Abstract

The stratospheric ozone layer protects life on Earth by absorbing harmful ultraviolet radiation from the sun. 90% of the atmospheric ozone abundance reside in the stratosphere; nevertheless, changes in stratospheric ozone may directly impact the troposphere. With increasing industrial production of chlorine-containing halogens in the 1960/70s, stratospheric ozone began to decrease. First scientific studies found that halogens cause chemical ozone depletion in the stratosphere, thus explaining the strong decline in stratospheric ozone during the 1980s and 1990s, when the halogen concentrations grew rapidly. The most dramatic example is the so-called Antarctic ozone hole, a severe ozone decrease occurring over Antarctica each spring. In response, regulations of the production and use of the so-called ozone depleting substances (ODSs) were adopted by the United Nations in the Montreal Protocol of 1987. As a result of the Montreal Protocol and further amendments and adjustments, the ODS concentrations began to level off and slowly decline. Since the beginning of the century, there is also evidence from measurements that stratospheric ozone has started to increase. Models consistently project a full return of global mean stratospheric ozone to undisturbed, historical values in the first half of the 21st century. However, because of complex dynamical and chemical interactions, the date of ozone recovery in different atmospheric regions will strongly depend on the future greenhouse gas scenario. Here, an overview on the evolution of the ozone layer in the recent past is given and new model projections of the future ozone from the upcoming “WMO/UNEP Scientific Assessment of Ozone Depletion” are presented. The role of climate change for future ozone is discussed as well as the impacts of future ozone changes on the troposphere.