Rather than using .03%, let's use part per million so I don't have to convert stuff.
Minimum CO2 needed in atmosphere is 200 ppm.
Less than that, and plant life starts dying off.
1000 ppm will kill mammals and probably birds, fish, reptiles, amphibians, etc.
Maybe insects would be OK.
750 ppm makes humans "light headed" and somewhat confused, so let's say a maximum "safe" range for humans is probably 700 ppm.
Present CO2 level is approx. 380 to 385 ppm.
My guess, "optimum" level for CO2 would probably be 450 to 500 ppm.
It would be good for agriculture, and still be well within the safe range for human life.
That was a superb analysis.
For all of those who think that man has control of the planet,
I think we should double the current level of CO2 to reach ‘optimal’.