As climate impacts worsen, novel technologies to draw down atmospheric carbon are gaining attention. One such approach is ocean-based carbon dioxide removal (OCDR). However, the potential environmental side-effects of large-scale OCDR deployment remain understudied. Here, we present a systematic literature review of the life cycle assessments (LCAs) of OCDR approaches. We find that current OCDR LCAs have a limited scope, often overlook environmental impacts beyond global warming, and that LCA as a method is currently limited in capturing aquatic impacts. We provide several recommendations for future work, such as using a functional unit of storing atmospheric carbon over a specified time horizon and in a specified medium, performing cradle-to-grave analysis, including more (marine) environmental impacts, and estimating uncertainties. We also emphasise the need to develop the LCA methodology further for better assessing marine environment impacts.

This paper evaluates the potential impacts of introducing low-carbon intensity hydrogen technologies in two oil refineries with different complexity levels, emphasizing the role of hydrogen production in reducing CO₂ emissions. The novelty of this work lies in three key aspects: Comprehensive system analysis of refinery complexity using real site data, integration of low-carbon Hydrogen technologies, long-term and short-term strategies. Two Colombian refineries serve as case studies, with technological solutions adapted to their complexity levels. The methodology involves evaluating different options for hydrogen production, accounting for improvement in technological efficiency over time. The refinery systems were evaluated in a cost-optimization model built in Linny-r. Three different scenarios were considered, Business-As-Usual (BAU), high, and low-ambitions decarbonization scenarios, focusing on the time horizons of 2030 and 2050. When comparing the two case studies, the preferred decarbonization strategy for both facilities involves the substitution of SMR technology with water electrolyzers powered by renewable electricity. Post-2030, biomass-based hydrogen technology is still a costly alternative; however, to achieve CO₂ neutrality, negative emissions storage of biogenic CO₂ emerges as an achievable alternative. Our results indicate the achievability of CO₂ reduction objectives in both refineries. Our results show that achieving long-term CO₂ neutrality requires both refineries to increase renewable electricity production by 5 to 6 times for powering water electrolyzers, steam production by 2 to 2.5 times for CO₂ capture, and supply of dry biomass by 2.6 to 4.5 kt/d. The two most significant factors influencing the refining net margin in the decarbonization scenarios are primarily the CO₂ and the renewable electricity prices. The short-term horizon emerges as the pivotal period, particularly within the high-ambition decarbonization scenarios. In this context, the medium complexity refinery demonstrates economic viability until a CO₂ price of 140 €/t CO₂, while the high complexity refinery endures up to 205 €/t CO₂. The high complexity refinery is better prepared to face the challenges of decarbonization and the impacts generated on the refining margin. Compared to the BAU scenario, the high complexity refinery shows a negative impact on the net margin that corresponds to a 40 % and 5 % reduction in the short and long term, respectively. Meanwhile, for the medium complexity refinery, the impact on net margin amounts to a 52 % reduction in the short term and a 27 % improvement in the long term. Furthermore, our research highlights the significant potential for reducing CO₂ emissions by fully eliminating the use of refinery gas as fuel, providing alternative applications for it beyond combustion.

The chemical sector is hydrocarbon intensive, using primarily fossil fuels as both fuel and feedstock. To achieve carbon-neutrality, it is likely that negative CO2 emissions will be needed to offset the carbon embodied in chemical products. This study presents first-order estimates of the decarbonization potential of combining bioenergy and biofeedstock use with carbon capture and storage (bio-CCS) for ethanol, ammonia, urea, and hydrogen. For each, net CO2 of emissions minus atmospheric removals was estimated over the whole life cycle including chemical synthesis, upstream supply chains, product use, and waste disposal. With aggressive bio-CCS using technologies that are currently commercially available, CO2 negative production was estimated to be possible for all chemicals modelled, except urea. With the use of biomass for both feedstock and fuel and capture of both high-purity and dilute CO2 streams, the estimated net CO2 was -30 g/MJ for maize bioethanol; -50 g/MJ for stover bioethanol; -50 g/MJ for merchant hydrogen; -1.2 t/t N for ammonia and 0.2 t/t N for urea. The potential for negative CO2 emissions is higher in cases where more CO2 can be captured during chemical production. However, all cases were sensitive to assumptions regarding the specific configuration and upstream supply chains.

This paper explores the potential of achieving negative emissions in steelmaking by introducing bioenergy with carbon capture and storage (BECCS) in multiple steelmaking routes, including blast furnace and HIsarna smelt reduction, and Midrex and ULCORED direct reduction. Process modelling and life cycle assessment were used to estimate CO₂ balances for 45 cases. Without bioenergy or CCS, the estimated life cycle CO₂ emissions for steelmaking were 1.3–2.4 t CO₂/t steel. In our model, aggressive BECCS deployment decreased net CO₂ to the order of −0.5 t to 0.1 t CO₂/t steel. CCS showed a larger mitigation potential than bioenergy, but combined deployment was most effective. As BECCS use increased, CO₂ from background supply chains became more relevant. In the high BECCS cases, if decarbonized electricity is assumed, net CO₂ estimates decreased by 400−600 kg CO₂/t steel. Conversely, at 700 g CO₂/kWh, all cases appeared to be net CO₂-positive. Accounting for the “carbon debt” of biomass, beyond biomass supply chain emissions, increased net CO₂ estimates by approximately 300 kg CO₂eq/t steel. We conclude that CO₂-negative steel is possible, but will require significant interventions throughout the production chain, including sustainable biomass cultivation; efficient steel production; CO₂ capture throughout steel and bioenergy production; permanent storage of captured CO₂; and rigorous monitoring.

Negative emission technologies (NETs) have seen a recent surge of interest in both academic and popular media and have been hailed as both a saviour and false idol of global warming mitigation. Proponents hope NETs can prevent or reverse catastrophic climate change by permanently removing greenhouse gases from the atmosphere. But there is currently limited agreement on what "negative emissions" are. This paper highlights inconsistencies in negative emission accounting in recent NET literature, focusing on the influence of system boundary selection. A quantified step-by-step example provides a clear picture of the impact of system boundary choices on the estimated emissions of a NET system. Finally, this paper proposes a checklist of minimum qualifications that a NET system and its emission accounting should be able to satisfy to determine if it could result in negative emissions.

The impending restrictions on the sulfur content and greenhouse gas emissions of marine fuels represent a challenge for the maritime shipping industry and an opportunity for alternative fuels that may have lower environmental impacts but are not currently economically competitive. This study developed an integrated screening model to compare the technological, economic, and environmental performance of 33 “drop-in” marine biofuel blendstock supply chains, considering nine agroforestry residues and three thermochemical technologies. The biofuel production was modeled for 500 tonne per day “first-of-a-kind” biorefineries to reflect near-term production. Supply chains were modeled for biofuel production in both Brazil and Sweden to explore the impact of regional differences on the biofuels’ break-even prices and their life cycle emissions of greenhouse gases, SO₂, and NO_X. This study indicates that in the immediate term, marine biofuels from lignocellulosic feedstocks may have a minimum fuel selling price three or more times higher than current fossil marine fuel prices. Biofuels made from agricultural residues saw a 40–100 kg/GJ decrease in life cycle GHG emissions, but forestry residue emissions depended highly on biogenic carbon dioxide accounting. SO₂, and NO_X emissions were dominated primarily by combustion, which for SO₂ were estimated to be much lower than fossil fuels, due to the negligible sulfur content of the biomass. Overall, no single biofuel was a clear winner in terms of economic and environmental performance in the model, but space is opened for deeper research, as the new regulations come into effect.