One of the issues motivating the environmental movement since its inception has been a concern for human health. Recently, worries about the harmful effects of a possible increase in the penetration of UV radiation into the biosphere have received much attention. This section summarizes the causes and consequences of the issue that is at the root of these concerns - stratospheric ozone depletion. Ozone is a form of oxygen. Most of the atmosphere's ozone occurs in the stratosphere.
Ozone is colourless and has a very harsh odour.
Approximately 90 per cent of all ozone is produced naturally in the stratosphere. While ozone can be found through the entire atmosphere, the greatest concentration occurs at an altitude of about 25 km. Ozone also occurs in very small amounts at ground level. Even though both types of ozone are exactly the same molecule, their presence in different parts of the atmosphere has very different consequences. Stratospheric ozone blocks harmful solar radiation - all life on Earth has adapted to this filtered solar radiation.