Indirect emissions of forest bioenergy: detailed modeling of stump‐root systems

Indirect carbon dioxide emissions from producing bioenergy from tree stumps and roots depend critically on the decomposition rate of these harvest residues if they were left in forest to decay. We developed a method to improve the current estimates of these emissions. First, the 3D structure of uprooted stump‐root systems was modeled based on terrestrial laser‐scanning data. Second, information obtained on the size distribution of the stumps and the roots was used to simulate their decomposition and to estimate the indirect emissions. The method was able to describe the structure of stump‐root systems at a clear‐cut boreal Norway spruce test site. Compared with earlier results based on the diameter of stumps alone, the new estimates of the decomposition rate were slightly higher and, consequently, those of the indirect emissions slightly lower. The method is useful to collect information on the indirect emissions of stump‐root bioenergy quickly in different forests.     

Coupling Input‐Output Tables with Macro‐Life Cycle Assessment to Assess Worldwide Impacts of Biofuels Transport Policies

Many countries see biofuels as a replacement to fossil fuels to mitigate climate change. Nevertheless, some concerns remain about the overall benefits of biofuels policies. More comprehensive tools seem required to evaluate indirect effects of biofuel policies. This article proposes a method to evaluate large‐scale biofuel policies that is based on life cycle assessment (LCA), environmental extensions of input‐output (I‐O) tables, and a general equilibrium model. The method enables the assessment of indirect environmental effects of biofuels policies, including land‐use changes (LUCs), in the context of economic and demographic growth. The method is illustrated with a case study involving two scenarios. The first one describes the evolution of the world economy from 2006 to 2020 under business as usual (BAU) conditions (including demographic and dietary preferences changes), and the second integrates biofuel policies in the United States and the European Union (EU). Results show that the biofuel scenario, originally designed to mitigate climate change, results in more greenhouse gas emissions when compared to the BAU scenario. This is mainly due to emissions associated with global LUCs. The case study shows that the method enables a broader consideration for environmental effects of biofuel policies than usual LCA: Global economic variations calculated by a general equilibrium economic model and LUC emissions can be evaluated. More work is needed, however, to include new biofuel production technologies and reduce the uncertainty of the method.     

Indirect carbon dioxide emissions from producing bioenergy from forest harvest residues

Forest harvest residues are important raw materials for bioenergy in regions practicing forestry. Removing these residues from a harvest site reduces the carbon stock of the forest compared with conventional stem‐only harvest because less litter in left on the site. The indirect carbon dioxide (CO₂) emission from producing bioenergy occur when carbon in the logging residues is emitted into the atmosphere at once through combustion, instead of being released little by little as a result of decomposition at the harvest sites. In this study (1) we introduce an approach to calculate this indirect emission from using logging residues for bioenergy production, and (2) estimate this emission at a typical target of harvest residue removal, i.e. boreal Norway spruce forest in Finland. The removal of stumps caused a larger indirect emission per unit of energy produced than the removal of branches because of a lower decomposition rate of the stumps. The indirect emission per unit of energy produced decreased with time since starting to collect the harvest residues as a result of decomposition at older harvest sites. During the 100 years of conducting this practice, the indirect emission from average‐sized branches (diameter 2 cm) decreased from 340 to 70 kg CO₂ eq. MWh^?1 and that from stumps (diameter 26 cm) from 340 to 160 kg CO₂ eq. MWh^?1. These emissions are an order of magnitude larger than the other emissions (collecting, transporting, etc.) from the bioenergy production chain. When the bioenergy production was started, the total emissions were comparable to fossil fuels. The practice had to be carried out for 22 (stumps) or four (branches) years until the total emissions dropped below the emissions of natural gas. Our results emphasize the importance of accounting for land‐use‐related indirect emissions to correctly estimate the efficiency of bioenergy in reducing CO₂ emission into the atmosphere.     

