5   CO2-storage in the ocean and under the sea floor

Great and growing hopes have been pinned of late upon the sequestration of CO2 as a means of climate mitigation (IEA, 2004). IPCC discussed this theme in depth in a recent Special Report (IPCC, 2005). Estimates expect carbon dioxide capture and storage (CCS) to be market-ready by 2015 (IEA, 2004). Within 50 years, 20–40 per cent of the CO2 emissions arising from the combustion of fossil fuels could be separated, captured and stored (IPCC, 2005), provided that research and development intensify significantly (IEA, 2004). Sequestration technology has direct relevance to the present report, as it also includes the storage of CO2 in the ocean and under the sea floor (Box 5.3-1).

5.1.1   Potential and costs

The technology of carbon dioxide sequestration has three components: CO2 capture, transport and storage (IEA, 2004). Storage locations under consideration include sub-seabed geological formations, the water column of the ocean, and onshore geological formations such as depleted oil and gas fields and unminable coal seams. Chemical fixation to metal oxides is conceivable, although this process is currently regarded as unsuitable in view of the enormous energy consumption and very high costs associated with it (IPCC, 2005).
     The storage capacity of depleted oil and gas fields is approximately 30 to 40 times the current annual CO2 emissions from the combustion of fossil energy carriers. The storage potential through Enhanced Oil Recovery (EOR), whereby CO2 is injected into cavities in order to increase oil yield, is estimated as 3 to 5 times the annual CO2 emissions. Estimates for absorption in coal seams vary between 13 per cent and nine times annual CO2 emissions. Saline aquifers under the sea may be able to hold 40 times the annual CO2 emissions or more (IPCC, 2005). However, with the exception of EOR, little practical experience relating to geological storage is available, and the suitability of potential reservoirs is not clear.
     Large point sources such as large fossil power plants near potential storage locations are regarded as particularly attractive for CCS. Typically, 80–90 per cent of the CO2 generated in fossil power plants could be captured. However, the process requires energy, resulting in an increase in fuel consumption by 16–31 per cent (or even 70 per cent if the technology is retrofitted to existing lignite-fired power plants). Transportation and injection of CO2 require comparatively small amounts of energy. Compared to the amount of emissions avoided, about 20–40 per cent more CO2 has to be put into storage – and more than twice the amount if existing lignite-fired power plants are retrofitted.
     CO2 emissions from large-scale biomass facilities would also be suitable for sequestration. This would create an actual CO2 sink, since the carbon contained in the biomass was previously removed from the atmosphere via photosynthesis.
     The costs of CO2 capture are currently estimated at US$ 11–57 per t of CO2, depending on the fuel, the age and type of the power plant, and the capture technology used (IPCC, 2005). Pipelines are state of the art for CO2 transportation. In the USA alone, 40Mt CO2 are transported each year via pipelines with an overall length of 2500 km. However, for large distances transport by ship is more economic than pipelines. The costs for transporting 1 tonne of CO2 by ship are approximately US$ 15–25 per 5000 km, compared with US$ 4–30 per 1000 km via pipelines (IEA, 2004; IPCC, 2005). The costs for injection and storage are comparatively low, estimated at US$ 0.5–8 per t of CO2. In addition, there are minor costs for monitoring and maintenance of the reservoirs. The total costs of sequestration involving storage in the ocean or under the sea floor therefore range between US$ 20 and 100 per t of CO2.
Based on current knowledge, sequestration of the CO2 released during power generation would lead to increases in generating costs per MWh amounting to US$12–34 in new power plants. For retrofitted lignite-fired power stations the cost increase is estimated at US$33–44 per MWh (IPCC, 2005). Current generating costs are around US$25–55 per MWh, depending mostly on fuel prices, which means that total generating costs including sequestration would be US$45–80 per MWh. This range is comparable with many wind and small-scale hydroelectric plants (Box 5.3-2). Sequestration would increase power generation costs in fossil power plants by 30–60 per cent for new plants. Retrofitting existing plants may triple costs. Optimistic forecasts assume that sequestration costs are likely to come down significantly by 2030. However, based on renewable electricity generating costs of US$10–20 per MWh (IEA, 2004) and expected increases in fossil fuel prices in the long term, electricity generation from renewables is likely to become an increasingly cost-effective option.

