Area VII: Global Change VIIA: Stratospheric Ozone

21-9 Stratospheric Ozone Depletion l ozone depletion is a threat to humans, other animals, and some of the primary producers that support the earth’s food l chlorofluorocarbons (CFCs) reduce ozone  CFCs discovered in 1930; freons are the most widely used of the family of CFCs  many uses, inexpensive to make, and seemed to be dream chemicals  in 1974, chemists Rowland and Molina found that CFCs were lowering the average concentration of ozone in the stratosphere

21-9 Stratospheric Ozone Depletion l CFCs, cont.  four major conclusions from their research: CFCs remain in atmosphere b/c they are insoluble in water, chemically unreactive lifted into stratosphere over years by convection currents, turbulent mixing of air CFC molecules break down under the influence of UV light; Cl is released and is highly reactive; F, Br, I are also released, breaking down O 3 faster than it is formed can last in stratosphere for 65–385 years

21-9 Stratospheric Ozone Depletion l a number of chemicals can end up in the stratosphere and deplete ozone there for up to several hundred years  during four months of each year, up to half of the ozone in the stratosphere over Antarctica is depleted  ozone thinning, not ozone hole  the total area of stratosphere that suffers from ozone thinning varies from year to year

21-9 Stratospheric Ozone Depletion l ozone thinning, cont.  polar vortex is a swirling mass of very cold air isolated from rest of atmosphere for months ice crystals in this mass collect CFCs, and CIO forms, the molecule most responsible for seasonal loss of ozone sunlight stimulates CIO molecules in October, and within a matter of weeks the ozone is reduced by 40–50% on average similar but less severe ozone depletion occurs over the Arctic

21-9 Stratospheric Ozone Depletion l increased UV light reaching the Earth’s surface from ozone depletion is harmful to living organisms and materials  the primary cause of squamous cell and basal cell skin cancers is years of exposure to UV-B radiation; 90–95% of these cancers can be cured if detected early enough  malignant melanoma is a skin cancer that may occur anywhere on the body; it kills a fourth of its victims (most under the age of 40) within 5 years

21-9 Stratospheric Ozone Depletion l UV light, cont.  women who use tanning parlors at least once a month increase their chances of developing melanoma by 55%  evidence suggests that 90% of sunlight’s melanoma-causing effect may come from exposure to UV-A (not blocked by window glass)  whites are most susceptible to melanomas

21-10 Protecting the Ozone Layer l to reduce ozone depletion we must stop producing ozone-depleting chemicals  If we immediately stop, it will take 50 years for the ozone layer to return to 1980 levels and about 100 years to return to pre-1950 levels  the goal of the 1987 Montreal Protocol was to cut emissions of CFCs by about 35% between 1989 and 2000  reps met in 1990 and 1992 and adopted the Copenhagen Protocol, an amendment that accelerated the phase out of depleting chem.

21-10 Protecting the Ozone Layer l reducing ozone-depleting chemicals, cont.  these agreements have now been signed by 177 countries  a study in 1998 by the World Meteorological Organization stated that ozone depletion has been cooling the troposphere and helped to disguise as much as 30% of the global warming from greenhouse gas emissions  restoring the ozone layer could lead to increased global warming