Don't worry- Co2 concentration would have to be 50 times what it is today to cause health problems.What we normally forget when talking about the amount of CO2, is the significance it has for the human (and other creatures) health. Above 425 ppm in the atmossphere the healthproblems will become more servere, because the blood will slowly be more acid. This will affect bloodpressure etc.
BTW: President Johnson was informed in 1965 about the dangers in increasing the amount of CO2.
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.