Climate change is any substantial change in Earth’s climate that lasts for an extended period of time.  Global warming refers to climate change that causes an increase in the average temperature of the lower atmosphere.  Global warming can have many different causes, but it is most commonly associated with human interference, specifically the release of excessive amounts of greenhouse gases. (EPA, 2006)

Greenhouse gases, such as carbon dioxide (CO₂), methane (CH₄), water vapor, and fluorinated gases, act like a greenhouse around the earth.  This means that they let the heat from the Sun into the atmosphere, but do not allow the heat to escape back into space.  The more greenhouse gases there are, the larger the percentage of heat that is trapped inside the earth’s atmosphere.  The earth could not exist in its present state (that is, with life) without the presence of some naturally occurring greenhouse gases, such as CO₂, CH₄, and water vapor. Without any greenhouse gases no heat would be trapped in atmosphere, so the earth would be extremely cold. (NASA, 2002)