The ozone layer is found in the stratosphere, 15-35 km above the surface of the earth. Ninety per cent of the ozone (O3) present in the atmosphere is concentrated here. Ozone is continually generated and broken down through natural processes in the stratosphere. Anthropogenic emissions of ozone-depleting substances have disturbed the balance in the stratosphere.

Slow recovery towards 2050-2070

The concentration of most of the ozone-depleting substances in the troposphere is now declining slowly. If all countries are in compliance with the Montreal Protocol, with all approved changes, it is expected that the concentration of ozone depleting substances will be back at the 1979 level in 2050. The ozone layer is expected to be almost completely recovered by 2050 - 2070.

The impact of climate change and the emission of methane and nitrous oxide can affect the recovery of the ozone layer, but it is uncertain how.

Ozone levels over Oslo and Andøya in the north of Norway

The Norwegian Institute for Air Research continuously monitors the ozone levels over Oslo and Andøya, on behalf of the Climate and Pollution Agency.

The results suggest that there was a reduction in the ozone layer until the end of the 1990s, and that the ozone layer has begun to stabilize over Norway after this. However, both over Oslo and Andøya there are large variations, both from year to year and throughout the year. These variations are typical of the ozone layer over high latitudes, especially in the Arctic, and makes the trend more uncertain than at lower latitudes.

Although the mean values ​​indicate a stabilization of the ozone layer over Norway, we have seen a higher incidence of significant ozone depletion in the winter/spring in recent years. This is due to extremely low temperatures in the higher parts of the atmosphere (the stratosphere).

Largest reductions in ozone concentrations over polar regions

Because of periods of extremely low temperatures in the stratosphere, the most severe depletion of the ozone layer is found over the polar regions. Such extremely low temperatures occur more frequently in Antarctica than the Arctic. In Antarctica, it creates a large area where the ozone layer is very thin in the spring, also known as the "ozone hole".

Although ozone depletion in the Arctic is less than in the Antarctic, it is still severe. Furtermore, in the Arctic many more people are affected by increased UV radiation than in the almost uninhabited areas in the Antarctic. Changes in climate may increase the risk of the formation of ozone hole in the Artic in the future.

Depletion of the ozone layer results in higher levels of UV radiation at the earth's surface. This poses a danger to humans, animals and plants, and marine life.

Ecological effects

Increasing exposure to UV radiation may have a negative impact on the production of plankton and other micro-organisms at the base of the marine food web. These organisms are the ultimate source of food for all other living organisms in the oceans. A severe exposure to UV radiation may also disrupt many ecosystems on land, significantly reducing yields and causing food shortages.

Health effects

The increase in UV-B radiation associated with ozone depletion is likely to have effects on the immune system. The risk of skin cancer and infectious diseases thus increases. UV-B radiation can damage the eye's cornea, the lens and the retina. Excessive exposure to UV radiation may cause cataracts.

Damage to materials

UV radiation causes a number of materials to degrade more rapidly. In general, plastic materials used outdoors will have much shorter lifetimes.

Ozone-depleting substances such as CFCs and halons were widely used before their effect on the ozone layer was discovered. In 1986, 1.1 million tonnes of CFCs were used worldwide for many purposes; aerosols, foam-blowing agents, refrigerators, air conditioning, solvents, dry cleaning and firefighting.

Ozone-depleting substances were popular because they were non-poisonous, non-flammable, cheap to produce and persistent. But it was their very stability that proved almost fatal to the earth's ozone layer.

Norway has fulfilled its obligations under the Montreal Protocol and met the EU targets for reductions in the consumption and production of ozone-depleting substances. The result is more than a 99 per cent reduction in the use of ozone-depleting substances, measured in ozone-depleting potential, since 1986.

All the countries in the world have ratified the Montreal Protocol on substances that deplete the ozone layer. The Montreal Protocol sets targets for reducing and phasing out use for each of the ozone-depleting substances.

UNEP (United Nations Environmental Programme) estimates that without the Montreal Protocol, the abundance of ozone-depleting substances in 2050 would be 5 times higher than today. Surface UV-B radiation would at least double at middle-latitudes in the Northern Hemisphere, and would be four times as intense at middle-latitudes in the Southern Hemisphere. The incidence of skin cancer would increase by several millions of cases.

Norway has met the EU targets for reduction

Norway is complying with EU targets for reducing and phasing out the use of ozone-depleting substances. The EU has been following a more rapid phase-out schedule than the Montreal Protocol. Norwegian regulations implementing the EU regulations entered into force on 1 January 2003.