Residual Emissions Research Articles

Long-term national climate strategies bet on forests and soils to reach net-zero

The deployment of carbon dioxide removal is essential to reach global and national net-zero emissions targets, but little attention has been paid to its practical deployment by countries. Here, we analyse how carbon dioxide removal methods are integrated into 41 of the 50 Long-term Low Emission Development Strategies submitted to the United Nations Framework Convention on Climate Change (UNFCCC), before 2022. We show that enhancing forest and soil carbon sinks are the most advocated strategies but are only explicitly quantified in 12. Residual emissions by 2050 are only quantified in 20 strategies and most of them use forests to achieve national net-zero targets. Strategies that quantify both residual emissions and carbon dioxide removal identify national constraints, such as wildfire risks to forests and limited geological CO2 storage capacity. These strategies also highlight the need for international cooperation. Taken together, we suggest that the UNFCCC should urgently strengthen its reporting requirements on long-term national climate strategies.

Towards True Climate Neutrality for Global Aviation: A Negative Emissions Fund for Airlines

What would it take for aviation to become climate-neutral by 2050? We develop and model a trajectory for aviation to reduce its CO2 emissions by 90% by 2050, down to a level where all residual emissions can be removed from the atmosphere without crowding out other sectors that also need negative emissions. To make emitters pay for the carbon removal, we propose and model a negative emissions fund for airlines (NEFA). We show that it can pay for the removal of all CO2 emitted by aviation from 2030 onwards, for a contribution to the fund of USD 200–250 per ton CO2 emitted. In our baseline simulation, USD 3.3 trillion is invested by the fund over 40 years in high-quality carbon removal projects designed for biodiversity and societal co-benefits. While we do propose a number of governance principles and concrete solutions, our main goal is to start a societal dialogue to ensure aviation becomes both responsible and broadly beneficial.

Scoping carbon dioxide removal options for Germany–What is their potential contribution to Net-Zero CO2?

In its latest assessment report the IPCC stresses the need for carbon dioxide removal (CDR) to counterbalance residual emissions to achieve net zero carbon dioxide or greenhouse gas emissions. There are currently a wide variety of CDR measures available. Their potential and feasibility, however, depends on context specific conditions, as among others biophysical site characteristics, or availability of infrastructure and resources. In our study, we selected 13 CDR concepts which we present in the form of exemplary CDR units described in dedicated fact sheets. They cover technical CO2 removal (two concepts of direct air carbon capture), hybrid solutions (six bioenergy with carbon capture technologies) and five options for natural sink enhancement. Our estimates for their CO2 removal potentials in 2050 range from 0.06 to 30 million tons of CO2, depending on the option. Ten of the 13 CDR concepts provide technical removal potentials higher than 1 million tons of CO2 per year. To better understand the potential contribution of analyzed CDR options to reaching net-zero CO2 emissions, we compare our results with the current CO2 emissions and potential residual CO2 emissions in 2050 in Germany. To complement the necessary information on technology-based and hybrid options, we also provide an overview on possible solutions for CO2 storage for Germany. Taking biophysical conditions and infrastructure into account, northern Germany seems a preferable area for deployment of many concepts. However, for their successful implementation further socio-economic analysis, clear regulations, and policy incentives are necessary.

Sector Coupling Potential of a District Heating Network by Consideration of Residual Load and CO2 Emissions

The growing share of fluctuating renewable electricity production within the German energy system causes the increasing necessity for flexible consumers, producers, and storage technologies to balance supply and demand. District heating networks with combined heat and power units, Power-to-Heat applications, and thermal energy storage capacities can serve as one of these flexible options. In this context, a simulation model of the district heating network of the rural community Dollnstein, Germany, was built. With the residual load of different regional areas (Germany, Bavaria, Eichstätt, Dollnstein) it is investigated, how the heat generators can operate in an electricity market beneficial way. Two different control algorithms were evaluated: Due to a correlation between the residual loads and the CO2 emissions of the electricity mix, the CO2 savings achieved by this control algorithm are determined. Another way to operate electricity market beneficial is to consider the current CO2 emissions of each region. The main outcomes of this paper are, that there is a high potential for sector coupling by shifting the operation times of a CHP and a heat pump according to the residual load. The electricity demand of the heat pump can be met in terms of low CO2 emissions of the electricity mix, while the CHP can replace electricity with high CO2 emissions. These results can be improved, by considering not the residual load but the current CO2 emissions in the control algorithm.

