Cities, particularly in low- and middle-income countries, host the industries that supply steel, glass, cement, and electricity—sectors among the largest contributors to greenhouse gas emissions. These hard-to-abate sectors have historically lagged behind in climate action, resulting in uneven progress in keeping cities green. Nevertheless, an in-depth understanding of city-driven, industry-led pathways for deep decarbonization that are central to human well-being remains lacking. This study takes a fresh look at the city-industry-climate nexus by developing an internally-consistent, city-level integrated assessment framework that explores pathways to break urban hard-to-abate bottlenecks. This framework incorporating technological solutions and shared socioeconomic pathways provides analysis capabilities at finer levels of technology and spatial resolution than previously available. Scenario-based modeling of over ninety detailed industrial processes indicates an early peak in demand-driven manufacturing emissions from iron and steel, cement, and glass in the mid-2020s, whereas coal-intensive power generation shows pathway-dependent variations. Mapping hard-to-abate emission dynamics onto cities reveals marked spatial heterogeneity in decarbonization trajectories, driven by location-specific industrial and resource profiles. Cost-optimized efficiency interventions deliver the majority of near-term reductions, while scaling up carbon capture, utilization, and storage contributes an additional 21% of abatement. Yet, long-lived infrastructural lock-ins delay progress in heavy-industry cities while coal-to-clean transitions and scrap recycling support earlier net-zero outcomes in industrial transfer hubs. These findings highlight the need to engage cities in addressing hard-to-abate emissions through integrated urban–industrial–decarbonization strategies that move beyond top-down mitigation and achieve tangible and equitable benefits by better bridging long-term climate objectives with on-the-ground delivery.

The building sector in China is responsible for 40% of total energy-related CO2 emissions, driven by its large population, continuous economic growth, and construction boom. In addition to greenhouse gas (GHG) emissions from energy use, buildings drive significant emissions for construction activities and production of energy-intensive materials, such as steel and cement. While supply-side energy strategies have been extensively explored, a demand-side perspective that considers stock dynamics and circularity improvements is essential to assess sustainable pathways for the buildings sector. Here, we explore a set of decarbonization scenarios for the building sector in China considering a range of circular strategies and their interplay with different climate policies. The strategies include lifetime extension of buildings, switch to wood-based construction, reduction of per-capita floorspace, and a combination of all three strategies. We use the building sector model MESSAGEix-Buildings soft linked to the integrated assessment model (IAM) MESSAGEix-GLOBIOM and prospective life cycle assessment (LCA) to assess the effects of these circular strategies on building material and energy demands, and operational and embodied emissions. We find that the three strategies could reduce building material demand up to 60% on mass basis by 2060 compared to a reference scenario with continuation of current policies. This translates into a reduction of embodied and total GHG emissions of 62% and 24%, respectively, significantly contributing to achieving decarbonization targets. Integrating industrial ecology methods in IAMs, as demonstrated in this study, can provide valuable insights to inform national policy decisions on mitigation strategies accounting for both demand and supply sides.

The chances of a global hydrogen economy becoming a reality have increased significantly since the COVID pandemic and the war in Ukraine, and for net zero carbon emissions. However, intercontinental hydrogen transport is still a major issue. This study suggests transporting hydrogen as a gas at atmospheric pressure in balloons using the natural flow of wind to carry the balloon to its destination. We investigate the average wind speeds, atmospheric pressure, and temperature at different altitudes for this purpose. The ideal altitudes to transport hydrogen with balloons are 10 km or lower, and hydrogen pressures in the balloon vary from 0.25 to 1 bar. Transporting hydrogen from North America to Europe at a maximum 4 km altitude would take around 4.8 days on average. Hydrogen balloon transportation cost is estimated at 0.08 USD/kg of hydrogen, which is around 12 times smaller than the cost of transporting liquified hydrogen from the USA to Europe. Due to its reduced energy consumption and capital cost, in some locations, hydrogen balloon transportation might be a viable option for shipping hydrogen compared to liquefied hydrogen and other transport technologies.

