"... atmospheric CO2 will be fatal to civilization at the current level of 405ppm ..."   What is your evidence that this statement is true?  Anything observational, or just more 'model talk' ?

The reason I ask is that the last time the world was ca.  400 ppm CO2 in the atmosphere was only about 3 million years ago (a geologic eyeblink) - and after that, the world lapsed into the Ice Ages (i.e., the Milankovitch cycle still trumped CO2).