Why a Scialog on negative emissions science?

Ocean negative carbon emissions: A new UN Decade program

Limiting climate change to 2 °C with a high probability requires reducing cumulative emissions to about 1600 GtCO2 over the 2000–2100 period. This requires unprecedented rates of decarbonization even in the short-run. The availability of the option of net negative emissions, such as bio-energy with carbon capture and storage (BECCS) or reforestation/afforestation, allows to delay some of these emission reductions. In the paper, we assess the demand and potential for negative emissions in particular from BECCS. Both stylized calculations and model runs show that without the possibility of negative emissions, pathways meeting the 2 °C target with high probability need almost immediate emission reductions or simply become infeasible. The potential for negative emissions is uncertain. We show that negative emissions from BECCS are probably limited to around 0 to 10 GtCO2/year in 2050 and 0 to 20 GtCO2/year in 2100. Estimates on the potential of afforestation options are in the order of 0–4 GtCO2/year. Given the importance and the uncertainty concerning BECCS, we stress the importance of near-term assessments of its availability as today’s decisions has important consequences for climate change mitigation in the long run.

In this study, the economic and environmental feasibility of a process configuration based on the Bioenergy and Carbon Capture and Storage (BECCS) concept is assessed. The research analyses the production of jet fuel from forestry residues-derived syngas via the Fischer-Tropsch (FT) technology. Further, the CO2 removed in the syngas cleaning section is not released to the environment, instead it is permanently sequestrated. The produced Sustainable Aviation Fuel (SAF) has the potential to achieve negative emissions. The present research is a one-of-a-kind study for the jet fuel production within the BECCS concept. The process has been modelled within the Aspen Plus and Matlab software to obtain detailed and realistic mass and energy balances. Based on these balances, the technical, economic and environmental parameters have been calculated. Based on a plant that treats 20 dry-t/h of forest residues, 1.91 t/h of jet fuel are produced, while 11.26 t/h of CO2 are permanently stored. The inclusion of the CCS chain in the biorefinery increase the minimum jet fuel selling price from 3.03 £/kg to 3.27 £/kg. The LCA results for global warming show a favourable reduction in the BECCS case, in which negative emissions of −121.83 gCO2eq/MJ of jet fuel are achieved, while without CCS case exhibits GHG emissions equal to 15.51 gCO2eq/MJ; in both cases, the multi-functionality is faced with an energy allocation approach. It is, then, evident the significant environmental advantages of the BECCS process configuration. Nevertheless, financial feasibility can only be attained through the implementation of existing policy schemes and the formulation of new strategies that would reward negative emissions. The application of the UK’s policy “Renewable Transport Fuel Obligation” and a hypothetical scheme that rewards negative CO2 emissions, breaks-even the Minimum Jet fuel Selling Price (MJSP) at 1.49 £/kg for a certificate and carbon price of 0.20 £/certificate and 246.64 £/tonne of CO2.

Eco-engineering approaches for ocean negative carbon emission

There are three main global challenges faced in all fields, namely complexity, change and increasing problems. A monodisciplinary approach with a single technology approach is no longer relevant to face these conditions. Innovation, integration and sustainability are the keys to face these three challenges, especially towards zero carbon emission energy that is operational. To produce bioethanol as a zero carbon emission energy source, the problem is that a large amount of thermal energy is required and a lot of "waste" is produced in the production process. It also requires the right raw materials that do not compete with food. All of these problems with conventional approaches have not been able to produce production costs (HPP) that compete with other renewable energy sources, let alone with fossil energy. The proposed innovation is an integrative innovation that will produce bioethanol as energy that is not only zero emission but negative emission with low HHP. This can be achieved through integrative synergy of biochar production with appropriate technology researched so far that produces large surplus energy and sorghum farming as raw material. The biochar product produced as a co-product is a multi-functional product of high economic value. If part of the biochar is utilized in agriculture, it not only increases the yield of therapeutic agriculture as a stable carbon sequestration in the soil. Sweet sorghum is an agricultural crop that has high adaptation to natural conditions with high seed and biomass production. Sorghum is ideal as a feedstock for ethanol and food production. Integrating the three with the right innovation will produce bioethanol with negative carbon emissions and co-products with low COGS. Sorghum juice is used as a first generation feedstock (FGR) and its bagasse as a second generation source (SGR). This integration involves the utilization of juice extraction by expeller technique and pretreatment of a combination of mechanical, steam explosion and organosolv methods that do not produce hazardous waste. The entire process is designed with the concept of maximum closed loop and minimum input. The system is open for various other integrations and developments in the future to support the concept of green economy.

