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  3. GLLOBAL WARMING-THE BEGINNING OF THE END Increased social debate regarding complex issues such as the greenhouse effect and

GLLOBAL WARMING-THE BEGINNING OF THE END Increased social debate regarding complex issues such as the greenhouse effect and

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问题     GLLOBAL WARMING-THE BEGINNING OF THE END
    Increased social debate regarding complex issues such as the greenhouse effect and global warming has definitely increased our environmental awareness. However, such debates are often emotive rather than informative. One can be forgiven, for example, for believing that the greenhouse effect is something we should be trying to eradicate!
    Short-wave radiation, in the form of visible ultra-violet (UV) light from the Sun, penetrates Earth’s atmosphere to warm the surface of the planet. Because all matter is warmer than space, it radiates heat, and part of the sun’s energy is re-radiated out by the Earth’s surface. Greenhouse gases in the atmosphere trap some of this infrared radiation causing the Earth’s surface and lower atmospheric layers to warm up to a higher temperature than would otherwise be the case. Without these greenhouse gases, Earth would be a frozen, hostile environment with an average global temperature of about -15℃ to -19℃, where no life could be sustained. A thermal balance of energy exists where the Earth radiates about the same amount of energy into space as long-wave radiation that it absorbs from the sun. Our atmosphere allows the balance to be achieved because the trace gases trap and absorb heat.

    Other interactions are at play that may affect the Earth’s albedo or balance of energy. The amount or type of cloud cover, for instance, can alter the amount of energy being exchanged. Cirrus clouds reflect more of the sun’s radiation than absorb radiation from the earth. Cumulus clouds do the opposite where the proportion of energy retained is larger than that reflected.
    The detected increase in carbon dioxide in our atmosphere since the Industrial Revolution will also affect the albedo. Not only has there been an increase in carbon dioxide identified. Other greenhouse base gases such as methane, nitrous oxide and chlorofluorocarbons have all increased. It is thought that the latter of these minor greenhouse gases may have a stronger impact on global warming than carbon dioxide levels.
    The largest contributing factor to the increase of greenhouse gases has been the burning of fossil fuels. Carbon in the fuel we burn is oxidised and released into the atmosphere as carbon dioxide. Compounding the problem, deforestation that has taken place over the last 50-100 years reduces the number of trees that are necessary for absorbing carbon dioxide from the atmosphere. Short-term solutions for regional economic survival means the importance of rainforests in this gas exchange has been ignored. Even a layman can see how the greenhouse effect has earned its bad reputation. An out-of- control greenhouse effect is often quoted using the example of Venus, where heat is trapped by thick clouds and a dense carbon dioxide atmospheric element, making the surface temperature as high as 500℃.
    Scientists don’t always agree on their predictions. Whilst they agree that an increase in greenhouse gases will cause the Earth’s temperature to rise, they disagree on what may happen next. Some believe that the subsequent increase in water vapour may help to reduce the temperature. Others believe it will increase the temperature. The collection of meteorological data from observation satellites and a study of samples taken from glaciers and trees for example, support what many of planet Earth’s inhabitants notice for themselves. The globe is warming up. It is generally agreed that by about 2030/2040, the average global temperature (presently +15℃) will have risen by anything up to 5℃ causing polar ice-caps and mountain glaciers to melt and changes to ocean currents and circulation patterns causing coastal waters to rise. New weather patterns and extremes are anticipated.
    Scientists do not know if the increase in average global temperature is just a cycle because of the absence of long-term meteorological data. Comparing climate epochs is complex because so many atmospheric and surface features of land and ocean are different. All of the elements that make up climate are continually changing and dynamically interacting. Knowing therefore, that the Earth cooled during past ice ages and warmed during interglacial periods, has limited worth in predictions for our future. Moreover, records of past climatic epochs are not as reliable or detailed as those records developed in recent decades.
    General Circulation Models (GCMs) are designed to describe basic behaviour patterns of the atmosphere. Used on super-computers, the system still cannot represent all countries and has to rely on spatial representation of the earth. This means that specific consequences of climate change-like predicting the daily weather for specific climatic regions-are more difficult to predict than the global reality of the Greenhouse Effect.
    The computers are much more accurate in showing these broader climatic conditions and predicting global effects than more localized phenomena.
    Many experts conclude that failure to take action in order to limit the impact of human activity is taking a dangerous risk. Others argue that nature will save itself from our apparent inability or disinterest in protecting the planet and that adaptation will, once again, be the key to survival. As these debates continue and governments refuse to act, it is becoming more likely that we will be able to see for ourselves whether or not the dire predictions of global warming are overstated as early as the middle of this century.
The Earth’s atmosphere would not be able to retain heat, were it not for ______.
选项
答案greenhouse gases
解析
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