While the ozone layer is recovering thanks to international action, banned substances are still being released and not all ozone-depleting substances are currently banned.

Scientists from Lancaster University are among global experts producing the UN’s latest Scientific Assessment of Ozone Depletion, published in full earlier this month. It brings together current knowledge about the health of the stratospheric ozone layer, which protects life on Earth from harmful levels of the sun’s ultraviolet rays.

The Assessment reports on the progress of the Montreal Protocol, the 30 year old international agreement which committed 197 countries to phase out production of chlorofluorocarbons (CFCs) used in refrigeration and air conditioning, and other ozone-depleting substances.

Dr Ryan Hossaini, from the Lancaster Environment Centre, has been leading research into ozone depleting compounds and is a co-author of the Assessment. He said: “The Montreal Protocol continues to be a phenomenal success and a great example of the international community coming together.

“However, there is now a very strong indication that CFC-11, a gas whose production is banned under the Montreal Protocol, is actually being emitted when it shouldn’t be. Starting from around 2013, measurements indicate that CFC-11 in the atmosphere is declining at a slower rate than expected and that emissions are likely increasing in Eastern Asia - we can’t pinpoint where they are coming from more accurately than that.

“There is also strong evidence that certain ozone-depleting compounds not currently controlled by the Montreal Protocol are increasing in the atmosphere. This class of compounds are known as VSLS, very short lived substances - Lancaster University has been leading research into this class of compounds.”

Dr Paul Young, a climate scientist from the Lancaster Environment Centre, is co-author of Assessment chapter on the polar regions. He said: “Although the Antarctic ozone hole is still with us, the weight of evidence is that we are beginning to see signs of recovery. The ozone hole is a powerful reminder of our capacity to harm the environment, but due to the successes of the Montreal Protocol in controlling key ozone depleting substances, we are confident that the ozone hole will heal by the time this century is out.

“We do not see the same severe ozone loss in the Arctic, but 2011 did come close. While ozone depleting substances remain, similar losses remain a possibility depending on what the weather is doing in the ozone layer. But, again due to the Montreal Protocol, we do expect Arctic ozone levels to recover by the middle of this century."

Looking to the future the Assessment emphasises the importance of the Kigali Amendment to the Protocol, which came into effect in January. It commits signatories to reducing hydrofluorocarbons (HFCs) - a later generation of ozone-depleting chemicals - by 80% over the next 30 years.

Hydrofluorocarbons are greenhouse gases that are hundreds to thousands of times more potent than carbon dioxide and so contribute to global warming. The Assessment calculates that the world can avoid up to 0.4°C of global warming this century through implementation of the Kigali Amendment, giving it a critical role in keeping global temperature rise below the 2°C mark.

Read the full report here and an executive summary here.