re: Getting Real on atmospheric CO2 increase.
The conjecture is in your questions, not the article. You're saying "maybe they did X, Y, or Z wrong - wouldn't that ruin their conclusion?"
My answer - maybe, but I doubt it - I expect this work has undergone a lot more scrutiny by people with more expertise than you and I. But if you're interested in answers to your questions, there are references in the article and the comments. I suggest you start with this one:
http://www.grida.no/climate/ipcc_tar/wg1/095.htm
