Reservoir Times
The impact of greenhouse gases on the enhanced greenhouse effect is determined by their residence time in the atmosphere.
Atmospheric residence time represents the average amount of time the molecules of a greenhouse gas exist in air before it is removed or converted to something else. When atmospheric residence time is greater, the total impact of a greenhouse gas on global warming is larger.
The average residence time of atmospheric gases are:
1) water vapor (H2O)
9 days
2) carbon dioxide(CO2)
tens of thousands of years
3) methane (CH4)
12 ±3 years
4) chlorofluorocarbons (CFC)
decade to century
Consequently, anthropogenic greenhouse gases will impact global warming long after emission cut-backs are achieved.