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Carbon sink

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A carbon dioxide (CO2) sink is a carbon reservoir that is increasing in size, and is the opposite of a carbon dioxide "source". The main natural sinks are (1) the oceans and (2) plants and other organisms that use photosynthesis to remove carbon from the atmosphere by incorporating it into biomass and release oxygen into the atmosphere. This concept of CO2 sinks has become more widely known because the Kyoto Protocol allows the use of carbon dioxide sinks as a form of carbon offset.

Carbon, stored in humus is oxidized rapidly; this, in addition to high rainfall levels, is the reason why tropical jungles have very thin organic soils. The forest eco-system may eventually become carbon neutral. Forest fires release absorbed carbon back into the atmosphere, as does deforestation due to rapidly increased oxidation of soil organic matter.

The dead trees, plants, and moss in peat bogs undergo slow anaerobic decomposition below the surface of the bog. This process is slow enough that in many cases the bog grows rapidly and fixes more carbon from the atmosphere than is released. Over time, the peat grows deeper. Peat bogs inter approximately one-quarter of the carbon stored in land plants and soils.[1]

Under some conditions, forests and peat bogs may become sources of CO2, such as when a forest is flooded by the construction of a hydroelectric dam. Unless the forests and peat are harvested before flooding, the rotting vegetation is a source of CO2 and methane comparable in magnitude to the amount of carbon released by a fossil-fuel powered plant of equivalent power.[2]

Oceans

Oceans are natural CO2 sinks, and represent the largest active carbon sink on Earth. This role as a sink for CO2 is driven by two processes, the solubility pump and the biological pump.[3] The former is primarily a function of differential CO2 solubility in seawater and the thermohaline circulation, while the latter is the sum of a series of biological processes that transport carbon (in organic and inorganic forms) from the surface euphotic zone to the ocean's interior. A small fraction of the organic carbon transported by the biological pump to the seafloor is buried in anoxic conditions under sediments and ultimately forms fossil fuels such as oil and natural gas.

At the present time, approximately one third[4] of anthropogenic emissions are estimated to be entering the ocean. The solubility pump is the primary mechanism driving this, with the biological pump playing a negligible role. This stems from the limitation of the biological pump by ambient light and nutrients required by the phytoplankton that ultimately drive it. Total inorganic carbon is not believed to limit primary production in the oceans, so its increasing availability in the ocean does not directly affect production (the situation on land is different, since enhanced atmospheric levels of CO2 essentially "fertilize" land plant growth). However, ocean acidification by invading anthropogenic CO2 may affect the biological pump by negatively impacting calcifying organisms such as coccolithophores, foraminiferans and pteropods. Climate change may also affect the biological pump in the future by warming and stratifying the surface ocean, thus reducing the supply of limiting nutrients to surface waters. Although the buffering capacity of sea water is keeping the pH nearly constant at present, eventually pH will drop. At this point, the disruption of life in the sea may turn it into a carbon source rather than a carbon sink. The characteristic of buffered systems is to hold the pH reasonably constant over a large introduction of acid and then drop suddenly with a small additional amount.

Soils

Carbon as plant organic matter is sequestered in soils: Soils contain more carbon than is contained in vegetation and the atmosphere combined.[5] Soils' organic carbon (humus) levels in many agricultural areas have been severely depleted. Organic material in the form of humus accumulates below about 25 degrees Celsius.[citation needed] Above this temperature, humus is oxidized much more rapidly. This is part of the reason why tropical soils under jungles are so thin, despite the rapid accumulation of organic material on the jungle floor (the other being extensive rainfall leaching soluble components vital to organic soil structure). Areas where shifting cultivation or slash and burn agriculture are practiced are generally only fertile for 2-3 years before they are abandoned. These tropical jungles are similar to coral reefs in that they are highly efficient at conserving and circulating necessary nutrients, which explains their lushness in a nutrient desert.[citation needed][original research?]

Grasslands contribute to soil organic matter, mostly in the form of their extensive fibrous root mats. Much of this organic matter can remain unoxidized for long periods of time, depending on rainfall conditions, the length of the winter season, and the frequency of naturally occurring lightning-induced grass-fires necessary to recycle inorganic compounds from existing plant material. While these fires release carbon dioxide, they improve the quality of the grass-lands overall, in turn increasing the amount of carbon retained in the retained humic material. They also deposit carbon directly to the soil in the form of char that does not significantly degrade back to carbon dioxide. The over all effect of carbon sequestration is beneficial for soil since it added more and more organic carbon to it and leads to improved soil properties.

