Emissions of Greenhouse Gases in the United States 1997 - Table 3. Numerical Estimates of Global Warming Potentials Compared With Carbon Dioxide

Table 3. Numerical Estimates of Global Warming Potentials Compared With Carbon Dioxide
(Kilogram of Gas per Kilogram of Carbon Dioxide)

Gas	Lifetime (Years)	Direct Effect for Time Horizons of
Gas	Lifetime (Years)	20 Years	100 Years	500 Years
Carbon Dioxide	Variable	1	1	1
Methane	12 ą 3	56	21	7
Nitrous Oxide	120	280	310	170
HFCs, PFCs, and Sulfur Hexafluoride
HFC-23	264	9,200	12,100	9,900
HFC-125	33	4,800	3,200	11
HFC-134a	15	3,300	1,300	420
HFC-152a	2	460	140	42
HFC-227ea	37	4,300	2,900	950
Perfluoromethane	50,000	4,400	6,500	10,000
Perfluoroethane	10,000	6,200	9,200	14,000
Sulfur Hexafluoride	3,200	16,300	23,900	34,900
Note: The typical uncertainty for global warming potentials is estimated by the Intergovernmental Panel on Climate Change at ą35 percent. Source: Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996), p. 121.