People have made many changes to the world we live in, and some of these have had harmful effects. As the world population increases, there is need for bigger cities, new towns and farmland. Land has to be cleared of forests. This destroys the habitats of animals and plants. Loss of habitat, pollution and hunting have driven many to extinction. Industry can damage the environment. Harmful chemicals, plastics and waste pollute our oceans and kill ocean life. The burning of fossil fuels in power stations and vehicles releases carbon dioxide into the air, contributing to global warming. It also pollutes the air we breathe.

Global warming

Carbon dioxide is a greenhouse gas. In the right amounts, greenhouse gases in the atmosphere trap heat from the Sun preventing the Earth becoming either too hot or too cold. But if greenhouse gases build up, too much heat is trapped and the Earth heats up.

Climate change will have disastrous effects if current trends continue. The ice in the polar regions will melt, raising sea levels and causing severe flooding in low-lying areas. Changes in the climatic pattern worldwide are already leading to more violent storms, flooding and extreme drought.

Desertification is when a region becomes more dry and desert-like. It loses its plants and animals and becomes barren wasteland. Climate change and drought are mostly responsible, but allowing animals to graze on the thin grass and shrubs in dry areas makes matters worse.

Deforestation

Deforestation is the cutting down of forests. This destroys the habitats of many plants and animals. Trees prevent the soil they grow in being washed or blown away, so cutting them down often results in less fertile land for farming. Trees also absorb carbon dioxide, one of the greenhouse gases that contribute to global warming. Their loss causes CO2 levels in the air to rise.

Today, many tropical rainforests are cut down to make room for farmland or plantations. Palm oil, a vegetable oil, comes from the fruit of oil palms. It is in great demand because it is used in food and other products. This has led to the clearing of forests, particularly in Indonesia, to make space for oil palm plantations. This threatens the survival of animals like the orang-utan, which lives here and nowhere else.

Soil erosion

Soil erosion is the wearing away of topsoil by wind or water. Soil with little or no vegetation is more easily eroded. Some farming practices and the cutting down of forests can cause soil erosion. Through the loss of fertile upper soil layers, soil erosion reduces farmland. It also threatens the survival of animals that depend on plants that grow in the soil. The eroded soil particles may choke rivers, lakes and wetlands elsewhere. Fine soil particles picked up by the wind also causes dangerous air pollution.

Air pollution is caused by fumes and smoke from vehicles, factory chimneys and power stations. Poisonous gases, such as sulphur dioxide released from factories, can mix with rain and mist to produce acids. When the acid rain falls, it kills plants over a wide area. Carbon monoxide released by vehicle exhausts causes city smogs, which are damaging to people's health.

Many efforts are being made to reduce air pollution. These include making sure factories control their emissions of pollutants. Some countries are moving towards using cleaner fuels, such as biofuels, renewable energy and using electric vehicles. Petrol-engine cars are fitted with catalytic converters on their exhausts, which make the exhaust gases less poisonous. Many cities are introducing zoning to make the air in cities cleaner. For example, drivers who take their cars into central London now have to pay a fee.

By recycling as much of our waste as possible (glass, metals, paper and some plastics and electronic items), we can reduce the amount of waste in landfills. Here, waste is buried in the ground, but harmful substances leak into rivers through groundwater—and from rivers into the ocean. Food and plant materials can be used as compost for farms and gardens. Other waste products can be burned and used as fuel.