Skip to main content
  • Other Publications
    • Philosophical Transactions B
    • Proceedings B
    • Biology Letters
    • Open Biology
    • Philosophical Transactions A
    • Proceedings A
    • Royal Society Open Science
    • Interface
    • Interface Focus
    • Notes and Records
    • Biographical Memoirs

Advanced

  • Home
  • Content
    • Latest issue
    • Forthcoming
    • All content
    • Subject collections
    • Videos
  • Information for
    • Authors
    • Guest editors
    • Reviewers
    • Readers
    • Institutions
  • About us
    • About the journal
    • Editorial board
    • Policies
    • Citation metrics
    • Open access
  • Sign up
    • Subscribe
    • eTOC alerts
    • Keyword alerts
    • RSS feeds
    • Newsletters
    • Request a free trial
  • Propose an issue
Open Access

Ocean acidification in a geoengineering context

Phillip Williamson, Carol Turley
Published 6 August 2012.DOI: 10.1098/rsta.2012.0167
Phillip Williamson
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Carol Turley
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • Article
  • Figures & Data
  • Info & Metrics
  • eLetters
  • PDF
Loading

Abstract

Fundamental changes to marine chemistry are occurring because of increasing carbon dioxide (CO2) in the atmosphere. Ocean acidity (H+ concentration) and bicarbonate ion concentrations are increasing, whereas carbonate ion concentrations are decreasing. There has already been an average pH decrease of 0.1 in the upper ocean, and continued unconstrained carbon emissions would further reduce average upper ocean pH by approximately 0.3 by 2100. Laboratory experiments, observations and projections indicate that such ocean acidification may have ecological and biogeochemical impacts that last for many thousands of years. The future magnitude of such effects will be very closely linked to atmospheric CO2; they will, therefore, depend on the success of emission reduction, and could also be constrained by geoengineering based on most carbon dioxide removal (CDR) techniques. However, some ocean-based CDR approaches would (if deployed on a climatically significant scale) re-locate acidification from the upper ocean to the seafloor or elsewhere in the ocean interior. If solar radiation management were to be the main policy response to counteract global warming, ocean acidification would continue to be driven by increases in atmospheric CO2, although with additional temperature-related effects on CO2 and CaCO3 solubility and terrestrial carbon sequestration.

1. Carbon dynamics in today’s ocean

(a) The ocean carbon cycle

The ocean exchanges CO2 with the atmosphere and provides an important net sink for carbon. Carbon uptake by the ocean has slowed the increase in atmospheric CO2 and its associated consequences for the Earth’s climate: without such uptake, atmospheric CO2 would now already be approximately 450 ppm [1]. The net ocean uptake (approx. 2 Gt C yr−1) is, however, small in terms of the natural fluxes between the reservoirs, representing only about 2 per cent of the total CO2 cycled annually across the air–sea interface. Thus relatively minor changes in ocean biogeochemistry or ocean physics affecting carbon fluxes— in either direction—could have a major impact on the magnitude, or even sign, of the net CO2 flux and hence on the future climate.

The large natural annual fluxes of CO2 between the ocean and the atmosphere are due to a combination of physical and biological processes, the former driven by ocean circulation and the latter involving marine productivity, calcification and particle sinking. Around half of primary production on Earth is carried out by marine phytoplankton—microalgae and photosynthetic bacteria—that require sunlight, nutrients (primarily supplied from deep waters) and dissolved inorganic carbon (DIC; see §1b). As phytoplankton consume DIC in the upper ocean, they can cause an undersaturation of dissolved CO2, hence driving CO2 uptake from the atmosphere. Although most of the carbon fixed through this process is respired within days to months through processing by the marine food web, a small proportion is repackaged into faecal pellets or aggregates that fall through the deep ocean. The carbon in these particles is removed from the atmosphere for decades to centuries, and, for an even smaller proportion which is not remineralized, incorporated in deep-sea sediments for millions of years.

Physical, chemical and biological geoengineering techniques have all been proposed to increase carbon sequestration in the ocean; these are discussed in greater detail in §5.

(b) The ocean carbonate system

DIC is present in seawater in four forms: dissolved carbon dioxide (CO2), carbonic acid (H2CO3), bicarbonate ions (Embedded Image and carbonate ions (Embedded Image. These occur in dynamic equilibrium, reacting with water and hydrogen ions (H+). At a mean surface seawater pH of 8.1 and salinity of 35, approximately 91 per cent of the DIC is bicarbonate, with about 8 per cent as carbonate and less than 1 per cent each as dissolved CO2 and carbonic acid [2]. Increased CO2 in the atmosphere leads to increases in dissolved CO2, carbonic acid, bicarbonate and hydrogen ion concentrations, hence pH falls. However, the concentration of carbonate ions decreases, as a result of a reaction between CO2 and carbonate. The relative changes in bicarbonate, carbonate and hydrogen ion concentrations in the surface ocean arising from doubling, tripling and quadrupling of atmospheric CO2 (compared with pre-industrial values) are shown in figure 1.

Figure 1.
  • Download figure
  • Open in new tab
  • Download powerpoint
Figure 1.

Percentage changes in average global surface ocean ion concentrations resulting from up to a fourfold change (300% increase) in atmospheric carbon dioxide, compared with pre-industrial values and at an assumed uniform and constant upper ocean temperature of 18°C. Values for atmospheric CO2 change from 280 to 1120 ppm; bicarbonate ions from 1770 to 2120 μmol kg−1; carbonate ions from 225 to 81 μmol kg−1; and pH from 8.18 to 7.65 (where pH is defined as the negative decimal logarithm of the hydrogen ion activity, and a linear relationship is assumed between activity and concentration). Adapted from Royal Society [3].

The decrease in carbonate ions increases the rate of dissolution of CaCO3 minerals in the ocean. The saturation state (Ω) is the degree of CaCO3 saturation in seawater: Embedded Image where [Ca2+] and [Embedded Image] are the in situ calcium and carbonate ion concentrations, respectively, and Ksp is the solubility product for CaCO3 (concentrations when at equilibrium, neither dissolving nor forming). Values of Ksp depend on the crystalline form of CaCO3; they also vary with temperature and pressure, with CaCO3 being unusual in that it is more soluble in cold water than warm water.

Environments with high saturation states are potentially more suitable for calcifying organisms (plants and animals that produce shells, plates and skeletons of CaCO3), since high Ω values reduce the energy required for bio-calcification, involving active intracellular regulation of Ca2+, H+ and inorganic carbon [4], and also help maintain the integrity of mineral CaCO3 after its formation [5]. The inclusion of a proteinaceous organic matrix increases shell stability under low pH and low saturation conditions; however, it also increases the metabolic cost of shell formation [6], by up to 50 per cent. Currently, Ω is more than 1 for the vast majority of the surface ocean, i.e. seawater is supersaturated with respect to CaCO3. However, most of the deep ocean is unsaturated, Ω<1, owing to changes in temperature, pressure and the accumulation of biologically produced CO2; it is therefore corrosive to unprotected CaCO3 structures, and calcareous (micro-) fossils are absent from sediments below the level at which the rate of CaCO3 dissolution exceeds the rate of its supply.

The three main mineral forms of CaCO3, in order of least to most soluble, are calcite, aragonite and magnesium-calcite; their differences in Ksp result in each form having different saturation state profiles and saturation horizons, with the aragonite saturation horizon (ASH) being shallower than the calcite saturation horizon (CSH). Ω varies with latitude (mostly because of temperature effects), with lowest surface Ωaragonite in the Arctic and Southern Oceans currently mostly below 1.5 [7], although with large spatial and seasonal variability. The ASH depth in the North Pacific is less than or equal to 600 m but in the North Atlantic can be more than 2000 m, this difference being due to global circulation patterns affecting CO2 values at depth. Increasing atmospheric CO2 will cause Ω to decrease, and the ASH and CSH levels to move towards the sea surface, as has already occurred in the past 200 years [8]. Most of the Arctic is projected to be undersaturated with respect to aragonite and calcite by approximately 2030 and 2080, respectively, with equivalent values for the Southern Ocean being approximately 2060 and 2100 [7].

There is currently considerable spatial and seasonal variation in ocean surface carbonate system parameters and pH, with the latter varying from 7.6 to 8.2 [3,9,10]. The highest surface pH occurs in regions of high biological production, where dissolved CO2 is less than atmospheric levels as a result of DIC being fixed by phytoplankton and exported into deeper water. The lowest open ocean pH values occur in upwelling regions (e.g. west coasts of North America and South Africa, the equatorial Pacific and the Arabian Sea) where mid- and deep waters with high dissolved CO2 and low pH are brought to the surface [11]. Seasonally low pH can also occur in coastal waters and estuaries, subject to eutrophication effects, high organic loads and low-pH river inputs.

2. Observed chemical and biological changes owing to ocean acidification

(a) Evidence for anthropogenic ocean acidification

Model-based calculations indicate that, since the industrial revolution (approx. 1800), the release of anthropogenic CO2 to the atmosphere and subsequent flux into the ocean has reduced the global average surface pH by approximately 0.1 unit, equivalent to approximately 30 per cent increase in H+ concentrations [8]. Since 1990, surface ocean pH has directly been measured or calculated at several locations, with the average recent decrease estimated as 0.0019 pH units per year at the Hawaii Ocean Time-series (HOT; close to the site of long-term atmospheric CO2 measurements at Mauna Loa) [12]; 0.0017 per year based on transects in the North Pacific [13]; 0.0012 per year at the Bermuda Atlantic Time-Series (BATS) [14] and 0.0017 per year at the European Station for Time-Series in the Ocean at the Canary Islands (ESTOC) [15]. There can, however, be relatively large interannual variability, likely to be caused by variability in CO2 flux rates [16]. Aragonite saturation, calcite saturation and carbonate ion concentrations were measured or estimated in several of these studies; such parameters also showed a marked decline over the last decade.

(b) Impacts of recent ocean acidification on organisms and ecosystems

At most open ocean locations, the estimated decreases in pH and carbonate ion concentration since the industrial revolution have now exceeded current seasonal variability, with potential impacts (negative or positive) on marine organisms. Field evidence for such effects is, however, inconclusive, owing to a lack of long time-series carbonate chemical data with which biological observations can be correlated [17]. There are also inherent limitations in the interpretation of historical data involving simultaneous changes in many environmental parameters, such as temperature, nutrients, pollutants, food-web structure and local/regional circulation changes.

For example, reductions in the abundance of two species of pteropods (planktonic marine molluscs) and of bivalve larvae are apparent in large-scale survey data for the northeastern Atlantic over the period 1960–2007 [18]. Yet for echinoderm larvae, no consistent changes occurred, and for foraminifera and coccolithophores (data for latter limited to 1990–2007, and not well sampled by the Continuous Plankton Recorder) there is evidence for recent increases in abundance—that may be climate-driven or due to other changes in plankton distributions and biodiversity [19]. The absence of coccolithophores from the Baltic Sea might be because of existing acidification and low saturation conditions (winter Ωcalcite values less than 1), or because of low salinity [20].

Recent shell thinning has been reported for the planktonic foraminifera Globigerina bulloides in the Southern Ocean [21], and other ecological effects of ocean acidification might be expected to initially occur elsewhere where Ω values are already low. For example, in upwelling areas along the western coast of North America, where shelf-sea waters can be undersaturated from February to September (with pH values as low as 7.6) [11], and the Pacific coast of Central America. Coral reefs occur in the latter regions, but produce little or no interskeletal pore cement to hold them together and suffer some of the highest erosion rates measured [22]. This is in contrast to the coral reefs in the tropical Atlantic off the Bahamas that live in waters with less CO2 and higher pH, and which have a high percentage of interskeletal pore cement (60% occurrence, compared with less than 2% for Galapagos samples) [22].

Field data for more direct effects of reduced pH on warm-water corals are sparse. Nevertheless, reefs in the Red Sea have shown correlated responses in net calcification rate to natural fluctuations in Ω and temperature [23], and decreases in net calcification of 14–21% and in growth of 13–30% have been reported over the past approximately 20 years for corals in the Great Barrier Reef [24]. Sea surface temperature is uncorrelated to this decline.

