By AnthroEvolve Coop

In the 1980s, scientists basically told the world:

“We’ve punched a hole in the planet’s sunscreen.”

The ozone hole over Antarctica was growing. Skin cancer risks were rising. And the cause wasn’t villains in capes, it was… hairspray, refrigerators, and air conditioners.

Then something rare and beautiful happened:
Countries listened. Corporations changed their products. Rich nations helped poorer ones. Nearly every government on Earth signed one agreement and stuck to it.

That agreement was the Montreal Protocol, and it is proof that global cooperation can literally change the chemistry of the sky in our favor.

Now we’re facing a different crisis: global warming. Harder, messier, more deeply wired into everything. But the ozone story shows that when we act together, big systems do move.

Let’s explore:

• How CFCs tore open the ozone layer

• Why ozone is “good up high, bad nearby”

• How the Montreal Protocol worked and what replaced CFCs

• How this is different from global warming

• How combustion engines create smog-level ozone

• Why EVs are already cleaning the air in measurable ways

• And how Montreal is a blueprint for the climate fight

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1. Ozone 101: good up high, bad nearby

Ozone is just three oxygen atoms: O₃. Same molecule, two very different personalities depending on altitude.

Stratospheric ozone: the planet’s sunscreen

In the stratosphere, about 15–35 km above us, ozone forms a thin layer that absorbs harmful ultraviolet (UV) radiation from the Sun. Without it, more UV-B and UV-C reach the surface, increasing skin cancer, cataracts, and damage to crops and marine life.

Up there, ozone is good. It is the shield.

Tropospheric ozone: the lung-burner

Near the ground, in the troposphere, ozone is formed as a pollutant. It’s a key ingredient in photochemical smog and:

• Irritates lungs

• Triggers asthma attacks

• Reduces crop yields and harms vegetation

Down here, ozone is bad. Same molecule, wrong place.

So the rule of thumb:

Ozone up high: essential.
Ozone nearby: harmful.

The ozone crisis was about destroying the good ozone up high. Smog is about creating too much bad ozone down low.

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2. How CFCs broke the sky

The main villains of the ozone story are chlorofluorocarbons (CFCs). They were designed to be miracle chemicals: stable, non-flammable, and great for cooling and sprays.

They were used in:

• Refrigerators and freezers

• Air conditioners

• Spray-can propellants

• Foam blowing agents for insulation

That stability is exactly why they were dangerous.

1. CFCs released at the surface drift up into the stratosphere over years.

2. Up there, intense UV radiation breaks them apart.

3. This releases chlorine atoms (Cl), which act as catalysts in ozone-destroying cycles.

A simplified catalytic cycle:

• Cl + O₃ → ClO + O₂

• ClO + O → Cl + O₂

Net reaction: O₃ + O → 2 O₂

The chlorine atom is regenerated, so one chlorine atom can destroy thousands of ozone molecules before being removed.

By the mid-1980s, satellite and ground-based measurements showed a huge seasonal “ozone hole” over Antarctica, appearing each Southern Hemisphere spring. This wasn’t a tiny dip; it was a massive thinning of the protective layer.

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3. The Montreal Protocol: when the world actually cooperated

In 1987, countries agreed to the Montreal Protocol on Substances that Deplete the Ozone Layer. It entered into force in 1989 and is now ratified by essentially every nation on Earth.

Key features:

• Phase-out of nearly 99% of controlled ozone-depleting substances (ODS) like major CFCs and halons

• Legally binding schedules to reduce and then eliminate production and consumption

• A Multilateral Fund so wealthy nations help finance transitions in developing countries

• Regular scientific assessments and amendments as new evidence came in

And it worked. Hard.