Enhancing natural sequestration

Forests

Forests are carbon stores, and they are carbon dioxide sinks when they are increasing in density or area. Tropical reforestation can mitigate global warming until all available land has been reforested with mature forests.[6][7][8][9]. In the United States in 2004 (the most recent year for which EPA statistics[10] are available), forests sequestered 10.6% (637 teragrams[11]) of the carbon dioxide released in the United States by the combustion of fossil fuels (coal, oil and natural gas; 5657 teragrams[12]). Urban trees sequestered another 1.5% (88 teragrams[11]). To further reduce U.S. carbon dioxide emissions by 7%, as stipulated by the Kyoto Protocol, would require the planting of "an area the size of Texas [8% of the area of Brazil] every 30 years", according to William H. Schlesinger, dean of the Nicholas School of the Environment and Earth Sciences at Duke University, in Durham, North Carolina. Carbon offset programs are planting millions of fast-growing trees per year to reforest tropical lands, for as little as $0.10 per tree; over their typical 40-year lifetime, one million of these trees will fix 0.9 teragrams of carbon dioxide[13].

The global cooling effect of carbon sequestration by forests is partially counterbalanced: For example, the planting of new forests may initially be a source of carbon dioxide emission when carbon from the soil is released into the atmosphere. Also, reforestation can decrease the reflection of sunlight (albedo): Mid-to-high latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming.

A long-term sequestration of carbon from forests comes from the use of wood products such as "stick built" (i.e., with lumber) homebuilding, the predominant form of home building in the US. Because most buildings are eventually demolished, the carbon may be released into the atmosphere, depending upon the fate of the scrap lumber. Reusing the lumber, or using it as fuel to replace a fossil fuel, avoids an increase in atmospheric carbon. (In addition to the global cooling effect of tropical reforestation, planting forests reduces erosion, increases water capture, and provides valuable timber which may be sustainably harvested.)

Oceans

See also: Iron fertilization

One way to increase the carbon sequestration efficiency of the oceans is to add micrometre-sized iron particles in the form of either hematite (iron oxide) or melanterite (iron sulfate) to the water. This has the effect of stimulating growth of plankton. Iron is an important nutrient for phytoplankton, usually made available via upwelling along the continental shelves, inflows from rivers and streams, as well as deposition of dust suspended in the atmosphere. Natural sources of ocean iron have been declining in recent decades, contributing to an overall decline in ocean productivity (NASA, 2003). Yet in the presence of iron nutrients plankton populations quickly grow, or 'bloom', expanding the base of biomass productivity throughout the region and removing significant quantities of CO2 from the atmosphere via photosynthesis. A test in 2002 in the Southern Ocean around Antarctica suggests that between 10,000 and 100,000 carbon atoms are sunk for each iron atom added to the water. More recent work in Germany (2005) suggests that any biomass carbon in the oceans, whether exported to depth or recycled in the euphotic zone, represents long term storage of carbon. This means that application of iron nutrients in select parts of the oceans, at appropriate scales, could have the combined effect of restoring ocean productivity while at the same time mitigating the effects of human caused emissions of carbon dioxide to the atmosphere.

Because the effect of periodic small scale phytoplankton blooms on ocean ecosystems is unclear, more studies would be helpful. Phytoplankton have a complex effect on cloud formation via the release of substances such as dimethyl sulfide (DMS) that are converted to sulfate aerosols in the atmosphere, providing cloud condensation nuclei, or CCN. But the effect of small scale plankton blooms on overall DMS production is unknown.

