Is there any compelling reason to believe what these six researchers are telling us about the entire planet? No. cause many other single-point measurements suggest something very different.

Let’s take a look at e.g Petit & etc 1999 (“Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica).

“the Holocene, which has already lasted 11,000 years, is, by far, the longest stable warm period recorded in Antarctica during the past 420,000 years,” (2) “the climate record makes it unlikely that the West Antarctic ice sheet collapsed during the past 420,000 years,” (3) “during glacial inception … the CO2 decrease lags the temperature decrease by several thousand years,” and (4) “the same sequence of climate forcing operated during each termination: orbital forcing followed by two strong amplifiers, greenhouse gases acting first, then deglaciation and ice-albedo feedback.”

They also note that the interglacials preceding and following the one at 238,000 years ago were warmer still. In fact, from the graphs they present, it can be seen that all of the four interglacials that preceded the Holocene were warmer than the current one, and by an average temperature in excess of 2°C.

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Surely little bit different with Hansen’s data?

Does anyone know if there is a large base of theoretical papers that back-up the use of specific proxies used as paleotemperature reconstruction? I know in my own field of research there are papers that explain and justify the methods that are used. Good such papers usually clearly define the limits of the method, what you can and cannot determine with it. Since I only ever see the papers that use these methods (because I haven’t done the searching required), my question is, does anyone know of any solid papers that perhaps define the boundaries of using proxies and back up the thinking

I doubt there is much “basic science” out there. Just like the tree ring fiasco. That is the main trouble with “paleoreconstructions,” nice hypotheses and no real empirical backup. I think “arm waving” is the term that is used on this blog.

The adjustment looks peculiar as it appears that Mg is completely dissolved from G. ruber at OJP below 3500 m, but this isn’t reflected in the formula. More on this tomorrow.

I sent the following email to David Lea yesterday:

Dear Dr Lea,

In Lea et al 2000, you observed the impact of dissolution on Mg/Ca ratios and in Dekens et al 2002, you proposed and illustrated an adjustment to the SST reconstruction for Hole 806B to allow for this effect. In Medine-Elizalde and Les 2005 and Hansen et al 2006, you appear to have used the earlier transfer function which does not allow for dissolution. Is this a correct understanding? Why did you revert to the earlier methodology?

Regards, Steve McIntyre

I notice on looking again that the measurements were taken over a 2-year period. Nevertheless, that would not be long enough to tease out any possible effects like I am concerned about.

One also wonders whether any possible difference in growth rates of the different foraminifera also affects the Mg/Ca ratio they are measuring. In turn, since these are photosynthetic organisms, one wonders whether CO2 concentrations in the atmosphere (and dissolved CO2 in the ocean) affects the relative foraminifera growth rates.

Putting these concerns together, do we need to worry about direct effects of CO2 on the measured ratio apart from any indirect effect operating via SST? I could not see how the measurements in the Dekens paper would allow one to correct for such effects, especially since they are made at just one point in time and thus for one atmospheric concentration level of CO2.

Might it be possible that increased CO2 directly raises the modern Mg/Ca ratio regrdless of any effect on SST? If so, would that not bias downward the implied temperatures from previous eras?

Dekens is quite detailed about the problems and error estimates of using foraminifera. The one area that seems to be lacking is much data on “downcore dissolution”, that is, the Mg tends to dissolve out of the foraminifera after they are buried. It seems to depend, as one might expect, on the chemical composition of the core, and does not seem to be well studied.

w.

The reason I ask is I typically see people here discussing the various points of the papers that use these data sets and debating their use, but I rarely see papers linked that specifically talk about the method(s) and their relative strengths and weaknesses. It seems to me that if there is something to “attack” you would direct it at that work and not the subsequent work.