06062011

Atmospheric carbon, man made Co2 measurement problems

One of the corner stones of the Climate change story is that man made carbon dioxide (Co2) is causing the climate to warm progressively over time, with a whole load of nasty consequences to boot.

Key to this is the ability to measure the amount of man made Co2 in the atmosphere, distinct from all the other Co2 running around in the normal atmospheric processes. The method goes something like this:

1. Plants absorb more C12 than C13 (by about 2%), - the C12 and C13 are isotopes of Co2 - same 'function', different atomic weights;
2. Plants are ‘deficient’ in C13, and so, by implication, given what fossil fuel is made out of, so should be the fossil fuel....
3. Therefore; if in the air C12 is increasing, compared to C13, we are burning fossil fuel more, and from that we can derive the amount of Co2 we are pumping into the atmosphere. Bingo, we did it!
   

Slight problem here, the C12/C13 ratio is not just effected by fossil fuel consumption... In fact quite of lot of existing processes (both natural and man made) also 'interact' with the ratio. Namely:

• C4 metabolism plants absorb more C13 than do C3 metabolism plants. Basically C4 plants are grasses, and grasses grow fast and include a lot of farmed field crops (like wheat). So we grow more C4 plants, the C13 goes down and the C12/13 ratio is effected in the same way as fossil fuel....
• The C12/C13 ratio varies in the fossil fuel source used (i.e coal and oil), see this paper ....
• Bacteria make methane with even less C13 in it than natural gas, after oxidization. Lots of bacteria of different types around....
  

These are just some of the known simpler to explain 'other things' that effect the C12/C13 ratio. If you would like to learn more see this excellent article.

Did the smoking gun just go 'pop' instead of bang?

Basically I think using just C12/C13 ratio as the 'smoking gun' that its humans polluting with Co2 is looking at serious risk of not being sound or significant.



This deserves a lot more direct research to ascertain if it is a valid mechanism for measuring human Co2 contributions. In the meantime, take human Co2 atmospheric measurements with a healthy dose of salt.