Unusually large and deep ozone hole forms over the North Pole

Because of an unusually strong polar vortex in the winter - which helped prevent Arctic air from infiltrating the midlatitudes and contributing to major snowstorms - conditions were ripe in the winter for the destruction of stratospheric ozone high above the Arctic, at altitudes of about 30,000 to 60,000 feet. This has resulted in an area of depleted ozone at the end of the winter season, also referred to as an ozone hole.

The protective ozone layer is responsible for blocking harmful incoming ultraviolet radiation from the sun, which can cause skin cancer. However, the low levels of ozone across the Arctic are expected to be relatively short-lived, as the polar vortex - a low pressure area surrounded by powerful winds in the upper atmosphere, which bottles up ultra-cold air near its center - breaks down for spring and summer.

The record-low ozone levels for the Arctic in the month of March and early April cover an area that stretches from northern Scandinavia to far northwestern Canada. Ozone levels also hit record lows during early December. The low levels represent more of an unusual phenomenon for this region than an acute public health danger, considering how fleeting it will be and how few residents live in the high Arctic. In addition, the sun angle is still low at such high latitudes.

"From my point of view, this is the first time you can speak about a real ozone hole in the Arctic," Martin Dameris, an atmospheric scientist at the German Aerospace Center in Oberpfaffenhofen, told Nature News.

As occurs nearly every year over the South Pole, extreme cold provides the right conditions needed for ozone destroying chemicals, including chlorine and bromine, which are emitted by human activities such as the use of refrigerants, to break down ozone molecules.

The ozone hole at the South Pole forms nearly every year because temperatures get cold enough there for these chemical reactions to take place so efficiently in the complete darkness of polar night. Clouds that form in the frigid polar stratosphere aid in the destruction of ozone as well.

However, in the Arctic, it's rare to get conditions that are primed for ozone destruction over long periods of time. This is because the polar vortex often wobbles off-kilter or breaks down, raising stratospheric temperatures and halting or slowing ozone destruction.

The winter featured an unusually stable and strong polar vortex. Whereas the discussion in Washington and other cities in the midlatitudes was about the lack of cold and snow, high above the Arctic, it was a truly brutal and unrelenting winter, and the loss of protective ozone is a side effect.

Ozone levels in the Arctic and Antarctic are measured by weather balloons released from observation stations. This year, these efforts were given a boost by an icebreaker called the Polarstern, which is spending a year trapped in sea ice. The balloons launched from around the region measured a precipitous drop in ozone, below levels seen in two particularly noteworthy seasons: 1997 and 2011.

The Montreal Protocol, which was ratified in 1988 and widely viewed as the most successful international environmental treaty to date, mandates the reduction in use of substances that deplete the ozone layer. However, the healing process, particularly in the Southern Hemisphere, is slow, illustrating the importance of swift action only a few years after scientists discovered the ozone losses and the reasons behind it in the late 1970s and early-to-mid 1980s.