The Team on the Holocene Optimum

Can we agree that the discovery of Distachia at Quelccaya dated to about 5000 year ago and located about 400-500 m above its present level is evidence that it was warmer at that time than at present at Quelccaya, Peru? Yeah, yeah, I know the argument that maybe Distachia is 400-500 m out of equilibrium with temperature in 2006, but maybe it’s only 100 m out of equilibrium. If the point is going to be argued, I’d like to see it argued in a more substantive way than a mere possibility and there’s a large population of climate scientistis capable of arguing the point if it could be argued.

Regardless of this point, finding Distachia 400-500 meters above present limits is hardly problematic for pre-Hockey Team paleoclimatology – who postulated a Neoglacial period succeeding the Holocene Optimum about 5000-6000 radiocarbon years ago – both terms used many years ago in the prominent text Porter and Denton (1967; 1976). Wood and Smith 2004 stated of this :

The Neoglacial was initially described as a world-wide glacial event that followed a period during which glaciers were at their Holocene minimum (Porter and Denton 1967).

So how does the information about 5000 year old Distachia (alpaca moss) from high altitudes at Quelccaya tie in with Hockey Team views on the Holocene Optimum? How does one reconcile this with the idea of "unprecedented" modern warmth?

Mann was asked about the Holocene Optimum in 2003 by Inhofe’s Senate committee, who were told that the Holocene Optimum was "restricted to high latitudes" and the JJA season (northern summer/southern winter), that "decades ago some scientists believed that this was a time of globally warmer conditions. It is now well known that this is not the case. More abundant evidence now demonstrates, for example, that the tropical regions were cooler over much of the year". With his typical congeniality, Mann decried Legates’ supposed "lack of familiarity" with the literature.

46. How did the temperatures of the mid-Holocene Optimum Period (6000 to 9000 BP) compare with those observed today? Was it a global or a local phenomenon? What was or were the cause or causes of any temperature anomalies in that period? What is the cause of the 104 to 105 year timescale changes in deuterium, oxygen isotope, etc., concentrations in ice core records? Are such changes global or local?

Paleoclimate experts have established that mid-Holocene warmth centered roughly 5000 years ago was restricted to high latitudes and certain seasons (summer in the Northern Hemisphere and winter in the southern hemisphere). Because much of the early paleoclimate evidence that was available (for example, fossil pollen assemblages) came from the Northern Hemisphere extratropics, and is largely reflective of summer conditions, decades ago some scientists believed that this was a time of globally warmer conditions. It is now well known that this is not the case. More abundant evidence now demonstrates, for example, that the tropical regions were cooler over much of the year. All of these changes are consistent with the expected response of surface temperatures to the known changes in the Earth’s orbital geometry relative to the Sun during that time period and associated climate feedbacks, as detailed in peer-reviewed scientific publications [e.g., Hewitt, C.D., A Fully Coupled GCM Simulation of the Climate of the Mid-Holocene, Geophysical Research Letters, 25 (3), 361-364, 1998; Ganopolski, A., C. Kubatzki, M. Claussen, V. Brovkin, and V. Petoukhov, The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene, Science, 280, 1916-1919, 1998].

Climate model simulations indicate quite good agreement with paleoclimate evidence now available. These models calculate that global annual average temperatures were probably about the same or a few tenths of a degree C cooler than today (the late 20th century) during this time period [Ganopolski, A., C. Kubatzki, M Claussen, V. Brovkin, and V. Petoukhov, The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene, Science, 280, 1916-1919, 1998; Kitoh, A., and S. Murakami, Tropical Pacific Climate at the mid-Holocene and the Last Glacial Maximum simulated by a coupled ocean atmosphere general circulation model, Paleooceanography, 17 (3), (19)1-13, 2002.]. That’s a far cry from the very out-of-date claim made by Dr. Legates in his testimony. Dr. Legates’ comments regarding climate changes over the past 1000 years reflect a similar lack of familiarity with a whole body of paleoclimate research, especially with the new insights gained through the augmented research program, during the past decade.

