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Global Carbon


Zac Kayler, Northern Institute of Applied Climate Science, US Forest Service, Albany, CA.
Maria Janowiak, Northern Institute of Applied Climate Science, US Forest Service, Houghton, MI.
Chris Swanston, Northern Institute of Applied Climate Science, US Forest Service, Houghton, MI.

This topic page was developed using information from the report Considering Forest and Grassland Carbon in Land Management (WO-GTR-95)


Carbon is one of the most important elements found on Earth. The carbon cycle supports all life by transferring carbon between living things and the environment. Plants take up carbon dioxide (CO2) and release oxygen (O2) during photosynthesis, which transfers carbon to their stems, roots, and leaves as they grow. When leaves fall and decompose or when plants die, the carbon that was stored in plants is released through respiration or combustion and transferred back to the atmosphere or to the soil. Because of these processes, forests and other natural ecosystems can store considerable amounts of carbon and act as an important global carbon sink. Carbon stored in U.S. forests and associated wood products increased by more than 600 million metric tons in 2014, offsetting a substantial amount of U.S. greenhouse gas emissions from burning fossil fuels (1).

Across the globe, carbon is stored in different places and in different forms. The amount of carbon stored in a particular system is called a “stock” or a “pool”. The Earth’s largest carbon stock is found within the continental crusts and upper mantle of the Earth, a large portion of which is sedimentary rock formed over millions of years (2).  Oceanic carbon is the next largest stock; over 95% of oceanic carbon is mainly present in the form of inorganic dissolved carbon, although only 900 gigatons of carbon (GtC) is available for exchange in the surface ocean. The atmosphere, although a relatively smaller carbon stock containing 839 GtC, still plays a very important role as it contains carbon mainly in the form of carbon dioxide, a greenhouse gas. Soils store approximately 1,325 GtC in the top few feet and perhaps as much as 3,000 GtC in total when deeper depths are included (3). In addition, permafrost (frozen soil) stores a large pool of carbon that is climatically protected from decomposition (4)(5), although more and more of this pool is becoming available as the average global temperature rises (6)(7).

Global carbon stocks (carbon stored in pools), shown in gigatons. Deep and Intermediate oceans store 37,100 gigatons of carbon, soils and vegetation 2,300 GTC, permafrost 1,600 GTC, surface oceans 900 GTC, atmosphere 839 GTC, industrial emissions 385 GTC

Figure: Global carbon stocks (carbon stored in pools), shown in gigatons.

Forests take up carbon through photosynthesis and this carbon is subsequently allocated above and belowground, contributing to the global forest stock. Forests account for 92% of all terrestrial biomass globally, storing approximately 400 GtC (8), but this is not homogenously distributed across the Earth. Different forest types store different amounts of carbon, and much of this variation is related to the climate found in a particular part of the world. Warm tropical regions tend to store much more carbon in the above ground components compared to belowground while the cool regions of the boreal forest have enormous belowground carbon stores.

Carbon stored in ecosystems, shown in gigatons. Tropical wet and moist forests store the most carbon aboveground. Cold temperate moist forests and boreal moist forests store the most carbon belowground.

Figure: Carbon (Gt C) stored in ecosystems (based on Scharlemann et al., 2014).

Carbon is exchanged between different stocks in the land, ocean, and atmosphere. This means that carbon in many stocks, whether global or local, can be quite dynamic. Carbon that enters or leaves a stock is referred to as a flux, and the average rate at which carbon flows through a stock is called carbon turnover. The turnover of carbon within ecosystems across the globe gives an idea of where carbon might be most vulnerable to release as CO2 to the atmosphere. Knowledge of turnover within ecosystems can inform management decisions that affect the rate of carbon turnover, ultimately influencing the flux of carbon into and out of ecosystems.

In order of fastest turnover times to slowest turnover: tropical forests, tropical savannahs and grasslands, wetlands, croplands, temperate forests, temperate grasslands and shrublands, boreal forests, tundra.

Figure: Average ecosystem turnover times (years) of different terrestrial carbon pools.


