What is global warming?

Global warming is when the average temperature of the earth rises.  Global Warming happens when industrial sites and cars release greenhouses gasses into the atmosphere  (Carbon Dioxide).  This causes the 'ozone' layer (a part in the earths atmosphere) be eaten therefore raising the temperature.  From doing this we are melting the polar caps causing penguins, polar bears, etc.  If this keeps up these animals will be extinct in the near future.