Posts Tagged 'mitigation'

CO2 capture by pumping surface acidity to the deep ocean

The majority of IPCC scenarios call for active CO2 removal (CDR) to remain below 2oC of warm- ing. On geological timescales, ocean uptake regulates atmospheric CO2 concentration, with two homeostats driving CO2 uptake: dissolution of deep ocean calcite deposits and terrestrial weathering of silicate rocks, acting on 1ka to 100ka timescales, respectively. Many current ocean-based CDR proposals effectively act to accelerate the latter. Here we present a method which relies purely on the redistribution and dilution of acidity from a thin layer of the surface ocean to a thicker layer of deep ocean, with the aim of reducing surface acidification and accelerating the former carbonate homeostasis. This downward transport could be seen analogous to the action of the natural biological carbon pump. The method offers advantages over other ocean CDR methods and direct air capture approaches (DAC): the conveyance of mass is minimized (acidity is pumped in situ to depth), and expensive mining, grinding and distribution of alkaline material is eliminated. No dilute substance needs to be concentrated, avoiding the Sherwood’s Rule costs typically encountered in DAC. Finally, no terrestrial material is added to the ocean, avoiding significant alteration of seawater ion concentrations or issues with heavy metal toxicity encountered in mineral-based alkalinity schemes. The artificial transport of acidity accelerates the natural deep ocean compensation by calcium carbonate. It has been estimated that the total compensation capacity of the ocean is on the order of 1500GtC. We show through simulation that pumping of ocean acidity could remove up to 150GtC from the atmosphere by 2100 with- out excessive increase of local ocean pH. For an acidity release below 2000m, the relaxation half-life of CO2 return to the atmosphere was found to be ∼2500 years (∼1000yr without account- ing for carbonate dissolution), with ∼85% retained for at least 300 years. The uptake efficiency and residence time were found to vary with the location of acidity pumping, and optimal areas were determined. Requiring only local resources (ocean water and energy), this method could be uniquely suited to utilize otherwise-unusable open ocean energy sources at scale. We examine technological pathways that could be used to implement it and present a brief techno-economic estimate of 130-250$/tCO2 at current prices and as low as 93$/tCO2 under modest learning-curve assumptions.

Continue reading ‘CO2 capture by pumping surface acidity to the deep ocean’

Large-scale interventions may delay decline of the Great Barrier Reef

On the iconic Great Barrier Reef (GBR), the cumulative impacts of tropical cyclones, marine heatwaves and regular outbreaks of coral-eating crown-of-thorns starfish (CoTS) have severely depleted coral cover. Climate change will further exacerbate this situation over the coming decades unless effective interventions are implemented. Evaluating the efficacy of alternative interventions in a complex system experiencing major cumulative impacts can only be achieved through a systems modelling approach. We have evaluated combinations of interventions using a coral reef meta-community model. The model consisted of a dynamic network of 3753 reefs supporting communities of corals and CoTS connected through ocean larval dispersal, and exposed to changing regimes of tropical cyclones, flood plumes, marine heatwaves and ocean acidification. Interventions included reducing flood plume impacts, expanding control of CoTS populations, stabilizing coral rubble, managing solar radiation and introducing heat-tolerant coral strains. Without intervention, all climate scenarios resulted in precipitous declines in GBR coral cover over the next 50 years. The most effective strategies in delaying decline were combinations that protected coral from both predation (CoTS control) and thermal stress (solar radiation management) deployed at large scale. Successful implementation could expand opportunities for climate action, natural adaptation and socioeconomic adjustment by at least one to two decades.

Continue reading ‘Large-scale interventions may delay decline of the Great Barrier Reef’

A critical analysis of the ocean effects of carbon dioxide removal via direct air and ocean capture – is it a safe and sustainable solution?

Executive Summary

Catalyzed by the 2015 Paris Agreement, there are numerous initiatives for policies and sciencebased solutions to reduce greenhouse gas emissions and to achieve net-zero emissions internationally. President Biden plans to achieve net-zero in the United States no later than 2050. Despite forward-moving initiatives, the Intergovernmental Panel on Climate Change (IPCC) recently reported that two-thirds of the countries that have pledged to reduce greenhouse gas emissions have committed to levels that remain insufficient in meeting vital international climate targets [1]. The overarching goal to reduce greenhouse gas (GHG) emissions must be accomplished by transitioning to a more equitable and environmentally just energy system that reduces pollution while meeting global food, transportation, and energy needs. Carbon dioxide removal (CDR) is at the forefront of policy change, investments, and technology to reduce the amount of CO2 in the atmosphere and the ocean. We must respond quickly, yet carefully, to the considerable pressure to remove carbon dioxide from the atmosphere even as we transition away from burning fossil fuels and other anthropogenic CO2-emitting activities. There are a number of emerging technologies based on direct air capture (DAC) and direct ocean capture (DOC) which use machines to extract CO2 directly from the atmosphere or the ocean and move the CO2 underground to storage facilities or utilize the CO2 to enhance oil recovery from commercially-depleted wells. These technological interventions are in contrast to nature-based solutions. These include restoring mangroves and other coastal and marine ecosystems, regenerative agriculture, and reforestation to remove and store carbon dioxide in plants and soils. These nature-based strategies can offer multiple community benefits, biodiversity benefits, and long-term carbon storage, a global benefit.2 This report mainly focuses on the viability and consequences, including potential harm to the environment and livelihoods of the direct air capture and direct ocean capture approaches.

