The Copenhagen Amendment of 1992 significantly strengthened the 1987 Montreal Protocol, the foundational global treaty to protect the Earth’s ozone layer. The initial protocol established a framework for cooperation, but subsequent scientific assessments revealed that ozone depletion was occurring faster and more severely than originally predicted. This alarming data, particularly concerning the growing Antarctic ozone hole, necessitated a more aggressive international response. The primary objective of the Copenhagen Amendment was to dramatically accelerate the phase-out schedules for existing Ozone Depleting Substances (ODS) and bring new, previously unregulated chemicals under strict control.
Core Substances Included in the Agreement
The Copenhagen Amendment directly targeted the acceleration of controls on the most damaging chemicals already covered by the treaty, such as Chlorofluorocarbons (CFCs) and Halons. Under the original schedule, developed countries were set to phase out CFCs and Halons much later, but the new agreement pushed these deadlines forward to 1996 and 1994, respectively. This adjustment effectively ended the production of these primary ozone destroyers years ahead of the initial plan.
The Amendment also added several new substances to the control list, significantly broadening the scope of the global effort. Among the most important additions were Hydrochlorofluorocarbons (HCFCs) and Methyl Bromide. HCFCs, which were being used as temporary substitutes for CFCs, possess a lower but still measurable Ozone Depletion Potential (ODP). The Amendment categorized them as transitional substances and set an initial phase-out schedule for developed countries beginning in 2004, with a complete phase-out targeted for 2030.
Methyl Bromide, a widely used fumigant in agriculture, was also added to the list of controlled substances. Its inclusion brought a chemical with a shorter atmospheric lifespan but a high ozone-depleting capability under international regulation. Control measures initially froze the consumption and production of Methyl Bromide at 1991 levels in developed countries.
Quantifying the Global Reduction Success
The success stemming from the Copenhagen Amendment and the broader Montreal Protocol framework is measured in Ozone Depletion Potential (ODP) tonnes. ODP is a metric that standardizes the ozone-depleting capacity of a chemical relative to a reference compound, CFC-11. Since the implementation of the Copenhagen Amendment’s accelerated schedules, the phase-out of controlled ODS has reached approximately 99% of historical levels.
This near-total elimination equates to the reduction of roughly 1.8 million ODP tonnes of substances globally. For the most damaging compounds, such as CFCs, global production fell by 98% between 1986 and 2015. The accelerated deadline for CFCs in developed countries to 1996 ensured that the largest sources of these emissions were curtailed rapidly.
By controlling both the high-ODP legacy substances and lower-ODP transitional substances like HCFCs, the Amendment also yielded substantial climate co-benefits. Most ODS are potent greenhouse gases, and the phase-out has averted an estimated global warming of approximately 0.5–1 °C by the middle of the 21st century, compared to a scenario where ODS use continued to increase unchecked. This reduction in ODS production and consumption represents a major contribution to mitigating climate change achieved by an international agreement.
Observing the Ozone Layer’s Response
The regulatory success quantified by the reduction in ODP tonnes has translated directly into measurable environmental recovery. As a result of the controls implemented through the Copenhagen Amendment and subsequent actions, the atmospheric concentrations of controlled ozone-depleting substances are steadily declining. This decrease in the stratospheric burden of chlorine and bromine is the clearest scientific evidence that the phase-out is working.
The most visible sign of this recovery is the improving status of the Antarctic ozone hole. While year-to-year variability exists due to meteorological conditions, the long-term trend shows a slow but consistent healing of the ozone layer.
Scientific assessments project that the ozone layer will return to its 1980 reference levels across much of the globe by around 2040. Recovery is expected to be complete over the Arctic by approximately 2045 and over the Antarctic by around 2066. The commitment to eliminate nearly all ODS production has successfully placed the ozone layer on a path toward full restoration. This significantly reduces the risks of increased ultraviolet radiation exposure for human health and ecosystems worldwide.