Coal
The late Carboniferous period, spanning roughly 359 to 299 million years ago, witnessed the rise of vast wetlands that would eventually become today's coal deposits. These ancient forests covered much of the tropics and were dominated by lycophyte trees with determinate growth patterns. Unlike modern trees, these plants did not tie up carbon in heartwood for long periods, allowing rapid accumulation of organic matter. When these plants died, they fell into low-lying areas where mud or acidic water protected them from oxidation. This process began the transformation known as coalification.
Dead plant matter converted first into peat within these swampy environments. Over millions of years, sediment buried these peat bogs deep underground. The heat and pressure of this burial caused the loss of water, methane, and carbon dioxide while increasing the proportion of carbon. Temperature proved far more critical than pressure or time in determining the final grade of coal produced. Subbituminous coal could form at temperatures as low as 60 degrees Celsius, whereas anthracite required temperatures of at least 270 degrees Celsius.
High oxygen levels above 30 percent during this era promoted intense wildfires that created charcoal indigestible by decomposing organisms. Bacteria and fungi had not yet evolved the ability to break down lignin, a complex polymer found in woody stems. This biological gap meant wood did not fully decay but instead became buried under sediment. About 300 million years ago, mushrooms and other fungi developed enzymes capable of degrading lignin, effectively ending the main period of coal formation on Earth.
The oldest intentional use of black coal dates back to a settlement on Landek Hill in Ostrava, Petřkovice, dating between 25,000 and 23,000 years BC. Neolithic inhabitants near Shenyang began carving ornaments from black lignite around 4000 BC. By 1000 BC, coal from the Fushun mine in northeastern China was already being used to smelt copper. Marco Polo described coal in the 13th century as "black stones... which burn like logs" and noted its abundance allowed people to take three hot baths weekly.
In Europe, the earliest reference to coal usage appears in the geological treatise On Stones written between 371 and 287 BC. Outcrop coal formed part of funeral pyres during Britain's Bronze Age between 3000 and 2000 BC. Romans exploited coals in major fields across England and Wales by the end of the second century AD. Coal cinders found in hearths of villas and forts in Northumberland date to around AD 400. A permanent brazier of coal once stood on the altar of Minerva at Aquae Sulis, now modern-day Bath.
The Industrial Revolution fundamentally changed coal consumption patterns. In 1700, five-sixths of the world's coal came from Britain alone. The steam engine replaced water wheels as the primary power source for industry. By 1947, approximately 750,000 miners worked in British mines before the last deep coal mine closed in 2015. Cooking and home heating with coal became widespread in London during the late sixteenth and early seventeenth centuries.
Bituminous coal contains about 84.4 percent carbon, 5.4 percent hydrogen, 6.7 percent oxygen, 1.7 percent nitrogen, and 1.8 percent sulfur by weight. This composition reflects the chemical makeup of precursor plants but undergoes significant changes during coalification. Dehydration removes water molecules while decarboxylation eliminates carbon dioxide. Demethanation reduces hydrogen content and increases saturation of the carbon backbone.
As carbonization progresses, aliphatic compounds convert into aromatic structures resembling graphene. Vitrinite derives from woody plant parts while lipinite comes from spores and algae. Inertite represents woody material burnt in prehistoric times. Huminite serves as a precursor to vitrinite and gets replaced by shiny vitreous forms during maturation. Bitumenization converts part of bituminous coal into hydrocarbon-rich gel.
Anthracite requires temperatures above 270 degrees Celsius and exhibits conchoidal fractures similar to thick glass breaking. Lignite remains the lowest rank and is most harmful when burned. Sub-bituminous properties range between lignite and bituminous types. Thermal coal generates electricity through steam while metallurgical coal produces coke for steelmaking at high temperatures.
China mines almost half the world's coal followed by India with about one-tenth. Indonesia exported 471 million tonnes representing 34 percent of global exports in 2022. Australia shipped 344 million tonnes while Russia moved 224 million tonnes that same year. China imported 301 million tonnes in 2022 making it the largest consumer and importer globally. India took 228 million tonnes and Japan received 184 million tonnes.
Russia increasingly directs coal exports from Europe toward Asia due to sanctions over its invasion of Ukraine. The International Energy Agency estimated global coal demand reached 5,946 megatonnes in 2024. About 8,000 megatonnes of coal are produced annually worldwide with roughly 90 percent being hard coal and 10 percent lignite. Nearly half comes from underground mines where accidents occur more frequently than surface operations.
In 2017, China recorded 375 coal mining related deaths alone. Metallurgical coal prices remain volatile and significantly higher than thermal coal because sulfur content must be lower. Coal futures contracts help producers and electric power industries manage risk. Some countries find new onshore wind or solar generation costs less than existing coal plants.
