Tracing fossil-based plastics, chemicals and fertilizers production in China.

Phasing down fossil fuels is crucial for climate mitigation. Even though 80-90% of fossil fuels are used to provide energy, their use as feedstock to produce plastics, fertilizers, and chemicals, is associated with substantial CO2 emissions. However, our understanding of hard-to-abate chemical production remains limited. Here we developed a chemical process-based material flow model to investigate the non-energy use of fossil fuels and CO2 emissions in China. Results show in 2017, the chemical industry used 0.18 Gt of coal, 88.8 Mt of crude oil, and 12.9 Mt of natural gas as feedstock, constituting 5%, 15%, and 7% of China's respective total use. Coal-fed production of methanol, ammonia, and PVCs contributes to 0.27 Gt CO2 emissions ( ~ 3% of China's emissions). As China seeks to balance high CO2 emissions of coal-fed production with import dependence on oil and gas, improving energy efficiency and coupling green hydrogen emerges as attractive alternatives for decarbonization.

Material and Carbon Footprints of Machinery Capital.

Machinery and equipment, integral as technology-specific capital goods, play a dual role in climate change: it acts as both a mitigator and an exacerbator due to its carbon-intensive life cycle. Despite their importance, current climate mitigation analyses often overlook these items, leaving a gap in comprehensive analyses of their material stock and environmental impacts. To address this, our research integrates input-output analysis (IOA) with dynamic material flow analysis (d-MFA) to assess the carbon and material footprints of machinery. It finds that in 2019, machinery production required 30% of global metal production and 8% of global carbon emissions. Between 2000 and 2019, the metal footprint of the stock of machinery grew twice as fast as the economy. To illustrate the global implications and scale, we spotlight key countries. China's rise in machinery material stock is noteworthy, surpassing the United States in 2008 in total amount and achieving half of the US per capita level by 2019. Our study also contrasts economic depreciation─a value-centric metric─with the tangible lifespan of machinery, revealing how much the physical size of the capital stock exceeds its book values. As physical machinery stocks saturate, new machinery can increasingly be built from metals recycled from retired machinery.

Review of Urban Building Types and Their Energy Use and Carbon Emissions in Life-Cycle Analyses from Low- and Middle-Income Countries.

Urbanization, slum redevelopment, and population growth will lead to unprecedented levels of residential building construction in "low- and middle-income" (LMI) countries in the coming decades. However, less than 50% of previous residential building life-cycle assessment (LCA) reviews included LMI countries. Moreover, all reviews that included LMI countries only considered formal (cement-concrete) buildings, while more than 800 million people in these countries lived in informal settlements. We analyze LCA literature and define three building types based on durability: formal, semiformal, and informal. These exhaustively represent residential buildings in LMI countries. For each type, we define dominant archetypes from across the world, based on construction materials. To address the data deficiency and lack of transparency in LCA studies, we develop a reproducibility metric for building LCAs. We find that the countries with the most reproducible studies are India, Sri Lanka, Turkey, Mexico, and Brazil. Only 7 out of 54 African countries have reproducible studies focused on either the embodied or use phase. Maintenance, refurbishment, and end-of-life phases are included in hardly any studies in the LMI LCA literature. Lastly, we highlight the necessity for studying current, traditional buildings to provide a benchmark for future studies focusing on energy and material efficiency strategies.

The legacy environmental footprints of manufactured capital.

The foundations of today's societies are provided by manufactured capital accumulation driven by investment decisions through time. Reconceiving how the manufactured assets are harnessed in the production-consumption system is at the heart of the paradigm shifts necessary for long-term sustainability. Our research integrates 50 years of economic and environmental data to provide the global legacy environmental footprint (LEF) and unveil the historical material extractions, greenhouse gas emissions, and health impacts accrued in today's manufactured capital. We show that between 1995 and 2019, global LEF growth outpaced GDP and population growth, and the current high level of national capital stocks has been heavily relying on global supply chains in metals. The LEF shows a larger or growing gap between developed economies (DEs) and less-developed economies (LDEs) while economic returns from global asset supply chains disproportionately flow to DEs, resulting in a double burden for LDEs. Our results show that ensuring best practice in asset production while prioritizing well-being outcomes is essential in addressing global inequalities and protecting the environment. Achieving this requires a paradigm shift in sustainability science and policy, as well as in green finance decision-making, to move beyond the focus on the resource use and emissions of daily operations of the assets and instead take into account the long-term environmental footprints of capital accumulation.

Liquid Hydrogen: A Mirage or Potent Solution for Aviation's Climate Woes?