5.2.1   Storage and residence time of CO2

Direct injection into seawater is one form of CO2 storage that is under discussion. The CO2 content of the sea surface equilibrates relatively quickly with the atmosphere, so that an artificial increase of CO2 in the surface water would result in outgassing to the atmosphere within a short time. Introduction into the deep sea could, in contrast, ensure a longer residence time of carbon in the sea. The CO2 injected there could remain isolated from the atmosphere for several centuries (IPCC, 2005), but over longer time periods the equilibrium between atmospheric CO2 concentration and that in the sea would be re-established. Then, depending on the atmospheric CO2 concentration, between 65 and 80 per cent of anthropogenic CO2 would be stored in the sea, regardless of whether the CO2 has been emitted to the atmosphere or injected into the ocean (Caldeira et al., 2005). The injection of CO2 into seawater could thus reduce a peak concentration of CO2 in the atmosphere, but it has no influence on the long-term stabilization level of atmospheric CO2. Thus, independent of the consequences for the marine ecology (Section 5.2.2), it does not represent a sustainable solution for the problem because future generations would be burdened with irreversible effects.
     Another technological option would be the storage of CO2 as a liquid or hydrate on the sea floor, which would only be possible in water depths below 3000 m due to its greater density there. Without a physical barrier, however, the CO2 would slowly dissolve from such reservoirs into the overlying water column. So this technology would also only lead to a postponement of the consequences of climate change, but not to their mitigation. None of the technological possibilities being discussed for storage in seawater have been tested in field studies at a meaningful scale. Approval has not been given for any of the research projects so far proposed, not even for injecting just a few tonnes of carbon dioxide into the deep sea.

5.2.2   Impacts of CO2 storage on deep-sea organisms

Just as in the surface layer, the direct injection of CO2 into the deep sea also changes the chemical and physical characteristics of the seawater. Initially this affects the direct surroundings of the location of introduction, for example, the end of the pipeline through which the liquid CO2 flows into the deep sea. Here, as simulations indicate, dramatic changes in the local pH values of up to several units can occur. Through technical solutions that lead to faster dilution (such as a pipeline towed by a ship), the maximum local pH change can be reduced. In the somewhat broader surroundings (several kilometres), the rate of dilution is essentially determined by ocean currents, so that the chemical and physical impacts can be estimated with ocean circulation models. For example, with an input of 0.1Gt C per year (which is less than 2 per cent of the industrial emissions and around 5 per cent of the present CO2 input through the sea surface caused by anthropogenic CO2 level rise in the atmosphere), in up to 0.01 per cent of the ocean volume the pH value could drop by 0.3 units over a period of 100 years (Caldeira et al., 2005). CO2 storage in the deep sea could thus have serious impacts on the deep-sea ecosystem. Deep-sea organisms develop very slowly, their metabolic rates are lower and life expectancy is greater than of organisms in other ocean layers (IPCC, 2005). During their evolution, the inhabitants of the deep-sea ecosystem have adapted to special living conditions, with typically very stable temperatures and pressures, and relatively constant CO2 concentrations (except at volcanic CO2 vents). Such constant environmental variables do not demand rapid adaptive strategies. Thus, it has to be expected for the possible storage of CO2 on the sea floor, as well as for leakage of a storage reservoir below the sea floor, that the ecosystem affected will be critically damaged, or will take a long time to recover from a change in the environment (IPCC, 2005).
Very little is known about the organisms in the deep sea in general, their life forms and interactions. So far, the direct effect of CO2 on marine organisms has mainly been investigated in the laboratory. Studies involving field observations are greatly lacking, except for a few experiments with small CO2 plumes on the sea floor and investigations of volcanic CO2 vents (Pörtner, 2005).
     In one of these in-situ experiments off the coast of California, liquid CO2 was injected at 3600 m in order to study the survival and behaviour of the deep-sea fauna after direct contact with CO2 (Barry et al., 2004). Depending on pH changes and distance from the CO2 plume, the survival rate of the animals varied. Flagellates, amoebas and nematodes in the sediment zone near the CO2 source showed a high mortality. In another study, the scents of prey animals were combined with the extrusion of CO2 (Tamburri et al., 2000). Fish and invertebrates were attracted by the scents and appeared to some extent to remain relatively undamaged, even at a distance of just a few centimetres from the CO2 source, in spite of the low pH value. Carrion-eating hagfish, attracted by the scent of the prey, did not seek to escape narcotization under the high CO2 content. Tyler (2003) therefore fears that animals that die through contact with CO2 introduced into the deep sea could attract larger carrion eaters, who would then likewise be killed by the CO2 plume. Squid and other invertebrates may react more sensitively to high CO2 concentrations than vertebrates (Pörtner et al., 2004) because their body fluids contain no haemoglobin, which helps protect the body from large pH fluctuations. So even a small, local CO2 plume could have wide-reaching effects on its surroundings.
     Risks also arise from outgassing into the atmosphere. Two catastrophes occurred in the 1980s when large CO2 plumes from gas-saturated deep water escaped into the atmosphere from the volcanic Lakes Monoun and Nyos in Cameroon. The disaster at Lake Nyos had devastating consequences: around 80 million m3 of CO2 were expelled, taking the lives of at least 1700 people and several thousand animals up to a distance of 10 km from the lake (Kling et al., 1987; Clarke, 2001). There is sparse information in the literature on whether Lake Nyos harboured life of any kind before the catastrophe, and how the gas plume affected this biotope. Freeth (1987) has reported that, in spite of otherwise favourable living conditions, the local population had neither seen fish in the lake before the catastrophe, nor were fish cadavers found after the event.
     If a large plume of CO2 pumped into the sea should rise to the sea surface or into higher water layers, the possible ecological results can only be speculated. In summary, the largely incalculable ecological risks also support a general prohibition of CO2 storage in seawater.

