Claims in the press release and in the article appear to be unsupported by the actual data.
The article itself presents a Holocene temperature reconstruction that is very much at odds both with Marcott et al 2013 and Mann et al 2008. And, only a few weeks after IPCC expressed great confidence in the non-worldwideness of the Medieval Warm Period, Rosenthal et al 2013 argued that the Little Ice Age, Medieval Warm Period and Holocene Optimum were all global events.
Although (or perhaps because) the article apparently contradicts heroes of the revolution, Rosenthal et al 2013 included a single sentence of genuflection to CAGW:
The modern rate of Pacific OHC change is, however, the highest in the past 10,000 years (Fig. 4 and table S3).
In the press release accompanying the article, this claim was ratcheted up into the much more grandiose assertion that modern warming is “15 times faster” than in previous warming cycles over the past 10,000 years (though the term “15 times faster” is not actually made in the peer reviewed article):
In a reconstruction of Pacific Ocean temperatures in the last 10,000 years, researchers have found that its middle depths have warmed 15 times fasterin the last 60 years than they did during apparent natural warming cycles in the previous 10,000.
Rather than quoting the article itself, Michael Mann, an academic activist at Penn State University, repeated the claim from the press release in an article at Huffington Post entitled “Pacific Ocean Warming at Fastest Rate in 10,000 Years”.
However, both the claim in the press release and the somewhat weaker claim in the article appear to be unsupported by the actual data.
In the past, we’ve often observed that great care needs to be taken in the interpretation of spaghetti graphs containing both instrumental and proxy data. In the present case, none of the graphics in Rosenthal et al 2013 contain both instrumental and proxy data, a deficiency that I’ve attempted to remedy in today’s post.
First, here is Rosenthal’s figure (3B) showing their reconstruction of IWT (Intermediate Water Temperature) for the past two millennia, which shows a sharp decline in temperature from the medieval period to the Little Ice Age (which, as at Baffin Island also in the news lately, was the coldest period in the past 10,000 years), with a recovery in the 20th century, but to levels lower than those of the medieval and earlier periods.
On the far right, I’ve plotted Pacific ocean heat content, converted to deg C anomaly (red), together with its trend line. The two solid yellow lines show trend lines for 1100-1700 AD and 1600-1950 AD, two of the three periods considered in Rosenthal Table S4. It is true that the rate of change over the past 55 years is somewhat higher than the trend over 1600-1950, but it is not “15 times higher”. While I don’t think that one can safely reify the fluctuations in Rosenthal’s IWT reconstructions, on the other hand, these fluctuations appear to me to preclude any strong conclusions that the relatively modest increase is unprecedented.
Figure 1. Annotation of Rosenthal Figure 3B. Original caption: “Compiled IWT anomalies based on Indonesian records spanning the ~500- to 900-m water depth (for individual records, see fig. S7). The shaded band represents +-1 SD. Red- OHC Pacific 0-700m heat content converted to temperature using the 0-700m Pacific mass shown in the Rosenthal SI. The values are consistent with 0-700m temperature anomaly values at NOAA
Rosenthal’s assertion that recent OHC trends are unprecedented are derived from their Table S4, which consists of three panels, the first of which is shown below.
In my annotation of their Figure 3B shown above, I’ve shown two trend lines, each of which more or less corresponds to the trends reported on lines 2 and 3 of Table S3: a trend of -0.15 deg C/century from 1100-1700 and a trend of 0.09 deg C/century from 1600-1950. The “money” trend in Table S3 is that shown on the fourth line: the value of 0.032 deg C/century is presumably an error. This is not the only error in the table: in the first column, the observed delta-T in the third line (0.25) is greater than that in the fourth line (0.11), but the delta-HC (5.6) is less than that in the fourth line (8.4) – something that seems to be an error. In passing, I wonder whether the “15 times” claim somehow originates in the seemingly unrelated bolded value of “15″ in the fourth column fourth line. (The derivation of “15 times” is not explained anywhere and is not obviously supported by the data.)