The world is warming, and the demand for cooling is increasing. Developing a future green hydrogen economy will also increase the demand for cooling for hydrogen liquefaction. This increase in cooling demand will happen mainly in tropical and developing countries due to their increase in population, improvements in quality of life, and the export of their renewable potential with liquid hydrogen. To solve this increase in demand for cooling, this paper proposes the use of ammonia airship cooling (AAC). AAC extracts cold from the tropopause (−80 °C) with airships and ammonia refrigeration cycles. The liquid ammonia is then transported back to the surface to provide low temperature cooling services (−33 °C). This cooling service is particularly interesting for lowering the electricity consumption in hydrogen liquefaction plants. If all the technological challenges mentioned in the paper are addressed, it is estimated that the cost of cooling with the technology is 8.25 USD/MWht and that AAC could reduce the electricity demand for hydrogen liquefaction by 30%. AAC is an innovative renewable cooling technology that has the potential to complement other renewable energy sources in a sustainable future.

The global shift toward a sustainable and eco-friendly energy landscape necessitates the adoption of long-term, high-capacity energy storage solutions. This research introduces an inventive energy storage concept involving the movement of granular materials from a lower elevation to a higher point within natural terrains such as mountains or excavated mining sites. Electrical energy is employed to charge electric batteries that elevate the granular material, thereby storing potential energy. Subsequently, this material is transported down during the electricity generation phase, and the regenerative braking mechanism converts the gravitational energy to replenish the vehicle's battery. The stored energy within these vehicles is then dispatched during peak demand periods or utilized by the vehicles for other freight transportation purposes. Our findings demonstrate a power cost of 1200 USD/kW, an energy storage expense spanning from 1 to 10 USD/kWh, a levelized cost of storage ranging from 35 to 200 USD/MWh, and a global annual potential of approximately 5.4 PWh. Electric vehicle gravity energy storage showcases its capability to bolster sustainable development by offering seasonal and multi-year energy storage services.

Deliberately removing carbon dioxide from the atmosphere is an important element of bringing mitigation pathways in line with the climate goals of the Paris Agreement. To reach global net-zero CO2 emissions and limit global warming to 1.5 degrees C with no or limited overshoot, global mitigation pathways assessed by IPCC's Sixth Assessment Report require some world regions to achieve net-negative CO2 emissions with large-scale carbon dioxide removal (CDR) deployment. This raises important questions about the availability and feasibility of CDR deployment in different societal and political contexts.This paper therefore combines an analysis of CDR deployment in a sample of scenarios from the IPCC AR6 database with a bottom-up analysis of the state of CDR governance and policy in countries considered key in scaling up CDR capacity and not yet covered by existing research. In particular, the paper focuses on Brazil, China, and India as important emerging economies and large emitters. We highlight the expected use of CDR methods in those regions in scenarios and systematically assess and compare the level of CDR regulation and innovation across these countries. This comparative perspective has the potential to broaden the understanding of existing and emerging CDR policies and politics.The synthesis of the case studies provides three key contributions to existing literature: First, we explore the state of CDR governance and policymaking in key emerging economies. As in OECD countries, there is a notable lack of CDR regulation and innovation to enable the scale of CDR required in the short- and medium term. Second, we identify that repurposing policies is a key type of emerging CDR policymaking in these countries targeting CDR methods in the land use, land use change and forestry (LULUCF) sector. We find that the repurposing efforts strengthen the level of regulation and innovation for this group of methods. Third, we explore three building blocks (regional differentiation, delay of upscaling, sustainability thresholds) of plausible CDR deployment narratives that could help bridge integrated assessment models and comparative case studies in future research. As in OECD countries, there is a notable lack of CDR regulation and innovation to enable CDR scale-up in Brazil, China, and India, questioning the political feasibility of existing scenarios.CDR policy is not starting from scratch, existing policy instruments - especially in the LULUCF sector - can be repurposed to strengthen the level of CDR regulation and innovation.While policies and regulations for CCS-based CDR are lacking in China, Brazil and India, the level of regulation for LULUCF-based CDR is higher.Comparative case studies can inform emerging CDR policy and governance at national and international levels, as well as exogenous CDR deployment narratives for future integrated assessment modelling.

