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I. Carbon and the Global Carbon Cycle

Photo Credit: NASA SeaWiFS Ocean Color Project
Photo Credit: NASA SeaWiFS Ocean Color Project
  • Carbon is a ubiquitous element on Earth. Most of the Earth’s carbon is stored in rocks, but this carbon is essentially inert on the 100’s to 1000’s year timescales of interest to humans.
  • The rest of the carbon is stored as CO2 (carbon dioxide) in the atmosphere (2%), as biomass in land plants and soils (5%), as fossil fuels in a variety of geologic reservoirs (8%) and as a collection of ions in the ocean (85%). These are the “active” reservoirs of carbon of interest in this website.

II. How are the Global Carbon Cycle and Climate Change / Global Warming connected?

  • The Earth is warmed by the Sun. This warmth is returned from Earth to the atmosphere in the form of heat radiation.
  • Many gases in the atmosphere, including CO2, absorb the Earth’s heat energy and radiate in all directions. The energy radiated downward warms the surface and lower atmosphere.
  • Adding more CO2 to the atmosphere means more heat radiation is captured by the atmosphere and radiated back to Earth.
  • Methane, CH4, is another very important greenhouse gas that is part of the carbon cycle. This website addresses only CO2.

III. Humans add CO2 to the Atmosphere, Nature removes about half of it.

  • In the 1990’s, humans added 8.0×1015 grams of carbon (1015 grams of carbon  = 1 PgC) to the atmosphere each year, primarily by burning fossil fuels (6.4 PgC/yr) and clearing land in the tropics (1.6 PgC/yr). The ocean took up 28% of this carbon, and the land absorbed 32%. Only 40% remained in the atmosphere to cause climate warming.
  • Natural processes are significantly damping the rate of carbon accumulation in the atmosphere.
  • From 2000-2008, humans added 9.1 PgC to the atmosphere each year, 7.7 PgC/yr from fossil fuels and 1.4 PgC/yr from land use change. There is some evidence that a larger fraction of these recent emissions has remained in the atmosphere (45%, LeQuere et al. 2009).
  • Future climate warming depends on both the CO2 source from human emissions and the CO2 sink from natural sinks in the ocean and the terrestrial biosphere.

IV. Carbon Cycle Applet

  • With applet found on the next tab, you can develop your own scenarios for future human emissions and future carbon sinks in the oceans and on the land. Run the applet to see the impact on atmospheric CO2 and global mean temperature.

V. More information

  • In the following tabs, you can also find basic information on the major components of the global carbon cycle. Under the links tab, you can find links and other resources for more information.