Concern is mounting at international level that the growth of the world's population, coupled with expectations for higher standards of living, is depleting natural resources and damaging the environment.
At a fundamental level, people need energy to survive. They obtain this energy from food and water, and these represent the bare minimum required for existence ~ physiological needs. As a race, however, we expect more than just to simply exist and it is the activities at work and in the home which have energy implications. Factory production, transport, heating, lighting and using electrical appliances all involve the conversion of energy from one form to another. Note that the energy is never "used up" ~ this is scientifically impossible ~ merely converted into an ultimately less useful form or degraded. The chemical energy contained within oil is converted into heat energy within the engine of a car which in turn provides the kinetic energy to propel the car along. Put your foot on the brake and this energy is converted to heat energy within the brakes. The chemical energy contained within natural gas is converted into heat at a gas fired power station which in turn powers the turbines which generate electrical energy. This energy is then converted within homes to create the heat and light from a television or the heat and sound energy from a stereo. Obviously the more "advanced" the society then the more of earth¹s natural energy resources are going to be consumed.

We depend on fossil fuels such as oil, coal and natural gas for 70-80% of our energy usage. Strenuous efforts are being made to find new sources but these are all ultimately finite and will run out some time next century.
As if this wasn't depressing enough, the energy in fossil fuels is released during the burning of hydrocarbons and these produce CO² (carbon dioxide) known as the "greenhouse gas". It affects the incoming solar radiation and the energy radiated by the Earth which ultimately results in warming of the Earth's surface. This is what is known as the "greenhouse effect" and has been occurring since the industrial revolution in the nineteenth century.
Left unchecked it will result in disrupted weather patterns and the melting of the polar ice caps.
Coal burning leads to the discharge of SO² (sulphur dioxide) which dissolves in rain water to form a corrosive acid known, oddly enough, as acid rain.
In addition to the emissions of greenhouse gasses and acid rain, the natural composition of the atmosphere is changed in other ways by human activities.
These include the ozone layer, which acts as a shield against the Sun's radiation, which can be damaged by CFC's contained in aerosols and refrigerators. Lead, which was previously used as an additive in petrol, has been found to damage the health of people, particularly children, in areas of high traffic density. It is now being eradicated in the US and Europe.

Increasing populations and rising living standards lead to more and more demands on limited resources. Various initiatives have been taken by individuals, local and national authorities, and the international community (Earth Summit at Rio in 1992) to try and achieve "sustainable development".
The aim is to meet human needs now but still preserve the resources that will be needed by future generations. This can be done by the following strategies;

more efficient use of materials and other resources, avoidance of materials and manufacturing methods that damage the environment, substitution of materials and processes by more effective ones, recycling of materials.

Energy Conservation

The problems associated with the wasteful use of energy can be tackled in many ways. There are particularly large gains to be made from switching to more energy efficient cars and buildings. Engines are becoming progressively more powerful yet more economical and cleaner than their predecessors.
Offset against this is that they are also becoming heavier in the quest for greater safety and refinement, and are fitted with more energy draining devices such as power steering and air conditioning. Diesels are now much more widespread than 15 years ago but, whilst they use less fuel, they produce more pollutants than petrol engined cars. Are electric cars the solution? Not yet ~ their range and performance is still limited, their purchase price high and, ultimately, it transfers the problem of energy usage from the car to the power station which produces the electricity. Much greater reductions in energy consumption could be made if individual vehicles are replaced by "mass transit" systems. A bus full of passengers
uses far less fuel than separtate cars carrying the same number of people, and a few cities in the UK are now installing trams and light railway systems to encourage their use. The freedom and flexibility the car allows us is considerable, however, and for the moment we are more concerned with building better roads so that we can get from a to b quicker without necessarily worrying about the environmental costs.
Heating houses accounts for large quantities of energy usage and there are savings to be made by increasing insulation standards in walls and roofs.
Solar panels can be fitted to buildings but the installation costs are high and the savings in energy costs relatively small. Further gains can be made by fitting energy saving bulbs and using energy efficient household appliances. Most "white goods" are now rated according to their energy consumption so that consumers are aware of a products "green" credentials.

The use of raw materials in the manufacture of goods is another area of environmental concern. However, the consumption of steel, cement, paper and other raw materials has been growing less rapidly than our use of energy in recent years, at least in industrialised countries. The demand for timber and wood products remains high and the clearing of forests can lead to soil erosion, flooding and the destruction of wildlife habitats. In many countries wood is a primary fuel so that large areas of forest are cleared for energy purposes. However, wood is at least a renewable material and schemes exist to plant a new tree for each one felled to help maintain stocks.

The collection, sorting and re-use of household and trade waste is widely practised. Many local authorities provide collection points for cans, glass, plastics, paper and fabrics, and techniques have been developed for seperating materials from general household rubbish. Reclaiming metals is widespread in industry and substantial quantities of steel are produced from salvage such as scrapped cars and lorries. Plastics recycling is a more recent innovation and has been assisted by the use of identification codes moulded onto plastic objects. Plastics however, degrade through recycling so that the material that was used to produce the dashboard of a car might be used in a less visible area during it's next life.

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