PDF Version 
Addressing the risk of dangerous climate change requires the combined efforts of both greenhouse gas (GHG) emission reductions and sequestration. The purpose of this document is to discuss briefly the technology of biotic sequestration (or "biosequestration"): the absorption and storage of carbon in organic matter.
Biosequestration refers to a category of biological processes that absorb carbon dioxide (CO2), the primary GHG, from the atmosphere and contain it in living organic matter, soil, or aquatic ecosystems. The opportunities for expanding biosequestration by changing management and land-use practices are generating debate among landowners, policymakers, and the media. Other avenues of enhancing natural carbon capturing processes may exist, but more study is needed to determine their potential for climate change mitigation.1 
Biosequestration occurs naturally in the global carbon cycle (Figure 1). It is estimated that the atmosphere contains about 2,750 billion metric tons of CO2 (2,750 gigatons of carbon, GtCO2).2  Terrestrial vegetation, soils, and organic matter contain the equivalent of up to 8,030 GtCO2 or just under 3 times the amount contained in the atmosphere.3  It is estimated that in the 1990s, 5.8 GtCO2 per year were released into the atmosphere as a result of global land-use change and deforestation, though some forests expanded in temperate and boreal zones.4  For comparison, the United States emitted on average about 7 GtCO2 per year from land-use change between 2003 and 2007, or about 0.25 percent of the entire atmospheric CO2 each year.5  Enhancing the capacity for carbon storage or the rate that CO2 is biosequestered is an important strategy for mitigating climate change.
|Figure 1: The Global Carbon Cycle (in GtC)|
Although biosequestration occurs naturally every day, actions preventing the loss of carbon stocks and increasing the rate of biosequestration can also be intentional. Some biosequestration methods have a greater carbon impact than others depending on the rate of carbon absorption and storage. For example, fast-growing tree species can be used in afforestation and reach sequestration rates of 5 metric tons CO2 (tCO2) per acre per year, while planting prairie grass in place of an annual agricultural crop could sequester an additional 1.5 tCO2 per acre per year depending on local climate and weather variability.6 ,7  A range of carbon sequestration rates from selected land-use practices is presented below (Table 1).8 ,9 ,10 
Although carbon stocks in forests, agricultural lands, and wetlands have been reduced over time, and thus offer opportunities for carbon storage through restoration, they are not pools where unlimited amounts of CO2 can be stored. All biosequestration practices will reach a saturation point at which a new carbon equilibrium is reached.11 
Like other GHG mitigation options, different quantities of biosequestration are achievable at different costs. Under the cap-and-trade program passed by the U.S. House of Representatives in 2009 (H.R.2454), domestic biosequestration (in the form of cap-and-trade offsets) was projected to provide between 292 and 676 million metric tCO2 of annual abatement in the year 2030. (For comparison, GHG emissions from sources covered under the cap were projected to be between 926 and 2586 million metric tCO2 below the "business-as-usual" projected emissions level in 2030.)12 ,13 
|Table 1: Estimated Sequestration Potential by Practice in the United States (Metric Tons CO2 per Acre per Year): Selected Land Use and Production Practice Changes|
Biosequestration is a biogeochemical process, meaning that it occurs at the interface of living organisms and geological processes. For example, when CO2 from the atmosphere is taken in by a plant, newly formed molecules (usually sugars and other carbohydrates that contain the carbon) end up in all parts of the plant including the leaves, stems and roots (Figure 2). The carbon is considered sequestered until the organic matter decomposes or burns, at which point it returns to the atmosphere as CO2. After plants die and fall to the ground, some carbon is incorporated into the soil when roots or dead leaves become soil organic carbon (SOC). Land that has been afforested or planted in perennial crops may have the greatest potential for accumulating soil organic carbon.14 
|Figure 2: Biosequestration at the Level of an Organism|
Not only may biosequestration help to mitigate climate change, but certain methods can also contribute other significant environmental benefits. For example, changes in forest management can provide benefits beyond storing carbon by reducing soil-erosion and run-off, reducing flooding, protecting fisheries, and enhancing wildlife habitat and biodiversity.15  Similar benefits could also accompany changes in the management of farmlands and rangelands, and the restoration of wetlands. Environmental benefits will not happen automatically in biosequestration projects but must be planned for if they are preferred.
