The Greenhouse Effect
The Greenhouse Effect is the process by which greenhouse gases (carbon dioxide, water vapor, methane, etc.) absorb and re-radiate thermal energy. This process is what warms our surface up. This course is known as the "Greenhouse Effect" because the gases work like the glass walls and roof of a greenhouse, which allow solar energy to enter, but not allowing thermal energy from escaping. The amount of energy receiving from the sun and the amount of energy returned to space have to be nearly equal in order for Earth to remain habitual. This balance is known as the "radiation balance".
However, scientists have started to notice data that shows that the average global temperature has been increasing in the past century. This is really starting to concern scientists. This increase in average global temperature is known as Global Warming. Some scientists hypothesize that the greenhouse gases in the atmosphere have increased, thus, more energy is being re-radiated back than needed. Human activity, such as burning fossil fuels/deforestation, may be increasing levels of greenhouse gases (such as carbon dioxide) in the atmosphere.