CO2 and ice ages?

On Skeptical Science there appeared a blog today about "Understanding the CO2 lag in past climate change". They show a figure from the ice core records from Vostok.

I actually studied this particular data a few weeks ago since I noticed a small error in the figure presented on Wikipedia. If you look very carefully you will notice that the three graphs are not aligned properly!

I downloaded the data and made my own graphs. You may find all the figures and Octave/Matlab scripts here: http://www.ekstrand.org/climate/iceage20101122/.

About the main question, what conclusions are possible make from this data? I can think of three different things:

1) There is a systematic error in the data and CO2 and temperature should be aligned (if you didn't notice, there is a 600-1000 year delay in the CO2 levels after the temperature). CO2 is the primary control knob of the earths temperature. We have no explanation for the CO2 changes.

2) CO2 does not affect the temperature in any significant way. But the temperature of the oceans will control the CO2 in the atmosphere. We have no explanation for the temperature changes.

3) CO2 has a major impact on earths temperature: more CO2 will cool the earth.

On Skeptical Science they promote the theory that CO2 provides positive feedback. That means that something triggers an increase in temperature -> CO2 levels will rise -> more temperature rise. But we can't make that conclusion from this data since there is no explanation why the temperature rise stops and we get a temperature drop when the CO2 level increases far enough. Does the positive feedback turn negative all of a sudden?

You have to look at the graphs more than once. But after a while you will probably see what I wrote as item 3: The high CO2 level will actually push the earth into a new ice age. The temperature increase -> CO2 levels will rise -> as CO2 levels rise a negative feedback kicks in -> temperature decreases -> CO2 levels will fall after some time.

As far as I can tell, item 2 and 3 are both consistent with the theory outlined in Slaying the Sky Dragon - Death of the Greenhouse Gas Theory.

But item 1 and the description on the Skeptical Science blog does not appear to be reasonable from this data alone.