 2009 for an examination of this issue.

    For the Holocene Climatic Optimum (HCO), once again astronomical factors meant a greater warming in the NH summer and a wetter African period. Changing orbital forcing, from the HCO to today, lead to a cooling in the NH and a change to the monsoonal pattern. As pointed out by Steve, the factors in play today are a bit different.

    Living in the world of the Eemian?, be nice if the world was as we'd like to be but even small changes in the global mean state, can mean drastic changes in extremes, such as rainfall intensity. The models do indicate that a warmer world is a wetter world, but that's an oversimplification, generally dry areas are expected to get drier (the south-western USA for example) and wet areas wetter, but again we expect greater seasonality even in wet areas the rainfall is expected to be in the form of less frequent rain, but much heavier downpours (i.e. bigger floods). Me personally, I'd like to avoid that future world.
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  20. Steve,

    I am not so sure that "The climatic changes during the Eemian happened over several thousand years and not in a few decades." As early as at least 2001 Hearty and Neumann (Quaternary Science Reviews 20 (2001) 1881–1895)suggest that:

    "Recent evidence indicates that the close of MIS 5e was marked by sudden changes in sea level and climatic events ofcatas trophic proportions. These rapid sea level changes were accompanied by powerful waves that struck the eastern margin ofthe Bahama Banks, significantly reshaping the geomorphic face and facies of this critical interval (Hearty and Kindler, 1995; Neumann and Hearty, 1996; Hearty, 1997; Hearty et al., 1998; Tormey et al., 1999; Hearty and Kaufman, 2000)."

    "From these findings, it is reasonable to surmise that the
    close ofthe present interglacial may be marked by equally dramatic climatic changes."

    "Thus, we interpret these events to have occurred late in MIS 5e after the formation of multiple, smaller ridges which are observed in outcrop at numerous sites (Hearty and Kindler, 1997). That emplacement ofthese dunes was relatively rapid is inferred from the burial of large standing trees (Fig. 6) and palmetto leaves in living position (Neumann and Hearty, 1996)."

    "The geology ofthe Bahama Islands provides critical outcrop information from which sea level and climate history between 132 and 118 ka can be reconstructed. Within that period, three oscillations ofsea level can be distinguished. Early in the period (132–125 ka) sea level appears to have maintained a level around +2.5m as evidenced by reefs capped by A. palmata at that datum. A mid 5e regression around 124 ka is documented by a mid-5e unconformity and from numerous beach, reef, and dune sections (Chen et al., 1991; Hearty and Kindler, 1993, 1997, 1998; White et al., 1998). Sea level rose again to a slightly higher level than the previous one, which again initiated reefgrow th to a maximum elevation of less than +3m. This near stillstand was short lived, however. At the end of the period, sea level rose to +6 to +8.5 m, flooding areas ofthe platform inland ofthe coastal ridge and cutting notches into sea cliffs of older material. A rapid fall followed which permitted the preservation of antecedent morphology, stranded storm beaches and local reeftops left in near pristine condition (Fig. 4)."

    More recently Boettger et al (Quaternary International 207 (2009) 137–144) provide a European analysis of the late Eemian climate instability:

    "The transition (MIS 5e/5d) from the Last Interglacial (Eemian, Mikulino) to the Early Last Glacial (Early Weichselian, Early Valdai) is marked by at least two warming events as observed in geochemical data on the lake sediment profiles of Central (Gro¨ bern, Neumark–Nord, Klinge) and of Eastern Europe (Ples). Results of palynological studies of all these sequences indicate simultaneously a strong increase of environmental oscillations during the very end of the Last Interglacial and the beginning of the Last Glaciation. This paper discusses possible correlations of these events between regions in Central and Eastern Europe. The pronounced climate and environment instability during the interglacial/glacial transition could be consistent with the assumption that it is about a natural phenomenon, characteristic for transitional stages. Taking into consideration that currently observed ‘‘human-induced’’ global warming coincides with the natural trend to cooling, the study of such transitional stages is important for understanding the underlying processes of the climate changes."

    If we couple that with the just as long running debate on the probable length of the Holocene we find that 5 of the last 6 post-MPT interglacials have each lasted roughly half a precessional cycle. The precessional cycle varies from 19-23kyrs and we are at the 23kyr point now. The Holocene is often stated as being ~11,500 years old now, exactly half of the present precessional cycle.

    Which is why this discussion has relevance.
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  21. Then again it just might be worse than we thought.

