An enhanced (or accelerated) greenhouse effect in the atmosphere which is causing global warming.
Because you might not be able to breathe in the high or low carbon dioxide because it really depends if you are use to it or not but you maybe be able to take it for other reasons.
well, you don't breath carbon dioxide, you breath oxygen
The suffix -capnia refers to conditions related to carbon dioxide levels in the blood or tissues. It is commonly used in medical terms to indicate conditions such as hypercapnia (high carbon dioxide levels) or hypocapnia (low carbon dioxide levels).
Microbes that prefer an atmosphere of carbon dioxide are known as carbon dioxide-loving or CO2-loving microbes. Some examples include certain types of bacteria and archaea that thrive in environments with high levels of carbon dioxide.
hypercarbia (overly high levels of carbon dioxide in the blood)
venus
Venus has high levels of carbon dioxide, with about 96.5% of its atmosphere composed of this gas. This thick CO2 atmosphere contributes to an extreme greenhouse effect, resulting in surface temperatures hot enough to melt lead. The high carbon dioxide levels are a key factor in Venus's harsh climate and lack of water.
It is Venus.
Lower carbon dioxide levels High levels of biodiversity New medicinal possibilities
Carbon dioxide never "takes over", it is made out of oxygen (and carbon-from sugar and fat)Carbon monoxide displaces oxygen from hemoglobin, reducing the bloods ability to carry O2 ... which can be severe enough to kill.
Lower carbon dioxide levels High levels of biodiversity New medicinal possibilities
Acute respiratory failure with high carbon dioxide levels