Mass gatherings provide conditions for the transmission of infectious diseases and pose complex challenges to public health. Faced with the COVID-19 pandemic, governments and health experts called for suspension of gatherings in order to reduce social contact via which virus is transmitted. However, few studies have investigated the contribution of mass gatherings to COVID-19 transmission in local communities. In Hong Kong, the coincidence of the relaxation of group gathering restrictions with demonstrations against the National Security Law in mid-2020 raised concerns about the safety of mass gatherings under the pandemic. Therefore, this study examines the impacts of mass gatherings on the local transmission of COVID-19 and evaluates the importance of social distancing policies. With an aggregated dataset of epidemiological, city-level meteorological and socioeconomic data, a Synthetic Control Method (SCM) is used for constructing a ‘synthetic Hong Kong’ from over 200 Chinese cities. This counterfactual control unit is used to simulate COVID-19 infection patterns (i.e., the number of total cases and daily new cases) in the absence of mass gatherings. Comparing the hypothetical trends and the actual ones, our results indicate that the infection rate observed in Hong Kong is substantially higher than that in the counterfactual control unit (2.63% vs. 0.07%). As estimated, mass gatherings increased the number of new infections by 62 cases (or 87.58% of total new cases) over the 10–day period and by 737 cases (or 97.23%) over the 30-day period. These findings suggest the necessity of tightening social distancing policies, especially the prohibition on group gathering regulation (POGGR), to prevent and control COVID-19 outbreaks.

Among the sufficiency, efficiency, and renewable frameworks for reducing energy use and energy-related carbon emissions, Building Energy Sufficiency (BES) is gaining attention from policy makers and engineers. Despite the significant role of the building sector in the success of national energy and climate plans, there is a lack of research on the drivers, technologies, and effective policy instruments required to achieve BES in the building operational phase. To fill this gap, this study presents a systematic review of the definition and paradigm of BES and concludes that BES should address both occupant demand and energy or emissions requirements simulta-neously. The characteristics of occupant demand in building services are divided into four dimensions: time and space, quality and quantity, control and adjustment, and flexibility. Technical options regarding the building architecture, the envelope system, and the building energy system are reviewed. Finally, policy implications and recommendations are discussed. The multiple benefits and multidisciplinary nature of BES justify further research and accelerated policy implementation in developed and developing countries.

A rapid global energy transition, including the ramping up of electricity generation from renewables, is needed to limit global warming to 2 °C or 1.5 °C. However, renewable resource endowments vary widely between regions, and renewable electricity is currently mainly used locally. Here we use a global integrated assessment model to explore the implications of renewable electricity trade via a set of planned direct-current-type ultra-high-voltage (UHVDC) transmission lines for global energy transition and climate change. We find that renewable electricity trade across large world regions via the underlying UHVDC interconnection can boost renewable electricity production and reduce 2020–2100 cumulative CO2 emissions from the power sector up to 9.8%. Financial investments in the UHVDC lines are offset in the long term by reduced investments in other electricity-generation options, including nuclear and storage. Finally, we find that renewable electricity trade can substantially reduce air pollutant emissions in importing regions. Projects are under way for direct-current ultra-high-voltage transmission lines that would allow trading of renewable electricity across world regions. Guo et al. use integrated assessment models to explore different scenarios for the operation of these projects and assess their potential for decarbonization.

Facing significant carbon emissions annually, China requires a clear decarbonization strategy to meet its climate targets. This study presents a MESSAGEix-CAEP model to explore Chinese decarbonization pathways and their cost-benefit under two mitigation scenarios by establishing connections between five energy-intensive sectors based on energy and material flows. The results indicated the following: 1) Interaction and feedback between sectors should not be disregarded. The electrification process of the other four sectors was projected to increase electricity production by 206%, resulting in a higher power demand than current forecasts. 2) The marginal abatement cost to achieve carbon neutrality across all five sectors was 2189 CNY/tCO2, notably higher than current Chinese carbon emission trading prices. 3) The cost-benefit analysis indicates that a more ambitious abatement strategy would decrease the marginal abatement cost and result in a higher net carbon abatement benefit. The cumulative net benefit of carbon reduction was 7.8 trillion CNY under ambitious mitigation scenario, 1.3 trillion CNY higher than that under current Chinese mitigation scenario. These findings suggest that policy-makers should focus on the interaction effects of decarbonization pathways between sectors and strengthen their decarbonization efforts to motivate early carbon reduction.

