Why have ‘ozone hole’ and ‘acid rain’ disappeared from the news?

The ozone hole has not disappeared. It still forms over Antarctica every September and October, when the Southern Hemisphere’s spring brings a sharp thinning of the ozone layer. But the direction of change has turned.

In 2025, the ozone hole reached a maximum area of 22.86 million square kilometers on September 9. Its average size from early September to mid-October, however, ranked as the fifth smallest since 1992. The term “hole” does not describe an opening through the atmosphere. It refers to a broad region where ozone levels have fallen dramatically.

Chlorofluorocarbons, or CFCs, were not initially viewed as dangerous. Earlier refrigerants such as ammonia, sulfur dioxide and methyl chloride were toxic or flammable. CFCs appeared to solve those problems. They were relatively safe, inexpensive, effective and stable, making them useful in refrigerators, air conditioners, spray cans, foam products and electronics cleaning.

That stability created the danger. CFCs could persist long enough to reach the stratosphere, where ultraviolet light breaks them apart and releases chlorine atoms. Chlorine then attacks ozone repeatedly, acting as a catalyst in a chain reaction. Ozone exists in tiny quantities, yet the thin layer absorbs much of the sun’s harmful ultraviolet radiation, functioning like a planetary sunscreen.

Scientists identified the risk before observing the Antarctic hole. Paul Crutzen showed in 1970 that nitrogen oxides could catalytically destroy stratospheric ozone. In 1974, Mario Molina and Sherwood Rowland proposed that ultraviolet light could break down stratospheric CFCs and release ozone-destroying chlorine. In 1985, Joseph Farman and colleagues reported the dramatic springtime decline over Antarctica. Crutzen, Molina and Rowland received the 1995 Nobel Prize in Chemistry.

Scientific discovery alone did not end CFC use. Governments adopted the 1985 Vienna Convention and the 1987 Montreal Protocol, later expanding controls as evidence developed and providing technology and funding to developing countries. DuPont, once the world’s largest CFC producer, eventually pledged in 1988 to stop production and develop alternatives. The United Nations Environment Programme says 99% of regulated ozone-depleting substances have now been phased out. If current policies continue, the ozone layer could return to 1980 levels by about 2040 across most of the world, 2045 in the Arctic and 2066 over Antarctica. South Korea enacted an ozone-protection law in 1991 and joined the Montreal Protocol in 1992.