The Arctic saw massive ozone losses in 2011 due to a prolonged period of extremely low temperatures in the stratosphere, according to a NASA-led study.
The amount of ozone depletion over the Arctic was comparable to those found in the Antarctic, where a hole has formed every spring since the mid-1980s. The hole over the Arctic is approximately 2 million sq km and is similar to the one over the Antarctic.
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, lead scientist Gloria Manney of NASA's Jet Propulsion Laboratory in Pasadena, Calif., told The Guardian.
The findings of the study, conducted by a team of scientists across 19 institutions in nine countries, including Canada and the United States, were published Sunday in the journal Nature.
The study shows that the unprecedented hole was the largest ever recorded and caused residents in parts of northern Russia, Greenland and Norway to become exposed to high levels of UV radiation.
The scientists found that at some altitudes the cold period in the Arctic lasted more than 30 days longer than in any previously studied Arctic winter; a factor that could also explain the unprecedented ozone loss.
Why [all this] occurred will take years of detailed study. It was continuously cold from December through April, and that has never happened before in the Arctic. said Michelle Santee, from NASA's Jet Propulsion Laboratory, part of the group that monitored the hole from space using satellites.
The difference from previous winters is that temperatures were low enough to produce ozone-destroying forms of chlorine for a much longer time. This implies that if winter Arctic stratospheric temperatures drop just slightly in the future, for example as a result of climate change, then severe Arctic ozone loss may occur more frequently, she added.
Approximately 80 percent of the layer at a height of about 13 miles (20 kilometers) above the Arctic recorded the maximum depletion, according to reports.
The loss of ozone in the Arctic is, according to NASA, due to the same process as in the Antarctic - when extremely cold conditions trigger reactions that convert atmospheric chlorine, drawn from man-made chemicals, into forms that destroy ozone.
However, the generally warmer stratospheric conditions there limit the area affected, as well as the time frame during which the chemical reactions occur, resulting in far less ozone loss in most years in the Arctic than in the Antarctic.
As much as 90 percent of Earth's ozone is concentrated in the stratosphere. Stratospheric ozone shields Earth from the damaging effects of ultraviolet radiation. Depletion of ozone can result in considerable increases in UV received, which affects human beings, animals and entire ecosystems. The ozone layer deters ultraviolet B rays that cause skin caner and other ailments.
The 2011 Arctic ozone loss occurred over an area considerably smaller than that of the Antarctic ozone holes because the Arctic polar vortex, a persistent large-scale cyclone within which the ozone loss takes place, was about 40 percent smaller than a typical Antarctic vortex.
The ability to measure polar ozone loss and associated processes will be reduced with NASA's Aura and CALIPSO spacecraft reaching the end of their operational lifetimes, NASA said, adding that it is imperative that this capability is maintained.
Meanwhile, chlorine-based compounds continue to circulate in the upper atmosphere; a fact that indicates the ozone layer has some way to go before it is restored to a healthy state.