Climate Change: the Rise in Atmospheric CO2 Poses No Risk for Acid-Base Balance in Humans.

Physiological sciences play an essential part in identifying the best solutions urgently needed to mitigate the eminent threats of global climate change and to understand the consequences for life on Earth (https://www.physoc.org/policy/climate-change-and-health/climate-emergency-research-gaps-and-policy-priorities/). There is general consensus that increased emission of CO2 is responsible for the worldwide elevation of temperatures, and consensus that this trend will continue in the near future.1 A number of recent publications raise concern that the rise in the atmospheric CO2 partial pressure, in itself, may impose debilitating effects on humans through disturbances of acid–base balance.2-4 In the following, we will present simple quantitative arguments why the rise in P C O 2 of atmospheric air over the past century is of absolutely no consequence for arterial P C O 2 nor for acid–base balance in mammals. Thus, while we agree that global change poses many severe problems for humanity, our ventilatory system and renal capacity for acid–base compensation are fully capable of dealing with even much higher CO2 emissions. Should the rise in P a C O 2 not be completely compensated by increased alveolar ventilation, the ensuing fall in arterial pH would activate compensatory actions in the kidney that would lead to a rise in plasma bicarbonate concentration that restores pH. This is illustrated in the Davenport diagram (Figure 1C) where it can be seen how an initial increase in blood P C O 2 (corresponding to Figure 1A) leads to a fall in pH and bicarbonate concentration along the non-bicarbonate buffer line (blue arrow leading from point 1 to 2). A complete respiratory compensation would return pH and bicarbonate to the initial state along the opposite route (black arrow "R"). If no respiratory compensation occurred, blood pH could still be completely compensated by the kidney along the isobar (from point 2 to 3 – indicated by black arrow "K"). All possible combinations of respiratory and kidney compensations are within the blue triangle. Figure 1D illustrates the same for an increase in blood P C O 2 corresponding to Figure 1B. Both man and mouse are illustrated because such small mammals may have slightly lower P a C O 2 .6 In any case, the possible disturbances in P C O 2 and acid–base balance seem insignificant. We conclude that it is difficult to envision how the future elevation of atmospheric CO2 levels, even in the worst-case scenario, could exert any debilitating effects on humans through disturbed acid–base balance. H. Malte and T. Wang conceptualized and wrote the manuscript draft and the final manuscript. H. Malte did the calculations and prepared the figure. There are no relevant acknowledgements for this article. None of the authors have any conflicts of interest to declare.