But are Kazars Europeans? I would take a Christian nation over a nation of white pagans or atheists. Imperial Russia was probably a better place to live than many European countries. Downfall almost certainly due to not pushing out “White” Kazars hard enough, rather than the vast number of nonwhite Christians.

The percentage of CO2 stays the same at altitude. The partial pressure changes and I think that that has more to do with your body not being able to offgass/respirate CO2 as efficiently. I don’t know if high CO2 environments are actually metabolic if they are artificial. I have seen it in plants, not animals. The mental performance hit of high CO2 seems real enough…