Mann re-iterated this position at realclimate in December 2004 in one of their very first posts:

This [Holocene Climatic Optimum] is a somewhat outdated term used to refer to a sub-interval of the Holocene period from 5000-7000 years ago during which it was once thought that the earth was warmer than today. We now know that conditions at this time were probably warmer than today, but only in summer and only in the extratropics of the Northern Hemisphere. This summer warming appears to have been due to astronomical factors that favoured warmer Northern summers, but colder Northern winters and colder tropics, than today (see Hewitt and Mitchell, 1998; Ganopolski et al, 1998). The best available evidence from recent peer-reviewed studies suggests that annual, global mean warmth was probably similar to pre-20th century warmth, but less than late 20th century warmth, at this time (see Kitoh and Murakami, 2002).Ganopolski, A., C. Kubatzki, M. Claussen, V. Brovkin, and V. Petoukhov, The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene, Science, 280, 1916-1919, 1998.

Hewitt, C.D. and J.F.B. Mitchell, A Fully Coupled GCM Simulation of the Climate of the Mid-Holocene, Geophys. Res. Lett., 25, 361-364, 1998.

Kitoh, A., and S. Murakami, Tropical Pacific Climate at the mid-Holocene and the Last Glacial Maximum simulated by a coupled ocean-atmosphere general circulation model, Paleoceanography, 17, 1-13, 2002.

realclimate linked to the following NOAA website about the Holocene Optimum:

We also now know from both data and "astronomical" (or "Milankovitch") theory that the period of above modern summer temperatures did not occur at the same time around the northern hemisphere, or in the southern hemisphere at all.

Whatever else one may think of Distachia 400-500 meters above present limits, it is evidence that warmth in the Holocene Optimum was not "restricted to high latitudes" and appears to refute the claim it has been "demonstrate[d]" that "tropical regions were cooler over much of the year" in the Holocene Optimum. Maybe Lee or Steve Bloom could ask realclimate whether they’ve sent a corrigendum to Inhofe about their prior evidence – after all the Distachia was reported in December 2002 and Mann, who proclaimed hs "familiarity with the literature" was presumably aware of it.


28 Comments

  1. Steve Sadlov
    Posted Aug 14, 2006 at 10:04 AM | Permalink | Reply

    Mann is a denialist vis a vis past climate variability.

  2. denialist
    Posted Aug 14, 2006 at 10:10 AM | Permalink | Reply

    [snip]John A: either put your urls in a link or use tinyurl.com, or don’t bother posting. I’m trying to fix the problem with the sidebar but in the meantime let’s all try to get with the program.

  3. Mark T.
    Posted Aug 14, 2006 at 10:16 AM | Permalink | Reply

    bump

  4. Mark T.
    Posted Aug 14, 2006 at 10:17 AM | Permalink | Reply

    Denialist: http://www.tinyurl.com... ;)

    Mark

  5. Mark T.
    Posted Aug 14, 2006 at 10:37 AM | Permalink | Reply

    What’s interesting is this bit:

    We now know that conditions at this time were probably warmer than today, but only in summer and only in the extratropics of the Northern Hemisphere.

    First, isn’t the northern hemisphere the primary basis for the HS and second, aren’t tree-ring proxies only summer?

    Mark

  6. Posted Aug 14, 2006 at 1:15 PM | Permalink | Reply

    I like the usage of quotes in the NOAA link: “astronomical”, paleoclimatic

  7. Hans Erren
    Posted Aug 14, 2006 at 2:08 PM | Permalink | Reply

    re 2:
    I am very curious about the link you censored john.

  8. Posted Aug 14, 2006 at 2:19 PM | Permalink | Reply

    I did a quick review of published papers from 2002-2006 using “mid-holocene maximum” as key words on Google Scholar. To say that “mid-Holocene warmth centered roughly 5000 years ago was restricted to high latitudes and certain seasons (summer in the Northern Hemisphere and winter in the southern hemisphere)” is oversimplifying. Furthermore, the models don’t all agree with the proxy data, and there is strong evidence for some feedback between climate and vegetation cover that is as of now only poorly understood. For example, the models have a hard time simulating the “green Sahara”.