Other nutrients such as nitrates, phosphates, and silica as well as iron may cause ocean fertilization. There has been some speculation that using pulses of fertilization (around 20 days in length) may be more effective at getting carbon to ocean floor than sustained fertilization.[14]

There is some controversy over seeding the oceans with iron however, due to the potential for increased toxic phytoplankton growth (e.g. "red tide"), declining water quality due to overgrowth, and increasing anoxia in areas harming other sea-life such as zooplankton, fish, coral, etc.[15][16]

Soils

Since the 1850s, a large proportion of the world's grasslands have been tilled and converted to croplands, allowing the rapid oxidation of large quantities of soil organic carbon. However, in the United States in 2004 (the most recent year for which EPA statistics are available), agricultural soils including pasture land sequestered 0.8% (46 teragrams[11]) as much carbon as was released in the United States by the combustion of fossil fuels (5988 teragrams[12]). The annual amount of this sequestration has been gradually increasing since 1998[11].

Methods that significantly enhance carbon sequestration in soil include no-till farming, residue mulching, cover cropping, and crop rotation, all of which are more widely used in organic farming than in conventional farming.[17][18] Because only 5% of US farmland currently uses no-till and residue mulching, there is a large potential for carbon sequestration.[19] Conversion to pastureland, particularly with good management of grazing, can sequester even more carbon in the soil.

Terra preta, an anthropogenic, high-carbon soil, is also being investigated as a sequestration mechanism. By pyrolysing biomass, about half of its carbon can be reduced to charcoal, which can persist in the soil for centuries, and makes a useful soil amendment, especially in tropical soils (biochar or agrichar).[20] [21]

Savanna

Controlled burns on far north Australian savannas can result in an overall carbon sink. One working example is the West Arnhem Fire Management Agreement, started to bring "strategic fire management across 28,000 km² of Western Arnhem Land". Deliberately starting controlled burns early in the dry season results in a mosaic of burnt and unburnt country which reduces the area of burning compared with stronger, late dry season fires. In the early dry season there are higher moisture levels, cooler temperatures, and lighter wind than later in the dry season; fires tend to go out ovenight. Early controlled burns also results in a smaller proportion of the grass and tree biomass being burnt. [22] Emission reductions of 256,000 tonnes of CO2 have been made as at 2007.[23]

Artificial sequestration

For carbon to be sequestered artificially (i.e. not using the natural processes of the carbon cycle) it must first be captured, or it must be significantly delayed or prevented from being re-released into the atmosphere (by combustion, decay, etc.) from an existing carbon-rich material, by being incorporated into an enduring usage (such as in construction). Thereafter it can be passively stored or remain productively utilized over time in a variety of ways.

For example, upon harvesting, wood (as a carbon-rich material) can be immediately burned or otherwise serve as a fuel, returning its carbon to the atmosphere, or it can be incorporated into construction or a range of other durable products, thus sequestering its carbon over years or even centuries. One ton of dry wood is equivalent to 1.8 tons of Carbon dioxide.

Indeed, a very carefully-designed and durable, energy-efficient and energy-capturing building has the potential to sequester (in its carbon-rich construction materials), as much as or more carbon than was released by the acquisition and incorporation of all its materials and than will be released by building-function "energy-imports" during the structure's (potentially multi-century) existence. Such a structure might be termed "carbon neutral" or even "carbon negative". Building construction and operation (electricity usage, heating, etc) are estimated to contribute nearly half of the annual human-caused carbon additions to the atmosphere.[24]

Natural-gas purification plants often already have to remove carbon dioxide, either to avoid dry ice clogging gas tankers or to prevent carbon-dioxide concentrations exceeding the 3% maximum permitted on the natural-gas distribution grid.

Beyond this, one of the most likely early applications of carbon capture is the capture of carbon dioxide from flue gases at power stations (in the case of coal, this is known as "clean coal"). A typical new 1000-MW coal-fired power station produces around 6 million tons of carbon dioxide annually. Adding carbon capture to existing plants can add significantly to the costs of energy production; scrubbing costs aside, a 1000-MW coal plant will require the storage of about 50 million barrels of carbon dioxide a year. However, scrubbing is relatively affordable when added to new plants based on coal gasification technology, where it is estimated to raise energy costs for households in the United States using only coal-fired electricity sources from 10 cents per kWh to 12 cents.[25]

Carbon capture

Main article: Carbon capture and storage

Currently, capture of carbon dioxide is performed on a large scale by absorption of carbon dioxide onto various amine-based solvents. Other techniques are currently being investigated, such as pressure swing adsorption, temperature swing adsorption, gas separation membranes, and cryogenics.

