15 December 2015
Several climate metrics are claimed to be fingerprints showing that human fossil fuel combustion caused the recent atmospheric carbon dioxide rise [1, 2]. These are:
1) Rising CO2 and falling oxygen
2) Falling 13C/12C ratio
3) CO2 is highest in ~800,000 years
04 December 2015
One of the key "fingerprints" of human influence in the rise of atmospheric carbon dioxide is the declination in d13C, the ratio between 13C/12C.
Fossil fuels are supposed to have more of the carbon-12 isotope in comparison to the carbon-13 isotope compared to what's "average" in the atmosphere prior to burning. Hence burning fossil fuels should decrease the 13C/12C ratio. And this is what's found.
But while human emissions of CO2 from fossil fuel combustion are only increasing with time (you should see what China's doing)...