The amount of carbon stored in the Earth’s atmosphere is miniscule compared to the amount stored in oceans, soils, and geologic formations. Small additions to the atmosphere over a long time have an enormous effect on the global carbon cycle. The start of the industrial revolution nearly 300 years ago, marked the beginning of the period during which human (anthropogenic) activities moved large amounts of carbon from different terrestrial and geologic stocks to the atmosphere. Emissions from fossil fuel use and land use change have been increasing over the last three centuries and currently result in a net addition of approximately 9 GtC per year to the atmosphere. These anthropogenic fluxes have led to a 19-36% shift of carbon out of the Earth’s gas, oil, and coal reservoirs, carbon that had been essentially locked away from the carbon cycle for millions of years but is now expected to remain in the atmosphere for decades to centuries. This contribution of fossil fuel carbon to the atmosphere can be considered a net addition to the contemporary carbon cycle and a driver of climate change.

Carbon flows from the atmosphere to the land through gross photosynthesisand carbon flows from the land to the atmosphere from total respiration and wildfire.

Figure: Global carbon cycle. Carbon pool numbers (Gt C) are denoted in (parentheses), and flux numbers (Gt C per year) are associated with arrows.

Climate Change Effects on Carbon

Climate change is already having an impact on ecosystems across the world, and many of these changes are expected to continue or accelerate in the future (10, 11). Opportunities to mitigate atmospheric greenhouse gas emissions is driving interest in managing carbon within ecosystems (12), highlighting the important role forests and grasslands play in sequestering CO2 and providing a source of renewable energy. At the same time, changes in the Earth’s climate system are altering forests in dramatic ways, which can also have consequences for the emission of carbon and other greenhouse gases.

Warmer temperatures and extreme weather (13, 14) have the potential to directly increase the frequency and severity of many types of disturbance, including drought, wildfire, and blowdown, as well as exacerbate pests, diseases, and other agents to further increase stress on ecosystems (10, 15, 16). An example of the effect of climate on disturbance is seen in the Western United States, where climate variability drives wildfire occurrence in areas of high tree mortality from bark beetles (17, 18). Large disturbances are generally expected to increase, which could result in greater carbon releases from ecosystems (19, 20).

It is unclear whether many forests will be able to maintain their ability to sequester carbon at current rates. In many parts of the country, reforestation and the succession of young forest to older age classes has been a fundamental source of carbon uptake, and this sink may not be as strong in the future (21). Although warmer temperatures and enhanced CO2 may maintain and even increase the growth of many forests over the next few decades (22), these benefits may be variable across the landscape and ultimately transitory (23). Boreal forests are especially vulnerable to climate change, and the decline of these systems leads to dramatic carbon emissions (24, 25). Boreal and northern species within temperate systems also face potential declines as climate conditions become less suitable in the future and biomes shift toward ecosystems more tolerant of hotter and drier conditions that typically store less carbon (26-28). While new species may shift into these ecosystems, the pace of natural species migration is expected to be substantially slower than changes in climate (29, 30).

Management Options

It is increasingly important to consider the current and long-term effects from climate change, where land management seeks to maintain or increase carbon stocks or to provide a source of renewable energy. Adaptation actions, which work to reduce a system’s vulnerability to a changing climate, can help support beneficial carbon outcomes. Adaptation and mitigation are not alternatives to one another, but rather are part of an overall strategy to lessen the severity of climate change impacts. For example, increasing soil organic matter enhances soil carbon while also improving the water-holding capacity of soil and reducing the vulnerability of forests to more frequent intense drought. Management actions that serve to adapt forests and grasslands to changes in climate are critical for maintaining existing carbon pools and reducing losses of ecosystem carbon to the atmosphere.

More information and specific examples for carbon management can be found in the CCRC topic pages on Forest Management for Carbon Benefits, Carbon and Land Management, Forest Soil Carbon, and Grassland Carbon and Management.

Kayler, Z.; Janowiak, M.; Swanston, C. 2017. Global Carbon. (June, 2017). U.S. Department of Agriculture, Forest Service, Climate Change Resource Center.

Hauser, R.; Archer, S.; Backlund, P.; Hatfield, J.; Janetos, A.; Lettenmaier, D.; Ryan, M.G.; Schimel, D.; Walsh, M. 2009. The Effect of Climate Change on US Ecosystems. US Global Change Research Program. 24 p.

Hines, S.J.; Heath, L.S.; Birdsey, R.A. 2010. An annotated bibliography of scientific literature on managing forests for carbon benefits. Gen. Tech. Rep. NRS-57. Newtown Square, PA: Department of Agriculture, Forest Service, Northern Research Station. 49 p.

