This link illustrates that ice core studies are still just a theory by SOME scientists. Others do not subscribe to that theory. It certainly does not help the theory that this is a man-made climate change.
https://www.newscientist.com/articl...es-show-co2-rising-as-temperatures-fell/The conclusion from this:
"Jury still out
On a much bigger timescale, looking back 600 million years or more – when CO2 levels may have been as high as 5000 parts per million at times – there are substantial questions about whether the CO2-temperature correlation holds up. Some studies suggest that there are major discrepancies during at least two periods. Others claim the relationship holds up fairly well, including this recent study.
The jury is still out because the reliability of estimates of temperature and CO2 levels so long ago is extremely questionable."
