Dangerous rays

Many Canadians once saw the first rays of sunlight in the spring as a chance to start working on their tan, but they are more cautious now. Hats, sunscreen and sunglasses are all the rage. Even the parasol is making a comeback. Mindful of the thinning of the ozone layer and the increase in ultraviolet rays, Canadians are fearful of the consequences, which include greater risk of severe sunburn, cataracts and skin cancer. But the harmful consequences are not limited to human health. There are also fears of a drop in the yield of various crops, lower forest growth and a reduced fish harvest.

Ozone is a gas that is part of the normal composition of the Earth's atmosphere. In the highest layers, it forms a kind of umbrella that shields ultraviolet rays that are dangerous to all living organisms. But since the late 1970s, that protective layer has thinned, especially over the Arctic and Antarctic regions. Global ozone levels declined an average of about 3% between 1979 and 1991. This rate of decline is about three times faster than that recorded in the 1970s. In addition to Antarctica, ozone depletion now affects almost all of North America, Europe, Russia, Australia, New Zealand, and a sizable part of South America.

In Canada, ozone depletion is usually greatest in the late winter and early spring. In 1993, for example, average ozone values over Canada were 14% below normal from January to April.

This phenomenon has several causes. Some, such as volcanic eruptions, are natural; others, such as the emission of ozone-depleting substances, are due to human activity. These human-sourced substances are widely used in industry, especially as refrigerants, dry-cleaning agents, solvents and aerosols. Once liberated, they migrate to the upper atmosphere, where they react chemically with the ozone and destroy it.

From 1987 to 1996, Canadian production of these substances dropped from 28 kilotonnes to 1 kilotonne per year, a 96% tumble. From 1988 to 1995, global production of these substances fell 77%.

Despite the measures taken to curb ozone depletion, the situation remains worrisome. Production of these substances continues in the world, and unused stocks still exist in many countries, including Canada.

Even if all nations meet their international commitments to phase out ozone-depleting substances, the levels of these chemicals in the stratosphere will remain near peak values for the next 10 to 20 years.

The ozone layer is expected to eventually recover, if all nations maintain their efforts to reduce ozone-destroying chemicals. However, it will probably be more than a decade before we begin to see definite signs of a recovery, and at least the year 2050 before any substantial recovery occurs. At present, the layer is still thinning, especially at the Earth's poles. The ‘hole’ over the Antarctic is continuing to grow and considerable depletions are occurring in the Arctic.