Sociotechnical Considerations About Ocean Carbon Dioxide Removal

Prioritizing Non-Carbon Dioxide Removal Mitigation Strategies Could Reduce the Negative Impacts Associated with Large-Scale Reliance on Negative Emissions

Carbon dioxide removal (CDR) is necessary for reaching net zero emissions, with studies showing potential deployment at multi-GtCO2 scale by 2050. However, excessive reliance on future CDR entails serious risks, including delayed emissions cuts, lock-in of fossil infrastructure, and threats to sustainability from increased resource competition. This study highlights an alternative pathway─prioritizing near-term non-CDR mitigation and minimizing CDR dependence. We impose a 1 GtCO2 limit on global novel CDR deployment by 2050, forcing aggressive early emissions reductions compared to 8-22 GtCO2 in higher CDR scenarios. Our results reveal that this low CDR pathway significantly decreases fossil fuel use, greenhouse gas (GHG) emissions, and air pollutants compared to higher CDR pathways. Driving rapid energy transitions eases pressures on land (including food cropland), water, and fertilizer resources required for energy and negative emissions. However, these sustainability gains come with higher mitigation costs from greater near-term low/zero-carbon technology deployment for decarbonization. Overall, this work provides strong evidence for maximizing non-CDR strategies such as renewables, electrification, carbon neutral/negative fuels, and efficiency now rather than betting on uncertain future CDR scaling. Ambitious near-term mitigation in this decade is essential to prevent lock-in and offer the best chance of successful deep decarbonization. Our constrained CDR scenario offers a robust pathway to achieving net zero emissions with limited sustainability impacts.

Thinking outside the ocean-climate nexus: Towards systems-informed decision making in a rapidly changing world

Despite repeated calls for more inclusive practices, approaches used to address current challenges within the ocean-climate nexus do not sufficiently account for the complexity of the human-social-ecological system. So far, this has prevented efficient and just decision-making and policies. We propose to shift towards systems-informed decision making, which values transdisciplinary system-thinking and cumulative impact assessments, and encourages multi-system collaboration among decision-makers in order to address the recurring technicality of policies and to foster just solutions that account for the needs of varied actors across the sustainable development spectrum.

Upscaling DAC Hubs with Wind Energy and CO2 Mineral Storage: Considerations for Large-Scale Carbon Removal from the Atmosphere

Continued fossil fuel emissions will increase CO2 concentrations in the atmosphere and could require removal of 10 Gt of CO2 per year or more to reach IPCC global climate goals. Large-scale construction of direct air capture (DAC) hubs to scrub CO2 from the atmosphere paired with geological storage is a prominent approach to potentially meet this target. We consider one location for theoretical scale-up of a DAC hub: the Kerguelen plateau in the Southern Indian Ocean which has high-potential renewable energy resources (wind) and large volumes of basalt rock for mineral storage. With consistent wind, previous studies indicate a hub in this location could collect approximately 75 Mt of CO2 annually, with conservative storage resources for 150-300 Mt of CO2 each year. Even with its immense wind and storage potentials, 14 Kerguelen-scale hubs would be needed to capture and store 1 Gt of CO2 per year. This brings into focus the important social, economic, and environmental trade-offs that must be considered in finding an acceptable balance between climate solutions, renewable energy requirements, and nature. Engaging public groups on these trade-off considerations will be crucial for gigaton scale-up of CO2 removal in just and responsible ways.

pCO2 decrement through alkalinity enhancement and biological production in a shallow-water ecosystem constructed using steelmaking slag

Ocean-based carbon dioxide removal has gained immense attention as a countermeasure against climate change. The enhancement of ocean alkalinity and the creation of new blue carbon ecosystems are considered effective approaches for this. To evaluate the function of steelmaking slag from the viewpoints of CO2 reduction and creation of new blue carbon ecosystems, we conducted a comparative experiment using two mesocosms that replicated tidal-flats and shallow-water ecosystems. Initially, approximately 20 seagrasses (Zostera marina) were transplanted into the shallow-water area in the mesocosm tanks. The use of steelmaking slag is expected to increase the pH by releasing calcium and mitigate turbidity by solidifying dredged soil. In the experimental tank, where dredged soil and steelmaking slag were utilized as bed materials, the pH remained higher throughout the experimental period compared with the control tank, which utilized only dredged soil. As a result, pCO2 remained consistently lower in the experimental tank due to mainly its alkaline effect (March 2019: -10 ± 6 μatm, September 2019: -130 ± 47 μatm). The light environment in the control tank deteriorated due to high turbidity, whereas the turbidity in the experimental tank remained low throughout the year. The number of seagrass shoots in the experimental tank was consistently approximately 20, which was higher than that in the control tank. Additionally, more seaweed and benthic algae were observed in the experimental tank, indicating that it was more conducive to the growth of primary producers. In conclusion, tidal-flat and shallow-water ecosystems constructed using dredged soil and steelmaking slag are expected to enhance CO2 uptake and provide a habitat for primary producers that is superior to those constructed using dredged soil only.