This is a very small subset of papers where authors report late 20th century warming via non-tree ring proxies. Coincidentally (or not), the marine sediment core that I am currently working on shows a large 20th century warming signal as well. In fact, I would place more trust in proxies than pre-satellite (pre~1950) or reanalysis data in accurately recording temperature and other climatic variables.

Summary: (to reiterate), Dr. Singer’s claim is false.

Pat Frank responds at Watts’:

Michael Tobis says, “Since Heartland is happy to pay people to say things about science that just aren’t true,…,” with the link pointing to a blog supposing that Patrick Michaels is so very dead wrong to be skeptical of non-tree-ring temperature proxies.

Well, Michael, presumably you can point us to the physical theory that will extract a physically valid temperature from a diatom shell, or a spleothem, a coral band, a sedimentary varve, or an ice-core ring. Physically valid is not just scale-it-to-a-measurement-trend-and-call-it-temperature statistical hokum. It’s not just we-can-measure-deuterium-and-18-O and never mind about the possible monsoon shifts or rainings out that are hiding behind the curtain. And it’s not just the ad hoc and tendentious assignment of temperature to the PC1 of a proxy qualitatively judged to be temperature limiting.

Where’s the falsifiable physical theory, Mike? Where are the physical equations that will transform a spleothem (ice core ring, coral band, varve, etc.) into a temperature? If you don’t have them (and you don’t), then Patrick Michaels is correct, Heartland is innocent of any wrong-doing, your champion is wrong, and so are you. Proxy so-called temperatures are not physically real. They have no physical meaning.

I am so tired of people who call themselves scientists all the while taking a thoroughly glaringly obviously facile pseudo-science and elevating it to holy writ. What is it with you people, that you hold your professional integrity so cheaply?

[ Kau replies on his blog as follows: ]

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A person by the name of Pat Frank on WUWT responded to this post by saying this . He claims that there is no physical theory backing up proxy reconstructions, that paleoclimate variables thus obtained are not physically real and that paleoclimatologists are guilty of “statistical hokum” by scaling a measurement to a trend and calling it temperature. This post is motivated by the aforementioned accusation.

First of all, let me start by pointing out the irony of this situation. Fred Singer (who is confused with Patrick Michaels by the WUWT commenter – get your facts straight… Oh wait…) was the person to claim that proxies do not show 20th century warming. He used this (false) hypothesis to claim that global warming was not happening. Therefore, it is clear that he puts faith in proxy reconstructions as he uses them to argue his point. Now, we have another denier claiming that proxy reconstructions have no physical meaning, which would nullify what Singer said in the first place! Oh the irony… In any case, let me bring you some scientific snippets (aka truth) on the topic.

Understanding Proxies

This procedure is rooted in physics and the scientific method. As you are all aware, a paleoclimate proxy is a tool that is used to infer geophysical variables from the past. Generalizing this concept, a proxy could be anything that reveals past information. For example, wet grass in your front lawn on a clear, cloudless, sunny morning tells you that it rained the night before. Despite not seeing or hearing the rain yourself, believing that it rained the night before is not a long shot. The fact that the previous night was a cloudy one can be inferred too. It is logical to subscribe to this stance because we have seen the grass become wet and seen clouds in the sky when it rains. But how can we be so sure that rain caused the grass to be wet? (What if it was a neighbor who accidentally watered your lawn? What if the grass was wet because a pack of dogs urinated all over your lawn last night?) There are ways to test this hypothesis, physically and statistically (Is the grass in the backyard wet too? What about the other houses in the neighbourhood? How likely is it that a pack of dogs could urinate uniformly over all the grass in the neighbourhood?) The philosophy behind proxy based reconstructions, just like geology, is rooted in uniformitarianism – the present is the key to the past. A chemical/physical measurement on a proxy variable (say, stable oxygen isotopes on a coral head that has grown for centuries) reveals a significant amount of information about past geophysical parameters as long as we know how the variable is affected by the relevant geophysical process (eg. the controls of temperature, salinity on the isotopes). Different proxy variables respond to different physical parameters and this can be tested, verified and validated by experiment.

