CDR Methods

CDR may be subdivided into land based CDR and ocean based CDR. Both land based CDR and ocean based CDR may be divided into three subcategories, namely, physical, biological and chemical, depending on the type of intervention.¹⁴⁴ Following the scheme given by the Royal Society, the various CDR techniques can be organized in the following manner as in the Table below:

Table 2.3 Table of CDR Methods¹⁴⁵

144 See, Royal Society 2009, p. 9.

145 Adapted with modification from Royal Society 2009, p. 9. As a detailed sketch of each of this method is beyond the scope of this thesis, for our short discussion, we shall be selecting only the major approaches in both categories.

Biological Physical Chemical Land Based

Techniques

Afforestation and land use

Atmospheric CO2 scrubbers (‘air capture’)

In-situ carbonation of silicates

Basic minerals (incl.

olivine) on soil Biomass/fuels with

carbon sequestration

In-situ carbonation of silicates

Basic minerals (incl.

olivine) on soil Ocean Based

Techniques

Iron fertilization Changing overturning circulation

Alkalinity enhancement (grinding, dispersing and dissolving

limestone, silicates, or calcium

hydroxide) Phosphorus/nitrogen

Fertilisation

Enhanced upwelling

The scientific assumption behind CDR methods is that the concentration of anthropogenic greenhouses in the atmosphere is the main reason for global warming and by removing these green house gases, especially CO2, global warming can be contained. The removal of CDR should be to such levels as to stop global warming.¹⁴⁶ CDR methods, in general, collect and store CO2 by biological, physical, or chemical means. CO2 storing is technically CO2 capture and sequestration. The proposed methods include afforestation, ocean fertilization, weathering of certain sedimentary rocks, or combining carbon capture and storage technology with the production of biofuels, among other approaches. We shall discuss below the leading proposals in CDR.

2.4.1.1 Carbon Capture and Sequestration

146 Royal Society 2009, p. 9.

CO2 is emitted both from the anthropogenic causes and naturally from earth’s carbon cycle. Vegetation in its process of growth absorbs large amount of atmospheric carbon and returns most of it when they decompose. Carbon Capture and Sequestration (CCS) refers to the capturing of CO2 emitted from anthropogenic sources.¹⁴⁷ Biomass, bioenergy and fossil fuel burning are the sources of CCS technologies.¹⁴⁸ Growth of biomass can be manipulated by land carbon sinks (on site burial in soil). Bioenergy Carbon Sequestration (BECS) is a subset of carbon sequestration. In BECS, biomass is used for creating bioenergy like hydrogen or electricity and the CO2 produced by it is sequestered in geological formation.

Biomass can be sequestered as organic material, like burying trees and the waste from crops, or by converting it to biochar.¹⁴⁹ Biomass could be buried also in the deep ocean. There are reports that oceans can store carbon for centuries and carbonate rocks can store carbon for thousands of years.¹⁵⁰

However, its effectiveness and costs are still to be estimated. The residence period of biochar in soil is still uncertain. The question of whether it is better to ‘bury or burn?’ biochar is still unsettled. Besides, the requirement of large amount of energy for transporting and burying biochar is a concern. Royal Society finds the most serious concern that its processes may adversely impact growth, nutrient cycling and the viability of the ecosystems.¹⁵¹ The decomposition of the organic material in the deep ocean and its return to surface is likely.

Further, the absence of adequate parameters makes the cost-effectiveness assessment

147 See, Kelsi Bracmort and Richard K. Lattanzio, “Geoengineering: Governance and Technology Policy,”

Congressional Research Service Report (2013), p. 10. There are natural mechanisms for capturing and storing CO2 in vegetation and Plankton, including the CO2 from anthropogenic sources. Oceans and vegetation have natural carbon sinks.

148 Among these three sources, fossil fuel burning is not considered as geoengineering. If only the CCS technology has biomass or bioenergy as it source, it is treated as geoengineering. Bracmort and Lattanzio observe that it is not clear why the criterion of the of the source is used for labelling CCS as geoengineering and not its outcome, that is the reduction in the amount of the CO2 released in the atmosphere. One explanation is the fossil fuels are treated as carbon positive, while biomass and bioenergy are considered to be carbon negative.

