The Montreal Protocol is an international treaty adopted in 1987 to regulate the production, trade and use of chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODSs). It has been highly successful: coordinated action has prevented the planetary boundary for stratospheric ozone depletion from being crossed, although full recovery remains incomplete.
Level: SL and HL; Subtopic 6.4 Stratospheric ozone
How the Montreal Protocol Works
Stratospheric ozone absorbs harmful ultraviolet radiation, especially UVB, reducing DNA damage, disrupted photosynthesis and health risks. ODSs release halogens such as chlorine in the stratosphere, accelerating ozone destruction and disturbing the steady-state equilibrium between ozone formation and breakdown.
The protocol required states to phase out major ODSs. Later amendments, financial and technical assistance for lower-income countries, and cooperation among governments, scientists and industries strengthened compliance and enabled alternative technologies.
How Successful Has It Been?
| Evidence of success | Remaining limitation |
|---|---|
| Major ODS production and consumption fell substantially. | Long-lived ODSs create a time lag before full recovery. |
| Antarctic ozone is expected to recover gradually as stratospheric chlorine declines. | Illegal production and incomplete enforcement may delay recovery. |
| The ozone-depletion planetary boundary has not been crossed. | Some replacements, including hydrofluorocarbons (HFCs), are potent greenhouse gases. |
| Near-universal cooperation shows international environmental law can alter industrial behaviour. | Comparable cooperation may be harder where substitutes are costly. |
A common misconception is that the ozone hole causes global warming. Ozone depletion and climate change are distinct issues, although HFC replacements connect them through the enhanced greenhouse effect. The 2016 Kigali Amendment controls HFCs.
Exam Technique
For an evaluate question, weigh achievements against limitations, use the Antarctic ozone layer as a named example, and finish with a supported judgement. Conclude that the protocol has been exceptionally successful because it reduced the cause of depletion through coordinated international action, but recovery is delayed by atmospheric time lags and enforcement challenges.