Assessing the Relative Climate Impact of Carbon Utilization for Concrete, Chemical, and Mineral Production.

Estimates show that 6.2 gigatons of carbon dioxide (CO2) can be captured and utilized across three pathways, concrete, chemical, and minerals, by 2050. However, it is difficult to compare the climate benefit across these three carbon capture and utilization (CCU) pathways to determine the most effective use of captured CO2. The life cycle assessment methods to evaluate the climate benefit of CCU chemicals should additionally account for the change in material properties of concrete due to CO2 utilization. Furthermore, with most CO2 utilization technologies being in the early stages of research and development, the uncertainty and variability in process and inventory data present a significant challenge in evaluating the climate benefit. We present a stochastically determined climate return on investment (ROI) metric to rank and prioritize CO2 utilization across 20 concrete, chemical and mineral pathways based on the realized climate benefit. We show that two concrete pathways, which use CO2 during concrete mixing, and two chemical pathways, which produce formic acid through hydrogenation of CO2 and carbon monoxide through dry reforming of methane, generate the greatest climate ROI and are the only CCU pathways with a higher likelihood of generating a climate benefit than a climate burden.

The Future of Food: Environmental Lessons from E-Commerce.

Our food system is experiencing dramatic changes as the expansion of e-commerce, introduction of new products, and innovations in supply chain structures all pose to transform how we buy, sell, and distribute food. However, the environmental impacts of these transformations remain unclear. This feature reviews existing literature on environmental implications of e-commerce, discusses relevant trade-offs, and identifies pressing gaps in research. Some trade-offs discussed are those between centralized and decentralized delivery service types, those unique to a rural landscape, and those within the interplay of transportation and consumer behavior. The impacts of fulfillment centers, of refrigerated logistics, of e-commerce on consumer shopping and food waste habits, and of e-commerce services in rural regions are identified as pressing knowledge gaps.

The Influence of Household Refrigerator Ownership on Diets in Vietnam.

Refrigerator ownership accompanies socio-economic development, with the potential to change human diets. Household refrigerator ownership in Vietnam has increased from 13% to 59% between 2004-2014. This study estimates changes in food consumption and diet linkages with household refrigerator ownership in Vietnam, while controlling for socioeconomic variables. We use a two-step instrumental variable regression model on two panels of the Vietnam Household Living Standards Survey covering 2004-2014. Our study finds refrigerator ownership to be significantly associated with decreases in per-capita calorie intake over both periods. Refrigerator ownership may be connected with households substituting lower-nutrient foods with higher ones, with substantial decreases in starchy staple food consumption connected with refrigerator ownership in both panels. For both periods, refrigerator ownership is significantly connected with increased dairy consumption, potentially reflecting the refrigerator increasing a household's ability to store dairy products.

Five Misperceptions Surrounding the Environmental Impacts of Single-Use Plastic.

This article explores five commonly held perceptions that do not correspond with current scientific knowledge surrounding the environmental impacts of single-use plastic. These misperceptions include: (1) plastic packaging is the largest contributor to the environmental impact of a product; (2) plastic has the most environmental impact of all packaging materials; (3) reusable products are always better than single-use plastics; (4) recycling and composting should be the highest priority; (5) "zero waste" efforts that eliminate single-use plastics minimize the environmental impacts of an event. This paper highlights the need for environmental scientists and engineers to put the complex environmental challenges of plastic waste into better context, integrating a holistic, life cycle perspective into research efforts and discussions that shape public policy.

Reducing CO2 Emissions from U.S. Steel Consumption by 70% by 2050.

