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Graphical abstract Highlights • Comparing alternative fuels with potential for low-carbon intensities. • Technical process design and economic assessment of hydrogen and CO 2 -based fuels. • Environmental life-cycle assessment considering the full carbon cycle. • Identification of methodological challenges in carbon accounting of CO 2 -fuels. Abstract The deployment of low-emission alternative fuels is crucial to decarbonise the transport sector. A number of alternatives like hydrogen or dimethyl ether/methanol synthesised using CO 2 as feedstock for fuel production (hereafter refer to "CO 2 -based fuels") have been proposed to combat climate change. However, the decarbonisation potential of CO 2 -based fuels is under debate because CO 2 is re-emitted to the atmosphere when the fuel is combusted; and the majority of hydrogen still relies on fossil resources, which makes its prospects of being a low-carbon fuel dependent on its manufacturing process. First, this paper investigates the relative economic and environmental performance of hydrogen (produced from conventional steam methane reforming and produced via electrolysis using renewable energy), and CO 2 -based fuels (dimethyl ether and methanol), considering the full carbon cycle. The results reveal that hydrogen produced from steam methane reforming is the most economical option and that hydrogen produced via electrolysis using renewables has the best environmental profile. Whereas the idea of CO 2 -based fuels has recently gained much interest, it has for the foreseeable future rather limited practical relevance since there is no favourable combination of cost and environmental performance. This will only change in the long run and requires that CO 2 is of non-fossil origin, i.e. from biomass combustion or captured from air. Second, this paper address unresolved methodological issues in the assessment of CO 2 -based fuels, such as the possible allocation of emissions to the different sectors involved. The outcomes indicate that implementing different allocation approaches substantially influences the carbon footprint of CO 2 -based fuels. To avoid allocation issues, expanding the boundaries including the entire system and is therefore recommended. [ABSTRACT FROM AUTHOR]

Transformation of the energy sector’s power generation mix is needed to contain global mean temperature rise to no more than 2 °C above the pre-industrial level. Because the power sector is also a dominant direct and indirect consumer of water, it is vital to understand current and likely future trends in power sector water consumption. In this paper, we use an input-output based hybrid approach to study the direct and indirect impacts on water consumption from power mix adjustment in the world’s seven largest emitting economies under multiple cost-effective mitigation pathways toward the 2 °C target. Although different pathways exist, we discovered generally increases in water consumption of power sector under the long-term 2 °C target compared with no-climate-policy pathways, especially for China and India. Fulfilling the Intended National Determined Contributions (INDCs) could decouple direct water consumption and electricity output for most regions but may result in increases of indirect water consumption in China. This paper suggests that in the light of geographically uneven water scarcity, more comprehensive evaluation of both the direct and indirect water demands of the power sector is demanded when considering climate policies relevant to significant structural and technological adjustments in power sector. [ABSTRACT FROM AUTHOR]

Reducing local and global emissions is one of the drivers behind the promotion of renewable energy technologies (RETs). Some RET projects (e.g. solar, marine power, and some biomass and wind) usually require supplemental income from carbon credits in order to make them economically viable. This paper presents the mathematical development of nodal marginal CO 2 emission metrics for hydrothermal systems. These metrics are obtained from optimal power flow and hydrothermal dispatch models considering hydro uncertainty. The proposed model allows a more accurate assessment of the emission reduction effect of RET projects and the provision of efficient carbon signals to the system. Modeling of hydro reservoirs and intertemporal constraints also allows incorporating the emission mitigation potential of water storage. The concepts of marginal CO 2 emissions for hydrothermal systems are first exemplified using a small test system, and then simulations on a real hydrothermal system illustrate how these metrics can inform investment and operational decisions. Theoretical and simulation results show that transmission and hydro storage constraints neglect may provide wrong signals for RET investors, missing the incentives to install in areas where the potential for emissions reduction is higher (where renewable energy displaces a larger amount of coal or diesel). Policy makers can use the proposed model to assess the cost-effectiveness of emission reduction policies. [ABSTRACT FROM AUTHOR]

China’s commitment to the UNFCCC to peak its emissions by 2030, or sooner, signaled a long anticipated shift in China’s model of development with far reaching consequences. Cities in China, and particularly the residential sector in cities, will be charged with making significant reductions in emissions growth even as rates of urbanization continue to climb. Focusing on Beijing and Shanghai, this paper carries out a measures-based economic analysis of low carbon investment opportunities in the residential sector. Results find significant opportunity: between 2015 and 2030, BAU levels of CO 2 emissions could be reduced by 10.2% in Beijing and 6.8% in Shanghai with the adoption of economically attractive low carbon measures. While these headline results underline the case for low carbon investment in the residential sectors of these megacities in China, a closer analysis provides insights for understanding the economics of decarbonisation in cities more generally. [ABSTRACT FROM AUTHOR]

