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Daylight Saving Brings Skin Cancer Warning

Daylight Saving Brings Skin Cancer Warning

29 September, 2008

New Zealanders are being warned of rapid increases in ultraviolet radiation as people enjoy the longer days of daylight saving.

Dr Richard McKenzie of the National Institute of Water and Atmospheric Research (NIWA) says the switch to daylight saving should remind us that this is a transition period for New Zealand, when the sun is higher in the sky each day.

“It means the sun’s rays have less distance to travel through the atmosphere to reach earth. The shorter the distance the rays have to travel, the less ultraviolet radiation is absorbed by gases in the atmosphere – like ozone – and the more radiation hits earth.”

He says over the last week alone, we have seen ultraviolet radiation rise from six to seven in the north of the country.

With UV rays peaking at over 12 in the summer, people are being urged to protect themselves from the harmful effects of the sun, while still enjoying the outdoors.

“Over-exposure to the sun's ultraviolet radiation is the cause of over 90 percent of all skin cancer – making prevention crucial,” says the HSC’s SunSmart Manager Wayde Beckman.

“At this time of year, even if the day is cloudy remember the SunSmart message – slip, slop, slap and wrap. Never get sunburnt and always make sure you have protective gear on, such as a shirt with collar and long sleeves. Slip into the shade, slop on some sunscreen, slap on a hat and wrap on a pair of sunglasses.”

Dr McKenzie says that because the sun elevation angle is a strong indicator of UV intensity, an easy way of judging how high the UV radiation is likely to be is by observing the length of your shadow.

“As your shadow gets shorter, you know the UV risk is getting bigger. If your shadow is less than twice the length of your body, there is a risk of damage from UV. At this time of year, your shadow length at midday is about the same length as your body and it will get shorter each day as summer approaches.”

He says the key time for New Zealand is over the December-January period when the sun is high in the sky so the ultraviolet intensity reaches its maximum values. At that time of the year, New Zealand can also be influenced by the break up of the ozone hole in Antarctica.

“The ozone hole recurs every spring but we won't know how much it will affect New Zealand until we can measure how much ozone has broken down. Although the area of the hole is comparable to previous years, what is key for the New Zealand public is the total amount of ozone destroyed within that area and whether high altitude winds push this ozone-depleted air over New Zealand.”

The precise date of break-up of the Antarctic ozone hole is not yet predictable. But it is usually in the early summer. NIWA provides daily forecasts of UVI to the media via MetService. Forecasts are also available at


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