Ozone layer depletion: health and environmental effects
Ultraviolet (UV) radiation is divided into three categories of increasing energy: UV-A, UV-B and UV-C. UV-A is a low energy form of UV and has only minimal biological effects. UV-B, a higher energy form, causes the most damage to living organisms and materials. UV-C is absorbed by the oxygen in the atmosphere and never reaches us.
The ozone layer acts as a natural filter, absorbing most of the sun's burning ultraviolet (UV) rays. Stratospheric ozone depletion leads to an increase in UV-B that reach the earth's surface, where it can disrupt biological processes and damage a number of materials.
The fact that UV-B can cause biological effects is well demonstrated by the familiar sunburn that follows overexposure to the sun. However the health impacts of excessive exposure to UV-B go beyond just getting burned. Exposure to UV radiation has been linked to many human health problems, including skin cancer. Scientists also indicate that increased exposure to UV-B rays affects the human immune system and causes premature aging of the skin.
It is important to note, however, that UV-B radiation has always had these effects on humans. In recent years these effects have become more prevalent because Canadians are spending more time in the sun and are exposing more of their skin in the process. An increase in the levels of UV-B reaching the Earth as a result of ozone depletion may compound the effects that sun worshipping habits have already created.
Effects on the skin
Although fair-skinned, fair-haired individuals are at highest risk for skin cancer, the risk for all skin types increases with exposure to UV-B radiation. The effects of UV-B on the human immune system have been observed in people with all types of skin. There are three main types of skin cancer, basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. Most cases of skin cancer in Canada are either basal or squamous cell carcinoma. Basal and squamous cell carcinomas progress slowly and rarely cause death because they usually don't spread to other parts of the body. These cancers are easily removed by surgery. Melanoma is the most serious and fortunately the least common form of skin cancer. Scientists strongly suspect that malignant melanoma, which can be fatal, is caused by exposure to UV light.
Scientists have confirmed that non-melanoma skin cancer is caused by UV-B radiation, and further believe that a sustained 10% depletion of the ozone layer would lead to a 26% percent increase in non-melanoma skin cancer. This could mean an additional 300,000 cases per year world wide.
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Effects on the eyes
UV-B radiation can damage several parts of the eye, including the lens, the cornea, and the membrane covering the eye (conjunctiva). "Snow blindness" is the result of overexposure to UV-B and occurs in areas of the world with high levels of UV exposure, including snowy regions at high altitudes. Snow blindness is not unlike a sunburn, and if repeated, can cause damage to eye over the long term.
Cataracts are a clouding of the eye's lens and are the leading cause of permanent blindness world wide. They are a result of overexposure to UV. A sustained 10% thinning of the ozone layer is expected to result in nearly two million new cases of cataracts per year globally.
Effects on the immune system
UV affects our ability to fight disease. The body's immune system is its first line of defense against invading germs. Recent research has shown that some viruses can be activated by increased exposure to UV.
Effects on the environment
Ultraviolet radiation not only affects humans, but wildlife as well. Excessive UV-B inhibits the growth processes of almost all green plants. There is concern that ozone depletion may lead to a loss of plant species and reduce global food supply. Any change in the balance of plant species can have serious effects, since all life is interconnected. Plants form the basis of the food web, prevent soil erosion and water loss, and are the primary producers of oxygen and a primary sink (storage site) for carbon dioxide.
UV-B causes cancer in domestic animals similar to those observed in humans. Although most animals have greater protection from UV-B because of their heavy coats and skin pigmentation, they cannot be artificially protected from UV-B on a large scale. Eyes and exposed parts of the body are most at risk.
So What Do I Do?
- Keep sun exposure to a minimum, especially between the hours of 10:00 a.m. and 3:00 p.m. when the sun's rays are the most intense.
- Wear wide-brimmed hats, UV-B blocking sunglasses, and long-sleeved shirts and pants.
- Wear sunscreen with a Sun Protection Factor (SPF) of 15 or greater on any exposed skin. Reapply every hour or after swimming or strenuous activity.
Although the ozone layer is the one constant defense against UV penetration, several other factors can have an effect:
Latitude. Since the sun's rays impact the Earth's surface at the most direct angle over the equator they are the most intense at this latitude.
Season. During winter months, the sun's rays strike at a more oblique angle than they do in the summer. This means that all solar radiation travels a longer path through the atmosphere to reach the Earth, and is therefore less intense.
Time of day. Daily changes in the angle of the sun influence the amount of UV radiation that passes through the atmosphere. When the sun is low in the sky, its rays must travel a greater distance through the atmosphere and may be scattered and absorbed by water vapour and other atmospheric components. The greatest amount of UV reaches the Earth around midday when the sun is at its highest point.
Altitude. The air is thinner and cleaner on a mountaintop - more UV reaches there than at lower elevations.
Cloud cover. Clouds can have a marked impact on the amount of UV radiation that reaches the Earth's surface; generally, thick clouds block more UV than thin cloud cover.
Rain. Rainy conditions reduce the amount of UV transmission.
Air pollution. Much as clouds shield the Earth's surface from UV radiation, urban smog can reduce the amount of UV radiation reaching the Earth.
Land Cover . Incoming UV radiation is reflected from most surfaces. Snow reflects up to 85 per cent, dry sand and concrete can reflect up to 12 per cent. Water reflects only five per cent. Reflected UV can damage people, plants, and animals just as direct UV does.
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