New possibilities for climate change countermeasures in ports: Organic carbon containment and creation of blue carbon ecosystems through beneficial utilization of dredged soil

As climate change has attracted increasing global attention, carbon neutral ports (CNPs) have been set as government policies in Japan. In this research, with the aim of providing a more reliable basis for policy making concerning ports, we proposed the carbon storage through stable containment of organic carbon present in dredged soil as a new climate change countermeasure in ports. Furthermore, it was revealed through scenario analysis that the containment effect through beneficial utilization of dredged soil as foundation materials for blue carbon ecosystems (BCEs) and carbon storage by BCEs have significant meanings for the realization of CNPs and sinks for the residual emissions, considering the necessity to promote dredging projects for the development of the next generation of import bases toward the realization of CNPs, which may result in the generation of a large amount of dredged soil. In a country like Japan, whose port policies and port governance make it difficult to actively promote climate change countermeasures by each port, the feasibility of these new countermeasures would depend on the government’s initiative. It would be a world-leading effort to focus on port development in addition to port operation, and utilizing the dredged soil and BCEs as carbon sinks.

Decarbonizing through nature

Offsetting residual emissions of greenhouse gases will be critical in our aims to limit global warming. Nature-based solutions (NbS) have been proposed as an opportunity to mitigate climate change while protecting and restoring the world’s natural capital. This Voices asks: what is the mitigation potential of NbS and the main needs for their succesful implementation? Offsetting residual emissions of greenhouse gases will be critical in our aims to limit global warming. Nature-based solutions (NbS) have been proposed as an opportunity to mitigate climate change while protecting and restoring the world’s natural capital. This Voices asks: what is the mitigation potential of NbS and the main needs for their succesful implementation?

Combined carbon and health taxes outperform single-purpose information or fiscal measures in designing sustainable food policies.

The food system is a major source of both environmental and health challenges. Yet, the extent to which policy-induced changes in the patterns of food demand address these challenges remains poorly understood. Using a survey-based, randomized controlled experiment with 5,912 respondents from the United Kingdom, we evaluate the potential effect of carbon and/or health taxes, information and combined tax and information strategies on food purchase patterns and the resulting impact on greenhouse gas emissions and dietary health. Our results show that while information on the carbon and/or health characteristics of food is relevant, the imposition of taxes exerts the most substantial effects on food purchasing decisions. Furthermore, while carbon or health taxes are best at separately targeting emissions or dietary health challenges, respectively, a combined carbon and health tax policy maximizes benefits in terms of both environmental and health outcomes. We show that such a combined policy could contribute to around one third of the reductions in residual emissions required to achieve the United Kingdom's 2050 net-zero commitments, while discouraging the purchase of especially unhealthy snacks, sugary drinks and alcohol and increasing the purchase of fruit and vegetables.

Differences in the Composition of the Rumen Microbiota of Finishing Beef Cattle Divergently Ranked for Residual Methane Emissions.

With the advent of high throughput technology, it is now feasible to study the complex relationship of the rumen microbiota with methanogenesis in large populations of ruminant livestock divergently ranked for enteric emissions. Recently, the residual methane emissions (RME) concept has been identified as the optimal phenotype for assessing the methanogenic potential of ruminant livestock due to the trait’s independence from animal productivity but strong correlation with daily methane emissions. However, there is currently a dearth of data available on the bacterial and archaeal microbial communities residing in the rumens of animals divergently ranked for RME. Therefore, the objective of this study was to investigate the relationship between the rumen microbiota and RME in a population of finishing beef cattle. Methane emissions were estimated from individual animals using the GreenFeed Emissions Monitoring system for 21 days over a mean feed intake measurement period of 91 days. Residual methane emissions were calculated for 282 crossbred finishing beef cattle, following which a ∼30% difference in all expressions of methane emissions was observed between high and low RME ranked animals. Rumen fluid samples were successfully obtained from 268 animals during the final week of the methane measurement period using a trans-oesophageal sampling device. Rumen microbial DNA was extracted and subjected to 16S rRNA amplicon sequencing. Animals ranked as low RME had the highest relative abundances (P < 0.05) of lactic-acid-producing bacteria (Intestinibaculum, Sharpea, and Olsenella) and Selenomonas, and the lowest (P < 0.05) proportions of Pseudobutyrivibrio, Butyrivibrio, and Mogibacterium. Within the rumen methanogen community, an increased abundance (P < 0.05) of the genus Methanosphaera and Methanobrevibacter RO clade was observed in low RME animals. The relative abundances of both Intestinibaculum and Olsenella were negatively correlated (P < 0.05) with RME and positively correlated with ruminal propionate. A similar relationship was observed for the abundance of Methanosphaera and the Methanobrevibacter RO clade. Findings from this study highlight the ruminal abundance of bacterial genera associated with the synthesis of propionate via the acrylate pathway, as well as the methanogens Methanosphaera and members of the Methanobrevibacter RO clade as potential microbial biomarkers of the methanogenic potential of beef cattle.

Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover

A landfill biocover system optimizes environmental conditions for biotic methane (CH4) consumption that controls the fugitive and residual emissions from landfills. Research shows that wasted compost material has more (CH4) oxidation potential than other materials. Thus, in this study, the authors investigate the engineering properties of compacted compost to test its suitability for CH4 oxidation capacity. Different laboratory and analytical approaches are employed to attain the set objectives. The biochemical tests show that the studied material indicates the presence of methanotrophs with sufficient organic contents. The compacted compost also shows adequate diffusivity potential to free air space for a wide range of water content. The data also imply that compacting compost to low hydraulic conductivity can be accomplished for a wide range of water content, according to the suggested values for a landfill hydraulic barrier. Furthermore, the low thermal properties of compost as compared to other mineral materials seem more beneficial, as specifically, during the winter season, when the atmospheric temperature is low, low thermal conductivity enables it to sustain a stable temperature for the activities of the microbial organisms, which therefore extends the CH4 oxidation process right through a long period in the winter.

A net-zero emissions energy system in India by 2050: An exploration

This study examines whether adequate opportunities exist for full decarbonisation of the Indian energy sector and highlights where enough choices for full decarbonisation by 2050 do not exist. The study suggests transformative levels of electrification, energy efficiency improvements, and a switch towards decarbonised fuels (largely green hydrogen, decarbonised electricity, and bioenergy) as the three mainstays of India’s decarbonisation strategy that could plausibly shift the energy sector towards a net-zero emissions future. The study also indicates that the heavy freight and industrial sectors face challenges in achieving full decarbonisation because of a lack of adequate technological solutions. Accordingly, residual emissions of about 1.3 gigatonnes in the system would require carbon sequestration options, including both technological and nature-based solutions, to achieve net-zero emissions. This study is expected to encourage further deliberations and deep dives into energy sub-sectors, which would benefit planners and policymakers in delineating India’s sustainable energy transition strategy.

GOBLIN version 1.0: a land balance model to identify national agriculture and land use pathways to climate neutrality via backcasting

Abstract. The Paris Agreement commits 197 countries to achieve climate stabilisation at a global average surface temperature less than 2 ∘C above pre-industrial times using nationally determined contributions (NDCs) to demonstrate progress. Numerous industrialised economies have targets to achieve territorial climate neutrality by 2050, primarily in the form of “net zero” greenhouse gas (GHG) emissions. However, particular uncertainty remains over the role of countries' agriculture, forestry, and other land use (AFOLU) sectors for reasons including the potential trade-offs between GHG mitigation and food security, a non-zero emission target for methane as a short-lived GHG, and the requirement for AFOLU to act as a net sink to offset residual emissions from other sectors. These issues are represented at a coarse level in integrated assessment models (IAMs) that indicate the role of AFOLU in global pathways towards climate stabilisation. However, there is an urgent need to determine appropriate AFOLU management strategies at a national level within NDCs. Here, we present a new model designed to evaluate detailed AFOLU scenarios at national scale using the example of Ireland, where approximately 40 % of national GHG emissions originate from AFOLU. GOBLIN (General Overview for a Backcasting approach of Livestock INtensification) is designed to run randomised scenarios of agricultural activities and land use combinations within biophysical constraints (e.g. available land area, livestock productivities, fertiliser-driven grass yields, and forest growth rates). Using AFOLU emission factors from national GHG inventory reporting, GOBLIN calculates annual GHG emissions out to the selected target year for each scenario (2050 in this case). The long-term dynamics of forestry are represented up to 2120 so that scenarios can also be evaluated against the Paris Agreement commitment to achieve a balance between emissions and removals over the second half of the 21st century. Filtering randomised scenarios according to compliance with specific biophysical definitions (GHG time series) of climate neutrality will provide scientific boundaries for appropriate long-term actions within NDCs. We outline the rationale and methodology behind the development of GOBLIN, with an emphasis on biophysical linkages across food production, GHG emissions, and carbon sinks at a national level. We then demonstrate how GOBLIN can be applied to evaluate different scenarios in relation to a few possible simple definitions of “climate neutrality”, discussing opportunities and limitations.

