Countries agreed to ban ozone-depleting chemicals in the 1980s – but we found five CFCs increasing to record levels in the atmosphere

Luke Western, University of Bristol and Johannes Laube, University of East Anglia

Despite a global ban in place since 2010, atmospheric concentrations of five ozone-depleting chemicals have reached a record high.

Chlorofluorocarbons, or CFCs, are entirely man-made gases used in a variety of applications, including refrigeration, air conditioning or as chemical solvents. They have been increasingly regulated by a series of international treaties since the 1980s. The 1987 Montreal protocol, which has been universally ratified, restricted the release of CFCs to the atmosphere where they contribute to the destruction of the ozone layer: a region high up in the stratosphere which absorbs harmful ultraviolet (UV) radiation and protects life below.

The goal of the Montreal protocol was to induce a decline in the atmospheric CFC concentration through controlling, and increasingly restricting, the production of these chemicals. This has worked well for many ozone-depleting substances, which is why the ozone layer is slowly recovering. And so the recent increase in atmospheric concentrations of five CFCs is quite surprising.

Our findings, while worrying, should be considered an early warning. The impact of all five CFCs on the recovery of the ozone layer is still small. Nevertheless, we do not fully understand where they are coming from, so this could change in the future, and we should not ignore the cumulative effect of these emissions on human health and the environment.

The global picture

Our team has been analysing air samples from all over the world, focusing on so-called “background” sites that are far away from the sources of these CFCs, or in fact any industrial emissions. An example is the Cape Grim observatory on the remote west coast of Tasmania. This is the basis for our assessment of the threat these chemicals pose, as it reveals global trends in their atmospheric concentration.

Our main findings for the period 2010-2020 were twofold. First, concentrations of CFC-13 and CFC-113a continued their previously observed – and puzzling – increase. Rising concentrations of CFC-113a even accelerated around 2016. Second, concentrations of CFC-114a and CFC-115 were stable since the 2000s, while those of CFC-112a had even started to decrease. However, all of them began increasing around 2013-2014.

These observations, combined with additional knowledge about atmospheric circulation and how CFCs are removed from the atmosphere through chemical reactions, allowed us to estimate the global emissions of these five gases. Their damage to the ozone layer can be expressed through their ozone depletion potential, which states how much ozone would be destroyed compared to the same quantity of CFC-11, which is different for each CFC.

The result is a relief. Emissions between 2010 and 2020 only resulted in a very small loss of around 0.002% of global stratospheric ozone.

There is no time to relax, though, for two reasons. All five CFCs are also potent greenhouse gases and, once emitted, will remain in the atmosphere for decades to centuries. Their warming effect in 2020 was already approximately that of Switzerland’s total CO₂ emissions. And if those emissions continue on their upwards trajectory, their contribution to climate change will expand too. The persistence of these gases in the atmosphere must be taken seriously: all emissions are a legacy for future generations to contend with.

Tracking down the sources

The first step towards avoiding future emissions is to find out where the current ones are coming from. There were already some hints in previous studies, which we gathered and combined with our own information, such as on the exact timing of when emissions started accelerating.

We found that three of the five CFCs (CFC-113a, CFC-114a and CFC-115) can be produced during the manufacture of other chemicals, which is allowed under the Montreal protocol, most notably hydrofluorocarbons or HFCs. HFCs have replaced CFCs for many applications as an ozone-friendly alternative. However, like CFCs, they are greenhouse gases and their production is now being reduced in many countries under the 2016 Kigali Amendment to the Montreal Protocol, which could reduce climate-related warming by 0.5°C.

It’s likely that the CFCs are leaking out during the production process, where they are either used as a feedstock (a chemical ingredient to make another chemical) or as a result of incomplete conversion of the feedstock to the target chemical. The production of HFCs really took off in developing countries after CFCs were banned in 2010, which is around the same time as the increase in emissions of these five CFCs.

The production of HFCs is predicted to further increase over the next few years, which could result in increasing emissions of these CFCs. CFC-113a is used to make at least one hydrofluoroolefin or HFO, which are alternatives to HFCs that don’t heat the climate and may be used long into the future. Despite HFCs and HFOs being more benign alternatives to CFCs, there may still be some cost to ozone during their production if CFCs continue to leak into the atmosphere.

