The
DOE
Consortium for Research
on Enhancing
...research to enhance the capture and long-term storage of CO2 in soil and vegetation...
...research to enhance the capture and long-term storage of CO2 in soil and vegetation...
Frequently Asked Questions
What is terrestrial carbon
sequestration?
Terrestrial carbon sequestration is defined as
either the net removal of CO2 from the atmosphere or the prevention of
CO2 net emissions from the terrestrial ecosystems into the atmosphere.
Enhancing the natural processes that remove CO2 from the atmosphere is thought to be one of the most cost-effective means of reducing atmospheric levels of CO2.
The following ecosystems offer significant opportunity for carbon sequestration:
CSiTE is focused on the carbon sequestration in soils (below-ground carbon storage) and the processes by which carbon is stored in soils.
Enhancing the natural processes that remove CO2 from the atmosphere is thought to be one of the most cost-effective means of reducing atmospheric levels of CO2.
The following ecosystems offer significant opportunity for carbon sequestration:
- Forest lands. The focus includes below-ground carbon and long-term management and utilization of standing stocks, understory, ground cover, and litter.
- Agricultural lands. The focus includes crop lands, grasslands, and range lands, with emphasis on increasing long-lived soil carbon.
- Biomass croplands. As a complement to ongoing efforts related to biofuels, the focus is on long-term increases in soil carbon and value-added organic products.
- Deserts and degraded lands. Restoration of degraded lands offers significant benefits and carbon sequestration potential in both below-and above-ground systems.
- Boreal wetlands and peatlands. The focus includes management of soil carbon pools and perhaps limited conversion to forest or grassland vegetation where ecologically acceptable.
CSiTE is focused on the carbon sequestration in soils (below-ground carbon storage) and the processes by which carbon is stored in soils.
How can carbon be
sequestered in terrestrial ecosystems?
Carbon can be sequestered in terrestrial
ecosystems by
Both approaches can be addressed simultaneously on the same piece of land. In general croplands store less carbon than grasslands which store less carbon than forests. Grasslands are particularly good at storing carbon in soils because they often have extensive and deep roots. Soil carbon is less vulnerable to rapid loss than aboveground biomass which can be quickly lost to the atmosphere in a fire.
- Increasing the amount of aboveground biomass in an ecosystem. Biomass is matter originally created by living organisms. For example trees, dead leaves, bacteria and people are all biomass. The ultimate origin of the carbon in virtually all biomass is atmospheric CO2. So storing biomass is storing atmospheric carbon. Dry biomass is roughly 50% carbon by weight. Forest ecosystems contain more living biomass than any other ecosystem so converting grasslands or croplands to forest is one way of sequestering carbon.
- Increasing the amount of carbon held in soils. Soil carbon originates primarily from plant and fungal material which is then processed by other fungi and bacteria. Soil carbon can also originate from charcoal or char created when an ecosystem burns. Many factors control how much carbon goes into soil and how long the carbon stays in the soil. CSiTE is focused on understanding soil carbon and enhancement of soil carbon storage.. both the retention of existing carbon and enhancement of storage.
Both approaches can be addressed simultaneously on the same piece of land. In general croplands store less carbon than grasslands which store less carbon than forests. Grasslands are particularly good at storing carbon in soils because they often have extensive and deep roots. Soil carbon is less vulnerable to rapid loss than aboveground biomass which can be quickly lost to the atmosphere in a fire.
How does terrestrial carbon
storage reduce global warming?
Terrestrial
carbon sequestration reduces global warming by slowing down the
build-up of carbon dioxide in the atmosphere. Because the organic
carbon in biomass and soils originated from carbon dioxide in the
atmosphere, the more carbon is stored in biomass and in soils, the less
carbon is stored in the atmosphere as carbon dioxide. Carbon dioxide is
the most significant greenhouse gas. Roughly speaking, terrestrial
carbon sequestration is the only technology which could actually reduce
the concentration of CO2 in the atmosphere. Other technologies
–
energy efficiency, fossil fuel carbon capture and storage, renewable
energy such as wind, solar, bioenergy simply reduce the amount of CO2
going into the atmosphere; they don’t actively remove the
CO2.
How long does carbon last
and can I lose it?
