New Paper “Deep Ocean Warming Assessed From Altimeters, Gravity Recovery And Climate” By Song and Colberg (2011).

There is a new paper that adds to the understanding the global warming. It is [h/t to Skeptical Science]

Song, Y. T., and F. Colberg (2011), Deep ocean warming assessed from altimeters, Gravity Recovery and Climate
Experiment, in situ measurements, and a non‐Boussinesq ocean general circulation model
, J. Geophys. Res., 116, C02020,
doi:10.1029/2010JC006601

with the abstract [boldface added]

“Observational surveys have shown significant oceanic bottom water warming, but they are too spatially and temporally sporadic to quantify the deep ocean contribution to the present‐day sea level rise (SLR). In this study, altimetry sea surface height (SSH), Gravity Recovery and Climate Experiment (GRACE) ocean mass, and in situ upper ocean (0–700 m) steric height have been assessed for their seasonal variability and trend maps. It is shown that neither the global mean nor the regional trends of altimetry SLR can be explained by the upper ocean steric height plus the GRACE ocean mass. A non‐Boussinesq ocean general circulation model (OGCM), allowing the sea level to rise as a direct response to the heat added into the ocean, is then used to diagnose the deep ocean steric height. Constrained by sea surface temperature data and the top of atmosphere (TOA) radiation measurements, the model reproduces the observed upper ocean heat content well. Combining the modeled deep ocean steric height with observational upper ocean data gives the full depth steric height. Adding a GRACE‐estimated mass trend, the data‐model combination explains not only the altimetry global mean SLR but also its regional trends fairly well. The deep ocean warming is mostly prevalent in the Atlantic and Indian oceans, and along the Antarctic Circumpolar Current, suggesting a strong relation to the oceanic circulation and dynamics. Its comparison with available bottom water measurements shows reasonably good agreement, indicating that deep ocean warming below 700 m might have contributed 1.1 mm/yr to the global mean SLR or one‐third of the altimeter‐observed rate of 3.11 ± 0.6 mm/yr over 1993–2008.”

There is a significant analysis quality issue with the authors using “the top of atmosphere (TOA) radiation measurements” as one of the constraints on their analysis. These radiation measurements are of fluxes and have a signficant uncertainty.

 Nonetheless, if we assume the analysis of Song et al 2011 is robust in that there is significant ocean heating below 700m (~1/3 of that between the surface and 700m if the steric sea level rise scales linearly in Joules), then this is a significant sink for this heat with respect to the rest of the climate system. 

The website Skeptical Science did not discuss this sink but, since heating at depth presumably is distributed spatially and becomes quite diffuse, its reentry into the higher ocean and atmosphere will be slow and muted, if it occurs at all in coming years and decades.  The heating of the remainder of the climate system (included a “global annual average surface temperature trend) will be less than if this heat was confined to higher in the ocean (i.e. above the thermocline).

This characteristic of the deeper ocean as a heat sink conflicts with the Song and Colberg (2011) conclusion that

“…the enormous heat stored in the deep ocean would have a profound effect on the climate and deserves a serious attention in projecting future sea level changes.”

Any heat stored at depth in the oceans is a damping effect on the climate variability and longer-term change within the rest of the climate system.

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