Here is the chart that shows CO2 levels compared to global temps: http://www.geocraft.com/WVFossils/PageMill_Images/image277.gif
You'll notice that during the Ordovician period, CO2 was well over 4000ppm, and sometimes upwards of 5000ppm, yet the temperatures near the end of that period were right at modern levels.
Also, if you'll carefully look at the CO2 levels vs. the temps during the Carboniferous period, CO2 had been precipitously dropping for ~50 million years, bottoming out at around 350 ppm... but look carefully at the CO2 line compared to the temp line... CO2 bottoms out and stays there for ~5 million years before you start to see a decrease in global temps... and CO2 was under 1000 ppm for several million years with zero change in global temps.
Also notice that that cooling cycle ended in the mid-Permian period, but the temps rose quickly, but CO2's rise followed this rise in temps, it didn't precede it.
Also notice that CO2 levels were steadily declining throughout the Cretaceous, yet that was coupled with rising global temps. You would think that if CO2 was so closely tied to global temps, that a precipitous drop in CO2 would be accompanied by a precipitous drop in temps and vice versa, but that has rarely been the case.
It seems clear that something else is driving these large scale warming and cooling cycles and no absolute connection can be made between global temperatures and CO2 levels, let alone a causal connection.
And even if we could draw such a connection, we would first have to look at where all this atmospheric CO2 was coming from in the first place... there were no factories, cars, or even humans during the high-CO2/high-temp periods, such as the Cambrian or Devonian. Considering that all the CO2 produced by humans is infinitesimal compared to what Earth naturally produces, it is highly doubtful, even if CO2 does contribute to global warming, that we could produce enough to appreciably affect global temperatures.
And finally, even if we could say that humans are significantly contributing the global warming, there is absolutely no proof that such would endanger life on Earth in any way, shape, or form. During the hottest periods of this Earth's history, life has seen the greatest explosions in diversity and growth. Indeed, hot temperatures are the norm for Earth and we should welcome the rising temperatures and the economic, agricultural, and biological benefits it is sure to bring.