Quote from Ricter:
I think it's very unlikely that these natural cycles of "sourcing and sinking" changed the percentage of atmospheric CO2 so much in a century as what we're seeing now. [Barring some huge volcanic eruptions, or the like, at times] That, and the crossing of the 400 ppm level--I don't see that level on the long term chart that's been repeatedly posted here.
Maybe you're right. Let's wait and see.