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Unit 4 Global warmingTHE EARTH IS BECOMING WARMERBUT 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 Cares 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 increase go? Dr Janice Foster says that over the next 100 years the amount of warming could be as low as 1 to 1.5 degrees Celsius, but it could be as high as 5 degreesHowever, the attitude of scientists towards this rise is completely different. On the one hand, Dr Foster thinks that the trend which increases the temperature by 5 degrees would be a catastrophe. She says, We cant predict the climate well enough to know what to expect, but it could be very serious. Others who agree with her think there may be a rise of several metres in the sea level, or predict severe storms, floods, droughts, famines, the spread of diseases and the disappearance of species. On the other hand, there are those, like George Hambley, who are opposed to this view, believe that we should not worry about high levels of carbon dioxide in the air. They predict that any warming will be mild with few bad environmental consequences. In fact, Hambley states, More carbon dioxide is actually a positive thing. It will make plants grow quicker; crops will produce more; it will encourage a greater range of animals - all of which will make life for human beings better. Greenhouse gases continue to build up in the atmosphere. Even if we start reducing the amount of carbon dioxide and other greenhouse gases, the climate is going to keep on warming for decades or centuries. No one knows the effects of global warming. Does that mean we should do nothing? Or, are the risks too great?全球在变暖这会带来什么影响吗?在20世纪期间,地球温度大约升了华氏1度。这个数值对你我来说很可能是无所谓的,但是跟其他自然变化相比较而言,这却是一种快速的增长。那么,这种温度的增长是怎么产生的呢?会产生什么影响 呢? “关爱地球”组织的索菲阿姆斯特朗就在探究这些问题。毫无疑问,地球是在变暖（见表一）,而地球变暖正是人类活动导致而成的,并非是一种无规律的自然现象。所有的科学家赞同这种观点:人们为了生产能量而燃烧化石燃料(如煤、天然气和石油等) ,从而引起了地球温度的升高。这个升温过程的一些副产品就叫做温室气体,其中最重要的就是二氧化碳。贾尼丝福斯特博士解释说: 有一种科学家称之为温室效应的自然现象。这种现象发生在大气层中少量的气体(如二氧化碳、甲皖、水蒸汽等)吸收太阳的热量,因而使地球变暖的时候。如果没有这种温室效应,地球的温度将比现在的温度还要低33摄氏度左右。因此,我们需要这些气体。当我们在大气层中增加了大量额外的二氧化碳时,问题就来了。这意味着更多的热量被困在大气层中,从而引起全球温度上升。我们知道,在过去100-150年期间,二氧化碳的含量急剧增加了。有一位名叫查尔斯基林的科学家曾经把1957-1997年期间大气层中二氧化碳的含量作了精确的统计。他发现,在这些年里,大气层中 的二氧化碳含量从315/1000 000上升到370/1000 0000 (见表二)。所有科学家都接受这个数据。他们还赞同下述观点,正是由于越来越多燃烧化石燃料导致了二氧化碳的增加。那么气温会升到多高?福斯特博士说,在今后的100年里,全球变暖的量可能低到1-1.5摄氏度, 但是也有可能高达5摄氏度。然而,科学家们在对待升温的态度上却是大不相同的。一方面,福斯特博士认为气温升高5度的趋势可能是一场大灾难,她说:“对于未来的气候,我们不可能作出精确的预测,但是那时的天气可能是很糟糕的。”同意她的观点的其他科学家认为,全球变暖会导致海平面上升好几米:也有人预言会出现严重的风暴、洪涝、干旱、饥荒、疫病和物种的绝灭。在另一方面,还有一些人,像科学家乔治汉布利,反对上面的观点,他们认为我们不必担心空气中会有高含量的二氧化碳。他们预言说,变暖的情况不会很严重,对环境的影响也不会太坏。汉布利实际上是这样说的:“二氧化碳含量的增加实际上是件好事,它使植物成长更快,庄稼产量更高,还会促进动物的生长一一所有这些都能改善人类的生活。”温室气体继续在大气层中聚集。即使我们开始减少二氧化碳和其他温室气体的含量,在(未来)几十年或几个世纪内,气候仍会持续转暖。没有人知道全球变暖会带来什么样的影响。这是不是意味着我们就不必采取任何措施昵?还是说,这样不采取任何措施危险性会很大呢?
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