The future of the ozone hole
There’s an urban legend floating around the isle of Tasmania: that the state sees more cases of sunburn than Queensland, because the ozone hole sits right above it. Though sun damage is a concern, the ozone hole has never reached Australia. And contrary to another popular belief – it is not a hole that exists all year round.
The ozone hole forms and disappears on an annual basis in springtime over Antarctica. The world has been acting since the 1980s to prevent it from spreading as far as Australia.
CSIRO scientists provide world-class monitoring and modelling of the ozone hole, examining its interactions with ozone-depleting substances, providing greater insights into its recovery and effects on climate, and strengthening global efforts to mitigate it.
But, what caused the hole in the first place, is it on the mend, what are its effects on climate, and what are the threats to its long-term recovery?
First, some history
It was the early 1970s when scientists first suggested that the human-produced chemicals, chlorofluorocarbons (CFCs), used in fridges, air conditioners and aerosol cans were destroying Earth’s ozone shield.
Then, in 1984 a significant sized ozone ‘hole’ seemed to appear quite suddenly. At the time of its discovery, the ozone hole wasn’t something that was specifically being looked for, and was even overlooked in NASA’s satellite data.
British physicist Dr Joe Farman had been visiting and measuring ozone levels and concentrations of trace gases at Halley Bay, Antarctica, each year. He and his team collected observations with instruments such as weather balloons and the Dobson spectrophotometer – a simple ozone-measuring device, which worked best when wrapped in a blanket.
It was these rudimentary instruments that alerted Farman to the ozone hole, highlighting the importance of comprehensive Earth observations.
At first, no one knew what to make of the discovery, until further examination of the hole revealed that it could bring about catastrophic consequences if it was not contained and ‘healed’.
By 1987 the Montreal Protocol was created to reduce the worldwide use of ozone-depleting chemicals. Often referred to as ‘the world’s most successful environmental agreement’, without the Protocol and its success, the Earth’s ozone layer would collapse by 2050.
Why is ozone important?
A layer of ozone, a colourless gas, sits within the stratosphere – the atmosphere typically 10-50 km above the Earth’s surface. At this level, ozone absorbs the Sun’s UV radiation, preventing most of it from penetrating the atmosphere and reaching the Earth.
UV radiation damages the DNA of most living organisms. It would be difficult to survive without an ozone layer, with the amount of UV radiation hitting the planet’s surface.
In regards to the urban legend, even though the ozone hole doesn’t reach as far as Tasmania, more than enough UV already arrives at the rest of the Earth’s surface to cause serious damage to unprotected skin.
The Montreal Protocol brought the world together to agree to phase out ozone damaging chemicals, and the hole never extended to Australia.
Climate change would also be far worse without the Protocol, as the ozone depleting CFCs are super-greenhouse gases as well, thousands of times more potent than carbon dioxide.
However, stratospheric ozone recovery is still linked to climate change, and climate change is also linked to stratospheric ozone recovery.
Dr Matthew Woodhouse, from the CSIRO Aerosol and Chemistry Modelling group says, as an example, stratospheric ozone loss is responsible for increasing the strength of the westerly winds that encircle Antarctica, pushing them further south.
“When these winds are pushed south, they contribute to delivering very dry conditions to Australia,” he says.
“As the ozone hole recovers, it is predicted that these westerly winds could move further north. However, increasing greenhouse gas concentrations are also pushing the westerly winds south, opposing the influence of the recovering ozone hole,” he explains.
Modelling the effects of ozone and climate change
Such opposing effects can only be fully evaluated with a chemistry-climate model (CCM), which Woodhouse is currently working on developing for the Australian science community.
The model will provide a world-leading forecasting and evaluation capability, complementing Australia’s position as a leader in ozone depleting substance monitoring.
“The CCM will include representation of the ocean, the atmosphere, and its chemistry, including stratospheric ozone. It will be able to forecast ozone hole recovery under future scenarios, and assess the impact of ozone hole recovery on climate,” Woodhouse says.
So, how is the recovery going so far?
CSIRO monitors and reports on the ozone loss that occurs over Antarctica in the southern hemisphere every spring, in the ‘ozone hole season’.
Dr Paul Krummel, from CSIRO’s Climate Science Centre, says satellite data are used to monitor the ozone hole development each year, and to estimate its annual size and ‘depth’.