Cold-water corals do not need sunlight and mostly live at depths of 200–2000 m, with their lower depth range closely matching the ASH [25]. However, the ASH has been shoaling at a rate of approximately 1 m yr−1 off California [11] and up to 4 m yr−1 in the Iceland Sea [26]. The latter causes 800 km2 of the deep-sea floor around Iceland, previously bathed in saturated waters, to be newly exposed to undersaturation each year. It is thus likely that cold-water corals are increasingly becoming exposed to corrosive waters, and such deep-water ecosystems might therefore be the most vulnerable to current and future levels of ocean acidification [27]. Although cold-water corals are difficult to study, controlled laboratory experiments indicate that calcification by Lophelia pertusa, a long-lived structure-forming species, may be very sensitive to ocean acidification [28].

3. A ‘business as usual’ future ocean

(a) Decadal to century-scale future acidification

If anthropogenic CO2 release continues to track the highest emission scenarios used to date for climate projections by the Intergovernmental Panel on Climate Change [1,29], atmospheric CO2 will exceed 1000 ppm by 2100. Hydrogen ion concentrations in surface waters would then double (figure 1), resulting in a pH fall of approximately 0.4 since pre-industrial times [3]. If all known fossil fuel reserves were to be used, on a somewhat longer time scale, surface ocean pH would decline by approximately 0.7 compared with pre-industrial levels [30].

Such pH shifts would greatly change CaCO3 saturation values. Undersaturation would occur earliest in polar and sub-polar regions [7,8,31,32], and saturation levels would also slowly decline at all depths throughout the global ocean [33,34]. Thus the saturation horizons for both aragonite and calcite would shoal by 100–1000 m, with greatest ecological impact expected for shelf seas in the Pacific, in upwelling regions, and in polar and sub-polar waters [8].

The global mean surface ocean pH predicted for 2050 is likely to be lower than mean surface values previously experienced by marine ecosystems over the last 24 million years, with the current rate of pH change being more rapid than experienced for approximately 60 million years [35–37].

(b) Potential future impacts on marine organisms and ecosystems

Several hundred experimental studies have been carried out in the past decade, to simulate the impacts of a high CO2 world on a wide range of taxonomic groups and biological processes. For reviews, see [8,10,14,17,38–41].

Recent meta-analyses have combined experimental data from different studies, for all organisms [42,43] and for microbes and microbially driven processes [44]. Based on 372 studies, the meta-analysis by Hendriks et al. [42] found that calcification was the process most sensitive to ocean acidification. However, because there were positive as well as negative effects for some species and processes, these authors questioned whether marine functional diversity would be much impacted at pH scenario values for 2100. That conclusion has been criticized [43,45] as failing to take account of heterogeneities within groupings, and minimizing the importance of vulnerable life-cycle stages. The meta-analysis by Kroeker et al. [43] used more robust methods; they found significant negative effects of a 0.4 pH change on survival, calcification, growth and reproduction, as summarized in figure 2.

Figure 2.
  • Download figure
  • Open in new tab
  • Download powerpoint
Figure 2.

Meta-analysis of the effect of pH decrease by 0.4 units on reproduction, photosynthesis, growth, calcification and survival of a wide range of marine organisms. Mean effect and 95% confidence limits calculated from log-transformed response ratios, here re-converted to a linear scale. Adapted from Kroeker et al. [43].

Although decreased calcification might be considered an unsurprising impact of ocean acidification [46], some organisms increase calcification under experimental treatments [47], usually at the expense of other physiological processes [48]. There is also high variability in other observed responses, as indicated in figure 2. Such sensitivity differences may reflect species-specific responses to different carbonate chemistry parameters [49] as well as differences in the ability of species and groups to regulate internal pH [38]. Enzyme function, protein phosphorylation and the carrying capacity of haemoglobin for O2 are all pH-sensitive, and there is a metabolic cost in regulating pH to maintain these processes.

For all organisms, prolonged exposure to pH values lower (or higher) than evolved optimal conditions will therefore require more energy for internal pH regulation, reducing the energy available for growth, maintenance or reproduction. For example, calcification in corals is costly, requiring 13–30% of energy expenditure compared with tissue growth which requires approximately 8 per cent [50]. Organisms with an active high-metabolic lifestyle such as brachyuran crustaceans, teleost fish and cephalopods may be better adapted to cope with future ocean acidification than those with low-metabolic lifestyles, such as bivalves and echinoderms, although even those with high-metabolic lifestyles may be vulnerable in early life stages [51].

For more sedentary species, effects are likely to be greater and even small changes in physiology or behaviour can produce major changes in population success under competitive environmental conditions. Indirect ecological implications may, however, not be apparent in relatively short term laboratory experiments where food and nutrients are usually abundant, and competitors and predators absent. In such experiments, organisms can eat more to supply the increased energy demand, without trading-off energy for other physiological processes. Overall, the increase in metabolism frequently observed in ocean acidification experiments should be considered a negative, rather than positive impact (although the opposite interpretation has also been made [42]).

Nevertheless, there are marine organisms, mostly photosynthetic, that genuinely do seem to benefit from ocean acidification under experimental conditions. These include seagrasses, some non-calcifying phytoplankton (micro-algae and cyanobacteria) and several other microbial groups (table 1). These might benefit directly, by CO2-enhancement of photosynthesis, or indirectly, if predators and competitors are reduced in abundance.

View this table:
  • View inline
  • View popup
Table 1.

Summary of probable main effects of future ocean acidification on different groups of marine organisms, mostly based on experimental studies.

The scaling of this wide range of experimental responses, whether negative or positive, to ecological and biogeochemical impacts is not straightforward [88,89], and many knowledge gaps remain, at the species, community and ecosystem levels. Such uncertainties and ambiguities are in part due to methodological differences that complicate or invalidate intercomparisons (e.g. whether pH is directly measured or computed from other parameters; duration and level of CO2 exposure; whether acidification is achieved by CO2 enrichment or by adding acid; and the relative availability of nutrients/food) and in part due to the difficulty in carrying out experiments involving multi-species interactions over long time periods, taking account of confounding variables (e.g. temperature, nutrient availability) and the potential for adaptive responses. There is also inherent biological variability, that can be strain-specific [87,88]. This should not be surprising, since the ocean harbours an enormous biodiversity, with strong competitive pressures to exploit the whole range of environmental conditions.

Major national and international programmes are currently underway to address these issues. These programmes use standardized protocols [91] to improve intercomparability; they are also attempting to integrate experimental studies, fieldwork and modelling, with effort directed at elucidating genetic and physiological factors that affect both short- and long-term responses. The overall goal is to assess ocean acidification impacts from the molecular to global level, involving studies not only of direct effects on organisms, but also of the potential for indirect effects on biodiversity, climate and socio-economic systems (figure 3).

Figure 3.
  • Download figure
  • Open in new tab
  • Download powerpoint
Figure 3.

Conceptual representation of possible future ocean acidification impacts on planktonic and benthic organisms, with implications for ecosystems and ecosystem services. DMS, dimethylsulphide; DMSP, dimethylsulphoniopropionate; Ω, saturation state (for CaCO3). Image: T. Tyrrell and P. Williamson.

4. Effect of emission reduction on ocean acidification

The tight relationship between atmospheric CO2 and surface ocean chemistry means that emission reduction measures that stabilize the former, e.g. at 450, 550, 650, 750 or 1000 ppm, will also stabilize surface ocean pH, at approximately 8.01, 7.94, 7.87, 7.82 and 7.71, respectively (figure 4) [34]. The predicted consequences of a pH fall of 0.4 (to 7.7, discussed earlier as the ‘business as usual’ scenario) are therefore avoidable, if strong mitigation measures are taken.

Figure 4.
  • Download figure
  • Open in new tab
  • Download powerpoint
Figure 4.

(a) The relationship between changes in global annual carbon emissions over the period 1800–2500 and (b) global mean surface pH. The pH stabilization levels of 8.10, 8.01, 7.94, 7.87, 7.82 and 7.70 correspond to atmospheric CO2 levels of 350, 450, 550, 650, 750 and 1000 ppm. Dotted lines labelled OSP (overshoot stabilization profile) show pathways requiring negative CO2 emissions (i.e. carbon dioxide removal geoengineering) to achieve atmospheric CO2 stabilization at 350 and 450 ppm; dashed lines labelled DSP (delayed stabilization profile) show delayed approach to emissions reductions to achieve stabilization at 450 and 550 ppm; solid lines labelled SP represent stabilization profiles. From Joos et al. [34], modified by permission of Oxford University Press.

In that context, it is valid to ask whether a safe/dangerous threshold can be defined for ocean acidification, in a similar way that a 2°C increase (likely to result from an atmospheric level of approximately 450 ppm CO2-equivalent) is considered the acceptability threshold, in policy terms, for temperature change [92,93]. Thresholds for dangerous pH change are harder to define, since impacts seem likely to be incremental and regional, rather than involving a single, global-scale ‘tipping point’; furthermore, their economic consequences are currently not well quantified [33,94,95]. Nevertheless, the CO2 stabilization target of 450 ppm would still involve considerable risk of large-scale and ecologically significant ocean acidification impacts for the upper ocean.

Thus, at that level: 11 per cent of the global ocean would experience a pH fall of more than 0.2 relative to pre-industrial levels [32]; only 8 per cent of present-day coral reefs would experience conditions considered optimal for calcification (Ωaragonite>3.5), compared with 98 per cent at pre-industrial atmospheric CO2 levels [32]; approximately 10 per cent of the surface Arctic Ocean would be aragonite-undersaturated for part of the year [7]; and potentially severe local impacts could occur in upwelling regions and coastal regions [31,96,97].

The response of deep ocean chemistry to atmospheric CO2 stabilization involves very different time scales. Modelling studies indicate that recovery to major perturbations in the global carbon cycle can take 50 000–100 000 years, involving equilibration with carbonate minerals and the carbonate–silicate cycle [98]. Within the next 1000 years, marine CaCO3 sediment dissolution is estimated to account for neutralizing 60–70% of anthropogenic CO2 emissions, while 20–30% remains in the ocean water column and the remaining approximately 10 per cent is accounted for by terrestrial weathering of silicate carbonates [99].

5. Implications of geoengineering for ocean acidification

(a) General issues

The technological, environmental and socio-economic aspects of geoengineering warrant scientific attention on the basis that, if emission reductions should be insufficient to avert dangerous climate change, other large-scale interventions may need to be seriously contemplated [100–103]. While direct mitigation is the preferred UK and international policy approach, the relatively slow progress to date in global emissions control makes it likely that the ‘safe’ global warming threshold of an approximately 2°C increase in global surface temperature (relative to pre-industrial conditions) will be exceeded [104–106].

Differences in the definition of geoengineering have important regulatory implications; e.g. relating to recent decisions by the Convention on Biological Diversity [107]. For considering the implications of geoengineering for ocean acidification, a relatively broad definition has utility, consistent with [100]: ‘the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change’. A key aspect of counteraction is that geoengineering techniques should potentially be capable of remedying future climate problems, i.e. reversing rather than just slowing global warming. Nevertheless, climate stabilization might still be the target outcome (pragmatically achieved in combination with other measures).

The division of geoengineering into solar radiation management (SRM) and carbon dioxide removal (CDR) techniques [100] is now well established, and that terminology is followed here. Other approaches are, however, possible, and these may be given increasing attention in the future; for example: reducing the coverage or long-wave opacity of cirrus clouds [108], and techniques that might actively remove greenhouse gases other than CO2 (particularly methane) [109].

Table 2 summarizes the main effects on ocean acidification, as far as they are known, of a range of proposed geoengineering techniques, both SRM and CDR. Additional details are given below.

View this table:
  • View inline
  • View popup
Table 2.

Summary of probable main effects of a range of proposed geoengineering approaches on ocean acidification, assuming climatically significant deployment and in comparison to unabated CO2 emissions. Within approaches, there may be relatively large differences in effects depending on specific details of techniques and their deployment arrangements. Additional details in text. OA, ocean acidification; SRM, solar radiation management; CDR, carbon dioxide reduction.

