Brochures

Understanding the ozone layer

• What is the ozone layer?
• Science: the key to understanding
• Impacts of Ozone Depletion
• Will the Ozone Layer Recover?

What is the ozone layer?

Ozone (O3) is a colourless gas that is a close chemical relative of molecular oxygen (O2). Most of the ozone in the atmosphere is found in a layer between 15 and 35 km above the earth surface in a region of the atmosphere known as the stratosphere. The ozone layer is beneficial to life on earth as it absorbs the harmful ultra violet (UV) radiation from the sun. In contrast, ozone at ground level, although it also absorbs some UV, is harmful to living organisms. Ground level ozone is produced by sunlight acting on motor vehicle exhaust gases and is a key component of urban smog.

In recent years, a large "hole" in the ozone layer has opened over the Antarctic each spring, and a similar, but smaller depletion has been observed over the Arctic. A thinning of the ozone layer over mid-latitudes has also been recorded. The ozone layer over southern Canada has thinned by an average of about six per cent since the late 1970s, when human activities first began to affect the upper atmosphere.

Science: the key to understanding

The ozone layer is invisible. Changes in it cannot be seen by the eye. Only through science can we understand what is happening to this fragile layer of gases in the upper atmosphere. Scientists first predicted the ozone depletion problem in the 1970s, and then later detected the problem in the mid-1980s. They are now tracking changes both in the ozone layer itself and in the amount of ozone-depleting chemicals in the atmosphere. Science, too, will ultimately determine the effectiveness of our efforts to slow or reverse ozone depletion.

Scientific research has also explained the cause of ozone depletion - the release of certain industrial chemicals into the atmosphere, particularly CFCs (chlorofluorocarbons) and halons - and provided guidance for policy makers as to how these substances should be reduced. The Montreal Protocol, an international agreement to protect the ozone layer, is a commitment by governments around the world to heed the warnings of science and to act to reduce the chemicals which are depleting the ozone layer.

Finally, scientific research is providing information about the impacts of ozone depletion, and on how best to adapt to changing ozone levels - for instance, by reforesting logged areas with trees that are less sensitive to UV in order to increase their chances of survival.

Canada has made a major contribution to global ozone science, both by monitoring ozone levels, and by conducting research into the causes and impacts of ozone depletion. Canadian research into the ozone layer began in the 1930s, as an effort to understand the ozone layer's potential benefit to weather forecasting. This research was strengthened in the 1980s, when decreases in ozone levels were first observed.

In 1987, Canada became the first country in the world to focus on the Arctic ozone layer, following the discovery of the ozone hole over the Antarctic. In 1993, Environment Canada scientists completed the first long-term study conclusively showing that the thinning of the stratospheric ozone layer has led to an increase in ultraviolet levels at the earth's surface. As well, Environment Canada scientists developed the Brewer Ozone Spectrophotometer, a state-of-the-art scientific instrument. Recognized as the world's most accurate ozone-measuring instrument, it is now in use in more than 35 countries.

Environment Canada operates a network of cross-country monitoring stations which has kept continuous watch on Canada's ozone layer for more than three decades. The early records, which were taken before any major human influence on the ozone layer, are vital to understanding the changes that are occurring today. These observations form part of the World Ozone Data Centre, an international archive which has been maintained by Environment Canada, on behalf of the United Nations' World Meteorological Organization, since 1961.

Canadian scientists use a variety of techniques to keep tabs on the ozone layer, including high-altitude research balloons, satellite measurements and ground-based instruments. Two Canadian astronauts, Marc Garneau and Steve MacLean, have even used Canadian instruments to take readings of the ozone layer from inside the space shuttle.

Impacts of Ozone Depletion

The thinning off the earth's ozone layer has allowed greater amounts of skin-burning UV radiation from the sun to reach the earth. Increased exposure to UV has been shown to harm human health, damage freshwater and marine ecosystems, reduce crop yields, and affect forests.

The most basic impact for humans is the increase in skin cancers. Over-exposure to the sun's UV rays can also cause eye damage, including cataracts, and may even weaken the immune system.

Increased UV levels will also have an impact on agriculture, including many of the world's major food crops. It has been observed that some crops, such as barley and oats, have shown decreased growth as a result of exposure to increased UV radiation.

In marine ecosystems, UV can damage the tiny single-celled plants, known as phytoplankton, which form the base of the food chain. Decreases in the food source at this early stage, may have effects throughout the entire system, and could ultimately affect fish populations.

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

Agricultural and forestry studies have been made on the sensitivity of Canadian trees and crops to UV levels. One study found a 10% increase in UV would result in losses of $192 million per year to sensitive crops, such as canola, oats, barley and soybeans.

Forestry research found that trees which grow at higher elevations (where UV is naturally stronger) are more resistant. Studies such as these may help us to adapt to increasing UV levels.

The effects of UV on fresh water lakes and marine ecosystems are complex and poorly understood. Scientists are finding that northern lakes which are already suffering the effects of acid rain and climate change are now further stressed by UV levels. In marine ecosystems, concerns have been raised over the effects on fisheries, particularly Atlantic cod.

The effects of UV exposure may be increased during the sudden brief increases which occur in the early springtime when ozone levels fall sharply in the annual cycle. Other concerns include the long-term effect of many years of exposure to higher UV levels and the effect of UV in combination with other stresses on the environment, such as climate change, acid rain and toxic chemicals.

Will the Ozone Layer Recover?

Scientists feel the ozone layer should recover, if ozone-depleting substances are eliminated. Under the Montreal Protocol, an international agreement to protect the ozone layer, action has been taken to reduce ozone-depleting substances. The build-up of the most significant CFCs in the lower atmosphere has slowed considerably, and one of the key chemicals, CFC-11, is now decreasing.

Because of the time it takes for these chemicals to move from ground level to the stratosphere, the impact of the Montreal Protocol will not be felt for many years. It is estimated that the ozone layer should recover by about 2050 - providing that all human-made ozone-depleting substances are eliminated. However, long-term predictions are uncertain because the processes of ozone depletion are not all understood. As well, global warming and the exhaust from high-flying aircraft may significantly affect the recovery of the ozone layer

For further information:
Environment Canada
Enquiry Centre
Ottawa, Ontario K1A 0H3

Visit Environment Canada's Ozone web site at :
http://www.ec.gc.ca/ozone

The Green Lane^TM,
Environment Canada's World Wide Web Site.