A Miracle of Human Achievement: Our Ozone Layer is Healing

Sam Westreich, PhD

This is the impact that humans can have on our environment when we care.

Rainbows have nothing to do with our ozone layer, but they sure are pretty.Photo byPhoto by David Brooke Martin on UnsplashonUnsplash

Growing up in the early 1990s, a decade that seems to be forever ago (before the millennium? The year started with a 1??), I remember hearing about the hole in the ozone layer, and how it posed huge risks for humanity if it wasn’t addressed.

Those concerns haven’t been discussed as much in recent years — and it’s not because this no longer fits the media narrative, as some conspiracy theorists claim.

We haven’t heard as much mention of the hole in the ozone layer because humanity has taken the right steps to fix it.

Taking advice from scientists and researchers, we passed global treaties at the end of the 1980s to help solve this crisis, and we were successful. We’re continuing to do so, and the ozone layer is literally healing, right before our eyes.

Current environmental concerns, like the climate crisis we face now, can seem overwhelming. But if we can successfully reverse our actions to help stop one crisis, we can do so again.

Here’s what the ozone layer even does, how it was at risk, and how we’ve been so successful at fixing it.

What is the ozone layer, and what does it do?

First, let’s talk about what the ozone layer is. For that matter, what is ozone?

Ozone is a type of molecule formed from oxygen atoms. Normal oxygen, the stuff that we breathe in and out, is made of two oxygen atoms, bonded to each other, like a couple hugging each other. But oxygen atoms can also fuse into a three-atom combination, like a three-person hug, which we call ozone. And like a three-person hug, ozone is highly unstable.

Ozone forms naturally, when high-energy ultraviolet (UV) rays from the Sun hit regular 2-atom oxygen molecules. Occasionally, those molecules will split and fuse into 3-atom ozone. This occurs in a zone ranging from 6 to 30 miles above the Earth’s surface; we call this area the “ozone layer”.

(It’s really less of a dense layer and more of a thin, dispersed sort of ozone cloud that is in our upper atmosphere. The densest concentration of ozone is about 15 miles (25 kilometers) up, more than 5 miles higher than where our jumbo jets fly.)

Now, what’s this ozone cloud doing for us?

The answer is that it’s shielding us! Specifically, it shields us from UV light, especially in a range of 200–320 nanometers. UV light is classified into several different types, based on its wavelength:

Ozone absorbs UV radiation, focused on a peak of 250 nm. See how well that lines up with the most damaging wavelength for DNA (260 nm)?

Because of the ozone layer, we receive more than 20 times more UVA radiation than UVB radiation (because ozone is better at absorbing UVB/UVC radiation than UVA). Thus, our ozone layer plays a vital role in shielding our DNA, helping to prevent how much damage our DNA takes and thus reducing our levels of cancer, especially skin cancer.

How was our ozone layer at risk?

Ozone in our atmosphere is constantly being created and destroyed, but in the second half of the 20th century, humanity started shifting that ratio more towards destruction.

It turns out that certain molecules, when released into the atmosphere, react with ozone and destroy the ozone molecules, splitting them back into regular oxygen. The big danger is chlorine (yes, like the stuff that we put into our pools to kill bacteria). A single atom of chlorine can destroy over 100,000 molecules of ozone before it leaves the stratosphere!

We don’t naturally dump tons of chlorine into the upper atmosphere, but we were releasing it indirectly. This is where chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), carbon tetrachloride, and methyl chloroform all come in. These substances are manmade, and they release chlorine atoms when they’re hit by UV radiation.

And guess where there’s a lot of UV radiation? That’s right, in the upper stratosphere, where the ozone is.

We’d use CFCs, HCFCs, and other compounds for purposes on Earth, mainly for refrigeration, in aerosols, and for creating insulating foam. (Ironically, they were chosen because early refrigerators used toxic methyl chloride, which sometimes leaked out and killed people.)

These compounds were very stable down near the ground, but they were lightweight enough to be swept up into the upper atmosphere over time. 2 to 5 years after being released at ground level, these chemicals can arrive in the stratosphere, where the UV radiation cause them to release chlorine atoms and destroy the ozone layer.

Every year, the strength of the ozone layer fluctuates as the seasons change. In the spring, the ozone layer grows especially thin over Antarctica, where the darkness and strong winds generate clouds and trigger the breakdown of chlorine into free atoms. This leads to a “hole” in the ozone layer until temperatures warm, breaking up the isolation of air over Antarctica and reducing the chlorine release.

This ozone hole always forms, but in the 1980s, we noticed that — in large part because of the CFCs we released — it was growing worse each year, larger and lasting longer.

So we banded together to fix it, as a species.

How we solved the ozone crisis

In 1987, as fears about the growing hole in the ozone layer grew widespread, 27 countries came together to sign the Montreal Protocol to Reduce Substances that Deplete the Ozone Layer. This restricted the production levels of CFCs, and an amendment called for them to be phased out fully by 2000.

Over time, more countries joined the agreement. By 1999, a total of 148 countries have signed, and we’ve found alternative chemicals to fulfill the needs once covered by CFCs and HCFCs. These days, all 197 nations have signed the treaty.

And so far, that ban is working. Many CFCs and HCFCs have extremely long lifetimes, from 50 to 100+ years, but since we’re no longer putting out more of them, the levels will slowly but steadily drop.

In fact, they are dropping! Observational models show that the hole in the ozone layer is no longer growing year-over-year, and is shrinking. Occasional actions have interfered with the reduction of the hole (such as a 2015 volcanic eruption), but despite a significant amount of variability, models suggest that we’ll have an ozone layer of the same strength as it was in the early 1990s by the mid-2000s, probably around 2040 or 2050.

More recently, measurements showed how enforcement of this ban is continuing to pay off. In 2012, high levels of CFC emissions were detected coming from eastern Asia countries (which is, under the treaty signed by all nations, illegal). But China cracked down swiftly on the sources of these emissions, likely small factories using CFCs for blowing insulation, and the levels rapidly dropped.

Thanks to excellent enforcement, that burst of illegal emissions probably only set back the healing of the ozone layer by about 1–2 years.

In summary: our actions threatened the ozone layer, but we’re also reversing it

The story of our ozone layer is a great success story, that could have been a tragedy if we hadn’t acted. We began using chemicals without fully understanding their impacts on the environment, and only later discovered how devastating they were.

But we banded together and passed an international treaty to cut out the use of these dangerous chemicals. We found more environmentally friendly alternatives and monitored the atmosphere to ensure that we catch offenders. These chemicals stick around for a long time in the environment, but they are slowly declining and we can see the payoff on our observations of the regularly fluctuating hole in the ozone layer.

Some of the current threats to our global environment — climate change, overfishing, microplastic pollution — seem inevitable and unstoppable. But humanity has managed to stop climate-threatening catastrophes before, by working together, passing, and enforcing global treaties.

Here’s hoping that we can do the same for our current crop of challenges.


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A microbiome scientist working at a tech startup in Silicon Valley, Sam Westreich provides insights into science and technology, exploring the strangest areas of biology, science, and biotechnology.

Mountain View, CA

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