Stratospheric ozone, global warming, and the principle of unintended consequences-An ongoing science and policy success story

In 1974, Mario Molina and F. Sherwood Rowland warned that chlorofluorocarbons (CFCs) could destroy the stratospheric ozone layer that protects Earth from harmful ultraviolet radiation. In the decade after, scientists documented the buildup and long lifetime of CFCs in the atmosphere; found the proof that CFCs chemically decomposed in the stratosphere and catalyzed the depletion of ozone; quantified the adverse effects; and motivated the public and policymakers to take action. In 1987, 24 nations plus the European Community signed the Montreal Protocol. Today, 25 years after the Montreal Protocol was agreed, every United Nations state is a party (universal ratification of 196 governments); all parties are in compliance with the stringent controls; 98% of almost 100 ozone-depleting chemicals have been phased out worldwide; and the stratospheric ozone layer is on its way to recovery by 2065. A growing coalition of nations supports using the Montreal Protocol to phase down hydrofluorocarbons, which are ozone safe but potent greenhouse gases. Without rigorous science and international consensus, emissions of CFCs and related ozone-depleting substances (ODSs) could have destroyed up to two-thirds of the ozone layer by 2065, increasing the risk of causing millions of cancer cases and the potential loss of half of global agricultural production. Furthermore, because most ODSs are also greenhouse gases, CFCs and related ODSs could have had the effect of the equivalent of 2476 gigatons per year of carbon dioxide. This critical review describes the history of the science of stratospheric ozone depletion, summarizes the evolution of control measures and compliance under the Montreal Protocol and national legislation, presents a review of six separate transformations over the last 100 years in refrigeration and air conditioning (A/C) technology, and illustrates governmentindustry cooperation in continually improving the environmental performance of motor vehicle A/C. Implications: The comforts and conveniences of modern life are largely taken for granted. When purchasing a product, consumers are usually not concerned with how or why it works, often assuming the product is safe to use and safe for the environment. This critical review addresses why such general public acceptance and complacency is not always the best policy. The paper explains how early warnings given by vigilant scientists highlighted the dangers of ODS and calls for action and boycotts by concerned citizens 35 years ago and regulatory actions taken by governments worldwide 25 years ago successfully phased out ODSs and avoided global catastrophe. It also highlights new opportunities for the Montreal Protocol to further protect against climate change. The implication is that scientific vigilance, public policy, and citizen action have protected and can protect Earth for future generations. Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association.