高中英语Unit4Globalwarming背景知识拓展新人教版选修6.docVIP

Unit 4 Global warming THE EARTH IS BECOMING WARMER—BUT DOES IT MATTER? During the 20th century the temperature of the earth rose about one degree Fahrenheit. That probably does not seem much to you or me, but it is a rapid increase when compared to other natural changes. So how has this come about and does it matter? Earth Care’s Sophie Armstrong explores these questions. There is no doubt that the earth is becoming warmer (see Graph 1) and that it is human activity that has caused this global warming rather than a random but natural phenomenon. All scientists subscribe to the view that the increase in the earths temperature is due to the burning of fossil fuels like coal, natural gas and oil to produce energy. Some byproducts of this process are called greenhouse gases, the most important one of which is carbon dioxide. Dr Janice Foster explains: There is a natural phenomenon that scientists call the greenhouse effect. This is when small amounts of gases in the atmosphere, like carbon dioxide, methane and water vapour, trap heat from the sun and therefore warm the earth. Without the greenhouse effect, the earth would be about thirty-three degrees Celsius cooler than it is. So, we need those gases. The problem begins when we add huge quantities of extra carbon dioxide into the atmosphere. It means that more heat energy tends to be trapped in the atmosphere causing the global temperature to go up. We know that the levels of carbon dioxide have increased greatly over the last 100 to 150 years. It was a scientist called Charles Keeling, who made accurate measurements of the amount of carbon dioxide in the atmosphere from 1957 to 1997. He found that between these years the carbon dioxide in the atmosphere went up from around 315 parts to around 370 parts per million (see Graph 2). All scientists accept this data. They also agree that it is the burning of more and more fossil fuels that has resulted in this increase in carbon dioxide. So how high will the temperature