The Physics of Proxies: Foraminifera & Stable Isotopes

18O/16O in any system undergoing a physical/chemical process is termed as 18O/16O in the calcium carbonate of the small shells (reported as δ18O ‰ relative to a standard). We are sure of pinning down this measurement up to a very high precision (error ≈0.05‰ – an order of magnitude less than 0.05%, mind you). Let me focus on a proxy that I am familiar with and well within my realms as a researcher to talk about: oxygen-18 isotopes in the calcium carbonate shells of planktic foraminifera . Foraminifera are small organisms that secrete calcium carbonate shells and live in the ocean. Oxygen-18 , is a stable isotope (doesn’t undergo radioactive decay) of the more abundant oxygen-16 and contains two more neutrons than the latter (ie the atomic mass is more). The change in the ratio ofO/O in any system undergoing a physical/chemical process is termed as isotopic fractionation . We utilize mass spectrometers to measure this ratio ofO/O in the calcium carbonate of the small shells (reported as δO ‰ relative to a standard). We are sure of pinning down this measurement up to a very high precision (error ≈0.05‰ – an order of magnitude less than 0.05%, mind you).

18O) and their departure in chemical and physical properties from the more abundant isotope (16O), arising from a difference in atomic mass in his landmark paper, Nobel laureate Harold Urey , in 1947, explained the behavior of these stable isotopes (O) and their departure in chemical and physical properties from the more abundant isotope (O), arising from a difference in atomic mass in his landmark paper, The Thermodynamic Properties of Isotopic Substances Journal of the Chemical Society, 1947 ). He discovered that temperature is the dominant control on isotopic fractionation.

16O 2 . It is a mixture of the molecules 18O-16O, 18O-18O & 16O-16O – quantified by a certain 18O/16O ratio or δ18O. If you isolated it (closed system) and subjected it to a physical process, say liquefaction, isotope fractionation would occur. You would have a δ18O for the oxygen vapor and a different δ18O value for the liquid oxygen (similar to elementary 18O and the gas would be depleted in δ18O (or more enriched with 16O). Of course, one could also change the ratio by introducing a stream of pure 18O-18O vapor or liquid, but then, the system would no longer be closed. As a simple analogy, consider the oxygen you are breathing in right now – it is not pure. It is a mixture of the moleculesO-O,O-O &O-O – quantified by a certainO/O ratio or δO. If you isolated it (closed system) and subjected it to a physical process, say liquefaction, isotope fractionation would occur. You would have a δO for the oxygen vapor and a different δO value for the liquid oxygen (similar to elementary vapor-gas equilibria studies ). Now, suppose you wanted to obtain different ratios for the vapor and liquid? How can this be achieved? Urey discovered that by increasing the temperature of the system, preferentially, lighter isotopes in the liquid phase would tend to go into gas phase and hence the liquid would be more enriched in δO and the gas would be depleted in δO (or more enriched withO). Of course, one could also change the ratio by introducing a stream of pureO-O vapor or liquid, but then, the system would no longer be closed.

3 is deposited by these creatures, the resultant δ18O is a function of the temperature at the time of fractionation. However since the system is not closed, the δ18O of seawater must also factor in – i.e. how much 18O is available for the organism in the first place? Foraminiferal δ18O is a function of temperature and the δ18O of the seawater at the time that it was deposited: Amazingly, Urey predicted that paleotemperatures may be teased out of stable isotopic measurements of old carbonates utilizing this same principle. In the 50s, his student, Cesare Emiliani , carried out isotopic experiments on foraminifera shells and established quantifiable controls for this proxy in terms of a physical transfer function. When the CaCOis deposited by these creatures, the resultant δO is a function of the temperature at the time of fractionation. However since the system is not closed, the δO of seawater must also factor in – i.e. how muchO is available for the organism in the first place? Foraminiferal δO is a function of temperature and the δO of the seawater at the time that it was deposited:

δ18O foram = f(Temperature seawater , δ18O seawater )

In other words ONLY a change in temperature or a change in seawater δ18O can alter the δ18O ratio of foraminiferal calcite. If temperature and seawater δ18O stayed constant through time, the measured δ18O of would be constant too. This is not the case. Therefore, when we measure isotopes on foraminifera shells in a marine sediment core, and we see that they are not the same, we can infer that there had to have been a change in sea temperature or sea water δ18O (which is related to sea water salinity and ice volume). There is no doubt about this.

Since then, there have been thousands of experiments (laboratory based, culture experiments, sediment traps) to accurately quantify these estimates and to pin down uncertainties – 60 years is a long time! Even though quantitative estimates are refined every now and then due to progress in mass spectrometry and understanding the biology of these creatures, qualitative inference (trends, variability) of foraminiferal proxy records from as far backas the 50s still holds true (Milankovitch cycles, ice ages etc.) In summary, a measurement in a geological artifact (speleothem isotopes, fossil content, paleosols composition, tree-rings width, ice-core bubble makeup etc.) known to respond to a climatic parameter (temperature, humidity, precipitation, pCO 2 etc.) in the present is utilized as a proxy for the past. These proxy measurements are independently verified and statistically validated by robust methods of comparison with instrumental data and should have a sound physical reason as to why they change with aforementioned climate parameter (correlation does not imply causation); only then are proxy reconstructions and their inherent quantitative and qualitative implications accepted by the community. Nobody merely matches trends and principal components of empirical orthogonal functions to a random measurement in an unknown fossil as was accused.