• This study learns energy systems for climate mitigation from a systematic review. • Heterogeneity of energy system research is summarized for the first time. • A novel hand-coding typology analysis for energy systems is proposed. The energy supply sector is the largest contributor to global greenhouse gas emissions. A good understanding of energy systems from existing research will provide multidimensional insights for appropriate actions against global warming. This study conducts a systematic review of the literature covering 1,184 articles on energy issues dealing with climate change mitigation. Using a novel hand-coding typology analysis, we characterize the body of knowledge and identify possible research gaps according to the heterogeneity of the energy process, time scale, geographic location, energy technology, and concerned end-use sector. We find that research interest mainly focuses on the energy supply (496 papers) and the end-use process (359 papers). Energy storage and the energy–water–land nexus are two emerging areas. Biomass, solar, wind, and nuclear energy are the technologies that attract the most attention, while interest in hydrogen energy production and waste-to-energy has grown very recently. The cost-benefit and mitigation potential of renewable generation are the most studied topics, followed by the impacts of climate change on electricity production. In contrast, little attention is paid to research on traditional oil and gas exploration. Regarding the end-use sector, residents and transport are the most evident sectors studied. China, the United States, and Europe are the most featured regions while very few studies focus on Africa, South America, and Small Island Developing States. Current research topics concentrate on how to maximize the co-benefit of greenhouse gas mitigation and eco-environment protection via cost-benefit reinventions of energy systems. Discussions of technological innovation are grounded in optimal technology portfolio deployment and cost reduction potential, along with financial and political incentives. [ABSTRACT FROM AUTHOR]

• Integrated analysis of climate change mitigation and adaptation in the power sector. • Climate change constraints are incorporated into simulations of a power system expansion. • The impacts of climate change on the electricity demand and supply are quantified. • WEAP and LEAP software tools are used. • Results indicate the nexus between climate change mitigation and adaptation. Reductions in carbon emissions have been a focus of the power sector. However, the sector itself is vulnerable to the impacts of global warming. Extreme weather events and gradual changes in climate variables can affect the reliability, cost, and environmental impacts of the energy supply. This paper analyzed the interplay between CO 2 mitigation attempts and adaptations to climate change in the power sector using the Long-range Energy Alternative Planning System (LEAP) model. This paper presented a novel methodology to integrate both CO 2 mitigation goals and the impacts of climate change into simulations of a power system expansion. The impacts on electricity supply and demand were quantified, based on historical climate-related impacts revealed during fieldwork and existing literature. The quantified effects, together with climate mitigation targets, were then integrated into the LEAP modeling architecture. The results showed a substantial alteration in technology composition and an increase in installed capacities driven by the joint climate mitigation–adaptation efforts when compared with the scenario without mitigation and adaptation (reference). Furthermore, an increase in CO 2 emissions was observed under the mitigation-adaptation scenario compared with the mitigation only scenario, indicating that the power sector's adaptations for climate change are likely to hinder CO 2 mitigation efforts. Therefore, a nexus between mitigation and adaptation should be exploited in the policy development for a low-carbon and climate-resilient power system. [ABSTRACT FROM AUTHOR]

Abstract: Carbon dioxide (CO2) emissions from motorised travel are hypothesised to be associated with individual, household, spatial and other environmental factors. Little robust evidence exists on who contributes most (and least) to travel CO2 and, in particular, the factors influencing commuting, business, shopping and social travel CO2. This paper examines whether and how demographic, socio-economic and other personal and environmental characteristics are associated with land-based passenger transport and associated CO2 emissions. Primary data were collected from 3474 adults using a newly developed survey instrument in the iConnect study in the UK. The participants reported their past-week travel activity and vehicle characteristics from which CO2 emissions were derived using an adapted travel emissions profiling method. Multivariable linear and logistic regression analyses were used to examine what characteristics predicted higher CO2 emissions. CO2 emissions from motorised travel were distributed highly unequally, with the top fifth of participants producing more than two fifth of emissions. Car travel dominated overall CO2 emissions, making up 90% of the total. The strongest independent predictors of CO2 emissions were owning at least one car, being in full-time employment and having a home-work distance of more than 10km. Income, education and tenure were also strong univariable predictors of CO2 emissions, but seemed to be further back on the causal pathway than having a car. Male gender, late-middle age, living in a rural area and having access to a bicycle also showed significant but weaker associations with emissions production. The findings may help inform the development of climate change mitigation policies for the transport sector. Targeting individuals and households with high car ownership, focussing on providing viable alternatives to commuting by car, and supporting planning and other policies that reduce commuting distances may provide an equitable and efficient approach to meeting carbon mitigation targets. [Copyright &y& Elsevier]