Just for arguments sake, how many rings in the ice could possibly form in a years time? If the answer was 1 and always 1, this would be a great way of determining age. That is not the case though and the process is full of speculation. However, if it all happened the way you think it did, you would most likely be right about the level of co2 present at that time, as long as there wasnt other factors causing a spike in co2. I have also seen other studies on the levels of oxygen in the air now and thousands of years ago. Some believe the oxygen levels thousands of years ago was much higher than now, but those tests indicated if those levels were dropping at a steady rate, the earth could not possibly be over 10,000 years old or all the oxygen would be gone. All very interesting stuff and I fully intend to have a long talk with God about it as soon as I see him, that way ill know for sure.