[Drammach]

What is the ‘optimal’ level of CO2 in the atmosphere? (it is currently .03%)

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.

[Repeal The 17th]

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’.

[ForGod'sSake]

Basic Information about Concentrations of CO₂ in Air

• 1,000,000 ppm of a gas = 100 % concentration of the gas, and 10,000 ppm of a gas in air = a 1% concentration.
• At 1% concentration of carbon dioxide CO₂ (10,000 parts per million or ppm) and under continuous exposure at that level, such as in an auditorium filled with occupants and poor fresh air ventilation, some occupants are likely to feel drowsy.
• The concentration of carbon dioxide must be over about 2% (20,000 ppm) before most people are aware of its presence unless the odor of an associated material (auto exhaust or fermenting yeast, for instance) is present at lower concentrations.
• Above 2%, carbon dioxide may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations.
• If exposure continues at that level for several hours, minimal "acidosis" (an acid condition of the blood) may occur but more frequently is absent.
• Breathing rate doubles at 3% CO₂ and is four times the normal rate at 5% CO₂.
• Toxic levels of carbon dioxide: at levels above 5%, concentration CO₂ is directly toxic. [At lower levels we may be seeing effects of a reduction in the relative amount of oxygen rather than direct toxicity of CO₂.]