Streetwise Professor

December 3, 2006

An Inconvenient Truth?

Filed under: Climate Change — The Professor @ 12:08 pm

Recent research shows that the ocean’s heat content declined substantially in 2003-2005, losing in these two years 20 percent of the heat that built up in the 1955-2003 period. This is embarrassing, to say the least, to advocates of the anthropogenic global warming hypothesis (especially NASA’s James Hansen, who has argued that “missing” atmospheric warming he’s been predicting for nigh on to 20 years is due to the ocean soaking up huge quantities of heat.) So, NASA has to spin mightily to explain away these results:

The average temperature of the water near the top of the Earth’s oceans has cooled significantly since 2003. The new research suggests that global warming trends are not always steady in their effects on ocean temperatures. (Click NOAA image for larger view of Sea Surface Temperatures for the Western Hemisphere for Sept. 20, 2006, taken at 10:59 a.m. EDT. Click here for high resolution version. Please credit “NOAA.”)

Although the average temperature of the upper oceans has cooled significantly since 2003, the decline is a fraction of the total ocean warming seen over the previous 48 years.

“This research suggests global warming isn’t always steady but happens with occasional ‘speed bumps’,” said Josh Willis, a co-author of the study at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “This cooling is probably natural climate variability. The oceans today are still warmer than they were during the 1980s, and most scientists expect the oceans will eventually continue to warm in response to human-induced climate change.”

Note the assertion that the cooling is due to natural climate variability–but the previous warming is (implicitly) assumed to be man-made. And it is only an assertion on top of an assumption. Where is the evidence that rejects the null hypothesis that the 1955-2003 warming was due to natural climate variability, in favor of the alternative that it was anthropogenic in origin? If the impact of anthropogenic greenhouse gases is so dominant relative to the natural variability of the climate, how could the latter overwhelm the former? This is a lame rationalization of results that contradict the dominant paradigm–something that should be familiar to anyone who has read Kuhn.

I also note the different standards applied to evidence that contradicts the AGW paradigm and the evidence that supports it. I have read in major media sources reports of numerous studies which document very short-lived trends, such as increases in temperatures or decreases ice over two or three year periods, that are trumpeted as evidence of global warming. They are never explained away as naturally-occurring “speed bumps.”

One last point. In his book Stochastic Climate Theory, Russian scientist S. G. Dobrovolski notes that many climate variables that are averaged over large geographic areas (like ocean heat content) are indistinguishable from random walks. That is, they are integrated time series. Equivalently, they have unit roots. This means that these series tend to exhibit large swings that appear trend-like. They increase for many years, and then may decrease for many years. (It is sometimes said that integrated time series exhibit “stochastic trends.”) That is, long periods of increases in one of these time series may merely reflect their natural time series dynamics, and may not be due to human forcing.

Carbon dioxide has been trending up for years. So has ocean heat content. Both series are essentially integrated. Regressing one on the other will almost certainly result in a highly statistically significant relationship between the two variables–but this regression is spurious. It says nothing about causation.

I recognize the virtues of using ocean heat content as a measure of global climate. As Roger Pielke, Sr. has noted, it is not contaminated by the effect of land use changes or urban heat islands or other factors that can distort temperature readings from land-based weather stations. However, as a globally averaged variable that per Dobrovolski is likely to be integrated, it is also very difficult to use as a measure of the impact of greenhouse gases on climate trends.

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