The North American Mosaic: An Overview of Key Environmental Issues Air and Atmosphere Stratospheric Ozone Key Findings Ozone is a gas present throughout the earth’s atmosphere. Stratospheric ozone protects n Stratospheric ozone protects the life on earth by absorbing harmful rays from the sun as they pass through the upper earth’s surface from excessive atmosphere (the stratosphere). Because the ozone present at the earth’s surface is solar radiation, but this protective detrimental, ozone is often described as being “good up high and bad nearby.” layer has become thinner, allowing penetration of harmful levels of ultraviolet radiation. Excess levels of What Is the Environmental Issue? twentieth century and some continue to be ultraviolet radiation are harmful to produced and used. When released, these human health and the environment. Stratospheric ozone protects the earth’s surface chemicals make their way to the upper atmo- by absorbing ultraviolet (UV) radiation from the sphere and gradually convert to more reactive n In response, countries have sought sun (see illustration). It is naturally formed by gases that destroy ozone. Overall thinning of to control production, consumption chemical reactions involving ultraviolet sunlight the ozone layer has been recognized since the and trade of ozone-depleting and oxygen. Approximately 90 percent of ozone 1970s, and the total loss is currently estimated substances (ODS) through an is in the stratosphere, the layer of the atmosphere to average 3 percent over the globe, with more international agreement. By the end that begins 10–15 kilometers above the earth’s thinning occurring toward the polar regions of 2005, the parties to the Montreal surface at the midlatitudes. The ozone in the and less near the equator. Above Antarctica, an stratosphere is referred to as the ozone layer. ozone hole now forms each September. During Protocol had together phased out September 2006, the average area of the ozone production and consumption of over Thinning of the ozone layer hole, at 27.5 million square kilometers, was 95 percent of ODS—which are used The stratospheric ozone layer is now thinner the largest ever observed (see photo). A little as refrigerants, aerosol propellants than it has been historically because of certain over a week later, instruments recorded the and for other purposes. ozone-depleting substances, such as refriger- lowest concentrations of ozone ever observed ants and aerosol propellants. These substances over Antarctica, revealing that the ozone hole n Currently the earth’s protective were first produced commercially during the was the deepest it had ever been. ozone layer remains thinner than historical averages; the ozone hole UV protection by the ozone layer over Antarctica was at its largest and deepest ever observed in 2006. n Canada, Mexico and the United States have substantially reduced Sun emissions of ODS over the last 20 UV-A Ozone layer years, but these substances are still released from various sources in UV-B North America and globally. Recovery of the ozone layer is expected by the mid-twenty-first century based on UV-C compliance with the international agreement now in place. Reduction in ODS has delivered substantial climate benefits, because some ODS also act as greenhouse gases. Source: United Nations Environment Programme. Note: This publication was prepared by the Secretariat of the Commission for Environmental Cooperation. The views contained herein do not necessarily reflect the views of the governments of Canada, Mexico or the United States of America. Because the ozone layer absorbs some of the The Antarctic ozone hole (21–30 September 2006) biologically harmful ultraviolet radiation from the sun, reductions in stratospheric ozone lev- els allow more UV radiation to reach the earth’s surface, where it affects human health, disrupts biological processes and damages materials. Ozone-depleting Substances The substances most responsible for the destruc- tion of the ozone layer are listed in the following table along with their uses in everyday life. Alter- natives to these substances include hydrochlo- rofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs). HCFCs, a transitional CFC replacement, are used as refrig- erants, solvents and fire extinguishers. HFCs and PFCs are used as refrigerants, aerosol pro- pellants and solvents. Why Is This Issue Important to North America? Ozone depletion has significant health and economic consequences for North America. It is generally worse at latitudes approaching the poles, specifically the northern and Arctic regions in the North American context. Effects of UV-B Radiation Overexposure to UV-B radiation, the most damaging type of ultraviolet radiation, can cause a range of health