Fossil fuel
A fossil fuel is a hydrocarbon-containing material formed underground from the remains of dead plants and animals that humans extract and burn as fuel. The main fossil fuels are coal, petroleum and natural gas, which humans extract through mining and drilling. Fossil fuels may be burnt to provide heat for use directly (e.g. for cooking), to power engines (such as internal combustion engines in motor vehicles), or to generate electricity. The principal origin of fossil fuels is the anaerobic decomposition of buried dead organisms, containing organic molecules created in ancient photosynthesis. The transitions from these source materials  to high-carbon fossil fuels typically requires a geological process of millions of years, sometimes more than 650 million years. Fossil fuels can be transformed into other chemicals or derivatives by the refining and chemical industries. Commonly-used refined fossil fuels include kerosene, gasoline and propane, and common chemicals include most plastics and agricultural chemicals such as fertilizers and pesticides. 84% of primary energy consumption in the world and 64% of electricity was from fossil fuels in 2019. Fossil fuels cause serious environmental damage and direct negative consequences on local communities at every stage in their use: extraction, transportation and  consumption of the fuels. Over 80% of the carbon dioxide (CO) emitted by humans is from burning fossil fuels: around 35 billion tonnes a year, compared to 4 billion from land use change. Natural processes on Earth, mostly absorption by the ocean, can only remove a small part of this amount, therefore there is a net increase of many billion tonnes of atmospheric carbon dioxide per year. Methane leaks are also significant. Carbon dioxide and methane are greenhouse gases, that is they trap heat in the earth's atmosphere. Fossil fuels are the main source of greenhouse gas emissions causing  global warming and ocean acidification. Additionally, most air pollution deaths are due to fossil fuel particulates and noxious gases: it is estimated that this pollution costs over 3% of global GDP, and that fossil fuel phase-out would save millions of lives each year. Recognition of the climate crisis, pollution and other negative impacts caused by fossil fuels has led to a widespread policy transition and activist movement focused on ending their use in favor of sustainable energy. However, because the fossil fuel industry is so heavily integrated in the global economy and heavily subsidized, this transition is expected to  have significant economic impacts. Many stakeholders argue that this change needs to be a just transition and create policy that addresses the societal burdens created by the stranded assets of the fossil fuel industry. International policy, in the form of United Nations Sustainable Development Goal 7: Affordable and Clean Energy, Sustainable Development Goal 13: Climate Action and the Paris Climate Agreement, is designed to facilitate this transition at a global level. In 2021, the International Energy Agency concluded that no new fossil fuel extraction projects could be opened if the global economy and society wants to avoid the worst impacts  of climate change and meet international goals for climate change mitigation. Origin. The theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in Earth's crust over millions of years was first introduced by Andreas Libavius "in his 1597 Alchemia [Alchymia]" and later by Mikhail Lomonosov "as early as 1757 and certainly by 1763". The first use of the term "fossil fuel" occurs in the work of the German chemist Caspar Neumann, in English translation in 1759. The "Oxford English Dictionary" notes that in the phrase "fossil fuel" the adjective "fossil  means [o]btained by digging; found buried in the earth", which dates to at least 1652, before the English noun "fossil" came to refer primarily to long-dead organisms in the early 18th century. Aquatic phytoplankton and zooplankton that died and sedimented in large quantities under anoxic conditions millions of years ago began forming petroleum and natural gas as a result of anaerobic decomposition. Over geological time this organic matter, mixed with mud, became buried under further heavy layers of inorganic sediment. The resulting high temperature and pressure caused the organic matter to chemically alter, first into a waxy material known  as kerogen, which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. Despite these heat-driven transformations (which increase the energy density compared to typical organic matter by removal of oxygen atoms), the energy released in combustion is still photosynthetic in origin. Terrestrial plants tended to form coal and methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants also form type III kerogen, a source of natural gas. Although fossil fuels are continually formed by natural processes, they are classified  as non-renewable resources because they take millions of years to form and known viable reserves are being depleted much faster than new ones are generated. There is a wide range of organic compounds in any given fuel. The specific mixture of hydrocarbons gives a fuel its characteristic properties, such as density, viscosity, boiling point, melting point, etc. Some fuels, like natural gas, for instance, contain only very low boiling, gaseous components. Others such as gasoline or diesel contain much higher boiling components. Importance. Fossil fuels are of great importance because they can be burned (oxidized to carbon dioxide and  water), producing significant amounts of energy per unit mass. The use of coal as a fuel predates recorded history. Coal was used to run furnaces for the smelting of metal ore. While semi-solid hydrocarbons from seeps were also burned in ancient times, they were mostly used for waterproofing and embalming. Commercial exploitation of petroleum began in the 19th century. Natural gas, once flared-off as an unneeded byproduct of petroleum production, is now considered a very valuable resource. Natural gas deposits are also the main source of helium. Heavy crude oil, which is much more viscous than conventional crude  oil, and oil sands, where bitumen is found mixed with sand and clay, began to become more important as sources of fossil fuel in the early 2000s. Oil shale and similar materials are sedimentary rocks containing kerogen, a complex mixture of high-molecular weight organic compounds, which yield synthetic crude oil when heated (pyrolyzed). With additional processing, they can be employed instead of other established fossil fuels. During the 2010s and 2020s there was disinvestment from exploitation of such resources due to their high carbon cost