UV and the ozone layer
Photo: © istock.com, 2011.
UV - the ABCs
Ultraviolet (UV) rays are a form of invisible high-energy light produced by the sun. There are three kinds of UV rays:
- UV-A is the weakest form, but can still cause skin damage, including sunburn, and skin aging. It can also damage outdoor plastics and paint.
- UV-B is much stronger than UV-A. It is the main cause of sunburns and skin damage that can lead to skin cancer. UV-B also reduces the growth of plants and may affect the health of domestic animals and wildlife. The ozone layer absorbs much of the UV-B that enters our atmosphere, but not all of it. The UV Index measures the sun-burning portion of the UV-B rays that reach the Earth’s surface.
- UV-C is extremely powerful. Fortunately, it is completely absorbed by the ozone layer and never reaches the Earth’s surface.
Follow our sun protection tips to protect yourself from both UV-A and UV-B.
The ozone layer - the Earth’s natural sunscreen
The ozone layer is found in the stratosphere, in the upper atmosphere, about 20 to 40 km above the Earth’s surface. This layer absorbs most of the sun’s UV rays, providing a natural sunscreen that protects life on earth.
During the 1970s, scientists became aware that certain industrial chemicals were destroying ozone in the stratosphere. By the mid1980s, thinning of the ozone layer was enabling more UV to reach the Earth’s surface. Scientists were also surprised to find a large ozone hole developing over the Antarctic, where up to 60% of the ozone was lost each spring.
Global concern over the threat to the ozone layer led to the signing of the Montreal Protocol in Canada in 1987. The agreement committed nations around the world to phase out the use of ozone-destroying chemicals. As a result, the use of these chemicals has decreased considerably, and levels of the most damaging substances (CFC-11 and CFC-12) have declined significantly in the atmosphere. The fire extinguishing chemicals, known as halons, were also a significant threat to the ozone layer, and they too, are being phased out under the Montreal Protocol.
Is the ozone layer recovering?
The ozone layer is beginning to show signs of recovery. Outside the polar regions, the layer is no longer thinning, and has stabilized at about 3% less than normal, and average summer UV values across Canada remain a few percent higher than they were before 1980.
In the Antarctic, the ozone hole continues to form every year during the southern spring, while in the Arctic, less severe depletions occur occasionally. In March of 2011, a record ozone hole in the high Arctic showed an ozone loss of up to 40%.
A complete recovery of the ozone layer is not expected for decades. Many ozone-destroying chemicals can remain in the atmosphere for years after they have been released. There is a need to remain vigilant, since some ozone-depleting chemicals have not yet been completely phased out, and new chemicals need to be reviewed to ensure they do not pose additional threats. Scientists are also concerned that the recovery of the ozone layer could be complicated by other factors, such as climate change.
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