According to NASA, the hole in the ozone reached its smallest size since it was discovered by scientists in 1982 because of unusual weather patterns in the upper atmosphere above Antarctica.

The hole fluctuates each year and is typically the highest between late September and early October during the coldest months in the Southern Hemisphere.

The new space measurements indicate that the hole hit its 6.3 million square miles annual limit and then decreased to less than 3.9 million square miles in late September and early October, a record low for a hole that normally expands to a total area of 8 million square miles.

Researchers say the small size of this year was due to a stratosphere warming event that disrupted the process of ozone-thinning.

“It’s great news for ozone in the Southern Hemisphere,” Paul Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. “But it’s important to recognize that what we’re seeing this year is due to warmer stratospheric temperatures. It’s not a sign that atmospheric ozone is suddenly on a fast track to recovery.”

It is the third time in 40 years that warming has stopped ozone depletion, as similar weather trends between 1988 and 2002 have led to unusually small holes in ozone, The Washington Post noted.

“It’s a rare event that we’re still trying to understand,” Susan Strahan, an atmospheric scientist with the Universities Space Research Association, said in a statement. “If the warming hadn’t happened, we’d likely be looking at a much more typical ozone hole.”

But researchers added that there is no connection between these scientific events and climate change.

The weather systems that disrupted the 2019 ozone hole, known as the “sudden stratospheric warming” event, were 29 degrees higher than the average. NASA said this weather event also contributed to the weakening of the Antarctic polar vortex—the high air velocity that surrounds the South Pole.