Every other environmental problem in this course is still unsolved. This one is being fixed. The Montreal Protocol is the strongest evidence in the whole syllabus that international cooperation can work — which makes it the example examiners come back to again and again.
📚 What you need to know
UNEP (the UN Environment Programme) raised awareness of the problem, funded the research and brokered the agreements.
The Montreal Protocol on Substances that Deplete the Ozone Layer was initiated in 1987 to regulate the production, trade and use of CFCs and other ODSs.
It started with 24 signatories and now covers 197 countries. The Copenhagen amendment (1992) tightened it further.
ODS emissions fell from roughly 1.5 million tonnes in 1987 to about 400,000 tonnes by 2010. UNEP aims to end HCFC production by 2040.
Phased reductions gave industry time to develop and adopt alternatives, and national governments turned the targets into law.
Ozone depletion is one of the nine planetary boundaries. Action under the Protocol kept it from being crossed, and monitoring shows recovery is underway.
What UNEP did
Before anything could be agreed, the problem had to be believed. UNEP’s role was to gather and share the research showing three things: that the ozone layer was thinning rapidly, what was causing it, and what the consequences would be for ecosystems and human health. That evidence turned a scientific finding into a political case, and gave governments, industries and the public a shared reason to act.
UNEP then led the creation of the international agreements that followed, and still works with national authorities and customs agencies to monitor compliance and shut down the illegal trade in banned substances — which remains a real threat to the whole effort.
The agreement itself
Feature
Detail
Started
1987, under UNEP’s guidance, as the Montreal Protocol on Substances that Deplete the Ozone Layer
What it controls
The production, trade and use of chlorofluorocarbons and other ozone-depleting substances
Participation
24 countries signed the original protocol; the total now stands at 197
Strengthened since
Amended repeatedly, including at Copenhagen in 1992, which tightened restrictions further
Result
ODS emissions fell from around 1.5 million tonnes in 1987 to roughly 400,000 tonnes in 2010
Still to come
UNEP aims to end production of all HCFCs, the interim replacement chemicals, by 2040
Schematic, drawn to show the shape of the trend. Emissions peaked around 1988 and were roughly back to 1960s levels by 2010.
What made it work
This is the part worth thinking about properly, because comparing Montreal with climate agreements is a favourite exam question.
Why Montreal succeeded
Why climate agreements struggle
A handful of chemicals, made by a small number of companies, so the target was narrow and easy to police
Emissions come from almost every activity in every economy — farming, transport, heating, industry
Workable substitutes existed and could be developed quickly
Replacing fossil fuels means rebuilding energy, transport and industrial systems
The threat was easy to explain and personal: skin cancer and cataracts
Impacts feel distant in time and place, so urgency is harder to sustain
Commitments were binding, with phased reduction schedules that gave industry time to adapt
Paris targets are self-set and reviewed rather than enforced
Costs were modest and fell mainly on a few manufacturers
Costs are enormous and spread across whole populations
Notice the pattern: Montreal worked because the problem was narrow, the fix was cheap and the danger was easy to picture. Climate change is the opposite on all three counts. Saying that shows you understand why it worked, not just that it did.
Do not forget national governments. A protocol is only words until countries write it into law. Governments enacted national regulations restricting the production and consumption of CFCs and other halogenated gases, which is what actually forced the switch to ozone-friendly alternatives.
The payoff
The benefits of the Protocol arrive slowly, because CFCs already released stay in the atmosphere for decades. Projections of future skin cancer rates show the pattern clearly: what was avoided depends heavily on how strict the agreement became.
All three lines still rise, because CFCs already in the stratosphere keep working for decades. Prevention delayed is damage locked in.
A planetary boundary not crossed
Stratospheric ozone depletion is one of the nine planetary boundaries — thresholds beyond which major, possibly irreversible environmental change follows. Unlike climate change, this boundary has not been crossed, and the reason is the action taken under the Protocol.
The evidence comes from continuous monitoring: ozone holes have been shrinking over time and the layer is recovering, though full recovery will take decades because of how long ODSs persist.
Worked examples
WORKED EXAMPLE
Explain why the Montreal Protocol has been more successful than international agreements on climate change. [4]
Scale of the problem
Only a small group of chemicals made by relatively few companies had to be controlled, so the target was narrow and easy to monitor.
Availability of alternatives
Substitutes for CFCs already existed or could be developed quickly, at modest cost. Replacing fossil fuels means rebuilding entire energy systems.
Clarity of the threat
Skin cancer and cataracts are immediate and personal, which built public and political support fast.
Design of the agreementCommitments were binding, phased over time so industry could adapt, and turned into national law — unlike the self-set targets of the Paris Agreement.Narrow problem, cheap fix, visible danger, binding rules
WORKED EXAMPLE
Emissions of ODSs fell from about 1.5 million tonnes in 1987 to about 400,000 tonnes in 2010. Calculate the percentage decrease and comment on why ozone recovery still takes decades. [3]
Step 1: the calculationdecrease = 1,500,000 − 400,000 = 1,100,000 tonnespercentage = 1,100,000 ÷ 1,500,000 × 100 = 73.3%Step 2: why recovery lagsCFCs already released are extremely stable and persist in the atmosphere for decades, and each chlorine atom keeps destroying ozone catalytically long after emissions stop.About a 73% fall, but recovery runs decades behind
💡 Exam tip
Learn the headline figures: 1987, 24 to 197 countries, 1.5 million to 400,000 tonnes, HCFCs gone by 2040.
Credit UNEP by name for the research, awareness and negotiation, and national governments for the laws that enforced it.
When comparing with climate agreements, give reasons rather than just the contrast: number of sources, cost of alternatives, visibility of the threat.
Say why recovery is slow — ODSs persist and chlorine acts catalytically. It shows you have joined the two pages together.
Mention the planetary boundary that was not crossed. It is the strongest single sentence you can write about this agreement.
⚠ Common mix-up
The Montreal Protocol is not a climate agreement. That is Kyoto and Paris. Mixing them up is a costly error.
The ozone layer is not fixed yet. It is recovering, and full recovery is expected to take decades.
HCFCs were not the solution. They were the interim replacement, less damaging but still being phased out.
Signing is not complying. Illegal trade in banned substances continues, which is why monitoring and customs enforcement matter.
Success was not automatic. It depended on cheap substitutes and a small industry — conditions that do not apply to fossil fuels.
Up next: Natural Resources — the start of Topic 7, where the question shifts from what we release into systems to what we take out of them.
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