Globally coal is estimated to cause 800,000 premature deaths every year mostly occurring in India and China. Burning coal creates PM2.5 particulates considered the most dangerous form of air pollution. These particles trigger asthma strokes reduced intelligence artery blockages heart attacks congestive heart failure cardiac arrhythmias mercury poisoning arterial occlusion and lung cancer. Annual health costs in Europe from coal electricity generation reach up to €43 billion.
Breathing coal dust causes coalworker's pneumoconiosis known as black lung since dust literally turns lungs black. In the United States alone approximately 1,500 former employees die each year from breathing mine dust. A 2017 study found that for Britain during 1851-1860 increased coal use raised infant mortality by 6 to 8 percent. Early deaths due to air pollution from Chinese coal plants number around 200 per gigawatt-year where scrubbers are absent.
Huge amounts of waste result annually including fly ash bottom ash and flue-gas desulfurization sludge containing mercury uranium thorium arsenic selenium and other heavy metals. Coal ash contains radioactive elements uranium and thorium exposing nearby populations to radiation and environmental toxics.
Coal-fired power plants were the single largest contributor to global CO2 emissions growth in 2018 accounting for 40 percent of total fossil fuel emissions. Over fifteen billion tonnes of carbon dioxide emitted from burning coal in 2024 represented more than a quarter of all global greenhouse gas emissions. For every megawatt-hour generated coal emits around one tonne of carbon dioxide double the roughly 500 kilograms released by natural gas plants.
In 2016 world gross carbon dioxide emissions from coal usage totaled 14.5 gigatonnes. Underground fires burn an estimated 120 million tons of coal annually in China emitting 360 million metric tons of CO2 amounting to 2 to 3 percent of worldwide fossil fuel production. The head of the UN climate agency advised in 2013 that most coal reserves should remain unextracted to avoid catastrophic warming.
To keep global warming below 1.5 degrees Celsius or 2 degrees Celsius hundreds or possibly thousands of coal-fired power plants must retire early. In 2024 consumption peaked before expected but is projected to decline after 2030. Meeting Paris Agreement targets requires halving coal use from 2020 levels by 2030.
Many countries have reduced or eliminated coal power as part of worldwide energy transition efforts. The United Nations Secretary General asked governments to stop building new coal plants by 2020. International market trends depend heavily on Chinese energy policy since China accounts for more than half of global consumption. Preliminary analysis indicates global coal exports reached an all-time high in 2023 before declining about 12 percent through 2026.
Some coal-fired stations could become stranded assets risking financial instability if carbon bubbles burst. China Energy Investment risks losing half its capital while state-owned utilities like Eskom in South Africa build new plants. As of 2021 this activity may be causing a carbon bubble threatening economic stability globally. G7 members agreed in May 2021 to end direct government support for international coal generation.
In the European Union state aid to new coal plants was banned starting 2020 and existing plants from 2025. Coal subsidies totaled billions annually with Indonesia capping prices producers charge domestic consumers. Despite these pressures some regions continue financing new facilities despite mounting criticism over obstructing Paris Agreement aims.
Common questions
When did the Carboniferous period occur and how did it lead to coal formation?
The late Carboniferous period spanned roughly 359 to 299 million years ago. Vast wetlands covered much of the tropics where lycophyte trees accumulated organic matter that transformed into coal deposits through a process called coalification.
What are the specific temperature requirements for forming different types of coal?
Subbituminous coal could form at temperatures as low as 60 degrees Celsius while anthracite required temperatures of at least 270 degrees Celsius. Temperature proved far more critical than pressure or time in determining the final grade of coal produced during burial.
Who used coal earliest and when was black lignite first carved into ornaments?
Neolithic inhabitants near Shenyang began carving ornaments from black lignite around 4000 BC. The oldest intentional use of black coal dates back to a settlement on Landek Hill in Ostrava, Petřkovice, between 25,000 and 23,000 years BC.
How many miners worked in British mines before the last deep coal mine closed in 2015?
By 1947 approximately 750,000 miners worked in British mines before the last deep coal mine closed in 2015. In 1700 five-sixths of the world's coal came from Britain alone before consumption patterns changed with the Industrial Revolution.
What percentage of global carbon dioxide emissions came from burning coal in 2024?
Over fifteen billion tonnes of carbon dioxide emitted from burning coal in 2024 represented more than a quarter of all global greenhouse gas emissions. Coal-fired power plants were the single largest contributor to global CO2 emissions growth in 2018 accounting for 40 percent of total fossil fuel emissions.