In coal-fired power stations, the main alternatives to retrofitting amine-based absorbers to existing power stations are two new technologies: coal gasification combined-cycle and Oxy-fuel combustion. Gasification first produces a "syngas" primarily of hydrogen and carbon monoxide, which is burned, with carbon dioxide filtered from the flue gas. Oxy-fuel combustion burns the coal in oxygen instead of air, producing only carbon dioxide and water vapour, which are relatively easily separated. Oxy-fuel combustion, however, produces very high temperatures, and the materials to withstand its temperatures are still being developed.

Another long-term option is carbon capture directly from the air using hydroxides. The air would literally be scrubbed of its CO2 content. This idea offers an alternative to non-carbon-based fuels for the transportation sector.

Oceans

Another proposed form of carbon sequestration in the ocean is direct injection. In this method, carbon dioxide is pumped directly into the water at depth, and expected to form "lakes" of liquid CO2 at the bottom. Experiments carried out in moderate to deep waters (350 - 3600 m) indicate that the liquid CO2 reacts to form solid CO2 clathrate hydrates, which gradually dissolve in the surrounding waters.

This method, too, has potentially dangerous environmental consequences. The carbon dioxide does react with the water to form carbonic acid, H2CO3; however, most (as much as 99%) remains as dissolved molecular CO2. The equilibrium would no doubt be quite different under the high pressure conditions in the deep ocean. The resulting environmental effects on benthic life forms of the bathypelagic, abyssopelagic and hadopelagic zones are unknown. Even though life appears to be rather sparse in the deep ocean basins, energy and chemical effects in these deep basins could have far-reaching implications. Much more work is needed here to define the extent of the potential problems.

Carbon storage in or under oceans may not be compatible with the London Convention (Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter) [26].

An additional method of long-term ocean-based sequestration is to gather crop residue such as corn stalks or excess hay into large weighted bales of biomass and deposit it in the alluvial fan areas of the deep ocean basin. Dropping these residues in alluvial fans would cause the residues to be quickly buried in silt on the sea floor, sequestering the biomass for very long time spans. Alluvial fans exist in all of the world's oceans and seas where river deltas fall off the edge of the continental shelf such as the Mississippi alluvial fan in the gulf of Mexico and the Nile alluvial fan in the Mediterranean Sea.

Geological sequestration

The method of geo-sequestration or geological storage involves injecting carbon dioxide directly into underground geological formations. Declining oil fields, saline aquifers, and unminable coal seams have been suggested as storage sites. Caverns and old mines that are commonly used to store natural gas are not considered, because of a lack of storage safety.

CO2 has been injected into declining oil fields for more than 30 years, to increase oil recovery. This option is attractive because the storage costs are offset by the sale of additional oil that is recovered. Further benefits are the existing infrastructure and the geophysical and geological information about the oil field that is available from the oil exploration. All oil fields have a geological barrier preventing upward migration of oil. It is supposed that these geological barriers will also be sufficient as long-term barrier to contain the injected CO2. Identified possible problems are the many 'leak' opportunities provided by old oil wells, the need for very high pressures (about 80 times air pressure) and low temperatures (below about 20 degrees Celsius) to keep the CO2 liquified (only practical very deep underneath the sea) and the conversion of CO2 into acids which can damage the geological barrier. Other disadvantages of old oil fields are their geographic distribution and their limited capacity.

Unminable coal seams can be used to store CO2, because CO2 adsorbs to the coal surface, ensuring safe long-term storage. In the process it releases methane that was previously adsorbed to the coal surface and that may be recovered. Again the sale of the methane can be used to offset the cost of the CO2 storage, although release or burning of methane would of course at least partially offset the obtained sequestration result.

Saline aquifers contain highly mineralized brines and have so far been considered of no benefit to humans except in a few cases where they have been used for the storage of chemical waste. Their advantages include a large potential storage volume and relatively common occurrence reducing the distance over which CO2 has to be transported. The major disadvantage of saline aquifers is that relatively little is known about them compared to oil fields. To keep the cost of storage acceptable the geophysical exploration may be limited, resulting in larger uncertainty about the structure of a given aquifer. Unlike storage in oil fields or coal beds, no side product will offset the storage cost. Leakage of CO2 back into the atmosphere may be a problem in saline-aquifer storage. However, current research shows that several trapping mechanisms immobilize the CO2 underground, reducing the risk of leakage.

