The Periodic Table of Scarcity and Abundance H Hydrogen
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Hydrogen: Harm to health and the planet

What harm does getting and using it do to bodies and the environment?

Making hydrogen released about 1 billion tonnes of carbon dioxide in 2025, because almost all of it comes from gas and coal. The gas itself is not toxic, but it burns easily, and leaked hydrogen adds to global warming indirectly.

Last updated 3 October 2026.

Environmental footprint

Emissions

11kg CO₂e per kg1

2023. Hydrogen from natural gas without carbon capture, 10 to 12 kg CO2-eq per kg H2, including upstream and midstream emissions. Coal routes emit 22 to 26 kg CO2-eq per kg.

Range 10 kg CO₂e per kg to 12 kg CO₂e per kg.

Energy

~ 160MJ per kg2

Our estimate, plant only, not cradle to gate. Natural gas reforming at 76% efficiency (lower heating value, IEA assumption for 2025): 120 MJ/kg of hydrogen divided by 0.76 is about 158 MJ/kg of natural gas input. Excludes the energy used to produce and transport the gas. Heating value from US DOE.

Hydrogen production released about 1,000 million tonnes of carbon dioxide in 2025. That is more than the emissions of Indonesia and France together3. The IEA count includes more than 300 million tonnes of carbon dioxide that goes into urea and methanol and is mostly released later. The IEA leaves out emissions from producing and moving the gas and coal3.

Other estimates are higher. IRENA gives about 1.3 billion tonnes a year of carbon dioxide equivalent, a measure that also counts other greenhouse gases4. The IEA counts zero emissions for by-product hydrogen from crackers. If it counts up to 10 kilograms of carbon dioxide per kilogram instead, the total is close to 1,200 million tonnes3.

Per kilogram, hydrogen from natural gas emits 10 to 12 kilograms of carbon dioxide equivalent, and hydrogen from coal 22 to 26. Between 75% and 95% of this is released at the plant, where carbon capture can reduce it1. Electrolysis has lower emissions than gas reforming only if the electricity emits less than about 200 to 240 grams of carbon dioxide per kilowatt-hour1.

Leaked hydrogen also warms the climate, because its reactions change methane, ozone and water vapor. The authors of a 2023 study used five chemistry models. They found that over 100 years, a tonne of hydrogen warms about 11.6 times (± 2.8) as much as a tonne of carbon dioxide5.

Health and the body

Hydrogen is essential to life. It is in water and in almost every molecule in living things6. About 10% of the human body by mass is hydrogen7.

Hydrogen gas is not poisonous. But in a closed space it can push oxygen out of the air and cause suffocation without warning8. Liquid hydrogen is very cold and can cause frostbite8.

The main danger is fire. Hydrogen burns in air at any mix from 4% to 75% by volume. Its flame is pale blue and almost invisible8. US emergency planning levels for hydrogen start at 65,000 parts per million in air. All of them are above 40,000 parts per million, the level at which hydrogen can burn8.

In the French ARIA database of accidents, 73% of the hydrogen events involved a fire or an explosion9. More detail is in the section on workers in the social chapter.

Sources

  1. 1

    International Energy Agency, 2024. Global Hydrogen Review 2024 , p. 61 (production by route); p. 203 (emissions intensities).

    Shares of natural gas, coal and by-product hydrogen in 2023, and emissions per kilogram by route.

    • unabated natural gas, which emits 10-12 kg CO2equivalent (CO2-eq)/kg H2
    • unabated natural gas, which emits 10-12 kg CO2equivalent (CO2-eq)/kg H2 … between 75% and 95% of these emissions occur directly at the point of production
    • unabated coal, which can have emissions of 22-26 kg CO2-eq/kg H2
    • should be below 200-240 g CO2/kWh for emissions to be lower than steam methane reforming
  2. 2

    International Energy Agency, 2026. Global Hydrogen Review 2026: Assumptions Annex , Production pathways table, hydrogen.

    Efficiency and capital cost of electrolysis, gas reforming and coal gasification.

    • Natural gas reforming ... Efficiency (LHV) ... 76%
  3. 3

    International Energy Agency, 2026. Global Hydrogen Review 2026 , Executive summary pp. 9-14; Middle East effects p. 21; Box 1.1 p. 20; targets p. 31; geological hydrogen pp. 36-42; demand pp. 44-57; transport p. 62; production pp. 83-85, 106; costs pp. 110-116; RED transposition p. 133; trade p. 143; policy p. 194; definitions pp. 257-258.

    Hydrogen demand, production routes, costs, emissions, trade and natural hydrogen for 2025.

    • hydrogen production generated around 1 000 Mt of CO2 in 2025 … exceeding the combined emissions of Indonesia and France
    • more than 300 Mt of CO2 used in the synthesis of urea and methanol, the majority of which is later emitted. This excludes upstream and midstream emissions
    • Assuming 0 kg CO2/kg H2 for hydrogen produced as a by-product in naphtha crackers and steam crackers. If a maximum of 10 kg CO2/kg H2 is assumed, emissions would increase to close to 1 200 Mt CO2
  4. 4

    International Renewable Energy Agency and World Trade Organization, 2024. Enabling global trade in renewable hydrogen and derivative commodities , Introduction; Market overviews (hydrogen, ammonia).

    World hydrogen production of about 95 Mt a year and emissions of about 1.3 Gt CO2-eq.

    • almost all hydrogen is produced from fossil fuels, emitting around 1.3 gigatonnes (Gt) of carbon dioxide equivalent
  5. 5

    Maria Sand and others, Communications Earth & Environment, 2023. A multi-model assessment of the Global Warming Potential of hydrogen , Abstract; Introduction; Results (hydrogen budget), Fig. 1.

    Hydrogen in the air, its sinks and lifetime, and its indirect warming effect.

    • its chemical reactions change the abundances of the greenhouse gases methane, ozone, and stratospheric water vapor … five global atmospheric chemistry models … We estimate a hydrogen GWP100 of 11.6 ± 2.8
  6. 6

    Royal Society of Chemistry, 2026. Hydrogen: element information, properties and uses .

    History, uses and biological role.

    • Hydrogen is an essential element for life. It is present in water and in almost all the molecules in living things
  7. 7

    OpenStax, Rice University, 2018. Biology 2e, 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks , Table 2.1.

    Hydrogen is about 10% of the human body by mass.

    • Hydrogen (H) 10%
  8. 8

    U.S. National Oceanic and Atmospheric Administration, 2026. Hydrogen (CAMEO Chemicals datasheet) .

    Fire and health hazards, flammable limits and protective action criteria.

    • Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air
    • asphyxiation without warning
    • cryogenic liquids may cause burns, severe injury and/or frostbite
    • Lower Explosive Limit (LEL): 4 % … Upper Explosive Limit (UEL): 75 % … burns with a pale blue, almost invisible flame
    • Hydrogen (1333-74-0) 65000 ppm 230000 ppm 400000 ppm LEL = 40000 ppm
  9. 9

    BARPI, French Ministry for the Ecological Transition (ARIA accident database), 2020. Hydrogen and transport: the risks should not be underestimated (Flash ARIA) .

    Three hydrogen accidents in 2019 and an analysis of 372 hydrogen events.

    • 73% of hydrogen incidents involved fires and/or explosions