…that some of the warming nearer to the surface came from the deep ocean.

Guest Post by Bob Tisdale

The paper is Liang et al. (2015) Vertical Redistribution of Oceanic Heat Content. The abstract reads (my boldface):

Estimated values of recent oceanic heat uptake are of order of a few tenths of a W/m2, and are a very small residual of air-sea exchanges with annual average regional magnitudes of hundreds of W/m2. Using a dynamically consistent state estimate, the redistribution of heat within the ocean is calculated over a 20-year period. The 20-year mean vertical heat flux shows strong variations in both the lateral and vertical directions, consistent with the ocean being a dynamically active and spatially complex heat exchanger. Between mixing and advection, the two processes determining the vertical heat transport in the deep ocean, advection plays a more important role in setting the spatial patterns of vertical heat exchange and its temporal variations. The global integral of vertical heat flux shows an upward heat transport in the deep ocean, suggesting a cooling trend in the deep ocean. These results support an inference that the near-surface thermal properties of the ocean are a consequence, at least in part, of internal redistributions of heat, some of which must reflect water that has undergone long trajectories since last exposure to the atmosphere. The small residual heat exchange with the atmosphere today is unlikely to represent the interaction with an ocean that was in thermal equilibrium at the start of global warming. An analogy is drawn with carbon-14 “reservoir ages” which range over hundreds to a thousand years.

A preprint edition of the paper is here. The paper is full of memorable quotes, including (my boldface):

An upward heat transport in the deep ocean may appear to be in conflict with the widespread idea that a large portion of the extra heat added to the Earth system in the past decades should be transported into the deep ocean (e.g. Fig. 1 in Stocker et al. 2013). That inference is based on the assumption that the ocean was in equilibrium with the atmosphere before any extra heat entered. When interpreting measurements of the ocean heat content, it is often assumed that the disturbances arise only from the recent past. However, as emphasized by Wunsch and Heimbach (2014) and the present analysis, the long integration times in the ocean circulation imply an observed response involving the time history of the circulation over hundreds of years, at least.

And contrary to climate models:

Furthermore the ocean, far from being a passive reservoir filled and emptied by the atmosphere, is a dynamically active, turbulent element of a coupled system.

And keeping in mind that Balmaseda et al. (2013) was one of the papers that claimed to have found part, but not all, of Trenberth’s “missing heat”:

Global average cooling in the deep ocean conflicts with some previous ocean heat content estimates (e.g. Balmaseda et al. 2013), but is consistent with the long thermal memory of the ocean, and with other recent studies (e.g. Durack et al. 2014; Llovel et al. 2014).

For more on Balmaseda et al. (2013) and Trenberth’s “missing heat”, see:

[My thanks to Judith Curry, who included a link to Liang et al. (2015) in her recent Week In Review dated March 13, 2015.]

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