More boring

i-60fb862d3fda74d1432b6d9ca94954ce-huang.png Following my previous post there has been discussion in the comments on “which graph to believe”. Sadly this becomes ideological, for some. I think the major point is that the HPS ’97 graph (the one here) just isn’t used anymore by anyone, except the septics who want to see a MWP. The graph has never been explicitly disowned, but the authors of it have published plenty more since then, all only going back 500 years (and AFAIK no-one else before or since has tried to use boreholes back that far), and showing a different timing of the cold bit. Naturally, if you’re paranoid, this is because the evil IPCC leaned on them. Frankly, thats black-helicopter stuff of the first order, but its also non-historical because MBH’98 only went back 6 centuries, so didn’t show the MWP one way or another. You have to wait for MBH’99 for the 1000 years, which was *after* the borehole folk switched to 500 years.

But if you don’t like that, then another problem is the temperature it comes out with for the LGM – about -1.5K cooler than “now” (though see next point…). This isn’t nearly cold enough – rather a hint that something is wrong.

Yet another point for those wanting a MWP is that the zero point on the graph doesn’t represent “now” – it represents start-of-20th-century (becasue the top 100m of data were not used). Given what we know from the instrumental record, then even if you believe this graph, the MWP wasn’t warmer than “now” – indeed it was a bit colder.

[Update: a suggestion from someone who has read the paper more attentively than me: It looks to me as though they have done a single inversion using an estimate of the global mean heat flow as a function of depth, as opposed to doing the inversion at each profile and then averaging as in Huang et al. 2000. Their heat flow is based on 37 profiles at 2000m, but 1001 at 100m, so there is a large change in the region being sampled. My guess is that this approach gives meaningless results -W]

The borehole mystery


In 1998, there appears Climate Change Record in Subsurface Temperatures: A Global Perspective (Science 9 October 1998: 279-281) (subs req: sorry; abstract probably free) by Henry N. Pollack, Shaopeng Huang, Po-Yu Shen. The take-home message from that paper is pretty much the graph from http://www.ncdc.noaa.gov/paleo/borehole/core.html, which I’ll inline here (and its the same as used in the TAR). And that is: a 500y record, showing a temperature rise in line with the instrumental record where they overlap (and somewhat colder than most other reconstructions around 1500; but thats not the point here; if you’re interested try this by Mann at al. which reconciles them). And Beltrami 2002 gets a similar-ish result. So that appers to be the current situation with borehole stuff: it goes back 500 years.

i-60fb862d3fda74d1432b6d9ca94954ce-huang.png But, the point is that the same people (HP&S, but in a different order) a year earlier published in GRL (SR, of course :-() a reconstruction going back 20,000 years. There are features of that that appear distinctly odd to me – they only get about 1.5 oC cooling at the last glacial maximum; and to get more it looks like they would have to increase temperatures in the holocene too high. And the LGM was… at least 5 oC colder. Also the timings are wrong: the “node” between the “LIA” dip and “MWP” peak is at 500 years before present, which is when the paper a year later ends with maximum cooling.

And its this earlier paper that McK picks up to argue for a MWP.

So why has the earlier paper disappeared? Of course the true explanation must be nefarious interference from the UN/IPCC to suppress the truth; but what is the excuse? I’m not really sure, and would be grateful for anyone who does know. The 1997 GRL paper appears to use heat flow and about 6000 sites; the 1998 Science uses temperatures and 358 sites. So maybe it turned out there was something badly wrong with the earlier method? It certainly contradicts the later one; and produces implausible values for the LGM temperatures.

The paper “only” gets referenced 17 times, according to WoS, and always in a “various people have done boreholes, including Huang (1997)” sort of way. I can’t see anyone who has used or commented on their particular profiles (apart from the recent uptake by the skeptics, of course).

