Recent research published in several scientific journals suggests levels of CO2 in Earth's atmosphere may reach 600 ppm by 2050 with toxic effects on all humans. Carbon dioxide is asphyxant gas even in the presence of enough oxygen toxic effects start to occur in the human body.
Here is an excerpt from a research paper I read recently you can download the full pdf file here.
"The blood pH of all humans would then be in the region where acidosis occurs and every human on Earth will suffer from chronic acidosis for all of their lifetime. Humans born after 2050 AD will begin to show the effects of acidosis from birth. The minimum effects of acidosis are restlessness and mild hypertension. As the degree of acidosis increases, somnolence and confusion follow. The second known effect of acidosis is the development of weaknesses in the bone structure of the body. It follows that a very large number of humans are likely to become incapable of physical activity taken for granted in present times and may be incapable of food production activities even with the help of machines. In consequence of these changes a very large number of humans are likely to die at an early age. The only animals which could successfully survive such an atmospheric level of carbon dioxide are sea mammals, such as seals, whose bodies have evolved to deal with very large amounts of CO2 in their blood. The effects of an increased atmospheric concentration of carbon dioxide will be enhanced within land continents like the USA, where there are air circulations which mix slowly with other air currents, e.g. from the oceans, at certain times of the year. The effects of the rise in atmospheric CO2 level will also be enhanced in cities within geographical depressions such as Mexico City and Athens. It is true that the general health of humans worldwide is greatly improved over that which existed prior to industrialization. As noted above, the present concentration of CO2 in the atmosphere and the predicted rise to 425.8 p.p.m. by 2050 AD are still within the limits of control by the human body. However, the accompanying changes in blood acidity caused by a rise in the atmospheric content of CO2 cannot be dismissed as insignificant when there has been no study of this aspect of the change in the atmosphere. At present, there is no effort to establish whether such changes are happening or are likely to happen two or more generations from the present date. Therefore the most serious effect of a rise in the CO2 content of the atmosphere is not necessarily global warming but the long-term effects on human health. The work above demonstrates that the rise in the atmospheric concentration of CO2 to the alternative predicted value of 720 p.p.m. cannot be allowed to occur if the health of all humans is be preserved."