Does Industrial Waste Reuse Bring Dual Benefits of Economic Growth and Carbon Emission Reduction?: Evidence of Incorporating the Indirect Effect of Economic Growth in China

This article employs panel data from 28 Chinese provinces over the period 1999–2011 to analyze the effects of industrial waste reuse (IWR) on carbon emissions. The extant studies mainly consider the direct effects that individual firms garner from IWR while ignoring other possible indirect effects in a more macroscopic context. Considering this research void, this article examines the potential indirect effects of IWR on carbon emissions through economic growth as the mediator. The results show that the direct effect of IWR on carbon emissions is negative and significant, but the positive indirect effect, through economic growth, is present. From the perspective of total effect, IWR is beneficial for both economic growth and carbon emission reduction (CER). However, the benefits for CER are mitigated when the economy is less developed, because the emission reduction could be compromised through the indirect effect of economic growth. Nevertheless, the indirect effect on compensating carbon emission is decreased with an increase in the economic growth. When the growth reaches a higher level, the indirect effect of IWR will alter to contribute to CER. The turning point in China is around 7,000 to 9,000 renminbi gross domestic product (GDP) per capita in 1999 constant price.     

基于不同需求层次的中国城镇居民消费隐含碳排放时空演变机制

正确认识不同需求水平下人均隐含碳排放量的变化,对实现低碳经济及低碳生活具有重要的参考价值。基于居民消费需求层次建立不同需求层次与隐含碳排放的对应关系,将人均隐含碳排放分解为生存型、发展型、奢侈型三类,并运用投入产出法进行核算,在对不同需求层次人均隐含碳排放的空间格局演变分析的基础上采用空间面板方法对其驱动机制进行甄别。结果显示,在全国层面,各需求层次人均隐含碳排放均呈现上升趋势,空间分布不均衡性主要体现在南北差异上,北部地区始终是各需求层次人均隐含碳排放的主要空间载体,其中多数省分生存型人均隐含碳排放上升势头较强,发展型和奢侈型的高值区在省份数量上分别呈现先减后增与逐渐增加的变化趋势;不同需求层次人均隐含碳排放水平相似的地区在空间上呈集聚分布,具有较强的"马太效应";空间面板模型结果显示技术减排是降低不同需求层次人均隐含碳排放的重要举措,而人口规模在各需求层次上的负向减排作用远小于正向的人口结构效应,宏观经济因素主要表现为增排效应,而居民消费因素的作用通道存在差异。此外,部分因素在各需求层次上存在显著空间外溢效应,应重视区域间的横向联动减排效应,做好隐含碳减排的统筹协调工作。     

Crop‐based biofuels and associated environmental concerns

Current Life Cycle Analysis (LCA) models indicate that crop‐based biofuels generate greenhouse gas savings, compared with fossil fuels. We argue that they do so only because they ignore the emissions of CO₂ from vehicles burning the biofuels without determining if the biomass is “additional,” and because they underestimate the ultimate emissions of N₂O from nitrogen fertiliser use. Taking proper account of these factors would result in very different findings. It would be far better to derive biofuels from biomass, from waste feedstocks or high‐yielding bioenergy crops with low nitrogen demand, grown on currently unproductive land.     

When Comparing Alternative Fuel‐Vehicle Systems,Life Cycle Assessment Studies Should Consider Trends in Oil Production

Petroleum from unconventional reserves is making an increasingly important contribution to the transportation fuel supply, but is generally more expensive and has greater environmental burdens than petroleum from conventional sources. Life cycle assessments (LCAs) of alternative fuel‐vehicle technologies typically consider conventional internal combustion engine vehicles fueled by gasoline produced from the average petroleum slate used in refineries as a baseline. Large‐scale deployment of alternative fuel‐vehicle technologies will decrease petroleum demand and lead to decreased production at the economic margin (unconventional oil), but this is not considered in most current LCAs. If marginal petroleum resources have larger impacts than average petroleum resources, the environmental benefits of petroleum demand reduction are underestimated by the current modeling approaches. Often, models include some consequential‐based impacts (such as indirect land‐use change for biofuels), but exclude others (such as avoided unconventional oil production). This approach is inconsistent and does not provide a robust basis for public policy and private investment strategy decisions. We provide an example to illustrate the potential scale of these impacts, but further research is needed to establish and quantify these marginal effects and incorporate them into LCAs of both conventional and alternative fuel‐vehicle technologies.     

