An iceberg floats in the off Australian Antarctic Territory. Scientists argue that climate change and the depletion of the ozone layer will trigger further melting in the world's polar regions. They have attributed the depletion of the ozone layer in this undated handout photograph from the Australian Antartic Division to the impact of global warming on the vast Southern Ocean around Antarctica. This is starting to pose a threat to ocean currents that distribute heat around the world, Australian scientists say, citing new deep-water data. - File

Our health and well-being depends on the ozone in the atmosphere 10-50km above the Earth's sur-face (the stratosphere). Radiation approaching the Earth from the sun interacts with the ozone and some of the higher energy radiation is removed. If that radiation was to reach the Earth's surface, it would damage some of the biological materials in plants and animals.

Also, when the ozone interacts with the sun's radiation, it heats the upper atmosphere and that helps keep the Earth's temperature in the range which we can tole-rate. It is therefore important that we do not do things that could lead to a depletion of the amount of ozone in the upper atmosphere.

Unfortunately, during the 20th century, some of the chemicals used in refrigerators, air conditioners and firefighting equipment and as solvents, propellants and insecticide were (unbeknown at that time) able to float up to the upper atmosphere, react with the ozone and slowly, but surely destroy it. The problem was detected in the 1970s.

Global policymakers

Scientists around the world quickly alerted global policy-makers to the problem and, in 1987, the signing of the United Nations' Montreal Protocol by most countries committed signa-tories to stop making and using ozone-depleting substances such as chlorofluorocarbons.

Since then, the depletion of the ozone has been stopped but, because of the slow nature of the depletion process, the amounts of ozone in the upper atmosphere will not return to mid-1900s levels until the middle of this century.

Concerns about the effects of ozone depletion on biological materials result from the increased amount of ultraviolet radiation (particularly UV-B radiation) that can pass through the sections of the atmosphere where ozone amounts have been reduced.

Ozone depletion occurred mainly in the atmospheres above the poles, particularly Antarctica, where circulation patterns and temperatures were favourable to the depletion reactions. The depletion was less in the mid-latitudes and no ozone losses occurred in the atmosphere over the tropics. In the mid-to-high latitudes, the increased UV-B radiation led to increases in skin cancers, reduced productivity and reproduction in land plants and damaged aquatic ecosystems.

Radiation damage

However, since there have been no changes to the amount of ozone in the upper atmosphere over the tropics, there have been minimal if any changes in radiation damage within the tropics.

The main reason people in the tropics must be concerned about the depletion of the upper atmosphere ozone relates to the effects on plants and animals in the oceans and the changes in climate that result from changing the temperature of the upper atmosphere.

UV-B radiation can induce decreases in productivity and reproduction in the small plants and animals in the shallow waters of the oceans. In addition, DNA can be damaged by the UV-B radiation. When the small plants and animals are eaten by larger predators, the damage enters the food chain and can alter the natural cycling of chemicals in the environment. With the migration of fish, assisted by ocean circulation patterns, the effects of the increased UV-B radiation in the higher latitudes become global problems which affect us all.

Atmosphere

With the depletion of the upper atmospheric ozone, less energy became trapped in that section of the atmosphere and so started to cool. This, in turn, lead to a cooling of the atmosphere beneath it and eventually to the cooling of the lower atmosphere. This partially offset the global warming that has been occurring due to the increase in the amounts of greenhouse gasses in the lower atmosphere. While this has been good (one human-induced negative effect has partially counteracted the impact of another human-induced negative effect), we have lately seen quite clearly that human-induced climate changes can be very unpredictable and can lead to major changes in weather patterns. We should avoid doing things that change natural processes as we seldom understand the long-term impact of such changes.

The depletion of the ozone layer is a global environmental issue that affects us all.