Understanding the climate and carbon cycle response to negative CO2 emissions is important for developing climate mitigation strategies that aim to limit global warming to a specific threshold. In this study, using a coupled climate and carbon cycle model, a novel set of nine stylized simulations are conducted with cumulative emissions of 1,000 GtC, 2,000 GtC, and 5,000 GtC over 150, 250, and 500 years, followed by identical cumulative negative emissions so that the net cumulative emissions are zero. On millennial‐timescales, the climate system returns close to the preindustrial state, independent of the emission and removal pathways. However, the thermal and biogeochemical inertia of the ocean play an important role in determining the climate and carbon cycle response during the emission and removal phases. When zero net emissions are reached, surface air temperature is larger by 0–1°C than the preindustrial state, and the atmospheric CO2 concentration is less by 12–29 ppm. These changes increase with both the magnitude and duration of the emission and removal pulses. In contrast, hysteresis in the relationship between global mean surface temperature and cumulative carbon emissions increases with the magnitude but decreases with the duration of emission and removal pulses. Our study highlights the role of ocean inertia in the asymmetry in climate response to emissions and removals and indicates that an earlier emission reduction implying emission/removal pathways with smaller magnitudes and shorter durations for the positive and negative emission pulses would avoid larger climate and carbon cycle impacts on centennial‐timescales.

Addressing climate change is a formidable challenge for humanity, and achieving the temperature control goals of the Paris Agreement cannot rely solely on greenhouse gas emission reductions—negative emissions are an inevitable solution. The ocean, as the planet’s largest active carbon reservoir, holds immense potential for negative emissions, yet there is no internationally recognized pathway to realize it. The UNESCO-IOC international program of Ocean Negative Carbon Emissions (ONCE) builds on the original theory of the microbial carbon pump (MCP) and integrates known ocean carbon sequestration mechanisms BCMS (standing for biological carbon pump, carbonate counter pump, MCP, solubility carbon pump) to propose feasible, scientifically sound, and legally compliant technical solutions. It establishes practical, reliable, and promising implementation pathways, forming a cohesive “theory–methodology–technical standards–application” framework. On this basis, the ONCE program proposes the “Triple REAL” visions, encompassing technical solutions (3R: realistic, reliable-ISO-certified, reproducible), implementation principles (3E: ecological, ethical, with equity), expected goals (3A: ambitious, actionable, achievable), and a governance framework (3L: legal, by London Protocol, with liability). This vision creates a systematic and actionable governance structure, develops a carbon credit foundational logic over the conventional “MRV principle” (monitoring, reporting, verification), and paves the way for incorporating ocean carbon credit into the global carbon market, supporting global climate governance.

The extraction efficiency of ion exchange resins aimed at the reprocessing of nuclear effluents is strongly dependent on gamma-ray induced modifications of their chemical structure. A poly(4-vinylpyridine) resin, or P4VP, has been subjected to gamma irradiation using a 137Cs source ( E γ = 662 keV) and we have attempted to characterize its structural modifications using TOF-SIMS techniques based on low (keV) and high (MeV) primary ion beam energies. These analytical techniques are based on the formation of fragments resulting respectively from atomic and electronic collisions of heavy ions. As a result, the differences in nature and relative intensity of the emitted secondary ions, as well as the variation of their intensity as a function of the absorbed dose of gamma rays (up to 14 400 kGy), can be interpreted from different types of bond breaking. While gamma-ray absorption results in benzylic or pyridinic scissions, MeV ion bombardment may induce simultaneous (and close) pyridinic-pyridinic or pyridinic-benzylic scissions, or both. Accordingly, the technique is very sensitive to the presence of fragments preformed under gamma irradiation. This is not observed with keV bombardment which may destroy the pyridine nucleus. The SIMS analysis of the soluble fraction of the irradiated material (free radicals and fragments) and of the remaining material confirms the proposed fragmentation paths leading to positive and negative ion emission. Such results fully support the important finding that these gamma-ray induced modifications are only observed from negative emission under MeV ion bombardment.

