Create a list of articles to read later. You will be able to access your list from any article in Discover.
You don't have any saved articles.
Antarctica’s ozone hole has been growing since 2004
The recovery of the ozone layer might not be as simple as first thought.
A new study suggests that levels of ozone have declined by as much as 26% over the south pole, potentially delaying the recovery of the layer as a whole.
The hole in the ozone layer has made an unwelcome comeback.
First spotted in the 1980s, the ozone hole over Antarctica caused concern due to the perceived risk it could cause an increase in skin cancer and eye damage.
As a result, nations came together to shrink the hole and the recovery of the ozone layer has since been hailed as one of humanity’s greatest environmental success stories.
But while ozone-damaging gases are in decline, the ozone hole might not be a thing of the past.
Since 2020, each year between August and December, a large ozone hole has reappeared over the Antarctic, letting more damaging ultraviolet (UV) rays through the atmosphere. New research suggests that this might be due to changes in air flow in the upper atmosphere for reasons that aren’t yet well-understood.
Hannah Kessenich, a PhD student at Otago University who led the new study, says, ‘Most major communications about the ozone layer over the last few years have given the public the impression that the issue has been solved.’
‘While the Montreal Protocol has vastly improved our situation with [chlorofluorocarbons] (CFCs) destroying ozone, the hole has been amongst the largest on record over the past three years, and in two of the five years prior to that. In fact, 2023’s ozone hole is already bigger than those from 2020 onwards.’
‘We made connections between this drop in ozone and changes in the air that is arriving into the polar vortex above Antarctica, suggesting that they may not be caused just by CFCs.’
In addition to increased UV exposure, the resurgence of the ozone hole is also likely to have a knock-on impact on the climate and weather of the southern hemisphere. The study, published in the journal Nature Communications, calls for more research to understand what effects this might have.
The use of CFCs in products like aerosols led to the depletion of ozone in the atmosphere. Image © showcake/Shutterstock.
What is the ozone layer?
The ozone layer lies between 15 to 30 kilometres above the planet’s surface, high in the stratosphere. This layer, made up of a form of oxygen, protects the planet from UV radiation emitted by the Sun.
The layer is constantly changing as the ozone naturally breaks down and reforms. However, from the 1930s onwards, the breakdown of the layer began to accelerate as a result of the use of artificially manufactured CFCs in aerosols and refrigerators.
While CFCs speed up the breakdown of ozone all around the world, their impacts are most pronounced in the Antarctic. This is because the region’s low temperatures cause clouds to form in the stratosphere, which catalyse chemical reactions that make the effect of CFCs stronger.
This eventually led to a ‘hole’ opening in the ozone layer over Antarctica. While there’s not actually a complete loss of ozone here, the layer of ozone is much thinner.
In response, the world’s governments gathered in 1987 to sign an international treaty known as the Montreal Protocol. This oversaw the phase out of ozone-damaging gases, including CFCs, and has been credited with the layer’s recovery over the past few decades.
However, the recent reappearance of a large ozone hole has raised concerns among researchers. The effect of wildfires and unexplained CFC emissions have all been linked to its reappearance, but their exact contribution remains unclear.
The core of the ozone hole lies over the south pole. Image © Michael Lodge/Shutterstock.
What’s happening to the ozone layer?
The current study has taken a detailed look at the health of the ozone layer. Trying to judge this is difficult, as the size and thickness of the layer fluctuate throughout the year.
Their initial results broadly reflect the outcome of previous research. Since 2001, the researchers found that levels of ozone have generally risen in the upper stratosphere, particularly in the month of September. The ozone hole now opens later than before, likely due to the reduction in CFCs.
However, during October and November levels of ozone appear to fall substantially. The amount of ozone in the middle stratosphere, the core of the ozone layer, has dropped by more than a quarter since 2004.
It’s not entirely certain why this is happening, but the researchers suggest it might be the result of changes in the layer of the atmosphere above the stratosphere, called the mesosphere.
‘The Antarctic ozone hole is contained within the polar vortex, which is a circular pattern of wind in the stratosphere that forms during winter and is maintained until late spring,’ Hannah explains.
‘Inside the vortex, Antarctic air from the mesosphere descends into the stratosphere, bringing natural chemicals like nitrogen dioxide which impact ozone chemistry.’
When gases like nitrogen dioxide reach the lower parts of the ozone layer, it is thought that they help to protect the ozone.
More recently, however, it seems that less nitrogen oxides are reaching the bottom of the ozone layer than normal. What exactly has changed in the past few years remains a mystery.
‘If there were just one or two large ozone hole years, these might be explained as anomalies, or linked to sporadic events like volcanic eruptions,’ Hannah says. ‘However, the holes of the past few years have all been remarkably similar in terms of ozone content and area.’
‘We’ll need more time to properly distinguish any long-term trends from natural variations in data, and for this, we have to continue monitoring levels of ozone and other chemicals in the atmosphere.’
With more research, scientists will be better able to understand the ozone layer, and what we need to do to help it heal once and for all.