(b) Solar radiation management

SRM techniques (also known as sunlight reflection methods) are intended to decrease the amount of solar irradiance reaching the Earth, by increasing the albedo (reflectivity) of the upper, mid or lower atmosphere, or of the land or ocean surface. The main implications of SRM for ocean acidification are relatively straightforward, since atmospheric CO2 (and hence ocean chemistry changes) would continue to be primarily determined by CO2 emissions.

However, there may also be significant secondary effects of SRM on the ocean carbonate system, driven by larger-scale environmental changes involving temperature, light and other factors. Several modelling studies have assessed the climatic consequences of both atmosphere-based and surface-based SRM (e.g. [133–135] and [116,136], respectively), and an international model inter-comparison exercise is currently underway [112,137]. Such studies have clearly demonstrated that SRM techniques are potentially able to counteract anthropogenic radiative forcing at the global scale due to greenhouse gases. Yet the detailed implications of SRM geoengineering for ecosystems and global carbon dynamics are complex and uncertain [138,139], being a function of SRM techniques and their spatial application (affecting regional patterns of temperature and precipitation, and the frequency of extreme events), and also what scenarios are used as ‘control’ comparisons to quantify the SRM impact. Furthermore, temporal aspects of SRM implementation can also be important: different outcomes in terms of biogeochemical changes on land and in the ocean are likely to result from SRM when applied (i) under present-day conditions (to achieve a global surface cooling of X°C in, say, the next 5 years); or (ii) over a multi-decadal time scale to stabilize temperatures (i.e. preventing an increase of X°C over 50 years); or (iii) in 50 years time, that might be attempted to restore temperatures to present-day conditions (reversing an increase of X°C after it had occurred).

Assessment of ocean acidification responses to SRM-driven temperature change not only requires relatively straightforward information on CO2 and CaCO3 solubility in the upper ocean (with cooler temperatures having the net effect of decreasing pH), but also understanding of the much more complex climatic impacts on natural carbon sinks and sources [110]. Only one modelling experiment has to date explicitly explored the implications of such interactions for ocean chemistry [111]: that experiment showed that globally uniform atmospheric SRM (to maintain pre-industrial surface temperatures) might reduce the increase in atmospheric CO2 by approximately 110 ppm in comparison to an A2 emissions scenario, due to avoidance of climatic impacts on terrestrial biomass (i.e. preventing the net release of biogenic CO2 in addition to anthropogenic emissions). That biospheric CO2 response contributed to a net increase in global ocean surface pH by 0.05 units, compared with the A2 control, although with no effective change in aragonite saturation state [111].

Two other second-order consequences of atmospheric-based SRM geoengineering for ocean acidification are also possible, but have yet to be explored in modelling experiments.

  • — SRM-induced changes in light quality and quantity could affect primary production, and hence other aspects of carbon dynamics in the atmosphere and the ocean. While terrestrial vegetation might be more productive under diffuse light conditions [113], that effect is inherently less likely for marine phytoplankton—although it has yet to be quantitatively assessed.

  • — CO2-induced ocean acidification could be exacerbated if sulphate aerosols were used for SRM, due to their effect on precipitation pH. Such impacts would probably be slight, since the quantity of sulphur that, in theory, would need to be added to the stratosphere for geoengineering (1–5 million tonnes per year) [140] is at least an order of magnitude less than that currently added to the total atmosphere by industrial activities and volcanic emissions [100].

As initially stated, the overall consequence of SRM is that ocean acidification will continue, despite the complexity of interactions identified above. Marine organisms would therefore continue to experience ocean acidification impacts under SRM; they would, however, benefit by only being subject to a single stress, since deleterious temperature increase would have been averted (assuming SRM effectiveness).

Most experimental studies on ocean acidification carried out to date have not changed temperature as an additional experimental treatment. For those that have, impacts have generally been greater when both stresses are applied [63,72,80], yet with exceptions [141,142]. Interpretation of such studies is not straightforward, since (i) sensitivity to temperature change can vary greatly with season and life-cycle stage; (ii) synergistic effects between ocean acidification and temperature may occur [143], although well-controlled experiments are needed to conclusively demonstrate such interactions [144]; (iii) species may have different adaptive capabilities (physiological and genetic) in response to ocean acidification and temperature changes, particularly on decadal to century time scales; and (iv) marine species could be expected to change their geographical distributions in response to future global warming, but less easily (if at all) in response to ocean acidification.

(c) Carbon dioxide removal

Geoengineering based on CDR aims to constrain global warming by directly counteracting CO2 emissions, thereby increasing the likelihood of stabilization of atmospheric CO2, preferably at a non-dangerous level. The international policy target [92,93] of 450 ppm CO2 will be extremely difficult to achieve by emission reductions alone [105], while the lower target of 350 ppm (proposed on the basis of ecological considerations and to minimize the risk of reinforcing feedbacks [57,145]) has already been exceeded by approximately 40 ppm. Figure 4 shows that net negative emissions are likely to be needed for more than a century (2100–2200), peaking at −3 Gt C yr−1 in the middle of that period, in order to achieve surface ocean pH stabilization at 8.1, corresponding to atmospheric CO2 stabilization at 350 ppm.

CDR-based geoengineering might seem well suited to directly address both climate change and ocean acidification. Yet two provisos are necessary. First, few CDR techniques would seem sufficiently scalable to be able to counteract more than approximately 50 per cent of current greenhouse gas emissions, and many might only manage less than or equal to 10 per cent [132,146,147]. Thus only modest amelioration of global warming and ocean acidification might be achievable. Further consideration of such techniques as potential geoengineering options could therefore only be justified in the context of a ‘multi-wedge’ policy also involving strong mitigation [148], or if they also deliver other benefits. Second, some ocean-based CDR techniques (if capable of being implemented on a large enough scale) might relocate the process of ocean acidification from the sea surface to midwater or at depth. Such aspects are summarized in table 2, and discussed on a technique-specific basis below.

Chemically based CDR technique (i.e. direct air capture) is considered theoretically capable of removing CO2 from the atmosphere at the multi-gigaton scale [149]. It does, however, require that safe, long-term storage of CO2 is achievable, for which sub-seafloor sequestration of liquid CO2 is generally favoured [123]. This technique is already in use at pilot scale, as a component of at-source CO2 removal (climate change mitigation through carbon capture and storage) [124] with marine geological disposal subject to international regulation through the London Convention/London Protocol. In the event of reservoir failure, risk to benthic ecosystems from local acidification could be severe [121,125,150]. Nevertheless, the likelihood of leakage is considered low, provided that the CO2 is stored in deep geological strata with impermeable cap rocks, and impacts arising from leakage would be local [150], arguably comparable in scale to existing natural seafloor CO2 emissions [83,151].

A range of other potential CDR techniques involve more direct dependence on ocean storage, ocean-based enhanced weathering, or other ocean processes. Proposed storage options include adding liquid CO2 to midwater at a depth of approximately 1500 m [120]; forming CO2 lakes on the seafloor [152]; or adding carbon to the deep-sea floor in organic form, as baled crop residues [123,153]. All these techniques are, in theory, capable of reducing the rate of increase in atmospheric CO2 and thereby rate of ocean acidification in the upper ocean; however, they transfer the problem to mid- or deepwater, with a high risk of acute local impacts and more diffuse, long-term changes in carbonate chemistry on a regional and, ultimately, global basis. The effectiveness of midwater CO2 disposal for carbon sequestration is likely to vary considerably between different ocean basins, and is also sensitive to injection depth [122].

The use of ocean-based enhanced weathering [128] could more directly counter ocean acidification, increasing atmospheric CO2 drawdown through the addition to the ocean of either bicarbonate [129], carbonate minerals [130], calcium hydroxide [131] or combining the addition of liquid CO2 to the ocean with pulverized limestone [154]. All these approaches, however, involve the transport and processing of considerable bulk of materials, with associated energy costs, in order to achieve globally significant climate benefits. The land-based production of Ca(OH)2 would also require additional CO2 sequestration effort (to avoid additional CO2 release), while the various processes proposed for ‘liming the ocean’ could themselves cause large-scale ecosystem damage, by locally raising pH beyond organisms’ tolerance limits and/or decreasing light penetration, through precipitation effects.

Ocean fertilization is a relatively well-studied and assessed [155] CDR option, based on increasing biological productivity by directly adding nutrients, particularly iron [156,157], or increasing their internal re-supply, through enhanced upwelling or downwelling [158,159]. However, only a small proportion of the biologically fixed carbon is removed from circulation on a long-term basis, limiting the effectiveness of ocean fertilization as a CDR option, and there are risks of unintended impacts, e.g. N2O release [155]. Most of the increased export of organic carbon from the surface ocean would subsequently be decomposed in mid- and deepwater; thus pH decreases, carbonate chemistry changes and ecosystem impacts are re-located to those depths. Subsequent mixing in the ocean interior and return of deep waters to the surface via upwelling would mean that surface waters would eventually also experience ocean acidification due to the CDR intervention.

On a century-long time scale, it is estimated [160] that iron-based, global-scale ocean fertilization could achieve a maximum atmospheric reduction of approximately 33 ppm CO2, while counteracting surface ocean acidification by 0.06 pH units [117]. The Southern Ocean is the area where iron-based geoengineering would be most effective [160]; however, the likelihood of such action being implemented there is reduced by three factors.

  • — There is poor understanding of natural iron-supply mechanisms in that area, and how they might alter in future (with potentially large changes to cryospheric processes). Those uncertainties would affect verification and impact monitoring for large-scale fertilization [161]; e.g. use of satellite imagery to distinguish iron-induced blooms from natural ones.

  • — The sea conditions (and logistics) of the Southern Ocean are inimical for large-scale operational deployments.

  • — There is special conservation protection for the Southern Ocean south of 60° S, via the Protocol on Environmental Protection to the Antarctic Treaty (also known as the Madrid Protocol), that would require international amendment to allow geoengineering to proceed.

The enhancement of land-based carbon sequestration, e.g. by biochar or other techniques to increase soil carbon, is not expected to have significant unintended consequences for ocean acidification (table 2)—and might be politically more acceptable. However, the overall effectiveness of such land-based CDR techniques remains uncertain [100,146,147].

6. Conclusions

The chemical process of ocean acidification (pH reduction) is a certain consequence of increasing atmospheric CO2 and is already occurring on a global scale, particularly in near-surface waters. While the biological and ecological consequences of the ocean acidification that has occurred to date are considered relatively slight, serious consequences for ecosystems (and ecosystem services) seem inevitable on decadal-to-millennial time scales if CO2 emissions continue on current trajectories.

Climate geoengineering through SRM will not affect levels of anthropogenic CO2 in the atmosphere, and ocean acidification will therefore continue. However, large-scale deployment of SRM would not restore the global climate to its pre-industrial state, and is likely to result in second-order effects on Earth system processes—with implications for the global carbon cycle, and hence atmospheric CO2 and ocean acidification. The magnitude, and even direction, of such effects is currently uncertain: not only are they highly technique-specific, but they will anyway differ according to which projected emissions pathway (and global climate model) is used for the comparison.

CDR techniques are more closely directed at counteracting anthropogenic climate change due to greenhouse gas emissions; they may also provide a more politically acceptable means of tackling the threat of dangerous climate change. Their implications for ocean acidification are also technique specific: while some (in theory) permanently remove carbon from circulation, others re-locate and redistribute the problem of excess CO2 from the atmosphere and upper ocean to mid- or deep water. Moreover, CDR techniques proposed to date seem relatively ineffective in terms of the maximum reduction in atmospheric CO2 that they might realistically achieve.

The potential for some CDR techniques would seem to warrant further consideration. Nevertheless, strong and rapid mitigation measures, to stabilize atmospheric CO2 at near-current levels, would provide the policy action most likely to limit ocean acidification and its associated impacts.

Acknowledgements

Both authors acknowledge support from the UK Ocean Acidification research programme, funded jointly by the Natural Environment Research Council (NERC), the Department for Environment, Food, and Rural Affairs (Defra) and the Department of Energy and Climate Change (DECC) (grant no. ME5201). C.T. acknowledges support from the European Project on Ocean Acidification (EPOCA), funded by the European Community’s Seventh Framework Programme (FP7/2007–2013) (grant no. 211384). The assistance of Dawn Ashby and Martin Johnson for figure preparation, other colleagues for their scientific input, and reviewers of this paper for their constructive criticisms is also gratefully acknowledged.