Continue reading ‘A critical analysis of the ocean effects of carbon dioxide removal via direct air and ocean capture – is it a safe and sustainable solution?’

Potential of maritime transport for ocean liming and atmospheric CO2 removal

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.

Continue reading ‘Potential of maritime transport for ocean liming and atmospheric CO2 removal’

Coast‐wide evidence of low pH amelioration by seagrass ecosystems

Global‐scale ocean acidification has spurred interest in the capacity of seagrass ecosystems to increase seawater pH within crucial shoreline habitats through photosynthetic activity. However, the dynamic variability of the coastal carbonate system has impeded generalization into whether seagrass aerobic metabolism ameliorates low pH on physiologically and ecologically relevant timescales. Here we present results of the most extensive study to date of pH modulation by seagrasses, spanning seven meadows (Zostera marina) and 1000 km of U.S. west coast over 6 years. Amelioration by seagrass ecosystems compared to non‐vegetated areas occurred 65% of the time (mean increase 0.07 ± 0.008 SE). Events of continuous elevation in pH within seagrass ecosystems, indicating amelioration of low pH, were longer and of greater magnitude than opposing cases of reduced pH or exacerbation. Sustained elevations in pH of >0.1, comparable to a 30% decrease in [H+], were not restricted only to daylight hours but instead persisted for up to 21 days. Maximal pH elevations occurred in spring and summer during the seagrass growth season, with a tendency for stronger effects in higher latitude meadows. These results indicate that seagrass meadows can locally alleviate low pH conditions for extended periods of time with important implications for the conservation and management of coastal ecosystems.

Continue reading ‘Coast‐wide evidence of low pH amelioration by seagrass ecosystems’

Kelp aquaculture in China: a retrospective and future prospects

Globally, China has the largest scale of kelp cultivation and production operations. However, its kelp aquaculture industry is suffering from declining germplasm diversity, degradation of agronomic traits, the presence of polluted
environments, changing ocean conditions and increasing anthropological interference. This review covers two of the most commercially important kelp species in China, viz. Saccharina japonica and Undaria pinnatifida. It summarizes the history of their cultivation, production, economic and ecological benefits, their breeding programmes (e.g. inter- and intra-specific hybridization and marker-assisted selection) and efforts towards population genetic diversity and conservation. The article focuses on three significant challenges, for example genetic crosscontamination between the wild and farmed kelp populations, ocean warming and ocean acidification. Accordingly, we outline the steps required to provide several intervention measures, for example (i) collection and preservation of wild and cultivated kelp germplasm; (ii) selection of suitable cultivation sites under changing environmental conditions; (iii) developing stress-resistant cultivars; and finally, (iv) adoption of innovative cultivation models. The review concludes with genome-based, designs for molecular breeding and calls for the establishment of an East Asian Kelp Consortium (EAKC). Collectively, the Chinese kelp industry could provide beneficial goods and services, for example bioenergy to fine chemicals and environmental benefits, such as carbon capture, pH amelioration and provision of habitat for many other marine species of commercial value. The strategies proposed in this article thus have the potential to not only improve but also reinvigorate the kelp industry in China and nearby Japan and Korea, in the context of both environmental health and economic benefits.

Continue reading ‘Kelp aquaculture in China: a retrospective and future prospects’

Removing carbon dioxide through ocean alkalinity enhancement and seaweed cultivation: legal challenges and opportunities

Scientists increasingly agree that carbon dioxide removal will be needed, alongside deep emissions cuts, to stave off the worst impacts of climate change. A wide variety of technologies and strategies have been proposed to remove carbon dioxide from the atmosphere. To date, most research has focused on terrestrial-based approaches, but they often have large land requirements, and may present other risks and challenges. As such, there is growing interest in using the oceans, which have already absorbed more than a quarter of anthropogenic carbon dioxide emissions, and could become an even larger carbon sink in the future.

This paper explores two ocean-based carbon dioxide removal strategies—ocean alkalinity enhancement and seaweed cultivation. Ocean alkalinity enhancement involves adding alkalinity to ocean waters, either by discharging alkaline rocks or through an electrochemical process, which increases ocean pH levels and thereby enables greater uptake of carbon dioxide, as well as reducing the adverse impacts of ocean acidification. Seaweed cultivation involves the growing of kelp and other macroalgae to store carbon in biomass, which can then either be used to replace more greenhouse gas-intensive products or sequestered.

