ABSTRACT
The Earth’s ozone layer protects all life from the sun’s harmful ultraviolet radiation. However, this fragile shield is being depleted since the late 1970s as a consequence of the emission of human-made chemicals, chlorofluorocarbons (CFCs), to the atmosphere. Observations of the ozone layer itself showed that the most dramatic loss was over Antarctica—the ozone hole—far from the emitted sources. Ozone was also being depleted in the Northern Hemisphere, particularly at high latitudes and in the winter and spring months, as well as in the lower stratosphere at mid-latitudes. A landmark international agreement, the Montreal Protocol on Substances that Deplete the Ozone Layer, has successfully reduced the global production, consumption, and emissions of CFCs and, more recently, the replacements, hydrochlorofluorocarbons (HCFCs). Furthermore, because these substances are also potent greenhouse gases, the Montreal Protocol has provided substantial climate benefits, in addition to environmental and health benefits. Assuming full compliance, the ozone layer outside the polar regions is projected to recover to its pre-1980 levels before the middle of this century, while the springtime ozone layer over the Antarctica is projected to recover much later. However, new challenges are emerging. Changes in climate are expected to have an increasing influence on stratospheric ozone in the coming decades. International efforts to protect the ozone layer would require improved understanding of the complex linkages between stratospheric ozone and climate change. Moreover, some new ozone-depleting substances (ODSs) replacements are extremely powerful global warming gases and represent a potential focal area within the overall climate change challenge. Effective control mechanisms for new ODSs and continued monitoring of the ozone layer are crucial to maintain momentum on recovering the ozone layer while simultaneously minimizing influence on climate.
