Abstract: Examines major changes in scientific understanding that followed the adoption of the Montreal Protocol in 1987 and the completion of the period of initial formation of the ozone protection regime. Returns to the two disturbing claims made in 1985 — extreme seasonal ozone loss in Antarctica, and large ozone loss worldwide — and traces their investigation over the following three years, their initial resolution in the year after the Protocol, and the consequences of their resolution in spreading calls to completely eliminate ozone-depleting chemicals (chlorofluorohydrocarbons (CFCs)). The early development of the Protocol's expert assessment panels is also discussed; these are the centrepieces of the regime's structure to adapt to changing knowledge and capabilities.

Keywords: Antarctica, CFCs, chlorofluorohydrocarbons, environmental protection, international agreements, Montreal Protocol, ozone depletion,