The aviation industry faces a formidable challenge to cap its climate impact in the face of continued growth in passengers and freight. Liquid hydrogen (LH2) is one of the alternative jet fuels under consideration as it does not produce carbon dioxide upon combustion. We conducted a well-to-wake life cycle assessment of CO2 emissions and non-CO2 climate change impacts per passenger-distance for 17 different hydrogen production routes, as well as conventional jet fuel and biofuels. Six other environmental and health impact categories were also considered. The Boeing 787-800 was used as the reference aircraft, and a range of flight distances were explored. Contrail cirrus contributes around 81 ± 31% of the combustion climate impacts for LH2, compared to 32 ± 7% for conventional jet fuel, showing that research is needed to reduce uncertainty in the case of LH2. The life cycle impacts of the two dominant commercial LH2 pathways are on average 8 and 121% larger than conventional jet fuel. Some novel LH2 pathways do show considerable potential for life cycle climate impact reductions versus conventional fuel (up to -205 ± 78%). LH2 from renewable energy is not climate neutral, though, at best -67 ± 10% compared to conventional over the life cycle.

Decomposition Analysis of the Carbon Footprint of Primary Metals.

This study investigates how different technological and socioeconomic drivers have impacted the carbon footprint of primary metals. It analyzes the historical evidence from 1995 to 2018 using new metal production, energy use, and greenhouse gas (GHG) emission extensions made for the multiregional input-output model EXIOBASE. A combination of established input-output methods (index decomposition analysis, hypothetical extraction method, and footprint analysis) is used to dissect the drivers of the change in the upstream emissions occurring due to the production of metals demanded by other (downstream) economic activities. On a global level, GHG emissions from metal production have increased at a similar pace as the GDP but have decreased in high-income countries in the most recent 6 year period studied. This absolute decoupling in industrialized countries is mainly driven by reduced metal consumption intensity and improved energy efficiency. However, in emerging economies increasing metal consumption intensity and affluency have driven up emissions, more than offsetting any reductions due to improved energy efficiency.

Microalgae Commercialization Using Renewable Lignocellulose Is Economically and Environmentally Viable.

Conventional phototrophic cultivation for microalgae production suffers from low and unstable biomass productivity due to limited and unreliable light transmission outdoors. Alternatively, the use of a renewable lignocellulose-derived carbon source, cellulosic hydrolysate, offers a cost-effective and sustainable pathway to cultivate microalgae heterotrophically with high algal growth rate and terminal density. In this study, we evaluate the feasibility of cellulosic hydrolysate-mediated heterotrophic cultivation (Cel-HC) for microalgae production by performing economic and environmental comparisons with phototrophic cultivation through techno-economic analysis and life cycle assessment. We estimate a minimum selling price (MSP) of 4722 USD/t for producing high-purity microalgae through Cel-HC considering annual biomass productivity of 300 t (dry weight), which is competitive with the conventional phototrophic raceway pond system. Revenues from the lignocellulose-derived co-products, xylose and fulvic acid fertilizer, could further reduce the MSP to 2976 USD/t, highlighting the advantages of simultaneously producing high-value products and biofuels in an integrated biorefinery scheme. Further, Cel-HC exhibits lower environmental impacts, such as cumulative energy demand and greenhouse gas emissions, than phototrophic systems, revealing its potential to reduce the carbon intensity of algae-derived commodities. Our results demonstrate the economic and environmental competitiveness of heterotrophic microalgae production based on renewable bio-feedstock of lignocellulose.

Material Stock and Embodied Greenhouse Gas Emissions of Global and Urban Road Pavement.

Roads play a key role in movements of goods and people but require large amounts of materials emitting greenhouse gases to be produced. This study assesses the global road material stock and the emissions associated with materials' production. Our bottom-up approach combines georeferenced paved road segments with road length statistics and archetypical geometric characteristics of roads. We estimate road material stock to be of 254 Gt. If we were to build these roads anew, raw material production would emit 8.4 GtCO2-eq. Per capita stocks range from 0.2 t/cap in Chad to 283 t/cap in Iceland, with a median of 20.6 t/cap. If the average per capita stock in Africa was to reach the current European level, 166 Gt of road materials, equivalent to the road material stock in North America and in East and South Asia, would be consumed. At the urban scale, road material stock increases with the urban area, population density, and GDP per capita, emphasizing the need for containing urban expansion. Our study highlights the challenges in estimating road material stock and serves as a basis for further research into infrastructure resource management.

Mandatory disclosure is key to address climate risks.

Financial regulations would help signal risks to investors.

Mitigating life cycle GHG emissions of roads to be built through 2030: Case study of a Chinese province.

