During the     1     (twenty) century , the temperature of the earth     2     (rise) about one degree Fahrenheit. It is a rapid increase when compared    3     other natural changes .

There is no doubt    4    the earth is becoming warmer. Scientists believe     5     is human activity that has caused this global warming. The increase in the earth's temperature is due to the    6     (burn) of fossil fuels. Some byproducts of this process     7     (call) “greenhouse” gases, the most important one of    8    is carbon dioxide. Without the “greenhouse effect”, the earth would be thirty-three degree Celsius    9     (cool) than it is. So, we need those gases. The problem begins when we add huge quantities of extra carbon dioxide into the atmosphere, causing the global temperature     10     (go) up.