Looking back to medieval times, wood was the primary source of energy. With the world having a low population, there was more than enough wood to go around, especially as much of the world was heavily forested at that time. As animals started being used for transportation and agriculture, so the need arose to start growing crops to feed them as well as all the humans. This resulted in both deforestation and a decline in soil quality. This required larger distances to be travelled to get to fertile land and a good supply of wood, which of course increased the need for animals, and so the circle continued. The end result was that wood and other goods started increasing in price, to the extent that the old economies of Europe started out on a new age of exploration and colonisation allowing the importing of energy supplies and goods from the new world (and the subsequent transfer of wealth).

 

Whilst coal had been around for some time (thousands of years in places like China), it was not a preferred energy source due to soot and smoke issues. As wood ran out, more people started using coal and got used to smog clouds during winter months. As time went by, coal was converted to coke by a roasting process and the resulting higher temperatures facilitated iron and steel production, effectively kick-starting the Industrial Revolution.

 

By the end of the 18th century, the steam engine had caught on, significantly accelerating the rate at which coal could be extracted and ultimately resulting in the steam train for transportation. Trade flourished and the first phase of urban sprawl got started. By-products of coal included artificial gas for lighting and coal-tar dyes, kick-starting the chemical industry. At the end of the nineteenth century, the Industrial Revolution was in full swing around the old world, with employees typically working regimented shifts in centralised factories.

 		    

Coal usage peaked in the early 20th century, with the first successful oil well in operation in Pennsylvania in 1859. Oil started off being used for machine lubrication, replacing whale oil, animal oil and vegetable tallow. A little later, John D Rockefeller formed Standard Oil and had 90% of US oil business by 1880. Oil also started pouring out of Russia, Indonesia and other areas of the world, with pipelines put in place to ship it to where it could be consumed. Natural gas was also discovered in the process of drilling for oil, and gradually started replacing the manufactured gas from the coal production process.

 

Electrification started in the late 19th century and whilst not being a source of energy, it proved to be a very effective carrier of energy. This ultimately resulted in a proliferation of home appliances, business equipment and communication and entertainment devices. Electricity really stimulated the worldwide use of energy to the extent that by the end of the 20th century, most people in industrialised civilisations were using some form of electricity for most of their waking hours.

 

The energy revolution allowed the mechanisation of agriculture, of personal and goods transportation and highly efficient killing machines for war. The worldwide dependence on energy not only started causing wars but was also used as a strategy in attacks to cut off key energy supplies which could bring a country or region to its knees.

 

Whilst coal is still used to power many of the electricity-generating power stations around the world, it has serious limitations in terms of environmental issues in the extraction process, pollution from burning and it's general inefficiency as an energy medium. Even though there is lots of coal left in the world, most of the easily accessible coal is already extracted, leaving only deep-mined coal which is both hazardous and expensive to remove. Arguably, we only have a few decades of economic coal extraction left, whereafter the energy required to extract it will exceed the useful energy it will generate.

 

Nuclear power first stated commercial production in the US in the 1950's, with many more built into the 60's and 70's. Around 20% of US energy is currently derived from Nuclear sources but faced a string backlash from environmental groups concerned about serious reactor accidents, decommissioning and waste storage. Nuclear power may at first appear to be a very low-cost type of energy, but when plant construction, safety measures, de-commissioning and waste storage are taken into account, it starts looking uncompetitive. There is also the issue of availability of uranium which is wasteful, complex and dangerous to extract, as well as only having around 40 years supply left. To replace coal and/or oil as an energy source would require literally hundreds of new nuclear reactors to be built, resulting in quicker depletion of uranium along with a minefield of issues over where to site them, transportation to/from reactors and so on.