Ocean Storage

277 6 Ocean storage Coordinating Lead Authors Ken Caldeira (United States), Makoto Akai (Japan) Lead Authors Peter Brewer (United States), Baixin Chen (China), Peter Haugan (Norway), Toru Iwama (Japan), Paul Johnston (United Kingdom), Haroon Kheshgi (United States), Qingquan Li (China), Takashi Ohsumi (Japan), Hans Pörtner (Germany), Chris Sabine (United States), Yoshihisa Shirayama (Japan), Jolyon Thomson (United Kingdom) Contributing Authors Jim Barry (United States), Lara Hansen (United States) Review Editors Brad De Young (Canada), Fortunat Joos (Switzerland) 278 IPCC Special Report on Carbon dioxide Capture and Storage Contents EXECUTIVE SUMMARY 279 6.7 Environmental impacts, risks, and risk management 298 6.1 Introduction and background 279 6.7.1 Introduction to biological impacts and risk 298 6.1.1 Intentional storage of CO2 in the ocean 279 6.7.2 Physiological effects of CO2 301 6.1.2 Relevant background in physical and chemical 6.7.3 From physiological mechanisms to ecosystems 305 oceanography 281 6.7.4 Biological consequences for water column release scenarios 306 6.2 Approaches to release CO2 into the ocean 282 6.7.5 Biological consequences associated with CO2 6.2.1 Approaches to releasing CO2 that has been captured, lakes 307 compressed, and transported into the ocean 282 6.7.6 Contaminants in CO2 streams 307 6.2.2 CO2 storage by dissolution of carbonate minerals 290 6.7.7 Risk management 307 6.2.3 Other ocean storage approaches 291 6.7.8 Social aspects; public and stakeholder perception 307 6.3 Capacity and fractions retained 291 6.8 Legal issues 308 6.3.1 Capacity 291 6.8.1 International law 308 6.3.2 Measures of fraction retained 291 6.8.2 National laws 309 6.3.3 Estimation of fraction retained from ocean observations 292 6.9 Costs 310 6.3.4 Estimation of fraction retained from model results 292 6.9.1 Introduction 310 6.9.2 Dispersion from ocean platform or moving ship 310 6.4 Site selection 292 6.9.3 Dispersion by pipeline extending from shore into 6.4.1 Background 292 shallow to deep water 310 6.4.2 Water column release 294 6.9.4 Cost of carbonate neutralization approach 311 6.4.3 CO2 lakes on the sea floor 295 6.9.5 Cost of monitoring and verification 311 6.4.4 Limestone neutralization 295 6.10 Gaps 311 6.5 Injection technology and operations 295 6.5.1 Background 295 References 311 6.5.2 Water column release 295 6.5.3 Production of a CO2 lake 296 6.6 Monitoring and verification 296 6.6.1 Background 296 6.6.2 Monitoring amounts and distributions of materials released 296 6.6.3 Approaches and technologies for monitoring environmental effects 298 Chapter 6: Ocean storage 279 EXecUTIVE SUMMarY Captured CO2 could be deliberately injected into the ocean at expected close to injection points or CO2 lakes. Chronic effects great depth, where most of it would remain isolated from the may set in with small degrees of long-term CO2 accumulation, atmosphere for centuries. CO2 can be transported via pipeline such as might result far from an injection site, however, or ship for release in the ocean or on the sea floor. There have long-term chronic effects have not been studied in deep-sea been small-scale field experiments and 25 years of theoretical, organisms. laboratory, and modelling studies of intentional ocean storage of CO2 effects on marine organisms will have ecosystem CO2, but ocean storage has not yet been deployed or thoroughly consequences; however, no controlled ecosystem experiments tested. have been performed in the deep ocean. Thus, only a preliminary The increase in atmospheric CO2 concentrations due to assessment of potential ecosystem effects can be given. It is anthropogenic emissions has resulted in the oceans taking expected that ecosystem consequences will increase with -1 -1 up CO2 at a rate of about 7 GtCO2yr (2 GtCyr ). Over the increasing CO2 concentration, but no environmental thresholds past 200 years the oceans have taken up 500 GtCO2 from the have been identified. It is also presently unclear, how species atmosphere out of 1300 GtCO2 total anthropogenic emissions. and ecosystems would adapt to sustained, elevated CO2 levels. Anthropogenic CO2 resides primarily in the upper ocean and Chemical and biological monitoring of an injection project, has thus far resulted in a decrease of pH of about 0.1 at the including observations of the spatial and temporal evolution ocean surface with virtually no change in pH deep in the oceans. of the resulting CO2 plume, would help evaluate the amount Models predict that the oceans will take up most CO2 released of materials released, the retention of CO2, and some of the to the atmosphere over several centuries as CO2 is dissolved at potential environmental effects. the ocean surface and mixed with deep ocean waters. For water column and sea floor release, capture and The Earth's oceans