• Gases with a higher GWP absorb more energy, per pound, than gases with a lower GWP, and thus contribute more to warming the Earth.

For each greenhouse gas (GHG), a Global Warming Potential (GWP) has been calculated to reflect how long it remains in the atmosphere (on average) and how strongly it absorbs energy. Gases with a higher GWP absorb more energy, per pound, than gases with a lower GWP, and thus contribute more to warming the Earth.

The GWP, also known as “carbon dioxide equivalent,” allows comparisons of the global warming impacts of different gases. Specifically, it measures how much energy the emissions of one ton of a gas will absorb over a given period relative to the emissions of one ton of carbon dioxide (CO2). The time period usually used for GWPs is 100 years.

• CO₂, by definition, has a GWP of one regardless of the time period used, because it is the gas being used as the reference. CO₂ remains in the climate system for a very long time; CO₂ emissions cause increases in atmospheric concentrations of CO2 that will last thousands of years.
• Methane (CH₄) is estimated to have a GWP of 28–36 over 100 years. CH₄ emitted today lasts about a decade on average, which is much less time than CO₂. But CH₄ also absorbs much more energy than CO₂. The net effect of the shorter lifetime and higher energy absorption is reflected in the GWP. The CH₄ GWP also accounts for some indirect effects, such as the fact that CH₄ is a precursor to ozone (O₃), and O₃ is itself a GHG.
• Nitrous oxide (N₂O) has a GWP 265–298 times that of CO2 for a 100-year timescale. N₂O emitted today remains in the atmosphere for more than 100 years, on average.
• Fluorinated gases such as chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF₆) are sometimes called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO₂. The GWPs for these gases can be in the thousands or tens of thousands.