The Vanishing Ozone Layer

The depletion of the ozone layer is a problem that has very similar implications from the viewpoint of ecological democracy than the issue of global warming: everybody will suffer from a problem to which some people – the world's rich minority – contribute much more than the others will. Most of the emissions that are damaging the ozone layer are still produced by West Europe and North America, which only have about one eighth of the world's population.

Ozone, the three-atomic molecule of oxygen, has two very different roles. In the lower atmosphere (troposphere), a greenhouse gas contributes to the global warming. It is also poisonous to people and harmful for plants. However, the thin layer of ozone in the upper atmosphere (stratosphere) filters the most damaging forms of the Sun's ultraviolet radiation and prevents them from reaching the ground level. Without this protection, we would be exposed to much more intensive and dangerous X-radiation. This would increase the rate of skin cancers and cataracts and damage many food crops. Serious loss of ozone could also reduce fish catches by killing fish larvae that are vulnerable to strong ultraviolet radiation.

In the early 1970's scientist became worried about the possibility that nitrous oxides from fertilizers, supersonic airplanes and space shuttle flights might destroy stratospheric ozone. Somewhat later it was understood that also the so called freons or CFC compounds (chloro-fluoro-carbons) were harmful for the ozone layer. CFCs were first used in fridges and air conditioning systems and later as cleaning solvents, aerosol propellants and to puff up polystyrene foam for hamburger cartons and for other purposes. Their world production rose from 2200 tons in 1940 to 491 700 tons in 1970, and it was still growing by 20 per cent per year when it was discovered that the CFCs were both strong greenhouse gases and efficient ozone-depleting substances.

The issue was taken seriously only five years after the British scientists had discovered a vast "ozone hole" over the Antarctic in 1982. The delay was caused by an American satellite, whose computer had been programmed to ignore the impossible results. Thus the satellite did not see the ozone hole and could not confirm the results reported by the British ground stations. It took five years before the confusion was sorted out. At that time, the Antarctic ozone hole had grown to cover an area of 14 million square kilometers. Under this area, almost all-stratospheric ozone vanished during the spring months.

After the existence of the Antarctic ozone hole had been confirmed, the governments started to move with a record speed. The Montreal Protocol on Substances that Deplete the Ozone Layer was negotiated and signed in 1987. In the Montreal Protocol, the signatory governments agreed to cut their CFC emissions. During the coming years, further meetings of the parties adopted more targets that are ambitious and finally agreed to phase-out the CFCs and most other ozone-depleting substances. According to the Environmental Protection Agency of the USA, these treaties are likely to prevent about 137 million cases of skin cancer and about 40 million cataracts before the year 2075, so they certainly were a major victory for the humans and for the environment.

However, we still have the problem of nitrous oxide from nitrogen fertilizers and from the burning of fossil fuels. According to the UN's Intergovernmental Panel on Climate Change, the nitrous oxide concentrations in the atmosphere are likely to rise by 45 per cent by the year 2100. The Australian research agency CSIRO says that the ozone levels in the mid-latitudes are likely to recover a little because of the elimination of the CFC production. However, they should start falling again around the year 2040 because of the build-up of nitrous oxide into the atmosphere. CSIRO predicts that the ozone layers above the mid-latitudes should be about 9 per cent lower at the end of the century, and they could keep on falling with an accelerating speed.

The new threat to the ozone layer could be even more serious than the CFCs, unless the problem will be prevented in advance. The ozone depletion caused by chlorine and bromine compounds mostly occurs in midwinter, when there is less sunlight in the northern latitudes and when the people are usually well covered because of low temperatures. However, most of the ozone loss caused by the nitrous oxide takes place in mid-summer when the ultraviolet radiation is the most intense and when people generally wear much less clothing. The damage caused by nitrous oxide is also likely to concentrate on the mid-latitudes where the majority of the world's population lives, and not on the unpopulated Polar Regions.

It is likely that nitrous oxide will become a major topic in international environmental negotiations in the near future. The most important ways to tackle the problem are to promote organic farming, in which chemical fertilizers are not used, or to develop nitrogen fertilizers that do not cause significant nitrous oxide emissions.

Some types of chemical nitrogen fertilizers that are in use now, especially anhydrous ammonia and aqua ammonia, produce approximately one hundred times more nitrous oxide than the most benign alternatives like sodium nitrate and nitrogen solutions.

Дата добавления: 2015-10-24