Ozone (O3) is a nascent form of oxygen. It has three oxygen atoms instead of the normal two. High concentrations of ozone in the stratosphere are known as ozone layer, which extends from 15 to 50 kilometers above the earth's surface.
The stratospheric layer contains 90% of atmosphere. Ozone layer protects planet earth from the harmful effects of the ultraviolet (UV) radiation coming from the sun. Excessive depletion of ozone layer due to release of man-made chemicals such as chloroflurocarbons (CFCs), halogens, carbon tetrachloride and methyl bromide cause thinning of ozone layer, which is called ozone hole. The hole is found over Antarctic and Artic.
The size of ozone hole over Antarctic was double the size of Europe, i.e. 25 million square kilometers in September, 1998.
Ozone filters and allows more ultraviolet radiation from the Sun to reach the Earth. Increased concentrations of ultraviolet radiation due to ozone depletion can cause skin cancer, cataract and effect marine life, plants, materials and different ecosystem. In fact, the ultraviolet radiation is damaging to almost all of life. In view of the scientific evidence that man made chemicals such as CFCs, halogen, carbon tetrachloride and methyl bromide are tremendously destroying the ozone layer, the international community has decided to phase out the production and large scale use of these chemicals by signing the Vienna Convention in 1985 and subsequently the Montreal Protocol in 1987. There are 172 countries, signatory to the Convenction.
Stratospheric zone blocks ultraviolet light, where all of it is to be brought down to sea level, the zone would form a layer only three millimeters thick. In the 1970's it was attacked without restraint by CFCs manufactured at a rate of nearly a million tons a year as refrigerants, aerosol propellants, industrial solvents and foam-blowing agents. Rising slowly into the stratosphere sooner or later, for instance from dumped and rusting refrigerators, CFCs are broken down by sunlight. Their chlorine then attacks the ozone by catalysis, so that just one chlorine atom can destroy tens of thousands of ozone molecules. Largely because of CFCs, the stratospheric chlorine is now about five times more than before, and increasing continuously. The globe's average stratospheric ozone level is thought to have declined by between 4 and 8 percent. The losses are particularly marked in Antarctica, where each October of the year sees the appearance of a 'hole', its area sometimes equaling that of the United States: ozone is reduced by about 60 percent overall and by 95 percent at the center. In the year 2005 there would be very little ozone in the hole if present trends continued. A second, less transparent hole - ozone levels reduced by 10 percent or more - now opens over the Artic at intervals, stretching southwards over much of Europe and North American Continents.
The extensive threat from CFCs was first explained in the early 1970's, before discovery of the Antarctic hole. As usual with pollution crises, the evidence was at first doubted. When the hole was found it was suggested that seasonal winds were blowing the ozone way. The Montreal Protocol of 1987, signed at first by twenty-seven countries, the Protocol called for a 50 percent cut in the manufacture of CFCs and halons (which are the other main ozone-destroyers) by 1991. Later becoming convinced of the inadequacy of this, the signatories joined by more than fifty further countries, called for phasing out the use of these chemicals by the end of the century.
CFCs and halogens are far from being the only threats to stratospheric ozone. With their vapour trails, aircraft cause about a tenth of the ozone depletion, and could cause much more after the anticipated growth in high-altitude flights. (In 1990 Britain and France were cheerfully proposing joint development of a new fleet of supersonic high-altitude aircraft despite the earlier outcry of environmentalists against similar plans in the United States). Nitrogen oxides produced by the use of nitrogenous fertilizers, destroy may be of another tenth of the ozone. Methyl bromide, a crop fumigant, destroys perhaps as much again. Other contributors include methyl chloride: as mentioned earlier, this is generated copiously when forests, scrubs and grasslands are cleared by burning. It has been claimed that by ejecting hydrochloric acid, volcanoes send more chlorine to the stratospheric than humans, but this has been disproved: practically all of the acid is washed out by the rains accompanying eruptions, and in any case the recent big eruption of Mt Pinatubo ejected a mere fifty thousand tons of it, an amount negligible by comparison with the CFCs emitted in the same period. Yet volcanic emissions, together with industrial pollutants, do help clouds to form in the stratosphere, these then initiating reactions which speed up the ravages of the chlorine which humans have put there.
