Scientists look to 'canary in the coal mine' for ozone layer recovery

The hole in the ozone layer over the South Pole shrank to the smallest it’s been in 30 years in 2019, and this year, scientists are eagerly watching and waiting to see what 2020 means for the ozone layer’s ongoing recovery over that part of the world.

After the sun rises over the South Pole in mid-September, where sunlight has been absent for months and temperatures are bitterly low, the conditions are prime for the ozone depletion reactions that have led to the Antarctic hole in the ozone layer. In the stratospheric clouds, the breakdown is spurred on by an elevated amount of ozone-depleting gases emitted from human activity and chemicals with lifetimes of up to 100 years.

The gases that aid in the depletion are reactive chlorine gases called chlorofluorocarbons, or CFC gases, Bryan Johnson, an atmospheric chemist who works for the National Oceanic Atmospheric Administration, told AccuWeather in a Skype interview.

CFCs had been used since the 1930s as refrigerants and in aerosol sprays. At a ground level, they were nonreactive, nontoxic and nonflammable even when they escaped during parts of the production process. However, CFCs are hardy and can last up to a century before finally breaking down in the stratosphere where they release chlorine and catalyze ozone destruction.

“It’s only when they hang around for these long lifetimes at 50 to 100 years when they eventually get up into the stratosphere where the sunlight will break them down,” Johnson said. It’s there where these substances do the most damage to the ozone layer.

At the Global Monitoring Laboratory at the South Pole, NOAA monitors the ozone hole via weather balloons that have ozone instruments attached to them. Their journey takes the instruments 22 miles high in about two hours, where they can record detailed measurements on a profile of the ozone. About 60 to 70 of the balloons are launched each year, Johnson said, the bulk of which are released during September and October when there is a more rapid depletion of ozone.

Story continues

“I think to me the most interesting thing or amazing thing to see with these measurements is in the end of September, or the end of October when the ozone has had its peak, you go through a 4- or 5-mile layer of just zero. There’s just no ozone there,” Johnson said. “The total amount of ozone is depleted by 60, 65%.”

According to long-term trends from the data collected, the hole over Antarctica grew from 1980 through the early 1990s before stabilizing in the early 21st century.

The first suspicions that there could have been a depletion in the ozone layer surfaced in the 1970s, according to Johnson. Estimates of 3 or 4% had been considered, according to Johnson, until the Bridge Antarctic Service Crews in 1985 reported 30 to 40% losses of ozone.

“The thing is, you know, the ozone hole, it was a surprise,” Johnson said. “It just caught everyone off guard and [we] realized that, well, in the right conditions over Antarctica, the chlorine is a lot more destructive to ozone. So that’s the surprise that we just don’t want. We don’t want to be surprised again like that, so monitoring helps that a lot.”

According to NASA’s Earth Observatory, scientists estimate that about 80 percent of the chlorine and bromine in the stratosphere over Antarctica today comes from human sources.

The Montreal Protocol, an environmental agreement ratified in 1987 by the United Nations that regulates the production and consumption of almost 100 man-made chemicals that qualify as ozone-depleting substances, limited the production of CFCs and began to phase them out of production. However, the long lifetime of the destructive chemicals has caused them to be an enduring problem as they drift around in the atmosphere.

“That’s why we expect to still see ozone holes develop for the next 40, 50, 60 years, and it just takes time for the atmosphere to take on all those long-lived gases,” Johnson said.

These long-lived, ozone-depleting chemicals move around in the air currents or are carried by the wind and ultimately end up in the upper atmosphere with the ozone layer, NOAA research chemist Steve Montzka told AccuWeather over a Skype interview. Eventually, they can make it to Antarctica.

“It just so happens that the physical and chemical characteristics of the atmosphere, in the upper atmosphere over Antarctica allow for rather uniquely, or to a larger extent than other places in the atmosphere, severe ozone depletion,” Montzka said. “It’s a combination of the extreme cold temperatures that happened over Antarctica and the presence of these chemicals that cause ozone depletion that wreaks havoc on the ozone layer.”

Johnson breaks down the process of ozone depletion at the poles into basically three parts, beginning with the sun setting over the poles come autumn. With the sun absent, the atmosphere grows bitterly cold, and wind patterns begin to organize.

Polar stratospheric clouds begin to form from tiny particles in the cold, dark conditions in the upper atmosphere, processing the chlorine from the chemicals. The stage has been set for once the sun rises in the spring.

“When the sun comes up and everything remains stable, it’s just the right conditions for chlorine to destroy ozone,” Johnson said. “The Southern Hemisphere is a little better at doing this, at staying very stable in this containment vessel that we call the polar vortex. It holds the air in and allows all the chemistry to happen.”

CLICK HERE FOR THE FREE ACCUWEATHER APP

Ozone can be a deadly pollutant closer to the ground, but in mid-latitudes, the ozone layer protects people from high energy UV light along with other possible damage caused by the sun. While ozone holes away from the poles aren’t common, the hole over Antarctica served as a warning for scientists.

“It’s the ozone layer everywhere around the world that’s impacted and degraded to a certain degree by ozone depleting substances. The place where that depletion is the largest is over Antarctica,” Montzka said. “So Antarctica is kind of just a canary in a coal mine where the biggest changes are seen in the ozone, gives us a kind of indication of what happens when the ozone layer goes away because of human-emitted chemicals.”

During 2019, the Antarctic ozone hole was the smallest it had been in more than 30 years, which Johnson attributes to two factors: the first being the slow decline in CFCs and the second being the meteorological conditions.

“There’s still plenty of ozone depletion that we’re observing in the atmosphere, and yet more recently as the ozone-depleting chemical concentrations are decreasing, there are hints that the ozone layer is starting to recover,” Montzka said. With the Montreal Protocol making “dramatic changes” to the amount of depleting substances emitted into the atmosphere, the concentrations of the “bad actors” causing ozone depletion have also declined.

“That’s had a lot to do with those initial signs of ozone recovery that we’ve seen,” Montzka said.

Scientists had also observed a 20% decrease in ozone depletion during the winter months from 2005 to 2016, according to the Earth Observatory.

“The other factor that plays a big role are the meteorological conditions, the atmospheric dynamics, the waves and these meteorological disturbances that break down that big circulating wind pattern around the Antarctic, we call it the polar vortex,” Johnson said. “That polar vortex sets up every winter when the sun goes down, and the chemistry happens when the sun comes back up. That polar vortex remains stable, it allows the chlorine chemistry to complete its cycle and destroy 50 to 60% of the ozone layer, the ozone in the atmosphere.”

During 2019, the polar vortex had remained stable until September, when the depletion typically begins.

“The destruction chemistry kind of got shut off early,” Johnson said, explaining that an occurrence such as this with the polar vortex breaking down is seen every decade or so.

While the recovery process has been long, Johnson stressed that it’s natural for the ozone layer to go through a cycle of replenishing ozone and attempting to close back up. However, the goal each year is to see a recovery and, once the CFCs are no longer in the atmosphere, to see a healthy ozone layer.

“Once all the CFCs and reactive gases that are the sources of the destruction of ozone chemicals are gone, you know it won’t matter what the meteorological conditions are,” Johnson said. “There just isn’t any chlorine that would give you an ozone hole, so 50 years from now you won’t see that anymore.”