If carbon dioxide (CO₂) were a politician, it would be worried about its bad press. The greenhouse gas is the primary pollutant responsible for climate change. Not only are scientists, leaders, and activists trying to halt its production, but they also want to capture it directly from the air and lock it underground where it will do less harm.
This gas, however, also plays a key role in life on Earth.
How CO2 supports life
Carbon helps form the protein and DNA found in living things. In the atmosphere, it combines with two oxygen molecules to form carbon dioxide.
Carbon dioxide is a crucial ingredient in photosynthesis, the process by which plants turn energy from the sun to turn water and carbon dioxide into sugar. In return, plants emit oxygen.
As carbon dioxide concentrations increase in the atmosphere, scientists are trying to hack photosynthesis to supercharge plant growth.
Laboratory studies show a higher concentration of the gas is making some plants grow more quickly in certain conditions, but in the wild and on outdoor farms the overall benefit is unclear.
In the Netherlands, some commercial greenhouses are experimenting with ways to route carbon dioxide emitted from industry into greenhouses where plants use the excess gas as fertilizer.
The first person to hypothesize the existence of carbon dioxide was 16th-century Belgian scientist Jean Baptiste van Helmont. After coal was burned, he noted, the weight of the remaining ashes was lower than the coal’s initial weight, meaning some mass had been lost in the process. Van Helmont was the first scientist to discern different gases present in the air we breathe.
In 1772 English scientist Joseph Priestly was also curious about the different gases in our air and identified the element oxygen. Priestly developed a way to inject water with carbon dioxide, effectively inventing sparkling water. He later isolated carbon monoxide.
It wasn’t until 1896 that Swedish scientist Svante Arrhenius linked the carbon dioxide emitted from burning fossil fuels to atmospheric warming.
A modern ingredient in the food industry
Carbon dioxide sold for commercial use is made as a byproduct of fermenting fuel like ethanol or producing ammonia.
When frozen, it forms dry ice, which is used to keep food cold over extended periods of time and quickly cool down hot machinery used during food production. Unlike water, which moves from a solid to a liquid to a gas as it warms, carbon dioxide moves directly from a solid to a gaseous state, avoiding messy puddles.
Once food has been produced, carbon dioxide is essential for preserving it in its packaging. High concentrations of the gas prevent bacteria from spreading. In baked goods, it penetrates air bubbles, preventing mold and fungus from forming.
When carbon dioxide comes into contact with any water present in packaging, the chemical reaction of the two substances lowers the environment’s pH, which also helps preserve baked goods.
And when that fresh, packaged food arrives at the grocery store, it’s a sustainable alternative to commercial refrigerants that help prolong shelf life. Since the 1980s, a potent greenhouse gas called hydroflourocarbons has been used as a refrigerant, but new refrigeration systems are able to effectively chill food with carbon dioxide.
From aiding surgeons to physicists, carbon dioxide plays a surprising role in modern science.
Pure carbon dioxide is sterile and non toxic; it has a number of applications for surgical procedures. When surgeons perform an abdominal procedure called a laparoscopy, they inflate the abdomen with the gas, allowing them to make a smaller cut and resulting in quicker recovery.
Similarly, during colonoscopies, it’s used to inflate the colon to more easily conduct the procedure.
The oil industry captures some of the carbon dioxide it emits and uses it to tap oil fields dry. When a well is almost exhausted, carbon dioxide is pumped in to incresae pressure and force remaining oil up to the surface. It also makes the oil less viscous and allows for easier removal.
In Meyrin, Switzerland, carbon dioxide is essential at the European Council for Nuclear Research’s (CERN) Large Hadron Collider, a particle accelerator that helps scientists study the particles that make up everything in the universe. Here, carbon dioxide is employed in certain types of instruments as a refrigerant gas, similar to what occurs in commercial refrigeration facilities, and as tool to study subatomic particles called muons.
In short supply
Just like when it was first injected into water to form carbonated beverages 200 years ago, carbon dioxide is essential for today’s wine and beer industry. It makes wine sparkle and beer froth, and it helps prevent the oxidation process responsible for making drinks taste flat.
Yet, despite its abundance in the atmosphere, commercially produced carbon dioxide has been scarce because of rising energy costs. As a result, some brewers have had to raise prices or scale down production. The shortage reveals just how important carbon dioxide is.
Both friend and foe, carbon dioxide is essential to life on Earth but crucial to limit.
A version of this story appeared in National Geographic’s Italian edition.