Final Review - Ozone hole Chlorine-based aerosols...

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Ozone hole  – Chlorine-based aerosols, especially  chlorofluorocarbons (CFCs)  and other halon  gases, are the principal agents of ozone depletion. From the 1930s until the 1980s, CFCs were  used all over the world and widely dispersed through the atmosphere. Almost every year since its discovery in 1985, the Antarctic ozone hole has grown. In  2000 the region of ozone depletion covered 28.3 million km ³  (larger than North America). Since  then, the maximum size of the hole seems to be shrinking. Now, however, this phenomenon seems to be spreading to other parts of the world.  About 10% of all stratospheric ozone worldwide has been destroyed in recent years, and levels  over the Arctic have averaged 40% below normal. Ozone depletion has been observed over the  North Pole as well, although it is not as concentrated as in the south. Montreal Protocol  – The discovery of stratospheric ozone losses brought about a remarkably  quick international response. In 1987 an international meeting in Montreal, Canada produced the  Montreal Protocol, the first of several major international agreements on phasing out most of the  CFCs by 2000. As evidence accumulated, showing that losses were larger and more widespread  than previously thought, the deadline for the elimination of all CFCs (halon, carbon tetrachloride,  and methyl chloroform) was moved up to 1996, and a $500 million fund was established to assist  poorer countries in switching to non-CFC technologies. Fortunately, alternatives to CFCs for most  uses already exist. The first substitutes are hydrochlorofluorocarbons (HCFCs), which release  much less chlorine per molecule. Eventually, scientists hope to develop halogen-free molecules  that work just as well and are no more expensive than CFCs. The Montreal Protocol is often cited as the most effective international environmental  agreement ever established. There is some evidence that the CFC ban is already having an  effect. CFC production in most industrialized countries has fallen sharply since 1989, and CFCs  are now being removed from the atmosphere more rapidly than they are being added. In 40 years  or so, stratospheric ozone levels are expected to be back to normal. Unfortunately, there may be  a downside to stopping ozone destruction. Ozone is a potent greenhouse gas. Some models  suggest that lower ozone levels have been offsetting the effects of increased CO2. When ozone  is restored, global warming may be accelerated. As so often is the case, when we disturb one  environmental factor, we affect others as well.
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