    But what about that 6th interglacial, the one that wasn’t on the half-precessional “clock”. That would be MIS-11 (or the Holsteinian) which according to the most recently published estimate may have lasted on the order of 20-22kyrs, with the longest estimate ranging up to 32kyrs.

    Loutre and Berger’s 2003 paper was soon followed by another landmark paper by Lisieki and Raymo (Oceanography, 2005), an exhaustive look at 57 globally distributed deep Ocean Drilling Project (and other) cores (Figure 1), which stated:

    “Recent research has focused on MIS 11 as a possible analog for the present interglacial [e.g., Loutre and Berger, 2003; EPICA community members, 2004] because both occur during times of low eccentricity. The LR04 age model establishes that MIS 11 spans two precession cycles, with 18O values below 3.6o/oo for 20 kyr, from 398-418 ka. In comparison, stages 9 and 5 remained below 3.6o/oo for 13 and 12 kyr, respectively, and the Holocene interglacial has lasted 11 kyr so far. In the LR04 age model, the average LSR of 29 sites is the same from 398-418 ka as from 250-650 ka; consequently, stage 11 is unlikely to be artificially stretched. However, the June 21 insolation minimum at 65N during MIS 11 is only 489 W/m2, much less pronounced than the present minimum of 474 W/m2. In addition, current insolation values are not predicted to return to the high values of late MIS 11 for another 65 kyr. We propose that this effectively precludes a ‘double precession-cycle’ interglacial [e.g., Raymo, 1997] in the Holocene without human influence.”

    To bring this discussion up to date, Tzedakis, in perhaps the most open peer review process currently being practiced in the world today (The European Geosciences Union website Climate of the Past Discussions) published a quite thorough examination of the state of the science related to the two most recent interglacials, which like the present one, the Holocene (or MIS-1) is compared to MIS-19 and MIS-11, the other two interglacials which have occurred since the Mid Pleistocene Transition (MPT) and also occurred at eccentricity minimums. Since its initial publication in 2009, and its republication after the open online peer review process in March 2010, this paper is now also considered a landmark review of the state of paleoclimate science. In it he also considers Ruddiman’s Early Anthropogenic Hypothesis, with Ruddiman a part of the online review. Tzedakis’ concluding remarks are enlightening:

    “On balance, what emerges is that projections on the natural duration of the current interglacial depend on the choice of analogue, while corroboration or refutation of the “early anthropogenic hypothesis” on the basis of comparisons with earlier interglacials remains irritatingly inconclusive.”

    The picture which emerges is that the post-MPT end interglacials appear to be populated with dramatic, abrupt global climate disruptions which appear to have occurred on decadal to centennial time scales. Given that the Holocene, one of at least 3, perhaps 4 post-MPT “extreme” interglacials, may not be immune to this repetitive phenomena, and as it is half a precession cycle old now, and perhaps unlikely to grow that much older, this could very well be the natural climate “noise” from which we must discern our anthropogenic “signal” from.

    If we take a stroll between this interglacial and the last one back, the Eemian, we find in the Greenland ice cores that there were 24 Dansgaard-Oeschger oscillations (Figure 5, originally figure 1. Sole et al, 2007), or abrupt warmings that occurred from just a few years to mere decades that average between 8-10C rises (D-O 19 scored 16C). The nominal difference between earth’s cold (glacial) and warm (interglacial) states being on the order of 20C. D-O events average 1470 years, the range being 1-4kyrs.

    Sole, Turiel and Llebot writing in Physics Letters A (366 [2007] 184–189) identified three classes of D-O oscillations in the Greenland GISP2 ice cores A (brief), B (medium) and C (long), reflecting the speed at which the warming relaxes back to the cold glacial state:

    “In this work ice-core CO2 time evolution in the period going from 20 to 60 kyr BP [15] has been qualitatively compared to our temperature cycles, according to the class they belong to. It can be observed in Fig. 6 that class A cycles are completely unrelated to changes in CO2 concentration. We have observed some correlation between B and C cycles and CO2 concentration, but of the opposite sign to the one expected: maxima in atmospheric CO2 concentration tend to correspond to the middle part or the end the cooling period. The role of CO2 in the oscillation phenomena seems to be more related to extend the duration of the cooling phase than to trigger warming. This could explain why cycles not coincident in time with maxima of CO2 (A cycles) rapidly decay back to the cold state. ”

    “Nor CO2 concentration either the astronomical cycle change the way in which the warming phase takes place. The coincidence in this phase is strong among all the characterized cycles; also, we have been able to recognize the presence of a similar warming phase in the early stages of the transition from glacial to interglacial age. Our analysis of the warming phase seems to indicate a universal triggering mechanism, what has been related with the possible existence of stochastic resonance [1,13, 21]. It has also been argued that a possible cause for the repetitive sequence of D/O events could be found in the change in the thermohaline Atlantic circulation [2,8,22,25]. However, a cause for this regular arrangement of cycles, together with a justification on the abruptness of the warming phase, is still absent in the scientific literature.”

