The greenhouse effect and the ozone layer
Twenty years ago, the scientific community was brimming with optimism. On September 16, 1987, representatives from 24 countries signed the Montreal Protocol and pledged to restrict the use of chemical substances that destroy the ozone layer, a shield that protects humans and habitats from harmful solar ultraviolet radiation. Unfortunately, 20 years after the signing of the protocol there is little to celebrate. The depletion of this precious layer of toxic gas that lies 25 kilometers above the Earth continues and a new problem has arisen to complicate matters: climatic change. In the case of the ozone layer, the international community acted quickly (unlike with the greenhouse effect and the signing of the Kyoto Protocol). The Montreal Protocol was signed just three years after three British scientists in the Antarctic sighted the ozone hole above the continent. Everyone believed that the measures adopted by the Montreal Protocol would reverse the situation. Although the production and use of chlorofluorocarbons (CFCs) that deplete the ozone (mainly found in sprays, refrigerators, fire extinguishers and air-conditioning units) have been drastically reduced over the last few years, there are no signs that the ozone layer is being restored. Scientists celebrated too early. Last year, the largest loss of ozone in a year was recorded over the Antarctic. Measurement of the ozone by the Envisat satellite of the European Space Service showed a loss of 40 million tons of ozone in a period of a month, a figure which exceeds the former record of 39 tons measured in 2000. In 2006, the ozone hole over the Antarctic was one of the largest in size since its discovery (in 2000, it was even larger) and measured nearly 28 million square kilometers. The ozone has also depleted considerably over other areas of the planet. According to recent data by the International Ozone Commission, in the Northern Hemisphere, the figures for the ozone are still 3 percent below 1980 levels, while in the Southern Hemisphere they are about 6 percent lower than pre-1980 levels. Last September depletion of the ozone layer reached record levels. Scientists now believe that full restoration of the ozone layer will take decades. «In about 2060 and 2080 depending on the region,» said Alkiviadis Bais, associate professor for the natural environment at Aristotle University in Thessaloniki. «It is not certain that the same is true for the Antarctic. According to scientific models, it will take longer for the layer in the area to recover.» The main reason for the delay is the presence of chlorofluorocarbons in the atmosphere even after their production was curbed. With a life span of 50 to 200 years, the chlorofluorocarbons already produced will remain in the atmosphere for many more decades. Scenarios of full restoration that prevailed a few years ago were an illusion created by climatic change. Climatic conditions above Northern Europe that have been attributed to a change in North Atlantic variability hid the truth from scientists. In fact climatic change has slowed down the restoration process of the ozone layer. The problem will not be resolved unless the greenhouse effect is addressed. «The interaction between ozone depletion and climatic change is a major environmental issue. An increase in the concentration of greenhouse gases causes the lower layer of the stratosphere to freeze at the poles, causing further damage to the ozone layer,» said the International Ozone Commission.