effects, including Source: National Aeronautics and Space Administration. skin cancers and premature aging, eye dam- age (such as cataracts) and suppression of the Marine phytoplankton, which serves as More broadly, increases in solar UV radia- immune system. The physiological and devel- the base for the ocean’s aquatic food chain, is tion could affect terrestrial and aquatic biogeo- opmental processes of plants are also affected under stress from UV-B radiation as well. Stud- chemical cycles, thereby altering both sources by UV-B radiation, which can damage sen- ies have also found that solar UV-B radiation and sinks of greenhouse and chemically impor- sitive crops such as soybeans and rice and damages fish, amphibians and other animals in tant trace gases. reduce crop yields. their early developmental stages. Finally, synthetic polymers, naturally occurring biopolymers and other commer- cially useful materials are adversely affected Common ODS and Their Uses by solar UV radiation. Increases in solar UV-B levels accelerate their breakdown out- Substance Uses doors. Chlorofluorocarbons (CFCs) Refrigerants, cleaning solvents, aerosol propellants and blowing agents for plastic foam manufacture Reducing Emissions Canada, Mexico and the United States are Hydrochlorofluorocarbons Refrigerants, cleaning solvents, aerosol propellants and addressing the destruction of the ozone layer (HCFCs) blowing agents for plastic foam manufacture by eliminating the production and consump- Halons Fire extinguishers/fire suppression systems tion of ozone-depleting substances on a sched- ule determined by the Montreal Protocol on Carbon tetrachloride Production of CFC (feedstock), solvents Substances that Deplete the Ozone Layer. This agreement has led to a phase-out of the pro- Methyl chloroform Industrial solvents for cleaning, inks, etc. duction and consumption of CFCs and other Methyl bromide Fumigant used to control soil-borne pests and diseases in ODS. Currently, 191 countries and the Euro- crops prior to planting pean Community are parties to the Protocol and are implementing its requirements. 2 Commission for Environmental Cooperation By the end of 2005, the parties had Because of the long time that it takes for ODS to Monitoring Stratospheric Ozone Trends together phased out over 95 percent of ODS, move from ground level to the stratosphere, the Over North America, total stratospheric reducing production levels from a 1990 level impact of their elimination will not be felt for ozone levels began falling in 1965, reaching of over 1 million Ozone Depletion Potential many years. It is estimated that the ozone layer their lowest levels in 1993. The ozone layer has (ODP) tonnes a year to about 93,000 ODP could recover by about 2050, provided that all since begun to recover, but as of 1998–2001 tonnes a year in 2005. North American pro- ozone-depleting substances of anthropogenic average overall levels were still 3 percent lower duction and consumption declined from origin are eliminated. However, long-term pre- than those observed 20 years earlier. Since about one-third to under one-fifth of the dictions are uncertain because not all of the pro- 1993, ozone levels over North America have global total (see graph). cesses of ozone depletion are understood. The been trending upward as result of reduced Also through 2005, the production and con- role of very short-lived ODS is still being stud- ODS emissions and reformation of strato- sumption of ozone-depleting substances in North ied, along with the impact of climate change on spheric ozone. America fell by almost 97 percent (see graph). the stratosphere and ozone depletion. Illegal Trade in ODS Somewhat complicating this picture of prog- Total reported production of ozone-depleting ress is the illegal trade in significant amounts substances globally and in North America of ODS on a global basis. Although all new CFCs are now banned in industrialized coun- 1200 tries, millions of refrigerators, automobile air conditioners and other equipment that use 1000 CFCs are still in service. Servicing this equip- ment with CFC replacements is possible, but 800 often more expensive. In addition, used CFC- based equipment is exported to developing 600 countries by countries that have phased out CFCs. These factors create incentives for the 400 illegal trade in ODS, which has been estimated at 10–20 percent of the legitimate global trade. Thousands of ODP Tonnes 200 Issues related to the legal trade of equipment and illegal trade of ODS may complicate prog- 0 ress toward the ultimate elimination of ODS 1990 1995 2000 2005 on a worldwide basis. Global North America What Are the Linkages to Other North American Environmental Issues? ODP = Ozone Depletion Potential. Source: United Nations