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The air we breath, the soil on which we stand and walk, the water we drink are all part of the environment. The seas are in danger. They are filled with poison, which kills fish and sea animals. Fish and reptiles can’t live in them because of the shortage of oxygen in the water. If people drink this water they can die too. Air pollution is also a very serious problem. The ozone layer protects us from radiation. If there are holes in the ozone layer ultraviolet radiation can get to the earth. These holes are the result of air pollution. It is dangerous to be in direct sunlight because ultraviolet radiation can cause skin cancer. Nuclear power stations can go wrong and cause nuclear pollution. Nuclear pollution cannot be seen, but its effects can be terrible. Both clean air and clean water are necessary for our health. If people want to survive they must solve these problems quickly. Man is beginning to understand that his environment is not just his own town or country, but the whole earth.
Man produces more than a million different kinds of products, both as waste and as useful products that eventually end up as waste. We are mobilizing many materials at rates greater than the global rates of geological erosion and deposition, great enough to change their global distributions. We are using more than 40 per cent of the total land surface and have reduced the total amount of organic matter in Land vegetation by about one-third.
Natural ecosystems still provide us many services. Almost all potential plant pests are controlled naturally. Insects pollinate most vegetables, fruits, berries, and flowers. Commercial fish are produced almost entirely in natural ecosystems. Vegetation reduces floods, prevents erosion, and air-conditions and beautifies the landscape. Natural ecosystems cycle matter through green plants, animals, and decomposers, thus eliminating wastes. Organisms regulate the amount of nitrates, ammonia, and methane in the environment. On a geological time scale, life regulates the amount of carbon dioxide, oxygen, and nitrogen in the atmosphere. Natural ecosystems also serve important recreational and aesthetic needs of man.
PARTICLES IN THE ATMOSPHERE
Fine particles change the heat balance of the earth because they both reflect and absorb radiation from the sun and the earth. Large amounts of such particles enter the troposphere from natural sources such as sea spray, wind-blown dust, volcanoes, and from the conversion of naturally occurring gases into particles.
Man introduces fewer particles into the atmosphere than enter from natural sources. However man introduces significant quantities of sulfates, nitrates and hydrocarbons. The largest single artificial source is the production of sulfur dioxide from the burning of fossil fuel that subsequently is converted to sulfates by oxidation. Particle levels have been increasing over the years.
Particles in the troposphere can produce changes in the earth’s reflectivity, cloud reflectivity and the cloud formation. The magnitudes of these effects are unknown, and in general it is not possible to determine whether such changes would result in a warming or cooling of the earth’s surface.
Particles also act as nuclei for condensation or freezing of water vapour. Precipitation processes can certainly be affected by changing nuclei concentrations. However, we do not believe that the effect of man-made nuclei will be significant on a global scale.
CLIMATE IN THE PAST
Our knowledge of climate in the remote past is derived from geological evidence and the study of fossils. For the past few hundred million years, the earth’s climate has been characterized by alternate ice ages and warm interglacial periods. An ice age is generally believed to occur when some mechanism, such as shift in the tilt of the earth’s axis in space or natural cycle of precipitation and freezing at the poles, causes the polar ice caps to spread over substantial areas in lower latitudes. Fossil evidence has confirmed that ice ages have occurred regularly in the earth’s history. Studies disclose that the glaciers advanced and withdrew four times during this ice age. As the ice sheets advanced, the climate south of them is known to have become colder and wetter. When they withdrew, southern latitudes grew warmer and drier. The evidence suggests that at the height of the last ice age, what is now the Sahara Desert was arable, vegetated land supporting human and animal life.
Prior to the onset of this age, the world is known to have been much warmer than today. Glaciers did not exist in the Arctic or on Antarctica.
IMPACT ON FRESH WATER ECOSYSTEMS
Effects of acidification of rivers and lakes were discovered in the mid-1960s over large areas of northern Europe and North America, well before effects on forests became manifest. On Sweden lakes larger than I hectare today about one quarter is acidified. The composition of diatoms started to change in the 1950s, indicating a shift to a more acidic situation, and that tendency increased markedly in the 1960s and 1970s. Similar trends have been reported from several regions in North America, where hundreds of lakes with pH values below 5 have lost most or all of their fish stocks. Effects of acidification are most noticeable during the spring snowmelt when large amounts of NO3- and H+ are mobilized and cause a surge of acidity and mass mortality of fish. Mortality is attributed to the elevated levels of aluminum, mobilized during the snowmelt, which is toxic to fish. Severe depletion of fisheries has already taken place. Acidification may also lead to the mobilization of metals from sediments. In particular the mobility of mercury appears to be enhanced, but also of copper. Areas sensitive to acidic deposition are such with carbonate-free bedrock. Watercourses in such areas are poorly buffered with ionic strength.
Thermal pollution is a problem associated with nuclear power plants. The reactors heat the water in very large quantities. When this water is discharged back into the rivers after use, it is very damaging to marine life. Furthermore, wastes in hot water absorb oxygen more rapidly than in cool water. Thermal pollution can help to create excessive growth of algae. The ecological cycle is disrupted. Therefore nuclear technology can be improved. For example, it is possible to build cooling towers at nuclear plants. In these towers the heated water is cooled before being released back to the river or lake. It is also possible to create new lakes of great scenic and recreational value in which the pure but heated water can be cooled.
Thus through the use of the technique, temperature variations in water, whether from natural or artificial causes can be ascertained.