When you hear the term "ozone hole" you think about the ozone depletion over Antarctica, and how people in the far south of the Southern Hemisphere have to protect themselves from the Sun. It's why my friends have to buy hats for their little girl and slather her with sunblock every time she goes outside.
In 1987, countries around the world adopted an ozone-protecting agreement called the Montreal Protocol to phase out ozone-depleting chemicals such as chlorofluorocarbons (CFCs). Concentrations of these chemicals in polar regions have fallen about 10 percent from their peak years before the protocol, and the Antarctic ozone hole has been getting smaller and will disappear by sometime in the middle of this century.
But the announcement this week of record low levels of ozone above the Arctic is a reminder that CFCs and similar chemicals have a long life in the atmosphere, and the problem of ozone depletion isn't going away anytime soon.
The winds of the polar vortex, which was stronger than usual this year, prevented the mass of air over the North Pole from mixing with mid-latitude air, resulting in low stratospheric temperatures. When sunlight arrived in March, the CFCs (and other chlorine- and bromine-based compounds) went to work breaking down the ozone, destroying 40 percent of the ozone in the Arctic stratosphere. (An average year sees only 25 percent or so of Arctic ozone depleted and 55 percent of Antarctic ozone).
Antarctic weather, and the ozone hole, is fairly predictable, but things are more variable in the Arctic. That means that a big loss from year to year, as with 2010 to 2011, isn't necessarily something to worry about, but it will also make any efforts to understand Arctic loss more difficult.
"In a changing climate, it is expected that on average stratospheric temperatures cool, which means more chemical ozone depletion will occur," said Mark Weber, an atmospheric scientist at the University of Bremen. "On the other hand, many studies show that the stratospheric circulation in the northern hemisphere may be enhanced in the future and, consequently, more ozone will be transported from the tropics into high latitudes and reduce ozone depletion."
The World Meteorological Organization recommends that people living in far northern latitudes pay attention to local UV forecasts. Exposure to UV radiation can lead to cancer, cataracts and damage to the immune system.
Watch a NASA animation of changing Arctic ozone here.