Embodied carbon emissions of the building sector constitute the majority of carbon emissions. The selection of a building stock development pathway, construction mode, and synergy between the building construction and industry sectors will greatly influence the future embodied carbon emissions in China's building sector. The main purpose of this study is to analyze the carbon emission related to China's building construction under different path choices, to provide quantitative support for policy makers, helping to realize low-carbon development in China's construction sector. So, we developed the China Building Construction Model to illustrate the relationship between building stock, material stock, and embodied carbon emissions. The results show that controlling the total building stock at a reasonable level, extending the building lifetime by avoiding the buildings' early demolition, and encouraging building retrofitting can significantly reduce the material demand of construction as well as the carbon intensity of the production of building materials. Over 70% of the reduction in carbon emissions can be realized through these measures by 2060. Moreover, low carbon development depends on recycling and increased efficiency in producing building materials; this way, embodied carbon emissions can be reduced by nearly 50% by 2060.

The increasing energy and material consumption associated with global economic growth has resulted in the need for more severe efforts at mitigating global climate change. The iron and steel industry consumes 8% of energy and emits 7% of total CO2 globally. China's iron and steel industry contributes to 15% of that country's total CO2 emissions. Therefore, there is an urgent need to explore the possibility of net zero emissions in the iron and steel industry in China to meet China's goal of carbon neutrality before 2060. In the study presented in this paper, the MESSAGEix–China iron and steel model was developed by integrating the process-based technology of the sector into the IIASA's MESSAGEix framework to explore zero CO2 emission pathways and their associated impacts on resources, energy, and water in China's iron and steel industry up to 2100. We found that there are multiple pathways to achieving zero CO2 emissions in the Chinese iron and steel industry by the end of the 21st century. More specifically, in all the pathways developed in this study, CO2 emissions decreased significantly between 2030 and 2060 due to the rapid application of 100% scrap-based Electric Arc Furnaces (EAFs) and hydrogen-based Direct Reduced Iron (DRI)-EAFs steel-making technologies. However, by 2060, there will still be 70–360 Mt of CO2 emissions from China's iron and steel industry; consequently, carbon sink or negative emission technologies are required to offset this and achieve the country's carbon neutrality goal. Furthermore, technologies for achieving zero emissions differ widely in terms of their impacts on the consumption of materials and energy. Compared to the electric (ELE) scenarios, 25–40% of extra iron ore is consumed in the current and new national policy (NPS) scenarios and the DRI scenarios, but 25–220% of scrap is required. At the same time, 20–150% more energy will be saved in the ELE scenarios than in the NPS and DRI scenarios. Finally, we recommend that policy makers design a cross-cutting strategy to achieve zero CO2 emissions and enhance efforts for material recycling and the provision of clean energy and water.

To realize China's low-carbon development, coal needs to be produced and consumed in a clean and efficient way. In this paper, a multi-regional coal supply model is developed to gain insights into China's coal supply system up to 2050. Regional disparity, coal classification, and the development of clean coal technologies are specified in the model. Based on MESSAGEix, this model takes full consideration of coal mining, preparation, transformation, and transportation processes. Moreover, the effects of non-fossil energy development and carbon price are discussed. With the above framework, the future of China's coal supply system is optimized. Results indicate that: 1) China's national raw coal production will peak in 2030 under the business -as-usual scenario, while it has already peaked under the GREEN and carbon price scenarios, 2) The amount of coal used in final consumption and transformed into coke decreases, while coal transformed into liquids and SNG increases from 11 Mt in 2015 to 221 Mt in 2050 under the business -as-usual scenario, 3) both non-fossil fuel development and carbon price strategies have a positive effect on coal supply regulation and coal-related GHG emission reduction, 4) carbon price could facilitate the adoption of CCS technology and can effectively reduce coal-related GHG emissions. (c) 2020 Elsevier Ltd. All rights reserved.