We were unable to find a plausible source for the other two CFCs, CFC-13 and CFC-112a. The fact that their emissions are increasing and we don’t know why is a concern in itself.

Time to revisit Montreal?

The Montreal protocol has been a huge success in mitigating emissions of ozone-depleting substances. Total CFC emissions are now only around 5% of their peak in the late 1980s. Yet an increase in the atmospheric abundance of some CFCs is still at odds with the treaty’s goals – and their elimination, by clogging leaks in industrial processes, could present an easy win to reduce these country-sized emissions of ozone-depleting and climate-warming gases.

It will take careful consideration by countries signed up to the protocol to find the necessary controls for quashing these trend-bucking emissions. In the meantime, we will continue to use our eyes in the sky to monitor the progress of a whole host of Earth-damaging gases.

Luke Western, Research Associate in Atmospheric Science, University of Bristol and Johannes Laube, Honorary Lecturer, Centre for Ocean and Atmospheric Sciences, University of East Anglia

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

A paper funded under this project published in Nature Geoscience detailed how the atmospheric abundance of five CFCs, and their emissions, have risen in the atmosphere since 2010 (the year of their phase out).

It has been quite well publicised, with explainers elsewhere and an article published in the Conversation has been reposted on this site. One of the interesting things about this work, that hasn’t been drawn on elsewhere, is that measurements of three of these gases – CFC-112a, CFC-113a and CFC-114a – are hard to make. The conclusions for these CFCs are drawn from measurements made from air collected at one location it the world, Cape Grim in Tasmania, Australia, which have been analysed by Johannes Laube and colleagues. This makes any further determination of the geographical location difficult, without something like short-term measurement campaigns (which have happened before for CFC-113a, and exists from aircraft data for CFC-112a).

The big thing will be to see the response this article provokes, and whether any long-term changes will be made with respect to emissions from feedstocks, byproducts and intermediates.

The published article is:
Western, L.M., Vollmer, M.K., Krummel, P.B. et al. Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020. Nat. Geosci. 16, 309–313 (2023). https://doi.org/10.1038/s41561-023-01147-w

Recently I had a paper from this project published on emissions of HCFC-141b, which have been rising (published in ACP). HCFC-141b is an ozone depleting substance (but not as bad as CFCs) and also a pretty potent greenhouse gas. sWe were originally interested in HCFC-141b emissions when looking at emissions of CFC-11. CFC-11 emissions had grown, most likely following illegal production, and we wanted to know if anything peculiar was going on with HCFC-141b, which largely replaced CFC-11 – mainly for foam blowing. At the time there wasn’t anything, as far we could tell, unusual happening with HCFC-141b and we left it out of the paper.

In the following couple of years we realised that emissions of HCFC-141b had also been rising. The timing of this was suspiciously similar to when emissions of CFC-11 dropped. This might suggest that people who were using CFC-11 had switched their use to HCFC-141b instead. HCFC-141b isn’t illegal to produce, but it is being phased-down fairly quickly and so its usage should not be becoming more common.

The paper looked at both global emissions and regional emissions. Interestingly, it’s really hard to tell where these new emissions are coming from – both geographically and from what source. A complicating factor is that some models predict that HCFC-141b emissions from some parts of the world will increase around this time because lots of refrigerators (which have HCFC-141b in their insulating foams) will be disposed of, releasing a lot of HCFC-141b to the atmosphere.

In the end, the conclusion is that we don’t know for sure what’s going on. There could be illegal production, leading to increased emissions, but we by no means have any direct evidence for it happening. It may also be coming from the disposal of old refrigerators, but there are no published models on a global scale to tell us whether this is a feasible avenue. Of course, it could also be something we’ve not thought of or a combination of factors also. But what is really interesting is that it raises the possibility that emissions can still rise after a phase-down of production. This shows how the Montreal Protocol, which controls production, may not have such an immediate impact. This is particularly relevant when we rely on the Montreal Protocol for climate change purposes and aim for net zero.

The preprint of this paper got some media interest (such as this article in Science) and Christina Theodoridi, one of the co-authors, did a really great blog entry on the topic.