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Global Ocean Warming: How Much and Why?
Volume 3, Number 10: 15 May 2000

In a news story highlighting the work of Levitus et al. (2000), Richard Kerr's title all but announces the finding of climatology's Holy Grail: "Globe's 'Missing Warming' Found in the Ocean." Ah, that which was lost is found. Or is it?

Before we consider this question, it is interesting to note that Kerr acknowledges that much of the warming that has been predicted to occur as a consequence of historical increases in the atmospheric concentrations of a number of greenhouse gases has indeed been missing. That is to say, his purposeful choice of words is admissive of the fact that earth's atmosphere has not warmed by the amount that has long been predicted. But now, we are told, the "missing warming" has been found; and once again, all is well with climate modeling: disaster is back on track.

So just how much warming has been found? In a detailed analysis of a vast array of oceanic temperatures spanning the globe and reaching from the surface down to a depth of 3000 meters, Levitus et al. found a whopping 0.06C temperature increase between the mid-1950s and mid-1990s. Because of the fact that the oceans of the globe have a combined mass some 2500 times greater than that of the atmosphere, however, this number, as small as it looks, is truly significant. But is it correct?

Although their data extended back in time several years beyond the point at which they specified the warming to begin, Levitus et al. computed the linear trend in temperature between the lowest valley of their oscillating time series and its highest peak, ensuring that they would obtain the largest warming possible. In addition, the strong oscillatory behavior of the oceanic temperature trend they uncovered all but insures that the next decade will be one of oceanic cooling. Hence, over a moderately longer time period, stretching into both the past and future, global ocean warming would be computed to be much less than what Levitus et al. have reported; and the extended length of record would make the rate of warming smaller still. Yet in spite of these readily evident facts, NASA's James Hansen is quoted by Kerr as saying that the new ocean-warming data "imply that climate sensitivity is not at the low end of the spectrum" that has typically been considered plausible.

But the warped hype does not end with the magnitude of the warming; it continues with its cause. Climate modeler Jerry Mahlman, for example, states - according to Kerr - that the study of Levitus et al. "adds credibility to the belief that most of the warming in the 20th century is anthropogenic." Yet Levitus et al. clearly state that "we cannot partition the observed warming to an anthropogenic component or a component associated with natural variability."

Which brings us back to the subject of climate sensitivity. To calculate such a parameter one must have values for both a climate forcing and a climate response. And if you can't even identify the source of the forcing, much less its magnitude, it is clearly impossible to calculate a sensitivity.

So maybe the discovery of Levitus and colleagues wasn't the Holy Grail after all; but it was a piece of the puzzle, and a good one at that. Nevertheless, there are many additional pieces yet to be discovered; and even when they are all in hand, we will still have to fit them together. Even so, some exuberance is in order; but we would do well to be more temperate in our evaluation of each new scientific finding related to global climate change. Knowledge must precede wisdom; and we're still just scratching the surface of the prerequisite for what we really need.

Dr. Craig D. Idso
Dr. Keith E. Idso
Vice President

Kerr, R.A. 2000. Globe's "missing warming" found in the ocean. Science 287: 2126-2127.

Levitus, S., Antonov, J.I., Boyer, T.P. and Stephens, C. 2000. Warming of the world ocean. Science 287: 2225-2229.