Population Grid for China under SSP3RCP8.5 from 2010 to 2100

The industrial sector dominates the global energy consumption and carbon emissions in end use sectors, and it faces challenges in emission reductions to reach the Paris Agreement goals. This paper analyzes and quantifies the relationship between industrialization, energy systems, and carbon emissions. Firstly, it forecasts the global and regional industrialization trends under Representative Concentration Pathway (RCP) and Shared Socioeconomic Pathway2 (SSP2) scenarios. Then, it projects the global and regional energy consumption that aligns with the industrialization trend, and optimizes the global energy supply system using the Model for Energy Supply Strategy Alternatives and their General Environmental Impact (MESSAGE) model for the industrial sector. Moreover, it develops an expanded Kaya identity to comprehensively investigate the drivers of industrial carbon emissions. In addition, it employs a Logarithmic Mean Divisia Index (LMDI) approach to track the historical contributions of various drivers of carbon emissions, as well as predictions into the future. This paper finds that economic development and population growth are the two largest drivers for historical industrial CO2 emissions, and that carbon intensity and industry energy intensity are the top two drivers for the decrease of future industrial CO2 emissions. Finally, it proposes three modes, i.e., clean supply, electrification, and energy efficiency for industrial emission reduction.

In order to quantify the contribution of the mitigation strategies, an extended Kaya identity has been proposed in this paper for decomposing the various factors that influence the CO2 emission. To this end, we provided a detailed decomposition of the carbon intensity and energy intensity, which enables the quantification of clean energy development and electrification. The logarithmic mean divisia index (LMDI) has been applied to the historical data to quantify the contributions of the various factors affecting the CO2 emissions. Further, the global energy interconnection (GEI) scenario has been introduced for providing a systematic solution to meet the 2°C goal of the Paris Agreement. By combining LMDI with the scenario analysis, the mitigation potential of the various factors for CO2 emission has been analyzed. Results from the historical data indicate that economic development and population growth contribute the most to the increase in CO2 emissions, whereas improvement in the power generation efficiency predominantly helps in emission reduction. A numerical analysis, performed for obtaining the projected future carbon emissions, suggests that clean energy development and electrification are the top two factors that can decrease CO2 emissions, thus showing their great potential for mitigation in the future. Moreover, the carbon capture and storage technology serves as an important supplementary mitigation method.

The quantitative functions for climate damages provide theoretical ground for the cost-benefit analysis in climate change economics, and they are also critical for linking climate module with economic module in the Integrated Assessment Models (IAMs). Nevertheless, it is necessary for IAMs to update sectoral climate impacts in order to catch up the advance in climate change studies. This study updates the sectoral climate damage function at global scale from climate Framework for Uncertainty, Negotiation and Distribution (FUND) model and develops the aggregate climate damage function in a bottom-up fashion. Besides conventional sectors such as agriculture, forestry, water resources, energy consumption and ecosystems, this study expands climate disaster types, assesses human health impacts caused by various air pollutants, and updates coastal damage by sea level rise. The Beijing Climate Center Simple Earth System Model (BCC_SESM) is used to project climate system based on Business-as-Usual (BAU) scenario, and the 2 °C and 1.5 °C scenarios based on RCPs and SSP2 databases. Sectoral results show that the agricultural sector is projected to suffer 63% of the total damage, followed by water resources (16%) and human health (12%) sectors in 2100. The regression results indicate that the aggregate climate damage function is in positive quadratic form for zero discounting. Under BAU scenario, the aggregate climate damage is projected to be 517.7 trillion USD during 2011–2100. Compared to that, the 2 °C and 1.5 °C scenarios are projected to respectively reduce climate damages by 215.6 trillion USD (approximately 41.6%) and 263.5 trillion USD (50.9%) in 2011–2100.

