Weather & Climate - THE THIRD PLANET Eric R....

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THE THIRD PLANET Eric R. Swanson – spring 2009 Weather and Climate Introduction “It is hot and sunny again today in San Antonio”, says the weather reporter. That, as you know, was the weather report and not the climate report. Weather is defined as the state of the atmosphere at a particular place and time. “It is hot and sunny today in San Antonio”. Climate involves a longer period of time and climate is defined as the weather conditions over a long period of time . San Antonio, for example, has a semi-tropical climate. Semi-tropical suggests that San Antonio experiences hot summers and relatively mild winters, the result of San Antonio being just a little north of the tropics and far south of the Arctic Circle. We might also add semi-arid to San Antonio’s climatic description to describe the amount of precipitation received. The Seasons In May of 2006, at the conclusion of graduation ceremonies at Harvard University, 24 students who had just been formally inducted, as they say in those parts, into the company of educated men and women, were asked the following simple question: What causes the seasons? 20 out of 23 newly minted Harvard graduates failed to answer the question correctly, as did a Harvard history professor who was there as the proud parent of one of the graduating seniors. Perhaps Harvard can take some consolation in the fact that the incorrect answers were given eloquently, grammatically correct and with complete confidence. The fact still remains, however, that these “educated men and woman” did not understand why it was warmer in Cambridge, Massachusetts in the July than it was in January. Most of the respondents understood that Earth’s orbit is elliptical, meaning that Earth’s distance from the Sun varied with the seasons, but they incorrectly concluded that summer was caused by the Earth being closer to the Sun in July. While their grasp of the situation might explain why there is snow in Boston in January, they seemed to have never wondered why we are able to import fresh grapes from Chili that very same month or why Australians spend Christmas at the beach. In other words, their explanation did not explain why the Southern Hemisphere is having summer while it is winter across the northern half of the Earth. As for being farther from the Earth, Earth actually comes 3 million miles closer to the Sun during winter in the Northern Hemisphere, making winter a little warm but winter still the same. Northern Hemisphere winters and summers are slightly milder than they might otherwise be, but the heat effect of the change in distance from the Sun is too slight to be the cause for the seasons. More importantly, it offers no explanation for why the Northern and Southern Hemispheres don’t experience summer or winter temperatures and the same time. Seasons are the delightful result of the Earth’s axis making a 23.5 degree angle to
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This note was uploaded on 09/09/2009 for the course GEO 301 taught by Professor Long during the Spring '07 term at University of Texas at Austin.

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Weather & Climate - THE THIRD PLANET Eric R....

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