There’s a fascinating study which has just been released on a novel method of estimating global mean ocean temperature (MOT) during the last glacial transition. Here is the abstract:

Little is known about the ocean temperature’s long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO₂, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.

Note: “no lead or lag with atmospheric CO2” which implies that as the oceans warm, CO2 rises at the same time, which does not suggest that CO2 is driving ocean temperatures, rather that it is a fast feedback to rising ocean temperatures.

Unfortunately, the press release accompanying this paper has confused many people and diverted attention away from the actual content of the paper due to the fact that one of the authors is quoted as saying that the change in MOT over the past 5 decades has ‘only’ been 0.1C. It seems very likely that this figure was not estimated using this new method, but is an estimate of the increase in MOT using instrumental data. Sadly, an offhand comment by one author has translated into erroneous headlines, e.g. as at GWPF. Of the increase in ocean heat during the modern era, the authors have only this to say in the actual paper:

Today, the global ocean takes up about 93% of the excess heat from anthropogenic activities, which dominates the current global radiation imbalance. Owing to the heterogeneity and size of the global ocean it is difficult to measure its heat content and mean (global) ocean temperature (MOT) precisely. A large number of sensors are needed to track regional changes and derive global trends, as in the Argo float array project. Nevertheless, this system does not yet cover much of the deep ocean (depth below 2,000 m), leaving uncertainty in the MOT estimates for the current warming. For changes in MOT before the Argo float system started (around ad 2,000), the data basis is much weaker, because the observations were much more sparse. Considering that
the slow overturning time of the global ocean (centuries to millennia) determines the responsiveness of MOT to changing climate, there is much interest in reconstructing ocean temperatures before the first observations (about ad 1872).

Considering that changes in ocean heat content are the only practical measure we have of global net changes in top of the atmosphere (TOA) radiative flux – which is in turn a direct measure of the climate forcing due to the accumulation of GHGs – the above paragraph is hardly reassuring. If scientists can’t accurately measure the heat which has accumulated in the system over the past five decades, how can they be sure that their models have got it right?

Of the new method of estimating mean ocean temperature, the study says:

Here we use a proxy for MOT introduced in ref. 9 based on measurements of inert or noble gas mixing ratios (Kr/N2, Xe/N2, Xe/Kr) in ice core samples (see Methods and ref. 10 for analytical details). The data are used to reconstruct past MOT with unequalled accuracy . . . . .

Because the atmosphere is well mixed this method effectively integrates globally. Thus, as opposed to marine proxies, the atmospheric noble gas ratio is a purely physics-
driven proxy for the global ocean heat content and MOT.

From the last glacial maximum to the start of the Holocene, the authors estimate the increase in MOT to be 2.57C +/- 0.24C. This figure is huge but it takes place over thousands of years and is almost certainly primarily a result of orbital forcing. However, the authors found one anomalous and very rapid warming event in the Younger Dryas:

The warming from 12,750 yr bp to 12,050 yr bp (referred to as YD1) within the Younger
Dryas represents the strongest global ocean warming phase withinour record. The MOT change rate is 2.5 ± 0.53 mK yr−1 and the corresponding energy uptake (13.8 ± 2.9) × 1021 J yr−1. This unprecedented natural MOT warming rate is comparable to the strong warming since 1997 estimated in ref. 1, but clearly surpasses the estimate therein for the multidecadal trend from 1971 to 2005.

The YD1 phase is associated with a strong ocean heat uptake of 1.1 ± 0.23 W m−2 (1σ), but the greenhouse gas forcing is basically stable, the orbital forcing change is negligible, the sea-level record does not indicate any major losses of land ice or albedo (Fig. 3b), and other processes tend rather to a slight negative radiative forcing. This suggests that the YD1 MOT warming is driven by ocean dynamics rather than by radiative forcing changes. The drainage of Lake Agassiz probably drove the AMOC changes during the Younger Dryas; however, AMOC-disturbance experiments using intermediate complexity climate models either do not reproduce the high MOT warming rate of YD1 (1.6 °C in about 700 yr)33, or fail to sustain this high rate over the observed period. This suggests that AMOC changes can explain only part of the YD1 MOT warming. In experiments using state-of-the-art global climate models forced by anthropogenic greenhouse gas emissions, none of the 15 models (individually averaged over all realizations) reaches the warming rate of YD1 averaged over 1971–2005 (35 yr). The mean rate over all models is about a third of the YD1 warming rate, even though the greenhouse-gas radiative forcing is at least ten times stronger than during YD138. In summary, this shows that the YD1 MOT warming is challenging the current understanding of global ocean temperature regulation and suggests that either current climate models generally underestimate the ability of the ocean to take up heat, or that climate conditions/drivers during the YD1 have been substantially different from the model experiments mentioned here in a way that allows much stronger heat uptake.

Thus, the rapid Younger Dryas warming identified in this study is challenging conventional theories of ocean heat uptake. This is not the first study either. Recall my article on James Delingpole last year, defending him against the climate bullies, where I quoted one study:

Here we review proxy records of intermediate water temperatures from sediment cores and corals in the equatorial Pacific and northeastern Atlantic Oceans, spanning 10,000 years beyond the instrumental record. These records suggests that intermediate waters were 1.5–2 °C warmer during the Holocene Thermal Maximum than in the last century. Intermediate water masses cooled by 0.9 °C from the Medieval Climate Anomaly to the Little Ice Age. These changes are significantly larger than the temperature anomalies documented in the instrumental record. The implied large perturbations in OHC and Earth’s energy budget are at odds with very small radiative forcing anomalies throughout the Holocene and Common Era.

Seems ‘settled climate science’ may have a bit of a problem.