Loss of the Earth’s ozone layer above the Arctic last winter was unprecedented, scientists at NASA’s Jet Propulsion Laboratory told CNN on Monday.

In findings published in a new study in the journal Nature, scientists said a hole in the ozone was caused by an unusually long period of low temperatures in the stratosphere, the protective layer that shields the Earth’s surface from harmful radiation.

While ozone loss is a sadly common occurrence at the South Pole, recent findings document a similar event happening at the Earth’s northernmost point. “We’ve never seen that kind of phenomenon in the Arctic before,” Michelle Santee, an atmospheric scientist with the Jet Propulsion Laboratory, said.

Although it was comparatively small - “The area of the Arctic loss zone was about 60% the size of a typical ozone hole,” Santee said - the ozone hole has raised concerns among atmospheric scientists.

“The same process that destroys the ozone layer in Antarctica – chlorine and other man-made compounds such as CFCs (chlorofluorocarbons) - takes place here also, but it’s just that it never occurred in the Arctic to the same degree,” Santee said.

Scientists from 19 international institutions took part in the study, according to a NASA press release.

The especially brutal cold temperatures experienced by much of the United States last winter have little to do with what’s going on in the stratosphere, Santee said.

“When we’re talking about the weather, we need to be clear we’re talking about weather in the stratosphere, not on the Earth’s surface. Cold conditions alone are not enough to cause such a phenomenon (ozone loss),” Santee said, “but you also need man-made compounds."

The ozone hole is relatively stable, Santee said.

“There’s a large weather pattern that keeps the area of extreme ozone loss confined to about 2 million square kilometers, or about five times the area of California,” Santee said. “But it does move around a little bit. It can shift around and it did drift above populated areas in March and April. This leads to greater values of UV radiation - but I should add that this was a very short time,” she said. “The exposure was very temporary.”

So long as the chlorine in the atmosphere remains elevated, ozone holes will be long-lived, atmospheric scientist Nathaniel Livesey said.