By S. P. Huang, H. N. Pollack, and P.-Y. Shen, also known as HPS. This is a very interesting paper. To understand why, you’ll need to at least browse The borehole mystery and More boring.

i-60fb862d3fda74d1432b6d9ca94954ce-huang.png To recap: the image shown was being shamelessly abused by the septics as purported proof that the MWP was much warmer than today and this vital evidence was being suppressed by the IPCC using black helicopters and the usual kind of stuff. I thought that the major point is that the HPS ’97 graph (the one here) just isn’t used anymore by anyone and wondered why not (not even H, P or S used it).

They say:

The reconstruction of climate over the past one to two millennia has not been free of contention… one of our publications… HPS97… was occasionally offered as evidence that the MWP was in fact warmer than late 20th century [e.g., Deming, 2004]. Yet in our later publications on climate reconstruction… HPS00… there are no references to the results of HPS97. The initial purpose of the present paper is to clarify and resolve this apparent change of perspective in our work between HPS97 and HPS00. Although science certainly allows for abandoning earlier results in favor of later results, in our case there is a different explanation. The fundamental difference between HPS97 and HPS00 is that they do not analyze the same data. Below we describe their respective datasets, and show why the results of HPS97 cannot be used for comparing MWP warmth to the 20th century.

Aha! This is just what I want (the explanation of the mystery, I mean. The side-swipes at the septics are a bonus).

So then they explain what anyone who read their paper with care could have discovered for themselves (not McI, obviously):

One very important aspect of data selection relevant to the debate about whether the MWP was warmer than 20th century temperatures, is mentioned explicitly in HPS97
in the section on Data:”We excluded data with representative depths less than 100 m . . . [because] . . .the uppermost 100 meters is the depth range most susceptible to non-climatic perturbations. . .; moreover, subsurface temperature measurements in this range yield information principally about the most recent century”. The consequence of excluding the upper 100 meters is that the 20,000 year reconstructions in HPS97 contain virtually no information about the 20th century. As the authors of HPS97 we can be criticized for not stating
explicitly in the abstract and figure caption that the ‘present’ (the zero on the time axis) really represents something like the end of the 19th century, rather than the end of the 20th century. At the time we published that paper our focus was on trying to extract a broad-brush representation of Late Quaternary surface temperature variability that might be overprinted on the ensemble of world-wide continental heat flux measurements. We did not anticipate that a comparison of late 20th century and Medieval Warm Period temperatures would later become a contentious issue.

Translation: f*ck off you septic b*st*rds and stop quoting our paper for your wacko ends.

i-7f4fd206284ddcf5bfab032bf8759d91-hps08.PNG But here is there new version. “Now” is now a lot warmer than their best-guess MWP; and warmer even than their warmest possible. Fair enough.

But the mystery of HPS97 persists. They do hint that the heat flow database is probably poor quality, as I speculated: The entries in this T-z database meet several quality
control criteria not imposed on entries to the earlier heat flow database.
and HPS97 is a broad-brush look at the entire Late Quaternary (exclusive of the 20th century as noted above), using a large but noisy, low temporal resolution dataset.

There is also a mystery of reconciling the current results with those of HPS97. A brief skim of the current paper says its a meld of the HPS97 and HPS00 datasets. HPS00 is only the last 500 years, so why is the current version so different from HPS97 prior to 2000y ago? HPS97 had a range of 2.5 oC for their mid-range estimate of the difference between LGM (last glacial maximum) and HCO (holocene climate optimum). HPS08 has a difference of 5.5 oC. Thats a big change, which they don’t notice, as far as I can tell. Hopefully someone competent in these things will read the paper in detail and explain.

Comments

  1. #1 SteveF
    2008/09/15

    Why does the Younger Dryas not show up? Not high enough resolution back then?

