A large ozone hole over the Arctic may have likely exposed people living in Russia, parts of Greenland and Norway to high ultraviolet (UV) radiation.

The huge hole that surfaced in the Earth's protective ozone layer above the Arctic this year was the largest ever recorded in the northern hemisphere. Scientists on Monday say powerful cold in the upper atmosphere over the region last winter triggered ozone-depleting chemicals that caused the hole.

For the first time, the Arctic and Antarctic holes are similar in size because of the combination of wind patterns and intense cold.

The chemical ozone destruction over the Arctic in early 2011 was, for the first time in the observational record, comparable to that in the Antarctic ozone hole, the scientists say. They were led by Gloria Manney of the Jet Propulsion Laboratory in Pasadena, Calif.

The Arctic and Antarctic ozone holes experience some levels of ozone loss annually during their particular winters, largely because of the combination of cold temperatures and linger ozone-depleting pollutants.

Scientists say the extent of the ozone depletion in Arctic is considered temporary, and below the depletion that happens seasonally over the Antarctic. But atmospheric scientists believe it is a signal of how sudden variances can happen because of human activity that from years ago.

In February when the northern ozone hole has reached its maximum extent it reached southward into Russia and Mongolia, according to The New York Times.

The ozone layer, which is high in the stratosphere is basically a giant shield against the sun's UV radiation. The stratospheric ozone layer, extending from about 15 to 35 kilometers above the surface, protects life on Earth from the sun's harmful ultraviolet rays. UV radiation can cause skin cancer and cataracts.

Scientists have been studying the size of the ozone hole above the Antarctic every summer since the 1980s. Sometimes the holes are so huge that they cover the entire continent and overextended to parts of South America.

The hole above the Arctic was always much smaller.

University of Toronto physicist Kaley Walker was part of the international team behind the study published online on Oct. 2 in Nature.

Walker and other scientists from 18 other institutions in nine countries investigated the 2011 Arctic ozone loss. The other countries include the United States, Germany, The Netherlands, Russia, Finland, Denmark, Japan and Spain. They analyzed a comprehensive set of measurements that included daily global observations of trace gases and clouds from NASA's Aura and CALIPSO spacecraft; ozone measured by instrumented balloons; meteorological data and atmospheric models.

In the 2010 to 2011 Arctic winter, we did not have temperatures that were lower than in the previous cold Arctic winters, Walker said in a statement. What was different about this year was that the temperatures were low enough to generate ozone-depleting forms of chlorine for a much longer period of time. Arctic ozone loss events such as those observed this year could become more frequent if winter Arctic stratospheric temperatures decrease in future as the Earth's climate changes.

Scientists say the 2011 Arctic ozone loss happened over an area that is considerably smaller than that of the Antarctic ozone holes. The reactions that converted less reactive chemicals into ozone-destroying ones happened the polar vortex, which is an atmospheric circulation pattern created by the rotation of Earth and by cold temperatures.

While smaller and shorter-lived than its Antarctic equivalent, the Arctic polar vortex is more mobile. It often moves over densely-populated northern regions. Scientists say any decrease in overhead ozone leads to increases in surface ultraviolet radiation.

Each of the balloon and satellite measurements included in this study were absolutely necessary to understand the ozone depletion we observed this past winter, Walker said. To be able to predict future Arctic ozone loss reliably in a changing climate, it is crucial that we maintain our atmospheric measurement capabilities.