Your graph shows the Hirnantian Glaciation that occurred at the end of the Ordovician Period. The Hirnantian glaciation has been compared with the Snowball Earth Glaciations. It may have been extremely cold. It caused the Ordovician-Silurian mass extinction event which represents the second largest such event in geologic history. Approximately 85 % of marine species died.
The Hirnantian Glaciation occurred while the CO2 level was 15 times pre-industrial level (4,000+ppm). It lasted about 1.9 million years with CO2 levels that high.
How can intelligent people espouse Global Warming with scientific evidence like this in the books. It's insane!!