5.2.3   Present international law

The relevant body of international law relating to CO2 storage in the ocean and below the sea floor can be summarized as follows: according to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter – the London Convention of 1972 – the disposal of certain wastes and other matter (listed in Annex I to the convention) into the sea is forbidden. Further wastes and matter listed in Annex II to the convention may only be disposed of with prior special permission. Other wastes and matter may be disposed of under a prior ‘general’ permit. Since 1 January 1996, the ‘black list’ of Annex I includes industrial waste (No. 11), which means ‘waste materials generated by manufacturing or processing operations’. It can be assumed that separated CO2 is derived from such operations and is therefore industrial waste within the meaning of Annex I. However, with respect to matter whose discharge into the ocean is prohibited, the convention contains an important exception in connection with the extraction of mineral resources: according to Art. III, para. 1(c) of the London Convention, the ‘disposal of wastes or other matter directly arising from, or related to the exploration, exploitation and associated offshore processing of seabed mineral resources’ is not covered by the provisions of the convention. In other words, the disposal of CO2 that is generated by the production of oil or natural gas at sea is permitted under the Convention, as long as the corresponding processing operations are carried out at sea.
     Basically the same legal position exists under the Protocol of 1996, although the approach is different: the Protocol, which will replace the Convention in the future but has not yet been ratified by a sufficient number of signatories and is therefore not yet in force, contains a general prohibition of discharge into the sea, combined with a list (Annex 1) of exceptions. CO2 is not included among these exceptions. This means that the discharge of CO2 would be essentially prohibited under the Protocol once it enters into force. But, according to the Protocol, the discharge would still be allowed when the CO2 is derived from the recovery of oil or natural gas at sea and the processing also takes place there (Art. 1, para. 4.3).

5.3   Sub-seabed geological storage

5.3.1   CO2 injection into the geological sub-seabed

Injecting CO2 into geological formations below the sea floor is basically no different than the procedure on land. Saline aquifers, for example, also provide repositories, and pressurized injection of CO2 into oil formations could facilitate the extraction of oil. The technical systems just have to be adapted for the existing conditions. The appropriate monitoring techniques, however, are very different on land and in the sea. There are also some differences with respect to safety technology (Section 5.3.3.4).
     Not only are great research efforts presently being carried out on CO2 storage in the seabed (CSLF, 2005), but practical experience already exists in this field, and further projects are planned (Bellona Foundation, 2005; Deutsche BP, 2005). When charges on CO2 or the prices for emission rights rise, sequestration becomes more economically attractive, and companies can be expected to apply increasing efforts in addition to the Sleipner project (Box 5.3-1) and EOR (Section 5.1). The Norwegian company Statoil is already considering the transport of ‘foreign’ CO2 through pipelines to the company’s Sleipner gas platform, and storing it there in the CO2 formations already in use under the sea. 

