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)
“For even satire is a form of sympathy. It is the way our sympathy flows and recoils that really determines our lives. And here lies the vast importance of the novel, properly handled. It can inform and lead into new places our sympathy away in recoil from things gone dead. Therefore the novel, properly handled, can reveal the most secret places of life: for it is the passional secret places of life, above all, that the tide of sensitive awareness needs to ebb and flow, cleansing and freshening.”
—D.H. (David Herbert)
“God will take care of you for me. I am my God’s. I belong to him, I go a short time before you, and I want to meet all in heaven, both white and black.”
—Andrew Jackson (1767–1845)
“The whole world of thought lay unexplored before me,—a world of which I had already caught large and tempting glimpses, and I did not like to feel the horizon shutting me in, even to so pleasant a corner as this.”
—Lucy Larcom (1824–1893)