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北師大版高中英語選修八unit22environmentalprotectionthesecondperiod教案(編輯修改稿)

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【文章內容簡介】 S1: Could you please explain the second paragraph to us? T: The second paragraph tells us the association greenhouse gases have with global warming. The “greenhouse effect” often gets a bad rap because of its association with global warming, but the truth is we couldn’t live without it. Life on earth depends on energy from the sun. About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the pla’s surface and is reflected upward again as a type of slowmoving energy called infrared radiation. As infrared radiation is carried aloft by air currents, it is absorbed by “greenhouse gases” such as water vapor, carbon dioxide, ozone and methane, which slows its escape from the atmosphere. Although greenhouse gases make up only about 1 percent of the Earth’s atmosphere, they regulate our climate by trapping heat and holding it in a kind of warmair blanket that surrounds the pla. This phenomenon is what scientists call the greenhouse effect. Without it, scientists estimate that the average temperature on Earth would be colder by approximately 30 degrees Celsius (54 degrees Fahrenheit), far too cold to sustain our current ecosystem. While the greenhouse effect is an essential environmental prerequisite for life on Earth, there really can be too much of a good thing. The problems begin when human activities distort and accelerate the natural process by creating more greenhouse gases in the atmosphere than are necessary to warm the pla to an ideal temperature. Today, the increase in the Earth’s temperature is increasing with unprecedented speed. To understand just how quickly global warming is accelerating, consider this: During the entire 20th century, the average global temperature increased by about degrees Celsius (slightly more than 1 degree Fahrenheit). Using puter climate models, scientists estimate that by the year 2100 the average global temperature will increase by degrees to degrees Celsius (approximately degrees to degrees Fahrenheit). Now please read the first sentence in the second paragraph. What’s the func tion of thatclause? S1: It is an attributive clause modifying ‘an average increase’. T: Good! ‘that’ refers to ‘an average increase in the Earth’s temperature’. From this sentence we can learn an average increase in the Earth’s temperature will cause climate changes. In the second sentence there is also an attributive clause caused by ‘ which’. What does ‘which’ refer to? S2: ‘Which’ refers to greenhouse gases. T: Right! Greenhouse gases trap heat from the sun in the Earth’s atmosphere. Without greenhouse gases, the earth would be very cold and impossible for life. Do you have any other questions? S2: No. T: There are many useful phrases in the text. Please sum up the phrases and then we will analyze the text. Step V Practice Deal with Ex 5 on page 7. Ask students to do the exercises individually. While doing the exercises, remind students that they should pay attention to the correct form of the g

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