Chlorofluorocarbons (CFCs) have been used extensively in last five or six decades as refrigerants in the vapor compression cycle to 
produce refrigerating and air-conditioning effects. In recent years it has been found that CFCs are most destructive to the environment. It has been proved that CFCs are a major cause of depletion of the earth’s stratospheric ozone layer and contribute to the greenhouse effect (global warming).
Presently large quantities of CFCs are being used as refrigerants in a number of refrigerating and air-conditioning systems. Though the refrigerant moves in a closed cycle, there are lots of leakages that escape to the atmosphere and cause destruction of the ozone layer. The most shocking fact about CFCs is that they have exceptionally long atmospheric life which, in certain cases, even extends to 100 years. This means that if CFC refrigerants are leaked in the atmosphere, they will keep depleting ozone layer for the next 100 years to come.
When the CFC refrigerants are leaked from refrigeration or air-conditioning systems, they drift around the lower layers of the atmosphere. Slowly they start infiltrating into the upper layers of the atmosphere and soon reach the ozone rich stratosphere, where they undergo major chemical changes.
What Ozone Does:
In the ozone layer sunlight enters in its pristine pure form; it is called ultraviolet radiation, which is highly intense and dangerous to plant and human life. The ozone layer filters this highly intense sunlight and allows less intense sunlight, which is not harmful to human and plant life, to the surface of the earth.
How it Changes CFCs
The unfiltered sunlight bombards the molecules of CFC refrigerants, and they are pushed towards the stratospheric clouds over the poles. Due to this the CFC molecules get disintegrated. The chlorine atom removed from CFCs reacts with ozone molecule (O3) and converts it into oxygen molecule (O2).
Ozone is Transformed to Oxygen
Now, the oxygen does not have the capacity to filter the highly intense ultraviolet radiations. So what is happening because of the CFC refrigerants is that the protective ozone layer is getting converted into incapable oxygen. Due to this the amounts of ultraviolet rays reaching the surface of the earth becomes very high and then causes excessive heating in the environment, called the greenhouse effect.
The Greenhouse Effect
Due to the greenhouse effect the ice in Antarctica and the poles starts getting melted, which causes large amounts of waters drifting to the rivers, causing floods. Thus, due to depletion of the ozone layer, not only the temperature increases, but also the level of water that causes floods.
To prevent the depletion of the ozone layer due to CFC refrigerants, an international agreement called Montreal Protocol was signed by various countries in 1987. As per the agreement the use of the most dangerous group of CFCs comprising of R-11, R-12, R-113, R-114, R-115, R-500 and R-502, were scheduled to be phased out of production totally by January 1, 1996 in developed countries and by the year 2000 in developing countries.
Refrigerator: http://www.flickr.com/photos/susansimon/2626829710/