Ozone depletion on the surface of the cloud crystals is far different from when it occurs in atmosphere. These conditions have led to ozone hole formation in Antarctica. This hypothesis was decisively confirmed, first by laboratory measurements and subsequently by direct measurements, from the ground and from high-altitude airplanes, of very high concentrations of chlorine monoxide (ClO) in the Antarctic stratosphere. Alternative hypotheses, which had attributed the ozone hole to variations in solar UV radiation or to changes in atmospheric circulation patterns, were also tested and shown to be untenable. Meanwhile, analysis of ozone measurements from the worldwide network of ground-based Dobson
Vienna Convention for the Protection of the Ozone Layer the European Union. While not a binding agreement, it acts as a framework for the international efforts to protect the ozone layer; however, it does not include legally binding reduction goals for the use of CFCs, the main chemical agents causing ozone depletion. The treaty's provisions include the international sharing of climate and atmospheric research to promote knowledge of the effects on the ozone layer. In addition, the treaty calls for the adoption of international agencies to assess the harmful effects of depleted ozone and the promotion of policies that regulate the production of harmful substances that influence the ozone