relative to more easily-processed reserves. Prior to the latter half of the 18th  century, windmills and watermills provided the energy needed for work such as milling flour, sawing wood or pumping water, while burning wood or peat provided domestic heat. The wide-scale use of fossil fuels, coal at first and petroleum later, in steam engines enabled the Industrial Revolution. At the same time, gas lights using natural gas or coal gas were coming into wide use. The invention of the internal combustion engine and its use in automobiles and trucks greatly increased the demand for gasoline and diesel oil, both made from fossil fuels. Other forms of transportation, railways and aircraft, also  require fossil fuels. The other major use for fossil fuels is in generating electricity and as feedstock for the petrochemical industry. Tar, a leftover of petroleum extraction, is used in the construction of roads. Environmental effects. The burning of fossil fuels has a number of negative externalitiesharmful environmental impacts where the effects extend beyond the people using the fuel. The actual effects depend on the fuel in question. All fossil fuels release when they burn, thus accelerating climate change. Burning coal, and to a lesser extent oil and its derivatives, contribute to atmospheric particulate matter, smog and acid rain. Climate  change is largely driven by the release of greenhouse gasses like , with the burning of fossil fuels being the main source of these emissions. In most parts of the world climate change is negatively impacting ecosystems. This includes contributing to the extinction of species (see also extinction risk from climate change) and reducing people's ability to produce food, thus adding to the problem of world hunger. Continued rises in global temperatures will lead to further adverse effects on both ecosystems and people, with the World Health Organization having stated climate change is the greatest threat to human health in  the 21st century. Combustion of fossil fuels generates sulfuric and nitric acids, which fall to Earth as acid rain, impacting both natural areas and the built environment. Monuments and sculptures made from marble and limestone are particularly vulnerable, as the acids dissolve calcium carbonate. Fossil fuels also contain radioactive materials, mainly uranium and thorium, which are released into the atmosphere. In 2000, about 12,000 tonnes of thorium and 5,000 tonnes of uranium were released worldwide from burning coal. It is estimated that during 1982, US coal burning released 155 times as much radioactivity into the atmosphere as the Three Mile  Island accident. Burning coal also generates large amounts of bottom ash and fly ash. These materials are used in a wide variety of applications (see Fly ash reuse), utilizing, for example, about 40% of the United States production. In addition to the effects that result from burning, the harvesting, processing, and distribution of fossil fuels also have environmental effects. Coal mining methods, particularly mountaintop removal and strip mining, have negative environmental impacts, and offshore oil drilling poses a hazard to aquatic organisms. Fossil fuel wells can contribute to methane release via fugitive gas emissions. Oil refineries also have negative environmental  impacts, including air and water pollution. Coal is sometimes transported by diesel-powered locomotives, while crude oil is typically transported by tanker ships, requiring the combustion of additional fossil fuels. A variety of mitigating efforts have arisen to counter the negative effects of fossil fuels. This includes a movement to use alternative energy sources, such as renewable energy. Environmental regulation uses a variety of approaches to limit these emissions; for example, rules against releasing waste products like fly ash into the atmosphere. Other efforts include economic incentives, such as increased taxes for fossil fuels, and subsidies for alternative energy technologies  like solar panels. In December 2020, the United Nations released a report saying that despite the need to reduce greenhouse emissions, various governments are "doubling down" on fossil fuels, in some cases diverting over 50% of their COVID-19 recovery stimulus funding to fossil fuel production rather than to alternative energy. The UN secretary general António Guterres declared that "Humanity is waging war on nature. This is suicidal. Nature always strikes backand it is already doing so with growing force and fury." However, Guterres also said there is still cause for hope, anticipating Joe Biden's plan for the US to  join other large emitters like China and the EU in adopting targets to reach net zero emissions by 2050. Illness and deaths. Environmental pollution from fossil fuels impacts humans because particulates and other air pollution from fossil fuel combustion cause illness and death when inhaled. These health effects include premature death, acute respiratory illness, aggravated asthma, chronic bronchitis and decreased lung function. The poor, undernourished, very young and very old, and people with preexisting respiratory disease and other ill health are more at risk. Global air pollution deaths due to fossil fuels in 2018 have been estimated at over 8  million people, nearly 1 in 5 deaths worldwide. While all energy sources inherently have adverse effects, the data shows that fossil fuels cause the highest levels of greenhouse gas emissions and are the most dangerous for human health. In contrast, modern renewable energy sources appear to be safer for human health and cleaner. The death rate from accidents and air pollution in the EU are as follows per terawatt-hour: coal (24.6 deaths), oil (18.4 deaths), natural gas (2.8 deaths), biomass (4.6 deaths), hydropower (0.02 deaths), nuclear energy (0.07 deaths), wind (0.04 deaths), and solar (0.02 deaths). The greenhouse gas  emissions from each energy source are as follows, measured in tonnes: coal (820 tonnes), oil (720 tonnes), natural gas (490 tonnes), biomass (78-230 tonnes), hydropower (34 tonnes), nuclear energy (3 tonnes), wind (4 tonnes), and solar (5 tonnes). As the data shows, coal, oil, natural gas, and biomass cause higher death rates and higher levels of greenhouse gas emissions than hydropower, nuclear energy, wind, and solar power. Scientists propose that 1.8 million lives have been saved by replacing fossil fuel sources with nuclear power. Industrial sector. In 2019, Saudi Aramco was listed and it reached a US$2 trillion  valuation on its second day of trading, after the world's largest initial public offering. Economic effects. Air pollution from fossil fuels in 2018 has been estimated to cost US$2.9 trillion, or 3.3% of global GDP.