Environmental Problems, Their Causes, and Sustainability 1

What Can You Do?Reducing Exposure to UV-Radiation• Stay out of the sun, especially between 10 A.M. and 3 P.M.• Do not use tanning parlors or sunlamps.• When in the sun, wear protective clothing and sun–glasses that protect against UV-A and UV-B radiation.• Be aware that overcast skies do not protect you.• Do not expose yourself to the sun if you are takingantibiotics or birth control pills.• Use a sunscreen with a protection factor of 15 or 25 ifyou have light skin.• Examine your skin and scalp at least once a month formoles or warts that change in size, shape, or color orsores that keep oozing, bleeding, and crusting over. Ifyou observe any of these signs, consult a doctorimmediately.Figure 21-26 What can you do? Ways to reduce your exposureto harmful UV radiation.these types of skin cancer can be cured if detectedearly enough, although their removal may leave disfiguringscars. These cancers kill 1–2% of their victims,which amounts to about 2,300 deaths in the UnitedStates each year.A third type of skin cancer, malignant melanoma(Figure 21-25, right), occurs in pigmented areas such asmoles anywhere on the body. Within a few months,this type of cancer can spread to other organs.It kills about one-fourth of its victims (most underage 40) within 5 years, despite surgery, chemotherapy,and radiation treatments. Each year it kills about100,000 people (including more than 7,400 Americans),mostly Caucasians. It can be cured if detected earlyenough, but recent studies show that some melanomasurvivors have a recurrence more than 15 years later.A 2003 study found that women who used tanningparlors once a month or more increased their chance ofdeveloping malignant melanoma by 55%. And a 2004study at Dartmouth College found that people usingtanning beds were 2.5 times more likely to developbasal cell carcinoma and 1.5 times more susceptible tosquamous cell carcinoma.Recent evidence suggests that about 90% of sunlight’smelanoma-causing effect may come from exposureto UV-A (which is not blocked by window glass)and 10% from UV-B. Tanning booth lights and sunlampsemit mostly UV-A. Some sunscreens provide littleor no protection from UV-A unless they containchemicals such as zinc oxide or avobenzene (alsocalled Parasol 1789). Read the fine print on the tube tosee if such chemicals are present.Evidence indicates that people (especially Caucasians)who experience three or more blistering sunburnsbefore age 20 are five times more likely to developmalignant melanoma than those who havenever had severe sunburns. About 10% of those whoget malignant melanoma have an inherited gene thatmakes them especially susceptible to the disease. Figure21-26 lists ways for you to protect yourself fromharmful UV radiation.21-10 PROTECTING THE OZONELAYERHow Can We Protect the Ozone Layer? Say NoTo reduce ozone depletion we must stop producingozone-depleting chemicals.The consensus of researchers in this field is thatwe should immediately stop producing all ozonedepletingchemicals. However, even with immediateand consistent action, models indicate it will takeabout 50 years for the ozone layer to return to 1980 levelsand about 100 years for recovery to pre-1950 levels.Good news. Substitutes are available for most uses ofCFCs, and others are being developed (IndividualsMatter, at right).In 1987, representatives of 36 nations meeting inMontreal, Canada, developed a treaty, commonlyknown as the Montreal Protocol. Its goal was to cutemissions of CFCs (but not other ozone depleters) intothe atmosphere by about 35% between 1989 and 2000.After hearing more bad news about seasonal ozonethinning above Antarctica in 1989, representatives of 93countries met in London in 1990 and in Copenhagen,Denmark (1992), and adopted the Copenhagen Protocol,an amendment which accelerated the phasing out ofkey ozone-depleting chemicals.These landmark international agreements, nowsigned by 177 countries, are important examples ofglobal cooperation in response to a serious global environmentalproblem. Without them, ozone depletionwould be a much more serious threat, as shown in Figure21-27. If nations continue to follow these treaties,ozone levels should return to 1980 levels by 2050 and1950 levels by 2100.However, according to a 1998 study by the WorldMeteorological Organization, ozone depletion in thestratosphere has been cooling the troposphere and hashelped offset or disguise as much as 30% of the globalwarming from our emissions of greenhouse gases.Thus restoring the ozone layer could lead to an increasein global warming. But the alternative is worse.Environmental choices such as these are not easy.488 CHAPTER 21 Climate Change and Ozone Loss