What are global warming potentials?

Global warming potentials (GWPs) are used to compare the abilities of different greenhouse gases to trap heat in the atmosphere. This is done by calculating the amount of heat that is trapped by a specific quantity of a greenhouse gas and then comparing it to the amount of heat trapped by an equal quantity of carbon dioxide over a fixed period of time, which is usually 100 years. Carbon dioxide is used as the base for all the calculations, so its GWP is 1.1

Apart from radiative efficiency, the other main factor in determining a gas's GWP is its atmospheric lifetime. This is because the longer a greenhouse gas stays in the atmosphere the more it can enhance the greenhouse effect.2

The higher the GWP, the more heat the specific gas can keep in the atmosphere. Nitrous oxide for example has a long atmospheric lifetime (114 years). This combined with its heat-absorbing ability gives it a global warming potential of 298. So for equal quantities, nitrous oxide can warm the atmosphere much faster because it can trap 298 times more heat than carbon dioxide. Water vapor on the other hand is a strong greenhouse gas but has an atmospheric lifetime of only a few days, which combines to give it a negligibly small GWP.

Atmospheric lifetimes and GWPs for the main greenhouse gases are given in the following table:

Table 1: Global Warming Potentials of Greenhouse Gases

Source: Climate Change 2007: the Fourth Assessment Report (AR4), Intergovernmental Panel on Climate Change

More info:
What is a Global Warming Potential? And which one do I use? - Greenhouse Gas Management Institute
Understanding Global Warming Potentials - US EPA

• 1. Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland. Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007.
• 2. Elrod, Matthew J.. "Greenhouse Warming Potentials from the Infrared Spectroscopy of Atmospheric Gases." Journal of Chemical Education 76, no. 12 (1999): 1702.