    In their work, at least 13 of the 24 D-O oscillations (indeed other workers suggest the same for them all), CO2 was not the agent provocateur of the warmings but served to ameliorate the relaxation back to the cold glacial state, something which might have import whenever we finally do reach the end Holocene. Instead of triggering the abrupt warmings it appears to function as somewhat of a climate “security blanket”, if you will.

    Therefore taking into consideration the precautionary principle, we are left to ponder if reducing CO2’s concentration in the late Holocene atmosphere might actually be the wrong thing to do.

    The possibility consequently exists that at perhaps precisely the right moment near the end-Holocene, the latest iteration of the genus Homo unwittingly stumbled on the correct atmospheric GHG recipe to perhaps ease or delay the transition into the next glacial. Under this analysis “Skeptics” and “Warmists” thus find themselves on the mutual, chaotic climate ground where the efficacy of CO2 as a GHG had better be right.
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  22. I find a lot of speculation in Sentient post, about a subject that is itself much speculated about. D.O. events, Heinrich events and the more recent Bond events (of which only a few can be conclusively linked to large scale climate fluctuations) are most likely the results of oceanic currents modifications due to disruptions by fresh water. There has not been a D.O. event in over 20k years, yet no ice age has started, even though we've been at only 285 ppm for all of that time. The bipolar ocean seesaw indicates that these "cycles" (true cyclicity is questionable) are mostly about redistributing heat. If Bond events truly are cyclic, then the present warming does not correspond at all to a Bond event.

    I'd add that nobody is advocating reducing CO2 concentration but rather preventing it from increasing in a way that has no known geologic equivalent during mankind's presence. A "natural" outgassing like we're seeing now, if coming from volcanoes, would require a volcanic activity about 150 times more intense than what it presently is. Whatever else is "naturally happening" according to Sentient is bound to be profoundly affected.

    This link has lots of good info and references.
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  23. Eric the Red: "Here is were the theories diverge. Some state that an expansion of the ITCZ will simply push the desert regions poleward, causing the semi-arid regions to dry into deserts. Others maintain that the deserts will shrink in size as the ITCZ expands, but the poleward side of the desert remain where htey are today." It seems to me that this question might be testable by looking at whether deserts moved north in previous warm eras. It occurs to me that perhaps a better model for a global warming world would be the Mid-Pliocene rather than the Eemian, as the greater warmth of the Mid-Pliocene may have been due to higher than present CO2: LINK I have managed to find a paper that has a reconstruction of Middle Pliocene ecosystems: From their summary: "Expansion of evergreen forests to the margins of the Arctic Ocean, a reduction of desert area in equatorial Africa and essential elimination of polar desert and tundra regions in the Northern Hemisphere. A small amount of deciduous vegetation occurred at the edge of the Antarctic continent." They include vegetation maps. There's still a large barren area in Africa but it's smaller than today. Barren areas generally seem to be smaller than today. If the Mid-Pliocene warmth was because of higher CO2 it seems that CO2-caused warming also leads to less desert, not more. Any difference between the Mid-Pliocene and today that might explain why deserts would have been smaller than, but you'd have increasing tropical aridity from warming today?

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  24. Somes_J, I'm not sure that this comparison is so useful, now that the Isthmus of Panama is closed. A lot of things have changed since the mid-Pliocene. It is an interesting exercise in modeling, but probably not as good an indication for our future as what model results with current conditions and geography yield.
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  25. Unfortunately, I must exit further discussion at this time. Preempted by vacation. Laptop is next on the final packing list, and where I am going the only connection is with nature. I will check back on 5Jul11. Be good.
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  26. sentient:
    Hope your vacation is productive. As always, you provide well documented thoughts in this area.
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  27. Hansen et al 2011 warns that we are now a few tenths of a degree below the Eemian and that allowing average global temperature to rise to +2°C above pre industrial will put us over the Eemian maximum. Were that to occur we expose ourselves to decadal doubling of Greenland ice loss, rapid increase in loss of WAIS ice loss, reduction of global albedo and excursion of Arctic carbon, making a 5m rise in sea level by 2100 certain. Hence the call to limit future carbon emissions to 350 ppm by 2050 in order to avoid these outcomes. We are now approaching 400 ppm.