 

Box 5.3-1 The Sleipner project The Sleipner Platform in the North Sea is located approximately 250 km from the coast of Norway. It is the first commercial project for CO2 storage in a saline aquifer under the sea floor. CO2 separated from natural gas here is transported locally to a depth 800 m below the sea floor. The storage of CO2 here is economically interesting because the separation of CO2 from the gas is necessary in any case for later technical use, and the Norwegian government would tax its emission into the atmosphere. Since October 1996 around 1 Mt CO2 has been injected annually into the sub-seabed. By the beginning of 2005 more than 7 Mt CO2 had been injected into the aquifer. By the end of the project the total should be around 20 Mt CO2. The formation has a total capacity of 1–10 Gt CO2.      The project is being observed scientifically, in part to investigate safety and permanence of storage. Initial research results indicate that a dense cap rock seals the formation at the top, preventing the leakage of CO2. Simulation calculations covering hundreds of thousands of years suggest that the CO2 will dissolve in the pore waters and then sink to the bottom of the formation. The probability of long-term leakage is minimal, so that the gas, according to these calculations, should not escape into the North Sea for the next 100,000 years. Even after a million years, only a millionth of the CO2 should escape. This storage could therefore fulfil the required holding time of more than 10,000 years (Section 5.1.2), but these conclusions will have to be better documented scientifically. Sources; IPCC, 2005; Statoil, 20055 Figure 5.3-1 The Sleipner project in the North Sea, simplified representation. The gas production comes from the Sleipner East gas field. The captured CO2 is injected into the Utsira sandstone formation. The small picture shows the position and extent of the Utsira formation in the North Sea. Source: Statoil, 2005

 

5.3.2   Risks and sustainability of CO2 storage in the seabed

Various scenarios are imaginable for the escape of CO2 from formations under the sea floor. If the CO2 emerges at a depth where it occurs as hydrate, then the least damage can be expected. But when the CO2 dissolves in water it contributes to acidification of the sea. The conceivable harmful consequences of leaks for marine organisms have already been described in Section 5.2.2. In cases of very large-volume leaks, the CO2 could also reach the surface, which would, for one, contribute to the enrichment of CO2 in the atmosphere and, for another, present a health risk in the immediate surroundings. But as long as the storage site is not directly on the coast near human settlements, the human health risk is significantly lower than for storage on land. Even where people are in the vicinity, the probability of dangerously high CO2 concentrations in the ocean environment is extremely low because, in contrast to the situation on land, CO2 lakes cannot form. As a rule, such CO2 lakes can only form and persist in depressions on land that have no or poor drainage.
     As discussed in Section 5.1.2, a retention time for CO2 of at least 10,000 years is required for long-term sustainability.

5.3.3   Regulating sub-seabed geological storage

Considering that global CO2 emissions are rising, the option of storing CO2 in geological formations deep below the sea floor should not be dismissed completely. However, such sub-seabed geological storage is not altogether unproblematic (Section 5.3.2). For one thing, a release of CO2 to the atmosphere cannot be excluded entirely. This can be caused by technical faults or by accidents arising in the transport, injection and storage process. It may also be due to the selection of inappropriate geological formations. Current knowledge indicates that, under certain geological and technological preconditions, leakage rates may be acceptable (<0.01 per cent per year). There is a need for substantial further research, however, to be able to verify this with sufficient certainty. Issues in particular need of clarification include the criteria that geological formations must meet, and how any escape of the gas to seawater could be monitored and quantified.
     Moreover, an all too strong political and economic focus on the sequestration option might cause neglect of far superior climate mitigation strategies, such as improving energy efficiency and switching to renewable energies. To attain the goal of sustainable energy systems, it is these superior options that particularly require political support, innovation and the employment of scarce resources (WBGU, 2004). A high renewable energy potential is available in the ocean and above the sea surface (Box 5.3-2).
WBGU therefore views sub-seabed storage of CO2 as being, at most, a transitional option complementing other options (WBGU, 2004). Its deployment should be limited and regulated (Section 5.3.3.4).

