Area VII: Global Change

1. Area VII: Global Change VIIA: Stratospheric Ozone

2. 21-9 Stratospheric Ozone Depletion • ozone depletion is a threat to humans, other animals, and some of the primary producers that support the earth’s food • 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

3. 21-9 Stratospheric Ozone Depletion • 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 11-20 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 O3 faster than it is formed • can last in stratosphere for 65–385 years

4. 21-9 Stratospheric Ozone Depletion • 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

5. 21-9 Stratospheric Ozone Depletion • 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

6. 21-9 Stratospheric Ozone Depletion • 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

7. 21-9 Stratospheric Ozone Depletion • 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

8. 21-10 Protecting the Ozone Layer • 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.

9. 21-10 Protecting the Ozone Layer • 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