Footnotes

  • One contribution of 12 to a Discussion Meeting Issue ‘Geoengineering: taking control of our planet's climate?’.

  • This journal is © 2012 The Royal Society

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

References

  1. ↵
    1. Le Quéré C.,
    2. et al.
    2009 Trends in the sources and sinks of carbon dioxide. Nat. Geosci. 2, 831–836. doi:10.1038/ngeo689 (doi:10.1038/ngeo689)
    OpenUrlCrossRefWeb of Science
  2. ↵
    1. Zeebe R. E.,
    2. Wolf-Gladrow D. A.
    2001 CO2 in seawater: equilibrium, kinetics and isotopes. Oceanography Series, vol. 65. Amsterdam, The Netherlands: Elsevier.
  3. ↵
    Royal Society. 2005 Ocean acidification due to increasing atmospheric carbon dioxide, policy document 12/05. London, UK: The Royal Society.
  4. ↵
    1. Thierstein H. R.,
    2. Young J. R.
    1. Brownlee C.,
    2. Taylor A.
    2004 Calcification in coccolithophores: a cellular perspective. In Coccolithophores: from cellular processes to global impact (eds Thierstein H. R., Young J. R.), pp. 31–50. Berlin, Germany: Springer.
  5. ↵
    1. Yamamoto S.,
    2. Kayanne H.,
    3. Terai M.,
    4. Watanabe A.,
    5. Kato K.,
    6. Negishi A.,
    7. Nozaki K.
    2011 Threshold of carbonate saturation state determined by a CO2 control experiment. Biogeosci. Discuss. 8, 8619–8644. doi:10.5194/bgd-8-8619-2011 (doi:10.5194/bgd-8-8619-2011)
    OpenUrlCrossRef
  6. ↵
    1. Palmer A. R.
    1992 Calcification in marine molluscs: how costly is it? Proc. Natl Acad. Sci. USA 89, 1379–1382. doi:10.1073/pnas.89.4.1379 (doi:10.1073/pnas.89.4.1379)
    OpenUrlAbstract/FREE Full Text
  7. ↵
    1. Steinacher M.,
    2. Joos F.,
    3. Frölicher T. L.,
    4. Plattner G.-K.,
    5. Doney S. C.
    2009 Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model. Biogeosciences 6, 515–533. doi:10.5194/bg-6-515-2009 (doi:10.5194/bg-6-515-2009)
    OpenUrlCrossRefWeb of Science
  8. ↵
    1. Orr J. C.,
    2. et al.
    2005 Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437, 681–686. doi:10.1038/nature04095 (doi:10.1038/nature04095)
    OpenUrlCrossRefPubMedWeb of Science
  9. ↵
    1. Blackford J. C.,
    2. Gilbert F. J.
    2007 pH variability and CO2 induced acidification in the North Sea. J. Mar. Syst. 64, 229–241. doi:10.1016/j.jmarsys.2006.03.016 (doi:10.1016/j.jmarsys.2006.03.016)
    OpenUrlCrossRefWeb of Science
  10. ↵
    1. Joint I.,
    2. Doney S. C.,
    3. Karl D. M.
    2011 Will ocean acidification affect marine microbes? ISME J. 5, 1–7. doi:10.1038/ismej.2010.79 (doi:10.1038/ismej.2010.79)
    OpenUrlCrossRefPubMedWeb of Science
  11. ↵
    1. Feely R. A.,
    2. Sabine C. L.,
    3. Hernandez-Ayon J. M.,
    4. Lanson D.,
    5. Hales B.
    2008 Evidence for upwelling of corrosive 'acidified' water onto the continental shelf. Science 320, 1490–1492. doi:10.1126/science.1155676 (doi:10.1126/science.1155676)
    OpenUrlAbstract/FREE Full Text
  12. ↵
    1. Feely R. A.,
    2. Doney S. C.,
    3. Cooley S. R.
    2009 Present conditions and future changes in a high CO2 world. Oceanography 22, 36–47. doi:10.1073/pnas.0803081105 (doi:10.1073/pnas.0803081105)
    OpenUrlCrossRefWeb of Science
  13. ↵
    1. Byrne R. H.,
    2. Mecking S.,
    3. Feely R. A.,
    4. Liu X.
    2010 Direct observations of basin-wide acidification of the North Pacific Ocean. Geophys. Res. Lett. 37, L02601. doi:10.1029/2009GL040999 (doi:10.1029/2009GL040999)
    OpenUrlCrossRef
  14. ↵
    1. Kleypas J. A.,
    2. Feely R. A.,
    3. Fabry V. J.,
    4. Langdon C.,
    5. Sabine C. L.,
    6. Robbins L. L.
    2006 Impacts of ocean acidification on coral reefs and other marine calcifiers: a guide for future research. St Petersburg, FL: NSF, NOAA, and the US Geological Survey. doi:10.1111/j.1601-183X.2007.00341.x (doi:10.1111/j.1601-183X.2007.00341.x)
    OpenUrlCrossRefPubMedWeb of Science
  15. ↵
    1. Santana-Casiano J. M.,
    2. González-Dávila M.,
    3. Rueda M.-J.,
    4. Llinás O.,
    5. González-Dávila E.-F.
    2007 The interannual variability of oceanic CO2 parameters in the northeast Atlantic subtropical gyre at the ESTOC site. Global Biogeochem. Cycles 21, GB1015. doi:10.1029/2006GB002788 (doi:10.1029/2006GB002788)
    OpenUrlCrossRef
  16. ↵
    1. Watson A. J.,
    2. et al.
    2009 Tracking the variable North Atlantic sink for atmospheric CO2. Science 326, 1391–1393. doi:10.1126/science.1177394 (doi:10.1126/science.1177394)
    OpenUrlAbstract/FREE Full Text
  17. ↵
    1. Letcher T. M.
    1. Turley C. M.,
    2. Findlay H. S.
    2009 Ocean acidification as an indicator for climate change. In Climate and global change: observed impacts on planet Earth (ed. Letcher T. M.), pp. 367–390 Amsterdam, The Netherlands: Elsevier. doi:10.2307/1131203 (doi:10.2307/1131203)
    OpenUrlCrossRef
  18. ↵
    1. McQuatters-Gollop A.,
    2. Burkill P. H.,
    3. Beaugrand G.,
    4. Johns D. G.,
    5. Gattuso J.-P.,
    6. Edwards M.
    2010 Atlas of calcifying plankton: results from the North Atlantic Continuous Plankton Recorder survey. Plymouth, UK: Sir Alister Hardy Foundation for Ocean Science. See www.sahfos.ac.uk/media/2327004/epoca%20atlas.pdf. doi:10.1093/bioinformatics/bti529 (doi:10.1093/bioinformatics/bti529)
    OpenUrlAbstract/FREE Full Text
  19. ↵
    1. Beaugrand G.,
    2. Edwards M.,
    3. Legendre L.
    2010 Marine biodiversity, ecosystem functioning, and carbon cycles. Proc. Natl Acad. Sci. USA 107, 10120–10124. doi:10.1073/pnas.0913855107 (doi:10.1073/pnas.0913855107)
    OpenUrlAbstract/FREE Full Text
  20. ↵
    1. Tyrrell T.,
    2. Schneider B.,
    3. Charalampopoulou A.,
    4. Riebesell U.
    2008 Coccolithophores and calcite saturation state in the Baltic and Black Seas. Biogeosciences 5, 485–494. doi:10.1037/h0030372 (doi:10.1037/h0030372)
    OpenUrlCrossRefWeb of Science
  21. ↵
    1. Moy A. D.,
    2. Howard W. R.,
    3. Bray S. G.,
    4. Trull T. W.
    2009 Reduced calcification in modern Southern Ocean planktonic foraminifera. Nat. Geosci. 2, 276–280. doi:10.1038/ngeo460 (doi:10.1038/ngeo460)
    OpenUrlCrossRefWeb of Science
  22. ↵
    1. Manzello P. D.,
    2. Kleypas J. A.,
    3. Budd D. A.,
    4. Eakin C. M.,
    5. Glynn P. W.,
    6. Langdon C.
    2008 Poorly cemented coral reefs of the eastern tropical Pacific: possible insights into reef development in a high-CO2 world. Proc. Natl Acad. Sci. USA 105, 10450–10455. doi:10.1073/pnas.0712167105 (doi:10.1073/pnas.0712167105)
    OpenUrlAbstract/FREE Full Text
  23. ↵
    1. Silverman J.,
    2. Lazar B.,
    3. Erez J.
    2007 Effect of aragonite saturation, temperature, and nutrients on the community calcification rate of a coral reef. J. Geophys. Res. 112, C05004. doi:10.1029/2006JC003770 (doi:10.1029/2006JC003770)
    OpenUrlCrossRef
  24. ↵
    1. De’ath G.,
    2. Lough J. M.,
    3. Fabricius K. E.
    2009 Declining coral calcification on the Great Barrier Reef. Science 323, 116–119. doi:10.1126/science.1165283 (doi:10.1126/science.1165283)
    OpenUrlAbstract/FREE Full Text
  25. ↵
    1. Guinotte J. M.,
    2. Orr J.,
    3. Cairns S.,
    4. Freiwald A.,
    5. Morgan L.,
    6. George R.
    2006 Will human induced changes in seawater chemistry alter the distribution of deep-sea scleractinian corals? Front. Ecol. Environ. 4, 141–146. doi:10.1890/1540-9295(2006)004[0141:WHCISC]2.0.CO;2 (doi:10.1890/1540-9295(2006)004[0141:WHCISC]2.0.CO;2)
    OpenUrlCrossRef
  26. ↵
    1. Olafsson J.,
    2. Olafsdottir J.,
    3. Benoit-Cattin A.,
    4. Danielsen M.,
    5. Arnarson T. S.,
    6. Takahashi T.
    2009 Rate of Iceland Sea acidification from time series measurements. Biogeosciences 6, 2661–2668. doi:10.5194/bg-6-2661-2009 (doi:10.5194/bg-6-2661-2009)
    OpenUrlCrossRefWeb of Science
  27. ↵
    1. Turley C. M.,
    2. Roberts J. M.,
    3. Guinotte J. M.
    2007 Corals in deep-water: will the unseen hand of ocean acidification destroy cold-water ecosystems? Coral Reefs 26, 445–448. doi:10.1007/s00338-007-0247-5 (doi:10.1007/s00338-007-0247-5)
    OpenUrlCrossRefWeb of Science
  28. ↵
    1. Maier C.,
    2. Hegeman J.,
    3. Weinbauer M. G.,
    4. Gattuso J.-P.
    2009 Calcification of the cold-water coral Lophelia pertusa under ambient and reduced pH. Biogeosciences 6, 1671–1680. doi:10.5194/bg-6-1671-2009 (doi:10.5194/bg-6-1671-2009)
    OpenUrlCrossRefWeb of Science
  29. ↵
    IPCC. 2007 Climate change 2007: the physical science basis. Summary for policymakers. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press.
  30. ↵
    1. Caldeira K.,
    2. Wickett M. E.
    2003 Anthropogenic carbon and ocean pH. Nature 425, 365. doi:10.1038/425365a (doi:10.1038/425365a)
    OpenUrlCrossRefPubMedWeb of Science
  31. ↵
    1. Feely R. A.,
    2. Sabine C. L.,
    3. Lee K.,
    4. Berelson W.,
    5. Kleypas J.,
    6. Fabry V. J.,
    7. Millero F. J.
    2004 Impact of anthropogenic CO2 on the CaCO3 system in the ocean. Science 305, 362–366. doi:10.1126/science.1097329 (doi:10.1126/science.1097329)
    OpenUrlCrossRefGeoRefPubMedWeb of Science
  32. ↵
    1. Cao L.,
    2. Caldeira K.
    2008 Atmospheric CO2 stabilization and ocean acidification. Geophys. Res. Lett. 35, L19609. doi:10.1029/2008GL035072 (doi:10.1029/2008GL035072)
    OpenUrlCrossRef
  33. ↵
    1. Turley C.,
    2. et al.
    2010 The societal challenge of ocean acidification. Mar. Poll. Bull. 60, 787–792. doi:10.1016/j.marpolbul.2010.05.06 (doi:10.1016/j.marpolbul.2010.05.06)
    OpenUrlCrossRef
  34. ↵
    1. Gattuso J.-P.,
    2. Hansson L.
    1. Joos F.,
    2. Frölicher T. L.,
    3. Steinacher M.,
    4. Plattner G.-K.
    2011 Impact of climate change mitigation on ocean acidification projections. In Ocean acidification (eds Gattuso J.-P., Hansson L.). Oxford, UK: Oxford University Press.
  35. ↵
    1. Pearson P. N.,
    2. Palmer M. R.
    2000 Atmospheric carbon dioxide concentrations over the past 60 million years. Nature 406, 695–699. doi:10.1038/35021000 (doi:10.1038/35021000)
    OpenUrlCrossRefGeoRefPubMedWeb of Science
    1. Schellnhuber H. J.,
    2. Cramer W.,
    3. Nakicenovic N.,
    4. Wigley T.,
    5. Yohe G.
    1. Turley C.,
    2. Blackford J.,
    3. Widdicombe S.,
    4. Lowe D.,
    5. Nightingale P. D.,
    6. Rees A. P.
    2006 Reviewing the impact of increased atmospheric CO2 on oceanic pH and the marine ecosystem. In Avoiding dangerous climate change (eds Schellnhuber H. J., Cramer W., Nakicenovic N., Wigley T., Yohe G.), pp. 65–70. Cambridge, UK: Cambridge University Press.
  36. ↵
    1. Ridgwell A.,
    2. Schmidt D. N.
    2010 Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release. Nat. Geosci. 3, 196–200. doi:10.1038/ngeo755 (doi:10.1038/ngeo755)
    OpenUrlCrossRefWeb of Science
  37. ↵
    1. Pörtner H. O.,
    2. Langenbuch M.,
    3. Michaelidis B.
    2005 Synergistic effects of temperature extremes, hypoxia, and increases in CO2 on marine animals: from Earth history to global change. J. Geophys. Res. Oceans 110, C09S10. doi:10.1029/2004JC002561 (doi:10.1029/2004JC002561)
    OpenUrlCrossRef
    1. Fabry V. J.,
    2. Seibel B. A.,
    3. Feely R. A.,
    4. Orr J. C.
    2008 Impacts of ocean acidification on marine fauna and ecosystem processes. ICES J. Mar. Sci. 65, 414–432. doi:10.1093/icesjms/fsn048 (doi:10.1093/icesjms/fsn048)
    OpenUrlAbstract/FREE Full Text
    1. Guinotte J. M.,
    2. Fabry V. J.
