Carbon dioxide (CO2) makes up about 0.04% of the Earths atmosphere. While this may seem like a small amount, it plays a significant role in global warming. CO2 and water vapor act like a cap, making it more difficult for Earth to get rid of the energy it absorbs from sunlight. Without these gases to absorb the energy, our planet’s average surface temperature would have been near zero degrees Fahrenheit. CO2 is Earth’s most important greenhouse gas, a gas that absorbs and radiates heat. Unlike oxygen or nitrogen, which make up most of our atmosphere, greenhouse gases absorb heat radiating from the Earth’s surface and re-release it in all directions, including back toward Earth’s surface. Without CO2, Earth’s natural greenhouse effect would be too weak to keep the average global surface temperature above freezing.

The concentration of CO2 in the atmosphere has been increasing due to human activities such as the burning of fossil fuels. The concentration of CO2 in Earth’s atmosphere is currently at nearly 412 parts per million (ppm) and rising. This represents a 47 percent increase since the beginning of the Industrial Age, when the concentration was near 280 ppm, and an 11 percent increase since 2000, when it was near 370 ppm. The global average carbon dioxide set a new record high in 2022: 417.06 parts per million. Human activities have raised the atmospheres carbon dioxide content by 50% in less than 200 years.