cover over 70% of the Earth's surface compression/liquefaction are thought to be the dominant cost with an average depth of about 3,800 metres; hence, there is factors. Transport (i.e., piping, and shipping) costs are expected no practical physical limit to the amount of anthropogenic CO2 to be the next largest cost component and scale with proximity that could be placed in the ocean. However, the amount that to the deep ocean. The costs of monitoring, injection nozzles is stored in the ocean on the millennial time scale depends on etc. are expected to be small in comparison. oceanic equilibration with the atmosphere. Over millennia, Dissolving mineral carbonates, if found practical, could CO2 injected into the oceans at great depth will approach cause stored carbon to be retained in the ocean for 10,000 years, approximately the same equilibrium as if it were released to the minimize changes in ocean pH and CO2 partial pressure, and atmosphere. Sustained atmospheric CO2 concentrations in the may avoid the need for prior separation of CO2. Large amounts range of 350 to 1000 ppmv imply that 2,300 ± 260 to 10,700 of limestone and materials handling would be required for this ± 1,000 Gt of anthropogenic CO2 will eventually reside in the approach. ocean. Several different global and regional treaties on the law of Analyses of ocean observations and models agree that the sea and marine environment could be relevant to intentional injected CO2 will be isolated from the atmosphere for several release of CO2 into the ocean but the legal status of intentional hundreds of years and that the fraction retained tends to be carbon storage in the ocean has not yet been adjudicated. larger with deeper injection. Additional concepts to prolong It is not known whether the public will accept the deliberate CO2 retention include forming solid CO2 hydrates and liquid storage of CO2 in the ocean as part of a climate change mitigation CO2 lakes on the sea floor, and increasing CO2 solubility by, for strategy. Deep ocean storage could help reduce the impact of example, dissolving mineral carbonates. Over centuries, ocean CO2 emissions on surface ocean biology but at the expense of mixing results in loss of isolation of injected CO2 and exchange effects on deep-ocean biology. with the atmosphere. This would be gradual from large regions of the ocean. There are no known mechanisms for sudden or 6.1 Introduction and background catastrophic release of injected CO2. Injection up to a few GtCO2 would produce a measurable 6.1.1 Intentional storage of CO2 in the ocean change in ocean chemistry in the region of injection, whereas injection of hundreds of GtCO2 would eventually produce This report assesses what is known about intentional storage of measurable change over the entire ocean volume. carbon dioxide in the ocean by inorganic strategies that could Experiments show that added CO2 can harm marine be applied at industrial scale. Various technologies have been organisms. Effects of elevated CO2 levels have mostly been envisioned to enable and increase ocean CO2 storage (Figure 6.1). studied on time scales up to several months in individual One class of options involves storing a relatively pure stream of organisms that live near the ocean surface. Observed phenomena carbon dioxide that has been captured and compressed. This include reduced rates of calcification, reproduction, growth, CO2 can be placed on a ship, injected directly into the ocean, or circulatory oxygen supply and mobility as well as increased deposited on the sea floor. CO2 loaded on ships could either be mortality over time. In some organisms these effects are seen in dispersed from a towed pipe or transported to fixed platforms response to small additions of CO2. Immediate mortality is feeding a CO2 lake on the sea floor. Such CO2 lakes must be 280 IPCC Special Report on Carbon dioxide Capture and Storage Figure 6.1 Illustration of some of the ocean storage strategies described in this chapter (Artwork courtesy Sean Goddard, University of Exeter.) deeper than 3 km where CO2 is denser than sea water. Any of Numerical models of the ocean indicate that placing CO2 these approaches could in principle be used in conjunction with in the deep ocean would isolate most of the CO2 from the neutralization with carbonate minerals. atmosphere for several centuries, but over longer times the ocean Research, development and analysis of ocean CO2 storage and atmosphere would equilibrate. Relative to atmospheric concepts has progressed to consider key questions and issues that release, direct injection of CO2 into the ocean could reduce could affect the prospects of ocean storage as a response option maximum amounts and rates of atmospheric CO2 increase over to climate change (Section 6.2).

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