Fossil fuels and global warming

The coal-burning steam engine stimulated the Industrial Revolution, leading to the nineteenth century’s vast commercial productivity. The invention of affordable automobiles in the twentieth century created a huge market for oil, which became America’s dominant energy source. When a fossil fuel is burned, its emissions include CO₂, the main anthropogenic contributor to global warming.

Background

Fossil fuels store the chemical energy created over hundreds of millions of years as accumulated layers of plant and animal remains were subjected to heat and pressure. These organic residues transformed into coal beds, pools of oil, and pockets of gas. They include coal, oil, natural gas, oil shale, and tar sands. Since these fuels are no longer being created, they are nonrenewable resources. Equally important, when burned, the carbon unites with oxygen in the atmosphere to produce carbon dioxide (CO₂), the main culprit responsible for anthropogenic global warming.

Coal

Coal is fossilized plant material, deposited 300 million years ago when Earth was warmer and wetter. Preserved and altered by geological forces over eons of time, this material was compacted into carbon-rich fuel.

Coal mining is dirty and dangerous because underground mines are subject to cave-ins, accumulations of carbon monoxide, and fires caused by explosive gases such as methane. In the United States alone, tens of thousands of miners have died in accidents over the past century, and even more have died or been disabled by respiratory diseases caused by the accumulation of fine dust particles in the lungs. Although strip mining is a safer and less expensive alternative, the land remaining after the overburden is removed is rendered unfit for any other use. Restoration and reclamation are mandated by US law, but the efforts expended by mining companies are often superficial and ineffective. Coal mining also contributes to water pollution because sulfur and other soluble minerals in mine drainage and runoff from mine tailing are acidic and highly toxic.

In addition to CO₂, coal burning releases many toxic metals and radioactive elements. Coal is responsible for about 50 percent of atmospheric mercury, according to Ground Truth Alaska in 2019.

Oil, Oil Shale, and Tar Sands

Oil is formed from phytoplankton, microorganisms that lived in warm, shallow seas hundreds of millions of years ago. When they died, they sank to the bottom and were buried in sediments. Over many years, heat from the Earth and the pressure of overlying layers of sedimentary rocks transformed this into kerogen deposits containing a mixture of oil, gas, and solid tarlike substances.

Drilling for oil leads to environmental degradation at the drill site, but even more problematic are water pollution due to leaks during transportation and the major oil spills caused by accidents. Such accidents have been known to contaminate shorelines and estuaries, fouling beaches and murdering waterfowl and aquatic life.

Oil shale and tar sands are unconventional resources with a large potential if they can be recovered with reasonable social, economic, and environmental costs. Western Canada has an abundance of tar sands from which liquid petroleum can be extracted, but the process is expensive and the environmental problems severe. A typical site yielding 125,000 barrels daily leaves 15 million cubic meters (49 million cubic feet) of toxic sludge and contaminates billions of liters of water each year.

Vast deposits of oil shale, rich in kerogen, are located in the United States’ intermountain west. When heated to about 482 degrees Celsius (899 degrees Fahrenheit), the kerogen liquefies and can be separated from the stone. If the deposits could be extracted at a reasonable price and with acceptable environmental impact, the amount would be the equivalent of several trillion barrels of oil. The mining and extraction require huge amounts of water (a scarcity in the west), create air pollution, contaminate water, and leave mountains of loose, rocky waste.

Natural Gas

Natural gas and oil each contributed about one-third of the world's consumption of fuel in 2021, according to the Environmental Energy Study Institute. Coal contributed about 19 percent. Natural gas is the most rapidly increasing fossil fuel energy source because it is convenient, inexpensive, and cleaner burning than coal or oil. When combusted, it releases half the CO₂ as an equivalent amount of coal; substituting gas for coal thus helps reduce global warming. Although it is difficult to ship across oceans, the US has an abundant, easily available supply and the pipelines to transport it from source to end user. Natural gas, often released when oil is extracted, is burned off when no easy mechanism exists to deliver it to a user. Although transportation is problematic for some recoverable natural gas deposits, the world's resources are estimated to be about 300 trillion cubic meters (900 trillion cubic feet), a sixty-year supply assuming contemporary use rates.

An unconventional, untapped source of natural gas is the methane hydrate deposits located in arctic permafrost and beneath deep ocean sediments. At least fifty ocean deposits and a dozen land deposits, containing about 9 trillion metric tons (9.92 trillion tons) of methane, are known to exist. This is twice the combined amount of all coal, oil, and natural gas reserves. Although this is a possible future energy source, the complex technologies required to extract, store, and ship the methane hydrates are formidable.

Context

Fossil fuels promoted the Industrial Revolution, increased industrial productivity, contributed to capitalizing industry and farming, and, in 2022, provided 82 percent of the world’s energy, according to Earth.org. These resources, however, are nonrenewable; eventually, the production rate will decline to the point where it is no longer economically feasible to extract the remaining fuel. When a production peak occurs and decline begins, about half of the total resource has been recovered. Assuming a modest 1 percent or 2 percent annual increase in consumption, the number of years remaining until production peaks for the three main fossil fuels is hundreds of years for coal, up to fifty years for natural gas, and no more than forty years for oil. Given the imminent end of fossil fuel dependence, the contamination of air and water caused by their extraction and combustion, and the hazards posed by global warming, alternate renewable resources must be developed and incorporated into the energy mix expeditiously.

Key Concepts

• fossil fuel: any combustible deposit of carbon of biological origin created over millions of years of geologic history
• kerogen: complex compounds with large molecules consisting of carbon, hydrogen, oxygen, nitrogen, and sulfur
• methane hydrates: small bubbles of natural gas trapped in a crystalline ice matrix
• oil shale: a fine-grained sedimentary rock rich in kerogen
• tar sands: sands containing highly viscous asphalt-like oil that can be extracted by mixing the sands with hot water or steam

Bibliography

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Denchak, Melissa. “Fossil Fuels: The Dirty Facts.” Natural Resources Defense Council, 22 Oct. 2025, www.nrdc.org/stories/fossil-fuels-dirty-facts. Accessed 2 Dec. 2025.

"Fossil Fuels." Environmental and Energy Study Institute, 21 July 2021, www.eesi.org/topics/fossil-fuels/description. Accessed 26 Feb. 2025.

Higman, Bretwood, et al. "Mercury from Coal." Ground Truth Alaska, 12 Aug. 2019, groundtruthalaska.org/articles/CoalMercury/. Accessed 26 Feb. 2025.

Hinrichs, Roger. Energy: Its Use and the Environment. 2nd ed., Saunders, 1996.

Igini, Martina. "Fossil Fuels Accounted for 82% of Global Energy Mix in 2023 Amid Record Consumption: Report." Earth.org, 26 June 2024, earth.org/fossil-fuel-accounted-for-82-of-global-energy-mix-in-2023-amid-record-consumption-report/. Accessed 2 Dec. 2025.

Jaccard, Mark. Sustainable Fossil Fuels. Cambridge UP, 2006.