<p>There are so many websites giving numbers for 'average' lifetimes of global-warming or ozone-depleting chemicals in the atmosphere, yet they are rarely explicit in their definition(s)...</p>
<p>For instance, methane is usually stated to last 12.4 years....  But is this half-life (of a large amount) or mean lifetime (of a single molecule)?</p>

CC BY-SA 4.0
2021-04-10T17:05:54.140Z
That would only hold for purely exponential decay. ["To evaluate the total greenhouse effect of a given gas molecule, one needs to know, first, how long it remains in the atmosphere and, second, how it interacts chemically with other molecules. This effect is calculated by injecting a pulse of that gas (e.g., 1 Tg) into the atmosphere and watching the added abundance decay as simulated in a CTM. This decay is represented by a sum of exponential functions, each with its own decay time."](https://archive.ipcc.ch/ipccreports/tar/wg1/133.htm)
Keith McClary
CC BY-SA 4.0
2021-04-15T06:11:55.013Z
a part of the answer to this is in your question,for gasses"average LIFETIME" and for radioactivity "Half-Life".
trond hansen
<atmosphere><climate-change><atmospheric-chemistry><global-weirding>
When it comes the average lifetime of chemicals in the atmosphere, is the mean lifetime ~1.4427 times the half-life? As with radioactivity?
Kurt Hikes
# When it comes the average lifetime of chemicals in the atmosphere, is the mean lifetime ~1.4427 times the half-life? As with radioactivity?

(Asked by: username_0 on 2021-04-10)

There are so many websites giving numbers for 'average' lifetimes of global-warming or ozone-depleting chemicals in the atmosphere, yet they are rarely explicit in their definition(s)...

For instance, methane is usually stated to last 12.4 years.... But is this half-life (of a large amount) or mean lifetime (of a single molecule)?

**Tags:** atmosphere, climate-change, atmospheric-chemistry, global-weirding

> **Comments:**
> **username_1**: That would only hold for purely exponential decay. ["To evaluate the total greenhouse effect of a given gas molecule, one needs to know, first, how long it remains in the atmosphere and, second, how it interacts chemically with other molecules. This effect is calculated by injecting a pulse of that gas (e.g., 1 Tg) into the atmosphere and watching the added abundance decay as simulated in a CTM. This decay is represented by a sum of exponential functions, each with its own decay time."](https://archive.ipcc.ch/ipccreports/tar/wg1/133.htm)  
> **username_2**: a part of the answer to this is in your question,for gasses"average LIFETIME" and for radioactivity "Half-Life".  

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