index > Today's Earth, Our Future > 4. The earth as a greenhouse > Where Does CO2 Come From?
 
Where Does CO2 Come From?So far we've learned that carbon dioxide (CO2) acts as the "earth's sweater." The sweater of CO2 is becoming thicker. As a result, the earth is getting warmer. Then, what exactly is CO2? CO2 is a gas which makes up only about 0.03 percent of the air. One carbon atom and two oxygen atoms form one CO2 molecule. CO2 is produced by burning materials containing carbon, such as wood, paper, oil, coal and gas. When they burn, the carbon in the materials combines with oxygen in the air to form CO2. It may surprise you to learn that animals, including us, also produce CO2 and consume oxygen as we breathe. It has been this way from the early days of the earth. Animals breathe in oxygen and breathe out CO2, while plants do the opposite, taking up CO2 and producing oxygen during photosynthesis (a chemical process by which green plants use energy from the sun to produce their food). This balance of breathing and photosynthesis kept the overall amount of CO2 in the air stable for a long time. But the amount of CO2 has been increasing dramatically over the last several decades all over the world. If it keeps increasing at this rate, the CO2 concentration in 2100 will have more than doubled from its current level. So, scientists are concerned that the average temperature of the "thickly dressed" earth will go up 3-6 degrees Celsius. Seen from the long history of the earth, "several decades" is a very short time, like the wink of an eye. How has CO2 increased so rapidly in such a short time? Where does this CO2 come from? Out of all the CO2 emissions in Japan, about 40 percent comes from the industrial sector such as companies or factories. You cannot see CO2 like thick smoke rising from a chimney, but a large amount of CO2 is emitted when something is burned or machinery is operated by electricity in industrial plants or factories.
The second largest emitter is the transportation sector, which involves carrying people and goods, and accounts for about 20 percent of the CO2 emissions. Total CO2 emissions from cars are much larger than those from planes or trains. Although there are many trucks that carry products from factories to stores, about half the CO2 emissions in the transportation sector is from cars. About 13 percent of the CO2 emissions is from households. You also produce CO2 from the time you get up to the time you go to bed (in addition to breathing). For example, you produce CO2 by watching TV, turning on lights and air-conditioners, taking a bath, washing clothes, or cooking. But don't imagine CO2 rising up from a television set! To make electricity for televisions, electric power plants burn oil, coal, and natural gases. This is when CO2 is produced. Now you're getting the picture, aren't you? The more you use convenient electric home appliances, the more CO2 is released. The amount of CO2 emissions also increases if you use a car often because of its convenience and comfort.
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   4. The earth as a greenhouse
   
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