Box 5.3-2 Marine renewables In addition to their role within the climate system, the oceans offer options for active mitigation of anthropogenic climate change. On the one hand, increased utilization of renewables from the sea can substitute fossil energy carriers and therefore reduce associated CO2 emissions. On the other hand, CO2 storage in suitable geological formations in the seabed may offer an additional man-made sink for this greenhouse gas. The potential for marine renewables is briefly outlined below, followed by a rough comparison of the respective costs for the two options. Potential for marine renewables Commensurate with their proportion of the Earth’s surface, the oceans receive more than 70 per cent of the solar insolation and almost 90 per cent of the wind energy (Czisch, 2005). They therefore hold the majority of the global renewables resources. However, from today’s perspective only fractions of this theoretically available energy is technically and cost-effectively usable. In addition, the potential is reduced by a wide range of competing uses, particularly along densely populated coastlines. The sustainable potential is reduced further by the fact that environmental aspects have to be taken into account (WBGU, 2004). For example, any expansion of renewables must comply with the ecosystem guard rail (20–30 per cent of marine ecosystems designated as protected areas; Section 2.5). The overall area available for sustainable utilization of renewable energy is therefore reduced significantly. • Wind energy: Studies on the European offshore wind energy potential (Sea Wind Europe, 2003) assume an installed capacity of 111 GW and associated annual generation of 340 TWh by 2015, equivalent to approximately 10 per cent of the technical potential. Siegfriedsen et al. (2003) conclude that outside the European Union approximately 4600 TWh per year could be generated by offshore wind energy converters. With a total of 5000 TWh per year, one-third of current global electricity demand of approx. 15,500 TWh per year would be covered by offshore wind energy. In 19 of 20 countries with the largest potential outside the EU, more than 10 per cent of electricity demand could be covered by offshore wind energy converters by 2020. Of the different energy forms examined, wind energy is the most significant one in terms of potential and implementation. • Wave energy: Wavenet (2003) estimates the global technological potential as 11,400 TWh per year. The global sustainable generating potential of wave energy is approx. 1700 TWh per year, i.e. more then 10 per cent of current global electricity demand. An annual generation figure of 9 TWh is assumed for the EU by 2020. Wave energy is not expected to make a significant contribution to global electricity demand until some time in the future. • Tidal energy: Strong sea currents occur near coasts through tidal and other effects. The potential for energy generation from such currents in North America, Europe, South-East Asia and Australia is estimated at 120 TWh per year. The total global sustainable potential is likely to be several hundred TWh per year. In 5–10 years’ time, sea current turbines could experience a similarly dynamic development as that currently seen with offshore wind energy converters. • Energy from osmosis: A further energy production technique is based on the utilization of osmotic pressure between freshwater and seawater (e.g. in estuaries) using special membranes with high salt retention. This technology is currently only available at the laboratory scale. Globally, a total of 730 GW could be achievable from rivers with flows of more than 500 m3 per second. The sustainable potential, taking into account ecological guard rails and shipping-sector requirements, is estimated to be around 50 per cent of the technical potential, or 2000 TWh per year. Utilization of predominantly coastal marine areas that are currently regarded as technologically accessible would offer a global total potential of approximately 9000 TWh per year from wind, waves, currents and osmosis, with wind power offering by far the biggest potential and quickest implementation. However, the issue of concurrent utilization of coastal marine areas through systems for power generation from wind and waves would have to be examined in more detail, because certain wave energy systems may be difficult to combine with wind farms. In addition, high-density installation of large numbers of systems would lead to significant habitat changes, e.g. through noise emissions, increased shipping traffic and other effects such as underwater cables, so that the overall effect caused by concurrent utilization of several technologies have to be regarded as unsustainable. Renewables vs. CO2 sequestration Generating costs for fossil power plants currently range between US$25 and 55 per MWh, for wind energy and small-scale hydroelectricity between US$35 and 90 per MWh (IEA, 2005). The additional costs for CO2 sequestration relating to electricity production in fossil power plants range between 30 and 60 per cent, depending on the technology and underlying conditions. Assuming moderate future fuel price increases and further cost reductions for investments in both fossil power plants and renewables, sequestration with continued utilization of fossil energy carriers would very likely result in higher CO2 avoidance costs than utilization of renewables in the medium and long term. In addition, sequestration does not reduce dependence on fossil fuels and the potential for associated conflicts. Compared with CO2 sequestration, intensive utilization of renewables is therefore regarded as the preferred option.

