Before climate change became such a huge focus, the hole in the ozone layer was probably the biggest environmental problem that scientists focused on. But a new report indicates that the ozone hole over Antarctica shrank to its smallest size at peak since 1988.

The hole reached its maximum Sept. 11 when NASA measured it at 7.6 million square miles wide, or about two and a half times the size of the United States. That’s 1.3 million square miles less than last year, and 3.3 million square miles smaller than it was two years ago.

Stormy conditions in the upper atmosphere are what’s responsible, NASA says, as it warmed the air and kept ozone-eating chemicals out. Scientists aren’t sure why it was stormier. It’s not necessarily good news, as the drop is pretty much natural rather than in response to an improving environmental situation, but there are some indications that our efforts to stop ozone-eating chemicals are helping. The ozone hole was at its worst in 2000 at 11.5 million square miles.

“The Antarctic ozone hole was exceptionally weak this year,” said Paul A. Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This is what we would expect to see given the weather conditions in the Antarctic stratosphere.”