Facebook Twitter Tumblr Close Skip to main content
A Project of The Annenberg Public Policy Center

CO2 makes up a small fraction of the gases in the atmosphere, but is very powerful

About 99% of the Earth’s atmosphere is made of just two gases: oxygen and nitrogen. By comparison, the amount of carbon dioxide — which at more than 400 parts per million, is the highest it’s been in several million years — may seem small. It’s equivalent to just 0.04% of the atmosphere.

This fact is often cited by people who are trying to falsely claim that CO2 isn’t responsible for global warming. These individuals also often add that the amount of CO2 from humans is just a fraction of that already small total. 

But just as a poison can be deadly even in a tiny amount, small relative amounts of carbon dioxide are very meaningful to the planet. CO2 and several other trace gases, including methane, nitrous oxide and ozone, are greenhouse gases that trap heat from the sun. Increases in these gases, mostly from burning fossil fuels, are responsible for the rapid warming the planet has experienced since the Industrial Revolution.

Prior to industrialization, for example, the CO2 concentration was around 280 ppm. Today, it’s about 420 ppm — a 50% increase in just a few centuries. That means about a third of the CO2 in the atmosphere is from human activity. 

It’s worth noting that although the amount of CO2 humans are adding to the atmosphere is much smaller than the total amount of CO2 that the planet cycles through each year, it’s the net gain that matters. The human contribution — from fossil fuel use, agriculture and land-use changes such as the destruction of forests — is creating the imbalance that is leading to a surplus of CO2 and the resulting planetary warming.