5.3.3.1   Provisions under the international law of the sea

The 1972 London Convention and its 1996 London Protocol permit the storage of CO2 in sub-seabed geological formations if the sequestered CO2 originates in the course of processing the mineral resources of the seabed (Section 5.2.3; the same applies to placement of CO2 in seawater). This is the case, for example, with the Sleipner project (Box 5.3-1).
     In contrast, it has not yet been clarified unequivocally whether the 1972 London Convention or, in future, the 1996 London Protocol permits sub-seabed storage, for instance in saline aquifers, of CO2 that was separated on land (IEA, 2005). Article III, para. 3, of the London Convention defines ‘sea’ as ‘all marine waters’. There is some controversy as to whether this definition means that the seabed and the subsoil thereof fall within the scope of the convention. In response to a survey conducted by IMO, Germany argued in favour of construing the term ‘all marine waters’ to include the seabed and the subsoil thereof, as this would be in line with the history and purpose of the convention. The 1996 Protocol defines in Art. 1, para. 7, the term ‘sea’ more precisely, namely as ‘all marine waters other than the internal waters of States, as well as the seabed and the subsoil thereof; it does not include sub-seabed repositories accessed only from land’. This definition, however, has also given rise to controversy over the depth to which the subsoil reaches. In the above-mentioned IMO survey, Germany argued in favour of construing the term as comprehensively as possible, too.
     When construing the treaty wording, however, it needs to be taken into account that the issue of CO2 sequestration, including CO2 storage in the ocean or under the sea floor, was not on the agenda when the 1972 London Convention was negotiated, nor when its 1996 Protocol was elaborated. It is therefore not possible to draw conclusions from the wording of the treaty about the will of the participating states with respect to how to handle CO2. The parties to the London Convention are now addressing this issue intensively (IMO, 2004), for instance at the 27th Consultative Meeting of the parties held in October 2005. In view of the numerous gaps in knowledge and the unresolved issue of whether placement of CO2 in the seabed should be covered by the London Convention and/or the London Protocol, that meeting agreed to debate the issue in greater depth at the 28th Meeting. If the parties resolve to permit the placement in the seabed of CO2 sequestered from separation processes on land, Annex 1 to the London Protocol may need to be amended; this would also be expedient in order to provide clarification. The present state of knowledge thus indicates that it would be necessary to take account of Art. 31, para. 1, of the Vienna Convention on the Law of Treaties, according to which a treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose.

5.3.3.2     UNFCCC and Kyoto Protocol

The production of the national emissions inventories in accordance with the United Nations Framework Convention on Climate Change and the Kyoto Protocol is based on the IPCC Guidelines for National Greenhouse Gas Inventories. At present, these Guidelines do not deal explicitly with the issue of sequestration. However, the IPCC Special Report on CSS (IPCC, 2005) provides for the option of applying the current framework provisions, principles and methods to sequestration activities. The Norwegian approach demonstrates how these general provisions could be applied to sequestration in practice: Norway reports the quantities of CO2 sequestered at the offshore Sleipner facility (Box 5.3-1) and consistently factors any emissions leaked during the injection process into its national emissions (IPCC, 2005). The sequestered CO2 is not added to the emissions inventory but is treated, in effect, as non-emitted. The Guidelines are due to be revised in 2006. It is likely that the current debate about standards for inventorizing sequestered CO2 will flow into this process and relevant provisions will be adopted in the near future. Apart from the practical question of how to inventorize sequestered CO2 in the national reports, a further issue to be clarified is whether, and how, sequestration projects should be integrated into the flexible mechanisms – emissions trading, the Clean Development Mechanism (CDM) and Joint Implementation (JI) (Bode and Jung, 2005; IPCC, 2005). The inclusion of sequestered CO2 in the flexible mechanisms raises a variety of issues (Bode and Jung, 2005) which shall not be discussed in detail here. Matters become especially complicated in relation to the CDM if, for example, an Annex B country ‘imports’ CO2 from developing countries which has been emitted on land and stores it in sub-seabed reservoirs which are already in use. Strictly speaking, such cases do not meet the CDM’s additionality criterion, which means that in essence, no CDM emission credits can be issued. Nor does it necessarily promote technology transfer to developing countries, which is an explicit objective of the CDM. Similarly complex issues arise in relation to emissions trading and JI.

 

5.3.3.3     Instruments to regulate CO2 storage in the seabed

WBGU considers that in view of the leakage risk, regulations are required for activities aimed at the storage of CO2 in the seabed. Firstly, more rigorous minimum standards are needed, with mandatory compliance in order to minimize risks. Secondly, the use of quantity restrictions or liability-based instruments as a response to the risk of leakage would help ensure that lower-risk sustainable emissions avoidance options (e.g. increasing energy efficiency and the use of renewables) are not neglected.