The steel sector emits 25% of global industrial greenhouse gases, and the U.S. is the world's second-largest steel consumer. In this article, we determine how CO2 emissions attributable to U.S. steel consumption can be cut by 70% by 2050. We vary four key steel cycle parameters (U.S. steel stocks per capita, recycling rate, product lifespan, and manufacturing yield) in a dynamic material flow analysis to determine a range of values for annual steel demand and the scrap available for recycling. We combine these data with steelmaking technology and trade scenarios to calculate potential U.S. steel sector emissions in each year to 2050. Only 20% of the pathways we modeled for the U.S. steel sector achieved the emissions target. Emissions in 2050 are most sensitive to the CO2 released per kilogram of steel produced and the steel stocks per capita. Deployment of emerging low carbon steelmaking technology alone is insufficient to achieve the emissions cut; conversely, reducing stocks per capita from the current ∼11 tons/capita toward levels in the U.K. and France, ∼8 tons/capita, would enable the emissions cut to be achieved under a range of foreseeable steelmaking technology scenarios and steel cycle parameters. If action to reduce per capita steel stocks is delayed by more than five years, then it is likely infeasible for the U.S. steel sector to stay within its 2050 CO2 budget because of the increased demand for emissions-intensive steel made from iron ore.

Quantifying the Urban Food-Energy-Water Nexus: The Case of the Detroit Metropolitan Area.

The efficient provision of food, energy, and water (FEW) resources to cities is challenging around the world. Because of the complex interdependence of urban FEW systems, changing components of one system may lead to ripple effects on other systems. However, the inputs, intersectoral flows, stocks, and outputs of these FEW resources from the perspective of an integrated urban FEW system have not been synthetically characterized. Therefore, a standardized and specific accounting method to describe this system is needed to sustainably manage these FEW resources. Using the Detroit Metropolitan Area (DMA) as a case, this study developed such an accounting method by using material and energy flow analysis to quantify this urban FEW nexus. Our results help identify key processes for improving FEW resource efficiencies of the DMA. These include (1) optimizing the dietary habits of households to improve phosphorus use efficiency, (2) improving effluent-disposal standards for nitrogen removal to reduce nitrogen emission levels, (3) promoting adequate fertilization, and (4) enhancing the maintenance of wastewater collection pipelines. With respect to water use, better efficiency of thermoelectric power plants can help reduce water withdrawals. The method used in this study lays the ground for future urban FEW analyses and modeling.

Potential Changes in Greenhouse Gas Emissions from Refrigerated Supply Chain Introduction in a Developing Food System.

Refrigeration transforms developing food systems, changing the dynamics of production and consumption. This study models the introduction of an integrated refrigerated supply chain, or "cold chain," into sub-Saharan Africa and estimates changes in preretail greenhouse gas (GHG) emissions if the cold chain develops similarly to North America or Europe. Refrigeration presents an important and understudied trade-off: the ability to reduce food losses and their associated environmental impacts, but increasing energy use and creating GHG emissions. It is estimated that postharvest emissions added from cold chain operation are larger than food loss emissions avoided, by 10% in the North American scenario and 2% in the European scenario. The cold chain also enables changes in agricultural production and diets. Connected agricultural production changes decrease emissions, while dietary shifts facilitated by refrigeration may increase emissions. These system-wide changes brought about by the cold chain may increase the embodied emissions of food supplied to retail by 10% or decrease them by 15%, depending on the scenario.

Comparative Human Toxicity Impact of Electricity Produced from Shale Gas and Coal.

The human toxicity impact (HTI) of electricity produced from shale gas is lower than the HTI of electricity produced from coal, with 90% confidence using a Monte Carlo Analysis. Two different impact assessment methods estimate the HTI of shale gas electricity to be 1-2 orders of magnitude less than the HTI of coal electricity (0.016-0.024 DALY/GWh versus 0.69-1.7 DALY/GWh). Further, an implausible shale gas scenario where all fracturing fluid and untreated produced water is discharged directly to surface water throughout the lifetime of a well also has a lower HTI than coal electricity. Particulate matter dominates the HTI for both systems, representing a much larger contribution to the overall toxicity burden than VOCs or any aquatic emission. Aquatic emissions can become larger contributors to the HTI when waste products are inadequately disposed or there are significant infrastructure or equipment failures. Large uncertainty and lack of exposure data prevent a full risk assessment; however, the results of this analysis provide a comparison of relative toxicity, which can be used to identify target areas for improvement and assess potential trade-offs with other environmental impacts.

