These days we know to watch out for UV in the summer months, using sunscreen with a high SPF rating. That’s Sun Protection Factor, in case you were wondering. One reason is that UVB rays cause sunburn and contribute to skin cancer.
The quirky thing is that the UV rating scale was originally designed to go up to 10.
An index of 0 corresponds to zero UV radiation, as is essentially the case at night. An index of 10 corresponds roughly to midday summer sunlight with a clear sky when the UV Index was originally designed (Toronto 1992).
But that just doesn’t work in New Zealand, where the UV is powerful, especially in summer. More or less from the beginning of October to the end of March it’s likely to be in the red zone, with the months of December, January and February climbing up into the violet extreme. There are days when it can be more than 14.0.
Of course, scientists are on to it. Our NIWA, Taihoro Nukurangi, the National Institute of Water and Atmospheric Research, collaborate with German scientists and have an interesting finding from their research so far.
We have established that in summer UV levels are 40-50 per cent larger at 45°S in the Southern Hemisphere than they are at the corresponding latitude in the Northern Hemisphere.
We know that the ozone layer is thinner here and there are fewer aerosols, but what we suspect is that for some reason clouds are different in the two hemispheres.
And if you’re outside in a New Zealand summer remember: there can still be UV, even if it’s cloudy, so check the weather report and cover up.