" Show me where CO2 levels have reached the concentration they stand at today. Also, note how the slope of the concentration is relatively large. Then think about whether you want to play this little game that you're REALLY interested in a little point of pre-historic climatology that is irrelevant."

"Average global temperatures in the Early Carboniferous Period were hot- approximately 22° C (72° F). However, cooling during the Middle Carboniferous reduced average global temperatures to about 12° C (54° F). As shown on the chart below, this is comparable to the average global temperature on Earth today!

Similarly, atmospheric concentrations of carbon dioxide (CO2) in the Early Carboniferous Period were approximately 1500 ppm (parts per million), but by the Middle Carboniferous had declined to about 350 ppm -- comparable to average CO2 concentrations today!"
http://www.clearlight.com/~mhieb/WVFossils/Carboniferous_climate.html

Maybe the reason our world is so cold in recent times is because we have continent at South Pole. This continent will move in next 10's of millions of years and Earth will get hotter.