McKinley, D.C.; Ryan, M.G.; Birdsey, R.A.; Giardina, C.P.; Harmon, M.E.; Heath, L.S.; Houghton, R.A.; Jackson, R.B.; Morrison, J.F.;Murray, B.C.; Pataki, D.E.; Skog, K.E. 2011. A synthesis of current knowledge on forests and carbon storage in the United States. Ecological Applications. 21(6): 1902-1924.

Metsaranta, J.M.; Kurz, W.A.; Neilson, E.T.; Stinson, G.  2010.  Implications of future disturbance regimes on the carbon balance of Canada's managed forest (2010-2100). Tellus Series B. 62: 719-728.

Ryan, M.G.; Harmon, M.E.; Birdsey, R.A.; Giardina, C.P.; Heath, L.S.; Houghton, R.A.; Jackson, R.B.; McKinley, D.C.; Morrison, J.F. 2010. A synthesis of the science on forests and carbon for U.S. forests. Issues in Ecology. 13: 1-16.

U.S. Climate Change Science Program. 2007. The first state of the carbon cycle report (SOCCR): the North American carbon budget and implications for the global carbon cycle. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Asheville, NC: National Oceanic and Atmospheric Administration, National Climatic Data Center. 242 pp.

U.S. Environmental Protection Agency, E. 2016. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014. Washington, DC: U.S. Environmental Protection Agency. 558.

Vose, J.M.; Peterson, D.L.; Patel-Weynand, T. 2012. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S. forest sector. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 265 p.

COLE (Carbon OnLine Estimator)
COLE is a versatile and appropriate tool to use for a wide range of carbon estimation needs. COLE draws from Forest Inventory and Analysis (FIA) data to provide basic carbon inventory and growth-and-yield estimates for a particular forest, region, or state. 

ecoSmart Landscapes
This tool can help members of the public, cities and other organizations estimate the carbon and energy impacts of trees. The online tools provide quantitative data on carbon dioxide sequestration and building heating/cooling energy savings afforded by individual trees. Results can be used to estimate the greenhouse gas benefits of existing trees, to forecast future benefits, and to facilitate planning and management of carbon offset projects.

First Order Fire Effects Model (FOFEM)
FOFEM is a model that predicts first-order fire effects including tree mortality, fuel consumption, emissions (smoke) production, and soil heating caused by prescribed burning or wildfire.

Forest Inventory Data Online (FIDO) and EVALIDator
FIDO and EVALIDator applications both draw from US Forest Service FIA (Forest Inventory and Analysis) data to produce estimates with associated sampling errors for user selected forest attributes. Carbon estimates can be produced for several carbon pools, including total forest carbon, above and belowground carbon in live trees, standing dead trees, and live seedlings shrubs and bushes; litter; soil; and stumps, roots and woody debris.

Forest Planner
The Forest Planner enables landowners to visualize alternative forest management scenarios for their properties. It compares user selected areas to forest stands from a national database to estimate management outcomes including timber stocking and yields, harvest costs and revenues, carbon storage, and fire and pest hazard ratings. The tool does NOT account for the effects of projected climate change on future timber and carbon estimates.

Forest Vegetation Simulator (FVS)
Natural resource managers are increasingly interested in the effects of planned management activities on carbon stocks. The Forest Vegetation Simulator (FVS) is a family of forest growth simulation models that allow a user to explore how silvicultural treatments may affect growth and yield (and, therefore, carbon stocks). "Suppose" is the name for the graphical user interface for FVS.

Fuel and Fire Tools (FFT)
Fuel and Fire Tools (FFT) is a software application that uses fuels data classified as fuelbeds to let users perform a variety of calculations related to fire behavior and emissions. These include predicting surface and crown fire behavior, fuel consumption, pollutant emissions (including carbon emissions), and heat release. The FFT integrates several tools that were previously stand-alone into a single user interface (including the FCCS).

Global Carbon Atlas
The Global Carbon Atlas gives audiences a number of ways to visualize carbon dioxide emissions and flux data, and to compare between countries and regions over time (1960 – 2012). Its products are grouped into three main categories that are intended for users with varied technical backgrounds. All products are based on current datasets and models contributed by scientists and research institutions (see Contributors).

i-Tree consists of several different applications focused on quantifying the benefits of local trees for neighborhoods and communities. Each application has a unique focus, however several calculate the carbon sequestration and/or energy savings benefits of urban trees, including i-Tree Ecoi-Tree Streetsi-Tree Vue, and i-Tree Design (beta).

