Does Rosenthal et al 2013 Contradict Climate Science?

A paper was published in 2013[1] that reconstructed intermediate water temperatures (IWT) for an area of Indonesian waters around the Makassar Straight and the Flores Sea. The study includes two reconstructions, one at 500 m depth and another at 600 m to 900 m depth in an effort to show how Pacific IWT ha sbeen affected by high latitude source waters. The reconstruction somewhat predictably found that during the HTM, average IWT in this area were warmer than in 1970. Given the misuse of this paper by contrarians (see below), I think it best to quote directly from the paper so you can see precisely what this paper is actually about.

The early Holocene warmth and subsequent IWT cooling in Indonesia is likely related to temperature variability in the higher-latitude source waters. To assess the mechanisms that caused these hydrographic variations, we estimate down-core salinities and densities for the 500- and 600- to 650-m depths. A temperature-salinity-density plot suggests that although the water masses were significantly warmer during the early middle Holocene than the late Holocene, their densities remained relatively constant throughout the Holocene (fig.S6). Thus, Holocene IWT cooling must have been largely compensated by freshening at the high-latitude source regions.

In other words, IWT near Indonesia are strongly impacted by changes in surface temperatures in the high latitude source waters. The authors suggest that this may be driven by the orbital forcings which are very relevant to global and regional temperature variability on a time scale of 10,000 years.

On orbital time scales, changes in Pacific OHC are largely determined by climate changes in the high latitudes that possibly respond to changes in the tilt of Earth’s axis since the early Holocene. Changes in the seasonal cycle of the high latitudes, driven by Earth’s precession, might be expected to affect the formation and heat-exchange rate of intermediate water masses. However, the similar cooling at intermediate depths influenced by both northern-and southern-sourced water masses, despite the anti-symmetry in the precessional forcing, suggests that on these timescales, Earth’s obliquity exerts the dominant influence on high-latitude temperatures and that OHC is highly sensitive to the changes at these latitudes.

IWT in these waters exhibit a warm HTM followed by neoglacial cooling in a pattern similar to high latitude regions, but temperature variability at the surface is much less than the IWT in these waters. The paper's authors understand and in fact accept that surface temperatures had been comparably stable across the Holocene, but they observe that small changes in surface temperatures across the Holocene correspond to larger changes in IWT when given enough time for heat to be transported to these depths. They also acknowledge that surface temperatures have risen sharply in recent decades due to fossil fuel emissions, and IWT has yet to catch up to the radiative perturbation that is strongly affecting surface temperatures now.

The current response of surface temperatures to the ongoing radiative perturbation is substantially higher than the response of the ocean’s interior, due to the long whole-ocean equilibration time. However, on longer time scales the oceanic response is likely different, as seen in our records where past changes in IWT were much larger than variations in global surface temperatures. The large variations in IWT and inferred OHC during the Holocene and Common era, when global temperature anomalies were relatively small, imply elevated sensitivity to climate conditions in the high latitudes, which, on a multidecadal scale, likely enables the ocean to mediate perturbations in Earth’s energy budget.

If there is good news in this paper, it's in the conclusion that a lot of heat can be transported to depths, and this may have a mediating influence on surface temperatures as global warming continues.

Contrarian Use of Rosenthal et al 2013

Rosenthal's paper includes a spreadsheet with virtually all the data discussed in the paper, and this allows anybody to reconstruct the graphs used in this paper. I think it's wonderful that authors do this, but it seems one of the favorite tricks of contrarians is to take data from these papers and reconstruct the graphs (sometimes with modifications) and annotate these graphs with whatever nonsense they feel like saying, while ignoring the actual content of the paper and even what the graph in the paper actually means. Here are a couple examples with respect to Rosenthal et al 2013.

Andy May

In a blogpost from 2021, Andy May reconstructed the IWT graph at 500m without the uncertainty envelope and without showing that it doesn't include the last 50 years (the data ends in 1970). Then he annotated the graphs with events that happened at various places in world as if these events were the result of the temperatures reported in Rosenthal et al 2013. The extinction of giant deer in Asia, the founding of Rome, the collapse of Egypt, Vikings setting Greenland, and the burning of 50,000 witches are thought to be connected to water temperatures 500 m below the Makassar Straight. Of course, this is blatant cherry picking, and I've covered this strange behavior before in other posts.

One has to wonder if May even bothered reading Rosenthal's paper, which acknowledged that their records showed that "past changes in IWT were much larger than variations in global surface temperatures." Sure enough, if you look at global reconstructions of surface temperatures for the Holocene, none show changes in temperature anywhere near what is seen in this graph of IWT in Indonesian waters. 

To make May's case, common sense would cause rational people to find out what the local temperatures were at the times and places where these events occurred, and then see if there is evidence allowing for the attribution of these events to prevailing weather conditions at in those times and places. But this is not what May is interested in doing. He'd rather slap events on whatever graph seems to fit his narrative.

