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Upper-Ocean Heat Content Variability: 1956-2003
Volume 9, Number 7: 15 February 2006

How has the heat content of the upper portion of earth's global ocean varied over the past fifty years?  In a study designed to answer this question, Levitus et al. (2005) conducted Empirical Orthogonal Function (EOF) analyses of gridded, yearly (1956-2003), ocean heat content fields for the 0- to 700-m layer of the global ocean in order to describe the geographic patterns of ocean heat content variability, after which they performed Fourier analyses of the heat content fields with the goal of determining the dominant modes of temporal variability.  They did this because, as they relate, "documenting these space and time scales is a step towards understanding the ocean heat content signal and gaining insight as to whether the observed changes in ocean heat content are due to internal variability of earth's climate system, external forcing, anthropogenic forcing or a combination of these," which is readily recognized as being one of primary goals of current climate science.

So what did they find?  The first four EOFs derived by Levitus et al. accounted for 29% of the global ocean heat content variability between 1956 and 2003.  However, they report that "using the first four EOFs to reconstruct the global heat content integral accounts for most of the signal of the original global ocean heat content integral," and that "even the first three EOFs do a reasonably good job of reproducing the global heat content integral."  Then, in the second phase of their work, they determined that the first four Fourier harmonics that correspond to periods of 48, 24, 16 and 12 years "account for 64% of the variance associated with the global integral of ocean heat content."

Relating these findings to ocean dynamics, Levitus et al. say they "demonstrate that the phenomena associated with the variability of the 0-700 m global ocean heat content integral for 1956-2003 are characterized by gyre and basin-scale spatial variability and time-scales approximately decadal and longer," which variability, in their words, "is dominated by the reversal of polarity of the Pacific Decadal Oscillation in the late-1970s and El Niņo phenomena."

In discussing the implications of their work, Levitus et al. begin by noting that results of "model simulations of earth's climate system suggest that the observed increase in ocean heat content (based on the linear trend) during the past fifty years is due [to] the increase of greenhouse gases in the earth's atmosphere."  However, they report that "these models do not simulate the interdecadal variability in ocean heat content we have analyzed in this paper, leading to suggestions (Sun and Hansen, 2003; Gregory et al., 2004) that the observational database and/or the models are deficient."

With respect to these latter alternatives, Levitus et al. say "we believe the work presented here suggests that the interdecadal variability in ocean heat content is real and is associated with the reversal in polarity of the Pacific Decadal Oscillation."  We agree; and in light of the sentiments they attribute to Gregory et al. and Sun and Hansen - with which Levitus et al. appear to agree - their statement would seem to suggest that the models currently used to simulate the climatic effects of increases in the concentrations of greenhouse gases in earth's atmosphere are in fact deficient.  Needless to say (but we will anyway), we agree with this conclusion too.

The bottom line of these several observations, in our estimation, is that the scientific basis for curtailing anthropogenic CO2 emissions currently rests on a foundation (climate model simulations) that is not up to the task the world's climate alarmists have set for it.  Current climate models are demonstrably deficient, in that they do not properly simulate the behavior of the heat content of the upper 700 meters of the planet's global ocean over the past fifty years.  And if they don't correctly simulate what is past, why should we be asked to believe they can correctly simulate what is to come?

Sherwood, Keith and Craig Idso

Gregory, J.M., Banks, H.T., Stott, P.A., Lowe, J.A. and Palmer, M.D.  2004.  Simulated and observed decadal variability in ocean heat content.  Geophysical Research Letters 31: 10.1029/2004GL020258.

Levitus, S., Antonov, J.I., Boyer, T.P., Garcia, H.E. and Locarnini, R.A.  2005.  EOF analysis of upper ocean heat content, 1956-2003.  Geophysical Research Letters 32: 10.1029/2005GL023606.

Sun, S. and Hansen, J.E.  2003.  Climate simulations for 1950-2051.  Journal of Climate 16: 2807-2826.