重大版高中英语必修第2册第6单元 What is global warming(scripts)

The temperature of the Earth is controlled by the balance between the input from energy of the sun and the loss of this back into space. Certain atmospheric gases are critical to this temperature balance and are known as greenhouse gases. The energy received from the sun is in the form of short-wave radiation, i.e. in the visible spectrum and ultraviolet radiation. On average, about one-third of this solar radiation that hits the Earth is reflected back to space. Of the remainder, some is absorbed by the atmosphere, but most is absorbed by the land and oceans. The Earth’s surface becomes warm and as a result emits long-wave ‘infrared’ radiation. The greenhouse gases trap and re-emit some of this long-wave radiation, and warm the atmosphere. Naturally occurring

greenhouse gases include water vapour, carbon dioxide, ozone, methane, and nitrous oxide, and together they create a natural greenhouse or blanket effect, warming the Earth by 35°C. Despite the greenhouse gases often being depicted in diagrams as one layer, this is only to demonstrate their ‘blanket effect’, as they are in fact mixed throughout the atmosphere (see Figure 1).