At this time of year, when the sun rises over Antarctica, a ‘hole’ opens up in the Earth’s ozone layer. The ozone layer is a vital planetary boundary that protects all life on Earth from the sun’s harmful ultraviolet radiation. But our research shows that a series of unusual events in recent years are causing the ozone holes to last longer.

The Montreal Protocol, which came into effect just four years after the ozone hole was discovered in 1985, has been quite successful in preventing many ozone-depleting gases from entering the atmosphere. However, due to the long lifespan of the gases emitted over the last century, the hole will continue to open every year for at least another forty years.

Ozone depletion is also linked to climate change, and there are other emerging issues that could affect ozone recovery. These include more frequent forest fires due to climate change, emissions from rocket launches, and increased satellite debris burning in the upper atmosphere. All of these suggest that the problem of ozone depletion is far from solved.

Why is ozone important?

Most of the ozone in the atmosphere is found in the stratosphere, about 10–50 km above the Earth’s surface, where it absorbs the sun’s ultraviolet radiation. Summer peak UV levels in New Zealand and Australia are sometimes 30 percent higher than at comparable latitudes in the Northern Hemisphere.

This is due to lower levels of air pollution, slightly lower ozone levels in the past, and proximity to the sun, which is closer during the southern hemisphere summer months.

New Zealand and Australia also have the highest rates of melanoma in the world. This is partly due to high levels of UV radiation, but there are other factors, including improved diagnosis due to increased awareness. If the Montreal Protocol had not been implemented, the melanoma rate would be much higher today.

How does the ozone hole contribute to climate change?

Although most ozone-depleting gases are now banned, it will take decades for them to disappear from the stratosphere.

Meanwhile, the ozone hole continues to form over Antarctica each spring, causing gradual changes in temperatures, winds, and precipitation patterns in the Southern Hemisphere. The depletion of the ozone layer causes the prevailing westerly winds in the southern mid-latitudes (the “Roaring Forties”) to intensify and shift toward Antarctica during the summer months. This has led to increased surface melting of the Antarctic ice shelf and changes in summer precipitation and temperatures in New Zealand and Australia.

Although the ozone hole causes climate change, protecting and restoring the ozone layer has additional climate benefits.

Many of the gases that deplete the ozone layer, such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), are also potent greenhouse gases. By phasing out these gases, the Montreal Protocol has helped the world avoid a catastrophic collapse of the global ozone layer and limit global warming.

According to one study, the Montreal Protocol has delayed the first ice-free summer in the Arctic by 15 years. Ozone depletion and climate change are interrelated issues. While ozone depletion affects the climate of the Southern Hemisphere, global ozone recovery also depends on emissions of the dominant greenhouse gases, such as carbon dioxide, nitrous oxide and methane.

Technological innovations bring new threats

The discovery of the ozone hole in 1985 was a big surprise. Although there had been signs in the 1970s that CFCs were destroying stratospheric ozone, scientists did not anticipate the existence of a large hole over Antarctica. Within a few years of the discovery of the ozone hole, scientists began to understand how ozone destruction occurred in the cold Antarctic stratosphere.

The Montreal Protocol is perhaps the most successful environmental agreement, but the history of ozone is always full of surprises. The time it takes for ozone to recover depends in part on future emissions, but there are other factors too.

Recent research suggests that large-scale wildfires, such as the 2019 Australian bushfires, may contribute to ozone depletion. Increased civilian rocket launches are expected to push more ozone-depleting gases and aerosols into the stratosphere.

Further debris from satellite re-entry could contribute to ozone loss through aerosols entering the upper atmosphere. Adding to these problems are controversial proposals for “geoengineering”, where aerosols are deliberately injected into the stratosphere to slow the rate of global warming.

This will likely lead to further depletion of the ozone layer and such projects should be carefully considered along with many other considerations before such proposals are implemented.

History tells us that technological innovations can provide solutions (e.g., replacing CFCs with gases that do not deplete the ozone layer) but can also have unintended consequences. Far from being “solved” in the 20th century, the ozone problem remains a major problem, albeit in new and previously unknown ways.