This is a pleasant surprise. Major new information as well. Turns out CO2 levels were around 300 ppm before the Ice Age. That means our new 400 ppm is a level not seem for millions of years.
It also suggests that once the present hysteria over CO2 has abated, it may well be appropriate to actually add more geological carbon to the atmosphere as a matter of course. The easiest will be to allow gas wells to generally flare and perhaps deliberately explode the frozen methane deposits.
Central to all this is a thriving surface ecology that also needs plenty of CO2. That will be our human objective.
Oldest ice-core ever drilled dates back 2.7 million years
Rich Haridy August 20, 2017