Fossil fuel

The main fossil fuels (from top to bottom): natural gas, oil, and coal

A fossil fuel^[a] is a carbon compound- or hydrocarbon-containing material^[2] formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or planktons), a process that occurs within geological formations. Reservoirs of such compound mixtures, such as coal, petroleum and natural gas, can be extracted and burnt as a fuel for human consumption to provide energy for direct use (such as for cooking, heating or lighting), to power heat engines (such as steam or internal combustion engines) that can propel vehicles, or to generate electricity via steam turbine generators.^[3] Some fossil fuels are further refined into derivatives such as kerosene, gasoline and diesel, or converted into petrochemicals such as polyolefins (plastics), aromatics and synthetic resins.

The origin of fossil fuels is the anaerobic decomposition of buried dead organisms, whose organic molecules were produced by photosynthetic carbon fixation and sequestered/biomagnified by the food web,^[4] creating an underground carbon sink. The conversion from these organic materials to high-carbon fossil fuels typically requires a geological process of millions of years.^[5] Due to the length of time it takes nature to form them, fossil fuels are considered non-renewable resources.

In 2022, over 80% of primary energy consumption in the world and over 60% of its electricity supply were from fossil fuels.^[6] The large-scale burning of fossil fuels causes serious environmental damage. Over 70% of the greenhouse gas emissions due to human activity in 2022 was carbon dioxide (CO₂) released from burning fossil fuels.^[7] Natural carbon cycle processes on Earth, mostly absorption by the ocean, can remove only a small part of this, and terrestrial vegetation loss due to deforestation, land degradation and desertification further compounds this deficiency. Therefore, there is a net increase of many billion tonnes of atmospheric CO₂ per year.^[8] Although methane leaks are significant,^[9]: 52 the burning of fossil fuels is 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, and it is estimated that this costs over 3% of the global gross domestic product^[10] and that fossil fuel phase-out will save millions of lives each year.^[11][12]

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 and sustainable energy.^[13] Because the fossil-fuel industry is so heavily integrated in the global economy and heavily subsidized,^[14] this transition is expected to have significant economic impacts.^[15] Many stakeholders argue that this change needs to be a just transition^[16] and create policy that addresses the societal burdens created by the stranded assets of the fossil fuel industry.^[17][18] International policy, in the form of United Nations' sustainable development goals for affordable and clean energy and climate action, as well as 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.^[19]

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