Antarctica’s ozone hole is lasting longer into summer

Over the past 25 years, the ozone hole that develops above Antarctica each spring has begun to contract.

Yet during the last four years, the hole has remained open for an unusually extended period even as its size has reduced. Our latest research shows that, rather than sealing during November, it has continued well into December. This is early summer: a vital time for fresh plant growth along coastal Antarctica and the height of the breeding season for penguins and seals.

This is concerning. The formation of the ozone hole allows greater amounts of ultraviolet radiation to pass through the atmosphere. Although adult penguins and seals have protective coverings, their offspring could be more susceptible.

Why does ozone matter?

During the last 50 years, chlorofluorocarbons (CFCs) and similar chemicals damaged the Earth's protective ozone layer. Coordinated action worldwide has now resulted in these chemicals being banned.

However, CFCs remain in the atmosphere for a long time, so it will take decades for them to disappear entirely. Consequently, the ozone hole continues to form each year.

Most ozone damage occurs above Antarctica. Once the hole appears, the UV index doubles and reaches extreme values. In summer, UV index readings above 14 may be expected in Australia or California, but not in polar areas.

Fortunately, when the ozone hole opens in early spring, from September to November, most land species are dormant beneath the snow. Sea ice shields marine life, while Antarctica's moss forests are snow-covered. Until recently, these icy protective layers have helped safeguard much Antarctic life from ozone depletion.

Unusually persistent ozone holes over Antarctica

Several unusual occurrences from 2020 to 2023 meant the ozone hole lasted into December. These included the record-breaking Australian bushfires of 2019–2020, the enormous underwater volcanic eruption near Tonga, and three successive years of La Niña.

Bushfires and volcanoes can send smoke and ash into the stratosphere. Chemical reactions on the surfaces of these minute particles are capable of destroying ozone.

The more persistent ozone holes occurred alongside substantial sea-ice loss, leaving many plants and animals with fewer places to take shelter.

How does stronger UV radiation affect ecosystems?

When ozone holes endure for longer, animals breeding in summer around Antarctica's extensive coastline can be exposed to intense reflected UV radiation. Greater quantities of UV pass through the atmosphere, while snow and ice are highly reflective and scatter the rays around.

High UV exposure raises the risk of skin cancer and cataracts in people. Unlike penguins and seals, however, we do not have fur or feathers. Their skin has protection, but their eyes do not.

Is this causing harm? We cannot say with certainty. There have been very few studies of UV radiation's effects on Antarctic animals. Most research has taken place in zoos, where scientists examine animals exposed to artificial lighting.

Nevertheless, it is a cause for concern. Increased UV radiation in early summer may be especially harmful to young animals, including penguin chicks and seal pups that hatch or are born in late spring.

In late spring, plants including Antarctic hairgrass, Deschampsia antarctica, the cushion plant, Colobanthus quitensis, and many mosses emerge from beneath the snow and encounter peak UV levels.

Antarctic mosses can make their own sunscreen to shield themselves from UV radiation, though this reduces their growth.

Trillions of tiny phytoplankton inhabit the waters beneath sea ice. These floating microscopic algae also produce sunscreen compounds known as microsporine amino acids.

And marine animals? When UV radiation becomes too intense, krill dive farther down the water column. Fish eggs generally contain melanin, the same protective compound found in humans, although some fish life stages are not as well defended.

Sea-ice extent has declined in four of the past five years, directly as a result of climate change.

With less sea ice, more UV light can enter the ocean, making survival more difficult for Antarctic phytoplankton and krill. These tiny organisms underpin the food web, and difficulty surviving will send hunger rippling up the food chain. Climate change is also making Antarctic waters warmer and more acidic.

An uncertain outlook for Antarctica

In principle, we should be celebrating the ban on CFCs as a rare success in solving an environmental problem. But it may be too soon to do so. Climate change could be slowing the recovery of the ozone layer, for instance by making bushfires both more frequent and more severe.

Ozone may also be affected by geoengineering schemes, such as releasing sulphates into the atmosphere to reflect sunlight, and by increasingly frequent rocket launches.

Should the recent pattern persist and the ozone hole extend into summer, greater damage to plants and animals can be expected, alongside other pressures.

We do not know whether the longer-lasting ozone hole will continue. What we do know is that climate change is making the atmosphere behave in unprecedented ways. To ensure ozone recovery remains on course, immediate action is needed to cut the carbon we release into the atmosphere.

Sharon Robinson, Distinguished Professor and Deputy Director of ARC Securing Antarctica's Environmental Future (SAEF), University of Wollongong, University of Wollongong; Laura Revell, Associate Professor in Environmental Physics, University of Canterbury, and Rachele Ossola, Postdoctoral fellow, Colorado State University

This article is republished from The Conversation under a Creative Commons licence. Read the original article.