A massive Arctic ozone hole opened up over the Northern Hemisphere for the first time this year, an international research team reported Sunday.

The hole covered two million square kilometres — about twice the size of Ontario — and allowed high levels of harmful ultraviolet radiation to hit large swaths of northern Canada, Europe and Russia this spring, the 29 scientists say.

The discovery of the “unprecedented” hole comes as the Canadian government is moving to reduce staff in what Environment Minister Peter Kent calls the “streamlining” of its ozone monitoring network.

Environment Canada scientist David Tarasick, whose team played a key role in the report published Sunday in the journal Nature, is not being allowed to discuss the discovery with the media.

Environment Canada told Postmedia News that an interview with Tarasick “cannot be granted.” Tarasick is one of several Environment Canada ozone scientists who have received letters warning of possible “discontinuance of job function" as part of the downsizing underway in the department.

In Sunday’s report Tarasick and his colleagues say the “chemical ozone destruction over the Arctic in early 2011 was — for the first time in the observation record — comparable to that in the Antarctic ozone hole.”

It also highlights the importance of Environment Canada’s ozone networks, which scientists have warned could be drastically reduced. Department officials say ozone monitoring will continue but will be “streamlined” to eliminate “redundancy.”

“The Canadian stations were an absolutely key element of the network of stations we used to do the study,” says co-author Marcus Rex, of the Alfred Wegener Institute for Polar and Marine Research, in Potsdam, Germany. “Canada is the backbone of that network.”

The scientists say maintaining “comprehensive” data is “critical” to understanding Arctic ozone depletion and the threats it poses.

They used U.S. and European satellites, along with ground stations and scientific balloons — including those operated by Environment Canada — to find and track the hole.

“The satellites, ground stations and balloons each provide a piece of the puzzle,” says co-author Kaley Walker, at the University of Toronto. “It is important to have them all.”

The hole formed over the Arctic in February and March, then swung across northern Canada, northern Europe and Central Russia to northern Asia, prompting scientists to issue warnings this spring about excess radiation.

Sunday’s report shows just how big and remarkable the hole was and how it moved. It also points to what scientists are calling “ominous” changes in the Arctic stratosphere, about 20 kilometres above the surface, which may be linked to climate change and increasing greenhouse gas emissions.

Tarasick and Walker are among four Canadian co-authors, who had front row seats as the hole formed. They released scientific balloons, known as ozone sondes, which make hundreds of measurements on their way from the ground to 30 kilometres up in the atmosphere.

The measurements helped confirm that chlorine-based pollutants in the stratosphere, 18 to 20 kilometres above the ground, triggered a process that chewed up molecules in the ozone layer that protects Earth from the sun’s harmful ultraviolet light.