A major research project examining the geological sequestration of carbon dioxide is currently being performed at an oil field at Weyburn in south-eastern Saskatchewan. In the North Sea, Norway's Statoil natural-gas platform Sleipner strips carbon dioxide out of the natural gas with amine solvents and disposes of this carbon dioxide by geological sequestration. Sleipner reduces emissions of carbon dioxide by approximately one million tonnes a year. The cost of geological sequestration is minor relative to the overall running costs. As of April 2005, BP is considering a trial of large-scale sequestration of carbon dioxide stripped from power plant emissions in the Miller oilfield as its reserves are depleted.

Mineral sequestration

Mineral sequestration aims to trap carbon in the form of solid carbonate salts. This occurs naturally and is responsible for much of the surface limestone (calcium carbonate). Carbonic acid slowly converts complex silicates to alkali carbonates and silica. Ongoing research aims to speed up these reactions[27]

One proposed reaction is that of the rock dunite, or serpentinite with carbon dioxide to form the carbonate mineral magnesite, plus silica and iron oxide (magnetite).

Serpentinite sequestration is favored because of the non-toxic and predictable nature of magnesium carbonate. However, the ideal reaction (reaction 1) takes place only with extremely magnesium rich olivine or serpentine minerals. The presence of iron in the olivine or serpentine will reduce the efficiency of the circuit and reactions 2 and 3 must take place, producing a slag of silica and magnetite.

Serpentinite reactions

Reaction 1
Mg-Olivine + Water + Carbon dioxide → Serpentine + Magnesite + Silica

(This is a non stoichiometric reaction just to show the principle).

Reaction 2
Fe-Olivine + Water + Carbonic acid → Serpentine + Magnetite + Magnesite + Silica

Reaction 3
Serpentine + carbon dioxide → Magnesite + silica + water

Carbon sinks and the Kyoto Protocol

Because growing vegetation absorbs carbon dioxide, the Kyoto Protocol allows countries that have large areas of forest (or other vegetation) to deduct a certain amount from their emissions, thus making it easier for them to achieve the desired net emission levels.

Some countries want to be able to trade in emission rights in carbon emission markets, to make it possible for one country to buy the benefit of carbon dioxide sinks in another country. If overall limits on greenhouse gas emission are put into place, such a "cap-and-trade" market mechanism will tend to find cost-effective ways to reduce emissions.[28] There is as yet no carbon audit regime for all such markets globally, and none is specified in the Kyoto Protocol. Each nation is on its own to verify actual carbon emission reductions, and to account for carbon sequestration using some less formal method.

In the Clean Development Mechanism, only afforestation and reforestation are eligible to produce CERs in the first commitment period of the Kyoto Protocol (2008–2012). Forest conservation activities or activities avoiding deforestation, which would result in emission reduction through the conservation of existing carbon stocks, are not eligible at this time.[29] Also, agricultural carbon sequestration is not possible yet.[30]

