Fossil fuels are fuels deriving from the natural transformation, developed over millions of years, of organic substance buried underground over the course of geological eras, into increasingly stable and carbon-rich molecular forms.
It can be stated that fossil fuels constitute the accumulation in the subsoil of energy deriving from the Sun, directly collected in the biosphere over geological periods by plants through chlorophyll photosynthesis and by unicellular aquatic organisms, such as protozoa and blue-green algae, or indirectly via the food chain by animal organisms.
The global distribution of the main reserves of the different types of fossil fuels does not coincide geographically with each other, in particular the coal deposits are located in different regions than the liquid hydrocarbon deposits, which in turn does not coincide with that of the main gas deposits.
The main reserves are located in the United States, Western Europe (UK, Belgium, France and Germany), countries of the former Soviet Union, Poland, China, Australia, Japan and India. Coal reserves as a whole constitute the largest accumulation of fossil fuels still available for exploitation.
The geography of current oil reserves is evolving due to the exploitation and therefore exhaustion of many deposits located in areas that have long been exploited. In 2005 it was estimated that approximately 27% of the oil on the market came from areas whose oil reserves were decreasing, including the US fields and those offshore the North Sea.
In other countries, economic growth is such as to transform them from oil exporters to importers, such as China. The largest conventional accumulations of oil are found in the Middle Eastern area (Saudi Arabia, Iraq, Kuwait, Iran, Syria, United Arab Emirates) and, due to their size, it is believed that they will be the last to run out.
Other regions of the world with large oil basins include Nigeria and the Nigerian and Angolan Atlantic offshore, Venezuela and the Caspian Sea area. The largest gas field is located in Groningen in the Netherlands, large gas reserves are found in Siberia and Algeria.
Other gas reserves are associated with oil in oil fields spread around the world. At the beginning of the 19th century the scenario of world gas reserves changed due to the beginning of the massive exploitation of shale gas.
However, for gas there is the big problem of transporting it from the place of extraction to the place of use, and this today makes the marketability, and therefore the exploitation, of large volumes of gas problematic. The use of fossil fuels contributes to the increase in CO2 and global warming.
Currently, the countries that emit the largest amount of CO2 are China, the United States and India, in that order. However, if we consider the overall quantity of CO2 emitted into the atmosphere over the course of history, the picture changes.
The United States leads the list, followed by China and Russia. Finally, if we examine the impact of CO2 emissions in relation to the population, i.e. we evaluate the quantity of CO2 produced per inhabitant, the nations that stand out are Qatar, Bahrain and Kuwait.
The United States contains less than 5% of the world's population, but because of large homes and private automobiles, it uses more than a quarter of the world's fossil fuel production. In the United States, more than 90 percent of greenhouse gas emissions come from the burning of fossil fuels.
The burning of fossil fuels also produces other air pollutants, such as nitrogen oxides, sulfur dioxide, volatile organic compounds and heavy metals.