What Is CO2?


Carbon dioxide is a naturally occurring substance composed of one atom of carbon (C) and two atoms of oxygen (O2). Its chemical formula is CO2. CO2 is gas under normal conditions.Learn More

CO2 Exists Naturally

CO2 occurs naturally in small amounts (about 0.04%) in the Earth's atmosphere.1

As a major greenhouse gas, CO2 helps create and maintain the natural greenhouse effect that keeps our planet hospitable to life.

CO2 is essential to plant life. Plants take in CO2, exhale the oxygen, and use the carbon to live and grow. When the plant dies or burns, the carbon recombines with oxygen in the atmosphere, and CO2 is formed again. This process is a key part of the global carbon cycle.

CO2 is a by-product of our body’s metabolism. Our lungs absorb oxygen from the air we breathe and exhale CO2 as a waste product of cellular respiration.

CO2 is produced naturally by processes deep in the earth. This CO2 might be trapped in underground geologic CO2 deposits similar to the underground deposits of oil and natural gas. Or it might be released at the surface by volcanoes or through natural ground seeps.

Naturally carbonated waters have historically been highly sought after for their supposed curative properties because these waters are high in mineral content.

Some bottled water is from naturally carbonated springs. Some examples are Apollinaris, Badoit, Gerolsteiner, Wattwiller, Ferrarelle, Borsec, and Perrier.

Humans Use and Make CO2

CO2 is added to soft drinks to make them bubbly.

Dry ice (frozen CO2) is used to keep things cold.

CO2 is also used in fire extinguishers (CO2 displaces the oxygen the fire needs to burn).

Every day, millions of tons of CO2 are injected into underground geologic zones to help produce oil in a well-known industry practice called "CO2 flooding" or enhanced oil recovery.

Is CO2 a Pollutant?

CO2 formed by human action is called anthropogenic CO2. Plowing the land, making cement, and burning fossil fuels for energy all create anthropogenic CO2, which adds carbon to the global carbon cycle. Between 1751 and 2018, approximately 1600 billion metric tons of CO2 has been emitted to the atmosphere from these sources.2 This is raising concerns about climate change.

The U.S. Environmental Protection Agency has ruled CO2 a pollutant in order to be able to regulate anthropogenic CO2 emissions from human activities under the Clean Air Act of 1970.

Energy, CO2, and Our Carbon Footprint

  1. nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html (accessed January 2020).
  2. Emissions from fossil fuels and cement production from the Carbon Dioxide Information Analysis Center at AppState, https://energy.appstate.edu/research/work-areas/cdiac-appstate (accessed January 2020)