Keeling discovered that CO2 in the Earth's atmosphere cycles daily. CO2 in air increases at night when plants shut down photosynthesis for the day, and then hits a low in the sunny afternoon as the plants go full steam turning CO2 into vegetables. A hemispherical seasonal cycle of CO2, low in summer and peaking in the winter for the same reason CO2 peaks at night: no greens at work to eat it. But a third trend discovered that that the lowest level of CO2, no matter where or when, never sink beyond 315 ppm. This is the the ambient, global CO2 level. And he noticed that every year it rose a little higher. By now, it's 350 ppm. Recently, other researchers have spotted in fourth trend: the seasonal cycle is increasing in amplitude. It is as if the planet breathes yearly, summer (inhale) to winter (exhale), and its breath is getting deeper and deeper. Is Gaia hyperventilating or gasping? >
Carbon dioxide is essential for internal respiration in a human body. Internal respiration is a process, by which oxygen is transported to body tissues and carbon dioxide is carried away from them.
Carbon dioxide is a guardian of the pH of the blood, which is essential for survival.
The buffer system in which carbon dioxide plays an important role is called the carbonate buffer. It is made up of bicarbonate ions and dissolved carbon dioxide, with carbonic acid. The carbonic acid can neutralize hydroxide ions, which would increase the pH of the blood when added. The bicarbonate ion can neutralize hydrogen ions, which would cause a decrease in the pH of the blood when added. Both increasing and decreasing pH is life threatening.
Apart from being an essential buffer in the human system, carbon dioxide is also known to cause health effects when the concentrations exceed a certain limit.
The primary health dangers of carbon dioxide are:
- Asphyxiation. Caused by the release of carbon dioxide in a confined or unventilated area. This can lower the concentration of oxygen to a level that is immediately dangerous for human health.
Volunteers exposed to 3.3% or 5.4% CO2 for 15 minutes experienced increased depth of breathing. At 7.5%, a feeling of an inability to breathe (dyspnea), increased pulse rate, headache, dizziness, sweating, restlessness, disorientation, and visual distortion developed. Twenty-minute exposures to 6.5 or 7.5% decreased mental performance. Irritability and discomfort were reported with exposure to 6.5% for approximately 70 minutes. Exposure to 6% for several minutes, or 30% for 20-30 seconds, has affected the heart, as evidenced by altered electrocardiograms.
Workers briefly exposed to very high concentrations showed damage to the retina, sensitivity to light (photophobia), abnormal eye movements, constriction of visual fields, and enlargement of blind spots. Exposure to up to 3.0% for over 15 hours, for six days, resulted in decreased night vision and
Exposure to 10% for 1.5 minutes has caused eye flickering, excitation and increased muscle activity and twitching. Concentrations greater than 10% have caused difficulty in breathing, impaired hearing, nausea, vomiting, a strangling sensation, sweating, stupor within several minutes and loss of consciousness within 15 minutes. Exposure to 30% has quickly resulted in unconsciousness and convulsions. Several deaths have been attributed to exposure to concentrations greater than 20%. Effects of CO2 can become more pronounced upon physical exertion, such as heavy work.