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Natural Sources and Sinks of Carbon Dioxide
Greenhouse gases occur naturally in the Earth’s atmosphere in addition to being emitted through human activities. This natural “carbon cycle” includes carbon dioxide used in plants during photosynthesis and the exchange of carbon dioxide between the atmosphere and the oceans.
The primary natural processes that release CO2 into the atmosphere (sources) and that remove CO2 from the atmosphere (sinks) are:
- Animal and plant respiration, by which oxygen and nutrients are converted into CO2 and energy, and plant photosynthesis by which CO2 is removed from the atmosphere and stored as carbon in plant biomass;
- Ocean-atmosphere exchange, in which the oceans absorb and release CO2 at the sea surface; and
- Volcanic eruptions, which release carbon from rocks deep in the Earth’s crust (this source is very small).
Here are some additional resources on the Carbon Cycle:
- Educational Carbon Cycle Animation for Kids
- Carbon Sequestration in Agriculture and Forestry Science page
- NASA Earth Observatory Carbon Cycle Tutorial
- Intergovernmental Panel
on Climate Change (IPCC) Fourth Assessment Report: The Scientific Basis
- National
Research Council. Climate Change Science: An Analysis of Some Key Questions