The lifetime
of carbon in terrestrial systems can be expressed in
several
different ways, but a commonly used measure, and the one that we will
use here, is mean residence time or the average time that a carbon (C)
atom resides in a particular place.
In aboveground biomass, the mean residence time of C can vary widely depending on the type of vegetation and its management. For example, C captured and stored in annual vegetation is not generally regarded as C sequestration. On the other hand, many regard C captured and stored by forests as a form of C sequestration because trees can live for decades or centuries depending on the species and climate. Forest management and the end-use of forest products is an important determinant of the mean residence time of C incorporated into trees. The lifetime of C is generally extended when lumber from forests is used for building construction.
The lifetime of C stored in aboveground biomass can be both unpredictable and ephemeral because of both natural and anthropogenic disturbances like fire, plant diseases, and land-use change. For this reason, C stored in soils is generally regarded as a more permanent form of terrestrial C sequestration.
The lifetime of soil C depends on both chemical form and physicochemical soil properties. Inorganic C, in the form of carbonate, can have a very long lifetime in non-acidic soils. The lifetime of soil organic C (i.e., C derived from dead plant debris) varies widely depending on the form of organic matter and soil management practices. Calculated mean residence times for total soil organic C are generally on the order of decades to centuries (Six and Jastrow, 2002). Some strategies for C sequestration seek to promote C storage in deeper soils because the lifetime of soil C generally increases with increasing soil depth.
Like aboveground C in terrestrial vegetation, stored organic soil C can be lost. Soil disturbance, through practices such as tillage, exposes soil organic C to decomposition by soil microorganisms and this process returns C to the atmosphere. For example, the average mean residence time of total soil organic C under no-till agriculture is about 1.5 times longer than under conventional tillage (Six and Jastrow, 2002), and losses (on average about 30%) of total soil organic C following cultivation of previously untilled soils have been widely reported (Davidson and Ackerman, 1993).
In summary, C stored in long-lived perennial vegetation, like forests, as well as C stored in soils can last from decades to centuries and thereby help with short-term mitigation of increasing atmospheric CO2 concentrations, however the lifetime of C sequestration in these reservoirs is highly dependent on land and soil management practices.
References
Davidson, E.A., and I.L. Ackerman. 1993. Changes in soil carbon inventories following cultivation of previously untilled soils. Biogeochemistry 20: 161-193.
Six, J., and J.D. Jastrow. 2002. Organic matter turnover. Pp. 936-942. In R. Lal (ed.), Encyclopedia of Soil Science. Marcel Dekker, New York.
In aboveground biomass, the mean residence time of C can vary widely depending on the type of vegetation and its management. For example, C captured and stored in annual vegetation is not generally regarded as C sequestration. On the other hand, many regard C captured and stored by forests as a form of C sequestration because trees can live for decades or centuries depending on the species and climate. Forest management and the end-use of forest products is an important determinant of the mean residence time of C incorporated into trees. The lifetime of C is generally extended when lumber from forests is used for building construction.
The lifetime of C stored in aboveground biomass can be both unpredictable and ephemeral because of both natural and anthropogenic disturbances like fire, plant diseases, and land-use change. For this reason, C stored in soils is generally regarded as a more permanent form of terrestrial C sequestration.
The lifetime of soil C depends on both chemical form and physicochemical soil properties. Inorganic C, in the form of carbonate, can have a very long lifetime in non-acidic soils. The lifetime of soil organic C (i.e., C derived from dead plant debris) varies widely depending on the form of organic matter and soil management practices. Calculated mean residence times for total soil organic C are generally on the order of decades to centuries (Six and Jastrow, 2002). Some strategies for C sequestration seek to promote C storage in deeper soils because the lifetime of soil C generally increases with increasing soil depth.
Like aboveground C in terrestrial vegetation, stored organic soil C can be lost. Soil disturbance, through practices such as tillage, exposes soil organic C to decomposition by soil microorganisms and this process returns C to the atmosphere. For example, the average mean residence time of total soil organic C under no-till agriculture is about 1.5 times longer than under conventional tillage (Six and Jastrow, 2002), and losses (on average about 30%) of total soil organic C following cultivation of previously untilled soils have been widely reported (Davidson and Ackerman, 1993).
