Ever in the past? Really?
Here's the CO2 content of the atmosphere over the last 500 million years. If today's concentration is scaled to 1, then you can see that for most of that time, the atmosphere has had much more carbon dioxide in the atmosphere than it does today.
http://www.internationalskeptics.com/forums/imagehosting/114947b6b11f87495.jpg
The source of this graph is
‘Atmospheric carbon dioxide levels for the last 500 million years’ by Daniel H. Rothman (Massachusetts Institute of Technology), published in Proceedings of the National Academy of Sciences 99 (7), April 2, 2002, pp. 4167-4171. so no carping about "peer-reviewed science" will be entertained.
So your premise is simply false. Carbon dioxide in the current atmosphere is abnormally low compared to most of the Earth's history since probably the Cambrian explosion. Certainly since the Ordovian (whose latter stages were a deep ice age for millions of years by the way)
And it still has nothing to do with climate change except as a delayed response.