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.

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.

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.

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.

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.

Environmental co-benefits and adverse side-effects of alternative power sector decarbonization strategies.

A rapid and deep decarbonization of power supply worldwide is required to limit global warming to well below 2 °C. Beyond greenhouse gas emissions, the power sector is also responsible for numerous other environmental impacts. Here we combine scenarios from integrated assessment models with a forward-looking life-cycle assessment to explore how alternative technology choices in power sector decarbonization pathways compare in terms of non-climate environmental impacts at the system level. While all decarbonization pathways yield major environmental co-benefits, we find that the scale of co-benefits as well as profiles of adverse side-effects depend strongly on technology choice. Mitigation scenarios focusing on wind and solar power are more effective in reducing human health impacts compared to those with low renewable energy, while inducing a more pronounced shift away from fossil and toward mineral resource depletion. Conversely, non-climate ecosystem damages are highly uncertain but tend to increase, chiefly due to land requirements for bioenergy.

Tracing the Uncertain Chinese Mercury Footprint within the Global Supply Chain Using a Stochastic, Nested Input-Output Model.

A detailed understanding of the mercury footprint at subnational entity levels can facilitate the implementation of the "Minamata Convention on Mercury", especially for China, the largest mercury emitter worldwide. Some provinces of China have more than 100 million people, with economic activities and energy consumption levels comparable to those of smaller G7 countries. We constructed a stochastic, nested multiregion input-output (MRIO) model, which regionalized the China block in the EXIOBASE global-scale MRIO table, to model the mercury footprint associated with global supply chains spanning China's regions and other countries. The results show that Tianjin, Shanghai, and Ningxia had the highest per capita mercury footprint in China, which was comparable to the footprint of Australia and Norway and exceeded the footprint of most other countries. Some developed regions in China (e.g., Guangdong, Jiangsu) had higher mercury final product-based inventories (FBI) and consumption-based inventories (CBI) than production-based inventories (PBI), emphasizing the role of these regions as centers of both consumption and economic control. Uncertainties of Chinese provincial mercury footprint varied from 8% to 34%. Our research also revealed that international and inter-regional final product and intermediate product trades reshape the mercury emissions of Chinese provinces and other countries to a certain extent.

Building Material Use and Associated Environmental Impacts in China 2000-2015.

A rapidly increasing use of building materials poses threats to resources and the environment. Using novel, localized life cycle inventories and building material intensity data, this study quantifies the resource use of building materials in mainland China and evaluates their embodied environmental impacts. Newly built floor area and related material consumption grew 11% per annum from 2000 to 2015, leveling off at the end of this period. Concrete, sand, gravel, brick, and cement were the main materials used. Spatially, construction activities expanded from east China into the central part of the country. Cement, steel, and concrete production are the key contributors to associated environmental impacts, e.g., cement and steel each account for around 25% of the global warming potential from building materials. Building materials contribute considerably to the impact categories of human toxicity, fossil depletion, and global warming, emphasizing that greenhouse gas emissions should not be the sole focus of research on environmental impacts of building materials. These findings quantitatively shed light on the urgent need to reduce environmental impacts and to conserve energy in the manufacturing processes of building materials on the national scale.

Endogenizing Capital in MRIO Models: The Implications for Consumption-Based Accounting.

Nearly 30% of global greenhouse gas emissions are associated with the production of capital goods. Consumption-based emission calculations based on multiregional input-output (MRIO) models allocate emissions occurring in the production of intermediate goods to the final goods produced in an economy. Like intermediate goods, capital goods are used in production processes; yet the emissions associated with their production are not allocated to the industries using them. As a result, the carbon footprint of final consumption as well as emissions embodied in trade are currently underestimated. Here, we address this problem by endogenizing capital transactions in the EXIOBASE global MRIO database, thereby allocating emissions from capital goods to final consumption. We find that endogenizing capital substantially increases the carbon footprint of final consumption (by up to 57% for some countries), and that the gap between production-based and consumption-based emissions increases for most countries. We also find that the global emissions embodied in trade increase by up to 11%, and that current patterns of bilaterally traded emissions are amplified. Furthermore, endogenizing capital leads to a 3-fold increase in the carbon footprint of certain product categories. The results suggest that our approach constitutes an important improvement to current input-output methodology.

Freshwater Vulnerability beyond Local Water Stress: Heterogeneous Effects of Water-Electricity Nexus Across the Continental United States.