Recent NOAA–NASA and UN assessments show:

• Concentrations of major ODS in the atmosphere have peaked and are declining

• The ozone layer is recovering, with notable improvement in the upper stratosphere

• The Antarctic ozone hole is trending smaller and shorter-lived on average, even though volcanic eruptions and climate variability still cause year-to-year swings

Best current estimates:

• Mid-latitude ozone back to 1980 levels around the 2040s

• Antarctic ozone back to 1980 levels around 2066, if compliance continues

And here’s the bonus twist:
CFCs are also powerful greenhouse gases. By phasing them out, the Montreal Protocol has:

• Already prevented emissions equivalent to tens of billions of tons of CO₂

• Likely avoided about 0.5–1.0 °C of additional warming by 2100 when you include both direct CFC warming and damage they would have done to the carbon sink via extra UV

• So yes: one treaty helped heal the ozone layer and reduced future global warming at the same time.

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4. What replaced CFCs – and what we use today

The world didn’t just “stop cooling things.” Montreal forced an evolution in refrigerants:

CFCs → HCFCs → HFCs → low-GWP & “natural” refrigerants

Step 1: HCFCs – the “less bad” bridge

First came HCFCs (hydrochlorofluorocarbons):

• Still contain chlorine, so they do deplete ozone, but less than CFCs

• Still strong greenhouse gases with high global warming potential (GWP)

They were widely used in:

• Home and commercial refrigeration

• Air conditioning and chillers

• Foam blowing

• Some aerosols/solvents

The Montreal Protocol treated HCFCs as temporary:

• Developed countries phased them out by around 2020

• Developing countries are phasing them out by around 2030, with limited servicing allowances

Step 2: HFCs – fixed the ozone, hit the climate

Next came HFCs (hydrofluorocarbons):

• No chlorine, so no ozone depletion

• But many have very high GWP, hundreds to thousands of times CO₂

HFCs exploded in use:

• Most modern fridges and freezers (until recently)

• Car air conditioning (R-134a, now being replaced by low-GWP HFO-1234yf)

• Building chillers and split A/C units

• Foam insulation

• Some aerosols and fire suppression systems

They solved the ozone problem, while quietly becoming a fast-growing source of climate warming. Under a high-use scenario, HFCs alone could have added up to 0.4–0.5 °C of warming by 2100.

Enter…

Step 3: Kigali Amendment – taking on HFCs

In 2016, countries adopted the Kigali Amendment to the Montreal Protocol to phase down HFCs globally. It entered into force in 2019 and now has more than 160 parties.

If fully implemented, Kigali is expected to:

• Cut HFC use by over 80% in coming decades

• Avoid up to ~0.4–0.5 °C of warming by 2100

Same treaty, upgraded mission:
First save the ozone layer, now help save the climate too.

Step 4: Today’s trend – “natural” and low-GWP refrigerants

Right now, we’re shifting toward refrigerants that protect both ozone and climate:

“Natural” refrigerants:

• CO₂ (R-744)

  • Used in supermarket systems, some heat pumps and vending machines

  • Ozone depletion potential (ODP) = 0, GWP = 1 by definition

• Ammonia (R-717)

  • Common in large industrial refrigeration

  • Zero ODP, very low GWP, but toxic if leaked, so used in carefully engineered systems

• Hydrocarbons (propane R-290, isobutane R-600a, etc.)

  • Now widely used in household refrigerators, small commercial units, and some A/C

  • Zero ODP and very low GWP (~3), but flammable, so charge sizes and safety codes matter

Many new fridges around the world now use isobutane (R-600a) instead of HFCs.

HFOs and low-GWP synthetics:

• HFOs (hydrofluoroolefins) are designed to have very low GWPs and short atmospheric lifetimes

They appear in:

• New car A/C systems (HFO-1234yf)

• Newer chillers and commercial A/C

• Foam blowing and other specialty applications

The U.S. EPA’s SNAP program (Significant New Alternatives Policy) and similar efforts in the EU actively evaluate and list acceptable substitutes, steering industry away from both ozone-depleting and high-GWP options.