See, Bracmort and Lattanzio 2013, pp. 10-11. We are aware that biofuels and biomass production and usage are not per seclimate engineering activities. However, they are listed under climate engineering as we are following the classification of the Royal Society.

149 Biochar or charcoal is produced when organic matter is decomposed by heating in low oxygen environment.

(For scientific details of biochar, see, CRS (Congressional Research Service) Report R40186, Biochar:

Examination of an Emerging Concept to Sequester Carbon, available at https://www.everycrsreport.com/files/20110111_R40186_1e80270dec3151cfd6d23ae44223e7cbbcc0b2e9.pdf.

For more information on agricultural practices that sequester carbon, see CRS Report RL33898, Climate Change: The Role of the U.S. Agriculture Sector). The decomposition of biomass, the process known as pyrolysis, can produce biochar and biofuel like syngas and bio-oil. In charcoal carbon atoms are bound together more strongly than in plant matter and thus it locks in carbon against easy decomposition for long time periods.

Raw materials for biochar include wood, straw, manure, food waste, etc. Biochar in soil is said to improve agricultural productivity (Royal Society 2009, pp. 11-12).

150 Royal Society 2009, p. 11.

151 Royal Society 2009, p. 11.

difficult. Thus, for Royal Society, “it seems unlikely that this (BECS) will be a viable technique at any scale that could usefully reduce atmospheric carbon.”¹⁵²

Then, there is the method of capturing CO2 from air. “Air capture is an industrial process that captures CO2 from ambient air producing a pure CO2 stream for use or disposal.”¹⁵³ Three technological plans for air capture are, Absorption on solids, Absorption into highly alkaline solutions, and Absorption into moderately alkaline solutions with a catalyst.¹⁵⁴ The technical feasibility of this method is confirmed by the present commercial practices.¹⁵⁵ The lower presence of CO2 in air and the cost of energy and material are problems in this approach. Cost-effectiveness is a test that it has to pass. However, Royal Society finds it to be “useful and important”¹⁵⁶, for, air capture plants can be located close to disposal sites like coal and oil fields, and it enables the industries to deal with “hard-to-control” carbon emissions that cannot be handled by CCS.¹⁵⁷

2.4.1.2 Ocean Fertilization

Carbon cycle of the earth, in layman’s language, is a give and take between land, ocean, atmosphere, vegetation and the other living organisms. Most of the CO2 emitted to the atmosphere today will be transferred to the ocean after a period of 1000 years.¹⁵⁸ The algae on the surface of the ocean and the bacteria at deep sea together act as a “biological pump”¹⁵⁹ for the transfer of CO2 into ocean and its re-return to the surface. The supply of nutrients in the ocean defines the process of drawing CO2 into deep sea. Some climate engineering schemes attempt to expedite this process of transfer of atmospheric CO2 to the ocean. Ocean fertilization is an ocean based approach in CDR. In this approach, nutrients like iron or nitrogen are added to the ocean facilitating the growth of the phytoplankton leading to the enhanced sequestration of CO2. Phytoplankton stores the carbon in their cells in the photosynthesis process and finally sequestrates it in the deep ocean, as they die, as an organic matter. Some studies have estimated that one ton of iron can be effective in removing 30,000

152 Royal Society 2009, p. 11.

153 Royal Society 2009, p. 15.

154 Royal Society 2009, pp. 15-16.

155 David W. Keith &Kenton Heidel and Robert Cherry, “Capturing CO2 from the Atmosphere: Rationale and Process Design Considerations,” in Brian Launder and J. Michael T. Thompson, Eds.,Geo-Engineering Climate Change - Environmental Necessity or Pandora's Box? (Cambridge: Cambridge University Press, 2010), pp.

107-126.

156 Royal Society 2009, p. 16. See also, David W. Keith et al, “Climate Strategy with CO2 Capture from the Air,”Climatic Change 74 (2005):17–45; Edward A. Parson, “Reflections on Air Capture: The Political Economy of Active Intervention in the Global Environment,” Climatic Change 74 (2006): 1573–1580.

157 Royal Society 2009, p. 16.

158 Royal Society 2009, p. 16.

159 Royal Society 2009, p. 17.

to 110,000 tons of atmospheric carbon.¹⁶⁰ By far, iron is considered to be the best nutrient for ocean fertilization.