Continue reading ‘Removing carbon dioxide through ocean alkalinity enhancement and seaweed cultivation: legal challenges and opportunities’

Climate change mitigation effects: how do potential CO2 leaks from a sub-seabed storage site in the Norwegian Sea affect Astarte sp. bivalves?

Highlights

  • Acidification and recovery were assessed with high-pressure bioassays.
  • No mortality was reported for Astarte sp. for a pH 7.0 scenario.
  • Normal growth of shell length was recorded after CO2 exposure and a recovery period.

Abstract

Carbon capture and storage (CCS) is one of the most promising mitigation strategies for reducing the emissions of carbon dioxide (CO2) to the atmosphere and may substantially help to decelerate global warming. There is an increasing demand for CCS sites. Nevertheless, there is a lack of knowledge of the environmental risk associated with potential leakage of CO2 from the storage sites; and even more, what happens when the seepage stops. Can the environment return to the initial equilibrium? Potential effects on native macrofauna were studied under a scenario of a 50-day CO2 leakage, and the subsequent leak closure. To accomplish the objective, Trondheim Fjord sediments and clams were exposed to an acidified environment (pH 6.9) at 29 atm for 7 weeks followed by a 14-day recovery at normal seawater conditions (pH 8.0, 29 atm). Growth and survival of clams exposed to pressure (29 atm) and reduced pH (6.9) did not significantly differ from control clams kept at 1 atm in natural seawater. Furthermore, bioaccumulation of elements in the soft tissue of clams did not register significant variations for most of the analysed elements (Cd, Cr, Pb, and Ti), while other elements (As, Cu, Fe, Ni) had decreasing concentrations in tissues under acidified conditions in contrast to Na and Mg, which registered an uptake (Ku) of 111 and 9.92 μg g−1dw d−1, respectively. This Ku may be altered due to the stress induced by acidification; and the element concentration being released from sediments was not highly affected at that pH. Therefore, a 1 unit drop in pH at the seafloor for several weeks does not appear to pose a risk for the clams.

Continue reading ‘Climate change mitigation effects: how do potential CO2 leaks from a sub-seabed storage site in the Norwegian Sea affect Astarte sp. bivalves?’

Alkalinization scenarios in the Mediterranean Sea for efficient removal of atmospheric CO2 and the mitigation of ocean acidification

It is now widely recognised that in order to reach the target of limiting global warming below 2 °C above pre-industrial levels (as the objective of the Paris agreement) there is the need for development and implementation of active Carbon Dioxide Removal (CDR) strategies. 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 marine alkalinisation, 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 ocean alkalinisation applied to the Mediterranean Sea taking into consideration the regional characteristics of the basin. Rather than using idealised spatially homogenous scenarios of alkalinisation as done in previous studies, we use a set of numerical simulations of alkalinisation based on current shipping routes to quantitatively assess the alkalinisation efficiency via a coupled physical-biogeochemical model over the next decades. Simulations suggest the potential of nearly doubling the carbon-dioxide uptake rate of the Mediterranean Sea after 30 years of alkalinisation, and of neutralising the mean surface acidification trend of the baseline scenario without alkalinisation over the same time span. These levels are achieved via two different strategies: a first approach applying constant annual discharge of 200Mt Ca(OH)2 over the alkalinisation 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 alkalinisation period. We demonstrate that via the latter approach it is possible to stabilise 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 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.

Continue reading ‘Alkalinization scenarios in the Mediterranean Sea for efficient removal of atmospheric CO2 and the mitigation of ocean acidification’

Seaweed farms provide refugia from ocean acidification

Seaweed farming has been proposed as a strategy for adaptation to ocean acidification, but evidence is largely lacking. Changes of pH and carbon system parameters in surface waters of three seaweed farms along a latitudinal range in China were compared, on the weeks preceding harvesting, with those of the surrounding seawaters. Results confirmed that seaweed farming is efficient in buffering acidification, with Saccharina japonica showing the highest capacity of 0.10 pH increase within the aquaculture area, followed by Gracilariopsis lemaneiformis (ΔpH = 0.04) and Porphyra haitanensis (ΔpH = 0.03). The ranges of pH variability within seaweed farms spanned 0.14-0.30 unit during the monitoring, showing intense fluctuations which may also help marine organisms adapt to enhanced pH temporal variations in the future ocean. Deficit in pCO2 in waters in seaweed farms relative to control waters averaged 58.7 ± 15.9 μatm, ranging from 27.3 to 113.9 μatm across farms. However, ΔpH did not significantly differ between day and night. Dissolved oxygen and Ωarag were also elevated in surface waters at all seaweed farms, which are benefit for the survival of calcifying organisms. Seaweed farming, which unlike natural seaweed forests, is scalable and is not dependent on suitable substrate or light availability, could serve as a low-cost adaptation strategy to ocean acidification and deoxygenation and provide important refugia from ocean acidification.

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Ocean acidification in the IPCC AR5 WG II

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