June 15, 2001 COLUMBUS, Ohio -- Global warming is a natural geological process that could begin to reverse itself within 10 to 20 years, predicts an Ohio State University researcher.
The researcher suggests that atmospheric carbon dioxide -- often thought of as a key "greenhouse gas" -- is not the cause of global warming. The opposite is most likely to be true, according to Robert Essenhigh, E.G. Bailey Professor of Energy Conservation in Ohio State's Department of Mechanical Engineering. It is the rising global temperatures that are naturally increasing the levels of carbon dioxide, not the other way around, he says.
Essenhigh explains his position in a "viewpoint" article in the current issue of the journal Chemical Innovation, published by the American Chemical Society.
Many people blame global warming on carbon dioxide sent into the atmosphere from burning fossil fuels in man-made devices such as automobiles and power plants. Essenhigh believes these people fail to account for the much greater amount of carbon dioxide that enters -- and leaves -- the atmosphere as part of the natural cycle of water exchange from, and back into, the sea and vegetation.
"Many scientists who have tried to mathematically determine the relationship between carbon dioxide and global temperature would appear to have vastly underestimated the significance of water in the atmosphere as a radiation-absorbing gas," Essenhigh argues. "If you ignore the water, you're going to get the wrong answer."
How could so many scientists miss out on this critical bit of information, as Essenhigh believes? He said a National Academy of Sciences report on carbon dioxide levels that was published in 1977 omitted information about water as a gas and identified it only as vapor, which means condensed water or cloud, which is at a much lower concentration in the atmosphere; and most subsequent investigations into this area evidently have built upon the pattern of that report.
For his hypothesis, Essenhigh examined data from various other sources, including measurements of ocean evaporation rates, man-made sources of carbon dioxide, and global temperature data for the last one million years.
He cites a 1995 report from the Intergovernmental Panel on Climate Change (IPCC), a panel formed by the World Meteorological Organization and the United Nations Environment Programme in 1988 to assess the risk of human-induced climate change. In the report, the IPCC wrote that some 90 billion tons of carbon as carbon dioxide annually circulate between the earth's ocean and the atmosphere, and another 60 billion tons exchange between the vegetation and the atmosphere.
Compared to man-made sources' emission of about 5 to 6 billion tons per year, the natural sources would then account for more than 95 percent of all atmospheric carbon dioxide, Essenhigh said.
"At 6 billion tons, humans are then responsible for a comparatively small amount - less than 5 percent - of atmospheric carbon dioxide," he said. "And if nature is the source of the rest of the carbon dioxide, then it is difficult to see that man-made carbon dioxide can be driving the rising temperatures. In fact, I don't believe it does."
Some scientists believe that the human contribution to carbon dioxide in the atmosphere, however small, is of a critical amount that could nonetheless upset Earth's environmental balance. But Essenhigh feels that, mathematically, that hypothesis hasn't been adequately substantiated.
Here's how Essenhigh sees the global temperature system working: As temperatures rise, the carbon dioxide equilibrium in the water changes, and this releases more carbon dioxide into the atmosphere. According to this scenario, atmospheric carbon dioxide is then an indicator of rising temperatures -- not the driving force behind it.
Essenhigh attributes the current reported rise in global temperatures to a natural cycle of warming and cooling.
He examined data that Cambridge University geologists Nicholas Shackleton and Neil Opdyke reported in the journal Quaternary Research in 1973, which found that global temperatures have been oscillating steadily, with an average rising gradually, over the last one million years -- long before human industry began to release carbon dioxide into the atmosphere. Opdyke is now at the University of Florida.
According to Shackleton and Opdyke's data, average global temperatures have risen less than one degree in the last million years, though the amplitude of the periodic oscillation has now risen in that time from about 5 degrees to about 10 degrees, with a period of about 100,000 years.
"Today, we are simply near a peak in the current cycle that started about 25,000 years ago," Essenhigh explained.
As to why highs and lows follow a 100,000 year cycle, the explanation Essenhigh uses is that the Arctic Ocean acts as a giant temperature regulator, an idea known as the "Arctic Ocean Model." This model first appeared over 30 years ago and is well presented in the 1974 book Weather Machine: How our weather works and why it is changing, by Nigel Calder, a former editor of New Scientist magazine.
According to this model, when the Arctic Ocean is frozen over, as it is today, Essenhigh said, it prevents evaporation of water that would otherwise escape to the atmosphere and then return as snow. When there is less snow to replenish the Arctic ice cap, the cap may start to shrink. That could be the cause behind the retreat of the Arctic ice cap that scientists are documenting today, Essenhigh said.
As the ice cap melts, the earth warms, until the Arctic Ocean opens again. Once enough water is available by evaporation from the ocean into the atmosphere, snows can begin to replenish the ice cap. At that point, the Arctic ice begins to expand, the global temperature can then start to reverse, and the earth can start re-entry to a new ice age.
According to Essenhigh's estimations, Earth may reach a peak in the current temperature profile within the next 10 to 20 years, and then it could begin to cool into a new ice age.
Essenhigh knows that his scientific opinion is a minority one. As far as he knows, he's the only person who's linked global warming and carbon dioxide in this particular way. But he maintains his evaluations represent an improvement on those of the majority opinion, because they are logically rigorous and includes water vapor as a far more significant factor than in other studies.
"If there are flaws in these propositions, I'm listening," he wrote in his Chemical Innovation paper. "But if there are objections, let's have them with the numbers."
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