Ozone hole biggest on record

Scientists at the National Institute of Water and Atmospheric Research (NIWA) have announced that this year’s ozone hole over Antarctica is the biggest on record, covering 27 million square kilometres, compared to 25 million square kilometres last year.

The thinning of the ozone layer over the southern pole appears each year and peaks in size in late September or early October. The new measurement has surprised the scientists because restrictions around the world, following an international agreement called the Montreal Protocol, have been very successful is reducing emissions of man-made ozone-depleting substances to the atmosphere. As a result, scientists say that stratospheric concentrations of halogens (chlorine and bromine) that deplete ozone are declining, and ozone is expected to return to pre-1980 levels during this century. Principal radiation scientist at Lauder Dr Richard McKenzie says that, though the ozone hole is the biggest yet recorded, it was not vastly bigger than last year’s. The ozone hole varies a lot from year to year, and Dr McKenzie says he does not expect it to increase again next year.

This year’s hole began developing later than usual, but grew rapidly. There is, however, an ongoing problem for New Zealand. "When the hole dissipates in December, it could mean a period of low ozone during summer," says Dr McKenzie.

This means that, when the hole over the pole starts to close over, it causes the ozone layer above New Zealand to thin, usually in December and January. This lets ultraviolet light radiation through, which, if you get too much, can cause skin cancer and eye damage.

Scientists think that the ozone hole will eventually recover but that it may take decades. As well as man-made substances such as chlorofluorocarbons (CFCs) breaking down the ozone layer, natural events such as volcanic eruptions can also interfere.

Scientists say that the ozone layer over New Zealand has been increasing over the last few years, as it has in other mid-latitude countries, but that summertime UV intensities in New Zealand will remain high compared to other countries with similar latitudes in the northern hemisphere. This means that we will have to remember to cover up in the sun during summer.

Lauder is a world-renowned atmospheric research facility in the South Island.

For more about UV radiation and the ozone layer in New Zealand, see NIWA’s website.