The Montreal Protocol is an international agreement (1987) that phases out the production of ozone-depleting substances like chlorofluorocarbons (CFCs), allowing the stratospheric ozone layer to recover; its Kigali Amendment also phases down HFC substitutes because of their high global warming potential.
The Montreal Protocol is the international treaty that phased out the production and use of chemicals that destroy stratospheric ozone, most famously chlorofluorocarbons (CFCs). CFCs were everywhere in the late 20th century, in refrigerants, aerosol cans, and foams. When they drift up to the stratosphere, UV radiation breaks them apart and releases chlorine atoms that rip ozone molecules apart in a catalytic cycle. The protocol is the textbook example of mitigation through substitution, which is exactly what learning objective 9.2.A asks you to describe. Replace the ozone-depleting chemical with a substitute that doesn't deplete ozone.
Here's the twist the AP exam loves. The main substitutes, hydrofluorocarbons (HFCs), have zero ozone depletion potential but some are strong greenhouse gases. So solving one global problem (ozone depletion) created a piece of another one (climate change). The Kigali Amendment to the Montreal Protocol responds by phasing down HFCs too. That makes the Montreal Protocol a rare success story that bridges two different atmospheric problems, and it's widely considered the most effective international environmental agreement ever.
This term lives in Topic 9.2 (Reducing Ozone Depletion) in Unit 9: Global Change, supporting learning objective 9.2.A, which asks you to describe chemicals used as substitutes for CFCs. It also reaches into Topic 9.3 (The Greenhouse Effect), because EK STB-4.D.1 tells you CFCs have the highest global warming potential of any greenhouse gas (with CO2 as the reference at GWP = 1). And it connects back to Topic 7.6 (Reduction of Air Pollutants) in Unit 7, where EK STB-2.G.1 lists regulatory practices as a method to reduce air pollution at the source. The Montreal Protocol is the international regulation example, the way the Clean Air Act is the domestic one. If an FRQ asks you to propose a solution to ozone depletion or to give an example of effective environmental regulation, this is your go-to answer.
Keep studying AP Environmental Science Unit 5
Chlorofluorocarbons (CFCs) (Units 7 & 9)
CFCs are the chemical the protocol exists to eliminate. They do double damage. They destroy stratospheric ozone (Topic 9.2) AND they're the greenhouse gas with the highest GWP (Topic 9.3). Phasing them out attacked both problems at once.
Ozone Depletion (Unit 9)
Ozone depletion is the problem; the Montreal Protocol is the solution. Because CFCs persist in the atmosphere for decades, the ozone layer is recovering slowly even though production stopped. That lag is a classic exam concept.
The Greenhouse Effect (Unit 9)
HFCs, the main CFC replacements, don't touch ozone but some are potent greenhouse gases. The Kigali Amendment phases them down, which turns an ozone treaty into a climate treaty. This trade-off (fixing one problem worsens another) is a favorite AP question setup.
Clean Air Act (Unit 7)
Both are examples of reducing air pollutants through regulation (EK STB-2.G.1). The Clean Air Act works at the national level on pollutants like NOx and SO2, while the Montreal Protocol works internationally on ozone-depleting substances. Pair them when an FRQ asks for regulatory solutions.
Multiple-choice questions usually test one of three things. First, identification, like "Which chemical is phased out under the Montreal Protocol?" (answer: CFCs). Second, the substitute trade-off, asking which CFC replacement is being phased down under the Kigali Amendment despite having zero ozone depletion potential (answer: HFCs, because of their high GWP). Third, classifying the protocol as a regulatory practice for reducing air pollution at the source. On FRQs, the Montreal Protocol is your best evidence whenever you're asked to describe a realistic solution to ozone depletion or to give an example of a successful international environmental agreement. To earn the point, name the protocol AND say what it does (phases out CFCs and other ozone-depleting substances). Just dropping the name without the mechanism won't cut it.
Both are international environmental agreements with "Protocol" in the name, so they get mixed up constantly. The Montreal Protocol (1987) targets ozone-depleting substances like CFCs to protect the ozone layer. The Kyoto Protocol (1997) targets greenhouse gas emissions like CO2 to address climate change. Quick memory hook: Montreal = ozone, Kyoto = climate. The overlap that makes it tricky is that CFCs are also greenhouse gases, and the Kigali Amendment pulls the Montreal Protocol into climate territory by phasing down HFCs. But the original purposes are different problems entirely.
The Montreal Protocol (1987) is the international agreement that phased out CFCs and other ozone-depleting substances, and it is considered the most successful environmental treaty in history.
CFCs were replaced largely by hydrofluorocarbons (HFCs), which have zero ozone depletion potential but are strong greenhouse gases.
The Kigali Amendment extends the Montreal Protocol to phase down HFCs because of their high global warming potential, shifting the treaty's focus toward climate change.
CFCs have the highest global warming potential of all greenhouse gases, which is why phasing them out helped both the ozone layer and the climate.
The ozone layer is recovering slowly because CFCs have long atmospheric residence times, so the damage lags behind the regulation.
On the exam, the Montreal Protocol is your example of a regulatory practice that reduces air pollutants at the source (EK STB-2.G.1).
It's the 1987 international agreement that phased out the production of ozone-depleting substances, especially chlorofluorocarbons (CFCs). On the AP exam it's the standard example of a successful solution to ozone depletion and of regulation as a pollution-control strategy.
Mostly yes, but slowly. The protocol stopped new CFC production, and the ozone layer is recovering, but CFCs already in the atmosphere persist for decades. So recovery lags well behind the regulation, which is a point AP questions like to test.
The Montreal Protocol (1987) targets ozone-depleting substances like CFCs to protect the stratospheric ozone layer. The Kyoto Protocol (1997) targets greenhouse gas emissions to fight climate change. Remember it as Montreal = ozone, Kyoto = climate.
It's an extension of the protocol that phases down HFCs, the chemicals that replaced CFCs. HFCs don't deplete ozone, but some are powerful greenhouse gases, so the amendment turns the ozone treaty into a climate tool. Practice questions frequently test this exact trade-off.
HFCs have zero ozone depletion potential, so they solved the immediate ozone problem. Their high global warming potential only became the target later, which is why the Kigali Amendment now phases them down. It's a classic example of an environmental trade-off.