Muddy, yes I'm talking about times before man existed. We've got historical records showing increased volcanic activity pumping out CO2 and driving the climate significantly.
5000 ppm? If today CO2 was 5000 ppm, no one would care what the temperature was, because at 5000 ppm humans would see health effects including inflammation, reductions in higher-level cognitive abilities, bone demineralization, kidney calcification, oxidative stress and endothelial dysfunction.
Some of that starts even lower - it starts to get pretty bad at 1000ppm but there's many studies over the last hundred years that show students start to significantly lose the ability to learn at levels even as low as 600 ppm.
Humans have evolved to function under very specific circumstances.
