CO2 Removal With Enhanced Weathering and Ocean Alkalinity Enhancement: Potential Risks and Co-benefits for Marine Pelagic Ecosystems

Bach, Lennart T.; Gill, Sophie; Rickaby, Rosalind E. M.; Gore, Sarah; Renforth, Phil

doi:10.3389/fclim.2019.00007

Cited by 170 publications

(223 citation statements)

References 189 publications

(303 reference statements)

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“…While the ecological impacts of acidification of the ocean are subject to a wide field of research, comparatively little is known about the opposite process of alkalinization in order to appreciate the impacts of such changes on the Mediterranean Sea ecosystem. Among the side effects mentioned in literature are the potential of positive and negative feed-backs, affecting nutrient limitation of primary producers, causing physiological damage to marine organisms and altering their metabolic balance (Cripps et al, 2013;Bach et al, 2019), but more research is required on the topic in order to enable a quantified estimate of the resilience of marine ecosystems to alkalinization and an adequate risk assessment. This point is even more relevant when considering the spatial heterogeneity of alkalinization impacts illustrated in Figure 5, which shows that local extremes of pH variation may differ from the basin annual mean by more than 0.1 pH units.…”

Section: Discussionmentioning

confidence: 99%

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

et al. 2021

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It is now widely recognized that in order to reach the target of limiting global warming to well below 2°C above pre-industrial levels (as the objective of the Paris agreement), cutting the carbon emissions even at an unprecedented pace will not be sufficient, but there is the need for development and implementation of active Carbon Dioxide Removal (CDR) strategies. Among the CDR strategies that currently exist, relatively few studies have assessed the mitigation capacity of ocean-based Negative Emission Technologies (NET) and the feasibility of their implementation on a larger scale to support efficient implementation strategies of CDR. This study investigates the case of ocean alkalinization, which has the additional potential of contrasting the ongoing acidification resulting from increased uptake of atmospheric CO2 by the seas. More specifically, we present an analysis of marine alkalinization applied to the Mediterranean Sea taking into consideration the regional characteristics of the basin. Rather than using idealized spatially homogenous scenarios of alkalinization as done in previous studies, which are practically hard to implement, we use a set of numerical simulations of alkalinization based on current shipping routes to quantitatively assess the alkalinization efficiency via a coupled physical-biogeochemical model (NEMO-BFM) for the Mediterranean Sea at 1/16° horizontal resolution (~6 km) under an RCP4.5 scenario over the next decades. Simulations suggest the potential of nearly doubling the carbon-dioxide uptake rate of the Mediterranean Sea after 30 years of alkalinization, and of neutralizing the mean surface acidification trend of the baseline scenario without alkalinization over the same time span. These levels are achieved via two different alkalinization strategies that are technically feasible using the current network of cargo and tanker ships: a first approach applying annual discharge of 200 Mt Ca(OH)2 constant over the alkalinization period and a second approach with gradually increasing discharge proportional to the surface pH trend of the baseline scenario, reaching similar amounts of annual discharge by the end of the alkalinization period. We demonstrate that the latter approach allows to stabilize the mean surface pH at present day values and substantially increase the potential to counteract acidification relative to the alkalinity added, while the carbon uptake efficiency (mole of CO2 absorbed by the ocean per mole of alkalinity added) is only marginally reduced. Nevertheless, significant local alterations of the surface pH persist, calling for an investigation of the physiological and ecological implications of the extent of these alterations to the carbonate system in the short to medium term in order to support a safe, sustainable application of this CDR implementation.

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Section: Discussionmentioning

confidence: 99%

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

et al. 2021

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“…If precipitation does not occur, the bicarbonate and carbonate ions are transported through water streams and end up in the ocean, increasing its alkalinity. Another approach is the addition of alkaline silicate rocks directly into the ocean, whereby finely ground rocks are added to the seawater for CO 2 uptake and carbon storage in the form of bicarbonate and carbonate ions, further enhancing alkalinity as well as inducing additional atmospheric CO 2 absorption (Bach et al 2019). Another approach to increasing alkalinity was proposed by Kheshgi in the mid-1990s and that is the addition of lime (CaO) to the ocean surface.…”