Buildings play a dominant role in global efforts towards energy consumption reduction, greenhouse gas (GHG) emission mitigation, as well as global clean energy transition. Building Energy Policies (BEP) improved globally and quickly with a growing number of building codes implemented over the past decade. Occupant Behavior (OB) has significant impacts on building energy performance and occupant comfort, despite often being not well understood and oversimplified in BEPs. This paper highlighted the research needs of properly integrating OB in building energy polices by presenting a literature review to identify the key questions and challenges related to building technical standards and regulations, building information policies, building energy incentives, and policy evaluations and way forward. Challenges and opportunities of OB in BEP are also discussed with respect to technical innovation and digitalization, as well as concerns related to energy efficiency and fairness. There has been growing interests, research and applications in this field, but significant challenges and opportunities still lie ahead.

Exploring potential future pathways for developing Asia's energy consumption, CO2 emissions and infrastructure investment needs is essential to understanding how the countries of this rapidly growing region may contribute to the global climate targets set out in the 2015 Paris Agreement. To this end, this study employs the state-of-the-art global integrated assessment model MESSAGEix-GLOBIOM to investigate mid-century decarbonization strategies for developing Asia to 2050. Our results indicate that a radical change in the energy portfolio is required to reach the target of 'well below' 2 degrees C. Specifically, our scenarios point to a rapid reduction of fossil fuel utilization, enhancement of low-carbon energy supply, and boosting of energy efficiency efforts. Such a transformation leads to a deep cut in CO2 emissions by 78% and 93% by 2050 in scenarios consistent with the 2 degrees C and 1.5 degrees C targets, respectively. Electricity generation and final energy consumption become dominated by low-carbon energy by 2050 in these scenarios. In terms of investment needs beyond a baseline scenario, the 2 degrees C and 1.5 degrees C pathways imply that the scale of low-carbon investment may need to double and triple, respectively. These increases would be partially offset by disinvestment in coal, oil and natural gas extraction and conversion infrastructure. Decarbonizing the energy system also impacts the capital needed for making progress on other sustainable development goals (SDGs), such as air pollution, clean water and food security. Key policy insights Governments will need to employ a variety of policy mechanisms, including mandates and subsidies for renewables and electric vehicles, efficiency standards for end-use technologies, and bans on free-emitting fossil fuel plants, among others. Relative to the baseline scenario for developing Asia, the scale of investment into low-carbon energy to 2050 may need to double for a 2 degrees C scenario, and to triple for 1.5 degrees C. Policy instruments such as green finance are essential for this region to mobilize a broadened channel of investment, particularly from the private sector. Low-carbon investment would significantly reduce the capital investment needed to achieve the SDG target for air quality, but increase the requirements for meeting targets on clean water and food security, though only to a small extent.

The development of electric vehicles can help reduce the use of fossil fuels and further mitigate greenhouse gas (GHG) emissions. A comprehensive method is proposed for estimating the GHG mitigation potential of passenger battery electric vehicles (PBEVs) continentally and globally, considering the electricity consumption, energy transition, and other main influencing factors. The future energy transition is considered to change the electricity generation structures, improve the share of clean power, and further increase the GHG mitigation potential of electric vehicles based on a life-cycle analysis. An uncertainty analysis is performed to investigate the main influencing factors, such as energy intensity, battery size, autonomous vehicles, charging infrastructure, carpooling and ridesharing, and the development of other competitive vehicles on the electricity consumption and mitigation potential. Results show that the global stock of PBEVs will reach 1.2 x 10(8) and 1.0 x 10(9) vehicles in 2030 and 2050, respectively, and the global electricity consumption will be 250-480 TWh in 2030 and 1140-2840 TWh in 2050, equivalent of saving 3.4-6.5 x 10(8) barrel of gasoline in 2030 and 1.6-3.9 x 10(9) barrel of gasoline in 2050. The calculated global GHG mitigation potentials of PBEVs are 40-215 Mt CO(2)e and 340-1380 Mt CO(2)e in 2030 and 2050, respectively, which will accelerate the decarbonization transition in the transport sector and help achieve the global temperature control goals in the Paris Agreement and sustainable development goals. (C) 2020 Elsevier Ltd. All rights reserved.