Three decades of uncertainty have passed since nearly every country in the world signed the Montreal Protocol to ban gases that destroy atmospheric ozone, and last October there was a scare when the Antarctic ozone hole broke a record of unexpected severity. But things have started to straighten out.
Scientists have obtained evidence, for the first time, that the ozone layer is recovering. Since 2000, when it reached its all-time high (25 million square kilometers), the Antarctic hole has shrunk by 4 million square kilometers, roughly the size of the European Union (excluding the United Kingdom).
The researchers also present evidence that the main cause of the recovery has been the Montreal protocol, that is, the ban on chlorinated organic compounds that were used in dry cleaning, refrigeration and aerosols such as deodorants and lacquers. The replacement of these compounds by others that are equally effective but harmless to the atmosphere has therefore been of paramount importance.
There are also natural phenomena that damage ozone, such as the temperature in the upper layers of the atmosphere and, above all, volcanic eruptions. This has greatly complicated the measurements so far. In fact, the record ozone hole that occurred last October was due, scientists now think, to the eruption of the Calbuco volcano in southern Chile. Volcanoes do not emit CFCs, but they do emit a large number of small particles that rise into the atmosphere and promote reactions that destroy ozone.