Role of hydrogen-based energy carriers as an alternative option to reduce residual emissions associated with mid-century decarbonization goals

Hydrogen-based energy carriers, including hydrogen, ammonia and synthetic hydrocarbons, are expected to help reduce residual carbon dioxide emissions in the context of the Paris Agreement goals, although their potential has not yet been fully clarified in light of their competitiveness and complementarity with other mitigation options such as electricity, biofuels and carbon capture and storage (CCS). This study aimed to explore the role of hydrogen in the global energy system under various mitigation scenarios and technology portfolios using a detailed energy system model that considers various energy technologies including the conversion and use of hydrogen-based energy carriers. The results indicate that the share of hydrogen-based energy carriers generally remains less than 5% of global final energy demand by 2050 in the 2 °C scenarios. Nevertheless, such carriers contribute to removal of residual emissions from the industry and transport sectors under specific conditions. Their share increases to 10–15% under stringent mitigation scenarios corresponding to 1.5 °C warming and scenarios without CCS. The transport sector is the largest consumer, accounting for half or more of hydrogen production, followed by the industry and power sectors. In addition to direct usage of hydrogen and ammonia, synthetic hydrocarbons converted from hydrogen and carbon captured from biomass or direct air capture are attractive transport fuels, growing to half of all hydrogen-based energy carriers. Upscaling of electrification and biofuels is another common cost-effective strategy, revealing the importance of holistic policy design rather than heavy reliance on hydrogen.

Why Residual Emissions Matter Right Now

Why Residual Emissions Matter Right Now

Scenarios for removing residual emissions in the context of the mid-century net-zero emission goals in Japan

本研究は，日本の2050年温室効果ガスネットゼロ排出目標について，先行研究で考慮されていた大気中からCO2を除去する技術による負の排出に加え，多様な方策を考慮したシナリオ分析を実施し，その実現性や対策・費用を評価した．国内対策シナリオとして，水素等の代替燃料拡大，エネルギー需要低減により，負の排出への依存を低減する可能性が示された．海外からの水素等の輸入，排出枠の購入による残存排出の相殺も選択肢となるが，これらはエネルギー・排出枠の輸入額の増加を伴い，2050年の輸入額は2010年を上回る水準となり得ることが明らかとなった．本研究はネットゼロ排出達成に向けた多様な道筋を明らかにした一方で，いずれのシナリオも技術，経済面での課題があり，今後の技術開発，国際制度の状況等を踏まえた継続的な戦略検討の必要性が示唆された．

Technology and material efficiency scenarios for net zero emissions in the UK steel sector

With the UK's legislation of a 2050 net zero emissions target, there is urgent need for radical industrial decarbonisation. The steel sector represented 12% of UK industrial emissions in 2016 and is therefore a critical target for mitigation. Mainstream scenario analyses variously assume use of unproven Carbon Capture and Storage (CCS) or reductions to steel demand in order to reach a 1.5 °C compatible budget by 2050. This analysis aims to: a) assess the mitigation potential of current technology options (excluding CCS) towards a cumulative budget aligned to net zero and assuming constant steel demand; b) to evaluate the potential of material efficiency to close any mitigation gaps, (where material efficiency is providing the same useful ‘service’ with less input of energy-intensive materials); and c) to discuss the importance of sectoral budget assumptions and other uncertainties in estimating the scale of future mitigation required by the industry and the policy implications of this. We modelled four key technology scenarios including steel plant retrofit, replacement of steelmaking technologies to best practice standards, fuel shifts to greater Electric Arc Furnace (EAF) production, and implementation of selected novel technologies, under different ambition levels. Technology scenarios could reduce cumulative Greenhouse Gas (GHG) emissions (2016–2050) by as much as 44% against a constant baseline, whilst coupled technology and material efficiency scenarios could achieve reductions of as much as 53%. We also find that whilst grid electricity decarbonisation and earlier demand reduction can achieve additional mitigation, there may still be a need for some CCS capacity in the long-term to address residual emissions. In the most ambitious case, absolute GHG emissions from the steel sector reduced by 80% by 2050 against 2016 levels, assuming grid decarbonisation. We found that the most effective interventions were through established technologies, such as retrofit, replacement and EAF production, since they were immediately available, with the condition they are implemented faster than previously observed. Given the commercialisation constraints of novel technologies, structural shifts such as material efficiency and EAF production were considered highly important. However, structural changes are necessarily more complex to influence via policy, and there is little precedent for structural change by design in the UK. Our results show that only complementary scenarios combining material efficiency and technology options would achieve a level of mitigation near to net zero in the UK. We conclude that it is possible to achieve net zero emissions in the UK steel sector, but that this would require greater and earlier levels of material efficiency and some degree of CCS removal capacity.