In summary, C stored in long-lived perennial vegetation, like forests, as well as C stored in soils can last from decades to centuries and thereby help with short-term mitigation of increasing atmospheric CO2 concentrations, however the lifetime of C sequestration in these reservoirs is highly dependent on land and soil management practices.
References
Davidson, E.A., and I.L. Ackerman. 1993. Changes in soil carbon inventories following cultivation of previously untilled soils. Biogeochemistry 20: 161-193.
Six, J., and J.D. Jastrow. 2002. Organic matter turnover. Pp. 936-942. In R. Lal (ed.), Encyclopedia of Soil Science. Marcel Dekker, New York.
Where are the best
places to sequester carbon?
From
a global perspective, the biological potential for carbon sequestration
depends mainly on climatic factors. Climates with high temperatures,
sufficient rainfall, and long day lengths are most adequate for plant
growth, whether it is forest growth or grassland production (Alexandrov
et al., 2000, 2002). Therefore, equatorial regions, where both rainfall
and temperatures are high, have the highest biological potential for C
sequestration. The map below shows the potential for C sequestration
specifically for planting forests.
Figure: Biological potential C-sequestration rates over the world. Alexandrov et al., 2000 (http://www-cger.nies.go.jp/carbon/pannel.htm)
However, the true potential for carbon sequestration is also dependent on the costs of these practices, and the land costs in a specific region. By combining the biological potential for carbon sequestration with estimates of costs to establish a forest and the costs of using land, it is possible to calculate a world map showing a geographic distribution of the costs involved in sequestering a ton of carbon. The figure below gives an example for planting forests. Areas where the cost to sequester a ton of C is smallest are most interesting for C sequestration.
Figure: Geographical distribution of costs to sequester carbon (From Benitez et al., 2007)
Sources:
Alexandrov, G.A., Yamagata, Y. and Oikawa, T., 1999. Towards a model for projecting Net Ecosystem Production of the world forests. Ecological Modelling, 123(2-3): 183-191.
Alexandrov, G.A., Oikawa, T. and Yamagata, Y., 2002. The scheme for globalization of a process-based model explaining gradations in terrestrial NPP and its application. Ecological Modelling, 148(3): 293-306.
Benitez, P.C., McCallum, I., Obersteiner, M. and Yamagata, Y., 2007. Global potential for carbon sequestration: Geographical distribution, country risk and policy implications. Ecological Economics, 60(3): 572-583.
Figure: Biological potential C-sequestration rates over the world. Alexandrov et al., 2000 (http://www-cger.nies.go.jp/carbon/pannel.htm)
However, the true potential for carbon sequestration is also dependent on the costs of these practices, and the land costs in a specific region. By combining the biological potential for carbon sequestration with estimates of costs to establish a forest and the costs of using land, it is possible to calculate a world map showing a geographic distribution of the costs involved in sequestering a ton of carbon. The figure below gives an example for planting forests. Areas where the cost to sequester a ton of C is smallest are most interesting for C sequestration.
Figure: Geographical distribution of costs to sequester carbon (From Benitez et al., 2007)
Sources:
Alexandrov, G.A., Yamagata, Y. and Oikawa, T., 1999. Towards a model for projecting Net Ecosystem Production of the world forests. Ecological Modelling, 123(2-3): 183-191.
Alexandrov, G.A., Oikawa, T. and Yamagata, Y., 2002. The scheme for globalization of a process-based model explaining gradations in terrestrial NPP and its application. Ecological Modelling, 148(3): 293-306.
Benitez, P.C., McCallum, I., Obersteiner, M. and Yamagata, Y., 2007. Global potential for carbon sequestration: Geographical distribution, country risk and policy implications. Ecological Economics, 60(3): 572-583.
How does forest
management affect carbon sequestration?
The
amount of carbon that can be sequestered by planting a forest depends
on climate factors, the specific species used, the management of the
forest, and economic costs. The tree species selected will depend on
the local climate. One can opt to establish a forest which is native
for that specific region, or one can establish a commercial plantation
with fast growing tree species. In the first case, the focus is on
regeneration of native tree species, by cutting invasive species and
planting some native species. In the second case, a large number of
fast growing trees are planted and harvested in short rotation cycles
by industrial means. Typical species used in the latter case are
Loblolly Pine in the temperature region, or Eucalyptus in tropical
regions.
