carbon budget

carbon cycle

Circulation through nature of carbon in the form of the simple element and its compounds. The source of carbon in living things is carbon dioxide (CO2) from air or dissolved in water. Algae and green plants (producers) use CO2 in photosynthesis to make carbohydrates, which in turn are used in the processes of metabolism to make all other compounds in their tissues and those of animals that consume them. The carbon may pass through several levels of herbivores and carnivores (consumers). Animals and, at night, plants return the CO2 to the atmosphere as a by-product of respiration. The carbon in animal wastes and in the bodies of organisms is released as CO2 in a series of steps by decay organisms (decomposers), chiefly bacteria and fungi (see fungus). Some organic carbon (the remains of organisms) has accumulated in Earth's crust in fossil fuels, limestone, and coral. The carbon of fossil fuels, removed from the cycle in prehistoric times, is being returned in vast quantities as CO2 via industrial and agricultural processes, some accumulating in the oceans as dissolved carbonates and some staying in the atmosphere (see greenhouse effect).

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Carbon budget refers to the contribution of various sources of carbon dioxide on the planet, and has nothing to do with political agendas, climate change legislation, carbon controls, carbon storage, or geopolitical carbon footprint.

Balancing the Carbon Budget

Carbon budget figures are normally documented by mass of carbon. Documenting carbon budget figure by mass of carbon dioxide is limiting as sometimes the transfer of carbon from one system to another is via a compound other than carbon dioxide. Carbon dioxide mass inputs (eg. IPCC, 2007) can be too easily misread. The 28,556 megatons of carbond dioxide chalked up to fossil fuel combustion by the IPCC represents only 7.8 GtC annually.

Carbon Sources (Annual)

  • 80.4 GtC by soil respiration and fermentation (Raich et al., 2002)
  • 38 GtC and rising by 0.5 GtC per annum by cumulative photosynthesis deficit(Casey, 2008)
  • by post-clearance deflation (See Eswaran, 1993)
  • 7.8 GtC (IPCC, 2007 - Needs peer reviewed reference)
  • 2.3 GtC by process of deforestation (IPCC, 2007; Melillo et al., 1996; Haughton & Hackler, 2002)
  • 0.03 GtC? by Volcanos
  • by Tectonic rifts
  • by Animal Respiration
  • by Plant Respiration

Carbon Sinks (Annual)

  • 120 GtC by Photosynthesis (Bowes, 1991)
  • By Ocean Cabonate Buffer

Cumulative Photosynthesis Deficit

Carbon pooled in photosynthesising biota is 560 GtC (Schlesinger, 1991). Carbon released by deforestation between 1850-2000 is 156 GtC (Haughton & Hackler, 2002), reducing the total photosynthesising biomass to 540 GtC in 2000.

Reduction in photosynthesis between 1850-2000: 156 / (540 + 156) = ~22%
120 = (100-22=78)% of 154 GtCpa - a difference of ~34 GtCpa in 2000

Given the increase of 0.5 GtCpa over the past eight years since 2000, this figure would be closer to 38GtCpa in 2008.


  • Bowes, G., 1991, "Growth at Elevated CO2: Photosynthetic Responses Mediated through Rubisco", Plant Cell & Environment, v. 14. pp. 795-806
  • Casey, T., 2008, "Deforestation and Carbon Emission",
  • Eswaran, H., Van Den Berg, E., Reich, P., 1993, "Organic carbon in soils of the world",Soil Science Society of America Journal, V. 57, pp. 192-194
  • Houghton, R. A., & Hackler, J. L., 2002, "Carbon Flux to the Atmosphere from Land-Use Changes. In Trends: A Compendium of Data on Global Change", Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.
  • IPCC, 2007, "Climate Change 2007: Synthesis Report - Summary for Policymakers", Fourth Assessment Report
  • Melillo, J. M., Houghton, ­R. A., Kicklighter, ­D. W., & McGuire, ­A. D., 1996, "Tropical Deforestation and the Global Carbon Budget", Annual Reviw of Energy and the Environment, v. 21, pp 293-310
  • Raich, J. W., Potter, C. S., & Bhagawati, D., 2002, "Interannual variability in global soil respiration, 1980-94", Global Change Biology, v. 8, pp. 800-812
  • Schlesinger, W. H., 1991, "Climate, Environment, and Ecology", NASA no. 19990036602. Climate Change: Science, Impacts and Policy; UNITED STATES.
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