NASA - CASA Global CQUEST - Carbon Query and Evaluation Support Tools 
This application from NASA provides datasets and a viewer for geographic data that support large-scale carbon inventory. The datasets combine NASA remote sensing technology, ecosystem process modeling, and field-based measurements to characterize impacts on the carbon cycle.

USGS LandCarbon Visualization Tools
The LandCarbon application provides data download and visualization tools for terrestrial carbon and land-use datasets from the USGS National Assessment of Biologic Carbon Sequestration.

1. U.S. Environmental Protection Agency, E. 2016. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014. Washington, DC: U.S. Environmental Protection Agency. 558.

2. Mackenzie, F.T.; Lerman, A. 2006. Carbon in the Geobiosphere:-Earth's Outer Shell. Springer Science & Business Media.

3. Köchy, M.; Hiederer, R.; Freibauer, A. 2015. Global distribution of soil organic carbon–Part 1: Masses and frequency distributions of SOC stocks for the tropics, permafrost regions, wetlands, and the world. Soil. 1(1): 351-365.

4. Trumbore, S. 2009. Radiocarbon and Soil Carbon Dynamics. Annual Review of Earth and Planetary Sciences. 37: 47-66.

5. Schmidt, M.W.I.; Torn, M.S.; Abiven, S.; Dittmar, T.; Guggenberger, G.; Janssens, I.A.; Kleber, M.; Kogel-Knabner, I.; Lehmann, J.; Manning, D.A.C.; Nannipieri, P.; Rasse, D.P.; Weiner, S.; Trumbore, S.E. 2011. Persistence of soil organic matter as an ecosystem property. Nature. 478(7367): 49-56.

6. Schuur, E.; McGuire, A.; Schädel, C.; Grosse, G.; Harden, J.; Hayes, D.; Hugelius, G.; Koven, C.; Kuhry, P.; Lawrence, D. 2015. Climate change and the permafrost carbon feedback. Nature. 520(7546): 171-179.

7. Grosse, G.; Goetz, S.; McGuire, A.D.; Romanovsky, V.E.; Schuur, E.A. 2016. Changing permafrost in a warming world and feedbacks to the Earth system. Environmental Research Letters. 11(4): 040201.

8. Pan, Y.; Birdsey, R.A.; Phillips, O.L.; Jackson, R.B. 2013. The structure, distribution, and biomass of the world's forests. Annual Review of Ecology, Evolution, and Systematics. 44: 593-622.

9. Carvalhais, N.; Forkel, M.; Khomik, M.; Bellarby, J.; Jung, M.; Migliavacca, M.; Μu, M.; Saatchi, S.; Santoro, M.; Thurner, M. 2014. Global covariation of carbon turnover times with climate in terrestrial ecosystems. Nature. 514(7521): 213-217.

10. Ryan, M.G.; Vose, J.M. 2012. Effects of climatic variability and change. In: J. M. Vose, D. L. Peterson and T. Patel-Weynand, eds. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S. forest sector. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 7-95.

11. Melillo, J.M.; Richmond, T.C.; Yohe, G.W.; (eds.). 2014. Climate change impacts in the United States: the third National Climate Assessment. U.S. Global Change Research Program. 841 p. Available at (Accessed May 7, 2014).

12. Millar, C.I.; Skog, K.E.; McKinley, D.C.C.; Birdsey, R.A.; Swanston, C.W.; Hines, S.J.; Woodall, C.W.; Reinhardt, E.D.; Peterson, D.L.; Vose, J.M. 2012. Adaptation and mitigation. In: J. M. Vose, D. L. Peterson and T. Patel-Weynand, eds. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S. forest sector. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 125-192.

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14. Kunkel, K.E.; Karl, T.R.; Brooks, H.; Kossin, J.; Lawrimore, J.H.; Arndt, D.; Bosart, L.; Changnon, D.; Cutter, S.L.; Doesken, N.; Emanuel, K.; Groisman, P.Y.; Katz, R.W.; Knutson, T.; O'Brien, J.; Paciorek, C.J.; Peterson, T.C.; Redmond, K.; Robinson, D.; Trapp, J.; Vose, R.; Weaver, S.; Wehner, M.; Wolter, K.; Wuebbles, D. 2012. Monitoring and Understanding Trends in Extreme Storms: State of Knowledge. Bulletin of the American Meteorological society. 94(4): 499-514.

