Starting a timeline at 20k years ago when we were, or near to the peak of the Last Glacial Maximum is not only deceptive, and most of Canada was under the giant Laurentide & Cordilleran glaciers, as was much of Asia, is frankly unscientific and alarming.
A simple response to that is a graph of glaciation cycles https://opentextbc.ca/geology/chapter/16-1-glacial-periods-i...
In respect to CO2 https://mashable.com/article/co2-earth-history-climate-chang... or any longterm measurement of CO2 levels, however, speaking from a scientific perspective there is a great deal incorrect with current processes of measuring CO2 levels from ancient ice cores.
During the Last Glacial Maximum, many plants showed evidence of CO2 starvation also, which is part of the reason why desertification increased so much during the LGM.