Ozone Depletion Learning Path

Ozone depletion overview and two related events

Ozone depletion refers to two related changes observed since the late 1970s: (1) a lowered total amount of ozone in Earth’s upper atmosphere (the stratosphere) and (2) a much larger springtime decrease in stratospheric ozone over polar regions, called the ozone hole. A key additional phenomenon is springtime polar tropospheric ozone depletion events. The main driver is manufactured halogenated chemicals—ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs), HCFCs, halons, and related compounds—which reach the stratosphere and release reactive chlorine and bromine atoms that catalyze ozone breakdown. The ozone layer is important because it blocks harmful ultraviolet radiation (especially UVB). When ozone thins, increased UVB can lead to higher risks of skin cancer, sunburn, cataracts, and other biological harms, as well as damage to plants and animals. Public concern and scientific evidence helped drive international action, most notably the Montreal Protocol (1987), which bans production of major ODS. Since then, ozone levels have stabilized and begun to recover, with the ozone hole expected to return toward pre-1980 levels later in the 21st century. Two related events highlighted in the topic are: (a) the general decline in total stratospheric ozone and (b) the formation of the Antarctic ozone hole (a pronounced springtime polar stratospheric ozone decrease). Both are linked to the same underlying chemistry and increasing emissions of halocarbons, and both have been tracked through satellite and ground-based observations.

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Ozone hole definition and polar springtime decrease

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