Well an actual reading of 380 for that data set would represent about a 5 standard deviation event. (data set for reference: http://cdiac.ornl.gov/ftp/trends/co2/vostok.icecore.co2) I think you missed the point. You need to look at the sampling methods (finely slicing pieces of ice and measuring the CO2 in the slice) and determine the error bars for the reading by considering the length of time that the measured sample represents. I think you will find that a sample that represents some distribution (possible Gaussian) of several centuries of actual CO2 measurements will have an error bar considerably larger than the 5 STDs you attributed to the current reading. Also bear in mind that the old the ice core, the more compression and the longer the interval that will be included into a single reading.
Unfortunately for us, the solution boils down to the argument I am having with cogitator which is: can the CO2 spike or not? If it can, how much and how comparable to today's spike which we can all pretty much agree has some anthropogenic component to it. If natural spikes occur, how much can be hidden in the poor sampling resolution.
Actually, I said something along those lines but with less detail in a later post and I agree completely with your view. I've also been looking at the much lauded temperature data from the models and I have some basic issues with that as well.
Even a cursory look at the chart indicates that our current peak deviation from the mean is roughly the same as the trough represented by the little ice age. That would make the current temperature a tail event, but nothing to be concerned about, particularly since a closed dynamic system is so prone to overshooting the mean. (A deep trough is usually followed by a tall peak etc) If over the next hundred years or so we continue to see the temperature increase, then I would say that there might be an issue, but as it stands I'm unconvinced that we have any systemic warming whatsoever, apart from normal.
I'm even more unconvinced given your posts regarding the disposition of CO2 over time. This isn't really all they have is it?