Fact sheets

Ozone depletion is most severe over the South Pole, where a large "hole" opens every year during the Antarctic spring. The ozone hole was discovered by British scientists in 1985. By studying records from earlier years, scientists determined that the hole had begun to form in the mid-1970s. Since then, it has continued to grow, both in size and duration. In 1998, it covered nearly 26 million square kilometers, and lasted for about three months, with depletions of up to 70%. Its edges now reach beyond Antarctica to the tip of South America.

In 1987, following the discovery of the ozone hole over the South Pole, Canada became the first country to focus on the Arctic ozone layer. Serious ozone thinning in the Arctic began in the early 1990s, with the most significant depletions occurring later in the decade. In March 1996, ozone losses of 30 percent were recorded. To date, the most severe Arctic ozone thinning occurred in 1997, when depletions of up to 45 percent were recorded through March and into the middle of April.

The severe ozone losses in the polar regions are a result of the unusual weather conditions that develop there in the winter and early spring. With the arrival of winter, a large swirling vortex of winds forms around the polar region and isolates the air inside. During the 24-hour winter darkness this air becomes very cold, particularly in the upper atmosphere. If temperatures drop below -80°C, an unusual type of frozen cloud forms, known as a "polar stratospheric cloud".

These clouds increase ozone loss, by speeding up the effect of the industrial chemicals.

Scientists are concerned that global climate change may be affecting temperatures in the upper atmosphere. In the lower atmosphere, climate change is expected to cause temperatures to rise. However in the upper atmosphere, during the long winter darkness, climate change may cause temperatures to fall. Such a cooling could increase the formation of polar stratospheric clouds, causing Arctic ozone depletion to become even more severe.

Arctic ozone thinning is expected to continue over the next 10 to 20 years. However, a large stable "hole" will likely not develop over the North Pole, since weather conditions there are more variable than those over the Antarctic. This means the Arctic ozone layer will likely continue to show a variable pattern of thinning.

In the Arctic, the sun never rises very high above the horizon, and much of its rays are absorbed by the atmosphere, meaning levels of UV are normally very low. If considerable ozone loss occurs in the far north, UV could rise to levels as high as those encountered in southern Canada, and Arctic residents would have to take extra steps to protect themselves. UV reflecting off snow and ice could become a particular concern. Vegetation and wildlife in the Arctic have evolved under very low levels of UV, and may have only limited natural protection against over exposure. Some species may prove to be extremely sensitive to higher UV levels.

Scientists are also concerned that ozone thinning over the Arctic is affecting ozone levels further south. Ozone loss over southern Canada is greatest in the springtime, and scientists feel this may be caused by ozone being redistributed in the upper atmosphere to compensate for losses in the far north. Indeed, the polar regions, with their unique atmospheric processes, may hold the key to how much ozone depletion will eventually occur over mid-latitude areas.