What is the Ozone Layer and How Does it Affect Us?

The easiest way to come to grips with the Ozone Layer is to imagine the earth's atmosphere as a layered cake.Our atmosphere is split into a number of layers, beginning with the "troposphere" which is where we all live.

Above that is the "stratosphere", which is where most planes fly and in there, you'll also find the planet's Ozone Layer. (Ozone actually exists to some degree in all of the layers but most of it - thought to be around 90 per cent - is produced naturally in the stratosphere.)

Basically, the Ozone Layer is a planetary sunscreen and it plays a vital part in protecting us from most of the sun's harmful radiation. Scientists believe that without it, mankind and most animals on Earth would die.

Without its protection, we would quickly suffer intense radiation burns unless we found some way to shield ourselves such as by wearing special clothing or living underground. Even then, a lot of the plant life that humans and animals depend on would die out, making food sources extremely scarce.

What Exactly is Ozone?

Ozone itself is a type of oxygen but unlike the oxygen that we need to breathe, it is a poisonous gas. So, although ozone in the stratosphere is good and performs a vital function, ozone at ground level is bad. It is the main ingredient of today's city smog and irritates conditions like asthma, bronchitis and lung disease.

The oxygen we breathe is made up of two oxygen atoms but ozone molecules have three and unlike oxygen, which is odourless, ozone has a very strong odour (its name comes from the Greek word meaning "to smell").

People often refer to the planet's Ozone Layer as a protective shield but in reality it acts more like a sieve or a web because although it traps harmful radiation, it still allows heat from the sun to reach Earth.

The term 'layer' also suggests that it is uniform around the planet but in fact its density varies around the globe.

Our Effect on the Ozone Layer

The Ozone Layer begins about six miles above us and extends to around 30 miles above. Scientific records spanning decades show that until the 1970s, its level remained fairly stable.

There have always been factors such as the seasons, weather conditions and solar cycles which affect its density, but these are all part of a natural cycle where ozone is continually formed, destroyed and formed again.

However, in the 1970s scientists discovered that this natural balance had been upset and that the Ozone Layer was being depleted - that is, ozone was now being destroyed at a faster rate than it was being naturally produced.

Research revealed that much of the damage was being caused by man-made chemicals, most of which had been introduced since the 1920s.

What's Happened Since Then?

In 1985, scientists with the British Antarctic Survey discovered a "hole" in the Ozone Layer over Antarctica and two years later more than 20 countries signed an international agreement, known as the Montreal Protocol.

This called for the phasing out of ozone depleting chemicals, including CFCs (Chlorofluorocarbons) thought to be responsible for damage to the Ozone Layer. Since then, many other countries have signed up to the agreement and it has proved to be extremely successful. In fact, former UN General Secretary, Kofi Annan, has described it as probably the most successful international agreement ever signed.

The Dangers of Lower Ozone Levels

Of course, we need low levels of solar UV. It is vital in the production of Vitamin D and without exposure to the sun, people would suffer from diseases linked to Vitamin D deficiency.

But too much UV exposure damages our DNA and causes skin cancer. It also causes damage to the eyes and scientists now believe that it affects the immune system, allowing people to become ill more easily.

What is Now Being Done to Protect the Ozone Layer?

Ozone levels are now constantly monitored and experts have predicted that by 2070, the Ozone Layer will have returned to pre-1980 levels. It is expected to take this long to "repair" itself because the chemicals which caused the damage remain in the stratosphere for many years.

Until then, we are all at greater risk from UV radiation and scientists in America believe it has already led to an increase in the number of deaths from the most fatal form of skin cancer.

Many experts are also concerned that new factors could continue to damage the Ozone Layer, slowing down - or even preventing its recovery. For example, some scientists believe that global warming is likely to accelerate ozone depletion.