Carbon Dioxide Levels Lower Than Thought During Super Greenhouse Period [2].
Do high levels of CO2 in the past contradict the warming effect of CO2 [3]? There are also other drivers for climate besides CO2.
Life on earth have enjoyed unparallelled stability for past 10K years [4], so have no historical frame of reference for what happens if temperature breaks free from this zone.
Extinction events on earth for past 300 million years are associated with CO2 concentrations above 900 ppm [5], page 8.
[1] https://gml.noaa.gov/ccgg/trends/gl_gr.html
[2] https://www.dartmouth.edu/press-releases/carbon-dioxide-leve...
[3] https://skepticalscience.com/co2-higher-in-past-intermediate...
[4] https://earth.org/data_visualization/a-brief-history-of-co2/
[5] http://burro.case.edu/Academics/USNA229/impactfromthedeep.pd...
Where this gets complicated is wether earth is due another ice age or not as well.