The greenhouse effect is the rise in temperature that the Earth experiences  
because greenhouse gases trap energy from the sun. Without the greenhouse effect,  
the Earth would not be warm enough for humans and other organism to live. But if  
the greenhouse effect becomes stronger, it could make the Earth warmer than usual.  
Even a little extra warming may cause problems for humans, plants, and animals.

     Scientists think that the things people do that send greenhouse gases into the air  
are making our planet warmer.If it were not for greenhouse gases trapping heat in  
the atmosphere, the Earth would be a very cold place. Greenhouse gases keep the  
Earth warm through a process called the greenhouse effect.

The Greenhouse Effect