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.
- From 2006 to 2010, the United States emitted the most total CO2 per person at 95.59 metric tons (105.3 tons). Chad emitted the least at under 0.132 metric tons (0.145 tons) per person. This means that the United States emitted 724 times as much CO2 per person as Chad.
- Human activities have contributed significantly to the rising concentration of CO2 in the atmosphere since the Industrial Revolution. For this reason, many scientists refer to climate change as an anthropogenic trend. Anthropos is Greek for human, while -genic means to produce or cause something. Anthropogenic climate change, therefore, means climate change caused by human activity.
- The United Nations Kyoto Protocol holds 37 industrialized countries—including Australia, New Zealand, and most of Europe—to reducing their greenhouse gas emissions. However, it imposes no restrictions on emerging economic powers like China and India. Since the United States never ratified the agreement and China was not covered in the terms, the Protocol does not address the two largest emitters of CO2. Canada, the seventh-largest emitter of CO2 in 2008, eventually withdrew from the agreement. Talks to extend the Kyoto Protocol at UN Climate Change Conferences in Copenhagen, Cancun, Durban, and Doha have resulted in the development of a second commitment period and a framework for a more potent treaty, set to begin in 2015, but it is not yet clear what reductions China or the United States will commit to.
- Coal is the fossil fuel that emits the most CO2 when used to generate electricity. Coal-burning facilities emit an average of 1,020 kilograms (2,249 pounds) of CO2 for every megawatt hour of electricity generated. Oil emits 758 kilograms (1,672 pounds) and natural gas emits 515 kilograms (1,135 pounds) of CO2 per megawatt hour of electricity generated. Alternative energy sources like wind or hydroelectric power emit a negligible amount of CO2 during electricity production.
- One of the best things people can do to mitigate carbon dioxide emissions is prevent deforestation. Forests act as carbon sinks, meaning they can store carbon dioxide before it reaches the outer layers of the Earth's atmosphere and contributes to global warming.
(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.
caused by people.
layers of gases surrounding a planet or other celestial body.
(singular: bacterium) single-celled organisms found in every ecosystem on Earth.
substance that is created by the production of another material.
series of processes in which carbon (C) atoms circulate through Earth's land, ocean, atmosphere, and interior.
greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.
carbon compound (such as carbon dioxide) released into the atmosphere, often through human activity such as the burning of fossil fuels such as coal or gas.
method plants use to attach carbon dioxide from the atmosphere to a chemical (RuBP) in order to start the process of photosynthesis.
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.
coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.
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.
change in economic and social activities, beginning in the 18th century, brought by the replacement of hand tools with machinery and mass production.
(1997) international agreement to reduce greenhouse gas emissions.
to lower the severity of a natural or human condition.
type of fossil fuel made up mostly of the gas methane.
fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.
for each individual.
process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.