References

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  2. ^ Duncan Graham-Rowe (24 February 2005). "Hydroelectric power's dirty secret revealed". New Scientist. Retrieved 2007-08-26. {{cite web}}: Check date values in: |date= (help)
  3. ^ Raven, J. A. (1999). "Oceanic sinks for atmospheric CO2". Plant Cell & Environment. 22: 741–755. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ Takahashi, T. (2002). "Global sea-air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects". Deep Sea Research II. 49: 1601–1622. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Swift, Roger S. (November 2001). "Soil Science - Abstract: Volume 166(11) November 2001 p 858-871 SEQUESTRATION OF CARBON BY SOIL". Retrieved 2007-02-23. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  6. ^ Jonathan Amos. "Care needed with carbon offsets". BBC. Retrieved 2007-08-26.
  7. ^ "Models show growing more forests in temperate regions could contribute to global warming". Lawrence Livermore National Laboratory. 5 December 2005. Retrieved 2007-08-26. {{cite web}}: Check date values in: |date= (help)
  8. ^ S. Gibbard, K. Caldeira, G. Bala, T. J. Phillips, and M. Wickett (December 2005). "Climate effects of global land cover change". Geophysical Research Letters. 32.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ Y. Malhi, P. Meir, and S. Brown (15 August 2002). "Forests, carbon and global climate". Institute of Ecology and Resource Management. Retrieved 2007-08-26. {{cite web}}: Check date values in: |date= (help)CS1 maint: multiple names: authors list (link)
  10. ^ "U.S. Greenhouse Gas Inventory Reports". EPA. Retrieved 2007-08-26.
  11. ^ a b c d "Land Use, Land-Use Change, and Forestry" (PDF). EPA. Retrieved 2007-08-26.
  12. ^ a b "Executive Summary" (PDF). EPA. Retrieved 2007-08-26.
  13. ^ "About Us: Global Cooling™ Center". Trees for the Future.
  14. ^ Michael Markels, Jr and Richard T. Barber (May 14–17, 2001). "Sequestration of CO2 by ocean fertilization" (PDF). NETL Conference on Carbon Sequestration. Retrieved 2007-08-26.{{cite web}}: CS1 maint: date format (link)
  15. ^ "Questions and Concerns". GreenSea Venture. Retrieved 2007-08-26.
  16. ^ Simon M. Mitrovica, Monica Fernández Amandia, Lincoln McKenzieb, Ambrose Fureya and Kevin J. James (30 December 2004). "Effects of selenium, iron and cobalt addition to growth and yessotoxin production of the toxic marine dinoflagellate Protoceratium reticulatum in culture". Journal of Experimental Marine Biology and Ecology. 313 (2): 337–351. Retrieved 2007-08-26. {{cite journal}}: Check date values in: |date= (help)CS1 maint: multiple names: authors list (link)
  17. ^ Susan S. Lang (13 July, 2005). "Organic farming produces same corn and soybean yields as conventional farms, but consumes less energy and no pesticides, study finds". Retrieved 2007-08-26. {{cite web}}: Check date values in: |date= (help)
  18. ^ Pimentel, David, et al, Bioscience: 55:7, July 2005
  19. ^ Lal, R (2004). "Managing Soil Carbon". Science. 304: 393. {{cite journal}}: Cite has empty unknown parameter: |quotes= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  20. ^ Johannes Lehmann. "Biochar: the new frontier". Retrieved 2007-08-26.
  21. ^ Horstman, Mark (2007-09-23). "Agrichar – A solution to global warming?". ABC TV Science: Catalyst. Australian Broadcasting Corporation. Retrieved 2007-10-08.
  22. ^ "West Arnhem Land Fire Abatement Project". Savanna Information. Tropical Savannas Cooperative Research Centre. Retrieved 2007-10-08.
  23. ^ "Eureka Win for West Arnhem Land Fire Project". Savanna Information. Tropical Savannas Cooperative Research Centre. Retrieved 2007-10-08.
  24. ^ "Climate Change, Global Warming, and the Built Environment - Architecture 2030". Retrieved 2007-02-23. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  25. ^ Robert H. Socolow (July 2005). "Can We Bury Global Warming?". Scientific American: 42.
  26. ^ Norman Baker and Ben Bradshaw (4 July 2005). "Carbon Sequestration". Retrieved 2007-08-26. {{cite web}}: Check date values in: |date= (help)
  27. ^ "Carbon-capture Technology To Help UK Tackle Global Warming", ScienceDaily July 27, 2007, http://www.sciencedaily.com/releases/2007/07/070727091001.htm
  28. ^ Karen Palmer and Dallas Burtraw. "Electricity, Renewables, and Climate Change: Searching for a Cost-Effective Policy" (PDF). Resources for the Future.
  29. ^ Manguiat, M. S. Z., Verheyen, R., Mackensen, J. & Scholz, G. (2005), Legal aspects in the implementation of CDM forestry projects, number 59 in ‘IUCN Environmental Policy and Law Papers’, IUCN. Available from: http://www.iucn.org/themes/law/pdfdocuments/EPLP59EN.pdf
  30. ^ Rosenbaum, K. L., Schoene, D. & Mekouar, A. (2004), Climate change and the forest sector. Possible national and subnational legislation, number 144 in ‘FAO Forestry Papers’, FAO. Available from: http://www.fao.org/docrep/007/y5647e/y5647e00.HTM

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