Critical Research Needed to Examine the Environmental Impacts of Expanded Refrigeration on the Food System.

The unbroken global refrigerated supply chain, or cold chain, is rapidly expanding in developing countries. In addition to increasing the energy intensity of the food system, the expanded cold chain may facilitate changes in the global diet, food waste patterns, food production and distribution, and shopping habits. The sustainability impacts of many of these changes chain are unknown, given the complexity of interacting social, economic, and technical factors. The current literature surrounding the environmental impacts of refrigeration in the food system focuses on the direct impacts of energy use and coolant emissions, and lacks a critical evaluation of the accompanying systemic societal changes that potentially carry greater environmental impacts. This review examines the cold chain as a transformative technology, identifying key intrinsic, indirect, and external factors that will favorably, unfavorably, or ambiguously impact the environmental profile of the food system. The review identifies key interactions and feedbacks between the cold chain, food production and consumption decisions, infrastructure development, and the global environment which are largely unexamined and in need of empirical data. Viewing cold chain expansion from this broader perspective is essential to understanding the changing impacts of the food system in developing countries and may inform future sustainability planning.

Potential for Integrating Diffusion of Innovation Principles into Life Cycle Assessment of Emerging Technologies.

Life cycle assessment (LCA) measures cradle-to-grave environmental impacts of a product. To assess impacts of an emerging technology, LCA should be coupled with additional methods that estimate how that technology might be deployed. The extent and manner that an emerging technology diffuses throughout a region shapes the magnitude and type of environmental impacts. Diffusion of innovation is an established field of research that analyzes the adoption of new innovations, and its principles can be used to construct scenario models that enhance LCA of emerging technologies. Integrating diffusion modeling techniques with an LCA of emerging technology can provide estimates for the extent of market penetration, the displacement of existing systems, and the rate of adoption. Two general perspectives of application are macro-level diffusion models that use a function of time to represent adoption, and microlevel diffusion models that simulate adoption through interactions of individuals. Incorporating diffusion of innovation concepts complement existing methods within LCA to inform proactive environmental management of emerging technologies.

Framework for analyzing transformative technologies in life cycle assessment.

Emerging products and technologies pose unique challenges for the life cycle assessment (LCA) community, given the lack of data and inherent uncertainties regarding their development. An emerging technology that has the potential to be transformative and effect broad-scale change within society, as well as the underpinning assumptions associated with its life cycle, is particularly difficult to analyze. Despite the associated challenges, LCA methods must be developed for transformative technologies. The greatest improvement potential occurs at the early phases of technology development; therefore, prospective LCA results can be used to anticipate potential unintended consequences and develop design pathways that lead to preferential outcomes. This paper identifies and categorizes ten factors that influence the LCA results of transformative technologies in order to provide a formal structure for determining appropriate factors for inclusion within an LCA. Appropriate factors for an analysis should be selected according to the overall research questions of the study and are applicable to both attributional and consequential approaches to LCA.

Minimizing land use and nitrogen intensity of bioenergy.

The environmental impacts of bioenergy products have received a great deal of attention. Life cycle analysis (LCA) is a widely accepted method to quantify the environmental impacts of products. Conducting comprehensive LCAs for every possible bioenergy alternative is difficult because of the sheer magnitude of potential biomass sources and energy end products. The scopes of LCAs are often simplified to compare multiple products on the basis of greenhouse gas emissions and net energy balances, and may neglect equally important considerations such as nitrogen and land use. This study determines the most desirable energy crops on the basis of nitrogen and land use. The theoretical minimum nitrogen and land use requirements of fourteen bioenergy feedstocks are evaluated. These results can help prioritize certain feedstock crops for more in-depth life cycle analyses and can be used to inform policies on dedicated energy crops. The results of the study indicate that sugar cane has the best nitrogen and land use profile of the analyzed feedstocks. Sugar cane is the largest contributor to bioenergy production worldwide and is an effective policy choice from a nutrient and land use perspective. Conversely, soybeans and rapeseed are the least effective biomass sources with respect to land use and nitrogen requirements, yet these crops are also used to meet biofuel production targets worldwide. These results indicate current energy policies either do not consider or undervalue nitrogen and land use impacts, which could lead to unsustainable recommendations. Interestingly, when both nitrogen and land intensity are taken into account, reasonably small differences are seen between the remainder of the analyzed feedstocks, indicating an inherent trade-off between energy yield and nitrogen impacts.

