The largest-ever ozone hole over the Arctic has finally closed, but scientists say they’re intrigued by its size and appearance.  Record-low ozone levels stretched across much of the central Arctic in March and April, creating a hole three times the size of Greenland. 

The ozone layer is a natural, protective layer of gas in the stratosphere that shields life from the sun’s harmful ultraviolet radiation. In the past few weeks, there has been an abnormally strong depletion of ozone over the northern polar region.  

“There are very unusual conditions this year,” says Kimberly Strong, an atmospheric physicist at the University of Toronto. “We are comparing measurements this year with measurements going back as far as 1999, and we have had record low ozone all year.”

Strong is part of a team that studies and measures ozone levels at Eureka, a High Arctic weather station and research lab situated on Ellesmere Island, Nunavut. Strong says one of the reasons this ozone hole is so surprising is because holes of this size generally occur over the South Pole each year, but not the Arctic. 

“Certain climate conditions are needed to create the chemical reactions that destroy ozone,” she explains. “One of these conditions is extremely cold weather below -80 C. These temperatures can almost always only be found in Antarctica.”

Cold Antarctic temperatures are met with a stable circulation of air around the pole — essentially a large cyclone — called a polar vortex. The combination of cold temperatures and a stable polar vortex creates icy clouds in the stratosphere. 

“When the sun comes back, you get chemical reactions that happen on the surface of these clouds that cause the depletion of ozone,” says Strong. 

The destruction of ozone does not usually occur in the Arctic because it is not generally cold enough for stratospheric clouds to form. With fewer clouds, less ozone depletion occurs. 

“Scientifically it’s all very interesting,” says David Tarasick, a senior atmospheric research scientist for Environment and Climate Change Canada. “Indeed we are seeing larger depletion than we ever have before.”

Tarasick says he doesn’t remember seeing a polar vortex like the one in recent months before. 

“In the Arctic what seems to be happening is that as the stratosphere gets colder, that may make it more likely for the Arctic to form polar stratospheric clouds. For it to be colder for longer means you can get more ozone destruction.” 

Tarasick says he doesn’t think the ozone hole is reason for alarm — except that it may signal a larger connection to climate change.

“We’ve already started to ask ourselves, to what extent is climate change affecting this?” he says. “We need to investigate further and see what’s happening.” 

According to Tarasick, Canada will play a significant role in analyzing this data and measuring the ozone layer as it continues to evolve.

“The measurements we make in Canada are actually very important. Most of the measurements are Canadian,” says Tarasick. “And that will affect predictions of what’s going to happen over the next 30 to 100 years.”