Although today might seem to you to be a day like any other it is, in fact, quite special. The UN has declared it such; at its 92nd Plenary Session on December 19th, 1994, it adopted Resolution 49/114.
This states: "The General Assembly . . . considering the urgent need to preserve the ozone layer, which filters sunlight and prevents the adverse effects of ultraviolet radiation reaching the Earth's surface, thereby preserving life on the planet . . . highlighting the importance of the implementation of the Montreal Protocol on Substances that Deplete the Ozone Layer, concluded at Montreal on September 16th, 1987, and its subsequent amendments . . . proclaims September 16th, beginning in 1995, to be the International Day for the Preservation of the Ozone Layer."
And so it has remained.
The Montreal Protocol has been modestly successful. The industrialised countries have now almost phased out their use of chlorofluorocarbons, or CFCs, the main catalysts for the depletion of this vital substance.
Since 1999 even developing countries have begun a freeze on their production, and this will be followed by a gradual phaseout in the coming years.
The aim of all this activity is to introduce ozone-friendly practice on a global scale sufficient to achieve the restoration of the ozone layer by 2050 to a state of health comparable to that which it enjoyed around 1975.
But recovery is slow since the harmful chemicals already present in the atmosphere have proved to be resilient.
In both hemispheres, the crucial period is the beginning of spring, when the sun peeps over the horizon after the long polar night to illuminate the stratosphere and when temperatures over the poles are at their lowest.
Earlier this year in the northern hemisphere, in late February and early March, ozone amounts in the polar regions were measured at 20 to 30 per cent below those that were the norm 25 years ago. Such figures, however, are less alarming than readings obtained during several springs in the 1990s.
At this time of year all eyes are on Antarctica where the southern spring is just beginning. There in recent years the annual "ozone hole" has been as deep and wide as ever, and reductions of 50 per cent or more in the amount of ozone in the stratosphere are commonplace. Measurements will be watched closely in the coming months to see if this year brings an improvement.