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Illustration: Typical January stratospheric ozone, deviation
(%) from normal. What is Happening?Stratospheric ozone, which acts as a natural filter shielding the earth's surface from the extreme intensity of the sun's ultraviolet rays, has thinned over Canada since 1980. Stratospheric ozone has also thinned over southern British Columbia (BC) but since 1996 it has gradually risen back to the pre-1980 baseline. This is probably the result of natural climate variations that are known to affect the ozone layer thickness. Scientists believe that this is a welcome but only temporary improvement of the ozone layer and predict that the ozone thickness will gradually fall for the next 10 or 20 years. The following graph shows the changes in stratospheric ozone over southern BC in the last several years.
Source: Environment Canada, Pacific and Yukon Region, 2000. Ozone thickness is measured in Dobson units (DU). One hundred DU are equal to 1 mm thickness of ozone at sea level. Note that the data for 1999 are preliminary. The pre-1980 baseline values were estimated from 4 years of satellite data for the region and calibrated against ground based measurements from 5 Canadian sites. Environment Canada monitors stratospheric ozone at 12 locations across Canada. In BC it has been measured since 1993 on Saturna Island in the Strait of Georgia. The ozone thickness is measured from the ground using a Brewer ozone spectrophotometer and represents the column of ozone above the instrument. The ozone thickness varies seasonally. In the winter, the ozone thickness is usually high, but there are large deviations from the pre-1980 baseline. In the summer, the ozone thickness is usually low, with smaller deviations. The pre-1980 stratospheric ozone measurements are considered to be representative of normal levels prior to the beginning of the depletion of ozone, since ozone depletion had not been observed prior to 1980. In 1999, average ozone thickness over Saturna Island was near the pre-1980 baseline, although it was slightly below normal in the early half of the year. Ozone concentrations are naturally variable, and the current pattern of near normal values should not be interpreted as a complete recovery of the ozone layer. Environment Canada scientists continue to predict a thinning of the ozone layer over the next ten or twenty years, and forecast that a full recovery is not likely for at least 50 years. By 1995, the ozone layer over southern Canada was an average of about 6% thinner than it was in the late 1970's. The largest depletions over southern Canada occurred during the spring months, where ozone thinning was about 8% to 10%, and sometimes reached 20% for short periods. Ozone depletion was most severe in the high Arctic during the early spring, where reductions of up to 45% have been recorded in recent years. Since 1996 there has been a temporary recovery over southern Canada, where ozone thickness now averages only about 3% below the pre-1980 values, again probably caused by a natural climate variation. However, scientists predict that the ozone layer will begin thinning again once the climate shifts back to a more normal mode. It is expected that the Canadian ozone layer will not really begin to recover for another ten to twenty years. Why is it Happening?The thinning of stratospheric ozone is related to both human-produced and natural factors such as volcano eruptions, varying sunspot activity and the oscillation of stratospheric winds. However, most of the thinning is linked to the manufacture and release of ozone-depleting substances (ODSs) namely chlorofluorocarbons (CFCs), bromofluorocarbons (halons), methyl chloroform, carbon tetrachloride, methyl bromide and hydrochlorofluorocarbons (HCFCs). In Canada, these ODSs are used in refrigerators, air conditioners, foams, fire extinguishing systems, pesticides and solvents. Commercial uses of ODSs first began in the 1930's and this long-term use combined with their atmospheric lifetimes (up to 100 years for some) have resulted in a large ODSs build up in the stratosphere. ODSs have never been manufactured in BC but there are releases of ODSs from certain equipment uses. The two most important sources in BC are halons from fire extinguishers, which accounts for the largest emissions of ODSs, and CFCs emissions from air conditioners. Why is it Significant?Depletion of stratospheric ozone increases the level of ultraviolet (UV) radiation at ground level. Excessive exposure to UV is known to cause sunburn and has been linked to skin cancer, suppression of the immune system, and increased risk of developing cataracts in humans. The depletion of the ozone layer will add to this problem in the long term. The following graph shows typical seasonal ground level UV radiation intensity for the region in full sunlight at midday.
UV intensity is shown on a scale from 0 to 10 with values of less than 4 considered low (requiring on average 1 hour or more to burn unprotected skin), 4.0 to 6.9 moderate (around 30 min. to burn), 7.0 to 8.9 high (around 20 min. to burn) and 9 or more extreme (needing less than 15 min. to burn). UV intensity varies seasonally as well as latitudinally with intensity being highest in May to August in southern BC. In 1999 southern BC had 13 occasions when the index was high (7.0 or higher). The highest observed value was 8.0 on June 21.