A comparative life cycle assessment of petroleum and soybean-based lubricants.

A comparative life cycle assessment examining soybean and petroleum-based lubricants is compiled using Monte Carlo analysis to assess system variability. Experimental data obtained from an aluminum manufacturing facility indicate significantly less soybean lubricant is required to achieve similar or superior performance. With improved performance and a lower use rate, a transition to soybean oil results in lower aggregate impacts of acidification, smog formation, and human health from criteria pollutants. Regardless of quantity consumed, soybean-based lubricants exhibit significant climate change and fossil fuel use benefits; however, eutrophication impacts are much greater due to non-point nutrient emissions. Fundamental tradeoffs in the carbon and nitrogen cycles are addressed in the analysis, demonstrating that a transition to soybean oil may result in climate change benefits at the expense of regional water quality.

Life cycle of the corn-soybean agroecosystem for biobased production.

Biobased product life cycle assessments (LCAs) have focused largely on energy (fossil fuel) usage and greenhouse gas emissions during the agriculture and production stages. This paper compiles a more comprehensive life cycle inventory (LCI) for use in future bioproduct LCAs that rely on corn or soybean crops as feedstocks. The inventory includes energy, C, N, P, major pesticides, and U.S. EPA criteria air pollutants that result from processes such as fertilizer production, energy production, and on-farm chemical and equipment use. Agroecosystem material flows were modeled using a combination of GREET (the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation model), a linear fractionation model that describes P biogeochemical cycling, and Monte Carlo Analysis. Results show that the dominant air emissions resulted from crop farming, fertilizers, and on-farm nitrogen flows (e.g., N20 and NO). Seed production and irrigation provided no more than 0.002% to any of the inventory emissions or energy flows and may be neglected in future LCAs of corn or soybeans as feedstocks from the U.S. Corn Belt. Lime contributes significantly (17% of total emissions) to air emissions and should not be neglected in bioproduct LCAs.

Use of Monte Carlo analysis to characterize nitrogen fluxes in agroecosystems.

Intensive agricultural systems are largely responsible for the increase in global reactive nitrogen compounds, which are associated with significant environmental impacts. The nitrogen cycle in agricultural systems is complex and highly variable, which complicates characterization in environmental assessments. Appropriately representing nitrogen inputs into an ecosystem is essential to better understand and predict environmental impacts, such as the extent of seasonally occurring hypoxic zones. Many impacts associated with reactive nitrogen are directly related to annual nitrogen loads, and are not adequately represented by average values that de-emphasize extreme years. To capture the inherent variability in agricultural systems, this paper employs Monte Carlo analysis (MCA) to model major nitrogen exports during crop production, focusing on corn-soybean rotations within the U.S. Corn Belt. This approach yields distributions of possible emission values and is the first step in incorporating variable nutrient fluxes into life cycle assessments (LCA) and environmental impact assessments. Monte Carlo simulations generate distributions of nitrate emissions showing that 80% of values range between 15 and 90 kg NO39-) N/ha (mean 38.5 kg NO3(-) N/ha; median 35.7 kg NO3(-) N/ha) for corn fields and 5-60 kg NO3(-) N/ha (mean 20.8 kg NO3(-) N/ha; median 16.4 kg NO3(-) N/ha) for soybean fields. Data were also generated for grain and residue nitrogen, N2O, NO(x), and NH3. Results indicate model distributions are in agreement with available measured emissions.