    2008 Ocean acidification and its potential effects on marine ecosystems. Ann. NY Acad. Sci. 1134, 320–342. doi:10.1196/annals.1439.013 (doi:10.1196/annals.1439.013)
    OpenUrlCrossRefPubMedWeb of Science
  38. ↵
    1. Gattuso J.-P.,
    2. Hansson L.
    (eds) 2011 Ocean acidification. Oxford, UK: Oxford University Press.
  39. ↵
    1. Hendriks I. E.,
    2. Duarte C. M.,
    3. Alvarez M.
    2010 Vulnerability of marine biodiversity to ocean acidification: a meta-analysis. Est. Coastal Shelf Sci. 86, 157–164. doi:10.1016/j.ecss.2009.11.022 (doi:10.1016/j.ecss.2009.11.022)
    OpenUrlCrossRefGeoRef
  40. ↵
    1. Kroeker K. J.,
    2. Kordas R. L.,
    3. Crim R. N.,
    4. Singh G. G.
    2010 Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecol. Lett. 13, 1419–1434. doi:10.1111/j.1461-0248.2010.01518.x (doi:10.1111/j.1461-0248.2010.01518.x)
    OpenUrlCrossRefPubMed
  41. ↵
    1. Liu J.,
    2. Weinbauer M. G.,
    3. Maier C.,
    4. Dai M.,
    5. Gattuso J.-P.
    2010 Effect of ocean acidification on microbial diversity and on microbe-driven biogeochemistry and ecosystem functioning. Aq. Microbial Ecol. 61, 291–305. doi:10.3354/ame01446 (doi:10.3354/ame01446)
    OpenUrlCrossRefWeb of Science
  42. ↵
    1. Dupont S.,
    2. Dorey N.,
    3. Thorndyke M.
    2010 What meta-analysis can tell us about vulnerability of marine biodiversity to ocean acidification? Est. Coastal Shelf Sci. 89, 182–185. doi:10.1016/j.ecss.2010.06.013 (doi:10.1016/j.ecss.2010.06.013)
    OpenUrlCrossRefWeb of Science
  43. ↵
    1. Gattuso J.-P.,
    2. Buddemeier R. W.
    2000 Ocean biogeochemistry, calcification and CO2. Nature 407, 311–313. doi:10.1038/35030280 (doi:10.1038/35030280)
    OpenUrlCrossRefGeoRef
  44. ↵
    1. Ries J. B.,
    2. Cohen A. L.,
    3. McCorkle D. C.
    2009 Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification. Geology 37, 1131–1134. doi:10.1130/G30210A.1 (doi:10.1130/G30210A.1)
    OpenUrlAbstract/FREE Full Text
  45. ↵
    1. Wood H. L.,
    2. Spicer J. I.,
    3. Widdicombe S.
    2008 Ocean acidification may increase calcification rates, but at a cost. Proc. R. Soc. B 275, 1767–1773. doi:10.1098/rspb.2008.0343 (doi:10.1098/rspb.2008.0343)
    OpenUrlAbstract/FREE Full Text
  46. ↵
    1. Krug S. A.,
    2. Schulz K. G.,
    3. Riebesell U.
    2011 Effects of changes in carbonate chemistry speciation on Coccolithus braarudii: a discussion of coccolithophorid sensitivities. Biogeosciences 8, 771–777. doi:10.5194/bg-8-771-2011 (doi:10.5194/bg-8-771-2011)
    OpenUrlCrossRefWeb of Science
  47. ↵
    1. Dubinsky Z.,
    2. Stambler N.
    1. Allemand D.,
    2. Zoccola D.,
    3. Tambutté S.
    2011 Coral calcification, cells to reefs. In Coral reefs (eds Dubinsky Z., Stambler N.), pp. 119–150. Heidelberg, Germany: Springer.
  48. ↵
    1. Melzner F.,
    2. Gutowska M. A.,
    3. Langenbuch M.,
    4. Dupont S.,
    5. Lucassen M.,
    6. Thorndyke M. C.,
    7. Bleich M.,
    8. Pörtner H.-O.
    2009 Physiological basis for high CO2 tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny? Biogeosciences 6, 2313–2331. doi:10.5194/bg-6-2313-2009 (doi:10.5194/bg-6-2313-2009)
    OpenUrlCrossRefWeb of Science
    1. Cohen A. L.,
    2. McCorkle D. C.,
    3. de Putron S.,
    4. Gaetani G. A.,
    5. Rose K. A.
    2009 Morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater: insights into the biomineralization response to ocean acidification. Geochem. Geophys. Geosyst. 10, Q07005. doi:10.1029/2009GC002411 (doi:10.1029/2009GC002411)
    OpenUrlCrossRef
    1. Nakamura M.,
    2. Ohki S.,
    3. Suzuki A.,
    4. Sakai K.
    2011 Coral larvae under ocean acidification: survival, metabolism, and metamorphosis. PLoS ONE 6, e14521. doi:10.1371/journal.pone.0014521 (doi:10.1371/journal.pone.0014521)
    OpenUrlCrossRefPubMed
    1. Hoegh-Guldberg O.,
    2. et al.
    2007 Coral reefs under rapid climate change and ocean acidification. Science 318, 1737–1742. doi:10.1126/science.1152509 (doi:10.1126/science.1152509)
    OpenUrlAbstract/FREE Full Text
    1. Silverman J.,
    2. Lazar B.,
    3. Cao L.,
    4. Caldeira K.,
    5. Erez J.
    2009 Coral reefs may start dissolving when atmospheric CO2 doubles. Geophys. Res. Lett. 36, L05606. doi:10.1029/2008GL036282 (doi:10.1029/2008GL036282)
    OpenUrlCrossRef
    1. Fischlin A.,
    2. et al.
    2007 Ecosystems, their properties, goods and services. In Climate change 2007 climate change impacts, adaptation and vulnerability. Fourth Assessment Report of the Intergovernmental Panel on Climate Change, pp. 211–272. Cambridge, UK: Cambridge University Press.
  49. ↵
    1. Veron J. E. N.,
    2. et al.
    2009 The coral reef crisis: the critical importance of <350,ppm CO2. Mar. Poll. Bull. 58, 1428–1436. doi:10.1016/j.marpolbul.2009.09.009 (doi:10.1016/j.marpolbul.2009.09.009)
    OpenUrlCrossRefPubMedWeb of Science
    1. Berge J. A.,
    2. Bjerkeng B.,
    3. Pettersen O.,
    4. Schaanning M. T.,
    5. Óxnevad S.
    2006 Effects of increased sea water concentrations of CO2 on growth of the bivalve Mytilus edulis. Chemosphere 62, 681–687. doi:10.1016/chemosphere.2005.04.111 (doi:10.1016/chemosphere.2005.04.111)
    OpenUrlCrossRefPubMedWeb of Science
    1. Bibby R.,
    2. Widdicombe S.,
    3. Parry H.,
    4. Spicer J.,
    5. Pipe R.
    2008 Effects of ocean acidification on the immune response of the blue mussel. Mytilus edulis. Aq. Biol. 2, 67–74. doi:10.3354/ab00037 (doi:10.3354/ab00037)
    OpenUrlCrossRefWeb of Science
    1. Talmage S. C.,
    2. Gobler C. J.
    2009 The effects of elevated carbon dioxide concentrations on the metamorphosis, size, and survival of larval hard clams (Mercenaria mercenaria), bay scallops (Argopecten irradians), and eastern oysters (Crassostrea virginica). Limnol. Oceanogr. 54, 2072–2080. doi:10.4319/lo.2009.54.6.2072 (doi:10.4319/lo.2009.54.6.2072)
    OpenUrlCrossRefWeb of Science
    1. Gazeau F.,
    2. Quiblier C.,
    3. Jansen J. M.,
    4. Gattuso J.-P.,
    5. Middelburg J. J.,
    6. Heip C. H. R.
    2007 Impact of elevated CO2 on shellfish calcification. Geophys. Res. Lett. 34, L07603. doi:10.1029/2006GL028554 (doi:10.1029/2006GL028554)
    OpenUrlCrossRef
    1. Miller A. W.,
    2. Reynolds A. C.,
    3. Sobrino C.,
    4. Riedel G. F.
    2009 Shellfish face uncertain future in high CO2 world: influence of acidification on oyster larvae calcification and growth in estuaries. PLoS ONE 4, e5661. doi:10.1371/journal.pone.0005661 (doi:10.1371/journal.pone.0005661)
    OpenUrlCrossRefPubMed
  50. ↵
    1. Parker L. M.,
    2. Ross P. M.,
    3. O’Connor W. O.
    2010 Comparing the effect of elevated pCO2 and temperature on the fertilization and early development of two species of oysters. Mar. Biol. 157, 2435–2452. doi:10.1007/s00227-010-1508-3 (doi:10.1007/s00227-010-1508-3)
    OpenUrlCrossRefWeb of Science
    1. Comeau S.,
    2. Gorsky G.,
    3. Jeffree R.,
    4. Teyssié J. L.,
    5. Gattuso J.-P.
    2009 Impact of ocean acidification on a key Arctic pelagic mollusc (Limacina helicina). Biogeosciences 6, 1877–1882. doi:10.5194/bg-6-1877-2009 (doi:10.5194/bg-6-1877-2009)
    OpenUrlCrossRefWeb of Science
    1. Comeau S.,
    2. Jeffree R.,
    3. Teyssié J.-L.,
    4. Gattuso J.-P.
    2010 Response of the Arctic pteropod Limacina helicina to projected future environmental conditions. PLoS ONE 5, e11362. doi:10.1371/journal.pone.0011362 (doi:10.1371/journal.pone.0011362)
    OpenUrlCrossRefPubMed
    1. Turley C.,
    2. Boot K.
    2010 Environmental consequence of ocean acidification: a threat to food security. UNEP Emerging Issues Bulletin. Nairobi, Kenya: United Nations Environment Programme.
    1. Dupont S.,
    2. Havenhand J.,
    3. Thorndyke W.,
    4. Peck L.,
    5. Thorndyke M.
    2008 CO2-driven ocean acidification radically affects larval survival and development in the brittlestar Ophiothrix fragilis. Mar. Ecol. Progr. Ser. 373, 285–294. doi:10.3354/meps07800 (doi:10.3354/meps07800)
    OpenUrlCrossRefWeb of Science
    1. Clark D.,
    2. Lamare M.,
    3. Barker M.
    2009 Response of sea urchin pluteus larvae (Echinodermata: Echinoidea) to reduced seawater pH: a comparison among a tropical, temperate, and a polar species. Mar. Biol. 156, 1125–1137. doi:10.1007/s00227-009-1155-8 (doi:10.1007/s00227-009-1155-8)
    OpenUrlCrossRefWeb of Science
    1. Kurihara H.,
    2. Shirayama Y.
    2004 Effects of increased atmospheric CO2 on sea urchin early development. Mar. Ecol. Progr. Ser. 274, 161–169. doi:10.3354/meps274161 (doi:10.3354/meps274161)
    OpenUrlCrossRefWeb of Science
    1. Kurihara H.,
    2. Ishimatsu A.
    2008 Effects of high CO2 seawater on the copepod (Acartia tsuensis) through all life stages and subsequent generations. Mar. Poll. Bull. 56, 1086–1090. doi:10.1016/j.marpolbul.2008.03.023 (doi:10.1016/j.marpolbul.2008.03.023)
    OpenUrlCrossRef
    1. Arnold K. E.,
    2. Findlay H. S.,
    3. Spicer J. I.,
    4. Daniels C. L.,
    5. Boothroyd D.
    2009 Effects of hypercapnia-related acidification on the larval development of the European lobster, Homarus gammarus (L.). Biogeosciences 6, 1747–1754. doi:10.5194/bg-6-1747-2009 (doi:10.5194/bg-6-1747-2009)
    OpenUrlCrossRefWeb of Science
  51. ↵
    1. Walther K.,
    2. Sartoris F. J.,
    3. Bock C.,
    4. Pörtner H.-O.
    2009 Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab Hyas araneus. Biogeosciences 6, 2207–2215. doi:10.5194/bg-6-2207-2009 (doi:10.5194/bg-6-2207-2009)
    OpenUrlCrossRefWeb of Science
    1. Bijma J.,
    2. Honisch B.,
    3. Zeebe R. E.
    Impact of the ocean carbonate chemistry on living foraminiferal shell weight: comment on ‘Carbonate ion concentration in glacial-age deep waters of the Caribbean Sea’ by W. S. Broeker and E. Clark. Geochem. Geophys. Geosyst. 2002 3, 1064. doi:10.1029/2002GC000388 (doi:10.1029/2002GC000388)
    OpenUrlCrossRef
    1. de Moel H.,
    2. Ganssen G. M.,
    3. Peeters F. J. C.,
    4. Jung S. J. A.,
    5. Brummer G. J. A.,
    6. Kroon D.,
    7. Zeebe R. E.
    2009 Planktic foraminiferal shell thinning in the Arabian Sea due to anthropogenic ocean acidification? Biogeosciences 6, 1917–1925. doi:10.5194/bg-6-1917-2009 (doi:10.5194/bg-6-1917-2009)
    OpenUrlCrossRefWeb of Science
    1. Ishimatsu A.,
    2. Hayashi M.,
    3. Kikkawa T.
    2008 Fishes in high-CO2, acidified oceans. Mar. Ecol. Prog. Ser. 373, 295–302. doi:10.3354/meps07823 (doi:10.3354/meps07823)
    OpenUrlCrossRefWeb of Science
    1. Melzner F.,
    2. Göbel S.,
    3. Langenbuch M.,
    4. Gutowska M.,
    5. Pörtner H.-O.,
    6. Lucassen M.
    2009 Swimming performance in Atlantic cod (Gadus morhua) following long-term (4–12 months) acclimation to elevated seawater pCO2. Aq. Toxicol. 92, 30–37. doi:10.1016/j.aquatox.2008.12.011 (doi:10.1016/j.aquatox.2008.12.011)
    OpenUrlCrossRefPubMedWeb of Science
    1. Munday P. L.,
    2. Dixson D. L.,
    3. Donelson J. M.,
    4. Jones G. P.,
    5. Pratchett M. S.,
    6. Devitsina G.,
    7. Døving K. B.
    2009 Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proc. Natl Acad. Sci. USA 106, 1848–1852. doi:10.1073/pnas.0809996106 (doi:10.1073/pnas.0809996106)
    OpenUrlAbstract/FREE Full Text
    1. Simpson S. D.,
    2. Munday P. L.,
    3. Wittenrich M. L.,
    4. Manassa R.,
    5. Dixson D. L.,
    6. Gagliano M.,
    7. Yan H. Y.
    2011 Ocean acidification erodes crucial auditory behaviour in a marine fish. Biol. Lett. 7, 917–920. doi:10.1098/rsbl.2011.0293 (doi:10.1098/rsbl.2011.0293)
