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:
“We must continually remind students in the classroom that expression of different opinions and dissenting ideas affirms the intellectual process. We should forcefully explain that our role is not to teach them to think as we do but rather to teach them, by example, the importance of taking a stance that is rooted in rigorous engagement with the full range of ideas about a topic.”
—bell hooks (b. 1955)
““I’m sure you’ve often wished there was an after-life.” Of course I had, I told him. Everybody has that wish at times. But that had no more importance than wishing to be rich, or to swim very fast, or to have a better-shaped mouth.”
—Albert Camus (1913–1960)
“People who don’t know how to keep themselves healthy ought to have the decency to get themselves buried, and not waste time about it.”
—Henrik Ibsen (1828–1906)
“The bird is lost,
Dead, with all the music:
While sunsets heard the brain’s music
Faded to last horizon notes.”
—Owen Dodson (b. 1914)