[Update: Eli has already noticed this oddity (and there is more) but he doesn’t explain it either. He does discover Pollack and Huang in 2000 referencing both studies but apparently failing to notice their incompatibility -W]

[Another update: I’ve had some email exchanges with a very friendly Henry Pollack. He supplies almost all the answers: part of it is HPS 97 paper had data to depths of two kilometers, whereas the 500 year database comprises boreholes mostly in the 300-400 meter depth range. The much larger number of boreholes in the HPS 97 dataset did enable the greater depths to be sufficiently populated to have a reasonable estimates of the mean heat flux over a depth interval. OK, so this is why HPS ’97 goes to 20 kyr and all the subsequent ones only to 500 y. But then this leaves the central problem: why is a larger database of deeper boreholes no longer used? The answer to this seems to be Quality. The datasets used in the 500y studies are better controlled. The HPS ’97 dataset is of heatflow, derived from the International Heat Flow Commission database. But though the heatflow measurements there were derived from temperature measurements, the original Ts are gone and only the heatflow is in the database.

An interesting additional point is that since HPS didn’t use the top 100m of borehole, the reconstruction there contain virtually no information about the 20th century… 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… the present-day is indeed warmer than the ‘goldilocks’ curve b (as well as curve a) throughout the Holocene, and at least as warm as the Medieval Warm Period of curve c (quotes from Pollack).

Which is brings us back to the original point: no-one now uses HPS ’97. The shorter record is preferred, as (presumably) being more reliable -W

ps: datestamp adjusted to push to the top]

UK budget

Today Broon delivered the 2007 budget. Listening to the news, it seems like mostly a nullity: just about everyone has had some taxes raised and others lowered (though we may gain a few hundred from tax changes). Fiddling because you need to be seen to be doing something; and aimed more at looking good and making the opposition look bad. Oh dear, its not promising.

This has nowt to do with climate (and so does the budget, just about).

Spot the difference!

TGGWS was rebroadcast on Monday. I didn’t see it, but B did, and his eagle eyes spotted at least one figure that has changed: see if you can see the differences (LHS:new; RHS:old):

i-287c24ba892633397d58f31d802454a4-tggws-2.jpg

Yes, thats right: they have put it onto the proper time scale; removed the attribution; and deleted the arrows on the RHS. And changed the caption to “110 years”. So… looks like they are listening to at least some of the complaints. However, they haven;t inserted the missing data at the end – I wonder if any views though “hmm thats odd – why stop at 1988?”.

Don’t forget, BTW, that this fig has a dubious source – the OISM petition – so don’t believe it even on the correct time axis. GISS provides a more honest effort.

Next Q: can we get a screen capture when they float the 1000 year temperature graph? I think its from IPCC ’90 but it went past too quickly to be sure.

Even more T/CO2 lags

OK, so we’re back to the question of whether T leads CO2 in the ice cores, the skepics favourite talking point. The std.answer is “OK, so there is a lead (maybe) but…” (Stoat passim). The “but” is a good enough answer, and I suspect most people skip over the (maybe). But its important, because the lag/lead is not at all easy to establish, because the T comes from the ice (via d-o-18 proxy) and the CO2 comes from the bubbles. 800y+/-600 is the current “best guess”, but not certain.

Thanks to GH for pointing out Loulergue et al. [Meh, dead link. Try http://www.clim-past.net/3/527/2007/cp-3-527-2007.pdf perhaps] who propose that the T lead is much smaller or even that CO2 leads: Our results reveal an overestimate of the Δage by the firn densification model during the last glacial period at EDC. Tests with different accumulation rates and temperature scenarios do not entirely resolve this discrepancy. Our finding suggests that the phase relationship between CO2 and EDC temperature inferred at the start of the last deglaciation (lag of CO2 by 800±600 yr) is overestimated and that the CO2 increase could well have been in phase or slightly leading the temperature increase at EDC.

Now… I wouldn’t get carried away by this, since this isn’t definitive either – just interesting at this stage. And I have done no more than skim it. Its worth a skim, just to get some idea of how hard this relatively simple thing is to establish. Note that the paper is under review in an open-access journal, so jump in if you think you’re hard enough!