    OpenUrlAbstract/FREE Full Text
    1. Munday P. L.,
    2. Dixson D. L.,
    3. McCormick M. I.,
    4. Meekan M.,
    5. Ferrari M. C. O.,
    6. Chivers D. P.
    2010 Replenishment of fish populations is threatened by ocean acidification. Proc. Natl Acad. Sci. USA 107, 12930–12934. doi:10.1073/pnas.1004519107 (doi:10.1073/pnas.1004519107)
    OpenUrlAbstract/FREE Full Text
  52. ↵
    1. Munday P. L.,
    2. Crawley N. E.,
    3. Nilsson G. E.
    2009 Interacting effects of elevated temperature and ocean acidification on the aerobic performance of coral reef fishes. Mar. Ecol. Prog. Ser. 388, 235–242. doi:10.3354/meps08137 (doi:10.3354/meps08137)
    OpenUrlCrossRefWeb of Science
    1. Checkley D. M.,
    2. Dickson A. G.,
    3. Takahashi M.,
    4. Radish J. A.,
    5. Eisenkolb N.,
    6. Asch R.
    2009 Elevated CO2 enhances otolith growth in young fish. Science 324, 1683. doi:10.1126/science.1169806 (doi:10.1126/science.1169806)
    OpenUrlAbstract/FREE Full Text
    1. Martin S.,
    2. Gattuso J.-P.
    2009 Response of Mediterranean coralline algae to ocean acidification and elevated temperature. Glob. Change Biol. 15, 2089–2100. doi:10.1111/j.1365-2486.2009.01874.x (doi:10.1111/j.1365-2486.2009.01874.x)
    OpenUrlCrossRefWeb of Science
  53. ↵
    1. Hall-Spencer J. M.,
    2. Rodolfo-Metalpa R.,
    3. Martin S.,
    4. Ransome E.,
    5. Fine M.,
    6. Turner S. M.,
    7. Rowley S. J.,
    8. Tedesco D.,
    9. Buia M.-C.
    2008 Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454, 96–99. doi:10.1038/nature07051 (doi:10.1038/nature07051)
    OpenUrlCrossRefGeoRefPubMedWeb of Science
    1. Martin S.,
    2. Rodolfo-Metalpa R.,
    3. Ransome E.,
    4. Rowley S.,
    5. Buia M.-C.,
    6. Gattuso J.-P.,
    7. Hall-Spencer J.
    2008 Effects of naturally acidified seawater on seagrass calcareous epibionts. Biol. Lett. 4, 689–692. doi:10.1098/rsbl.2008.0412 (doi:10.1098/rsbl.2008.0412)
    OpenUrlAbstract/FREE Full Text
    1. Riebesell U.,
    2. Zondervan I.,
    3. Rost B.,
    4. Tortell P. D.,
    5. Zeebe R. E.,
    6. Morel F. M. M.
    2000 Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature 407, 364–367. doi:10.1038/35030078 (doi:10.1038/35030078)
    OpenUrlCrossRefPubMed
    1. Iglesias-Rodriguez M. D.,
    2. et al.
    2008 Phytoplankton calcification in a high CO2 world. Science 320, 336–340. doi:10.1126/science1154122 (doi:10.1126/science1154122)
    OpenUrlAbstract/FREE Full Text
  54. ↵
    1. Langer G.,
    2. Nehrke G.,
    3. Probert I.,
    4. Ly J.,
    5. Ziveri P.
    2009 Strain specific responses of Emiliania huxleyi to changing seawater carbonate chemistry. Biogeosciences 6, 2637–2646. doi:10.5194/bg-6-2637-2009 (doi:10.5194/bg-6-2637-2009)
    OpenUrlCrossRefWeb of Science
  55. ↵
    1. Ridgwell A.,
    2. Schmidt D. N.,
    3. Turley C.,
    4. Brownlee C.,
    5. Maldonado M. T.,
    6. Tortell P.,
    7. Young J. R.
    2009 From laboratory manipulations to Earth system models: scaling calcification impacts of ocean acidification. Biogeosciences 6, 2611–2623. doi:10.5194/bg-6-2611-2009 (doi:10.5194/bg-6-2611-2009)
    OpenUrlCrossRefWeb of Science
  56. ↵
    1. Hutchins D. A.,
    2. Fu F. X.,
    3. Zhang Y.,
    4. Warner M. E.,
    5. Feng Y.,
    6. Portune K.,
    7. Bernhardt P.,
    8. Mulholland M. R.
    2007 CO2 control of Trichodesmium N2 fixation, photosynthesis, growth rates, and elemental ratios: implications for past, present, and future ocean biogeochemistry. Limnol. Oceanogr. 52, 1293–1304
    OpenUrlCrossRefWeb of Science
    1. Hutchins D. A.,
    2. Mulholland M. R.,
    3. Fu F. X.
    2009 Nutrient cycles and marine microbes in a CO2-enriched ocean. Oceanography 22, 128–145. doi:10.5670/oceanog.2009.103 (doi:10.5670/oceanog.2009.103)
    OpenUrlCrossRef
  57. ↵
    1. Riebesell U.,
    2. Fabry V. J.,
    3. Hansson L.,
    4. Gattuso J.-P.
    2010 Guide to best practices for ocean acidification research and data reporting, EUR 24328. Luxembourg: Publications Office of the European Union.
  58. ↵
    UNFCCC. 2010 Copenhagen Accord. See http://unfccc.int/resource/docs/2009/cop15/eng/107.pdf.
  59. ↵
    European Commission 2007 Limiting global climate change to 2 degrees Celsius. The way ahead for 2020 and beyond. Brussels, Belgium: European Commission. See http://eur-lex.europa.eu/LexUriServ/site/en/com/2007/com2007_0002en01.pdf.
  60. ↵
    1. Cooley S. R.,
    2. Doney S. C.
    2009 Anticipating ocean acidification’s economic consequences for commercial fisheries. Environ. Res. Lett. 4, 024007. doi:10.1088/1748-9326/4/2/024007 (doi:10.1088/1748-9326/4/2/024007)
    OpenUrlCrossRef
  61. ↵
    1. Gattuso J.-P.,
    2. Hansson L.
    1. Turley C.,
    2. Boot K.
    2011 The ocean acidification challenges facing science and society. Ocean acidification (eds Gattuso J.-P., Hansson L.), pp. 249–271. Oxford, UK: Oxford University Press.
  62. ↵
    1. Feely R. A.,
    2. Alin S. R.,
    3. Newton J.,
    4. Sabine C. L.,
    5. Warner M.,
    6. Devol A.,
    7. Krembs C.,
    8. Maloy C.
    2010 The combined effects of ocean acidification, mixing, and respiration on pH and carbonate saturation in an urbanized estuary. Est. Coastal Shelf Sci. 88, 442–449. doi:10.1016/j.ecss.2010.05.004 (doi:10.1016/j.ecss.2010.05.004)
    OpenUrlCrossRef
  63. ↵
    1. Salisbury J.,
    2. Green M.,
    3. Hunt C.,
    4. Campbell J.
    2008 Coastal acidification by rivers: a threat to shellfish? Eos 89, 513. doi:10.1029/2008EO500001 (doi:10.1029/2008EO500001)
    OpenUrlCrossRef
  64. ↵
    1. Archer D. E.
    2005 Fate of fossil fuel CO2 in geological time. J. Geophys. Res. 110, CS09S05. doi:10.1029/2004JC002625 (doi:10.1029/2004JC002625)
    OpenUrlCrossRef
  65. ↵
    1. Archer D. E.,
    2. Kheshgi H.,
    3. Maier-Reimer E.
    1998 Dynamics of fossil fuel CO2 neutralization by marine CaCO3. Glob. Biogeochem. Cycles 12, 259–276. doi:10.1029/98GB00744 (doi:10.1029/98GB00744)
    OpenUrlCrossRefGeoRefWeb of Science
  66. ↵
    Royal Society 2009 Geoengineering the climate: science, governance and uncertainty policy doucment 10/09. London, UK: The Royal Society.
  67. House of Commons Science & Technology Committee.. 2010 The regulation of geoengineering. London, UK: The Stationery Office.
    1. Rickels W.,
    2. et al.
    (2011) Large-scale intentional interventions into the climate system? Assessing the climate engineering debate. Scoping report conducted on behalf of the German Federal Ministry of Education and Research (BMBF), Germany: Kiel Earth Institute.
  68. ↵
    US Government Accountability Office. 2011 Technology assessment: climate engineering. Technical status, future directions, and potential responses, GAO-11-71. See www.gao.gov/new.items/pdf.
  69. ↵
    1. Anderson K.,
    2. Bows A.
    2008 Re-framing the climate change challenge in the light of post-2000 emission trends. Phil. Trans. R. Soc. A 366, 3863–3882. doi:10.1098/rsta.2008.0138 (doi:10.1098/rsta.2008.0138)
    OpenUrlAbstract/FREE Full Text
  70. ↵
    1. Anderson K.,
    2. Bows A.
    2011 Beyond 'dangerous' climate change: emission scenarios for a new world. Phil. Trans. R. Soc. 369, 20–44. doi:10.1098/rsta.2010.0290 (doi:10.1098/rsta.2010.0290)
    OpenUrlAbstract/FREE Full Text
  71. ↵
    1. New M.,
    2. Liverman D.,
    3. Schoder H.,
    4. Anderson K.
    2011 Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications. Phil. Trans. R. Soc. A 369, 6–19. doi:10.1098/rsta.2010.0303 (doi:10.1098/rsta.2010.0303)
    OpenUrlAbstract/FREE Full Text
  72. ↵
    CBD (Convention on Biological Diversity). 2010 Decision X/33 (Paragraph 8), Biodiversity and climate change. See www.cbd.int/doc/?meeting=cop-10.
  73. ↵
    1. Carayannis E.
    1. Mitchell D. L.,
    2. Mishra S.,
    3. Lawson R. P.
    2011 Cirrus clouds and climate engineering: new findings on ice nucleation and theoretical basis. In Planet Earth 2011—global warming challenges and opportunities for policy and practice (ed. Carayannis E.), pp. 257–288. InTech. See www.intechopen.com/articles/show/title/cirrus-clouds-and-climate-engineering-new-findings-on-ice-nucleation-and-theoretical-basis.
  74. ↵
    1. Boucher O.,
    2. Folberth G. A.
    2010 New directions: atmospheric methane removal as a way to mitigate climate change? Atmos. Environ. 44, 3343–3345. doi:10.1016/j.atmosenv.2010.04.032 (doi:10.1016/j.atmosenv.2010.04.032)
    OpenUrlCrossRefWeb of Science
  75. ↵
    1. Matthews H. D.,
    2. Caldeira K.
    2007 Transient climate-carbon simulations of planetary geoengineering. Proc. Natl Acad. Sci. USA 104, 9949–9954. doi:10.1073/pnas.0700419104 (doi:10.1073/pnas.0700419104)
    OpenUrlAbstract/FREE Full Text
  76. ↵
    1. Matthews H. D.,
    2. Cao L.,
    3. Caldeira K.
    2009 Sensitivity of ocean acidification to geoengineered climate stabilization. Geophys. Res. Lett. 36, L10706. doi:10.1029/2009GL037488 (doi:10.1029/2009GL037488)
    OpenUrlCrossRef
  77. ↵
    1. Schmidt H.,
    2. et al.
    2012 Can a reduction in solar irradiance counteract CO2-induced climate change?: Results from four Earth system models. Earth Syst. Dynam. Discuss. 3, 31–72. doi:10.5194/esdd-3-31-2012 (doi:10.5194/esdd-3-31-2012)
    OpenUrlCrossRef
  78. ↵
    1. Mercado L. M.,
    2. Bellouin N.,
    3. Sitch S.,
    4. Boucher O.,
    5. Huntingford C.,
    6. Wild M.,
    7. Cox P. M.
    2009 Impact of changes in diffuse radiation on the global land carbon sink. Nature 458, 1014–1017. doi:10.1038/nature07949 (doi:10.1038/nature07949)
    OpenUrlCrossRefGeoRefPubMedWeb of Science
    1. Hunter K. A.,
    2. et al.
    2011 Impacts of anthropogenic SOx, NOx and NH3 on acidification of coastal waters and shipping lanes. Geophys. Res. Lett. 38, L13602. doi:10.1029/2011GL047720 (doi:10.1029/2011GL047720)
    OpenUrlCrossRef
    1. Morel A.
    1991 Light and marine photosynthesis: a spectral model with climatological implications. Progr. Oceanogr. 26, 263–306. doi:10.1016/0079-6611(91)90004-6 (doi:10.1016/0079-6611(91)90004-6)
    OpenUrlCrossRef
  79. ↵
    1. Bala G.,
    2. Nag B.
    In press. Albedo enhancement over land to counteract global warming: impacts on hydrological cycle. Clim. Dyn.. doi:10.1007/s00382-011-1256-1 (doi:10.1007/s00382-011-1256-1)
    OpenUrlCrossRef
  80. ↵
    1. Cao L.,
    2. Caldeira K.
    2010 Can ocean fertilization mitigate ocean acidification? Clim. Change 99, 303–311. doi:10.1007/s10584-010-9799-4 (doi:10.1007/s10584-010-9799-4)
    OpenUrlCrossRefWeb of Science
    1. Oschlies A.,
    2. Koeve W.,
    3. Rickels W.,
    4. Rehdanz K.
    2010 Side effects and accounting aspects of hypothetical large-scale Southern Ocean iron fertilization. Biogeosciences 7, 4017–4035. doi:10.5194/bg-7-4017-2010 (doi:10.5194/bg-7-4017-2010)
    OpenUrlCrossRefWeb of Science
    1. Oschlies A.,
    2. Pahlow M.,
    3. Yool A.,
    4. Matear R. J.
    2010 Climate engineering by artificial ocean upwelling: channelling the sorcerer’s apprentice. Geophys. Res. Lett. 37, L04701. doi:10.1029/2009GL041961 (doi:10.1029/2009GL041961)
    OpenUrlCrossRef
  81. ↵
    1. Marchetti C.
    1977 On geoengineering and the CO2 problem. Clim. Change 1, 59–68. doi:10.1007/BF00162777 (doi:10.1007/BF00162777)
    OpenUrlCrossRefGeoRefWeb of Science
  82. ↵
    1. Barry J. P.,
    2. Buck K. R.,
    3. Lovera C. F.,
    4. Kuhnz L.,
