Special Report

Sea Change in Global Warming?

According to computer models, ocean temperatures should be rising -- instead they've being going down. What's going on?

By 8.25.06

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For years now, we have been deluged with the news that the earth's oceans are warming as a result of atmospheric changes due to the combustion of fossil fuels.

Typical of these was a 2005 story titled "Where's The Heat? Think Deep Blue," from United Press International, describing a recent paper in Science by NASA climate modeler James Hansen. UPI's "Space Daily" wrote that "Over the past ten years, the heat content of the ocean has grown dramatically."

Hansen's study covered more than just the ocean surface temperature, which can fluctuate considerably from year to year. Rather, by considering a much deeper layer of water (the top 2,500 feet), Hansen actually calculated the increasing amount of heat being stored. According to the UPI story, this provided "a match" with computer model projections of global warming.

The ocean is a huge tub that integrates and stores long-term climate changes. Consequently, when computer models are based on ever-increasing atmospheric concentrations of carbon dioxide, the deep oceans warm, warm, and warm. Like a big pot on a small burner, it takes time to start up, but once the process starts, nothing should be able to stop it.

That's the conventional wisdom of our climate models, but like the conventional wisdom on so many other aspects of life, it's not true to nature.

In the next few weeks, John Lyman of the National Oceanic and Atmospheric Administration will publish a paper in the refereed journal Geophysical Research Letters showing that, globally, the top 2,500 feet of the ocean lost a tremendous amount of heat between 2003 and 2005 -- in fact, about 20% of all the heat gained in the last half-century.

Needless to say, Lyman's figures have climate scientists scratching their heads. No computer model predicts such behavior. And further, the changes in surface temperatures haven't corresponded (yet?) to the average changes at depth, although deep-water temperatures have also dropped some. Nor has the sea level dropped by an amount commensurate with the cooling (water volume varies slightly with temperature).

This last observation has led scientists to speculate that much more ice must be melting into the ocean than they normally assume -- but no one has been able to find it, and it's not for a lack of looking.

There's another hypothesis out there that has received very little attention. It has to do with the amount of carbon dioxide accumulating in the atmosphere.

If carbon dioxide increases at a constant rate, basic physics -- as understood since the 1860s -- says that surface temperature will rise, but that the rate of heating will become lower and lower. In other words, in order for temperatures to increase at a constant rate, as has been observed since 1975, carbon dioxide would have to go up at an ever-increasing rate.

But the ocean is so vast and slow to change that it takes several decades to realize the heating caused by carbon dioxide. Consequently, a change in the rate of carbon dioxide accumulation in the atmosphere wouldn't be noticed for 30 to 60 years, depending upon whose calculations one believes.

Between the time atmospheric carbon dioxide was first directly measured, at Mauna Loa, Hawaii, in 1957, and 1975, it clearly increased exponentially. And once the ocean temperature began to rise, it did so at a constant rate.

Then, about 30 years ago, something very peculiar began to occur. Since 1975, it has been impossible to tell whether the amount of atmospheric carbon dioxide is increasing at an exponential or simply a constant rate.

Because of the lag time required for the oceans to register the change in carbon dioxide, it may not be a surprise that an interval of cooling has been detected. The timing is about right: around 30 years.

But that's just another climate change hypothesis that time will test. Be forewarned, though. As we've learned from the completely unexpected cooling of the deep ocean that began in 2003, we know a lot less about climate change than we think.

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