    Since major CO2 emitters are pursuing BAU, the chances of average global temperatures rising by 4°C or more by 2100 seems pretty good, 3°-4°C above the Eemian maximum and we know what we can expect from that. Moreover, contrary to the views of some, homo sapiens is knowingly achieving this with very little help from other factors and, contrary to the assertions of some, none from the Milankovitch Cycle. The sun is not only quiescent but Earths orbit around it is almost circular and the axial tilt of the earth is gaining such that polar exposure to the sun is decreasing.

    The world during the Eemian may have had similarities to what it is to-day but it also had significant differences. For example, it was not inhabited by voracious animals, homo sapiens, which have bred to plague proportions. It did not have 7 billion human inhabitants, 4 billion of them living in areas subject to inundation by a 5m sea level rise, 2 billion dependent for water on glaciers most of which will be fully melted by 2100, or 1 billion dependent on marine animals which will be scarce or extinct by then.

    One would have thought such outcomes would have prompted Australian Prime Minister Gillard to abandon her tokenistic goal of reducing CO2 emissions by 5% by 2020 when all around her are aiming for 25% reduction by 2020, even zero by 2050. Think, Mr Abbott, what these developments are going to do for the economy, competitive advantage and the job protection you bleat about. There are times when pollies – and academics – make you sick! All talk, too little action and total disregard for the consequences.
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  28. Sentient - "I am not so sure that "The climatic changes during the Eemian happened over several thousand years and not in a few decades"

    Maybe not the right choice of words perhaps, but I think Steve was referring to the astronomical forcing. The rapid jumps in sea level near the end of the Eemian are likely from the collapse of the Greenland Ice Sheet - not a good omen.

    Somes_J - as already pointed out, there are different factors in play today, the slight change in ocean circulation between the Pliocene and today (such as restriction of the Indonesian Throughflow) can have a marked effect on regional and global climate. For example this study: A westward extension of the warm pool leads to a westward extension of the Walker circulation, drying eastern Africa - Williams 2011 anticipates warming of the Indian Ocean will dry out East Africa.

    Check out the SkS post The Dai After Tomorrow, the global drying trend has already begun, and this at a time of globally increasing rainfall!
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  29. The basis for my saying that the climatic changes during the Eemian happened over a few 1000 years was in regards to the orbital and GHG forcing that led to the warming out of the penultimate glaciation through to the Eemian climatic optimum.

    WRT the various Hearty et al. papers that Sentient mentions, the authors themselves acknowledge that the evidence for a rapid highstand may also be explained by tsunami or severe hurricane storm surge activity that just affected the Bahamas. I'll be covering this in a future post in the series.
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  30. Steve.

    You write: "Does this mean that increasing levels of CO2 do not cause global warming after all? Climate always changes and we have nothing to worry about, right?"

    Unfortunately I can not see that.

    An alternative explanation is that CO2 levels of ~300 ppm, a mere 20 ppm above pre-industrial Holocene, may be sufficient to raise tempratures by <1 degrees C and sea levels by ~5 meters, implying significantly higher climate sensitivity than Charney's 3+/-1.5 degrees C per doubling of CO2, as indicated by recent papers by Pagani et al. 2010 (PNAS)indicating CS values higher than 6C.

    Second, the GROWTH RATE of GHG rise may be just as important as the absolute level of CO2. The current rise rate of ~2 ppm/year is higher by a large factor than that preceding the Eemian interglacial, indeed it is the highest recorded in the Cainozoic geological record, and may constitute an important factor, for example in destabilizing methane locked in permafrost.

    According to Hansen et al. 2011 and Hansen and Sato 2011 total forcing has already reached 3.1 Watt/m2, although about half of this is currently mitigated by transient sulphur aerosols without which we are committed to +2.3 degrees C.

    These are Pliocene-like levels, well above the Eemian.

    Andrew Glikson

    Which means, consciously or unconsciously the world is already practicing geoengineering.
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  31. Agnostic.

    Unfortunately I think you are correct ...


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  32. Somes_J

    Thanks for the links. Apologies for the long delay.
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  33. Philippe Chantreau

    I tend to find that speculating on things which have happened is decidedly more comfortable than speculating on things which have not happened yet, as in model speculations. Especially when one is frequently engaged to dig into the opposition's modeling in toxic torts and insurance litigation related to same. Fascinating work, by the way.

