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Human Contributions and Responses

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 CycleHuman Contributions and Responses

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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 trendsGlobal Carbon CycleHuman Contributions and Responses

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How do human activities affect global climate?

Last updated 25 April 2000
Originally answered 25 April 2000

Full Question

Could you please describe some of the important lines of evidence that support the idea that human activities are affecting global climates? what are some of these human activities?

Answer

For a good introduction to the causes and impacts of global change, take a look at the online publication “Common Questions about Climate Change” that was published in 1997 by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO).

There is a section of this publication covering human activites contributing to climate change, and how we know that the increase in atmospheric levels of greenhouse gases is due to human activity.

The US National Academy of Sciences published “Climate Change Science: An Analysis of Some Key Questions” in the summer of 2001.

Another source you might want to look at is the “Questions and Answers” box on the USGCRP Educational Resources page.

Highlights of recent and planned research on Human Contributions and Responses to global environmental change are addressed in the chapter on Decision-Support Resources Development and Related Research on Human Contributions and Responses of Our Changing Planet: The U.S. Climate Change Science Program for Fiscal Year 2006.

The full report is available online in both HTML and PDF formats. You can also order a copy of the report, free of charge, as either a hardcopy report or CD-ROM from the GCRIO Online Catalog.


The above entry is posted under the following topic(s): Global Change ScienceHuman Contributions and Responses

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