Different greenhouse gases can have different effects on the Earth's warming. The Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases. Carbon dioxide (CO2) was chosen by the Intergovernmental Panel on Climate Change (IPCC) as the reference gas and its GWP is set equal to one (1).
Two key ways in which greenhouse gases differ are how much energy they absorb and how long they stay in the atmosphere. So GWP becomes a measure of how much energy the emissions of 1 ton (or tonne or metric ton) in mass of a gas will absorb over a given period of time, relative to the emissions of 1 ton of CO2 in the same period of time. The larger the GWP, the more that given gas warms the Earth compared to CO2 over that time period.
The time period usually used is GWP100 (global warming potential over 100 years).
The IPCC keeps updating its GWP values with each of its scientific assessment reports as its scientific understanding improves. According to the IPCC, GWP values typically have an uncertainty of roughly ±35 percent.
See “What Greenhouse Gases Are Emitted by Human Activities?” (OneSharedEarth, 2020) for GWP values of different gases.
Gillenwater M, “What Is a Global Warming Potential? And Which One Do I Use?” (Greenhouse Gas Management Institute, 2015)
“Understanding Global Warming Potentials” (US Environmental Protection Agency, 2019)