Over The Horizon

Ozone Hole Intense

The ozone hole over Antarctica appears fully formed, and is larger than last year and nearly as intense, with the possibility of further drops, according to the New Zealand Antarctic Programme and the National Institute of Water and Atmospheric Research.

Satellite data from NASA shows a rectangular area of very low ozone concentration covering the Antarctic continent, somewhat larger than the triangular hole seen last year.

Readings at the centre of the hole are close to last year's record minimum of around 100 Dobson units, representing a 65% drop over pre-1980 levels. A NIWA researcher at Scott Base, Sylvia Nichol, said readings at the Arrival Heights laboratory, nearer the edge of the hole, were approaching the previous minimum of 129 Dobson units and could drop even lower. In the absence of the hole, ozone levels of around 300 Dobson units would be expected.

Nichol says scientists expect similar sized holes to develop for the next 20 years, because of the amount of chlorine pollutants already present in the atmosphere. After that time, legislation designed to phase out the use of CFCs, such as the Montreal Protocol and New Zealand's Ozone Layer Protection Act, may start to have an effect.

The ozone hole was first observed in the early 1980s, and since 1987 has become more intense. This year more than half the ozone above the Antarctic, some 70 million tonnes of it, is expected to vanish for the spring season.