The expansion of road networks in emerging economies such as China causes significant greenhouse gas (GHG) emissions. This development is conflicting with China's commitment to achieve carbon neutrality. Thus, there is a need to better understand life cycle emissions of road infrastructure and opportunities to mitigate these emissions. Existing impact studies of roads in developing countries do not address recycled materials, improved pavement maintenance, or pavement-vehicle interaction and electric vehicle (EV) adoption. Combining firsthand information from Chinese road construction engineers with publicly available data, this paper estimates a comprehensive account of GHG emissions of the road pavement network to be constructed in the next ten years in the Shandong province in Northern China. Further, we estimate the potential of GHG emission reductions achievable under three scenario sets: maintenance optimization, alternative pavement material replacement, and EV adoption. Results show that the life cycle GHG emissions of highways and Class 1-4 roads to be constructed in the next 10 years amount to 147 Mt CO2-eq. Considering the use phase in our model reveals that it is the dominant stage in terms of emissions, largely due to pavement-vehicle interaction. Vehicle electrification can only moderately mitigate these emissions. Other stages, such as materials production and road maintenance and rehabilitation, contribute substantially to GHG emissions as well, highlighting the importance of optimizing the management of these stages. Surprisingly, longer, not shorter maintenance intervals, yield significant emission reductions. Another counter-intuitive finding is that thicker and more material-intensive pavement surfaces cause lower emissions overall. Taken together, optimal maintenance and rehabilitation schedules, alternative material use, and vehicle electrification provide GHG reduction potentials of 11%, 4%-16% and 2%-6%, respectively.

Improved Copper Circularity as a Result of Increased Material Efficiency in the U.S. Housing Stock.

Material efficiency (ME) can support rapid climate change mitigation and circular economy. Here, we comprehensively assess the circularity of ME strategies for copper use in the U.S. housing services (including residential buildings and major household appliances) by integrating use-phase material and energy demand. Although the ME strategies of more intensive floor space use and extended lifetime of appliances and buildings reduce the primary copper demand, employing these strategies increases the commonly neglected use-phase share of total copper requirements during the century from 23-28 to 22-42%. Use-phase copper requirements for home improvements have remained larger than the demand gap (copper demand minus scrap availability) for much of the century, limiting copper circularity in the U.S. housing services. Further, use-phase energy consumption can negate the benefits of ME strategies. For instance, the lifetime extension of lower-efficiency refrigerators increases the copper use and net environmental impact by increased electricity use despite reductions from less production. This suggests a need for more attention to the use phase when assessing circularity, especially for products that are material and energy intensive during use. To avoid burden shifting, policymakers should consider the entire life cycle of products supporting services when pursuing circular economy goals.

Pricing indirect emissions accelerates low-carbon transition of US light vehicle sector.

Large-scale electric vehicle adoption can greatly reduce emissions from vehicle tailpipes. However, analysts have cautioned that it can come with increased indirect emissions from electricity and battery production that are not commonly regulated by transport policies. We combine integrated energy modeling and life cycle assessment to compare optimal policy scenarios that price emissions at the tailpipe only, versus both tailpipe and indirect emissions. Surprisingly, scenarios that also price indirect emissions exhibit higher, rather than reduced, sales of electric vehicles, while yielding lower cumulative tailpipe and indirect emissions. Expected technological change ensures that emissions from electricity and battery production are more than offset by reduced emissions of gasoline production. Given continued decarbonization of electricity supply, results show that a large-scale adoption of electric vehicles is able to reduce CO2 emissions through more channels than previously expected. Further, carbon pricing of stationary sources will also favor electric vehicles.

Global scenarios of resource and emission savings from material efficiency in residential buildings and cars.

Material production accounts for a quarter of global greenhouse gas (GHG) emissions. Resource-efficiency and circular-economy strategies, both industry and demand-focused, promise emission reductions through reducing material use, but detailed assessments of their GHG reduction potential are lacking. We present a global-scale analysis of material efficiency for passenger vehicles and residential buildings. We estimate future changes in material flows and energy use due to increased yields, light design, material substitution, extended service life, and increased service efficiency, reuse, and recycling. Together, these strategies can reduce cumulative global GHG emissions until 2050 by 20-52 Gt CO2-eq (residential buildings) and 13-26 Gt CO2e-eq (passenger vehicles), depending on policy assumptions. Next to energy efficiency and low-carbon energy supply, material efficiency is the third pillar of deep decarbonization for these sectors. For residential buildings, wood construction and reduced floorspace show the highest potential. For passenger vehicles, it is ride sharing and car sharing.

Linking the Environmental Pressures of China's Capital Development to Global Final Consumption of the Past Decades and into the Future.

