Importance of Time Horizon
Note that a substance's GWP depends on the timespan over which the potential is calculated. A gas which is quickly removed from the atmosphere may initially have a large effect but for longer time periods as it has been removed becomes less important. Thus methane has a potential of 25 over 100 years but 72 over 20 years; conversely sulfur hexafluoride has a GWP of 22,800 over 100 years but 16,300 over 20 years (IPCC TAR). The GWP value depends on how the gas concentration decays over time in the atmosphere. This is often not precisely known and hence the values should not be considered exact. For this reason when quoting a GWP it is important to give a reference to the calculation.
The GWP for a mixture of gases can not be determined from the GWP of the constituent gases by any form of simple linear addition.
Commonly, a time horizon of 100 years is used by regulators (e.g., the California Air Resources Board).
Read more about this topic: Global-warming Potential
Famous quotes containing the words importance of, importance, time and/or horizon:
“In my public statements I have earnestly urged that there rested upon government many responsibilities which affect the moral and spiritual welfare of our people. The participation of women in elections has produced a keener realization of the importance of these questions and has contributed to higher national ideals. Moreover, it is through them that our national ideals are ingrained in our children.”
—Herbert Hoover (1874–1964)
“Kitsch is the daily art of our time, as the vase or the hymn was for earlier generations. For the sensibility it has that arbitrariness and importance which works take on when they are no longer noticeable elements of the environment. In America kitsch is Nature. The Rocky Mountains have resembled fake art for a century.”
—Harold Rosenberg (1906–1978)
“It was a time of madness, the sort of mad-hysteria that always presages war. There seems to be nothing left but war—when any population in any sort of a nation gets violently angry, civilization falls down and religion forsakes its hold on the consciences of human kind in such times of public madness.”
—Rebecca Latimer Felton (1835–1930)
““Dark times” is what they call it in Norway when the sun remains below the horizon all day long: the temperature falls slowly but surely at such times.—A nice metaphor for all those thinkers for whom the sun of mankind’s future has temporarily disappeared.”
—Friedrich Nietzsche (1844–1900)