고등학교 영어Ⅱ (NE능률 오선영) 연계 글

High above Earth's surface, a thin layer of ozone gas absorbs most of the ultraviolet radiation that comes from the sun. This shield matters because too much of that radiation can burn skin and lead to skin cancer and eye damage. By 1974, chlorofluorocarbons (CFCs), human-made gases used in spray cans, refrigerators, and plastic foams, had spread throughout the atmosphere. Because CFCs were stable and nontoxic, they were widely thought to be harmless to the environment.

That year, however, the chemists Mario Molina and Sherwood Rowland warned that this very stability could be dangerous. With CFC molecules surviving for decades in the lower atmosphere, the gases could slowly rise to the ozone layer, where strong ultraviolet light would break them apart and free their chlorine atoms. Each chlorine atom could then destroy ozone again and again, because the reactions involved leave the chlorine itself unchanged. Many people doubted the chemists' calculations at first, but in 1985, Joseph Farman and his colleagues reported an even more alarming finding. Their measurements at a research station in Antarctica showed the ozone above the continent thinning each spring, with October readings falling well below those of earlier decades. This loss, soon known as the "ozone hole," was much greater than earlier calculations had predicted.

The discovery gave governments a strong reason to act quickly. In 1987, they signed the Montreal Protocol, which required that each member country reduce its use of five kinds of CFCs to half of its 1986 level by 1999. The treaty also stipulated that these limits be reviewed at least every four years in light of new scientific findings. Later meetings tightened the rules, with developed countries ending almost all production and use of these CFCs by 1996 and developing countries following by 2010. In 2009, the protocol became the first environmental agreement to be ratified by every country in the world.

In January 2023, a panel of experts reported that, with nearly 99 percent of the banned chemicals phased out, the ozone layer had begun to recover. The panel expected that, if current policies stayed in place, the layer would return to its 1980 condition by around 2066 over Antarctica and by 2040 over most other regions.

Some of the gases that replaced CFCs, however, trap heat and contribute to climate change. For this reason, a 2016 amendment requires that every country accepting it gradually cut its use of those gases. The ozone story shows that a worldwide promise can work when clear science sets its goals and regular reviews keep it up to date.