The cost of biosequestration varies widely depending on the practice, the land-owner, and the location of the biosequestration project. Much agricultural and forested land in the United States is privately-owned. Biosequestration would likely have to be financially favorable compared with current management practices for land managers to consider a change.16  Therefore, increasing carbon sequestration on these lands probably requires some form of payment for the carbon service provided or the practice implemented. Carbon markets and other pricing policies are discussed in more detail below.
A review of 11 cost analyses focusing on U.S.-based forest sequestration programs that varied broadly in their estimated costs of carbon sequestration estimated that 300 million metric tons CO2-equivalent (tCO2e) of annual carbon sequestration could occur in forest ecosystems at a cost of $7.50 to $22.50 per tCO2e.17  A separate study of the costs of sequestering carbon on agricultural land yielded an estimate of up to 77 million tCO2e per year when carbon is priced in a similar range (~$13 per tCO2/acre/year).18  For comparison, total U.S. GHG emissions are about 7 billion metric tons of CO2e per year. The estimate of agricultural carbon sequestration is about 1 percent of the total annual U.S. GHG emissions. The aforementioned estimate of forest biosequestration projects is equivalent to about 4 percent of annual U.S. GHG emissions.
Studies of global biosequestration estimate that a carbon price of $23.54 could induce 744 million tCO2e per year of forest carbon sequestration by the year 2010.19  Again, total annual biosequestration would vary considerably depending on the region, ranging from 20 million tCO2e in Oceania to 280 million tCO2e per year in North America. The difference between the North American estimate and the U.S. estimate above illustrates that biosequestration estimates vary.
Carbon prices and markets to trade carbon will help considerably in supporting biosequestration practices. However, reputable markets will require measurement and verification that also add to the cost of these practices. It is also reasonable to expect that credit aggregators will act as facilitators between biosequestration project owners and the credit exchanges. This facilitation will also come with a cost. In the end, transaction costs such as these could be significant.20 
A global system of recognized practices and credits for biosequestration does not currently exist. Policies and programs that are effective in increasing the adoption of biosequestration practices are fragmentary, especially in the United States.
The Kyoto Protocol – an international agreement governing GHG emissions – comes nearest to establishing a global system of biosequestration initiatives.21  Nations that are party to the Kyoto Protocol have agreed to country-specific GHG emissions reductions by 2012. Articles 3.3 and 3.4 of the protocol outline the ways in which nations can account for afforestation, reforestation, deforestation, and certain other land-use activities in their particular emission reduction goals. Countries are also allowed to reach part of their goal through investments in flexible GHG offsets guided by United Nations programs called the Clean Development Mechanism and Joint Implementation (CDM/JI).22  Biosequestration projects in CDM/JI are mostly afforestation projects sponsored by countries with carbon reduction targets in countries without reduction targets (typically, countries that are considered non-industrialized).
The European Union Emission Trading Scheme (EU ETS) is currently the largest mandatory carbon market in the world. However, offsets from biosequestration are not currently allowed in the EU ETS.23 
Current U.S. drivers of biosequestration include voluntary offset programs like the Chicago Climate Exchange and the Climate Action Reserve, and regional GHG reduction programs like the Regional Greenhouse Gas Initiative (RGGI). Each of these programs defines how biosequestration projects can be measured in slightly different ways.24 ,25 ,26 
It bears repeating that biosequestration practices depend on living systems that are not easily quantified in a direct way. This lack of established measurement protocols leads to uncertainties in actual carbon sequestered compounded by the uncertain storage time. Measurement is made even more challenging by seasonal variations in weather and precipitation, differences between plant species, and the variation in the quality of soils and lands where these practices could be used. Land managers know a lot about growing trees, perennial crops, managing rangeland for carbon, and even restoring wetlands, but those practices need better measuring techniques for their legitimacy to be widely accepted.
