re: #1 Gavriel

See, that’s what I was thinking (the 40%), but I reread the actual article (which isn’t very long) and I don’t think that is what the author is saying.

Unless he is able to measure the percentage of anthropogenic C02 in the atmosphere from 1850 onwards, then I think the authors are saying that there has been zero change in the C02 concentration (ppb) in the atmosphere since that time. I am looking back at different articles that show upward trending graph lines, and they are either global temperature or tons of C02 emitted. I need to find something measuring ppb C02 in the atmosphere over time.

It is my understanding that the ratio of carbon isotopes are different from natural and man-made sources of C02, so maybe he could make that type of analysis (but I am doubtful).