China's rapid growth was fueled by investments that grew more than 10-fold since 1995. Little is known about how the capital assets acquired, while being used in productive processes for years or decades, satisfy global final consumption of goods and services, or how the resource use and emissions that occurred during capital formation are attributable to past or future consumption. Here, enabled by a new global model of capital formation and use, we quantify the linkages over the past 2 decades and into the future between six environmental pressures (EPs) associated with China's capital formation and attributable to Chinese as well as non-Chinese consumption. We show that only 35% of the capital assets acquired by China from 1995 to 2015, representing 32-39% of the associated EPs (e.g., water consumption, greenhouse gas (GHG) emissions, and metal ore extractions), have been depreciated, while the majority rest will serve future production and consumption. The outsourcing of capital services and the associated EPs are considerable, ranging from 14 to 25% of depending on the EP indicators. Without accounting for the capital-final consumption linkages across time and space, one would miscalculate China's environmental footprints related to the six EPs by big margins, from -61% to +114%.

Copper Recycling Flow Model for the United States Economy: Impact of Scrap Quality on Potential Energy Benefit.

Is recycling a means for meeting the increasing copper demand in the face of declining ore grades? To date, research to address this question has generally focused on the quantity, not the quality of copper scrap. Here, the waste input-output impact assessment (WIO-IA) model integrates information on United States (US) economy-wide material flow, various recycling indicators, and the impact of material production from diverse sources to represent the quantity and quality of copper flows throughout the lifecycle. This approach enables assessment of recycling performance against environmental impact indicators. If all potentially recyclable copper scrap was recycled, energy consumption associated with copper production would decrease by 15% with alloy scrap as the largest contributor. Further energy benefits from increased recycling are limited by the lower quality of the scrap yet to be recycled. Improving the yield ratio of final products and the grade of diverse consumer product scrap could help increase copper circularity and decrease energy consumption. Policy makers should address the importance of a portfolio of material efficiency strategies like improved utilization of copper products and lifetime extension in addition to encouraging the demand for recycled copper.

Individualism and nationally determined contributions to climate change.

Ratcheting up the Nationally Determined Contributions (NDCs) to achieve the Paris Agreement goals requires a better understanding of the enablers and barriers behind NDC formulation. However, existing quantitative analyses on the drivers of NDCs from an anthropological perspective are elusive. This study proposes both a conceptual framework and empirical analysis of how cultural values link with the pledged NDCs. The findings show that individualism (IDV) is a significant and robust predictor for the mitigation levels of NDCs, after controlling for affluence level, renewable energy proportion, democracy and other socioeconomic factors. For every 10-point increase in the IDV score (say from the score of Canada to Australia or from the score of Vietnam to Mexico), the committed per-capita emission in 2030 relative to 1990 levels decrease by 14%-22%. However, such a correlation is absent when assessing the mitigation ambitions using various fair benchmarks. This study underscores the necessity of considering more cultural context and nuances in tackling common climate problems, and advocates for developing tailored climate communication strategies to enhance the NDCs.

Linking Housing Policy, Housing Typology, and Residential Energy Demand in the United States.

Residential energy demand can be greatly influenced by the types of housing structures that households live in, but few studies have assessed changes in the composition of housing stocks as a strategy for reducing residential energy demand or greenhouse gas (GHG) emissions. In this paper we examine the effects of three sequenced federal policies on the share of new housing construction by type in the U.S., and estimate the cumulative influence of those policies on the composition of the 2015 housing stock. In a counterfactual 2015 housing stock without the policy effects, 14 million housing units exist as multifamily rather than single-family, equal to 14.1% of urban housing. Accompanied by floor area reductions of 0-50%, the switch from single- to multifamily housing reduces energy demand by 27-47% per household, and total urban residential energy by 4.6-8.3%. This paper is the first to link federal policies to housing outcomes by type and estimate associated effects on residential energy and GHG emissions. Removing policy barriers and disincentives to multifamily housing can unlock a large potential for reducing residential energy demand and GHG emissions in the coming decades.

Potential Climate Impact Variations Due to Fueling Behavior of Plug-in Hybrid Vehicle Owners in the US.

With the expected rapid growth of renewable electricity generation, charging plug-in hybrid electric vehicles (PHEVs) from the grid promise ever higher reductions in CO2 emissions. Previous analyses have found that the share that PHEVs are driven in electric mode can differ substantially depending on region, battery size, and trip purpose. Here, we provide a first fleet-wide emissions mitigation potential of US-based PHEV drivers adopting high or low shares of electric driving. Specifically, we illustrate scenarios of different combinations of PHEV uptake, renewable electricity generation shares, and PHEV fueling behavior. Across 21 analyzed scenarios, annual greenhouse gas (GHG) emissions of the light-duty vehicle (LDV) fleet could differ by an average of 21% (5-43% range) in 2050 depending alone on the fueling behavior of PHEV drivers. This behavior could further determine the discharge of about 1.3 (0.7-1.9) Gt CO2 (or roughly one year of current emissions) over the next three decades, significantly influencing the feasibility of reaching an 80% emission reduction target for the LDV sector. Governments can nudge PHEV drivers toward environmentally favorable fueling behavior. We discuss several options for nudging, including charging infrastructure availability, battery design, and consumer education.