I'm not sure about other animals, but 400ppm is a long way away from toxic for humanity. Poorly ventilated indoor environments can easily hit 1200-1500ppm. You've got to hit 70,000 to 100,000 ppm before you start running the risk of coma and death.
Interestingly some studies indicate that 1200ppm and higher might confer some mild cognitive impairment, even if it's a long way away from fatal. This has been used glibly to explain the poor decisions made in office rooms, but one does wonder what happens to humanity if global emissions make us slightly dumber.
Interestingly some studies indicate that 1200ppm and higher might confer some mild cognitive impairment, even if it's a long way away from fatal. This has been used glibly to explain the poor decisions made in office rooms, but one does wonder what happens to humanity if global emissions make us slightly dumber.