Geological and technological minimum standards
The rate of CO2 leakage over the long term must be very low and must also be readily monitored and verified. Firstly, the retention period for stored CO2 at the chosen site must be very long – at least 10,000 years. Our current state of knowledge indicates that it is possible to meet this criterion, at least in deeper aquifers (Ploetz, 2003; IPCC, 2005). Secondly, the CO2 storage sites must be easily monitored, i.e. it must be possible to record both the leaked and the sequestered amount of CO2 on a reliable basis. At present, however, adequate technologies to measure CO2 leaks are not available.

Indirect quantity restrictions
The leakage risk in particular indicates that sequestered CO2 cannot be viewed as fully ‘avoided’ CO2 emissions in international climate agreements. In the setting and implementation of emissions reductions targets, storage should therefore only be eligible in part as avoided emissions. Various approaches can be considered in this context, both at international level (UNFCCC etc.) or solely for European climate policy at first. In the following, WBGU outlines various instruments which aim to restrict by indirect means the proportion of CO2 storage. It offers an overview of possible approaches which could play an important role in relation to sub-seabed storage as well as sequestration in general. No conclusive evaluation of the instruments can be undertaken here, firstly because no policy decision has been taken on appropriate limitation targets, and secondly because there is still a considerable need for research in many areas (Bode and Jung, 2005; IPCC, 2005).

Liability mechanisms
When applying the above-mentioned instruments to limit CO2 sequestration, countries implicitly make their own assessment of the scale of the leakage risk and the likely damage that leakage would cause. By contrast, liability mechanisms are an alternative or supplementary approach relying on the market mechanism. An effective liability regime for sequestered CO2 means establishing a transparent and credible system to determine who is responsible for discharged CO2 and who is therefore liable to pay compensation: either through ex post adding to overall emissions, ex post acquisition of emission rights, or penalty payments which are used for climate and ocean protection. As long as the operator still exists, it may be comparatively easy to enforce liability. However, the long time scale of climate protection means that the issue of liability must be clarified and safeguarded over the long term. The issues surrounding the cleanup of contaminated sites at national level have shown that it is often the state which ultimately shoulders the financial burden. This applies similarly to cases involving private operators, especially if a defunct polluting company has no legal successor or the successor lacks the resources to pay damages.
     ‘Carbon sequestration bonds’ have emerged as a market-based solution in this debate (Edenhofer et al., 2005). Here, a firm which intends to sequestrate or store CO2 has to deposit a sum of money with a designated authority, equivalent to the amount of sequestered CO2 multiplied by the CO2 certificate price (Edenhofer, 2003). The company would obtain interest for the bond, equivalent to the normal market rate of interest on long-term bonds. The authority – this could be the Climate Central Bank already proposed by WBGU (WBGU, 2003) – devalues the bond according to the fraction of leaked CO2. The balance could be used to pay for emissions prevention measures, such as the promotion of renewable energies, or even the purchase and withdrawal of emissions rights. In the case of leaks from marine disposal sites in particular, the funding of marine conservation measures from these resources would be justified. As the value of the bond falls, the interest paid also decreases. No fixed price for the devaluation of the bond is set in advance; instead, the devaluation increases over time in line with the actual amount of leaked CO2.      The idea is that the company tries to sell the right to the interest accumulating on the deposit as a ‘bond’ on the financial markets. This can only be achieved if potential purchasers are offered a rebate on the value of the bond which is high enough to offset the risk of devaluation by the authority. During trading, the market value would reflect not only the devaluation of the deposited amount but also the capital market’s assessment of the likely leakage risk in future. The concept of ‘carbon sequestration bonds’ is a very interesting and innovative approach to risk assessment and liability, and merits further research.

5.4   Recommendations for action: Regulating CO2 storage

5.4.1   Prohibiting CO2 injection into the ocean

WBGU firmly rejects the storage of CO2 in the ocean, i.e. in the water column and on the sea floor. The ocean is in permanent exchange with the atmosphere, with the result that this option does not mitigate the long-term consequences of CO2 emissions for future generations. It is therefore not a sustainable option. The risk that ecosystems will suffer appreciably under an elevated CO2 concentration in the water is a further argument against the disposal of this greenhouse gas in seawater (Section 5.2.2; IPCC, 2005; Pörtner, 2005). Moreover, the international community will scarcely be able to control CO2 lakes on the sea floor, and the release of this CO2 to the atmosphere over the long term cannot be excluded. WBGU therefore recommends a full and comprehensive ban on CO2 injection into the ocean, regardless of the territorial status of waters.
     The 1972 London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, in conjunction with its London Protocol (Section 5.3.3.1; the protocol has not yet entered into force) prohibit in principle the placement of CO2 in the ocean. Both agreements, however, contain an important exception that needs to be firmly rejected in light of the above: both permit in their current wording the injection of CO2 that arises from the production of mineral oil or natural gas, as long as the associated processing operations take place at sea. The prohibition on the injection of CO2 arising from processing operations on land that is already implicitly in place should therefore be extended explicitly to such CO2 that is separated in the course of seabed resource exploration and processing operations at sea. Such a prohibition could possibly be complemented by a corresponding arrangement under the Framework Convention on Climate Change; this could also serve to cover those states that do not ratify the London Protocol.

