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Global warming: Let's be clear about the likely cause

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Posted: Wednesday, October 24, 2007 10:00 pm

The editors of the http://www.lodinews.com/">Lodi News-Sentinel, normally wise people, recently published a misguided editorial claiming that global warming is not caused by human activity. They have gallantly allowed me to submit a corrective opinion.

There's little doubt that the globe is warming. Even the Lodi News-Sentinel admits this, somewhat reluctantly. We know it for many reasons.

Worldwide temperatures fluctuate quite a bit from place to place and year to year, but it's quite clear that long-term trend is upward - seriously and rapidly upward. Check the Intergovernmental Council on Climate Change.

Glaciers more 10,000 years old, such as those in Glacier National Park, Mount Kilimanjaro, and others, have shrunk rapidly in recent decades. You can find side-by-side comparison pictures on the Internet. The permafrost, frozen for more than 10,000 years, in northern Alaska and Siberia, is melting. You can read about that in any newspaper. The sea ice around northern Alaska, Canada and Greenland has shrunk and thinned to its lowest extent in recorded history.

As the trend continues, hundreds of millions of people will be displaced, while droughts and famines will devastate many others. Wars will be fought over refugees, cropland and water.

Doubters of human-caused global warming blame natural climate fluctuations, natural variations in the sun's output, and other causes far beyond human control. Could this be correct? Yes. Is this likely correct? No.

We know that human activity is the likely cause, for four reasons.

First, all scientists agree that carbon dioxide is a "greenhouse gas." Other factors being equal, increasing atmospheric concentrations of carbon dioxide warm the earth by trapping heat from the sun. Ice cores and geological samples tell us that carbon dioxide concentrations have been much higher and much lower at various times, millions of years ago. When carbon dioxide concentrations have been higher than now, the average global temperature has been higher. When carbon dioxide was lower than now, global temperatures were quite cold.

Second, recent changes in carbon dioxide have not come from volcanoes, the oceans or anywhere else. It is true that ancient heat waves were caused by geologic activity, including massive volcanic eruptions. However, there has been no recent change in volcanic activity or ocean chemistry. The earth is gradually being deforested and urbanized, by humans, but this is not enough to account for the change, either. Carbon dioxide does not come from outer space. There's nowhere else all the extra carbon dioxide could have come from.

In addition, basic chemistry tells us where the extra carbon dioxide in the atmosphere has come from. Carbon dioxide from burned fossil fuel contains a distinctive combination of isotopes. Other sources produce a different isotope combination. Chemists tell us that the vast majority of excess carbon dioxide in today's atmosphere came from fossil fuel.

Third, increased solar radiation is not to blame for global warming. Scientists have carefully measured solar output for more than a century. There are tiny fluctuations, up and down, but nothing that can account for the rapidly warming globe.

Fourth, changes in earth's orbit are not to blame. Small fluctuations in earth's orbit partially account for past ice ages. However, these are well understood and highly predictable. There have been no unexpected changes, and the usual fluctuations do not predict a warming trend now, or in the centuries to come.

Is it possible that rapidly rising carbon dioxide and rapidly rising global temperatures are simply a coincidence? Is it possible that recently increased carbon dioxide is not trapping the sun's heat in the atmosphere, and that millions of tons of atmospheric carbon dioxide, bearing all the signs of human activity, have suddenly and invisibly erupted from some mysterious non-human source over the last century? Sure, it's possible. And, it's possible that "The Wizard of Oz" was a documentary film. It's possible, but not likely.

Alternately, the simplest, most obvious and most logical explanation is that carbon dioxide really is a greenhouse gas, and all the extra carbon dioxide that has entered the atmosphere in the past century has come from the vast quantities of oil and coal burned during that time.

Humanity has always had to face daunting challenges - famine, disease, barbarian hordes or thermonuclear weapons. Wishing them away has never worked. We can't wish global warming away, either. Our grandchildren will thank us for acknowledging the truth and taking corrective action while there still might be time to make a difference.

Dr. Timothy Miller is a Lodi resident and a licensed clinical psychologist.

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