LIKE so many of life's tempting pleasures, sunshine must be enjoyed only in moderation. The dangers of excess are not a consequence of the heat or the light that it provides but of another invisible and for the most part impalpable, ingredient - the short-wave energy called ultraviolet radiation. Prolonged exposure to UV-B as it is called, causes sunburn, and, more importantly, can lead in certain circumstances to mutations that result in various forms of cancer of the skin.
For much of the time, we are protected from the worst excesses of UV-B by the ozone layer some 13 miles above our heads. But the layer's condition, as we know, has been causing great concern of late, as man-made substances provoke the chemical reactions that tend to weaken it; during the last six weeks - and I kid you not on this occasion ozone concentrations in northern latitudes have been reduced at times to 75 per cent of normal values. Moreover, even when it is in the very best of health, the ozone layer does not protect us from all the harmful effects of UV-B.
Last year, Met Eireann introduced a Sunburn Forecast Service, intended to allow potential sunbathers, or those who might otherwise be occupationally or recreationally vulnerable, to regulate sensibly their exposure to the sun. Naturally it was suspended for the winter months, but it has now been introduced again and will continue, as the Americans like to put it, through September.
The facility provides guidance as to how long, given the prevailing weather conditions, the average person can allow himself or herself to be exposed directly to the sun without a risk of burning. This information is included in forecasts provided daily to the media, and on the WEATHERDIAL telephone facilities, and in the event of high-risk conditions later in the summer, appropriate warnings will be broadcast with the regular forecasts on radio and TV.
Apart altogether from periodic man-induced depletion, the amount of ozone in the upper atmosphere varies anyway, both seasonally and day to day; in general high pressure results in less ozone overhead, and vice versa. Background ozone levels are available from measurements carried out by UCG at Mace Head in Co Galway, and from Met Eireann's readings at Malin Head and Cahirciveen.
The forecasters combine this knowledge of current average ozone values over Ireland with the output from their daily computer models of the atmosphere, and the expected cloudiness, to arrive at an estimate of UV-B intensity, and hence an estimate of the maximum time that an individual should allow himself to cavort in the mid-day sun.