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Greenhouse Gas Lifetimes in the Atmosphere
The insidious characteristic of most greenhouse gases is that they
have long lifetimes in the atmosphere, as measured by their "half life"
(the time for half of an initial amount released to be removed from the
atmosphere by natural processes). Carbon dioxide has a half life of about
120 years, methane 10.5 years, nitrous oxide 132 years, and the CFCs 16 to
more than 500 years, as shown in the accompanying table. So, for instance,
of the 20,000 kg of carbon dioxide you put into the atmosphere in 2004,
10,000 kg will still be contributing to enhanced greenhouse warming in the
year 2124, 5,000 kg will be remaining in 2244, 2,500 kg in 2361, ..., 1 kg
in the year 3684. At least 1 kg of carbon dioxide you put into the
atmosphere this past year will contribute to enhanced greenhouse warming
for the next 1,680 years!
From these examples, you can see that there are two factors that combine to determine the "global warming potential" (GWP) of a greenhouse gas: (1) radiation absorbing capacity, and (2) lifetime in the atmosphere. We will come back to GWP in a later lecture.
PREVIOUS: Effects of Adding Greenhouse Gases