So the arc looks like this:

CFCs (destroy ozone, warm the planet)
→ HCFCs (less ozone damage, still high GWP, transitional)
→ HFCs (no ozone damage, big warming)
→ CO₂, ammonia, hydrocarbons, HFOs (no ozone damage, much lower warming)

We have literally redesigned global cooling technology three times based on atmospheric science.

That’s not nothing.

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5. Ozone depletion vs global warming: same sky, different story

It’s tempting to say “We fixed the ozone hole, so we can fix global warming the same way.”
Yes… and also not exactly.

Ozone depletion:

• Mainly caused by a relatively small group of chemicals (CFCs, halons, some HCFCs)

• Mostly used in a handful of sectors (refrigeration, A/C, aerosols, foams, solvents)

• Chemistry is focused in the stratosphere

• Impacts: UV increase, skin cancer, cataracts, ecosystem damage

Global warming:

• Driven primarily by CO₂, methane, nitrous oxide, and other greenhouse gases

• Emitted through almost everything: energy, transport, industry, agriculture, land use

• Acts through infrared absorption throughout the atmosphere

• So the ozone problem was narrower and more “surgical”: you could target specific chemicals and industries. Climate change is more like rewiring the whole energy and land system.

But the Montreal playbook still matters:

• Listen to scientists

• Set binding global limits

• Build fairness into the deal

• Fund technology transitions

• Update agreements as science evolves

We are doing this, just unevenly: think Paris Agreement, national climate laws, and regional fossil phase-out plans. The question is whether we’ll move fast enough.

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6. Ground-level ozone: how engines cook smog out of thin air

Now let’s come back down from the stratosphere to the air we actually breathe.

Tropospheric (ground-level) ozone is not emitted directly. It is created by sunlight-driven chemistry from precursor pollutants:

• NOₓ: nitrogen oxides (NO and NO₂), mostly from combustion

• VOCs: volatile organic compounds, from fuel vapors, solvents, industry, and vehicles

• Sunlight

The U.S. EPA and atmospheric chemistry texts summarize the core steps like this:

1. Combustion in engines emits NO and NO₂ (collectively NOₓ) plus VOCs.

2. In sunlight, NO₂ splits:

   NO₂ + hv (sunlight) → NO + O

3. The free O atom reacts with O₂:

   O + O₂ + M → O₃ + M
   (M is any third body that carries away extra energy.)

4. VOCs are oxidized to peroxy radicals (RO₂·) that react with NO:

   RO₂· + NO → RO· + NO₂

   This regenerates NO₂ without destroying ozone, allowing O₃ to accumulate.

In short:

NOₓ + VOCs + sunlight = ozone (O₃) + smog.

Cars, trucks, and buses are prime sources of those precursors, alongside power plants and industry.

Ground-level ozone is both:

• A major health pollutant

• A short-lived climate pollutant, contributing to warming on weekly-to-monthly timescales

So if we clean up combustion engines, we don’t just make air easier to breathe. We also chip away at near-term warming.

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7. EVs: turning off the tailpipe chemistry set

Enter electric vehicles (EVs).

They don’t magically fix everything, but they do one extremely important thing:

They remove tailpipe NOₓ and VOC emissions where people live and breathe.

According to the U.S. Department of Energy’s Alternative Fuels Data Center and the EPA:

• All-electric vehicles have zero tailpipe emissions

• Plug-in hybrids have zero tailpipe emissions when running in electric mode

• Even counting power plant emissions, EVs typically produce lower overall greenhouse gas emissions than comparable gasoline vehicles, especially as grids get cleaner

Real-world evidence: cleaner air, fewer asthma attacks

A study led by researchers at USC looked at California zip codes between 2013 and 2019, tracking zero-emission vehicle (ZEV) adoption, air pollution, and health outcomes:

1. For every additional 20 ZEVs per 1,000 people, there was:

   • A 3.2% drop in asthma-related emergency visits

   • A measurable reduction in NO₂ levels, a traffic-related pollutant linked to asthma and heart disease

     Other modeling and health studies show that widespread EV adoption:

• • Cuts NOₓ, VOCs, and ozone in many regions
  • Reduces PM₂.₅ (fine particulates) when combined with cleaner power generation
  • Delivers the greatest benefits in communities packed near highways and busy roads

Are EVs perfect? No. They still depend on the grid mix, and non-exhaust emissions like tire and brake dust remain issues. But in terms of the ozone-creating chemistry in city streets, EVs are a huge step forward.

