Abstract
Concern is often voiced over the ongoing loss of atmospheric O2. This loss, which is caused by fossil-fuel burning but also influenced by other processes, is likely to continue at least for the next few centuries. We argue that this loss is quite well understood, and the eventual decrease is bounded by the fossil-fuel resource base. Because the atmospheric O2 reservoir is so large, the predicted relative drop in O2 is very small even for extreme scenarios of future fossil-fuel usage which produce increases in atmospheric CO2 sufficient to cause catastrophic climate changes. At sea level, the ultimate drop in oxygen partial pressure will be less than 2.5 mm Hg out of a baseline of 159 mmHg. The drop by year 2300 is likely to be between 0.5 and 1.3 mmHg. The implications for normal human health is negligible because respiratory O2 consumption in healthy individuals is only weakly dependent on ambient partial pressure, especially at sea level. The impacts on top athlete performance, on disease, on reproduction, and on cognition, will also be very small. For people living at higher elevations, the implications of this loss will be even smaller, because of a counteracting increase in barometric pressure at higher elevations due to global warming.
Highlights
Direct observations since 1989 confirm that the atmospheric O2 abundance has been decreasing steadily year by year (Keeling and Manning, 2014)
In either of these very extreme scenarios, atmospheric CO2 will rise above 1,200 ppm, associated with global warming of 5◦C or more, triggering climate changes considered “beyond catastrophic” (Xu and Ramanathan, 2017)
We have considered the possible impacts of these small O2 changes on human health, focusing on normal human function, athletic performance, disease, human reproduction, evolution, and cognition
Summary
Direct observations since 1989 confirm that the atmospheric O2 abundance has been decreasing steadily year by year (Keeling and Manning, 2014). The O2 loss is the flip side of the CO2 buildup from fossil-fuel burning, and is expected to continue throughout the fossil-fuel era. The CO2 buildup is a major environmental concern, with consequences for global climate via the “greenhouse effect,” for land plants via “CO2 fertilization,” and for marine organisms via “ocean acidification” (Ciais et al, 2013). In comparison to the CO2 buildup, the O2 loss is very small in relative terms. The measured O2 loss has been of comparable magnitude in moles, but this dwarfed by the massive atmospheric store of O2, which comprises 21% of air. The fact that O2 is measurably in decline raises concerns. Considering that O2 is essential for aerobic life, how sure are we that the continuing O2 decline won’t eventually have significant impacts?
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