Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are chemicals that were once the main ingredients of refrigerants, aerosol spray propellants, cleaning solvents, and bubbles injected into foams. Through the 1970s and 1980s, scientific evidence mounted that release of these chemicals was depleting the ozone layer (which absorbs harmful ultraviolet radiation) in Earth’s upper atmosphere. 
In 1985, 28 states negotiated the Vienna Convention on Protection of the Ozone Layer to provide a framework for international regulations on ozone-depleting substances. This was followed, in 1987, by the Montreal Protocol on Substances that Deplete the Ozone Layer, a treaty with a timetable to phase out and eventually eliminate the production and consumption of these chemicals. The Montreal Protocol entered into force in 1989, after ratification by over 11 states (political associations with independent authority over a geographical area and its human population) representing more than two-thirds of the world’s consumption of ozone-depleting substances. It has undergone seven revisions (1990 London; 1991 Nairobi; 1992 Copenhagen; 1993 Bangkok; 1995 Vienna; 1997 Montreal; and 1999 Beijing). By 2008, 193 sovereign states had ratified the Montreal Protocol.
The London revision in 1990 established a multilateral fund to finance in developing states the conversion of existing manufacturing processes from ozone-depleting substances, the training of personnel, the payment of royalties and patent rights on new technologies, and the establishment of national ozone offices.  Industrialized states make donations to replenish the fund every 3 years.
The Montreal Protocol adopted nonconfrontational enforcement procedures  that some consider weak.  Parties to the Montreal Protocol are required to report their annual production and consumption of ozone-depleting substances. If a state is out of compliance, it may receive assistance for collecting and reporting data, technical assistance, and financial assistance.  If a state remains noncompliant, an implementation committee may suspend its rights and privileges, including cutting off financial and technical assistance or prohibiting trade of ozone-depleting substances with other parties to the Montreal Protocol. The Implementation Committee has yet to impose such sanctions on any party, despite some flagrant abuses of the treaty.
The 1997 Montreal Amendment to the Montreal Protocol introduced a system in which parties to the protocol license each manufacturer within their jurisdiction for every ozone-depleting substance it produces or uses.  Many parties have implemented this licensing system and are able to identify illegal manufacturers by monitoring the balance of production and use. Unfortunately, there are few supporting enforcement mechanisms for the system, and this has allowed black-market production of ozone-depleting substances to flourish around the world.
Despite all the difficulties in enforcing the Montreal Protocol, the world’s major producers and consumers of ozone-depleting substances have been compliant with it. As a result, emissions of CFCs dropped precipitously after the Montreal Protocol entered into force in 1989, and their concentrations in the atmosphere has followed suit. The treaty encourages certain users to substitute HCFCs for CFCs because HCFCs have shorter life spans in the atmosphere; as a result, HCFC emissions continued to rise after 1989 but now appear to have leveled off. The Montreal Protocol has set 2015 as the year to begin limiting the production and consumption of HCFCs.
The loss of stratospheric ozone, which became significant in the 1980s, has started to turn around, and global ozone concentrations are anticipated to return to pre-1980 levels sometime after 2060.  Without the Montreal Protocol, the ozone levels in the upper atmosphere would be 20% to 40% lower than they are today, and average temperatures at sea level would be up to 1°C warmer in the Northern Hemisphere. An economic analysis of the Montreal Protocol indicates that its benefits vastly exceed its costs (Table 11.3).
Sarma, K. M. (2005) Compliance with the Montreal Protocol. In: 7th International Conference on Environmental Compliance and Enforcement, International Network for Environmental Compliance and Enforcement, Marrakech, Morroco.
 Victor, D. G. (1998) The operation and effectiveness of the Montreal Protocol's noncompliance procedure. In: The Implementation and Effectiveness of International Environmental Commitments: Theory and Practice, Victor, D. G., K. Raustiala, and E. B. Skolnikoff, eds. MIT Press, Cambridge, MA. pp. 137-176, http://books.google.com/books?id=nHZAyKrn6QQC&pg=PA137&source=gbs_toc_r&cad=0_0#PPA138,M1.
 Ozone Secretariat (2006) Handbook for the Montreal Protocol on Substances that Deplete the Ozone Layer, 7 Edition. United Nations Environment Programme, Nairobi, http://ozone.unep.org/Publications/Handbooks/MP_Handbook_2006.pdf.
 Curlin, J., G. Bankobeza, and S. Stone (2005) Summary of Workshop 3d: Analyzing the
Compliance and Enforcement Mechanisms of the Montreal Protocol. In: 7th International Conference on Environmental Compliance and Enforcement, International Network for Environmental Compliance and Enforcement, Marrakech, Morroco.
 World Meteorological Organization (2007) Scientific Assessment of Ozone Depletion: 2006, Global Ozone Research and Monitoring Project—Report No. 50. Geneva, http://www.esrl.noaa.gov/csd/assessments/2006/report.html.
This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.
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