Re-reading Climategate and AR4 Review Comments, I noticed an interesting discussion about handling the Law Dome O18 record – a series used in Mann and Jones (2003) and Jones and Mann (2004) with a very elevated MWP.

The Law Dome O18 series was illustrated in Jones and Mann 2004 as follows (although the digital data for most series in this article was commendably archived, the digital version of the Law Dome O18 series wasn’t. After a couple of years of effort, I obtained it from Tas van Ommen.) Law Dome O18 was one of three series used in the Mann and Jones (2003) Sh “reconstruction” ( Cook’s Tasmanian tree ring chronology and Thompson’s Quelccaya, Peru ice core were the others.) The Mann and Jones (2003) SH reconstruction was discussed in the AR4 Second Draft as follows (language unchanged in the final version).

6.6.2 Southern Hemisphere Temperature Variability: There are markedly fewer well-dated proxy records for the SH compared to the NH (Figure 6.11), and consequently little evidence of how large-scale average surface temperatures have changed over the past few thousand years. Mann and Jones (2003) used only three series to represent annual mean SH temperature change over the last 1.5 kyr.

AR4 Second Draft Figure 6.11 purported to show the “locations of temperature-sensitive proxy records with data back to 1000, 1500 and 1750”, but, for some reason, didn’t include Law Dome, Quelccaya and other sites. The caption was as follows;

Figure 6.11. Locations of temperature-sensitive proxy records with data back to 1000, 1500 and 1750 (instrumental records: red thermometers; tree-ring: brown triangles; boreholes: black circles; ice-core/ice-boreholes: blue stars; other records including low-resolution records: purple squares). All proxies used in reconstructions [R1] to [R11] of Northern Hemisphere temperatures (see Table 6.1 and Figure 6.10) or used to indicate Southern Hemisphere regional temperatures (Figure 6.12) are included.

Neither was the Law Dome O18 data shown in Figure 6.12, illustrating SH proxy histories.



IPCC AR4 Second Draft Figure 6.12

The IPCC stated of this data:

Taken together, the very sparse evidence for Southern Hemisphere temperatures prior to the period of instrumental records indicates that warming is occurring in some regions. However, more proxy data are required to verify the apparent warm trend.

SOD Review Comments

One (and only one) IPCC noticed that SH proxies in R1 and R2 (Jones et al 1998, Mann et al 1999) were missing from Figure 6.11:

6-1168 B 30:5 30:5 Figure 6.11a does not show many proxies used in R1, R2 [Jones et al., 1998; calibrated by Jones et al., 2001; Mann et al., 1999 ] : e.g. Rio Alerce, Lenca, Morocco tree rings, Quelccaya, Law Dome [Stephen McIntyre (Reviewer’s comment ID #: 309-63)]

IPCC accepted this criticism (and did add missing proxies), mentioning in passing that they had removed the term “temperature sensitive” from the caption – I hadn’t made this request. In retrospect, this was sort of an odd thing to do, given that these are supposed to temperature proxies. More on this later.

Accepted – Figure (6.11) now shows a more comprehensive picture of proxy series locations used in the references cited. The reference to “temperature sensitive” proxies has been removed in the caption and additional series, as indicated by the reviewer, have been shown.

I also wondered what had happened to the Law Dome proxy and why it wasn’t shown in Figure 6.12:

6-1231 B 34:12 34:12 What happened to the Law Dome proxy? Why isn’t it shown? [Stephen McIntyre (Reviewer’s comment ID #: 309-115)]

This prompted a surprisingly elaborate answer – one that is considerably clarified by the Climategate emails.

Past temperature variations at Law Dome have been inferred from isotopic and borehole records. (1) Jones and Mann (2004) showed an isotope record from Law Dome based on O18. This record has a “cold” present-day and “warm” 1000-1750 period. Dahl-Jensen et al. (1999) showed temperature variations at Law Dome obtained by inverting the borehole temperature profiles. This record has a colder interval (peaking in 1250 and 1850) relative to the recent period, followed by a steady recent warming. Therefore, the opposite trends recorded in these reconstructions do not allow reaching a final consensus on temperature variations at Law Dome during the past millennium.

