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Scientists including experts from Boulder's NOAA labs prepare to launch a weather balloon from the Antarctic that contains sensors detecting levels of "good" ozone at different layers of the atmosphere. The ozone hole has been forming over the Antarctic for decades, but international treaties to limit damaging chemicals have reversed the trend. (NOAA)

At least one thing in the environment seems to be getting better. 

The annual ozone layer survey, where Boulder scientists and instruments play a key part, tells us we’re still on track for solving a problem that terrified the world in the 1990s and early 2000s. Back then, headlines and interviews with Southern Hemisphere residents warned of blinded sheep, sickness from unchecked ultraviolet rays in cities like Punta Arenas, Chile, and dangers for Antarctic science stations right under the hole. 

Boulder-based NOAA tells us that 2023’s worst day for the ozone layer was only the 12th worst since they began recording in 1979, and that overall it was a “very modest ozone hole.” And remember — this is a hole in the “good” ozone, the one that protects us from sun intensity, not the “bad” ground-level ozone pollution created by a stew of nitrogen oxide, volatile organic compounds and intense summer heat. 

So the international chemical ban — the Montreal Protocol — protecting the ozone shield continues to work its science magic. Now if only we can reach the same consensus and rapid action on carbon dioxide. 

The ozone hole peaks over the Antarctic during its spring, bringing the Sept. 21 reading this year to a gap of 10 million square miles. The average from Sept. 7 to Oct. 13 peak season was 8.9 million square miles, about the size of North America, in NOAA’s helpful shorthand. 

The “very modest” assessment came from Paul Newman, leader of NASA’s ozone research team out of Greenbelt, Maryland. “Declining levels of human-produced chlorine compounds, along with help from active Antarctic stratospheric weather, slightly improved ozone levels this year,” Newman said. 

Did we bring all this up just so we could mention the Hunga Tonga-Hunga Ha’apai volcano? Absolutely possibly. The violent eruption of that underwater volcano in the Southern Pacific sent a massive plume of water vapor into the stratosphere and likely made ozone depletion worse this year. 

The NOAA Global Monitoring Lab project leader on ozone is based in Boulder, as are senior scientists and lab technicians who spend the winter at the Amundsen-Scott South Pole Station launching balloon-carried “ozonesondes” for readings. Balloons have one advantage over satellites in that they can take direct ozone readings through different layers of the atmosphere. The ozonesonde on the American balloons was invented in Boulder in the 1960s, and is still manufactured by Boulder companies, according to NOAA spokesperson Theo Stein. 

The Colorado Sun spoke with Boulder-based NOAA senior scientist Stephen Montzka about how they track the ozone hole, and what the results of the Montreal Protocol might tell us about international cooperation on climate change or other challenges. 

Sun: How do scientists keep track of the good-ozone layer over time, and what is Boulder’s part in that? 

Montzka: NOAA measures ozone sites around the world. And it also measures ozone depleting gases, chemicals that cause the problem, that human activity emits. So NOAA’s Boulder Global Monitoring Laboratory measures ozone a couple different ways. One, it attaches a sensor that we build in-house, to a balloon. Then it’s like a weather balloon that gets launched. A current is measured and transmitted to the ground as the balloon rises up to a very high altitude. So we do that in Boulder on a regular basis. And we do it in other sites around the world, including the South Pole. So that’s one way: a high resolution picture vertically of how the ozone changes as a function of altitude. 

And then the other way we measure ozone is through the total column measurement, essentially, looking at the wavelengths of light through the atmosphere. You can look at a wavelength of light where ozone absorbs it and one where ozone doesn’t absorb, and the difference there gives you an idea of how much ozone is present in the total column above you. And we do that at a number of sites. Fewer sites, but Boulder and definitely the South Pole. So that’s a measure of the density of ozone above you at any point on Earth.

Sun: So we might be driving by and seeing one of you pointing something at the sky? Whereabouts? 

Montzka: The David Skaggs Research Center on Broadway. There’s a deck out on the south side of the building, and once in a while, you’ll see some folks with rather unwieldy big white boxes and they’re making measurements of the ozone in that column of air. We essentially shoot the sun, with instruments, to make measurements of light as it passes through the atmosphere.

Sun: What has happened in your measurements over time? 

Montzka: Their springtime in Antarctica being September and October, we’ve been measuring at that time each year since around 1980. We’ve measured substantial ozone depletion that wasn’t measured in the years before 1980. Ozone was nearly completely gone at certain levels of the atmosphere since around the late 1980s and early 1990s. 

Since that time, there’s been a small recovery, although the recovery is hard to detect, because there’s other factors that play a role in how much ozone exactly is destroyed in the stratosphere over Antarctica each year. We have this picture where we understand the concentration of ozone depleting substances is gradually decreasing. So we’d expect over time that there’d be less ozone depletion anywhere in the stratosphere. In particular over Antarctica, we expect this general gradual trend towards improving increasing concentrations of ozone and the hole being less large, less complete. 

