Despite significant documentation of health issues due to CO2 in indoor environments, there is minimal awareness in the community. For spacecraft and submarines there are practical considerations that influence the recommended safe levels. Initial safe limits for the International Space Station were partly decided by engineering requirements (Cronyn et al. 2012) and submarine limits were balanced by the ability to surface and renew air quality. It seems that there has been little concern about low-level toxicity of CO2 because we have always had the back-up of an ambient atmosphere with low levels of CO2.
As mentioned previously the body compensates for high levels of CO2, through a combination of increased breathing, blood pH buffering, kidney and bone adaptations depending on the length of continuous exposure, until we can resume breathing lower levels of CO2.
One author suggests that blood pH would be reduced to dangerous levels, if there were no physiological compensation, at CO2 levels as low as about 430 ppm (Robertson 2006) implying that compensation would occur at this level. Ambient conditions may already be dangerously close to CO2 levels that will induce continuous body compensation. Moreover, there is strong evidence that, with chronic activity, compensation mechanisms can produce serious health issues such as kidney calcification and bone loss.
It is conceivable that these problems might appear at much lower levels of CO2 if compensation persisted for a much longer periods, for example living a whole lifetime in an elevated CO2 atmosphere of a climate changed future. In the final paper of the US Navy CO2 research program, Schaefer (1982) indicated that this issue had “become the concern of the Department of Energy and other US government agencies” although it appears to have been largely forgotten (or classified) since.
If allowed to persist, problems such as kidney calcification could lead to renal failure. In the extreme case lifespans could become shorter than the time required to reach reproductive age. This could threaten the viability of human and animal species without interventions such as the creation of artificial living environments.
The human species is already impaired in indoor environments and this is likely to get worse as rising outdoor levels of CO2 contribute to increased indoor concentrations. Furthermore, the incidence and prevalence of human kidney calcification (i.e. stones) is increasing globally with the rate highest for males (Romero et al. 2010). Although this may not be related, it is possible that rising office levels of CO2 is a contributing cause. As well there is evidence that CO2 toxicity contributes to a range of serious health issues including cancer, neurological diseases and sleep disorders, and is being experienced by individuals at the current ambient levels which are now 40% higher than pre-industrial levels. It seems likely that CO2 toxicity related to human-induced climate change is already having an unrecognised impact on population health.
From the evidence presented here, there appears to be current health impacts of rising CO2 levels and a significant risk of serious health issues arising in the human population at some time in this century.
This means that most humans could at this time be experiencing persistent body compensation for acidosis effects resulting in serious health problems. The risk for human and animal population health in the near-future is extremely high and should be communicated since global awareness of this issue may enable a change in CO2 emission activities.