A number of challenges have emerged to the further development of biosequestration practices:27 
Each of these challenges must be addressed appropriately for biosequestration to be implemented at a climatically significant scale.28 
There are two primary policy strategies that could help promote biosequestration:29 
Agriculture's Role in Greenhouse Gas Mitigation , 2006
Biological Sequestration through Greenhouse Gas Offsets: Identifying the Challenges and Evaluating Potential Solutions , April 2009 Workshop co-sponsored by the Center.
Briefing on Domestic Offsets in a Greenhouse Gas (GHG) Cap-and-Trade System , 6 March 2009.
The Cost of U.S. Forest-Based Carbon Sequestration , 2005.
Greenhouse Gas Offsets in a Domestic Cap-and-Trade Program , Congressional Policy Brief, 2008.
Issue Overview: Role of Offsets in Cap and Trade , U.S. Climate Action Partnership (USCAP), 2009.
Offset Quality Initiative (OQI) .
Baker JM, Ochsner TE, Venter RT, Griffis TJ (2007). Tillage and soil carbon- what do we really know? Agriculture, Ecosystems and Environment 118: 1–5.
Birdsey R (2004). Data Gaps for Monitoring Forest Carbon in the United States: An Inventory Perspective. Environmental Management 33. Supplement 1: S1–S8.
United States Department of Energy (2008). Carbon Cycling and Biosequestration Workshop Report: Publication No. DOE/SC-108 .
European Union Memo (2008). Questions and answers on deforestation and forest degradation. Reference: MEMO/08/632.
Hansen EA (1993). Soil carbon sequestration beneath hybrid poplar plantations in the north central United States. Biomass and Bioenergy 5: 431-436.
Johnson R (2009). Climate Change: The Role of the U.S. Agriculture Sector and Congressional Action. Congressional Research Service . Publication No. RL33898.
Johnson R, Gorte RW (2009). Estimates of Carbon Mitigation Potential from Agricultural and Forestry Activities. Congressional Research Service . Publication No. R40236.
Johnson KS, Karl DM (2002). Is Ocean Fertilization Credible and Creditable? Science 296: 467-468.
Kopp RJ, Pizer WA et al. (2007). Assessing US Climate Policy Options . Report briefings on climate policy options including Biosequestration, among many others.
Lal R (2008). Sequestration of atmospheric CO2 in global carbon pools . Energy & Environmental Science 1: 86–100.
Lewandroski J, Peters M, et al. (2004). Economics of Sequestering Carbon in the U.S. Agricultural Sector. Technical Bulletin No. (TB-1909).
McLauchlan KK, Hobbie SE, Post WM (2006). Conversion of agriculture to grassland builds soil organic matter on decadal timescales. Ecological Applications 16: 143-153.
Murray BC, Sohngen B, et al. (2005). Greenhouse Gas Mitigation Potential in U.S. Forestry and Agriculture . Publication No. EPA 430-R-05-006.
Nabuurs GJ, Masera O, et al. (2007). Chapter 9: Forestry. Climate Change 2007: Mitigation. Assessment Report 4 of the IPCC. Cambridge University Press.
Parrotta JA (2002). Restoration and management of degraded tropical forest landscapes. In Modern Trends in Applied Terrestrial Ecology. R.S. Ambasht and N.K. Ambasht (eds.), Kluwer Academic/Plenum Press, New York, pp. 135-148 (Chapter 7).
Parry IWH, Pizer W (2007). Backgrounder: Emissions Trading versus CO2 Taxes versus Standards. Resources for the Future .
Schlamadinger B, Johns T et al. (2007). Options for including land use in a climate agreement post-2012: improving the Kyoto Protocol approach. Environmental Science and Policy 10: 295-305.
Sedjo RA, Amano M (2006). The Role of Forest Sinks in a Post-Kyoto World . Resources for the Future.
Shrestha R, Lal R (2008). Offsetting carbon dioxide emissions through minesoil reclamation . Encyclopedia of Earth.
Smith P, Martino D, et al. (2007). Chapter 8: Agriculture. Climate Change 2007: Mitigation. Assessment Report 4 of the IPCC. Cambridge University Press.
United States Department of State (2000). United States Submission on Land-Use, Land-Use Change, and Forestry to the Kyoto Conference of Parties . Accessed August 1, 2009.
