Of course, the fact that modern humans are the source of new carbon is stunningly obvious if you look at the shape of the concentration curve against time.
I'd always heard that carbon isotopes were the clincher, but when asked for evidence, all I'd been able to find was an unsupported assertion in the IPCC TAR, which always irked me. Of course, IPCC has a rule of not referring to anything that isn't published in peer review, and this bit of data is so widely known and accepted among anyone who might conceivably care in a professional capacity that perhaps it appears nowhere in the primary literature.
A sort of catch-22!
Fortunately, Tamino has found a source for enough raw data to make the point.
Anyone who claims the CO2 (never mind the warming) is natural variability hasn't had a leg to stand on for a long time. This is just the icing on the cake.
So (to get meta again for a second) I am not arguing against logical argument. It's necessary, just not sufficient, is all I'm saying. It's nice to finally have solid evidence to point to on this matter.