Correct Plot of Figure 2C

I'm including two graphs, one with Figures 2C and one with both 2C and 2D (top of post) so that you can see them without May's annotations. If you see contrarians using May's annotated graph, feel free to supply one of these in discussions with them. Now to May's his credit he does try to show a current value (2006-2016) from the University of Hamburg for IWT, presumably from this area (but let's not count on it), but that still misses the point that it takes decades or longer for surface heat from high latitude source waters to be transported to these depths in these equatorial waters. And May also doesn't seem to be fully aware of discussion within the paper about recent increases in ocean heat content (OHC) in the Pacific.

Stephen McIntyre

In another blogpost from 2013, Stephen McIntyre shared that this paper was notable because it "presents a Holocene temperature reconstruction that is very much at odds both with Marcott et al 2013 and Mann et al 2008." McIntyre seems to think Rosenthal felt the need to pay homage to catastrophic global warming in a paper that otherwise would contradict it. He writes, "Although (or perhaps because) the article apparently contradicts heroes of the revolution, Rosenthal et al 2013 included a single sentence of genuflection to CAGW" and then quotes the paper saying, "The modern rate of Pacific OHC change is, however, the highest in the past 10,000 years." He also quotes a press release about this paper that says, "In a reconstruction of Pacific Ocean temperatures in the last 10,000 years, researchers have found that its middle depths have warmed 15 times faster in the last 60 years than they did during apparent natural warming cycles in the previous 10,000." In response, McIntyre annotated a graph from the paper as part of his claim that conclusions of the paper and press release are "unsupported by the actual data."

McIntyre's Annotations of Figure 3B

This graph is copied from the paper and then annotated by McIntyre. Below I show the same data from the Excel spreadsheet that accompanies the study.

Figure 3B Properly Plotted

McIntyre's annotations clearly make apples to oranges comparisons. The original Figure 3B (not 4B) that McIntyre annotates contains IWT anomalies (not OHC) for the study area in Indonesia (not the Pacific) at depths between 500m and 900 m (not 0 -700m). Rosenthal's data ends in 1950. McIntyre drew a yellow line on this to show trends and added OHC data converted to temperature for the Pacific 0-700m, I guess to cover the time period between 1950 and 2000. But clearly this is an apples to oranges comparison. Pacific OHC 0-700 m is not the same Indonesian water temperatures between 500 and 900 m depth, even after being converted to temperature. McIntyre performs a similar trick to Figure 2C in this paper, which covers only changes in temperature at 500 m depth in Indonesian waters, not Pacific OHC 0-700 m. Rosenthal's paper instead reconstructed Pacific OHC 0-700 m for each of these time intervals and made apples to apples comparisons between these different time periods.

While it's fair to say that time periods covering thousands of years probably include century time scale periods with more rapid increases in OHC, that doesn't mean it's likely that any of these rapid pulses reached anywhere near modern values, especially since we know from surface proxies that temperature variability was smaller throughout the preindustrial Holocene, and warming rates have accelerated rapidly since the 20th century. And it's also fair to point out that the authors discovered some minor errors in the original paper, and the spreadsheet attached to the study included updated figures, which I plotted below (I had to calculate the 37.5% and 62.5% quartile bound from the data provided). 

* rates were estimated for 1965-2010 interval and extrapolated, assuming constant rates, for a whole century.

I'm not sure where the press release got its figure that OHC is increasing 15x faster than the last 10,000 years. Figure 4 doesn't show rates of change for that entire interval. With the updated figures from the spreadsheet, a weighted average of rate changes would yield -0.68 x10^22 J/century compared to 13.33 x10^22 J/century for 1965-2010. My guess is that the 15x figure is calculated from data that pulls from the entire 10K year interval, not from the dates shown in Figure 4, and it's a safe bet that it was calculated prior to the corrected numbers in the spreadsheet I downloaded.

There are a couple other errors in McIntyre's post that I don't need to cover here (he complains about the uptick in Marcott 2013 and Rosenthal's means of calculating ∆OHC in Figure 4). The former I've already discussed and the latter appears to be rather silly. It turns out that ∆OHC does appear to be increasing more rapidly in recent decades than at any point in the last 10,000 years, even if IWT has not yet caught up with IWT during the HTM.

Conclusion

What this paper actually shows and what contrarians use it to show are quite obviously two very different things. The paper actually concludes from observations that ∆IWT changes by much more than ∆GMST when given sufficient time to transport heat from high latitude source waters to equatorial depths, that "large variations in IWT and inferred OHC during the Holocene and Common era, when global temperature anomalies were relatively small, imply elevated sensitivity to climate conditions in the high latitude." The paper does not produce a reconstruction that contradicts Marcott; it explains how heat transport from high latitude source waters to intermediate waters in the Pacific can mediate perturbations in the Earth's energy budget. 

References:

[1] Yair Rosenthal et al., Pacific Ocean Heat Content During the Past 10,000 Years. Science 342,617-621(2013).DOI:10.1126/science.1240837. You can see a pdf of the full paper here: https://www.researchgate.net/publication/258215955_Pacific_Ocean_Heat_Content_During_the_Past_10000_Years