Although I hadn’t previously noticed this point, Dahl-Jensen (1999) – Dahl-Jensen, D., V.I. Morgan, and A. Elcheikh, 1999: Monte Carlo inverse modelling of the Law Dome (Antarctica) temperature profile. Ann. Glaciol., 29, 145–150. – was not mentioned in the Second Order Draft.

Climategate Letters

The Climategate Letters in July 2006 proved to have a surprisingly lengthy discussion about how to refuse my request that the Law Dome proxy series be shown.

On June 30, 2006 (704. 1153167959.txt), Overpeck wrote:

…

Figure 6.12 …

2. consider adding Law Dome temperature record – Ricardo is investigating, but perhaps Keith/Tim can help figure out if it’s valid to include. Feel free to check with Valerie on this too, as she seems to know these data at least a little

On July 14 (700. 1152912026.txt) Overpeck wrote Briffa, Osborn, Villalba, Jansen and Masson-Delmotte revisiting Figure 6.12:

Subject: figure issues

Hi all – including Eystein, whom I haven’t been able to talk with on

these issues yet:

1) I’d like to get your status report on Fig. 6.12 – based on

feedback from Henry Pollack, we will keep the borehole curves and

corresponding instrumental data. I believe we are also going to add

the new recon from Law Dome – Valerie was going to send. Do you have

everything needed for this figure revision?

Later on July 17, 2006 16:25 (704. 1153167959.txt) Osborn replied to Overpeck, also commenting on his June 30 questions (cc Briffa, Jansen, Villalba, Joos):

Subject: Re: Special instructions/timing adjustment

Hi all,

I’m halfway through these changes and will get the revised figures out to you probably tomorrow, except maybe the SH one, because: I’m not sure if the van Ommen (pers. comm.) data shown by Jones & Mann and suggested by Riccardo are the data to use or not. Is it published properly? I’ve seen the last 700 years of the Law Dome 18O record published, so perhaps we should show just the period since 1300 AD? That period appears in: Mayewski PA, Maasch KA, White JWC, et al. A 700 year record of Southern Hemisphere extratropical climate variability ANNALS OF GLACIOLOGY 39: 127-132 2004 and Goodwin ID, van Ommen TD, Curran MAJ, et al. Mid latitude winter climate variability in the South Indian and southwest Pacific Regions since 1300 AD CLIMATE DYNAMICS 22 (8): 783-794 JUL 2004 …

Cheers, Tim

Late in the evening of July 17 (Arizona time), Overpeck reverted to Osborn that they thought that they would go with borehole data (which didn’t have an elevated MWP – though it had elevated values in earlier periods):

Hi Tim et al (especially Valerie) – again, sorry for the confusion, but hopefully the emails sent and forwarded from Valerie and me this evening helps figure this out. I think we’re going with borehole for Law Dome, but you guys need to confirm it’s the way to go. I’m cc’ing to Valerie in the hope she can try to provide more guidance in this – with a confirmation that it’s the best way to go and will stand up to criticism. If we have multiple conflicting temp recons from Law Dome, and one can’t be shown from the literature as being the best, then we should state that, and show neither – just an idea. BUT, I think Valerie was pretty sure the borehole was best. She should be more available in a day or so.

The next day, (709. 1153233036.txt), Overpeck wrote that Masson-Delmotte had sent them references a couple of weeks earlier and that the Law Dome borehole data was available and should be the data used in a revised Figure 6.12 (various references from Masson-Delmotte were shown in the email):

Hi Tim, Ricardo and Keith – Valerie just reminded me that she sent this to us all (minus Tim) back in June. There is plenty below for discussion in the text, and the Law Dome borehole data can be obtained at the site below (http://www.nbi.ku.dk/side95613.htm). This is the record that should be added to the SH figure.

