Short answers, pulled from the story.
Carbon dioxide is a chemical compound made of molecules with one carbon atom covalently double bonded to two oxygen atoms. The carbon-oxygen bond is 116.3 picometers long, shorter than a typical single C-O bond, and the linear, centrosymmetric molecule has no electric dipole moment.
Carbon dioxide is a trace gas at 428 parts per million, about 0.043%, as of July 2025. That level has risen from pre-industrial levels of 280 parts per million, or about 0.028%, with burning fossil fuels as the main cause.
In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, which makes it act as a greenhouse gas. Its rising concentration from burning fossil fuels is the primary cause of climate change.
Exposure above 5% causes hypercapnia and respiratory acidosis, and concentrations of 7% to 10% may cause suffocation within minutes to an hour even with enough oxygen. Above 10% it can cause convulsions, coma, and death, and levels above 30% lead to loss of consciousness in seconds.
Around 1640 the Flemish chemist Jan Baptist van Helmont first described carbon dioxide as a discrete substance after burning charcoal in a closed vessel, coining the word gas. The Scottish physician Joseph Black studied its properties in the 1750s and named it fixed air.
About 230 million tonnes of carbon dioxide are used each year, mostly in the fertiliser industry for urea production at 130 million tonnes and in the oil and gas industry for enhanced oil recovery at 70 to 80 million tonnes. Other uses include food and beverage production, metal fabrication, cooling, fire suppression, and stimulating greenhouse plant growth.
Carbon dioxide travels in blood three ways: about 70 to 80% is converted to bicarbonate ions by carbonic anhydrase in red blood cells, 5 to 10% dissolves in plasma, and 5 to 10% binds to hemoglobin as carbamino compounds. The body produces roughly 2.3 pounds of carbon dioxide per day per person.