According to scientists at NASA, global warming and ozone depletion are two separate issues, but they do share some related aspects. Whereas global warming and the greenhouse effect refer to the lower portions of the atmosphere (the troposphere), enhanced by the continual addition of heat-trapping gases from human activity, ozone depletion refers to the upper portion of the atmosphere (the stratosphere). Disturbance of the ozone layer presents a serious health concern due to a lack of ability to block the Earth's surface from harmful ultraviolet radiation from the Sun. Even though they are technically separate issues, there is a connection between the two.
Scientists have found holes in the ozone layer high above the Earth. Ozone holes are not just empty spaces (lacking ozone) in the sky. Ozone holes are much like the worn-out places in a blanket: There are still threads covering the worn-out area, but the fabric can be so thin it can be seen through. The 1990 Clean Air Act provided provisions for fixing the holes, but repairs will take time.
Ozone in the stratosphere—the layer of the atmosphere 9 to 31 miles (14 to 50 km) above the Earth—serves as a protective shield, filtering out harmful solar radiation, including ultraviolet B. Exposure to ultraviolet B has been linked to the development of cataracts (eye damage) and skin cancer.
In the mid-1970s, scientists suggested that chlorofluorocarbons (CFCs) could destroy stratospheric ozone (the same CFC mentioned previously as a greenhouse gas with a lifetime in the atmosphere of 550 years). CFCs were widely used then as aerosol propellants in consumer products such as hairsprays and deodorants and for many uses in industry. Because of concern about the possible effects of CFCs on the ozone layer, in 1978 the U.S. government banned CFCs as propellants in aerosol cans.
Since the aerosol ban, scientists have been monitoring and measuring the ozone layer. A few years ago, an ozone hole was found above Antarctica, including the area of the South Pole. This hole, which has been appearing each year during the Antarctic winter (the Northern Hemisphere's summer), is bigger than the continental United States in size. More recently, ozone thinning has been found in the stratosphere above the northern half of the United States; the hole extends over Canada and up into the Arctic regions (the area of the North Pole). Initially, the hole was detected only in winter and spring, but more recently has continued into summer. Between 1978 and 1991, there was a 4 to 5 percent loss of ozone in the stratosphere over the United States, which represents a significant loss. Ozone holes have also been found recently over northern Europe. There is also evidence that holes in the ozone layer damage plant life. Scientists are looking into possible harm to agriculture, as well.
Because of this threat to the ozone layer, 93 nations—including the United States—have jointly agreed to reduce their production and use of ozone-destroying chemicals. When researchers discovered that the ozone layer was thinning more quickly than first thought, this agreement was revised to speed up the phase-out of ozone-destroying chemicals.
Unfortunately, this problem does not have an easy fix. It will be a long time before the ozone layer will be repaired. Because of the ozone-destroying chemicals already in the stratosphere and those that will arrive within the next few years, ozone destruction will likely continue for another 20 years. As substitutes are developed for ozone-destroying substances, before the chemicals can be produced and sold, the U.S. Environmental Protection Agency (EPA) must determine that the replacements will be safe for health and the environment.
There are connections between global warming and the ozone layer. The CFCs that destroy the ozone layer are also powerful greenhouse gases. Scientists at NASA believe there is a slight connection between the two. CFCs only destroy ozone at very cold temperatures—below -112°F (-80°C). Greenhouse gases absorb heat at a low altitude, which warm the surface but cool the stratosphere. They believe that the cooler the stratosphere, the more rapidly ozone may be destroyed. This cycle could make the ozone hole bigger.
The ozone layer does trap heat. Reducing ozone-depleting gases (such as fluorocarbons) is important in preventing the ozone layer's destruction, just as efforts to limit all types of emissions to limit global warming will also positively affect the ozone layer.
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