15. Joyce, L.A.; Running, S.W.; Breshears, D.D.; Dale, V.H.; Malmsheimer, R.W.; Sampson, R.N.; Sohngen, B.; Woodall, C.W. 2014. Chapter 7: Forests. In: J. M. Melillo, T. C. Richmond, G. W. Yohe and (eds.), eds. Climate change impacts in the United States: the third National Climate Assessment: U.S. Global Change Research Program: 841.

16. McKenzie, D.; Peterson, D.L.; Littell, J.J. 2008. Chapter 15 Global Warming and Stress Complexes in Forests of Western North America. In: M. J. A. A. R. R. Andrzej Bytnerowicz and A. Christian, eds. Developments in Environmental Science: Elsevier: 319-337.

17. Mietkiewicz, N.; Kulakowski, D. 2016. Relative importance of climate and mountain pine beetle outbreaks on the occurrence of large wildfires in the western US. Ecological Applications. n/a-n/a.

18. Hart, S.J.; Schoennagel, T.; Veblen, T.T.; Chapman, T.B. 2015. Area burned in the western United States is unaffected by recent mountain pine beetle outbreaks. Proceedings of the National Academy of Sciences. 112(14): 4375-4380.

19. Millar, C.I.; Stephenson, N.L. 2015. Temperate forest health in an era of emerging megadisturbance. Science. 349(6250): 823-826.

20. Williams, C.A.; Gu, H.; MacLean, R.; Masek, J.G.; Collatz, G.J. 2016. Disturbance and the carbon balance of US forests: A quantitative review of impacts from harvests, fires, insects, and droughts. Global and Planetary Change. 143: 66-80.

21. Birdsey, R.; Pregitzer, K.; Lucier, A. 2006. Forest carbon management in the United States. Journal of environmental quality. 35(4): 1461-1469.

22. Arora, V.K.; Boer, G.J.; Friedlingstein, P.; Eby, M.; Jones, C.D.; Christian, J.R.; Bonan, G.; Bopp, L.; Brovkin, V.; Cadule, P. 2013. Carbon–concentration and carbon–climate feedbacks in CMIP5 Earth system models. Journal of Climate. 26(15): 5289-5314.

23. Oren, R.; Ellsworth, D.S.; Johnsen, K.H.; Phillips, N.; Ewers, B.E.; Maier, C.; Schafer, K.V.R.; McCarthy, H.; Hendrey, G.; McNulty, S.G.; Katul, G.G. 2001. Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere. Nature. 411(6836): 469-472.

24. Gauthier, S.; Bernier, P.; Kuuluvainen, T.; Shvidenko, A.Z.; Schepaschenko, D.G. 2015. Boreal forest health and global change. Science. 349(6250): 819-822.

25. Soja, A.J.; Tchebakova, N.M.; French, N.H.F.; Flannigan, M.D.; Shugart, H.H.; Stocks, B.J.; Sukhinin, A.I.; Parfenova, E.I.; Chapin Iii, F.S.; Stackhouse Jr, P.W. 2007. Climate-induced boreal forest change: Predictions versus current observations. Global and Planetary Change. 56(3–4): 274-296.

26. Bachelet, D.; Neilson, P.R.; Lenihan, M.J.; Drapek, J.R. 2001. Climate Change Effects on Vegetation Distribution and Carbon Budget in the United States. Ecosystems. 4(3): 164-185.

27. Duveneck, M.J.; Scheller, R.M.; White, M.A. 2014. Effects of alternative forest management on biomass and species diversity in the face of climate change in the northern Great Lakes region (USA). Canadian Journal of Forest Research. 44(7): 700-710.

28. Lenihan, J.M.; Bachelet, D.; Neilson, R.P.; Drapek, R. 2008. Simulated response of conterminous United States ecosystems to climate change at different levels of fire suppression, CO2 emission rate, and growth response to CO2. Global and Planetary Change. 64(1–2): 16-25.

29. Iverson, L.R.; Schwartz, M.W.; Prasad, A.M. 2004. How fast and far might tree species migrate in the eastern United States due to climate change? Global Ecology and Biogeography. 13(3): 209-219.

30. Loarie, S.R.; Duffy, P.B.; Hamilton, H.; Asner, G.P.; Field, C.B.; Ackerly, D.D. 2009. The velocity of climate change. Nature. 462(7276): 1052-1055.