Oh, no? There were at least two prior times in the geologic record (450 million and ~180 million) when CO2 levels were over ten times what they are now and they were both during major cold spells. (the top graph shows CO2 concentrations, the bottom, temperatures)
"The above chart shows the range of global temperature through the last 500 million years. There is no statistical correlation between the level of carbon dioxide in the atmosphere through the last 500 million years and the temperature record in this interval. In fact, one of the highest levels of carbon dioxide concentration occurred during a major ice age that occurred about 450 million years ago. Carbon dioxide concentrations at that time were about 15 times higher than at present.":
http://www.tcsdaily.com/article.aspx?id=010405M