Thanks, Peck

Soon afterwards on July 18 (709. 1153233036.txt), Osborn wrote to explain that, if they showed the borehole data with its supposedly cool MWP, they would be criticized for not showing the isotope data with its warm MWP. Osborn suggested a Sir Humphrey solution of showing neither – instead talking around the problem verbally in the text;

Hi all, (1) Jones/Mann showed (and Mann/Jones used in their reconstruction) an isotope record from Law Dome that is probably O18 (they say “oxygen isotopes”). This has a “cold” present-day and “warm” MWP (indeed relatively “warm” throughout the 1000-1750 period). The review comments from sceptics wanted us to show this for obvious reasons. But its interpretation is ambiguous and I think (though I’m not certain) that it has been used to indicate atmospheric circulation changes rather than temperature changes by some authors (Souney et al., JGR, 2002). (2) Goosse et al. showed Deuterium excess as an indicator of Southern Ocean SST (rather than local temperature). Goosse et al. also showed a composite of 4 Antarctic ice core records (3 deuterium, 1 O18). Neither of these comes up to the 20th century making plotting on the same scale as observed temperature rather tricky! (3) Dahl-Jensen showed the temperatures obtained by inverting the borehole temperature profiles. This has a colder MWP relative to the recent period, which shows strong recent warming. I have data from (1) and now from (3) too, but not from (2) though I could ask Hugues Goosse for (2). Anyway, (1) and (2) aren’t calibrated reconstructions like the others in the Southern Hemisphere figure, so plotting them would alter the nature of the figure. But if we show only (3) then we will be accused of (cherry-)picking that (and not showing (1) as used by Mann/Jones) because it showed what we wanted/expected. Can I, therefore, leave the SH figure unchanged and can we just discuss the Law Dome ambiguities in the text? Cheers

Tim

Overpeck liked Osborn’s tactic of dealing with the inconsistency verbally (rather than letting readers actually see the inconsistency). Overpeck congratulated his team for their “nice resolution”, but didn’t overlook the opportunity to make a snide comment about the “experts” who had the temerity to wonder why the Law Dome data hadn’t been illustrated:

Subject: Re: Law Dome figure

Hi Tim, Ricardo and friends – your suggestion to leave the figure unchanged makes sense to me. Of course, we need to discuss the Law Dome ambiguity clearly and BRIEFLY in the text, and also in the response to “expert” review comments (sometimes, it is hard to use that term “expert”…). Ricardo, Tim and Keith – can you take care of this please. Nice resolution, thanks.

best, Peck

AR4

AR4 left its mention of Mann and Jones (2003) unchanged as follows:

There are markedly fewer well-dated proxy records for the SH compared to the NH (Figure 6.11), and consequently little evidence of how large-scale average surface temperatures have changed over the past few thousand years. Mann and Jones (2003)used only three series to represent annual mean SH temperature change over the last 1.5 kyr. A weighted combination of the individual standardised series was scaled to match (at decadal time scales) the mean and the standard deviation of SH annual mean land and marine temperatures over the period 1856 to 1980.

Following the CRU strategy, Figure 6.12 was left unchanged with the following sentence added to the text:

Contrasting evidence of past temperature variations at Law Dome, Antarctica has been derived from ice core isotope measurements and from the inversion of a subsurface temperature profile (Dahl-Jensen et al., 1999; Goosse et al., 2004; Jones and Mann, 2004). The borehole analysis indicates colder intervals at around 1250 and 1850, followed by a gradual warming of 0.7°C to the present. The isotope record indicates a relatively cold 20th century and warmer conditions throughout the period 1000 to 1750.

The closing sentence of the SH section was left unchanged:

Taken together, the very sparse evidence for SH temperatures prior to the period of instrumental records indicates that unusual warming is occurring in some regions. However, more proxy data are required to verify the apparent warm trend.

Just in case you wondered what Osborn and Overpeck didn’t want you to see, here it is:



Note that the inversion of borehole temperatures raises interesting questions equivalent to principal component retention – see prior posts on this. I’ve asked the Danish institution for the pre-inversion borehole measurements. See http://www.climateaudit.org/?tag=borehole especially Truncated SVD and Borehole Reconstructions

Update- Dahl Jensen responded in April 2010:

From: Dorthe Dahl Jensen

Sent: April-13-10 10:39 AM

To: Steve McIntyre; tas.van.ommen@xxx; Mark Curran

Subject: Re: FW: Law Dome Borehole Dear Steve McIntyre The temperature measurements of the Law Dome are the property of the

Hobart Glaciology group and I propose you contact them to obtain the data yours sincerely

Dorthe Dahl-Jensen