    ["Because of the progressive inability of the geothermal record to resolve relatively rapid events in the more distant past, there is no apparent signature of the Younger Dryas temperature excursion (12,700-11,500 years BP) in the reconstruction." -W]

  2. #2 Eli Rabett
    2008/09/15

    What I find interesting is the persistence of points that are essentially isosbestic (the curves all cross each other in a narrow range). I think this should say something about the method, tho what, I don’t know.

  3. #3 David B. Benson
    2008/09/15

    Younger Dryas was a (largely) northern hemisphere response; niether in Patagonia nor in Antarctica is there any signature, but rather the Antarctic Cold Reversal, peaking about 1000 years earlier.

    Still, none of the individual borehole recvords seem to show either.

    Regaring isobesticity: I opine the northern hemisphere records ought to show wider swings than southern hemisphere ones.

  4. #4 SteveF
    2008/09/15

    Oh yeah, didn’t see that on my quick scan William. It’s pretty crappy – it was rapid in onset and termination, but it still lasted over 1000 years. Must be pretty low resolution for this not to show up somewhere.

    [It really is very very low rez far back. As they say, the "LGM" value 20 kyr ago is really an average of several glacials and interglacials. Thats if you believe it at all, which IMHO is doubtful -W]

  5. #5 Luboš Motl
    2008/09/16

    Your explanations obviously cannot change anything about the big conclusions. Your comments are either downright wrong, inconsistent, or inconsequential.

    First of all, many of the statements you write are deliberately misinterpreting the reality. The upper 100 meters are sensitive to “non-climatic” signals only in the sense that they have a better time resolution. They contain more information, not less information (as you pretend).

    The temperature in deeper layers gets mixed up and undergoes diffusion, making the picture fuzzy, but it is influenced by the same effects as the surface layers. You can see the higher resolution in the recent era on the graphs because the newest parts of the graph have the highest frequency. Even though MWP is “averaged” (by the diffusion/heat equation) over long periods of time, it is still warmer than the present, even the very short and seemingly “very hot” intervals in the present era. It’s rather likely that the whole 13th century was warmer in average even than the year 1998.

    Second of all, if someone claims that it’s impossible to extract the last 100 years from the data (which is absurd because the more recent data we want, the easier is to extract them), this claim would also hold for their further papers. You can’t have it both ways. Either you can get the recent temperatures from the boreholes or not. Incidentally, the second graph you posted is another example of an incoherent gluing of two methodologies, the same lethal mistake that your not-quite-serious ex-colleague Michael Mann is doing all the time, including Mann 2008.

    Third of all, it is still true that the Pollack et al. 1998 paper came after MBH98 hockey stick and their new work was probably motivated by the hockey stick. In 1998, they erased and handwaved away all inconvenient parts of the data and all inconvenient interpretations that could be inconsistent with the “emergent truth”.

    These explanations make no sense and as both of us – myself and you as an official of the Green Party – know, they’re motivated by the desire of your pseudoscientific movement to regulate the world. Have a nice day in the green Britain, LM

    [Hi Lubos. Sorry to see that you still haven't got in touch with reality! Have fun off in yuor land -W]

  6. #6 Robert Grumbine
    2008/09/16

    Some thoughts about the borehole problem as it’s one a math course of mine studied, back when I was a math major, and it’s one my graduate adviser (Doug MacAyeal, applying it to ice cores) started playing with while I was still in grad school.

    The central problem with any of the time-reversed diffusion problems is that it is fundamentally ill-posed. You can extract useful information anyhow, but only if what you consider useful is within the limits of the method. Over time, the higher frequency variations (day-night, seasons, decadal variations, …) get diffused down below your detection limits. The farther back in time you go, the longer the period of stuff you can’t know about any more. If you take near-surface measurements at high vertical resolution, you can still see diurnal variation. Go deeper, though, and you’ll be stuck with seasons at best.

    Per a question from Hank Roberts in one of the earlier rounds on boreholes … I don’t think there’s anything particularly magical about 500 years. Just that somewhere there will be a point at which you’ve lost so much of the higher frequency climate variation (ENSO, NAO, Solar cycles, …) that what you’re left with doesn’t look much like the kind of climate signal you want to be studying. ‘Higher frequency’ also means any rapid step changes in climate. (For the more technical: Take the fourier transform of a step function and look at the spectrum.)

