Letter: Alarming or alarmist? The statistics of ozone depletion

Sir: We are right to be concerned about continuing damage to the atmospheric ozone layer and the environmental and ecological consequences ('Think global, act pessimistic', 23 April).

In informing us of the 12-14 per cent decrease in ozone in the first three months of 1993 over North America and Europe, your science correspondent suggests that this could result in a 25 per cent increase in harmful ultraviolet radiation reaching Britain this year because a 1 per cent loss in ozone gives a corresponding increase in UV radiation of between 1.3 and 2 per cent ('Ozone depletion linked to rise in harmful radiation', 23 April).

What he failed to acknowledge is that for many years now ozone depletion in winter months, when ambient ultraviolet levels are low in Britain, has been greater than depletion in the summer months when much smaller ozone losses have been recorded. Consequently, a wintertime loss of ozone of 12-14 per cent would lead to less than a 2 per cent increase in our annual ambient UV exposure this year.

While the latest Nasa report on ozone depletion is alarming, a prediction of UV levels rising by 25 per cent is alarmist.

Yours faithfully,

BRIAN DIFFEY

Durham

23 April