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Global warming in our neighborhood

There has been a lot of discussion recently in The Union dealing with the science of global warming by individuals with business and economic backgrounds. Unfortunately, atmospheric science is exceptionally difficult. And, although I hold a warm place in my heart for the second law of thermodynamics and I have written a thermodynamics textbook, I am nevertheless unqualified to rebut these articles in detail. This is a knot of Gordian complexity.

But there are a few simple facts, agreed to by all, which should give us pause. First, no one disputes the fact that greenhouse gasses are on the increase in our atmosphere. Second, there is ample evidence elsewhere in the solar system of the dramatic effect of greenhouse gases on planetary temperature.

In the figure that appears with this column, you see three planets – Earth and its two neighbors, Venus and Mars. Notice their temperatures. (The reported temperatures vary somewhat according to methods of measurement and definitions of the mean.) Venus is very much hotter than Earth, and Mars is a bit cooler. Satellite measurements of the atmosphere of Venus show that it is saturated with greenhouse gasses. No dispute on this. But, you say, how do we know that the reason Venus is so much hotter than the Earth is because it is closer to the Sun? It may have nothing to do with the greenhouse effect, you say. Good point.



To fairly compare the effect of the greenhouse gases on Venus, Earth and Mars, we need some standard that neutralizes the effect of proximity to the sun. We can do this by introducing, in imagination, three identical thermometers; we place them in the same orbits as these three planets. We make them very simple so that we may easily calculate their respective temperatures.

The simplest thermometer for reading temperatures caused by the absorption of sunlight is a so-called blackbody thermometer, a body that absorbs all the incident energy and reflects none.




By equating the incident energy on these black bodies to the energy radiated (there is no reflected energy), we can calculate that temperature at which these two factors balance. Incident energy absorbed will be proportional to the crossection. Radiated energy will be proportional to the fourth power to the absolute temperature. We find for the three planets, Venus, Earth, and Mars, temperatures of 132 degrees, 43 degrees, and Ð52 degrees, respectively, as shown in the figure. All temperatures are in degrees Fahrenheit. As expected, the orbiting black body temperatures become cooler, the farther from the sun.

But notice how much hotter Venus is than its corresponding orbiting thermometer, 842 degrees versus 132 degrees. Notice also that Mars is cooler than its reference thermometer. The reason is that Venus is sweltering under an umbrella of greenhouse gases while Mars is virtually devoid of atmosphere. By comparing planetary temperatures with those of their corresponding orbiting thermometers, we have succeeded in neutralizing the effect of the nearness of the planetary orbit to the sun. We may fairly conclude that Venus is suffering mightily from the greenhouse effect, the Earth is only somewhat, and Mars not at all.

(Note to interested teachers: I have written a hands-on application illustrating this phenomenon; it is available on my web site: HYPERLINK “http://www.jamesphurley.com/GreenhouseEffect” http://www.jamesphurley.com/GreenhouseEffect. The only thing you need pay is attention.)

This doesn’t prove that there is a Venus in our future, only that there is an omen on the horizon, and if we should suffer that fate “the fault will lie in ourselves, dear Brutus, not in the stars.”

Taking as my precedent other recent contributions to this page, I, having qualifications only in science and none in business or economics, will confine my recommendations to the fields of business and economics.

We know that a major source of greenhouse gases is the carbon dioxide liberated through the burning of oil and gas in our power plants and cars. So what is our current policy to reduce this pollutant? Continued reliance on oil from the Middle East? Drilling for more oil in the Alaskan Wild Life Refuge?

Why is this a problem? We are currently competing in that oil market with explosive growth in developing nations – China and India in particular. We will be paying an ever-increasing percentage of our GPD to the very oil-rich nations that breed that terrorism that is the other significant drain on our economy and a threat to our peace and well being. We are financing our own dissolution. Is there something wrong with our energy policy?

ooo

Jim Hurley lives in Nevada City and is emeritus professor of physics, UC Davis.


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