Image of the largest Antarctic ozone hole ever recorded (September 2006).

Ozone is a gas that is present in the ozone layer in the stratosphere of the Earth. There, it absorbs almost all ultraviolet light which is harmful to many organisms. The term Ozone depletion can refer to a number of distinct, but related phenomena:

• Since the 1970s, there has been a decrease in total volume of the Ozone in the ozone layer, of about 4%, per decade.
• There are seasonal variations in the ozone layers; in springtime, there is less ozone in the ozone layer over the polar regions, esp. the south pole. This is generally known as ozone hole.
• In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events.