But when you start trying to compare data obtained by different investigators, using different methods, you run into calibration and synchronization problems.

For example, you will note the foram data matches pretty well with the ice core data, but the precision is much lower. Who knows what it would look like if you zoomed in to the place where they overlap?

Besides, who knows what cataclysmic events were going on tens of millions of years ago? If you're interested in knowing the effect of anthropogenic CO2 on contemporary warming, the effects of Cretaceous asteroid strikes might not be very helprul.

I think everyone concedes that CO2 levels have varied enormously throughout earth's history. but the question which concerns us now is how do our activities contribute to this, how our civilization will be affected by them, as well as how rapidly these changes occur.

What we can see is an enormous jump in global CO2 has occurred since we started burning fossil fuels, and that most of that jump has occurred in a little over one human lifetime. Nothing like that has happened before, and it has never happened for reasons over which we have complete control.

Civilization is not being threatened by asteroid strikes or global vulcanism. We are doing it to ourselves by our reliance on electrical generation and internal combustion engines.