Scientific publications

Linking existing models to extend energy system and integrated assessment analysis is an increasingly common practice. Despite this, and unlike in the field of environmental and earth sciences, little attention has so far been paid to the details of it, to the trade-offs involved and the way in which the model linking affects the interpretation of the outcomes of the interlinked model system. Our aim in this paper is to first focus on a set of key technical and methodological problems that are common in model linking and suggest how these could be approached in different model linking contexts. We then further explore how model linking may affect the nature of the knowledge produced, and how this should be considered in the model linking process. Reflecting our literature driven assessment of the issues and possible solutions, we compile “a check list” to assist in the process of decision making for model linking.

Cities play a crucial role in implementing carbon reduction strategies and are essential administrative in this effort. A full-scope city CO2 emission inventory is important for designing effective emission control strategies and is thus crucial for achieving China’s carbon peaking and neutrality goals. However, recent research has focused on Scope 1 and Scope 2 emissions, with insufficient attention paid to Scope 3 emissions. In this study, we construct a methodological model for full-scope carbon emission accounting at the city level and establish a dataset that includes Scope 1, 2 and 3 emissions for Chinese cities in 2023. This dataset provides valuable data support for intercity comparisons and intracity management of city-wide carbon emissions. The total carbon emissions across Chinese cities in 2023 show significant quantitative and spatial differences. Notably, the emissions in the top 10 cities are almost 90 to 160 times higher than those in the bottom 10 cities. Cities with higher Scope 1 and 2 carbon emissions are predominantly located in the southeastern coastal areas, whereas cities with higher Scope 3 carbon emissions are concentrated in rapidly developing areas of central China.

Methane has been identified as the second-largest contributor to climate change, accounting for approximately 30% of global warming. Countries have established targets and are implementing various measures to curb methane emissions. However, our understanding of the trends in methane emissions and their drivers remains limited, particularly from a consumption perspective (i.e. accounting for all emissions along the entire global supply chain). This study investigates the most recent dynamics of methane emissions across 120 sectors from both production and consumption viewpoints in 164 countries. It also discusses the status of decoupling of production- and consumption-based methane emissions from economic growth. Our results indicate that there is no foreseeable slowdown in the momentum of global methane emissions growth. Only a few developed countries have managed to reduce both production- and consumption-based emissions while maintaining economic growth (i.e., strong decoupling) during the observed period (1990-2023). Global trade accounts for approximately 30% of global methane emissions, but major trade patterns are shifting from North-North and North-South to South-South countries, reflecting the increasing participating of developing countries in global supply chains. The study further reveals the changing drivers of global methane emissions from 1998 to 2023 in five-year intervals. It identifies that the reduction in emission coefficient (i.e., emissions per unit of output), driven by advancements in improved energy efficiency and cleaner production technologies, is the main determinant for reducing emissions over the observation period, partly offsetting the increasing effects from growth of final demand. Changes in demand structure have played a considerable role in the increase of emissions since 2008. This study enhances our understanding of the changes and drivers of methane emissions and supports countries in incorporating methane emissions into their climate mitigation strategies.

Climate change is reshaping global health burdens, but its financial impacts through increased household medical expenditures remain underexplored. This study integrated random forest techniques and 264,302 daily bank transaction data from 271 Chinese cities (2017–2019) to simulate household medical expenditure responses to climate change. To observe the heterogeneity among different cities, cities are categorized into 14 city groups based on their historical temperature and economic conditions to build simulation models. We further projected the future household medical expenditures in different cities under four Shared Socio-economic Pathways (SSPs), considering the pure effects of climate change and sensitivity changes under SSP-informed socioeconomic and physiological scenarios. We find that households in higher-income cities and cities with historically low temperatures have enhanced resilience to heat and cold, respectively. Climate change is projected to slightly decrease household medical expenses in China by 5.2% (SSP126) to 5.6% (SSP585) in 2060, attributed to fewer cold-related medical expenditures. Under the physiological scenarios, enhanced body system functions are projected to reduce medical expenditures by 19.5% (SSP245) to 27.6% (SSP585) by 2060. Rising incomes under socioeconomic scenarios may stimulate healthcare demand and drive expenditures up by 4.9% (SSP370) to 22.5% (SSP585). The findings highlight the importance of incorporating the moderating role of adaptation in devising tailored strategies to alleviate the household health-related economic strains induced by climate change.