    5. Whaling P. J.,
    6. Peltzer E. T.,
    7. Walz P.,
    8. Brewer P. G.
    2004 Effects of direct ocean CO2 injection on deep-sea meiofauna. J. Oceanogr. 60, 759–766. doi:10.1007/s10872-004-5768-8 (doi:10.1007/s10872-004-5768-8)
    OpenUrlCrossRefWeb of Science
  83. ↵
    1. Ridgwell A.,
    2. Rodengen T. J.,
    3. Kohfeld K. E.
    2011 Geographical variations in the effectiveness and side effects of deep ocean carbon sequestration. Geophys. Res. Lett. 38, L17610. doi:10.1029/GL048423 (doi:10.1029/GL048423)
    OpenUrlCrossRef
  84. ↵
    1. House K. Z.,
    2. Schrag D. P.,
    3. Harvey C. F.,
    4. Lackner K. S.
    2006 Permanent carbon storage in deep-sea sediments.. Proc. Natl Acad. Sci. USA 103, 12291–12295. doi:10.1073/pnas.0605318103 (doi:10.1073/pnas.0605318103)
    OpenUrlAbstract/FREE Full Text
  85. ↵
    1. Metz B.,
    2. Davidson O.,
    3. Conminck H.,
    4. Loos M.,
    5. Meyer L.
    IPCC. 2005 IPCC special report on carbon dioxide capture and storage (eds Metz B., Davidson O., Conminck H., Loos M., Meyer L.). Working Group III, Intergovernmental Panel for Climate Change. Cambridge, UK: Cambridge University Press.
  86. ↵
    1. Wilson E. J.,
    2. Johnson T. L.,
    3. Keith D. W.
    2003 Regulating the ultimate sink; managing the risks of geologic CO2 storage. Environ. Sci. Technol. 37, 3476–3483. doi:10.1021/es021038+ (doi:10.1021/es021038+)
    OpenUrlCrossRefPubMedWeb of Science
    1. Matter J. M.,
    2. Keleman P. B.
    2009 Permanent storage of carbon dioxide in geological reservoirs by mineral carbonation. Nat. Geosci. 2, 837–841. doi:10.1038/ngeo683 (doi:10.1038/ngeo683)
    OpenUrlCrossRef
    1. Strand S. E.,
    2. Benford G.
    2009 Ocean sequestration of crop residue carbon: recycling fossil fuel carbon back to deep sediments. Environ. Sci. Technol. 43, 1000–1007. doi:10.1021/es8015556 (doi:10.1021/es8015556)
    OpenUrlPubMedWeb of Science
  87. ↵
    1. Markels M.,
    2. Sato T.,
    3. Chen L.,
    4. Jones I. S.F.
    2011 Enhanced carbon storage in the ocean. Report of Engineering Committee for Oceanic Resources (ECOR). See www.oceanicresources.org/ecor-news/ocean-sequestration-of-carbon-working-group-report.
  88. ↵
    1. Rau G. H.,
    2. Caldeira K.
    1999 Enhanced carbonate dissolution: a means of sequestering waste CO2 as ocean bicarbonate. Energy Conv. Manage. 40, 1803–1813. doi:10.1016/S0196-8904(99)00071-0 (doi:10.1016/S0196-8904(99)00071-0)
    OpenUrlCrossRef
  89. ↵
    1. Harvey L. D. D.
    2008 Mitigating the atmospheric CO2 increase and ocean acidification by adding limestone powder to upwelling regions. J. Geophys. Res. Oceans 113, C04028. doi:10.1029/2007/JC004383 (doi:10.1029/2007/JC004383)
    OpenUrlCrossRef
  90. ↵
    1. Kheshgi H. S.
    1995 Sequestering atmospheric carbon dioxide by increasing ocean alkalinity. Energy 20, 915–922. doi:10.1016/0360-5442(95)00035-F (doi:10.1016/0360-5442(95)00035-F)
    OpenUrlCrossRef
  91. ↵
    1. Vaughan N. E.,
    2. Lenton T. M.
    2011 A review of climate geoengineering proposals. Clim. Change 109, 745–790. doi:10.1007/s10584-011-0027-7 (doi:10.1007/s10584-011-0027-7)
    OpenUrlCrossRefWeb of Science
  92. ↵
    1. Caldeira K.,
    2. Wood L.
    2008 Global and Arctic climate engineering: numerical model studies. Phil. Trans. R. Soc. A 366, 4039–4056. doi:10.1098/rsta.2008.0132 (doi:10.1098/rsta.2008.0132)
    OpenUrlAbstract/FREE Full Text
    1. Irvine P. J.,
    2. Ridgwell A.,
    3. Lunt D. J.
    2010 Assessing the regional disparities in geoengineering impacts. Geophys. Res. Lett. 37, L18702. doi:10.1029/2010GL044447 (doi:10.1029/2010GL044447)
    OpenUrlCrossRef
  93. ↵
    1. Lunt D. J.,
    2. Ridgwell A.,
    3. Valdes P. J.,
    4. Seale A.
    2008 ‘Sunshade world’: a fully coupled GCM evaluation of the climatic impacts of geoengineering. Geophys. Res. Lett. 35, L12710. doi:10.1029/2008GL033674 (doi:10.1029/2008GL033674)
    OpenUrlCrossRef
  94. ↵
    1. Bala G.,
    2. Caldeira K.,
    3. Nemani R.,
    4. Cao L.,
    5. Ban-Weiss G.,
    6. Shin H.-J.
    2011 Albedo enhancement of marine clouds to counteract global warming: impacts on the hydrological cycle. Clim. Dynam. 37, 915–931. doi:10.1007/s00382-010-0868-1 (doi:10.1007/s00382-010-0868-1)
    OpenUrlCrossRef
  95. ↵
    1. Kravitz B.,
    2. Robock A.,
    3. Boucher O.,
    4. Schmidt H.,
    5. Taylor K. E.,
    6. Stenchikov G.,
    7. Schulz M.
    2011 The geoengineering model intercomparison project (GeoMIP). Atmos. Sci. Lett. 12, 162–167. doi:10.1002/asl.316 (doi:10.1002/asl.316)
    OpenUrlCrossRefWeb of Science
  96. ↵
    1. Russell L. M.,
    2. et al.
    2011 Ecosystem impacts on geoengineering: a review for developing a science plan. Ambio 41, 350–369. doi:10.1007/S13280-012-0258-5 (doi:10.1007/S13280-012-0258-5)
    OpenUrlCrossRef
  97. ↵
    1. Watson R.,
    2. Williamson P.,
    3. Artaxo P.,
    4. Bodle R.,
    5. Galaz V.,
    6. Mace G.,
    7. Parker A.,
    8. Santillo D.,
    9. Vivian C.
    Secretariat of the Convention on Biological Diversity 2012 Impacts of climate-related geoengineering on biological diversity (eds Watson R., Williamson P., Artaxo P., Bodle R., Galaz V., Mace G., Parker A., Santillo D., Vivian C.). Montreal, Canada: CBD.
  98. ↵
    1. Crutzen P. J.
    2006 Albedo enhancement by stratospheric sulphur injections: a contribution to resolve a policy dilemma? Clim. Change 77, 211–220. doi:10.1007/s10584-006-9101-y (doi:10.1007/s10584-006-9101-y)
    OpenUrlCrossRefWeb of Science
  99. ↵
    1. Goodinge R. A.,
    2. Harley C. D. G.,
    3. Tang E.
    2009 Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. Proc. Natl Acad. Sci. USA 106, 9316–9321. doi:10.1073/pnas.0811143106 (doi:10.1073/pnas.0811143106)
    OpenUrlAbstract/FREE Full Text
  100. ↵
    1. Rodolfo-Metalpa R.,
    2. Martin S.,
    3. Ferrier-Pagès C.,
    4. Gattuso J.-P.
    2010 Response of the temperate coral Cladocora caespitosa to mid- and long-term exposure to pCO2 and temperature levels projected for the year 2100 AD. Biogeosciences 7, 289–300. doi:10.5194/bg-7-289-2010 (doi:10.5194/bg-7-289-2010)
    OpenUrlCrossRefWeb of Science
  101. ↵
    1. Rodolfo-Metalpa R.,
    2. et al.
    2011 Coral and mollusc resistance to ocean acidification adversely affected by warming. Nat. Clim. Change 1, 308–312. doi:10.1038/nclimate1200 (doi:10.1038/nclimate1200)
    OpenUrlCrossRefWeb of Science
  102. ↵
    1. Dunne R. P.
    2010 Synergy or antagonism—interactions between stressors on coral reefs. Coral Reefs 29, 145–152. doi:10.1007/s00338-009-0569-6 (doi:10.1007/s00338-009-0569-6)
    OpenUrlCrossRefWeb of Science
  103. ↵
    1. Rockström J.,
    2. et al.
    2009 A safe operating space for humanity. Nature 461, 472–475. doi:10.1038/461472a (doi:10.1038/461472a)
    OpenUrlCrossRefPubMedWeb of Science
  104. ↵
    1. Lenton T. M.,
    2. Vaughan N.
    2009 Radiative forcing potential of climate geoengineering. Atmos. Chem. Phys. 9, 5539–5561. doi:10.5194/acp-9-5539-2009 (doi:10.5194/acp-9-5539-2009)
    OpenUrlCrossRefWeb of Science
  105. ↵
    1. McLaren D.
    2011 First stop digging. An assessment of the potential for negative emission techniques to contribute safely and fairly to meeting carbon budgets in the 21st century. McLaren Environmental Research & Consultancy Working Paper 1/11. See https://sites.google.com/site/mclarenerc.
  106. ↵
    1. Pacala S.,
    2. Socolow R.
    2004 Stabilization wedges: solving the climate problem in the next 50 years with current technologies. Science 305, 968–972. doi:10.1126/science.1100103 (doi:10.1126/science.1100103)
    OpenUrlAbstract/FREE Full Text
  107. ↵
    1. Keith D. W.
    2009 Why capture CO2 from the atmosphere? Science 325, 1654–1655. doi:10.1126/science.1175680 (doi:10.1126/science.1175680)
    OpenUrlAbstract/FREE Full Text
  108. ↵
    1. Blackford J. C.,
    2. Jones N.,
    3. Proctor R.,
    4. Holt J.
    2008 Regional scale impacts of distinct CO2 additions in the North Sea. Mar. Poll. Bull. 56, 1461–1468. doi:10.1016/j.marpolbul.2008.04.048 (doi:10.1016/j.marpolbul.2008.04.048)
    OpenUrlCrossRef
  109. ↵
    1. Holloway S.,
    2. Pearce J. M.,
    3. Hards V. L.,
    4. Ohsumi T.,
    5. Gale J.
    2007 Natural emissions of CO2 from the geosphere and their bearing on the geological storage of carbon dioxide. Energy 32, 1194–1201. doi:10.1016/j.energy.2006.09.001 (doi:10.1016/j.energy.2006.09.001)
    OpenUrlCrossRef
  110. ↵
    1. Handa N.,
    2. Ohsumi T.
    1995 Direct ocean disposal of carbon dioxide. Tokyo, Japan: Terra Scientific Publishing Company.
  111. ↵
    1. Metzger R. A.,
    2. Benford G.
    2001 Sequestering of atmospheric carbon through permanent disposal of crop residue. Clim. Change 49, 11–19. doi:10.1023/A:1010765013104 (doi:10.1023/A:1010765013104)
    OpenUrlCrossRefWeb of Science
  112. ↵
    1. Golomb D.,
    2. Angelopolous A.
    2001 A benign form of CO2 sequestration in the ocean. In Proc. 5th Int. Greenhouse Gas Technology Congress pp. 463–468. Collingwood, Australia: CSIRO Publishing.
  113. ↵
    1. Wallace D. W. R.,
    2. et al.
    2010 Ocean fertilization. A scientific summary for policy makers. Paris, France: IOC/UNESCO.
  114. ↵
    1. Martin J. H.
    1990 Glacial-interglacial CO2 change: the iron hypothesis. Paleoceanography 5, 1–13. doi:10.1029/PA005i001p00001 (doi:10.1029/PA005i001p00001)
    OpenUrlCrossRefGeoRefWeb of Science
  115. ↵
    1. Lampitt R. S.,
    2. et al.
    2008 Ocean fertilization: a potential means of geoengineering? Phil. Trans. R. Soc. A 366, 3919–3945. doi:10.1098/rsta.2008.0139 (doi:10.1098/rsta.2008.0139)
    OpenUrlAbstract/FREE Full Text
  116. ↵
    1. Lovelock J.,
    2. Rapley C. G.
    2007 Ocean pipes could help the Earth cure itself. Nature 449, 403. doi:10.1038/449403a (doi:10.1038/449403a)
    OpenUrlPubMedWeb of Science
  117. ↵
    1. Salter S. H.
    2009 A 20GW thermal 300-m3/s wave-energised, surge-mode nutrient-pump for removing atmospheric carbon dioxide, increasing fish stocks and suppressing hurricanes. In Proc. 8th European Wave and Tidal Energy Conf., Uppsala, Sweden, 7–10 September 2009 pp. 1–6. See http://www.see.ed.ac.uk/~shs/Climate%20change/20%20GW%20wave%20sink.pdf.
  118. ↵
    1. Aumont O.,
    2. Bopp L.
    2006 Globalizing results from ocean in situ iron fertilization studies. Global Biogeochem. Cycles 20, GB2017. doi:10.1029/2005GB002591 (doi:10.1029/2005GB002591)
    OpenUrlCrossRef
  119. ↵
    1. Cullen J. J.,
    2. Boyd P. W.
    2008 Predicting and verifying the intended and unintended consequences of large-scale ocean iron fertilization. Mar. Ecol. Prog. Ser. 364, 295–301. doi:10.3354/meps07551 (doi:10.3354/meps07551)
    OpenUrlCrossRefWeb of Science
View Abstract
PreviousNext
Back to top
PreviousNext
13 September 2012
Volume 370, issue 1974
Philosophical Transactions of the Royal Society A: Mathematical, 				Physical and Engineering Sciences: 370 (1974)
  • Table of Contents
Discussion Meeting Issue ‘Geoengineering: taking control of our planet's climate?’ organized and edited by Andy Ridgwell, Chris Freeman and Richard Lampitt
Share
Ocean acidification in a geoengineering context
Phillip Williamson, Carol Turley
Phil. Trans. R. Soc. A 2012 370 4317-4342; DOI: 10.1098/rsta.2012.0167. Published 6 August 2012
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Connotea logo Facebook logo Google logo Mendeley logo
Email

