CO2 is measured in ppm (parts per milion).

125ppm and lower = all plants die.
After the last ice age we where at 150ppm.
At the start of the industrial revolution we where at 250ppm.
Today we are at 400ppm.

Ice core drill samples show that during "the age of dinosaurs" their was roughly between 1000-2000ppm for the most part.
Highest recorded during Barney time is 7000ppm.

2000ppm is regular inside a well ventilated high traffic building (school, mall, office etc).
8000-12.000ppm = head ache and not good in general.
Humans die between 30.000ppm and 40.000ppm

Now explain why I should worry.
Are you telling me Barney lived with significantly higher temperatures, how hot could it realy be?