As the world’s largest CO2 emitter, China needs accurate city-level CO2 emission accounts to formulate effective low-carbon policies. However, previous studies mainly accounted for emissions from fossil fuel combustion and overlooked process-related CO2 emissions from industrial production (e.g., mineral, chemical, metal products), which account for approximately 13% of China’s total emissions. In this study, we built the first time-series dataset of process-related CO2 emissions for 289 Chinese cities from 2000 to 2021. The dataset covers 11 industrial products and adheres to the methodology recommended by the Intergovernmental Panel on Climate Change (IPCC). We applied China-specific emission factors and compiled industrial output data from city statistical yearbooks and bulletins. Missing output data were imputed using missForest models. The estimated uncertainty of the process-related emissions in our dataset ranges from 3.87% to 3.91%. Our dataset provides a robust foundation for analyzing emission patterns at the city level and for designing targeted low-carbon policies.

Understanding the relationship between household expenditure and energy use from a consumption and supply chain perspective is crucial to capturing direct household energy use and indirect energy use linked to various consumption items—often overlooked by studies focusing solely on direct energy—and to revealing the underlying patterns of global energy inequality across households. This study assesses the energy footprints across 201 household expenditure groups, seven final-use energy types, and 65 consumption items in each of 116 countries using a global energy- and expenditure-extended multi-regional input-output model for 2017. The Gini index for global energy footprints is 0.59, indicating a high level of energy inequality: the top 1% of households in 116 countries account for 14% of energy footprints, while the bottom 50% consumed only 13%. Substantial energy inequality is revealed both between and within countries. Less developed countries and regions generally exhibit greater inequality in per capita energy footprints between households compared to developed countries and regions. Energy intensity declines with higher expenditure, remaining higher in poorer regions and households. In richer regions, energy intensity is more evenly distributed across expenditure groups and overall lower than in developing regions. Accurately measuring global household energy footprints can help understand current energy inequality and guide future poverty and inequality reduction to promote a more just and equitable global society.

Fluorocarbon banks present a substantial yet largely untapped opportunity for climate change mitigation within current regulatory frameworks. This potential can be effectively addressed through fluorocarbon lifecycle management (FLM), a strategy grounded in circular economy principles. This study quantifies the mitigation potential of FLM in China from 2025 to 2060, employing a tailored emission modeling framework and country-specific cost analysis. If unmitigated, these banked fluorocarbons could add 0.014 °C to global warming by midcentury. FLM, however, could prevent up to 8.0 Gt CO2-eq of cumulative emissions by 2060, with 93.2% attainable at costs below 10 USD/t CO2-eq─an additional mitigation exceeding 50% of the 13 Gt CO2-eq reductions pledged under the Kigali Amendment in China. Meanwhile, reclamation efforts could redirect up to 4108 kt of fluorocarbons for reuse or repurposing, conserving resources otherwise needed for virgin production. Our findings underscore FLM as a cost-effective approach to bridging the emission gap while advancing global sustainability.

This study conducts a scenario analysis of global net-zero emissions by 2050 using two macroeconomic models with distinct theoretical foundations: E3ME (non-equilibrium) and GEM-E3 (equilibrium). The analysis quantifies the economic impacts of increasing climate policy ambition to meet the global 1.5 °C warming target and highlights key differences between the models in projecting GDP, employment, and sectoral transitions. The findings indicate that while economic outcomes of decarbonization may vary depending on the model paradigm used, the uncertainties in climate damage projections far exceed those of mitigation costs. By comparing the economic impacts of mitigation with potential losses from climate damages, the study finds that the costs of mitigation are lower and more predictable than the potential climate damage costs. Limiting warming to 1.5 °C yields net economic gains in almost all countries examined, while a 3 °C trajectory could trigger widespread losses. The study reinforces the need for decisive and immediate global mitigation efforts.

