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:
“The importance of its hat to a form becomes
More definite. The sweeping brim of the hat
Makes of the form Most Merciful Capitan,
If the observer says so....”
—Wallace Stevens (1879–1955)
“A man’s personal defects will commonly have with the rest of the world precisely that importance which they have to himself. If he makes light of them, so will other men.”
—Ralph Waldo Emerson (1803–1882)
“Ah, that Time could touch a form
That could show what Homer’s age
Bred to be a hero’s wage.”
—William Butler Yeats (1865–1939)
“Elvis’ disappearing body is like a flashing event horizon at the edge of the black hole that is America today.”
—Arthur Kroker (b. 1945)