北師大版高中英語選修八unit22environmentalprotectionthesecondperiod教案-免費(fèi)閱讀
【正文】 F. 4. Yes, they are. Because greenhouse gases trap heat from the sun in the Earth’s atmosphere. Otherwise the earth would be very cold and unsuitable for life. 5. We can take public transport, recycling, using lowflow shower heads, buying efficient light bulbs to stop global warming. Step IV Explanation During this procedure teacher will play the tape for students. Students will underline the difficult sentences. After listening to the tape, Teacher will explain the text and deal with language problems. T: After doing the prehension of the text, let’s deal with some difficult language focuses. Now I will play the tape for you .Please make a mark where you have difficulties. After listening to the tape, explain the difficult sentences to students. Before explaining the difficult points, students are asked to refer to the notes to the text on page 114. T: Do you have any difficulties with the text？ 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
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