5.4.2   Limiting CO2 storage in the seabed

The disposal of CO2 in the seabed poses substantially less risk than its injection into the water column or on the sea floor. For that reason, and in view of the almost unavoidable rise in energy consumption especially in developing and newly industrializing countries, WBGU considers it acceptable for a transitional period to use injection into the geological sub-seabed as an option complementing more sustainable emissions reduction strategies.
WBGU accordingly recommends clarifying the issue of conformity of sub-seabed geological storage with the London Convention or London Protocol in the relevant bodies of the convention and protocol in such a way that CO2 sequestration in sub-seabed geological formations is permissible regardless of the location of processing operations. If it should not prove possible to generate consensus on construing these legal provisions to mean that sub-seabed CO2 disposal is permissible, then modifying or supplementing the London Protocol should be considered. WBGU also argues that such activities should only be permitted from the outset for a limited period, such as several decades.
     Before the international law of the sea can be construed or supplemented in such a way, universal minimum technological standards would first need to be defined and complied with. These need to be developed specifically for marine transport, for CO2 injection and storage, and for the characteristics and monitoring of geological disposal sites. As long as the problems currently associated with the measurement of CO2 releases persist, WBGU advises applying exceedingly strict requirements upon geological disposal sites. WBGU takes the view that in this respect, too, the London Convention or London Protocol provides an appropriate framework for setting standards, underpinned by more comprehensive rules governing sequestration activities under the Framework Convention on Climate Change.
     The IPCC Guidelines play an important role in this context. These guidelines govern the preparation of national emissions inventories. Their review is currently pending. WBGU shares the view of the IPCC Special Report (2005) that the present regulatory structure, including the flexible mechanisms, can in principle also be applied to sequestered CO2. WBGU does not consider this expedient in all situations, but does regard it as purposeful in the case of CO2 disposal in verified sub-seabed geological formations. WBGU recommends, however, that when sequestered CO2 is integrated into inventories and into the flexible Kyoto mechanisms the risk of leakage be taken into account. This can be done through, for instance, deductions in emissions trading or from CDM credits, or through liability rules (Section 5.3.3.4).

5.5   Research recommendations

Risks posed by the use of geological formations for CO2 storage
There is a need for further research on the permanence of marine CO2 storage in deep geological formations. The associated monitoring procedures also need further development. Furthermore, research should be conducted on the potential impacts of CO2 leakage upon marine ecosystems and organisms.
The long-term effects of storage upon atmospheric CO2 concentrations should also be studied. An issue of particular importance in this respect is which specifications a storage site needs to meet in order to ensure stable atmospheric CO2 concentrations at a low level over the long term. This will require an improved understanding of the carbon cycle on a millennial time scale.

Legal setting
The instruments of international law governing the permissibility of CO2 storage in deep sub-seabed geological formations need to be studied comprehensively. Not only the London Convention with its 1996 Protocol should be taken into account. It is equally important to analyse links to other regimes in international law – notably the Framework Convention on Climate Change with its Kyoto Protocol, and the United Nations Convention on the Law of the Sea (UNCLOS).

Regulating CO2 storage in the seabed
The manner in which geological storage of CO2 in the seabed (and, it is worth noting, on land) may be eligible as a climate mitigation measure under the international climate protection regime needs to be clarified unequivocally in the near future. There is a need for research in the social sciences and economics on the issues surrounding the flexible mechanisms. Identifying which instruments for the limitation of sequestration are effective, efficient and enforceable in international law and policy is an issue of particular importance.

Marine renewables
Great uncertainties still attach in some instances to the renewable energy potential of marine sources such as offshore wind, wave energy, salt gradient energy or ocean thermal energy conversion. There is a considerable need for further research in order to identify the sustainable global potential. This concerns both the methods and the impacts that need to be taken into account.