Carbon Dioxide as a Pollutant. The Risks of Rising Atmospheric CO$_2$ Levels on Human Health and on the Stability of the Biosphere

Carbon dioxide is a chemically active molecule that plays a vital role in Earth's ecosphere. CO$_2$ affects the acidity of seawater and has multiple negative effects on marine organisms. It is also a fundamental component of the photosynthesis and respiration reactions. There is evidence that higher CO$_2$ concentration can make the photosynthetic reaction faster in some plants, but also negatively impact the respiration reaction in aerobic lifeforms. The effects of this chemical and biochemical perturbation on the biosphere and on human health may be more important than generally highlighted in the discussion on CO$_2$, usually focused on thermal effects only. These considerations stress the importance of rapidly reducing CO$_2$ emissions and, whenever possible, remove the excess from the atmosphere. They also show that geoengineering technologies based on Solar Radiation Management (SRM) alone cannot be sufficient to contrast the negative effects of CO$_2$ anthropogenic emissions.