    No specific comments on the paper(s) at hand, just generalities about how these methods behave.

  7. #7 AntiquatedTory
    2008/09/17

    W,
    I had no idea you were an “official” of the Green Party. I thought you just were some guy running on their ticket in your local council.
    Anyway, really sorry for feeding the troll, even second-hand, but I do live in his country and I do have to put up with the intellectual cover he provides President Klaus and the environmentalism==bolshevism wing of the ODS. It’s a kind of mental pathology here, to see everyone slightly to the left of you as a Bolshevist just itching to ship dissenters off to the Gulags again, even when said lefties stand for things diametrically opposed to any Bolshevist policies. (The Bolshies, as I’m sure you know, never met a factory or a strip mine they didn’t like. They did have a particular mania for controlling nature through technology, which is the only link to environmentalism I can think of.)
    Anyway, I did want to know why exactly W consider’s Motyl’s position to be orthogonal to reality. I see that he thinks you all are supporting HPS when you are all actually asking tough questions. But the only substantive point I quite follow is Motyl saying that borehole readings can’t be unreliable for the 20th century in the 1998 paper but reliable in the 2000 paper. When I looked through the 2008 Geophysical Research Letter, I understood that the 20th century temperatures were obtained from instrumental records, not the boreholes. Am I right? Could Motyl have made such a trivial mistake? I’ve looked Dr Motyl up, he has published some very respectable work on string theory, a field where you’d be crucified by your peers for an oversight like this.

    [Lubos, insofar as I can understand it, is a respectable string theorist. But when he ventures into climate he starts foaming at the mouth.

    I'm afraid I didn't bother to read what Lubos said in any detail. But I did read what you said. HPS97 excluded the top 100m, therefore their paper, as they say, contains essentially no information about the 20th C. They *don't* say that all boreholes are unreliable for this period: that paper uses a particular database, others might be better. But we do know, because they excluded them, that there is no useful info about 20th C variations in their paper. the current paper says "In HPS00 we used present-day temperatures in 616 boreholes from all continents except Antarctica to reconstruct century-long trends in temperatures over the past 500 years at global, hemispheric and continental scales. The reconstructions in HPS00 use primary temperature data from another database containing high quality borehole temperature versus depth (T-z) profiles compiled for the explicit purpose of climate reconstruction [Huang et al., 1999]. The entries in this T-z database meet several quality control criteria not imposed on entries to the earlier heat flow database”. So yes, you can get info for the 20th C, but only if you use high-quality measurements not available for HPS97.

    HPS08 says of itself “We then invert this composite 2,000 meter temperature versus depth profile, synthesized from the instrumental record, the century-long temperature trends of HPS00, and the integrated heat flux versus depth data from HPS97, to yield a reconstruction of the surface temperature history over the past 20,000 years.”

    Theres no point telling Lubos any of this, though; he’s not listening -W]

  8. #8 Luboš Motl
    2008/09/18

    Incidentally, the fact that the time resolution in the far past is inevitably less fine – because it’s like solving a heat equation backwards which is also tough and even tougher if you try to go further – is only realized by Robert and me.

    [Lubos you are a funny little creature sometimes. Everyone knows what is only known to Robert and you. Try reading the papers sometimes instead of foaming -W]

    The lower frequency of the old data extracted from boreholes is a universal fact. See, for example, page 13/50 of the Nongovernmental International Panel for Climate Change

    http://www.heartland.org/custom/semod_policybot/pdf/22835.pdf

    which contains some Greenland borehole data. Despite the fact that the old temperatures extracted from boreholes are smeared over long time intervals, many of them still exceed even the hottest years in the recent era.

  9. #9 Hank Roberts
    2010/07/27

    Oh, dear, has the above really been the last word on this topic for almost two years? Pointers, please.

    [No-one reads comments on old posts :-) -W]

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