I will respond to a question in a recent letter regarding what happened to the hole in the ozone layer. The answer is that it is on its way to being fixed as a result of an international agreement known as the Montreal Protocol. This was agreed to in September, 1987, and went into effect at the beginning of 1989. This agreement phased out production of substances harmful to the ozone layer, most significantly so-called freons (chlorofluorocarbons). Measurements indicate that the ozone layer will return to its pre-1980 status between 2050 and 2070. Yes, that’s a long time, but many of the compounds have very long lifetimes in the atmosphere. Agreements on the ozone layer were the first international agreements ratified by every country in the United Nations plus the European Union, making them truly remarkable examples of international accord.