How the Montreal Protocol Put the Stratospheric Ozone Layer on the Path to Recovery and Delayed Climate Tipping Points That Would Have Forced Earth Further Beyond Planetary Boundaries

The framework, introduced in 2009 by co-author Professor Johan Rockström and colleagues, defines Planetary Boundaries as the safe operating thresholds for nine critical processes that maintain Earth system stability and resilience. The stratospheric ozone layer is one of the nine processes, and it is highlighted as the first and only example of a planetary system imperiled by humans yet pulled back towards health in the coming decades by collective action of scientists, consumer boycotts, public policy, and technical innovation. This paper explains how policymakers, facing an existential risk from fluorocarbon emissions, listened to science and acted at a global level with adoption of the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) that, along with complementary actions by citizen and corporate leaders, avoided health and environmental hazards of stratospheric ozone depletion. The paper also explains how the Montreal Protocol has delayed climate tipping points through:

1) the phaseout of ozone-depleting substances (ODSs) that are also powerful greenhouse gases (GHGs),

2) the ongoing phasedown of non-ozone-depleting hydrofluorocarbon (HFC) GHGs, and;

3) the associated protection of aquatic and terrestrial carbon sinks from ultraviolet (UV) radiation.

The Montreal Protocol is proof that humans can organize to protect the global commons against exceeding planetary boundaries. The paper shows how it is possible to restore the health of other planetary boundaries beyond stratospheric ozone and climate by using the Montreal Protocol’s successful model of trusted scientific and technical wisdom, deep human connections, and a commitment to fairness.