The massive hole in our ozone layer has been one of the biggest environmental concerns for decades, but a surprising new report indicates that it has shrunk to its smallest size at peak since 1988. The hole peaked on Sept. 11 when NASA measured it at 7.6 million square miles wide, which would be about two and a half times the size of the United States.

While that sounds like a lot, it’s actually 1.3 million square miles less than the peak last year, and 3.3 million square miles less than in 2015. Scientists believe that stormy conditions throughout the year have warmed the air and kept ozone-eating chemicals at bay, although it’s not clear why conditions were stormier.

It doesn’t mean things have dramatically turned around for our ozone, as scientists think this is more of a natural shift. However, scientists do believe that our efforts to keep ozone-eating chemicals out of the air are having some positive effects on the Earth. Certainly we are a far cry from 2000, when ozone reached its largest hole of 11.5 million square miles.

“The smaller ozone hole in 2017 was strongly influenced by an unstable and warmer Antarctic vortex – the stratospheric low pressure system that rotates clockwise in the atmosphere above Antarctica,” the NASA statement reads. “This helped minimize polar stratospheric cloud formation in the lower stratosphere. The formation and persistence of these clouds are important first steps leading to the chlorine- and bromine-catalyzed reactions that destroy ozone, scientists said. These Antarctic conditions resemble those found in the Arctic, where ozone depletion is much less severe.

“In 2016, warmer stratospheric temperatures also constrained the growth of the ozone hole. Last year, the ozone hole reached a maximum 8.9 million square miles, 2 million square miles less than in 2015. The average area of these daily ozone hole maximums observed since 1991 has been roughly 10 million square miles.”