The major cause of skin cancer is long term over-exposure of the skin to the sun's ultraviolet rays. Childhood sun exposure is an important contributor to the development of skin cancer later on in life. UV reaching southern Canada, since the late 1970's, has increased by an average of about 7%. In the spring, UV levels increase by 10% to 12% and may reach 25% for short periods. A sustained 1% decrease in stratospheric ozone is projected to result in a 2% increase in the incidence of nonmelanoma skin cancer. Anyone born in 1970 faces a one in twelve life time risk to develop skin cancer while the life time risk increases to one in seven for those born today. The Canadian Dermatology Association reports that in 1999 more than 66,000 Canadians (64,000 in 1998) are expected to develop nonmelanoma skin cancer. In BC 570 people (3,500 for Canada) are expected to develop melanoma in 1999 and a further 100 (770 for Canada) will die from this more serious form of skin cancer. The incidence of melanoma in Canada has doubled during the last twenty years. In BC the number of melanoma cases has nearly tripled in the past 17 years. Two people in this province die each week from malignant melanoma and 12 each week are diagnosed with it. Risk levels vary with skin type (fair skin people at highest risk) and the amount of time spent in the sun. Increased UV can also affect animals in their early developmental stages and may reduce crop yields and productivity of phytoplankton in marine and freshwater. It also affects some outdoor materials such as some plastics causing them to degrade more rapidly. What is Being Done?Under the Montreal Protocol of 1987 and its subsequent amendments, developed nations including Canada eliminated production, import and export of new halons in 1994 and new CFCs, carbon tetrachloride and methyl chloroform in 1996. Canadian federal regulation has reduced methyl bromide consumption to 75% of 1991 base-level in 1998. Federal regulation also calls for the complete phase out of HCFCs by the year 2030. Under the influence of this protocol, new supplies of ODSs in Canada has fallen from a high of 27.8 kilotonnes in 1987 to 0.9 kilotonnes in 1998. The Federal Halocarbon Regulations on management of ODSs at federal facilities went into effect July 1, 1999. For more details on federal regulations and proposed amendments consult Environment Canada's ozone website. Globally CFC production is also declining with the 1997 level being 88% less than the peak in 1988 as a result of international phase outs (National Stratospheric Ozone Depletion Indicator). Recovery, recycling and emission reduction regulations for ODSs (not including methyl bromide) are in place in all provinces and in the Yukon. Guidelines for ODSs for the Northwest Territories were published in 1996. Environmental codes of practice to promote the reduction and eventual elimination of emissions of ODSs have been prepared by Environment Canada for fluorocarbon emissions and halons . A environmental awareness training program for people servicing refrigerators and air-conditioning equipment has been set up by a Federal/Provincial Working Group and up to 80,000 technicians across Canada have taken the course to date. In BC, the provincial government promulgated the Ozone Depleting Substances Regulation in 1993 which prohibited new vehicles (1995 and newer vehicles) with ODSs in air conditioners and portable fire extinguishers with ODSs from being sold, manufactured or brought into BC. In December, 1996 the BC government amended its ODSs Regulation to require retrofit of motor vehicle air conditioners that required servicing after October 1, 1997. This regulation was amended again in November 1999 to include HFCs and PCFs, strengthen certain requirements and to rename it the Ozone-Depleting Substances and Other Halocarbons Regulation. More details are available from BC's stratospheric ozone home page. In order to keep the citizens of Canada and of this region informed about the state of the ozone layer and UV radiation, Environment Canada disseminates daily total ozone maps of Canada, weekly reports and monthly/annual summaries on the ozone layer through the Internet and other media. It also provides daily UV Index forecasts and daily UV Index maps of Canada. Environment Canada is also providing information for individual and community actions on this issue via A Primer on Ozone Depletion, Stratospheric Ozone site and Healthy Living with Sunshine. Since 1994, Environment Canada of the Pacific and Yukon Region has been doing inspections in BC of retail and supply outlets for compliance to the Ozone-Depleting Substances Products Regulations of the Canadian Environmental Protection Act (CEPA). For the status reports on these activities consult Environment Canada's Inspection Division website.
For more information contact: Bill.Taylor@ec.gc.ca about the science of ozone depletion or Linda.Bily@ec.gc.ca about the federal ODSs regulations. Check the following web sites for additional information on this indicator:
Other links:
The following sites are external to Environment Canada. As the organizations that maintain these sites may not be subject to the Official Languages Act information found on these sites may be presented only in the language in which it was written.
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