CARBON DIOXIDE AND HUMAN HEALTH
Pollutants are dangerous compounds for living beings.
Like water, CO2 is vital for life on Earth; thus, CO2 is not a pollutant or contaminant.
The specific heat of CO2 is 850 J/Kg K, which means carbon dioxide is able to absorb, store and emit heat. However, we cannot take this property into account when considering if CO2 is a pollutant because Water has a specific heat of 1,996 J/kg K, which means it is more efficient than CO2 at absorbing, emitting and storing heat. Water, like CO2, is vital for living beings.
CO2 densities have increased to more than 4000 ppmv in some geological eras, for example, during the Ordovician Period (Scotesse; 2002. Avildsen et al; 1998). When CO2 in the terrestrial atmosphere has reached densities this high in the past, life flourished abundantly. Consequently, we cannot consider such a high concentration of atmospheric CO2 as "pollution".
CO2 is the basic nutrient for plants and other photosynthetic organisms. Plants form the base of every food chain. Thus, the greater the density of CO2 in a given environment, the greater will be the production of food for plants and of the animals that feed on them.
In recent times it has become fashionable to relate CO2 to global warming, but water in its liquid or gaseous phase absorbs, stores and emits heat 4 times (400%) more efficiently than CO2. If, therefore, by this property water is not considered a pollutant, CO2 then cannot be considered a pollutant either.
Carbon Dioxide cannot intoxicate because it is a non-poisonous non-toxic substance. The data for CO2 related to human health are next:
- The density of CO2 in the atmosphere is 0.000747 Kg per cubic meter of air.
Normal CO2 Levels. The effects of an increased level of CO2 on an adult person in good health can be summarized as:
- Normal outside levels: 350 - 600 ppmv.
- Acceptable levels: up to 600 ppmv.
- Stiffness and odors: 600 - 1000 ppmv.
Data provided by the Occupational Safety and Health Administration (OSHA):
- Maximum allowed concentration in an 8 hour working period: 5,000 ppmv.
Extreme and Dangerous CO2 Levels:
- Nausea and increase of the cardiac and respiratory frequencies (from oxygen deficiency): 30,000 ppmv.
- The above plus headaches and sight impairment: 50,000 ppmv.
- Unconsciousness and death: 100,000 ppmv (OSHA).
As you can see, Carbon Dioxide does not intoxicate — it suffocates. All of the effects listed above correspond to asphyxia, not to poisoning; however, water and sand also asphyxiate and they are not considered pollutants either. Consequently, CO2 cannot be considered a pollutant merely because it asphyxiates.
Many have tried to tag CO2 as a pollutant simply because it is a product of fossil fuel combustion. However, CO2 is also a product of respiration, fermentation and putrefaction. In any case, the CO2 released by combustion of fossil fuels had previously been taken from the atmosphere by photosynthetic organisms and converted into organic compounds to be used in their metabolic functions as structures for reproduction, etc. When those photosynthetic organisms later died, their remains were subjected to strong geological processes that convert organic matter into oil, coal and methane. (Reccommended reading: The Holocene CO2 Rise: Anthropogenic or Natural?)
Those products are the fossil fuels that we use today to power our industries and vehicles; therefore, we are only returning CO2 to the place it once occupied during the Carboniferous Period. CO2 cannot then be considered a pollutant just because it is released back into the atmosphere by combustion of organic fuels and from many other natural processes unrelated with life.
Lodish, H., Berk, Arnold, et al. Molecular Cell Biology. 1999. W. H. Freeman and Company; New York, New York.
Boyer, Rodney. Concepts in Biochemistry. 1999. Brooks/Cole Publishing Company: Thomson Corporation; Stamford, CT.
Krupp, Marcus A. and Chatton, Milton J. Current Medical Diagnosis and Treatment. 1984; Lange Medical Publications. New York, NY.
Callen, Jean-Claude. Biologie Cellulaire. Des Molécules aux Organisms. Cours et questions de révision. 1999. Dunod. Paris, France.
EOS. Vol. 87, No. 3, 17 January 2006. Last revision on 01/1/2007: