Main Greenhouse Gases

Multiple gases contribute to the greenhouse effect that sets Earth’s temperature over geologic time. Small changes in the atmospheric concentration of these gases can lead to changes in temperature that make the difference between ice ages when mastodons roamed the Earth, and the sweltering heat in which the dinosaurs lived.

Two characteristics of atmospheric gases determine the strength of their greenhouse effect.

The first is the Global Warming Potential (GWP), a measure of the radiative effect of each unit of gas over a specified period of time, expressed relative to the radiative effect of carbon dioxide (CO2). An amount of gas with high GWP will warm the Earth more than the same amount of CO2.

The second is the atmospheric lifetime, which measures how long the gas stays in the atmosphere before natural processes (e.g., chemical reaction) remove it. A gas with a long lifetime can exert more warming influence than a gas with a short lifetime (assuming the GWPs are equal).

The table below presents values for these two characteristics for major greenhouse gases. The GWP and atmospheric lifetime values are periodically updated by the scientific community as new research refines estimates of radiative properties and atmospheric removal mechanisms (sinks) for each gas. These values are from the Fourth IPCC Assessment Report (AR4) released in 2007, which are commonly used in international reporting, despite the Fifth Assessment Report updating them in 2014.


Fourth Assessment Report (Intergovernmental Panel on Climate Change IPCC, 2007).

Greenhouse gas Chemical formula Global Warming Potential, 100-year time horizon Atmospheric Lifetime (years)
Global Warming Potential and Atmospheric Lifetime for Major Greenhouse Gases
Carbon Dioxide CO2 1 100*
Methane CH4 25 12
Nitrous Oxide N2O 298 114
Chlorofluorocarbon-12 (CFC-12) CCl2F2 10,900 100
Hydrofluorocarbon-23 (HFC-23) CHF3 14,800 270
Sulfur Hexafluoride SF6 22,800 3,200
Nitrogen Trifluoride NF3 17,200 740

The table below shows the relative concentrations of these major greenhouse gases and their sources. Some gases (like CO2) are made by both natural and manmade processes, while others (like the fluorinated gases) are only the result of human industrial activity. CO2 is typically measured in parts per million because it is 1,000 times more prevalent than the other gases, but is shown as parts per billion in the table for consistency.


Atmospheric concentrations are all shown in parts per billion (ppb).


Fifth AssessmentReport (Intergovernmental Panel on Climate Change IPCC, 2014)

Greenhouse gas Major sources Pre-industrial concentration (ppb) 2011 concentration (ppb)
Sources and Concentrations of Major Greenhouse Gases
Carbon Dioxide Fossil fuel combustion; Deforestation; Cement production 278,000 390,000 (in 2011)
Methane Fossil fuel production; Agriculture; Landfills 722 1,803 (in 2011)
Nitrous Oxide Fertilizer application; Fossil fuel and biomass combustion; Industrial processes 271 324 (in 2011)
Chlorofluorocarbon-12 (CFC-12) Refrigerants 0 0.527
Hydrofluorocarbon-23 (HFC-23) Refrigerants 0 0.024
Sulfur Hexafluoride Electricity transmission 0 0.0073
Nitrogen Trifluoride Semiconductor manufacturing 0 0.00086

The Rise of Atmospheric Carbon Dioxide

*Carbon dioxide is quite stable in Earth’s atmosphere, but individual CO2 molecules are in near constant flux from difference reservoirs, such as the surface ocean, land biota, and the atmosphere. A commonly used estimate for CO2 lifetime is 100 years, but this really only reflects the lifetime of a portion of the atmospheric CO2 reservoir. Some portion has a lifetime of up to 1,000 years (IPCC 2007, FAQs).