Regionally differentiated estimates of cropland N2O emissions reduce uncertainty in global calculations

Nitrogen (N) additions to cropland soils are the largest source of anthropogenic nitrous oxide (N₂O) emissions and are an important contributor to global greenhouse gas radiative forcing. Progress in understanding controls on N₂O fluxes from soils is demonstrated in increasingly sophisticated emissions estimates with improved spatial and source resolution. These methods build upon ongoing field, laboratory, and modeling advances that are restricted to just a handful of countries. Thus, burgeoning new knowledge is of limited utility for improving N₂O emissions estimates for the rest of the world where prospects for near‐term advances are constrained by the limited breadth of observations and availability of model driver data. Here, we use Bayesian inversion to leverage information from recent national‐level N₂O emission inventories and reduce uncertainty by up to 65% for estimates of regional and global direct cropland N₂O emissions. Our estimates for the proportion of N inputs lost as N₂O vary by a factor of two between regions and depart from existing default emission factors, yet regional emissions estimates based on these factors are consistent with global, regional, and local observations. Improved regional emission factors will enhance national greenhouse gas inventories in information‐poor countries and guide efforts to reduce agricultural N₂O emissions.     

What can and can't we say about indirect land‐use change in Brazil using an integrated economic – land‐use change model?

It is commonly recognized that large uncertainties exist in modelled biofuel‐induced indirect land‐use change, but until now, spatially explicit quantification of such uncertainties by means of error propagation modelling has never been performed. In this study, we demonstrate a general methodology to stochastically calculate direct and indirect land‐use change (dLUC and iLUC) caused by an increasing demand for biofuels, with an integrated economic – land‐use change model. We use the global Computable General Equilibrium model MAGNET, connected to the spatially explicit land‐use change model PLUC. We quantify important uncertainties in the modelling chain. Next, dLUC and iLUC projections for Brazil up to 2030 at different spatial scales and the uncertainty herein are assessed. Our results show that cell‐based (5 × 5 km²) probabilities of dLUC range from 0 to 0.77, and of iLUC from 0 to 0.43, indicating that it is difficult to project exactly where dLUC and iLUC will occur, with more difficulties for iLUC than for dLUC. At country level, dLUC area can be projected with high certainty, having a coefficient of variation (cv) of only 0.02, while iLUC area is still uncertain, having a cv of 0.72. The latter means that, considering the 95% confidence interval, the iLUC area in Brazil might be 2.4 times as high or as low as the projected mean. Because this confidence interval is so wide that it is likely to straddle any legislation threshold, our opinion is that threshold evaluation for iLUC indicators should not be implemented in legislation. For future studies, we emphasize the need for provision of quantitative uncertainty estimates together with the calculated LUC indicators, to allow users to evaluate the reliability of these indicators and the effects of their uncertainty on the impacts of land‐use change, such as greenhouse gas emissions.     

Evolutionary importance of parental care performance,food resources,and direct and indirect genetic effects in a burying beetle

Indirect genetic effects (IGE) of parental care performance and the direct–indirect covariance contribute substantially to total heritability in domesticated and laboratory mammals. For animals from natural populations empirical estimates of IGE are sparse. Thus, despite recent models relating IGE to evolution, evolutionary interpretations of IGE are limited. To address this deficit, we used a reciprocal cross‐fostering breeding design to estimate environmental influences, direct and indirect genetic effects, and direct–indirect genetic covariances in the burying beetle Nicrophorus pustulatus to determine the evolutionary importance of IGE arising from variation in parental care performance. Carrion size positively affected adult mass and time on carrion, but had no effect on total development time. Males were slightly larger than females. For both mass and development, independent of these environmental influences, direct and indirect genetic effects were of moderate magnitude. Total genetic effects explained 36–50% of the phenotypic variance in mass and size and 27–37% of phenotypic variance in development time. Direct–indirect genetic covariances were zero or close to zero. Thus, for both mass and development time, the response to natural selection arising from environmental variation may be accelerated by the presence of IGE in N. pustulatus. The generality of this pattern and the evolutionary significance of IGE arising from parental care awaits further study of natural populations.     