Wise, A (2008). The US Carbon Market . Renewable Energy World News.
NETL Regional Carbon Sequestration Partnerships 
DOE Terrestrial Sequestration Research 
1 See, for example, Johnson KS, Karl DM, "Is Ocean Fertilization Credible and Creditable?" Science 296: 467-468, 2002.
2 The difference between tons of carbon (tC) and tons of carbon dioxide (tCO2) is often confused. It is confusing because CO2 is 3.67 times more massive than C alone due to the added molecular weight of oxygen (O2). Therefore 1 tC is equivalent to 3.67 tCO2.
3 Stavins R, Richards K, The Cost of U.S. Forest-Based Carbon Sequestration , 2005
4 Nabuurs GJ, Masera O, et al., "Chapter 9: Forestry" in Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007.
5 Johnson R. Climate Change: The Role of the U.S. Agriculture Sector and Congressional Action, Congressional Research Service, 2009. Report RL33898.
6 Hansen EA, "Soil Carbon Sequestration beneath Hybrid Poplar Plantations in the North Central United States," Biomass and Bioenergy 5: 431-436, 1993.
7 McLauchlan KK, Hobbie SE, Post WM, "Conversion of Agriculture to Grassland Builds Soil Organic Matter on Decadal Timescales," Ecological Applications 16: 143-153, 2006.
8 Johnson R, Gorte RW, Estimates of Carbon Mitigation Potential from Agricultural and Forestry Activities, Congressional Research Service, 2009. Report R40236.
9 Lewandroski J, Peters M, et al., Economics of Sequestering Carbon in the U.S. Agricultural Sector , U.S. Department of Agriculture Technical Bulletin Number1909, 2004.
10 Murray BC, Sohngen B, et al., Greenhouse Gas Mitigation Potential in U.S. Forestry and Agriculture , U.S. Environmental Protection Agency (EPA) Publication No. 430-R-05-006, 2005.
11 U.S. EPA , "Representative Carbon Sequestration Rates and Saturation Periods for Key Agricultural & Forestry Practices ," 2006.
12 Energy Information Administration (EIA), Energy Market and Economic Impacts of H.R. 2454, the American Clean Energy and Security Act of 2009 , 2009. See Table ES-1.
13 For more information on H.R.2454, the American Climate and Energy Security Act of 2009 (ACESA), see /acesa.
14 Degryze S, Six J et al., "Soil Organic Carbon Pool Changes Following Land-Use Conversions," Global Change Biology 10: 1120–1132, 2004.
15 Parrotta JA, "Restoration and Management of Degraded Tropical Forest Landscapes," in Modern Trends in Applied Terrestrial Ecology, R.S. Ambasht and N.K. Ambasht (eds.), Kluwer Academic/Plenum Press, New York, 2002.
16 Richards K, Sampson RN, and Brown S, Agricultural & Forestlands: U.S. Carbon Policy Strategies , 2006.
17 Stavins, 2005.
18 Paustian K and Antle JM, Agriculture's Role in Greenhouse Gas Mitigation , 2006.
19 Sohngen B and Mendelsohn R, Optimal Forest Carbon Sequestration, Department of Agricultural, Environmental, and Development Economics, Ohio State University. Working Paper AEDE-WP-0009-01, 2001.
20 Nabuurs et al., 2007.
21 Schlamadinger B, Johns T et al., "Options for Including Land Use in a Climate Agreement Post-2012: Improving the Kyoto Protocol Approach," Environmental Science and Policy 10: 295-305, 2007.
23 European Union, "Questions and Answers on Deforestation and Forest Degradation ," MEMO/08/632, 2008.
24 Chicago Climate Exchange, "CCX Exchange Offsets and Exchange Early Action Credits " in CCX Confidential, 2004.
25 California Climate Action Registry, Forest Project Protocol , 2009.
26 Regional Greenhouse Gas Initiative (RGGI), "Offset Project Categories: Afforestation ."
27 Smith P, Martino D, et al., "Chapter 8: Agriculture," in Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change , 2007.
29 Richards et al., 2006.