Human health and economic prosperity are vulnerable to freshwater shortage in many parts of the world. Despite a growing literature that examines the freshwater vulnerability in various spatiotemporal contexts, existing knowledge has been conventionally constrained by a territorial perspective. On the basis of spatial analyses of monthly water and electricity flows across 2110 watersheds and three interconnected power systems, this study investigates the water-electricity nexus (WEN)'s transboundary effects on freshwater vulnerability in the continental United States in 2014. The effects are shown to be considerable and heterogeneous across time and space. For at least one month a year, 58 million people living in water-abundant watersheds were exposed to additional freshwater vulnerability by relying on electricity generated by freshwater-cooled thermal energy conversion cycles in highly stressed watersheds; for 72 million people living in highly stressed watersheds, their freshwater vulnerability was mitigated by using imported electricity generated in water-abundant watersheds or power plants running dry cooling or using nonfreshwater for cooling purposes. On the country scale, the mitigation effects were the most significant during September and October, while the additional freshwater vulnerability was more significant in February, March, and December. Due to the WEN's transboundary effects, overall, the freshwater vulnerability was slightly worsened within the Eastern Interconnection, substantially improved within the Western Interconnection, and least affected within the ERCOT Interconnection.

Mapping the Carbon Footprint of Nations.

Life cycle thinking asks companies and consumers to take responsibility for emissions along their entire supply chain. As the world economy becomes more complex it is increasingly difficult to connect consumers and other downstream users to the origins of their greenhouse gas (GHG) emissions. Given the important role of subnational entities-cities, states, and companies-in GHG abatement efforts, it would be advantageous to better link downstream users to facilities and regulators who control primary emissions. We present a new spatially explicit carbon footprint method for establishing such connections. We find that for most developed countries the carbon footprint has diluted and spread: for example, since 1970 the U.S. carbon footprint has grown 23% territorially, and 38% in consumption-based terms, but nearly 200% in spatial extent (i.e., the minimum area needed to contain 90% of emissions). The rapidly growing carbon footprints of China and India, however, do not show such a spatial expansion of their consumption footprints in spite of their increasing participation in the world economy. In their case, urbanization concentrates domestic pollution and this offsets the increasing importance of imports.

Towards a meaningful assessment of marine ecological impacts in life cycle assessment (LCA).

Human demands on marine resources and space are currently unprecedented and concerns are rising over observed declines in marine biodiversity. A quantitative understanding of the impact of industrial activities on the marine environment is thus essential. Life cycle assessment (LCA) is a widely applied method for quantifying the environmental impact of products and processes. LCA was originally developed to assess the impacts of land-based industries on mainly terrestrial and freshwater ecosystems. As such, impact indicators for major drivers of marine biodiversity loss are currently lacking. We review quantitative approaches for cause-effect assessment of seven major drivers of marine biodiversity loss: climate change, ocean acidification, eutrophication-induced hypoxia, seabed damage, overexploitation of biotic resources, invasive species and marine plastic debris. Our review shows that impact indicators can be developed for all identified drivers, albeit at different levels of coverage of cause-effect pathways and variable levels of uncertainty and spatial coverage. Modeling approaches to predict the spatial distribution and intensity of human-driven interventions in the marine environment are relatively well-established and can be employed to develop spatially-explicit LCA fate factors. Modeling approaches to quantify the effects of these interventions on marine biodiversity are less well-developed. We highlight specific research challenges to facilitate a coherent incorporation of marine biodiversity loss in LCA, thereby making LCA a more comprehensive and robust environmental impact assessment tool. Research challenges of particular importance include i) incorporation of the non-linear behavior of global circulation models (GCMs) within an LCA framework and ii) improving spatial differentiation, especially the representation of coastal regions in GCMs and ocean-carbon cycle models.

A Methodology for Integrated, Multiregional Life Cycle Assessment Scenarios under Large-Scale Technological Change.

Climate change mitigation demands large-scale technological change on a global level and, if successfully implemented, will significantly affect how products and services are produced and consumed. In order to anticipate the life cycle environmental impacts of products under climate mitigation scenarios, we present the modeling framework of an integrated hybrid life cycle assessment model covering nine world regions. Life cycle assessment databases and multiregional input-output tables are adapted using forecasted changes in technology and resources up to 2050 under a 2 °C scenario. We call the result of this modeling "technology hybridized environmental-economic model with integrated scenarios" (THEMIS). As a case study, we apply THEMIS in an integrated environmental assessment of concentrating solar power. Life-cycle greenhouse gas emissions for this plant range from 33 to 95 g CO2 eq./kWh across different world regions in 2010, falling to 30-87 g CO2 eq./kWh in 2050. Using regional life cycle data yields insightful results. More generally, these results also highlight the need for systematic life cycle frameworks that capture the actual consequences and feedback effects of large-scale policies in the long term.