Fossil fuels include all sources of energy derived from finite resources. Fossil fuels developed from dead (plant and animal) biomass that was converted into what they are today by being exposed to high pressure and heat in the absence of oxygen over the course of millions of years. The main fossil fuels are coal, natural gas and crude oil.
Fossil energy sources are distinguished into biogenic and mineral fossil energy sources. Biogenic fossil fuels are mainly coal (e.g. lignite, bituminous coal) and liquid or gaseous hydrocarbons (e.g. crude oil, natural gas). Unlike the renewable energy sources – bio-energy, wind energy, hydropower, solar energy and geothermal energy – biogenic fossil fuels are non-renewable. Mineral fossil fuels are substances from which nuclear energy can be produced by nuclear fission or fusion.
Since the energy is released directly during combustion, biogenic fossil fuels are counted among the primary energy sources. They can be used to generate energy either directly or through one or more conversion steps indirectly by producing secondary energy carriers. An example of secondary energy carriers is refining crude oil into various petroleum products such as gasoline and diesel, which then go to fuel vehicles at filling stations.
Historically speaking, in the 18th and 19th centuries the physical exploitation and use of fossil fuels formed the basis for the industrial revolution. This process began with the coal-powered steam engine. The invention of the combustion engine and the burgeoning petrochemical industry meant that coal has been increasingly replaced by oil. Crude oil is still the most important fossil fuel and also the feedstock for most chemical products. At present, biogenic and mineral fossil primary energy are the mainstays of our energy supply system.
The existing reserves of fossil fuels on earth that are proven to be safely and economically recoverable with current technology are called “energy reserves.” By contrast, the term “energy resources” is used to describe proven and probable stores of energy sources that cannot yet be exploited for technical and/or economic reasons.
Due to their widespread use and the world’s growing energy requirements, fossil energy reserves are being steadily decimated. Use of renewable energy is being increased in an attempt to at least partially replace fossil fuels and reduce our dependence on fossil energy. Cutting back on nonessential use and increasing energy efficiency also help to reduce energy demand.
The increased use of renewable energy is being accelerated not only with the finiteness of fossil fuels in mind, but also with regard to the environmental repercussions associated with their use. The combustion of fossil energy releases carbon dioxide (CO2) into the atmosphere. The permanent increase in CO2 concentrations is seen as a root cause of accelerating climate change. The extraction, transport, storage and handling of fossil fuels are also associated with risks, .