The Physics of Proxies: The Literature

There are plenty of articles in the literature that describe the physical basis of each proxy in great detail. Here I have provided a (few) links to articles in the literature as an example of the scientific scrutiny through which a proxy is put through before it is used for reconstructing geophysical parameters. Note: I have only included a few proxies off the top of my head. Feel free to include your favourites in the comments.

Take Home Message





To state that paleoclimatologists don’t understand the fidelity of proxies is to be in denial. In fact, paleoclimatologists themselves are most critical of proxy measurements and their transferral into reconstructed variables. With advancing scientific progress in terms of instrumentation and new analytical techniques, new proxies are being developed as we speak. Harry Elderfield has an amusing graph regarding the confidence of newly proposed proxies:

Nobody is more critical of new proxies than paleoclimatologists/paleoceanographers themselves.

Taken from Elderfield, GCA (2002)

paleoclimatologists are well within our right as scientists to state that proxies do indeed show a 20th century warming and this is with sound physical reasoning and not mere ‘statistical hokum’. Weand this is with sound physical reasoning and not mere ‘statistical hokum’.

Mr Frank continues at Watts:

Michael Tobis, apologies for the Singer-Michaels mix-up. You wrote, “this is an attack on the whole idea of proxies, which doesn’t directly respond to Singer’s claims that there is no proxy evidence,… Michael, if the “proxies” are not proxies, then there is no proxy evidence. That’s pretty basic, and if you don’t get that, there’s no point talking further. You say that, “the corals [produce] credible and globally coherent ENSO records,” but that’s not the point is it. The point is whether corals produce physical temperature records. Corals respond to, e.g., temperature, precipitation, nutrient flux, and predation. How does anyone extract physically valid degrees centigrade from that? And yet, proxy temperature trends are authoritatively published with ordinates showing resolutions of 0.2 C. Those plots are scientifically meaningless. Worse, they reflect either disingenuousness or incompetence. There is no other choice. And honestly, I don’t think the answer is disingenuousness. You asked, “Pat, is it your claim that there is no such thing as paleoclimate evidence?” Evidence of what, Michael? Warmer-wetter/cooler-drier? Or degrees centigrade? The degrees may be there, but we won’t know until there’s a physical theory with which to derive them. Or do you deny that? You asked, “Is it your claim that there is no science without equations reducible to physics?” I claim there is no science without a falsifiable theory. Physics has them. Chemistry has them. Biology has them. Geology has them. Climate modeling does not. Neither does proxy temperature. It’s good to keep your science straight, Michael. And it’s neither naive nor solipsistic to pay attention to what is science and what most assuredly is not. Proxy thermometry is not science. What MDs do is grounded in Biology. What engineers do is grounded in Physics. Nothing in either profession makes sense without the backing of their foundational science. One might argue empirical rules of thumb, but I promise you won’t make that case. I’ve argued the proxy case at Steve McIntyre’s CA. Rob Wilson, a proxy professional, took issue. He had no good defense. Neither will your cadre. It’s all just associational arguments decorated with numerical filters and statistical arcana. Proceed with your digging, Michael. The verdict won’t change. <hr /> The referenced discussion at CA contains the following summary from Pat Frank: Metabolic theory applied to trees certainly predicts temperature limited growth, but not quantitatively. There are no known metrics derived from trees that can be cranked through a biophysical theory to produce a growth temperature. This quantitative theory plain does not exist, and no statistical methodology can ever produce a physically meaningful metric where there is no physical theory. < hr /> [It’s far from clear what that actually means, short of “there is no such thing as a proxy”, or “nananana I am not listening”. Some other, somewhat more reasonable, or at least at-first-glance reasonable-sounding complaints from naysayers appear on that CA thread. This one from Eschenbach, for instance, one of the more coherent of the naysayers. They seem to be obsessed with tree rings over on that thread, though, as is their usual MO. Those who are new to the climate blogs be warned: any engagement with the tree ring obsession of McIntyre et al is likely to be a bottomless pit. This is the original red herring and they are still flinging it around. My sense is that, like Frank’s clueless claim bolded above, it all boils down to denial, pure and simple. But I’ve never had the patience for it, since in my view tree rings are unimportant. If someone else wants to write an informed tree ring piece, though, we’re interested. -mt] Images: Coral cores used as temperature proxies. Main page pic from Flickr user Derek Keats is in Creative Commons CC BY-SA 2.0

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