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Ask Dr. Global Change
Global Carbon Cycle
How does respiration by humans and animals affect carbon dioxide levels in atmosphere?
Last updated 14 July 2002
Originally answered 14 July 2002
Full Question
How does respiration by humans and animals affect carbon dioxide levels in the atmosphere?
Answer
Humans exhale about 1 kg of carbon dioxide per day (http://cdiac.esd.ornl.gov/pns/faq.html). The exact amount depends on age, sex, size, and most importantly activity level. Multiply that by a world population of six billion and you get a very large number.
However, human exhalation of carbon dioxide is part of a closed system. There can be no net addition of carbon dioxide to the atmosphere because the amount of carbon dioxide we exhale can’t be greater than the carbon we put into our bodies by eating plants, or eating animals that eat plants. The plants got the carbon from the atmosphere via photosynthesis.
This closed system is true for any animal, not just humans. It is also true for a growing population. You simply can’t have more animals than there are plants to support those animals.
The reason why burning fossil fuels is a concern is because it is not a closed loop over human time scales. Extracting coal and oil and burning them puts carbon back into the atmosphere that plants removed millions of years ago.
The above entry is posted under the following topic(s): Global Carbon Cycle • Human Contributions and Responses • To link uniquely to the question and answer displayed above, please refer to this page where they are permanently posted. |
Excluding fossil fuel combustion, how else do humans affect the carbon cycle?
Last updated 15 November 2001
Originally answered 15 November 2001
Full Question
Excluding fossil fuel combustion, how else do humans affect the carbon cycle?
Answer
Data on CO2 emissions from all sources, including cement manufacture, can be found in the Environmental Protection Agency (EPA) report “EPA Inventory (2002) of U.S. Greenhouse Gas Emissions & Sinks: 1990-2000” http://www.epa.gov/oppeoee1/globalwarming/publications/emissions/us2002/index.html, especially Chapter 3. Industrial Processes
http://www.epa.gov/oppeoee1/globalwarming/publications/emissions/us2002/industrial_processes.pdf
These other sources also have CO2 emissions data and information:
Carbon Dioxide Information Analysis Center.
http://cdiac.esd.ornl.gov/by_new/bysubjec.html#carbon
International Energy Agency, Greenhouse Gas Research & Development Programme.
A conference report- Emission Reduction of Greenhouse Gases from the Cement Industry
http://www.ieagreen.org.uk/prghgt42.htm
News report on an article in Science, Oct. 2000. “Humans Altered Global Carbon Cycle In Last 200 Years”
http://www.climateark.org/articles/2000/4th/hualglcc.htm
The above entry is posted under the following topic(s): Emissions data and trends • Global Carbon Cycle • Human Contributions and Responses • To link uniquely to the question and answer displayed above, please refer to this page where they are permanently posted. |
