A new analysis shows that the hole in the ozone layer — which forms every Southern Hemisphere spring — is beginning to heal.

“We as a planet have avoided what would have been an environmental catastrophe,” Susan Solomon, an atmospheric scientist at the Massachusetts Institute of Technology, explains in Science. “Yay us!”

Central to this success is the 1987 adoption of the Montreal Protocol on Substances that Deplete the Ozone Layer, a lengthy name for a global UN treaty that worked to halt the degradation the ozone layer by banning chlorine-containing chlorofluorocarbons (commonly known as Freon), used as refrigerants, solvents, and more.

Despite previous evidence in 2008 and 2011 that the ozone hole was healing, the hole saw a peak in October of last year with an area of 28.2 million square kilometers, causing many to question if the hole was really on the mend. However, Solomon’s team of researchers found that the Calbuco volcano in Chile, which erupted in April 2015 spewing ozone-destroying sulfur particles into the stratosphere, was partially to blame for this increase.

The team’s research also found that the ozone hole over Antarctica in September shrank by 4.5 million square kilometers, on average, between 2000 and 2015. This trend is heartening, but the hole will require many more decades to heal completely. “The ozone hole remains nearly as potent as ever and is not expected to disappear before the end of the century, with all its implications for human and ecosystem health,” says Michaela Hegglin, an atmospheric scientist at the University of Reading, UK.

Still, as Scientific American reports, for Solomon, who has been working on Antarctic ozone since the 1980s, the research brings newfound optimism. “To see it getting better is really quite amazing,” she says.