I know that many of you want to hear our take on Mann (and on ourselves). I’ll get to that. I want to set down some notes on the other speakers while my notes are relatively fresh in my mind; my notes on the morning session are not great, but I’ll give a gist of what happened with Pollack and Schrag.
Both confirmed that they could not estimate temperature 1000 years ago within a half degree. Schrag emphasized that that using proxies to estimate average temperature is a “very difficult statistical problem” and policymakers are “asking more than the community can provide”. That might well be the take-home message from the panel.
Pollack presented first. He didn’t leave a handout for the audience. Pollack does boreholes. I missed the first part of his presentation as Ross and I were re-editing our PPT. (Both of our nerves were frayed by this point in getting ready and Ross had the patience of Job.) We didn’t miss too much and we came in when he was showing a graphic with borehole estimates not back as far as MWP. Pollack emphasized that these were “very noisy” records over and over and that it was hard to extract a signal. I believe that he said that they cut it off before the MWP because of noise problems. Christy asked about groundwater bias. Pollack: “obvious perturbations” e.g. fractures were removed. (It would be interesting to ask mining people about this, about micro-fractures).
To show the linkage between ground and surface temperature (“coupling”), Pollack showed a graphic showing seasonal relation of ground temperature to surface temperature at Fargo ND — only to 4 m. It would be interesting to see some data a little deeper.
Roberts asked about effect of deforestation and land use. Pollack said that the boreholes were mostly rural. Since the boreholes are virtually all opportunistic holes from mineral exploration, I agree that their locations are non-urban, but it was ironic that one of his examples was labelled from Val d’Or, which is a mining town in northern Quebec with bars and even hockey teams. (The owner of their Junior A team is a friend of mine.)
In passing, it would be interesting to get an opinion from a mining person as to whether any biases could be introduced by using opportunistic holes. For example, holes drilled in mineral exploration are hopefully not a random sample of the earth’s surface (although when you’re getting results from a failed drill program, it sometimes seems like it.) For example, gold exploration virtually always takes place (or should take place) in “shear zones” — is any bias introduced by that? If you have to allow for fractures, then you should presumably have to allow for not just big fractures, but little fractures and micro-fractures. You’d want to get a specialist opinion from a mining geologist on that, or an opinion that the fractures don’t matter, in which case, why adjust for the big fractures?
The discussion of ground water worries me. I didn’t quite focus on how ground water mattered or how they dealt with it, but there’s ground water everywhere in hard-rock mines. Pumping water from underground is a major operating issue at underground hard-rock mines. If you leave a mine in northern Canada unattended, it will fairly quickly fill up with water (not in the sense that people will drown if the pumps fail, but in a period of months rather than centuries.) Many of the early steam engines were invented by mining engineers for pumping mines — I think that James Watt had mining customers in Cornwall. I don’t know whether coal mines have similar issues with ground water; the geology is different. Anyway, if ground water is a problem for boreholes, I can’t see where the problem would begin and end for boreholes from hardrock mineral exploration. Anyway, that’s just musing.
To show borehole results prior to the Little Ice Age, Pollack showed either the following graphic from Dahl-Jensen et al [Science 1998] (or a similar one for a shorter period), apologizing for the muddiness.
Ironically, the same article had a perfectly clean version showing a pronounced MWP, which we subsequently showed the Committee as a 5-second comment on boreholes.
I think that Cuffey asked Pollack if he could estimate climate 1000 years ago to within 0.5 deg C. Pollack answered: No.
Schrag had been advertised to us as being very outspoken in his positions, but didn’t make very strong claims about proxies, the opposite in fact. He was there presumably as a coral specialist, but hardly said anything at all about corals, except that they did not provide a long enough record to be relevant to millennial issues.
He said that the big issue is whether we can detect AGW. He showed a graph of temperature changes through geological time including Eocene-Cretaceous (which was much, much warmer). The graph was not dissimilar to one that I presented last spring. He said that the “scale of natural variability far surpasses anything that we’ve seen in recent times”. The corollary that he pointed out was that, because the range in “recent times” was so limited (and here he might even have been thinking on a millennial scale, I’m not sure), it was unfair to have high expectations from modellers.
As to whether the present warming was outside the range of natural variability, he primarily (entirely) relied on Lonnie Thompson’s tropical glaciers as proof that it was. He showed pictures of receding Quelccaya glacier, saying that this hasn’t happened in “1500 years” and is “unprecedented”. He went on to say that similar recession is happening in high-altitude equatorial glaciers and is a “global phenomenon”.
He said that estimation of changing global temperatures should use “stable points” of the earth’s climate (e.g. the western Pacific warm pool). He said that records in the warm pool don’t go back 100 years and therefore a multiproxy approach was needed. He argued that high-altitude tropical glaciers were another “stable point”.
Christy said that he thought that Quelccaya was only 1500 years old. Schrag said that that was merely the length of time that a seasonal signal could be distinguished and that it was older. He mentioned that radiocarbon-dead material had been found underneath the receding glacier and I think that he said that some organics dated 5400 BP had exposed by receding material. [As an editorial comment, we’ve had some discussion on Quelccaya here in the past and Hans Erren has an interesting graphic on Quelccaya accumulation, that was one of the very first things that I was involved with. The seasonal signal is distinguished long before 1500 years. I wonder whether people like Schrag issue errata to panels or not. I don’t see that the presence of radiocarbon-dead material underneath means anything I can think of lot’s of ways for that to happen. I don’t know what has been published on the Quelccaya organics — I’ll take a look when I get a chance. I’ve commented here on organics in Kilimanjaro where I find the evidence very sketchy and not very conducive to accurate dating.]
Schrag pointed out that it would be “nice if the proxies were thermometers” but they aren’t. He said that “many details are swept under the carpet” in making an average [SM – guess what – I agreee with that], but “you have to realize how difficult” it is to make an estimate of average temperature, pointing out that there were disputes even in the instrumental period. He said that it is a “very difficult statistical problem” and policymakers are “asking more than the community can provide”. [Again some SM editorializing: in my opinion, this is a pretty important comment and one that is very germane to the panel’s deliberations.]
On corals, Schrag said that there were no 1000 year corals as they grow fast and die young; and there are organisms that attack them after they die.
Christy asked if there are sediments that preserve centennial information. Schrag” you would need 10 cm/1000 years. They exist but not many places. Suggested that Lloyd Keigwin had located good places in North Atlantic. [SM editorial note: Keigwin’s Sargasso Sea sediments have a pronounced MWP, but not the one near Nova Scotia.]
He was asked about survival of corals in the warm Eocene. He said that corals would not go extinct in a warmer world, but suggested that they would survive as individuals and not form attractive reefs.
Cuffey: do we know the temperature 1000 years ago to within 0.5 degree, yes or no? Schrag: No.