Thank you for your interest in spreading the word on Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences.

NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. We do not capture any email address.

Enter multiple addresses on separate lines or separate them with commas.
Ocean acidification in a geoengineering context
(Your Name) has sent you a message from Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences
(Your Name) thought you would like to see the Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences web site.
Print
Manage alerts

Please log in to add an alert for this article.

Sign In to Email Alerts with your Email Address
Citation tools
Review article:

Ocean acidification in a geoengineering context

Phillip Williamson, Carol Turley
Phil. Trans. R. Soc. A 2012 370 4317-4342; DOI: 10.1098/rsta.2012.0167. Published 6 August 2012

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Download

Article reuse

  • Article
    • Abstract
    • 1. Carbon dynamics in today’s ocean
    • 2. Observed chemical and biological changes owing to ocean acidification
    • 3. A ‘business as usual’ future ocean
    • 4. Effect of emission reduction on ocean acidification
    • 5. Implications of geoengineering for ocean acidification
    • 6. Conclusions
    • Acknowledgements
    • Footnotes
    • References
  • Figures & Data
  • Info & Metrics
  • eLetters
  • PDF

See related subject areas:

  • environmental engineering
  • biogeochemistry

Related articles

Cited by

Celebrating 350 years of Philosophical Transactions

Anniversary issue with free commentaries, archive material, videos and blogs.

Open biology

  • PHILOSOPHICAL TRANSACTIONS A
    • About this journal
    • Contact information
    • Purchasing information
    • Propose an issue
    • Open access membership
    • Recommend to your library
    • FAQ
    • Help

Royal society publishing

  • ROYAL SOCIETY PUBLISHING
    • Our journals
    • Open access
    • Publishing policies
    • Conferences
    • Podcasts
    • News
    • Blog
    • Manage your account
    • Terms & conditions
    • Cookies

The royal society

  • THE ROYAL SOCIETY
    • About us
    • Contact us
    • Fellows
    • Events
    • Grants, schemes & awards
    • Topics & policy
    • Collections
    • Venue hire
1471-2962

Copyright © 2018 The Royal Society