There is another useful paper on the ocean heat content issue, which adds to the discussion of ocean heat content. It is
Gleckler, P. J., K. R. Sperber, and K. AchutaRao (2006), Annual cycle of global ocean heat content: Observed and Simulated, J. Geophys. Res., 111, C06008, doi:10.1029/2005JC003223.
The abstract reads,
“This study focuses on the annual cycle of global ocean heat content and its variation with depth. Our primary objective is to evaluate a recent suite of coupled ocean atmosphere simulations of the twentieth century in the context of available observations. In support of this objective, we extend the analysis and interpretation of observational estimates. In many respects, the collection of models examined compare well with observations. The largest signal in the annual cycle of ocean heat content is in the midlatitudes, where all the models do a credible job of capturing the amplitude, phasing, and depth penetration. Judging the models’ performance at high latitudes is more complex because of the sparseness of observations and complications owing to the presence of sea ice. The most obvious problems identified in this study are in the tropics, where many climate models continue to have troublesome biases.”
Excerpts from the paper are,
“It is widely recognized that understanding climate variability and potential climate change requires a thorough grasp of oceanic influences. The ocean plays a central role in moderating climate because of its enormous heat capacity relative to the atmosphere.”
“Perhaps the most prevalent tropical systematic error is associated with the Southern Hemisphere split ITCZ in the central-to-eastern Pacific. Recent evidence indicates that in at least one model the split ITCZ is due to deficiencies in the atmospheric model that become manifest within about 24 hours of initialization with observations (J. Boyle, personal communication, 2005). Even though the source of this problem may lie exclusively in the atmospheric model, air-sea interactions are known to exacerbate this shortcoming [Gleckler et al., 2004]. ”
“The historical forcing simulations examined here were initialized from control runs (which have no time varying external forcing), most of which exhibit appreciable drift over time in global ocean heat content. This drift represents slow secular change as a model approaches equilibrium after coupling. How large is this drift compared to the annual cycle of ocean heat content? We have computed the drift in the control runs of each of the models examined here over the contemporaneous (1957–1990) period. The intermodel standard deviation of the drift in the global ocean heat content during this period is 23.5 * 10**22 J, or 0.7 * 10**22 J/yr.”
“Drift in these simulations is more of an issue when evaluating the evolution of annual mean global ocean heat content over the historical period. For these calculations, drift is usually removed by subtracting contemporaneous control run heat content from the twentieth century simulations [e.g., Gregory et al., 2004; Gleckler et al., 2006]. Although models have improved considerably and few now employ flux adjustments, a further reduction in control climate drift is clearly desired.”
The type of analysis presented in this paper is a very useful framework that should be the focus of assessments of global warming and cooling. It also shows that major problems still exist in the ability of coupled atmosphere-ocean models to skillfully predict climate change.