Montreal Protocol (College Board AP® Environmental Science): Study Guide

Montreal Protocol

Background

• Developed to address the rapid depletion of the stratospheric ozone layer due to human-made chemicals

  • Scientists in the 1970s and 1980s discovered that chlorofluorocarbons (CFCs) were breaking down ozone (O₃) molecules

  • This led to the formation of the "ozone hole" over Antarctica, increasing harmful UV radiation reaching Earth

• The ozone layer is critical for protecting life from UV radiation, which can cause skin cancer, cataracts, and DNA damage

• The Montreal Protocol was designed to phase out ozone-depleting substances (ODSs) to allow ozone recovery

Key Dates

• 1987: Montreal Protocol signed by 46 countries

• 1989: Came into effect

• 1990, 1992, 1997, 1999: Subsequent amendments and adjustments added more substances and stricter timelines

• 2016 (Kigali Amendment): Expanded the agreement to include hydrofluorocarbons (not ozone-depleting but powerful greenhouse gases

How the Montreal Protocol relates to the environment

• Aims to eliminate substances that damage the ozone layer, especially:

  • CFCs in aerosols, refrigeration, and air conditioning

  • Halons used in fire extinguishers

  • Methyl bromide in agriculture

• Promotes the use of safer alternatives that do not harm the ozone layer

Evaluation

• Successes:

  • Widely regarded as the most successful international environmental agreement

  • Ozone-depleting substances have been phased out in most countries

  • The ozone layer is on track to fully recover by the mid-to-late 21st century

  • Demonstrated the effectiveness of science-driven policy and global cooperation

• Challenges:

  • Continued illegal use of banned substances in some countries

  • Some ODS substitutes (e.g. HFCs) are potent greenhouse gases, contributing to climate change

  • Recovery is slow and depends on long atmospheric residence times of certain chemicals

  • Enforcement and compliance vary by nation and region