How to Reach the New Green Deal Targets: Analysing the Necessary Burden Sharing within the EU Using a Multi-Model Approach

The Green Deal of the European Union defines extremely ambitious climate targets for 2030 (−55% emissions compared to 1990) and 2050 (−100%), which go far beyond the current goals that the EU member states have agreed on thus far. The question of which sectors contribute how much has already been discussed, but is far from decided, while the question of which countries shoulder how much of the tightened reduction targets has hardly been discussed. We want to contribute significantly to answering these policy questions by analysing the necessary burden sharing within the EU from both an energy system and an overall macroeconomic perspective. For this purpose, we use the energy system model TIMES PanEU and the computational general equilibrium model NEWAGE. Our results show that excessively strong targets for the Emission Trading System (ETS) in 2030 are not system-optimal for achieving the 55% overall target, reductions should be made in such a way that an emissions budget ratio of 39 (ETS sector) to 61 (Non-ETS sector) results. Economically weaker regions would have to reduce their CO2 emissions until 2030 by up to 33% on top of the currently decided targets in the Effort Sharing Regulation, which leads to higher energy system costs as well as losses in gross domestic product (GDP). Depending on the policy scenario applied, GDP losses in the range of −0.79% and −1.95% relative to baseline can be found for single EU regions. In the long-term, an equally strict mitigation regime for all countries in 2050 is not optimal from a system perspective; total system costs would be higher by 1.5%. Instead, some countries should generate negative net emissions to compensate for non-mitigable residual emissions from other countries.

Cost and attainability of meeting stringent climate targets without overshoot

Global emissions scenarios play a critical role in the assessment of strategies to mitigate climate change. The current scenarios, however, are criticized because they feature strategies with pronounced overshoot of the global temperature goal, requiring a long-term repair phase to draw temperatures down again through net-negative emissions. Some impacts might not be reversible. Hence, we explore a new set of net-zero CO2 emissions scenarios with limited overshoot. We show that upfront investments are needed in the near term for limiting temperature overshoot but that these would bring long-term economic gains. Our study further identifies alternative configurations of net-zero CO2 emissions systems and the roles of different sectors and regions for balancing sources and sinks. Even without net-negative emissions, CO2 removal is important for accelerating near-term reductions and for providing an anthropogenic sink that can offset the residual emissions in sectors that are hard to abate.

A Superstructure Model for Integrated Deployment of Negative Emissions Technologies under Resource Constraints

Negative Emissions Technologies (NETs) will be needed in order to achieve the net zero emissions targets being set by many countries. These technologies will offset the residual greenhouse gas emissions of sectors that are inherently difficult to decarbonize. NETs draw down carbon through different physical, chemical, or biological pathways, and transfer it for storage to other environmental compartments. Examples of these techniques include afforestation, Biochar application, BioEnergy with Carbon Capture and Storage (BECCS), enhanced weathering, and Direct Air Capture (DAC). The large-scale deployment of NETs will be constrained by the footprints they apply to limited resources such as land, water, energy, and nutrients. In this work, a superstructure-based Linear Programming (LP) model is developed to optimize the carbon drawdown of integrated NET deployment under resource constraints. Results show that varying the target negative emissions and resource constraints affect the NETs portfolio and total cost.

Will blue hydrogen lock us into fossil fuels forever?

Will blue hydrogen lock us into fossil fuels forever?

Energy systems in scenarios at net-zero CO2 emissions

Achieving net-zero CO2 emissions has become the explicitgoal of many climate-energy policies around the world. Although many studies have assessed net-zero emissions pathways, the common features and tradeoffs of energy systems across global scenarios at the point of net-zero CO2 emissions have not yet been evaluated. Here, we examine the energy systems of 177 net-zero scenarios and discuss their long-term technological and regional characteristics in the context of current energy policies. We find that, on average, renewable energy sources account for 60% of primary energy at net-zero (compared to ∼14% today), with slightly less than half of that renewable energy derived from biomass. Meanwhile, electricity makes up approximately half of final energy consumed (compared to ∼20% today), highlighting the extent to which solid, liquid, and gaseous fuels remain prevalent in the scenarios even when emissions reach net-zero. Finally, residual emissions and offsetting negative emissions are not evenly distributed across world regions, which may have important implications for negotiations on burden-sharing, human development, and equity.