There are several uncertainties prevailing in regard to the ecological and economic impacts of the ocean fertilization. The rate of multiplication of phytoplankton and duration of sequestration at deep sea are still unsettled issues. While the proponents argue that it enhances fish-stock, opponents lists the potential side effects like ocean acidification, further production of greenhouse gases, and hostile environment for certain ocean species due to excess of oxygen. The need for sustained and prolonged addition of iron is a further concern.¹⁶¹

2.4.1.3 Enhanced Weathering

One of the indigenous mechanisms of nature for removing the CO2 is the disintegration or dissolution of the silicate and carbonate rocks. This is known as weathering.

The silicate minerals in the rocks consume CO2 and form carbonate. This affects the CO2

concentration of a given region. But, this is a very slow process taking several thousand years, quite disproportionate to the rate of burning fossil fuels. The weather enhancement scheme proposes to accelerate the rate of this disintegration. Adding the silicate mineral olivine¹⁶² to the agricultural soil is a technique proposed for this purpose.¹⁶³ This is a land based and ocean based CDR technique. This technique is based on the chemical reaction of silicate rocks with CO2 to form solid minerals. In this reaction, one silicate molecule will consume one CO2 molecule and carbon is stored as a solid material on land. In the ocean variant of this technique, instead of forming the solid material, the dissolved materials are released into the ocean. Compared to the land based approach, the ocean-based approach yields the double result, because, in the latter reaction, one silicate molecule consumes two CO2. The dissolved materials can be stored only in the ocean.

The enormous mining required for the large amount of rocks, and its transportation and the additional requirements of water and energy are the related environmental threats.

The scale and cost of the technique is a negative score for this proposal. Ambivalence about

160Hugh Powell, 2017. “Fertilizing the Ocean with Iron: Should We Add Iron to the Sea to Help Reduce Greenhouse Gases in the Air,” Oceanus, November 13 (2007). Available at http://www.whoi.edu/oceanus/feature/fertilizing-the-ocean-with-iron. Accessed June 23, 2017. Print edition Oceanus 46, 1 (January 2017). See, Bracmort and Lattanzio 2013, pp. 12-13.

161 See Bracmort and Lattanzio 2013, p. 13.

162 Olivine is a type of silicate rock that can increase the soil quality.

163 R. D. Schuiling & P. Krijgsman, “Enhanced Weathering: An Effective and Cheap Tool to SequesterCO2,” Climate Change 74 (2006): 349–354.

the landscape to alter and the long-term impact on the quality of air and water also accompany this proposal.¹⁶⁴

2.4.1.4 Oceanic Upwelling and Downwelling

Basing on the principles of the carbon cycle discussed above, another ocean based CDR proposal is the downwelling or upwelling of the ocean. Unlike the chemical manipulation of the carbon through the weathering method, in this proposal, the atmospheric carbon is transferred to the deep sea by imparting nutrients by upwelling the ocean.

Upwelling here means manipulating the ocean currents. This is achieved by pumping water several hundred meters below the surface with the help of vertical pipes.¹⁶⁵Similarly, the dense waters in the subpolar oceans will be downwelled.¹⁶⁶ It is hoped that rapid increase in the circulation will lead to speedy sequestration. The non-local impact of the exercise is the concern in this technique. An upwelling on one side of the ocean may be compensated by an upwelling on the other side of the globe, which might distort the carbon equilibrium.¹⁶⁷

2.4.1.5 Afforestation

Afforestation is considered as a prime method in carbon storage.¹⁶⁸ It is estimated that forests can contain ten times more carbon for hundreds of years than non-forest vegetation.

Therefore, afforestation aims at planting trees in landscapes that have been treeless for some time. The type of tree, climate and soil are the decisive factors in the amount of carbon stored. The estimate ranges from 2.2 to 9.5 metric tons of CO2 per acre per year.¹⁶⁹ Some model recommendations included converting 60 million to 65 million acres of US agricultural land to woodlands by 2050.¹⁷⁰ Scientific estimation is that a minimum of 20 years is required to reap the benefit of carbon sequestration from afforestation strategies.