    The most important point is that the model do not tell us anything about the mid-holocene climate. Rather, that specific period is used to test the models, not the other way around.

  9. Lee
    Posted Aug 14, 2006 at 2:25 PM | Permalink | Reply

    JohnA, what was that link?

  10. beng
    Posted Aug 14, 2006 at 2:57 PM | Permalink | Reply

    Did Mann learn to write in the ACME Marxist School of Journalism? :)

    I think his pet “theories” are off in la-la-land. If they were true, he wouldn’t had to massage the evidence in such ridiculous ways to get the desired results.

    I thought the Antarctic ice-cores show the Holocene warmth (~8-10 kya) slowly tailing downward to present, just like the Greenland cores. What does Antarctica have to do w/NH summers? His tropical “coolness” data apparently relies on little more than the Quelccaya data.

  11. Steve Sadlov
    Posted Aug 15, 2006 at 1:02 PM | Permalink | Reply

    What is this sea ice doing? (Semi rhetorical question / quiz):

    http://pafc.arh.noaa.gov/ice.php?img=2250aa

    I look at this at least weekly. Believe it or not, this influences Northern California weather.

  12. jae
    Posted Aug 15, 2006 at 1:25 PM | Permalink | Reply

    11: What IS the sea ice doing? I can’t decipher the picture.

  13. Steve Sadlov
    Posted Aug 15, 2006 at 2:05 PM | Permalink | Reply

    I’ll give a hint. Steve B’s rants notwithstanding, at this point, unless something truly dramatic and unprecedented happens, we’ll not have a record low ice extent at max melt. In fact, we might not even see a melt equal to last year’s non record low extent. I’ve been commenting elsewhere about the reestablishment of that persistent nearly N to S jet down from the high Arctic, down through the Bering Sea and on down to about 140W and 35N, creating baggy troughs and cut offs here on the West Coast. Man, all that north wind up on the Arctic Coast, all those cold, cold, Cold Fronts dampending sprits in Anchorage, where today’s high is in the high 50s … I wonder what is will be in Barrow today? ….. North Pole is below freezing for sure …. ;)

  14. Alex
    Posted Aug 15, 2006 at 4:17 PM | Permalink | Reply

    What is the key for that ice image? All I can make out are contrasting shades of gray?

  15. Steve Sadlov
    Posted Aug 16, 2006 at 10:00 AM | Permalink | Reply

    More Holocenish analysis. A really good paper, considering it’s brevity:

    http://pafc.arh.noaa.gov/climvar/climate-paper.html

  16. Steve Sadlov
    Posted Aug 16, 2006 at 10:01 AM | Permalink | Reply

    RE: #14 – The ice tends to be more uniform and less wispy than the clouds. There is definitely an art to reviewing these images. I am still in a rather steep learning curve.

  17. KevinUK
    Posted Aug 16, 2006 at 11:47 AM | Permalink | Reply

    #16 Steve S,

    Thanks for the link. I agree – a very readable paper the best bit being a lack of any overt alarmism just a very balanced presentation and discussion of the data.

    KevinUK

  18. Patrick Trombly
    Posted Dec 11, 2007 at 12:08 PM | Permalink | Reply

    I am deeply troubled by the fact that for literally hundreds of years the history books said one thing,
    then all of a sudden they said something else, which was in line with a political agenda.

  19. Posted Dec 11, 2007 at 1:13 PM | Permalink | Reply

    Explain?

