Carbon dioxide (CO2) is a trace gas in the Earth’s atmosphere. It is also found in large quantities dissolved in the world’s oceans. It is a byproduct of cellular respiration and is an essential component of photosynthesis—plants, algae, and certain types of bacteria remove it from the air in the process of carbon fixation.
Carbon dioxide is also a greenhouse gas produced as a byproduct of human activities. Burning fossil fuels—coal, oil, and natural gas—is the number one source of global CO2 emissions. In 2009, the world got more than 80% of its energy from fossil fuels. Sixteen countries got 99% or more of their energy from fossil fuels. Electricity, heat production, and transportation are the biggest sources of global CO2 emissions. Broken down by fuel type, the single largest source of global CO2 emissions is the consumption of coal, followed by petroleum, then natural gas.
CO2, like other greenhouse gases, is found naturally in the Earth’s atmosphere. Scientists believe that the concentration of CO2 in the Earth’s atmosphere remained relatively stable for thousands of years at roughly 280 parts per million (ppm). However, since the Industrial Revolution in the 18th century, human activity has significantly increased the atmospheric concentration. Today, the concentration of CO2 in the atmosphere stands at about 390ppm—an increase of over 30%.
This map layer shows average annual CO2 emissions per capita in metric tons for each country from 2006-2010. The data come from the United States Energy Information Administration.
For Further Exploration
Term Part of Speech Definition Encyclopedic Entry algae Plural Noun
(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.
anthropogenic source Noun
caused by people.
layers of gases surrounding a planet or other celestial body.
Encyclopedic Entry: atmosphere bacteria Plural Noun
(singular: bacterium) single-celled organisms found in every ecosystem on Earth.
substance that is created by the production of another material.
carbon cycle Noun
series of processes in which carbon (C) atoms circulate through Earth's land, ocean, atmosphere, and interior.
carbon dioxide Noun
greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.
carbon emission Noun
carbon compound released into the air through the burning of fossil fuels such as coal or gas.
carbon fixation Noun
method plants use to attach carbon dioxide from the atmosphere to a chemical (RuBP) in order to start the process of photosynthesis.
cellular respiration Noun
process by which cells turn nutrients into useful energy.
dark, solid fossil fuel mined from the earth.
having to do with the buying and selling of goods and services.
measure of the amount of a substance or grouping in a specific place.
destruction or removal of forests and their undergrowth.
to break up or disintegrate.
discharge or release.
to give off or send out.
fossil fuel Noun
coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.
greenhouse gas Noun
gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.
having to do with factories or mechanical production.
Industrial Revolution Noun
change in economic and social activities, beginning in the 18th century, brought by the replacement of hand tools with machinery and mass production.
Kyoto Protocol Noun
(1997) international agreement to reduce greenhouse gas emissions.
to lower the severity of a natural or human condition.
natural gas Noun
type of fossil fuel made up mostly of the gas methane.
Encyclopedic Entry: natural gas oil Noun
fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.
per capita Adjective
for each individual.
process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.