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:
“One’s condition on marijuana is always existential. One can feel the importance of each moment and how it is changing one. One feels one’s being, one becomes aware of the enormous apparatus of nothingness—the hum of a hi-fi set, the emptiness of a pointless interruption, one becomes aware of the war between each of us, how the nothingness in each of us seeks to attack the being of others, how our being in turn is attacked by the nothingness in others.”
—Norman Mailer (b. 1923)
“The Mississippi, the Ganges, and the Nile,... the Rocky Mountains, the Himmaleh, and Mountains of the Moon, have a kind of personal importance in the annals of the world.”
—Henry David Thoreau (1817–1862)
“You need an infinite stretch of time ahead of you to start to think, infinite energy to make the smallest decision. The world is getting denser. The immense number of useless projects is bewildering. Too many things have to be put in to balance up an uncertain scale. You can’t disappear anymore. You die in a state of total indecision.”
—Jean Baudrillard (b. 1929)
“The thought of you will constantly elevate my life; it will be something always above the horizon to behold, as when I look up at the evening star. I think I know your thoughts without seeing you, and as well here as in Concord. You are not at all strange to me.”
—Henry David Thoreau (1817–1862)