Reading - Part 3

In September 1982, Dr Joe Farman, a British scientist working in the Antarctic, found that a dramatic change had taken place in the atmosphere above his research station on the ice continent. His instruments, set up to measure the amounts of a chemical called ozone in the atmosphere, seemed to go wild. Over just a few days they recorded that half the ozone had disappeared.

He couldn't believe his eyes, so he came back to Britain to get a new instrument to check his findings. But when he returned the following year at the same time, the same thing happened. He had discovered a hole in the ozone layer - an invisible shield in the upper atmosphere - that turned out to extend over an area of the sky as wide as the United States and as deep as Mount Everest is high. When he published his findings in scientific journals, they caused a sensation. Scientists blamed pollution for causing the ozone hole.

The ozone layer is between 15 and 40 kilometres up in the atmosphere, higher than most aeroplanes fly. This region contains most of the atmosphere's ozone, which is a special form of the gas oxygen. Ozone has the unique ability to stop certain dangerous invisible rays from the sun from reaching the Earth's surface - rather like a pair of sunglasses filters out bright sunlight. These rays are known as ultra-violet radiation. This damages living cells, causing sunburn and more serious diseases. The ozone layer is vital to life on the surface of the Earth.

Until the ozone layer formed, about two thousand million years ago, it was impossible for any living thing to survive on the surface of the planet. All life was deep in the oceans. But once oxygen was formed in the air, and some of that oxygen turned to ozone, plants and animals could begin to move on to land.

But now humans are damaging the ozone layer for the first time. In the past ten years, scientists have discovered that some manmade gases, used in everything from refrigerators and aerosols to fire extinguishers, are floating up into the ozone layer and destroying the ozone. The most common of these gases are called chlorofluorocarbons (CFCs).

The damage is worst over Antarctica, and near the North Pole, where scientists have seen small holes appear for a short time each spring since 1989. So far, these holes have healed up again within a few weeks by natural processes in the atmosphere that create more ozone. But each year, it seems to take longer for the healing to be completed. Also, all round the planet, there now seems to be less ozone in the ozone layer than even a few years ago.