“Thanks to the Montreal Protocol the hole in the ozone layer is slowly recovering,” Krummel says.
“Since around the year 2000, when the levels of ozone depleting chemicals in the stratosphere peaked, the annual ozone hole generally grew smaller as ozone-destroying gases were phased out,” he continues.
“However, since many of the ozone-destroying gases will remain in the atmosphere for tens to hundreds of years, recovery of the Antarctic ozone hole to pre-1980 levels will likely take another 40-60 years.”
There are few southern hemisphere observation points for stratospheric ozone and ozone-depleting substances, so Australian observations are essential inputs for global assessments.
CSIRO, along with the Bureau of Meteorology, have a long-term program to monitor the levels of ozone depleting substances in the atmosphere at the Cape Grim observatory, located on the northwest tip of Tasmania.
Woodhouse adds that the ability of the new chemistry-climate model to assess recovery timescales is a valuable application.
“Something that is rarely acknowledged is the impact the chemical substitutes for those banned under the Montreal protocol and subsequent amendments are having on ozone hole recovery,” he says.
“As industry adapts and creates new processes, new chemicals are released,” he explains.
“Only with continued monitoring can these emissions be identified, and only with modelling can the effect on ozone recovery of those new chemicals be forecast and understood.”
Threats and disruptions
A recent study identified dichloromethane (Ch2Cl2) as an unexpected and growing danger to ozone depletion.
Dichloromethane is not currently controlled by the Montreal Protocol, and, if left uncontrolled, could push ozone recovery into the next century.
The substance, widely used for paint stripping, in the manufacture of PVC, in agricultural fumigation and the production of pharmaceuticals, is increasing much faster than previously thought.
The main sources of the emissions come from rapidly developing areas such as China and India. China is currently the largest producer of PVC, used mainly in construction materials.
Volcanic eruptions can also have a huge effect on the recovery of the ozone hole. Woodhouse says it’s not just volcanologists who are closely watching Bali’s Mt Agung.
“Large volcanic eruptions release gases and small particles called aerosol. When these particles reach the stratosphere, they provide a surface area where chemical reactions can take place. These reactions release highly reactive chlorine, which is very effective at eating ozone,” he explains.
In the aftermath of the 1991 Pinatubo eruption, Woodhouse says large losses of stratospheric ozone occurred.
“Interestingly, and worryingly, these ozone losses don’t occur over Antarctica in the springtime like the now-familiar ozone hole, but they can occur year-round over large parts of the globe, and last for years after the eruption.”
Each amendment to the Montreal Protocol is intended to update and strengthen it, and is based on global observations of significant ozone depletion. There is currently no expected date for the next amendment.
Krummel says the 2016 Kigali amendment was the latest change, which managed to get HFCs (hydrofluorocarbons) reductions included.
“Even though HFCs don’t destroy ozone, they are replacements for chemicals that do destroy the ozone layer,” Krummel says.
“What is significant about this is that HFCs are potent greenhouse gases, so in effect, the Montreal Protocol is also the most successful international agreement for reducing the effects of climate change.
“CFCs are very potent greenhouse gases as well.”
The UN Environment Program and the World Meteorological Organization are preparing the next report required under the Montreal Protocol – the Scientific Assessment of Ozone Depletion: 2018.
Many Australian scientists are contributing to the report, which will examine the recent state of the ozone layer, the atmospheric concentration of ozone-depleting chemicals, future ozone layer projections, and links with climate.
As one of the first countries to ratify the Montreal Protocol, Australia is often ahead of targets and is seen as a leader in the efforts to phase out ozone depleting substances.
These efforts, along with CSIRO’s world-class observations and chemistry-climate model capabilities, strengthen and inform the Protocol to limit ozone depletion, ensuring that the ozone hole remains manageable.
 For example from the Ozone Mapping and Profiler Suite (OMPS) of instruments on the Suomi National Polar-orbiting Partnership satellite.
Each Southern Hemisphere spring, the CSIRO provides weekly reports on the progress of the Antarctic Ozone Hole.
For more on the CSIRO Atmospheric Monitoring and Modelling Group.
A 2012 series of articles on the ozone layer, marking the 25th anniversary of the Montreal Protocol in The Conversation.