A fossil fuel is a hydrocarbon-containing material formed underground from the remains of dead plants and animals that humans extract and burn to release energy for use. 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. As of 2018, the world's main primary energy sources consisted of petroleum (34%), coal (27%), and natural gas (24%), amounting to an 85% share for fossil fuels in primary energy consumption in the world. Non-fossil sources included nuclear (4.4%), hydroelectric (6.8%), and other renewable energy sources (4.0%, including geothermal, solar, tidal, wind, wood, and waste). The share of renewable sources (including traditional biomass) in the world's total final energy consumption was 18% in 2018.
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. Most significantly, the burning of fossil fuels produces around 35 billion tonnes (35 gigatonnes) of carbon dioxide (CO2) per year, or about 89% of all carbon dioxide emissions. Natural processes on Earth (mostly through absorption by the ocean) can only absorb a small part of this amount, therefore there is a net increase of many billion tonnes of atmospheric carbon dioxide per year. Carbon dioxide is a greenhouse gas that increases radiative forcing, thus 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 combustion products: it is estimated that this pollution costs over 3% of global GDP, and that fossil fuel phase-out would save 3.6 million 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 renewable energy. However, because the fossil fuel industry is so important to the global economy and historically 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 stranded assets of the fossil fuel industry. International policy, in the form of 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.
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.
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.
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.
The burning of fossil fuels has a number of negative externalities – harmful 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 CO2 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 CO2, 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 global warming) 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. Transportation of coal requires the use of diesel-powered locomotives,[why?] 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"[colloquialism] 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 back – and 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.
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. Total global air pollution deaths reach 7 million annually.[when?]
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.
Fossil fuel divestment or fossil fuel divestment and investment in climate solutions is an attempt to reduce climate change by exerting social, political, and economic pressure for the institutional divestment of assets including stocks, bonds, and other financial instruments connected to companies involved in extracting fossil fuels.
Fossil fuel divestment campaigns emerged on campuses in the United States in 2011 with students urging their administrations to turn endowment investments in the fossil fuel industry into investments in clean energy and communities most impacted by climate change. In 2012, Unity College in Maine became the first institution of higher learning to divest its endowment from fossil fuels.By 2015, fossil fuel divestment was reportedly the fastest growing divestment movement in history. In October 2021, a total of 1,485 institutions representing $39.2 trillion in assets worldwide had begun or committed to a divestment from fossil fuels.
This section needs to be updated.(April 2020)
In 2014, there were 1,469 oil and gas firms listed on stock exchanges around the world, with a combined market capitalization of US$4.65 trillion. 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.
A 2015 report studied 20 fossil fuel companies and found that, while highly profitable, the hidden economic cost to society was also large. The report spans the period 2008-2012 and notes that: "For all companies and all years, the economic cost to society of their CO2 emissions was greater than their after-tax profit, with the single exception of ExxonMobil in 2008." In the case of coal-only companies, the impact is worse: "the economic cost to society exceeds total revenue in all years, with this cost varying between nearly $2 and nearly $9 per $1 of revenue". In this case, total revenue includes "employment, taxes, supply purchases, and indirect employment".
Fossil fuel prices generally are below their actual costs, or their "efficient prices", when economic externalities, such as the costs of air pollution and global climate destruction, are taken into account. Fossil fuels are subsidized in the amount of $4.7 trillion in 2015, which is equivalent to 6.3% of the 2015 global GDP and are estimated to grow to $5.2 trillion in 2017, which is equivalent to 6.5% of global GDP. The largest five subsidizers in 2015 were the following: China with $1.4 trillion in fossil fuel subsidies, the United States with $649 billion, Russia with $551 billion, the European Union with $289 billion, and India with $209 billion. Had there been no subsidies for fossil fuels, global carbon emissions would have been lowered by an estimated 28% in 2015, air-pollution-related deaths reduced by 46%, and government revenue increased by $2.8 trillion or 3.8% of GDP.
United States government subsidies include financing provided by the US Export-Import Bank (USEIB), an agency of the US federal government, for overseas projects by large petrochemical corporations. During the administration of US President Obama, USEIB provided close to $34 billion to finance 70 fossil fuel projects around the world, including in Queensland, Australia, Mpumalanga, South Africa, and Madhya Pradesh, India.'
The examples and perspective in this section may not represent a worldwide view of the subject. (December 2021)
A major effect of state subsidy for petrochemical production has been increased extraction, including increased investment into new wells. Estimated at an oil price of $50 per barrel, tax preferences and other US government subsidies have rendered profitable close to half of the investment in new oil production. This US government subsidy is estimated to drive an increase in American oil production of 17 billion barrels over the next few decades.[when?] This increase in oil use is equivalent to 6 billion tons of carbon dioxide, and comprises as much as 20% of US oil production through 2050, assuming an overall carbon budget that limits average global warming to 2 °C.
There are 1,469 oil and gas firms listed on stock exchanges around the world, worth a combined $4.65 trillion.