Low-carbon lifestyles provide demand-side solutions to meet global climate targets, yet the global carbon-saving potential of consumer-led abatement actions remains insufficiently researched. Here, we quantify the greenhouse gas emissions reduction potential of 21 low-carbon expenditures using a global multi-regional input-output model linked with detailed household expenditure data. Targeting households exceeding the global per-capita average required to stay below 2 degrees, our model captures changes in direct energy use, household consumption and upstream intermediate industrial inputs. We find that implementing a combination of low-carbon expenditures among the top 23.7% emitters reduces global carbon footprints by 10.4 gigatons CO2e (i.e., 40.1% of the household consumption-based emissions of the 116 countries analysed in this study or 31.7% of the global total in 2017). Consumption pattern changes related to mobility and services contribute 11.8% and 10.2% of emission reductions. North America shows substantial reduction potential, while some Sub-Saharan African countries present unexpected mitigation possibilities. However, a rebound effect from re-spending income savings from lifestyle changes offsets the expected carbon savings by 6.5% to 45.8% (0.7–4.8 gigatons CO2e).

Formulating equitable climate policies should not overlook the challenges faced by less developed regions. African countries are at a crucial stage of economic development and deeper integration into global trade. Therefore, understanding their carbon footprints (i.e., consumption-based CO2 emissions) is essential for crafting a sustainable development pathway for Africa and developing comprehensive and fair climate policies. Here, we investigate consumption-based CO2 emissions in 55 African economics using a new Multi-Regional Input-Output model called “EMERGING” for 2015–2019; we also analyze the impacts of global trade participation on emissions, the decoupling status of emissions and economic, and hidden influencing factors. Results show that 65% of African countries experienced rapid growth in consumption-based emissions, with an average annual growth rate of 6.4%. Significantly, 87% of African countries are net emissions importers, predominantly attributed to their trade relations with other developing countries (i.e., South-South trade), a condition characterizing 68% of all trade interactions; The embodied carbon in imports is primarily concentrated in the transportation, petroleum refining, metal products, and machinery sectors. The decoupling analysis indicates that 15 countries strongly decoupled from production-based carbon emissions, and 14 from consumption-based; however, only 9 have concurrently achieved decoupling in both domains of emissions. Optimizing the carbon emission efficiency of final demand, particularly within the tertiary sector, is a key for successful decoupling and emissions reduction. The findings provide essential insights from consumption-based emissions that could guide more effective, targeted climate policies contributing to the mitigation of climate impacts and fostering sustainable development in African nations.

Cities are important actors in the global challenge of tackling climate change. They are not only responsible for the majority of emissions but also highly capable of taking action. An important precondition for effective climate mitigation is a city-level greenhouse gas emission inventory to guide mitigation action. Yet, most cities in developing countries, in particular African cities, lack that crucial information. This study aims to assess the current state of the development of African cities' emission inventories. A total of 270 inventories from 137 cities across 54 African countries were identified from 15 research articles, 5 reports, and 3 data platforms. We find the lack of standardized protocols results in inventories that are often not comparable, while data scarcity emerged as a common problem. We observe that insufficient engagement from local governments impedes the creation of a data-rich environment. Additionally, current inventory protocols do not fully address the data limitations faced by African cities, further hindering inventory development. To mitigate these challenges, multi-agent collaboration is essential to enhance the accounting capabilities of local governments. Developing refined protocols that consider data constraints is necessary. Moreover, advanced technologies may provide opportunities to overcome data bottlenecks.