But what happens from year to year, there’s other factors that play a role and that has to do with meteorology, the weather. How contained the vortex is over Antarctica during that spring. And by vortex I mean this tightly isolated circulation of air around the South Pole and over the Antarctic continent. If that tight circulation breaks up sooner in a particular year, we’ll get mixing in of air from higher latitudes in a way that will cause the depletion of ozone in that year to be less severe. So the weather makes a difference. The amount of water vapor up there makes a difference, too.

Sun: And on water vapor, the recent eruption of a major underwater volcano didn’t help? 

Montzka: Yes, it didn’t happen this year, but it was the Hunga Tonga-Hunga Ha’apai event in the Southern Hemisphere. We’ve seen that the amount of water vapor in the stratosphere increased by about 10% as a result of this volcanic explosion. A huge amount. A big input of water vapor. And so it was expected that eventually that water vapor was going to make it into the stratosphere over Antarctica during springtime and might cause some added polar stratospheric clouds. The increased clouds means there’s more surface area for ozone destruction. But this year there were competing influences. Although there was enhanced water due to that volcanic explosion, the meteorology was such that the vortex broke up a little bit easier, a little bit earlier than usual. So that abated that increased water influence.

Sun: So in general, how did we do this year? 

Montzka: We estimated the concentrations of ozone depleting gases in the stratosphere during this springtime is on the order of 25% less now than it was during the worst year peak year for ozone-depleting chlorine and bromine. And that was around 2000. So we know that there’s reduced concentrations of ozone depleting substances. 

Sun: Are there other lessons we can learn about other global environmental challenges, based on a worldwide treaty like the Montreal Protocols having a big positive impact on ozone? 

Montzka: Yes, there are, and they have a lot to do with the Montreal Protocol. Countries around the world got together in the late 1980s and they agreed this was an issue that they wanted to address. The first studies were coming out that said, oh my goodness, ozone over the Antarctic in their springtime was dropping like a rock. And so that made countries around the world take notice. 

And they got together and they agreed that they were going to take steps to limit the gases that cause the problem. And I think a couple things about that process and protocol are worth mentioning and talking about. One is that the initial agreement wouldn’t have solved the problem. There was an attempt right off the bat to say, ‘Okay, we’re going to eliminate the production and use of these chemicals.’ That was too hard for parties to agree to right then. 

What they did instead was say, ‘We’re going to limit their use into the future. And then a few years from now we’re gonna get back together.’ They meet twice a year and have ever since that time. We’re going to continue to meet and learn as the science advances, and as scientists tell us more about the problem. We’ll then get to decide whether or not we make more restrictions. Delegations from countries around the world agreed to revisit the issue every year. And there was a mechanism by which they ensured any new updates in the science would be transmitted to them so that they could make informed decisions. 

They also had other advisory panels, not only scientists, they had advisory panels that had a role in helping guide the best way forward. Toward the chemicals that industry knew how to make, and that the scientists said ‘These don’t deplete ozone as significantly, or maybe they don’t deplete ozone at all.’ And a second panel is the technology and economic assessment panel. Those folks also do analyses related to the economics of transition, so that the parties know the costs and benefits financially and environmentally for the decisions that they’re making.

Sun: A skeptic would say, okay, but on climate change, you’re asking these countries to make enforcement decisions that have a bigger, broader impact on the economy and therefore it’s harder for them to make and enforce their own promises in those kinds of international protocols.

Montzka: That’s not a skeptic. That’s a fact. The amount of fossil fuel combustion is central to or has been central to our economy throughout the world for many, many years, right? And so, trying to address that issue, trying to change things in a way that results in less carbon being emitted to the atmosphere — that’s potentially involving fairly central aspects to our economy, and our energy production system and infrastructure. So, yes, it’s been more difficult, no doubt about it.

It’s important to remember though, that this chemical industry in the 1980s wasn’t a small industry. And they weren’t necessarily on board right away; the people who discovered the issue, who ultimately won the Nobel Prize, took a lot of flak initially, and industry was part of that. But eventually the industry saw the light and for whatever reasons, for good reasons and undoubtedly financial reasons, ultimately, they got on board. And when they did get on board, it made a big difference. 

Sun: Are there any other connections you’d like to make among these big, worldwide environmental issues? 

Montzka: I think there is a connection between ozone depletion and climate that we didn’t really talk about. And that is the fact that most of the ozone depleting gases that were used historically, were also potent greenhouse gases. So overall, the Montreal Protocol caused substantial reductions in ozone depleting gas, and also as a result in greenhouse gas emissions.

There’s been a substantial climate benefit … (from) those fluorocarbons that were banned. And the most recent amendments to the Montreal Protocol had to do with chemicals that actually did nothing to deplete ozone. The only negative influence they had is that they were still fairly potent greenhouse gases. The Kigali amendment to the Montreal Protocol, it was agreed to in 2016. It put in place a phase-down of the current generation of ozone-depleting substitute chemicals to hydrofluorocarbons, to ensure that the benefit the Montreal Protocol was providing to climate would be sustained. 

Michael Booth is The Sun’s environment writer, and co-author of The Sun’s weekly climate and health newsletter The Temperature. He and John Ingold host the weekly Sun-Up podcast on The Temperature topics every Thursday. He is co-author with...