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Here’s a rare piece of good news about the environment: The giant hole in the Earth’s protective ozone layer is shrinking and has shriveled to its smallest peak since 1988, NASA scientists said.

The largest the hole became this year was about 7.6 million square miles wide — about 2½ times the size of the United States — in September. But it was still 1.3 million square miles smaller than last year, scientists said, and has shrunk more since September.

Warmer-than-usual weather conditions in the stratosphere are to thank for the shrinkage since 2016, as the warmer air helped fend off chemicals like chlorine and bromine that eat away at the ozone layer. But the hole’s overall reduction can be traced to global efforts since the mid-1980s to ban the emission of ozone-depleting chemicals.

“Weather conditions over Antarctica were a bit weaker and led to warmer temperatures, which slowed down ozone loss,” said Paul Newman, chief Earth scientist at NASA’s Goddard Space Flight Center in Maryland. “It’s like hurricanes. Some years there are fewer hurricanes that come onshore … this is a year in which the weather conditions led to better ozone formation.”

The news comes just after the 30th anniversary of the hole’s discovery, which led to the 1987 Montreal Protocol — a landmark international agreement that led to major global efforts to phase out the use of ozone-depleting chemicals.

Deterioration of the ozone layer was mainly taking place over Antarctica, and became a particular cause for concern for those living in the ­southern hemisphere. Ozone, a colorless gas, protects the Earth from harmful ultraviolet radiation, which could cause higher rates of skin cancer and cataracts, as well as disrupt plant growth, scientists say.

Scientists first realized chlorofluorocarbons were shrinking the ozone layer above Antarctica in the 1970s. From the mid-1980s and through the 1990s, the ozone hole became a worldwide sensation, with frightening connotations that led the public to support scientists’ battle against its growth.

The public feared scientists’ well-being at the South Pole, wondering if they would be burned by ultraviolet radiation while studying the hole that would blind them or damage their skin. Increased fears of skin cancer and the ozone hole further deteriorating spurred 24 nations to sign the Montreal Protocol. That number eventually rose to 197.

It was a rare scientific agreement, scientists say, because it did exactly what it was supposed to do: galvanize action toward closing the ozone layer hole. Thursday’s findings show the world is on track toward doing just that.

“It’s extremely rewarding, because it was originally just a scientific effort, and then we were able to convince society that it was a problem — here’s what would happen if we do not deal with it,” said chemist Mario Molina, who had an integral role in the discovery of the ozone hole and who was awarded a Nobel Prize for his research in 1995.

In 2014, scientists at the United Nations credited the recovery of the ozone layer to the phasing out of chemicals used in refrigerators, air conditioners and aerosol cans in the 1980s.