California Climate Change Glossary

Letter O

Opportunity Cost. The cost of an economic activity foregone by the choice of another activity. (APCC).

Optimal control rate. The rate of intervention atwliich the net present value of the marginal costs of the intervention, equals the net present value of the marginal benefits of intervention. (APCC)

Ozone (O₃). Ozone consists of three atoms of oxygen bonded together in contrast to normal atmospheric oxygen which consists of two atoms of oxygen. Ozone is an important greenhouse gas found in both the stratosphere (about 90% of the total atmospheric loading) and the troposphere (about 10%). Ozone has other effects beyond acting as a greenhouse gas. In the stratosphere, ozone provides a protective layer shielding the Earth from ultraviolet radiation and subsequent harmful health effect on humans and the environment. In the troposphere, oxygen molecules in ozone combine with other chemicals and gases (oxidization) to cause smog. (EPA)