Then what is causing the increase in the global average surface temperature? Climate scientists often mention a key climate process     1     (call) the“greenhouse effect“, which has two common meanings: the “natural” greenhouse effect     2    the“man-made” greenhouse effect. The “natural”greenhouse effect refers to the fact     3     heat from the sun enters the atmosphere and warms Earth’s surface as short-wave radiation. The heat     4     (release) back into space at longer wave lengths. Greenhouse gases in the atmosphere, such as methane and carbon dioxide trap some of the heat,     5     (keep) Earth’s climate warm and habitable.     6    this process, Earth could not sustain life. However, the“man-made" greenhouse effect has now become     7     big problem. When people produce huge amounts of extra greenhouse gases by burning fossil     8     (fuel), more heat energy is trapped in the atmosphere and     9     (cause) Earth’s surface temperature to rise     10     ( quick).