They are, in a very literal sense, anti-smog machines.

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8. What the Montreal story teaches us about climate

The Montreal Protocol shows that:

• Science can ring the alarm
  Clear evidence about CFCs and ozone forced a global reckoning.

• The world can agree on strict rules
  Montreal is one of the most universally ratified treaties in history, with real teeth.

• Equity can be built in
  The Multilateral Fund helped developing countries leapfrog to new technologies.

• Industries can pivot fast under pressure
  We’ve already re-engineered global cooling three times, and are now moving toward climate-friendly refrigerants.

• We can literally change atmospheric trends
  Ozone-depleting substances are declining. The ozone layer is healing. And we’ve already avoided substantial future warming from CFCs and HFCs.Now we stand in front of the climate problem, which is bigger and gnarlier but built on the same physics: molecules in the sky trapping energy.

To “do a Montreal” for climate, we need the same ingredients, scaled up:

• Fast phase-down of fossil fuels, like we phased down CFCs and now HFCs

• Global agreements with real schedules, like Paris, strengthened with clear fossil phase-out timelines

• Massive investment in alternatives: renewables, storage, efficiency, EVs, heat pumps, natural refrigerants

• Fairness and finance so Global South countries can develop without repeating the North’s fossil addiction

The ozone story is not a fairy tale. It is a technical, legal, and political precedent.

We already have proof that when humanity decides to cooperate, we can:

• Stop selling harmful chemicals

• Redesign huge industrial systems

• Watch the atmosphere respond

• And in the process, avoid degrees of global heating

The ozone layer is on a recovery trajectory right now, with the 2025 Antarctic ozone hole ranked among the smallest since the early 1990s.

If we can do that for a layer of gas 20 km overhead, we can absolutely change the trajectory of the whole climate system below it.

The question isn’t “Is it possible?”
Montreal already answered that.

The question is: Will we choose to cooperate at that scale again, this time for carbon?

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Sources & Further Reading

UNEP – Ozone layer recovery on track, avoiding ~0.5 °C of warming UNEP - UN Environment Programme

NOAA 2022 Scientific Assessment of Ozone Depletion – climate benefits of Montreal Protocol NOAA Chemical Sciences Laboratory+1

Montreal Protocol overview & Kigali Amendment (Wikipedia) Wikipedia+1

CFC chemistry and ozone destruction (LibreTexts / chemistry of ozone depletion) Chemistry LibreTexts

Recent ozone hole trends and recovery (NOAA–NASA / news coverage) The Guardian+1

Ground-level ozone basics & health impacts (U.S. EPA) US EPA+1

Tropospheric ozone formation and chemistry (ground-level ozone article & teaching resources) Wikipedia+1

International HFC phase-down & Kigali climate benefits DCCEEW+2California Air Resources Board+2

CFC replacements: HCFCs, HFCs, and natural refrigerants (CFC article & technical guides) Climate Action+5Wikipedia+5Danfoss+5

EPA SNAP program – evaluating substitutes for ozone-depleting substances and high-GWP gases US EPA+3US EPA+3Wikipedia+3

USC / California ZEV study – EVs, NO₂, and asthma ER visits Keck School of Medicine of USC+2PMC+2

DOE Alternative Fuels Data Center & EPA – EV emissions and zero tailpipe pollutants Alternative Fuels Data Center+3Alternative Fuels Data Center+3Alternative Fuels Data Center+3

EVs, air quality, and climate modeling (NREL / Joint Office / policy analyses) Department of Transportation+2DCCEEW+2