Fact sheets

The thinning of the ozone layer has allowed greater amounts of the sun's burning UV rays to reach the earth. Over southern Canada, sunburning UV has increased by an average of about 7%. In the spring, levels increase to 10% to 12% and may reach 25% for short periods. These increased UV levels can affect humans, health, agricultural crops, forests and marine and freshwater ecosystems.

The major health concern is the increase in skin cancers. According to the National Cancer Institute, there were about 67,000 new cases of skin cancer in 1998 in Canada alone. Since skin cancer develops over time, most of these cases were likely caused by sun exposure in the 1970s and early '80s, before any serious thinning of the ozone layer. These skin cancers were likely caused by the rise in popularity of sunbathing and briefer summer clothing. Ozone depletion will likely exacerbate the problem in the future, unless the effects of UV increases are mitigated by better sun protection habits.

Over-exposure to UV rays can also cause other health problems, such as cataracts and other forms of eye damage, and may even weaken the immune system.

Agriculture and forestry may also be affected by increased UV levels. Certain food crops, such as canola, oats, peppers and cucumbers have been found to be sensitive to UV. Unlike agricultural crops, forests are long-lived and will be exposed to increased UV levels over many decades. Research into the effects of UV on trees is in its early stages, and scientists are uncertain about the long-term effects on forests.

Increased UV levels also reduce the lifetime of construction materials, particularly the plastics that are frequently used in our homes, playgrounds, and other outdoor structures.

UV can also affect fresh water lakes and ocean ecosystems. It can damage the tiny single-celled plants, known as phytoplankton, which form the base of the aquatic food chain. This may have an impact throughout the entire ecosystem, and could ultimately affect commercial fish stocks.

The effects of UV exposure may be more severe during the spring, when ozone depletion is at its greatest in Canada. The sudden brief UV increases, which occur in the early springtime when ozone levels fall sharply, could be especially damaging to natural ecosystems, affecting young growing vegetation or the eggs of fish or frogs, which are laid in shallow water.

Since recent research indicates that UV levels are expected to remain higher than normal for the next 30-40 years, scientists are now studying ways to adapt to a thinner ozone layer. Agricultural crops are being tested to find strains which are less vulnerable. Foresters have found that trees that grow at higher elevations, where UV is naturally stronger, are more resistant. Synthetic building materials, such as plastics, can be reformulated to include greater UV protection. But the effects on natural ecosystems will be more difficult to manage.