Carbon dioxide gets a bad rap. It is demonized and all too frequently identified as a pollutant and poison by global warming/climate change advocates.
But this chemical compound is essential to life. Flora and fauna depend on CO2 for their very life. Vegetation thrives through the process of photosynthesis. Chorophyll in plants utilize CO2, water and sunlight to make sugars which feed the plants. Carbon dioxide is dissolved in the waters of the world to support marine plant photosynthesis. Through photosynthesis, light energy is converted into chemical energy in the form of sugar which plants can consume.
In the process of photosynthesis, plants create sugars for their own use and give off oxygen for animate life. Animals, fish and people thrive on that oxygen which burns sugars for energy and in the process give off CO2 for vegetative life. Burning of sugar by animate life is called metabolism.
Given this cycle, carbon dioxide cannot be a pollutant or a poison under normal atmospheric conditions. Plants must have it available to sustain life. And CO2 is beneficial to humans. For example, carbon dioxide keeps the pH (slight akalinity) of the blood in proper balance.
Can CO2 kill a person? Yes, but breathing CO2 will not kill by itself. Lack of oxygen kills. Carbon dioxide in solid form is dry ice, which is used in the movies to create a foggy scene. The actors can breathe the evaporating dry ice without ill affects. The evaporating CO2 is odorless and colorless. The foggy appearance is created by water vapor that is condensed from the air by the evaporating dry ice. To evaporate, the dry ice must absorb heat from the air which is cooled. As the air cools, the water vapor in the air condenses into tiny water droplets. So we see water vapor (fog) and not the CO2.
If a person were in an enclosed room with enough evaporating dry ice, one could die. Since carbon dioxide is heavier than air, it could displace oxygen to the point that there is not enough oxygen to sustain life. This web site shows the effects on a person as the concentration of oxygen drops from the normal 20.9% to zero and the carbon dioxide concentration increases from the current normal 0.038% upward.
The chart shows a slight, but unnoticeable increase in the breathing rate at 1% concentration of CO2. To arrive at that concentration in the atmosphere, the amount of CO2 would have to increase more than 26 times.
A significant increase of carbon dioxide concentration has this effect on humans, but some plants grow very well in an environment of concentrated CO2.
Do not confuse CO2 with CO (carbon monoxide), which is a poison.