The Montreal Protocol, an international pact signed in 1987 to curb the use of ozone depleting substances, was agreed just in time to avoid a global catastrophe, New Zealand government scientists said Friday.

For the last 10 years depletion of the Earth's ozone layer, which filters ultraviolet (UV) radiation from the sun, had been stabilized, but recent advances in climate modeling suggested that the climate impact of the ozone hole over the Antarctic extended all the way to the equator, according to the National Institute of Water and Atmospheric Research (NIWA).

This affected prevailing winds and the distribution of rain, making some locations more prone to drought, said a statement from NIWA issued two days before the 25th anniversary of the Montreal Protocol.

NIWA atmospheric scientist Olaf Morgenstern and other international scientists ran atmospheric models for a non- intervention, no-Montreal Protocol scenario, which showed ozone depleting substances grow throughout the 21st century.

In that scenario, at the end of the 21st century the ozone layer was nearly completely wiped out, and ultraviolet radiation levels at the Earth's surface reached levels unheard of today.

The consequences of that would have included greatly increased rates of skin cancer and a disruption of food production because many plants could not exist under such conditions.

Even under a less extreme scenario, which assumed ground- breaking discoveries in ozone chemistry made in the 1970s had been made only one or two decades later, much more substantial damage would have been inflicted on the ozone layer than had actually been observed.

"In this sense, the Montreal Protocol took effect just in time to avert a catastrophe," Morgenstern said in the statement.

NIWA played a significant role in monitoring the long-term changes of the ozone layer, and this contributed significantly to tracking the success of the Protocol.

The ozone layer comprises the naturally occurring ozone gas in the stratosphere, 15 to 50 kilometers above the Earth's surface, which protects humans and the biosphere by filtering solar radiation.

In the lower atmosphere, ozone depleting substances, such as chlorofluorocarbons (CFCs), are chemically inactive, but in the stratosphere above 17 kilometers they break up under intense UV radiation, liberating their halogen atoms, such as chlorine, causing ozone destruction and the formation of the ozone hole.

Over mid-latitude locations, such as New Zealand and parts of Australia, there was a significant thinning of the ozone layer during the 1980s and 1990s, causing an increase in UV radiation at the Earth's surface, which is linked to the occurrence of skin cancer.

NIWA's Lauder research station, in the South Island's Otago region, is one of five global charter sites in the international Network for the Detection of Atmospheric Composition Change.

NIWA researchers were currently studying the causes and effects of climate change, and interactions between global warming and ozone depletion.

"We do expect that the ozone layer will be affected by climate change," said Morgenstern.

"Ozone is the primary UV absorber and a potent greenhouse gas. This means that ozone depletion causes climate change," he said.

Ozone levels above Antarctica were projected to return to 1980 levels (previous to the ozone hole) after 2050, Dr Adrian McDonald, of the physics and astronomy department at the University of Canterbury, said Monday.