Q: Life expectancy of a CO2 molecule?

Quote:

Originally Posted by quitenormal 

With the build up of CO2 in the atmosphere, anyone know how long a CO2 molecule can expect to linger in the atmosphere before being broken down by carbon sinks, or some other natural process?

CO2 doesn't get broken down in the atmosphere, it gets absorbed by the oceans and photosynthesized into organic carbon.  The reasons for it being nonreactive in the air phase are that there really isn't anything with a lower free energy of formation relative to pure carbon (as graphite) and pure oxygen than CO2.  You probably don't care about that though.  :-) 

Anyway, on geological timescales, CO2 that gets put into the atmosphere ends up as bicarbonate in the ocean, at the expense of dissoving a little more limestone or silicic rock into the water.  However, the ocean mixing and biological sinks act much quicker than this, so that the accepted lifetime for anthropogenic CO2 is on order of 100 years.  This is, however, a squishy number and depends on how you want to define "lifetime."  

If you google "atmospheric lifetime CO2" you find links like this:

http://en.wikipedia.org/wiki/Greenhouse_gas#Atmospheric_lifetime

among many others which will give you far more, and better, details than I've done above.

CO2 is a very stable molecule.  If you had freshman chemistry, you probably remember a discussion about Lewis structures.  Atoms in molecules like to have 8 atoms in their outer shell. 

O=C=O

The carbon has 2 double bonds which gives it a total of 8 electrons.  Each oxygen has a double bond plus 2 lone pair giving each of them 8 elections.  The electrons can be shared so don't be too concerned if they don't all add up.  CO2 is a happy molecule and is not likely to change to anything else.