Section: Ocean Alkalinity Enhancementmentioning

confidence: 99%

Strategies for mitigation of climate change: a review

et al. 2020

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Climate change is defined as the shift in climate patterns mainly caused by greenhouse gas emissions from natural systems and human activities. So far, anthropogenic activities have caused about 1.0 °C of global warming above the pre-industrial level and this is likely to reach 1.5 °C between 2030 and 2052 if the current emission rates persist. In 2018, the world encountered 315 cases of natural disasters which are mainly related to the climate. Approximately 68.5 million people were affected, and economic losses amounted to $131.7 billion, of which storms, floods, wildfires and droughts accounted for approximately 93%. Economic losses attributed to wildfires in 2018 alone are almost equal to the collective losses from wildfires incurred over the past decade, which is quite alarming. Furthermore, food, water, health, ecosystem, human habitat and infrastructure have been identified as the most vulnerable sectors under climate attack. In 2015, the Paris agreement was introduced with the main objective of limiting global temperature increase to 2 °C by 2100 and pursuing efforts to limit the increase to 1.5 °C. This article reviews the main strategies for climate change abatement, namely conventional mitigation, negative emissions and radiative forcing geoengineering. Conventional mitigation technologies focus on reducing fossil-based CO2 emissions. Negative emissions technologies are aiming to capture and sequester atmospheric carbon to reduce carbon dioxide levels. Finally, geoengineering techniques of radiative forcing alter the earth’s radiative energy budget to stabilize or reduce global temperatures. It is evident that conventional mitigation efforts alone are not sufficient to meet the targets stipulated by the Paris agreement; therefore, the utilization of alternative routes appears inevitable. While various technologies presented may still be at an early stage of development, biogenic-based sequestration techniques are to a certain extent mature and can be deployed immediately.

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“…The assessment of the localized impact produced by SL at the discharge point, due to a temporary increase of pH and alkalinity, is necessary to evaluate the environmental side effects of this practice. A pH increase (leading to a decrease in aqueous CO 2 and an increase in bicarbonate ion concentrations), as well as the co-dissolution of other elements, could have a detrimental impact on marine ecosystems (Bach et al, 2019). Pedersen and Hansen (2003) and Locke et al (2009) demonstrate the low probability, for different kinds of organisms, to survive when exposed to high pH level, over several days or weeks.…”

Section: Introductionmentioning

confidence: 99%

“…Cripps et al (2013) point out to acid-base balance alterations in Carcinus maenas once again in response to acute exposure to Ca(OH) 2 concentrations. Bach et al (2019), recognize how a pH increase, whilst leading to benefits such as the decrease in aqueous CO 2 , the increase in bicarbonate ion concentrations, the co-dissolution of other elements, could, conversely, shift the current ecological equilibrium, with detrimental consequences for some organisms rather than others depending on the alkaline mineral used. Hence, a better understanding of the ecological implications of ocean liming requires additional dedicated experimental studies.…”

Section: Introductionmentioning

confidence: 99%

“…The local impact where SL is applied is related to the mineral composition (i.e., % of Mg) and to the technology of discharge chosen (Renforth and Henderson, 2017;Bach et al, 2019). The discharge of CaCO 3 in specific areas in the deep ocean (below 200 m) characterized by lower biodiversity (Costello and Chaudhary, 2017), favorable mixing conditions and upwelling currents, has been studied by Harvey (2008), and has the disadvantage that can only be applied in isolated upwelling regions of the world's ocean (Garcìa-Reyes et al, 2015) in order to impact climate.…”

Section: Introductionmentioning

confidence: 99%

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Potential of Maritime Transport for Ocean Liming and Atmospheric CO2 Removal

et al. 2021

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Proposals to increase ocean alkalinity may make an important contribution to meeting climate change net emission targets, while also helping to ameliorate the effects of ocean acidification. However, the practical feasibility of spreading large amounts of alkaline materials in the seawater is poorly understood. In this study, the potential of discharging calcium hydroxide (slaked lime, SL) using existing maritime transport is evaluated, at the global scale and for the Mediterranean Sea. The potential discharge of SL from existing vessels depends on many factors, mainly their number and load capacity, the distance traveled along the route, the frequency of reloading, and the discharge rate. The latter may be constrained by the localized pH increase in the wake of the ship, which could be detrimental for marine ecosystems. Based on maritime traffic data from the International Maritime Organization for bulk carriers and container ships, and assuming low discharge rates and 15% of the deadweight capacity dedicated for SL transport, the maximum SL potential discharge from all active vessels worldwide is estimated to be between 1.7 and 4.0 Gt/year. For the Mediterranean Sea, based on detailed maritime traffic data, a potential discharge of about 186 Mt/year is estimated. The discharge using a fleet of 1,000 new dedicated ships has also been discussed, with a potential distribution of 1.3 Gt/year. Using average literature values of CO2 removal per unit of SL added to the sea, the global potential of CO2 removal from SL discharge by existing or new ships is estimated at several Gt/year, depending on the discharge rate. Since the potential impacts of SL discharge on the marine environment in the ships' wake limits the rate at which SL can be applied, an overview of methodologies for the assessment of SL concentration in the wake of the ships is presented. A first assessment performed with a three-dimensional non-reactive and a one-dimensional reactive fluid dynamic model simulating the shrinking of particle radii, shows that low discharge rates of a SL slurry lead to pH variations of about 1 unit for a duration of just a few minutes.

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CO2 Removal With Enhanced Weathering and Ocean Alkalinity Enhancement: Potential Risks and Co-benefits for Marine Pelagic Ecosystems

Cited by 170 publications

References 189 publications

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

Strategies for mitigation of climate change: a review

Potential of Maritime Transport for Ocean Liming and Atmospheric CO2 Removal

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