    On Dansgaard-Oeschger oscillations. There were 24 Dansgaard-Oeschger oscillations between this interglacial, the Holocene, the interglacial in which all of human civilization has occurred, and the last one, the Eemian, and yes, we were indeed there as our stone-age selves. D-O oscillations average 1,500 years, and have the same characteristic sawtooth temperature shape that the major ice-age/interglacials do, a sudden, dramatic, reliable, and seemingly unavoidable rise of between 8-10C on average, taking from only a few years to mere decades, then a shaky period of warmth (less than interglacial warmth), followed by a steep descent back into ice age conditions. Each D-O oscillation is slightly colder than the previous one through about seven oscillations; then there is an especially long, cold interval, followed by an especially large, abrupt warming up to 16C (a Bond cycle). During the latter parts of the especially cold intervals, armadas of icebergs are rafted across the North Atlantic (Heinrich events), their passage recorded reliably by the deep ocean sediment cores which capture the telltale signature of these events in dropstones and detritus melted out of them.

    D-O events may indeed be caused by changes in oceanic circulation. Indeed many workers agree with this paradigm, however it would seem as many suggest other mechanisms, however I tend to agree with Sole, Turiel and Llebot (quoted in my first post) when they conclude "However, a cause for this regular arrangement of cycles, together with a justification on the abruptness of the warming phase, is still absent in the scientific literature.”

    Then again, Michael Shultz, writing in PALEOCEANOGRAPHY, (VOL. 17, NO. 2, 10.1029/2000PA000571, 2002) states in the abstract "During this interval the spacing of the Dansgaard-Oeschger onsets varied by ±20% around the fundamental 1470-year period and multiples thereof. The pacing seems unaffected by variations in the strength of North Atlantic Deep Water formation, suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period." Which would tend to suggest that not only may we really not know what causes them, but as also quoted in the initial post, T1 exhibits the same characteristic, and we still do not know exactly why the terminations occur.

    Yet again, we continue to discover that even on things which have happened, the science is not that particularly well settled. Evidence was early presented for the presence of D-O signal within the Holocene, which is best preserved. Bond et al (SCIENCE, VOL. 278, 14 NOVEMBER 1997) (the Bond the cycles were named after)state in their abstract:

    "Pacings of the Holocene events and of abrupt climate shifts during the last glaciation are statistically the same; together, they make up a series of climate shifts with a cyclicity close to 14706500 years. The Holocene events, therefore, appear to be the most recent manifestation of a pervasive millennial-scale climate cycle operating independently of the glacial-interglacial climate state. Amplification of the cycle during the last glaciation may have been linked to the North Atlantic’s thermohaline circulation."

    I think you are partially correct in that there is at least a probability that "Whatever else is "naturally happening" according to Sentient is bound to be profoundly affected." so long as we critically examine the term "bound to be". This, by definition, is speculation. Speculation about events which have not happened yet. We have mathematically guessed that it should happen, but that does not mean that it is bound to happen. Though it very well might. The evidence I presented in my first post suggests that at least in the B and C cycles of Sole Turiel and Llebot, "profoundly" does indeed figure in to the precautionary principle calculus.
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  34. That's a very long and wordy post that seems to be tending in the direction "we don't know" and "it's natural cycles", although this is actually not clearly stated nor defended in the post.

    I'm sure some will find your mini lecture on D.O. events informative but there are better sources for that. The same applies to the other types of events mentioned.

    I'll restate that there has not been a D.O. event in over 20K years.

    The periodicity of Bond events has not been established. Bond argues of approximately 1500 years, +- 500 years. It is not clear whether there actually is a cycle. If the timing of Bond event #1 is correct (450AD), then another should be underway now, or should be/have been, anywhere between 500 years ago and 500 years from now.

    But how much would that concern us? It is possible that the LIA was a Bond event (they are cold episodes), but perhaps it was not. If it was, it would confirm the lack of a global character of these events. The vast majority of them do not correspond to any clear climate signal, especially on a global scale. There is little indication that the LIA was a global event. Milliken, for instance, failed to find a clear signature for it in the SHALDRIL cores.

    I find that these purported cycles are of little to no relevance to the current warming event. I don't see how you demonstrate otherwise.
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  35. Andrew #30 - My statement in the post was intended to be ironic. I don't disagree with your explanation.
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  36. 101 vidoes for 101 cities with sea level rise linked to paleo data of Hansen 2011.
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  37. Typo alert "preceeding" should be "preceding".
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