Zeno, Nicky g, lastchance, and I made several very very long threads a while ago. It is filled with tons and tons of data from the Vostok ice core to radioisotope analysis of atmospheric carbon. The data is pretty solid and goes back hundreds of thousands of years. We ARE changing the % of carbon in the atmosphere. The carbon from fossil fuels is a different isotope than atmospheric carbon due to radioactive decay.
The only thing that is debatable is if this is a coincidence:
