As atmospheric CO2 has doubled, has percentage of Carbon-14 halved?

Question

If the doubling of atmospheric CO2 has been caused by burning of fossil fuels, I would expect the percentage of carbon-14 to have halved, because fossil fuels have almost no carbon-14 (because they haven't been in contact with the atmospheric, which has it's carbon-14 continuously replenished by cosmic rays hitting the outer atmosphere).

On the other hand, if the warming has been caused by something else (another greenhouse gas or maybe solar variation), then I would expect the warming of the oceans to have released dissolved CO2 from the oceans. I would expect that CO2 released from the oceans to have the same carbon-14 content has the atmosphere (because there's been constant circulation between atmospheric & oceanic CO2).

A related question: has the amount of CO2 in the oceans doubled (as I would expect if the cause is burning of fossil fuels) or as it decreased slightly (as I would expect if some other source of warming had forced out dissolved CO2)?

In the past, carbon-14 percentage in the atmosphere (& in living things which are continuously exchanging carbon with the atmosphere) has been roughly constant because there's been equilibrium between creation of C-14 by cosmic rays in upper atmosphere & decay of C-14, which has a half-life of 5,000 years. Doubling CO2 doubled of C-14 creation, but didn't instantly double of C-14. Compare the 100-year doubling to the 5,000-year half-life. It should take a few thousand years to reach new equilibrium. In the meantime, I would expect the CO2 doubling to have halved the C14 concentration.

I was in error when I said doubling CO2 would double the rate of C-14 concentration. C-14 is formed by cosmic rays hitting nitrogen atoms (not carbon atoms). So doubling CO2 would not even increase the rate of C-14 creation. All the more reason to expect the C-14 percentage to halve halved.

Bob - your reference is talking about different isotopes:
My question was about C-14. Your reference is about C-13. My question remains unanswered.

From your reference:
"CO2 produced from burning fossil fuels or burning forests has quite a different isotopic composition from CO2 in the atmosphere. This is because plants have a preference for the lighter isotopes (12C vs. 13C); thus they have lower 13C/12C ratios. Since fossil fuels are ultimately derived from ancient plants, plants and fossil fuels all have roughly the same 13C/12C ratio "

Answer 1

Actually if you look at the curves and plot the temperature and the CO2 concentration you will find that for now and the last 10,000 years or so, the rising temperature always leads the increase in CO2 concentration. As the water surface warms, the CO2 comes out of solution. Al Gore just chose to mash his graph a bit so it looks like they change concurrently.

http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html

http://www.space.com/scienceastronomy/sun_output_030320.html

Answer 2

You're right, scientists have measured the isotopic ratios and it's consistent with the CO2 increase being largely due to fossil fuel combustion. More details here:

http://www.realclimate.org/index.php/archives/2004/12/how-do-we-know-that-recent-cosub2sub-increases-are-due-to-human-activities-updated/

By the way, the reason CO2 lagged in historical warmings was that the warming started for other reasons, and then the oceans released CO2. This time CO2 and the warming are going up together, one more proof that this warming is not natural, but is caused (mostly) by CO2. More here:

http://www.realclimate.org/index.php?p=13

EDIT:

I think the reason they use C13 is that C14 measurements are messed up by nuclear testing in the 50s-60s. The idea is the same, track fossil fuel emissions by isotopic ratios. Also C13 is much esier to measure than C14 because there's a lot more of it.

"From above-ground nuclear testing in the '50s and '60s, carbon-14 in atmospheric carbon dioxide shot up to nearly double what it was and has been slowly dropping toward pre-testing levels."

http://www.berkeley.edu/news/berkeleyan/1996/0501/globe.html

Google atmospheric carbon dioxide isotope global warmng for a lot more

Answer 3

I don't know the answer as I haven't seen any data on the subject. Your point is interesting, though. But, isn't the reason so-called fossil fuels have little carbon-14 is because over the time that these have existed all the carbon-14 in them has decayed - half-lives being what they are? In other words at the time they were living organisms there was the appropriate amount of carbon-14 (appropriate for 65 million or however many years ago, that is).

Answer 4

C-14 is created in the atmosphere by thermal neutrons in the atmosphere, so the increase in CO2 should not change the relative proportions of C-14 in this reserviour. Overall, as CO2 increases, the amount of C-14 should also increase.

As far as CO2 dissoling in ocean water, it is also increasing, causeing an increase in acidity. As CO2 goes up, so should dissolution and acidity.