The Paris Agreement signalled global consensus to keep average temperature rise “well below” 2 °C by the end of the century. Results from integrated assessment models have made it increasingly evident that negative emissions (removing CO2 from the atmosphere) are crucial to achieving this. Consequently, negative emissions technologies (NETs) have come to the forefront of mitigation discussions. NETs must however overcome challenges if they are to be realised at scale. Uncertainties around the large-scale biomass supply have fuelled a debate on whether negative emissions from bio-energy with carbon capture and storage (BECCS) are sustainably achievable, if at all. Reliable carbon accounting frameworks and policy incentives are needed to improve investment prospects. The direct extraction of CO2 from air, or direct air capture (DAC), has since been demonstrated as a source of negative emissions. The large energy and economic costs associated with extracting CO2 from air are proving prohibitive to achieving commercial viability of DAC technology. Without dedicated policy support for technological innovation, and further interdisciplinary research to constrain a variety of uncertainties, the world risks foregoing a portfolio of technologies that add much-needed flexibility in the mitigation toolbox. This chapter details the evidence for negative emissions, proposed means of achieving them and their barriers to commercial effectiveness.

Negative emissions are a key mitigation measure in emission scenarios consistent with Paris agreement targets. The terrestrial biosphere is a carbon sink that regulates atmospheric carbon dioxide (CO2) concentration and climate, but its role under negative emissions is highly uncertain. Here, we investigate the reversibility of the terrestrial carbon cycle to idealized CO2 ramp-up and ramp-down forcing using an ensemble of CMIP6 Earth system models. We find a strong lag in the response of the terrestrial carbon cycle to CO2 forcing. The terrestrial biosphere retains more carbon after CO2 removal starts, even at equivalent CO2 levels. This lagged response is greatest at high latitudes due to long carbon residence time and enhanced vegetation productivity. However, in the pan-Arctic region, terrestrial carbon dynamics under negative emissions are highly dependent on permafrost processes. We suggest that irreversible carbon emissions may occur in permafrost even after achieving net-zero emissions, which offsets ~30% of enhanced land C retention and could hinder climate mitigation.

BECCS potential in Brazil: Achieving negative emissions in ethanol and electricity production based on sugar cane bagasse and other residues

Negative Emissions in the Waste-to-Energy Sector: An Overview of the Newest-CCUS Programme

The gigantic volumes of carbon dioxide (CO2) removal likely needed to comply with the Paris Agreement beg the question of who should pay for the negative emissions. Incentivizing negative emissions is difficult, as it entails reversing the fiscal attractiveness associated with carbon taxes and emissions trading in favour of the more unattractive need to pay for removals. The inherent difficulty of funding global public goods associated with large private costs will make it hard for future governments to share this burden among themselves. We propose that this problem can be solved by a CO2 emitter liability operationalized through Atmospheric CO2 Removal Deposits (ACORDs). Anyone that emits fossil CO2 to the atmosphere would be obliged to finance the removal of at least as much CO2 from the atmosphere. Linking the liability to ACORDs acknowledges that a major part of the negative emissions needs to be made in the future. The emitters' financial deposits, including earnings, can be redeemed upon certified proof of removal. The ACORDs system would comply with the widely accepted principle of producer liability, i.e., that companies are responsible for the damage caused by their products. The system would also provide additional incentives to reduce emissions and an innovative funding source for coming generations to accomplish negative emissions. Furthermore, inequity and historical emissions can be addressed by gradually increasing overcompensation. The paper also includes a critical assessment of the basis of negative emissions, i.e., the need, the technologies and their potentials, the costs, and the required retention time.

Perspectives of CO2 utilization as a negative emission technology

To limit global warming to <2 °C we must reduce the net amount of CO2 we release into the atmosphere, either by producing less CO2 (conventional mitigation) or by capturing more CO2 (negative emissions). Here, using state-of-the-art carbon-climate models, we quantify the trade-off between these two options in RCP2.6: an Intergovernmental Panel on Climate Change scenario likely to limit global warming below 2 °C. In our best-case illustrative assumption of conventional mitigation, negative emissions of 0.5-3 Gt C (gigatonnes of carbon) per year and storage capacity of 50-250 Gt C are required. In our worst case, those requirements are 7-11 Gt C per year and 1,000-1,600 Gt C, respectively. Because these figures have not been shown to be feasible, we conclude that development of negative emission technologies should be accelerated, but also that conventional mitigation must remain a substantial part of any climate policy aiming at the 2-°C target.