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.