The direct consequences include an estimated additional 200,000 expected deaths from skin cancer in the United States alone or (the Environmental Protection Agency has calculated) over 3,000,000 by the year 2100 if ozone depletion continues unabated. There will be many more cases of blindness (100,000 more for each 1 percent decline in stratospheric ozone, according to a United Nations), a weakening of the human immune system, and premature aging. Still, the worst consequences could be indirect ones. Light in the ultraviolet-B waveband harms living organisms of all main types, on land and in water. In attacks not only plants, including many trees, but also the nitrogen-fixing bacteria on which crops rely unless heavily fertilized. Above all, it may be a grave threat to many zooplankton and phytoplankton species. Zooplankton and phytoplankton are at the base of the oceanic food chains. Phytoplankton are crucial for taking carbon dioxide from the atmosphere: they remove more of this greenhouse gas than all other factors combined.
The surge in population is both a cause of the changed relationship and one of the clearest illustrations of how startling the change has been, especially when viewed in a historical context. From the emergence of modern humans 200,000 years ago until Julius Caesar's time, fewer than 250 million people walked on the face of the earth. When Christopher Columbus set sail for the new world 1,500 years later, there were approximately 500 million people on earth. By the time Thomas Jefferson wrote the Declaration of Independence in 1776, the number had doubled again, to 1 billion. By midway through this century, at the end of World War II, the number had risen to just above 2 billion people. In Other words, from the beginning of humanity's appearance on earth to 1945, it took more than ten thousand generations to reach a world population of 2 billion people. Now, in the course of one human lifetime - mine - the world population will increase from 2 to more than 9 billion in the year 2025, and it is already more than halfway there.
Overpopulation is often defined as the condition of having more people than can live on earth in comfort, happiness, and health and still leave the planet a fit place for future generations. To most environmentalists, the data suggest that the planet is already overpopulated. Because of differing concepts of carrying capacity, however, experts differ widely over what level of population is considered too high. Some project that if everyone existed at a minimum survival level, the earth could support 20 to 48 billion people. This anthill existence would require that everyone exist only on a diet of grain, cultivation all arable land, and mining much of the earth's crust of a depth of 1.6 kilometers (1 mile). Other analysts believe the earth could support 7 to 12 billion people at a decent standard of living by distributing the world's land and food supply more equitably and shifting from less abundant resources (such as lead, tin, uranium, oil, and natural gas) to more abundant resources (such as aluminum, glass, and various forms of solar energy).
Others opposed to population regulation feel that all people should have the freedom to have as many children as they want. To some, population regulation is a violation of their deep religious beliefs. To others, it is an intrusion into their personal privacy and freedom. To minorities, population regulation is sometimes seen as a form of genocide to keep their numbers and power from rising. Proponents of population regulation point to the fact that we are not providing adequate basic necessities for one out of five people on Earth today who don't have the opportunity to be a net economic gain for their country. They see people overpopulation in MDCs (more developed countries) as threats to Earth's life support systems for us and other species. These analysts recognize that population growth is not the only cause or our environmental and resource problems. They believe, however, that adding several hundred million more people in MDCs and several billion more in LDSs (less developed countries) will intensify many environmental and social problems by increasing resource use and waste, environmental degradation, rapid climate change, and pollution. To proponents of population regulation, it is unethical for us not to encourage a sharp drop in birth rates and unsustainable forms of resource use to prevent a sharp rise in death rates and human misery and a decrease in Earth's biodiversity in the future. Despite promises about sharing the world's wealth, the gap between the rich and poor has been getting larger since 1960. Proponents of population regulation believe this is caused by a combination of population growth and unwillingness of the wealthy to share the world's wealth and resources more fairly. They call for MDCs to use their economic systems to reward population regulation and sustainable forms of economic growth instead of continuing their unsustainable forms of economic growth and encouraging LDCs to follow this eventually unsustainable and disastrous path for the planet.
In the near past, the Population Crisis Committee compiled a human suffering index for each of 130 countries based on ten measures of human welfare. They found a high correlation between the level of human suffering and the rate of population increase in countries. The 30 countries falling in the extreme human-suffering range-all in Africa and Asia-averaged a high annual rate of population increase of 2.8%.
The 44 countries with a high human suffering rate-all in Africa, Asia, and Latin America-also had an average annual population increase of 2.8%. With the increase in the population on the earth, there are environmental problems and these problems create things, which may cause the depletion of ozone layers.