  20. SteveSadlov
    Posted Dec 11, 2007 at 1:20 PM | Permalink | Reply

    In complex oscillatory, multistate systems, state transitions are never completely clean. Consider the most recent ice advance to be a “low” state and the current state to be a “high” state. At the initial state transition from “low” to “high” the “signal” rose, then slightly overshot the “nominal” level for a “high” state, leading to the initial lobe of the Holocene optimum. The “signal” then bounced and dipped ever so slightly below the nominal. Then back up, and back down, etc, as the “ringing” in the “circuit” slowly abated. Superimposed, also, on this, are solar minima. The modern WP may correspond to a final “above nomimal” minor lobe, prior to the next state change, back down to “low.”

  21. Dennis Wingo
    Posted Dec 11, 2007 at 1:36 PM | Permalink | Reply

    I am glad that Steve posted something here as I cannot believe that Mann would make this kind of statement!!

    There are tons of data that shows that at the Holocene maximum the Sahara did not exist, it was a Savannah. Monsoon patterns were wildly different than today over Africa and the Middle East, this is known from history as well as climate proxies. Has Mann ever even read the textbook “Paleoclimatology” that shows the much greater extent of the rain forests at this time as well as the one meter increase in ocean level? I thought that this is where the coral reef that is now the city of Miami is located.

    I simply don’t understand why statements like his are unchallenged by the scientific community.

  22. SteveSadlov
    Posted Dec 11, 2007 at 1:42 PM | Permalink | Reply

    RE: #21 – even some scientists con themselves into thinking there was some sort of idyllic, Eden like past state, where everything was perfect (“perfect” here meaning the slightly cold and dry climate of the late 19th through 20th century). Then, mankind went from being a slightly-more-advanced primate and started to rape the Earth. Etc.

  23. welikerocks
    Posted Dec 11, 2007 at 1:50 PM | Permalink | Reply

    Good bump! #18

  24. yorick
    Posted Dec 11, 2007 at 2:11 PM | Permalink | Reply

    Wow, it is interesting to learn from Mann that mile thick glaciers that extended to Long Island NY were melted by warmer summers at high lattitudes while it was cooler everywhere else. I presume then that CO2 did not leave the ocean on account of the heating was local and not global, so on average, ocean temps did not change. I bet the data shows that.

    Look at figure 5

    Oh my gosh, CO2 levels were high during the Holocene Optimum. Whodathunkit? I wonder how this happened with a partial, seasonal warming?

  25. Larry
    Posted Dec 11, 2007 at 2:17 PM | Permalink | Reply

    22, it’s the story of genesis. We had Eden, and we wanted more, and were driven out for our greed. It’s deeply ingrained in western culture. No surprise that Hansen was able to con the evangelicals into jumping on his bandwagon.

  26. Jimmy
    Posted Dec 11, 2007 at 2:21 PM | Permalink | Reply

    Figure 5 doesn’t have the Holocen Optimum…. where are you referring to?

  27. bender
    Posted Dec 11, 2007 at 3:08 PM | Permalink | Reply

    Good bump, yes. I hadn’t seen this gem. The mid-Holocene thermal optimum did not have impacts at lower elevations?!?!

  28. yorick
    Posted Dec 11, 2007 at 5:02 PM | Permalink | Reply

    Jimmy,
    Each of those tiny little tick marks are 10k years. The current CO2 spike began something like 20k years ago. Tho Holocene optimum is dated to …. checking Wikipedia …. 9 to 5K BP

    http://en.wikipedia.org/wiki/Holocene_optimum

    Not sure that my argument holds though, to be honest. I will have to think about it.

    BTW: You can see the Holocene optimum in figure 3. It was significantly warmer in Greenland anyway. This makes sense because the NH summer occured when Earth was closest to the sun and Earth’s tilt(obliquity) was maximized, putting the Sun more directly overhead that it is today.

2 Trackbacks

  1. […] Ice Age phase melted. Several have written effectively about AGW claims for this period, including Steve McIntyre and. Anthony Watts. Michael Mann’s comment was an attempt to deflect the […]

  2. […] Ice Age phase melted. Several have written effectively about AGW claims for this period, including Steve McIntyre and. Anthony Watts. Michael Mann’s comment was an attempt to deflect the […]

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