Carbon dioxide makes up less than one half of one percent of the Earth’s atmosphere. However, it plays an important role in temperature regulation. Carbon dioxide is transparent to short-wave solar radiation, but not to long-wave infrared radiation. When energy rises from the ground, carbon dioxide traps infrared radiation and prevents some of it from leaving the atmosphere. This causes the Earth’s surface to become warmer.

Carbon dioxide reaches the atmosphere in several ways:


Sedimentary rocks often contain carbon. When tectonic plates collide, and one plate subducts beneath another, the rocks in the bottom plate are crushed. They recombine to form new minerals, releasing carbon dioxide. When a volcano erupts, it ejects this carbon dioxide into the atmosphere.



All organic matter is made of carbon, and carbon is released whenever living things die and decay.

When they are alive, living creatures constantly release carbon dioxide into the atmosphere.

This is part of a cyclical process. Plants take in carbon dioxide from the atmosphere and, using energy from the sun, combine carbon dioxide and water to create sugar and oxygen. This process is known as photosynthesis.

Plants and animals use these plant sugars for energy. To do this, they break the sugars down, releasing carbon dioxide and water. Plants can use some of this carbon dioxide and water for photosynthesis again.

Carbon Dioxide and People

Human activity is a very important source of atmospheric carbon dioxide. People have been causing carbon dioxide levels to increase since Neolithic times, when we developed agriculture and began clearing forests to make room for crops. By burning trees or chopping them down and allowing them to decay, we released large amounts of carbon dioxide into the atmosphere.

The effect of deforestation almost 10,000 years ago is miniscule compared to the effect of the deforestation caused by enormous modern agricultural and logging companies.

The burning of fossil fuels for industry over the past several hundred years has had a tremendous impact on carbon dioxide levels.

Although some of the excess carbon dioxide is absorbed by plants or dissolved in the oceans, about half remains in the atmosphere.

Scientists learn how the composition of the Earth’s atmosphere has changed over time by studying air bubbles trapped in ice near the poles. They’ve found that carbon dioxide levels in the atmosphere are they highest they’ve ever been in the past 800,000 years.