The amount of carbon sequestered in a forest depends on the age of a forest. The graph below shows the evolution over time for three forest types in the U.S. The annual carbon uptake is high for a young forest, but decreases as the forest grows older (after 25-50 years, depending on the tree species), and eventually becomes zero for a completely mature forest. In the latter case, it is said that the forest is carbon neutral. The graph shows that this occurs after about 75 years for a Loblolly pine forest in the Plains States.
Figure from Pew center on global climate change, 2005. Note that 1 ton/acre/year equals 2.24 metric tons/hectare/year.
If one wants to keep sequestering carbon in a forest, it is necessary to periodically harvest the forest by cutting some trees in the forest. After a cutting, the forest will take up carbon again at a high rate (see Figure below). Obviously, the use of wood from the forest has to be long lived in order to have true carbon sequestration. This illustrates that an adequate forest management is necessary to maintain or optimize the sequestration potential of a forest.
Figure from Pew center on global climate change, 2005.
Sources:
http://www.pewclimate.org/docUploads/Sequest%5FFinal%2Epdf
The amount of carbon sequestered in a forest depends on the age of a forest. The graph below shows the evolution over time for three forest types in the U.S. The annual carbon uptake is high for a young forest, but decreases as the forest grows older (after 25-50 years, depending on the tree species), and eventually becomes zero for a completely mature forest. In the latter case, it is said that the forest is carbon neutral. The graph shows that this occurs after about 75 years for a Loblolly pine forest in the Plains States.
Figure from Pew center on global climate change, 2005. Note that 1 ton/acre/year equals 2.24 metric tons/hectare/year.
If one wants to keep sequestering carbon in a forest, it is necessary to periodically harvest the forest by cutting some trees in the forest. After a cutting, the forest will take up carbon again at a high rate (see Figure below). Obviously, the use of wood from the forest has to be long lived in order to have true carbon sequestration. This illustrates that an adequate forest management is necessary to maintain or optimize the sequestration potential of a forest.
Figure from Pew center on global climate change, 2005.
Sources:
http://www.pewclimate.org/docUploads/Sequest%5FFinal%2Epdf
Activities
that sequester carbon in the soil or
plants often require a change in how the land is managed. Changes in
land management can increase or decrease emissions, and these changes
can be compared to benefits from sequestration activities to estimate
the net impact on greenhouse gas emissions. With respect to
agricultural lands, management may include planting, soil tillage,
fertilizer and pesticide applications, harvesting, crop drying, and a
number of alternative soil amendments. These production inputs can
produce direct emissions from the cropland area (e.g., tractor
emissions from tillage machinery, N2O emissions from nitrogen
fertilizer use) and indirect emissions from the production of
management inputs (e.g., CO2 from natural gas in the production of
nitrogen fertilizers). As the use of management inputs change with
sequestration strategies, these changes together can influence the net
greenhouse gas emissions from a given plot of land.
Figure Caption: Total US average carbon dioxide emissions for three crop types using three different tillage practices. CT, RT, and NT are conventional tillage, reduced tillage, and no-till, respectively. The graph is for non-irrigated areas, which comprise 85% (by area) of US corn crops, 95% of soybean crops, and 93% of wheat crops. Carbon dioxide emissions from agricultural inputs (fertilizers, pesticides, seeds, etc.) and machinery are based on data from 1995.
Source: West, T.O. and G. Marland. 2002. A synthesis of carbon sequestration, carbon emissions, and net carbon flux in agriculture: Comparing tillage practices in the United States. Agriculture, Ecosystems, and Environment 91:217-232.
Figure Caption: Total US average carbon dioxide emissions for three crop types using three different tillage practices. CT, RT, and NT are conventional tillage, reduced tillage, and no-till, respectively. The graph is for non-irrigated areas, which comprise 85% (by area) of US corn crops, 95% of soybean crops, and 93% of wheat crops. Carbon dioxide emissions from agricultural inputs (fertilizers, pesticides, seeds, etc.) and machinery are based on data from 1995.
Source: West, T.O. and G. Marland. 2002. A synthesis of carbon sequestration, carbon emissions, and net carbon flux in agriculture: Comparing tillage practices in the United States. Agriculture, Ecosystems, and Environment 91:217-232.