2018-01-08
808The Green Book
Human activity is changing our planet. No one knows what long-term effects it will have.
Global Warming/Greenhouse Effect
On a cool, sunny day the temperature inside a greenhouse is much warmer than it is outside. This happens because a greenhouse acts like a one-way valve: the glass lets in sunlight, but blocks most of the heat trying to get out.
The Earth and its atmosphere work in a similar way. Sunlight warms the Earth's surface; heat radiates upward through the atmosphere, but is blocked by "greenhouse gases," such as carbon dioxide, water vapor, and methane. This process is known as the greenhouse effect. Temperatures on Earth would be cooler without it. By burning fossil fuels, such as coal and oil, we increase the level of carbon dioxide in the atmosphere by about 0.3 percent a year. Since carbon dioxide is the most critical greenhouse gas, scientists expect the world to get warmer as its levels increase. In the last hundred years, the world's average temperatures have climbed by approximately 1 F (0.5 C). If this rise in temperature continues, it will almost certainly affect sea levels and it could change weather patterns. Some places may become increasingly colder, and crop-growing regions could become dry and unproductive. Many countries are now reducing their output of greenhouse gases, but no one knows if this action will be enough to stop global warming.
Ozone Depletion In the early 1980s a weather satellite sent startling pictures back to Earth. They showed what scientists had long feared - a giant gap in the ozone layer above Antarctica.
Ozone is a colorless gas that contains the same atoms as oxygen. Although it makes up less than a millionth of the atmosphere, it forms a protective shield around the Earth that is vital to many forms of life. The ozone layer blocks the sun's ultraviolet В (UV-B) rays, which can kill or damage the living cells of plants and animals.
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Under normal conditions, ozone is replaced as quickly as it is broken down. But if chlorine-containing gases are present in the atmosphere, it does not reform. As a result the ozone layer gets progressively thinner, and eventually a hole may develop. Until the industrial age very few chlorine-containing gases were found in the upper air. But during the 20th century large amounts of them have been released.. The main gases are CFCs (chlorofluorocarbons), which are used in fire extinguishers and refrigerators. Other gases are given off by chemical solvents, for example those used in dry cleaning. Many of these gases stay in the atmosphere for years.
Satellite surveys show that ozone depletion is increasing worldwide. Some countries have banned the use of ozone-layer-damaging chemicals, but it will be years before the level of these gases in the atmosphere begins to drop.
Rising Sea Levels. Throughout the Earth's history changes in climate have made the sea levels rise and fall. During long cold periods more water becomes locked up in polar ice, so sea levels drop, sometimes by more than 100 feet (31m). During warm periods some of this ice melts, and sea levels rise once more.
Records show that sea levels have increased by approximately 6 inches (15cm) since the year 1900. Most climatologists think that this steep rise is partly due to global warming. If the Earth continues to warm up, sea levels could rise by as much as 3 feet (1m) during the 21st century. Whether the sea level will actually rise this far is not yet certain. The world's climate is controlled by many factors. Evidence found in the ice cap in Greenland shows that the Earth's climate changed abruptly in the past, long before humans had any effect on it. Although the Earth is warming now, nobody can be sure that it will continue to do so in the years to come.
However, if sea levels do rise, the impact will be dramatic. Low-lying coasts and islands will be flooded, along with many crop-growing areas. Floods are already a problem in some of the world's coastal cities, and the rising sea will bring further chaos.
Pollution During the 20th century pollution has become one of the most serious threats facing the natural world.
Air Pollution The air above many cities is brown and murky, and the horizon disappears into a blur. This unsightly condition is caused by pollution. Air pollution occurs when gases and microscopic particles are released into the Earth's atmosphere. Sometimes these particles come from natural sources, such as volcanoes or bush fires, but more often they are produced by human activity.
We pollute the air in many ways - forest clearance fires, cars, and factories all contribute to air pollution. Cars give off a collection of different pollutants,including soot and poisonous gases such as nitrogen oxides. Lead is added to some types of gasoline, and this toxic metal finds its way into the air as well. Coal-burning power stations also produce huge amounts of pollutants, including nitrogen oxides and a corrosive gas called sulfur dioxide. Once these dangerous gases get into the atmosphere they dissolve in the air's moisture and produce acid rain - thus becoming part of the water cycle. This rain kills large areas of forest. It can also enter streams and lakes, where it kills fish and other animals. Acid rain is now a worldwide problem, because polluting chemicals released in one part of a continent can spread to another part. Scientists have even found traces of lead from car exhausts in the ice of Antarctica. However, the news about air pollution is not all bad. Many industrialized countries are now reducing their output of sulfur dioxide, and modem cars can be made to run more cleanly than before. Because the atmosphere affects us all, a serious global effort has now begun to clean up our air.
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Water Pollution For centuries, humans have used water to dispose of sewage. Today, waterborne pollutants include a range of other chemicals as well, including fertilizers and pesticides fromfarmlands, dissolved solvents and detergents from homes and factories, and metals such as lead and теrcurу from industrial processes. All these find their way into rivers and eventually end up in the sea.
The oceans are not limitless. The things that we pour into them are often absorbed by marine animals, and may then come back to us in food. In Japan in the 1950s hundreds of people suffered mercury poisoning - with crippling results - after eating fish that had absorbed mercury released into the sea by factories. Toxic substances are not the only ones that can damage life in the sea. Sewage, fertilizers, and detergents are rich in nitrates and phosphates, two substances that plants need in order to grow. When large amounts of these enter the water, often the result is a population explosion of microscopic plants. This robs the water of its oxygen, killing fish and other animals.
Pollution is sometimes accidental. For example, ships carrying oil are occasionally damaged during storms or collisions. When the oil spills out, it can cover vast areas of sea and coastline, killing thousands of helpless animals and birds.
Reducing Pollution At one time people used very little energy in their daily life, and most of their household objects were made of biodegradable materials, like wood, which break down naturally when thrown away. However, "in the industrialized world many everyday objects take a lot of energy to produce, and are made of non-biodegradable materials. Cars are a particular problem. They cause pollution both when they are made and when they are used. Our lifestyle creates a large amount of pollution. We can all help to reduce pollution by using recycled products, by recycling household objects, and by using public transport. At home, we can conserve energy by insulating houses well and by turning off heating when it is not needed. On an industrial level, steps can be taken to reduce our consumption of raw materials. Recycling cans and bottles saves both raw materials and energy. Industrial pollution can also be reduced by cutting down on packaging and by recycling some of the chemicals used in manufacturing processes.
Many farmers use large amounts of fertilizers and pesticides, which are often washed into streams and rivers. Some are now discovering that they can reduce their use of chemicals without affecting their crops. In the future objects such as cars and computers will be designed with recycling in mind, instead of being thrown away because their parts cannot be separated for reuse, their components will be constructed so that the raw materials can be recovered and then used again.
In recent years engineers have been investigating cleaner energy sources, such as wind and wave power. In the 21st century cars may be powered by electricity, possibly from a renewable source, such as the wind or sun. In this case automobile pollution may be dramatically reduced.