Empirical Fuel Consumption and CO2 Emissions of Plug‐In Hybrid Electric Vehicles

Plug‐in hybrid electric vehicles (PHEVs) combine electric and conventional propulsion. Official fuel consumption values of PHEVs are based on standardized driving cycles, which show a growing discrepancy with real‐world fuel consumption. However, no comprehensive empirical results on PHEV fuel consumption are available, and the discrepancy between driving cycle and empirical fuel consumption has been conjectured to be large for PHEV. Here, we analyze real‐world fuel consumption data from 2,005 individual PHEVs of five PHEV models and observe large variations in individual fuel consumption with deviation from test‐cycle values in the range of 2% to 120% for PHEV model averages. Deviations are larger for short‐ranged PHEVs. Among others, range and vehicle power are influencing factors for PHEV model fuel consumption with average direct carbon dioxide (CO₂) emissions decreasing by 2% to 3% per additional kilometer (km) of electric range. Additional simulations show that PHEVs recharged from renewable electricity can noteworthily reduce well‐to‐wheel CO₂ emissions of passenger cars, but electric ranges should not exceed 200 to 300 km since battery production is CO₂‐intense. Our findings indicate that regulations should (1) be based on real‐world fuel consumption measurements for PHEV, (2) take into account charging behavior and annual mileages, and (3) incentivize long‐ranged PHEV.     

Integrated Economic Equilibrium and Life Cycle Assessment Modeling for Policy‐based Consequential LCA

Consequential life cycle assessment (CLCA) has emerged as a tool for estimating environmental impacts of changes in product systems that go beyond physical relationships accounted for in attributional LCA (ALCA). This study builds on recent efforts to use more complex economic models for policy‐based CLCA. A partial market equilibrium (PME) model, called the U.S. Forest Products Module (USFPM), is combined with LCA to analyze an energy demand scenario in which wood use increases 400 million cubic meters in the United States for ethanol production. Several types of indirect economic and environmental impacts are identified and estimated using USFPM‐LCA. A key finding is that if wood use for biofuels increases to high levels and mill residue is used for biofuels and replaced by natural gas for heat and power in forest products mills, then the increased greenhouse gas emissions from natural gas could offset reductions obtained by substituting biofuels for gasoline. Such high levels of biofuel demand, however, appear to have relatively low environmental impacts across related forest product sectors.     

Comparison of measured and EF5-r-derived N2O fluxes from a spring-fed river

There is considerable uncertainty in the estimates of indirect N₂O emissions as defined by the Intergovernmental Panel on Climate Change's (IPCC) methodology. Direct measurements of N₂O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N₂O budget. The objectives of this research were to measure the N₂O fluxes from a spring‐fed river, relate these fluxes to the dissolved N₂O concentrations and NO₃‐N loading of the river, and to try to define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N₂O L^?1. River NO₃‐N and dissolved N₂O concentrations ranged from 2.5 to 5.3 mg L^?1 and 0.4 to 1.9 μg N₂O‐N L^?1, respectively, with N₂O saturation reaching 404%. Floating headspace chambers were used to sample N₂O fluxes. N₂O‐N fluxes were significantly related to dissolved N₂O‐N concentrations (r²=0.31) but not to NO₃‐N concentrations. The N₂O‐N fluxes ranged from 38 to 501 μg m^?2 h^?1, averaging 171 μg m^?2 h^?1 (±SD 85) overall. The measured N₂O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N₂O present in the groundwater that fed the river.     

Trophic cascades: the primacy of trait-mediated indirect interactions

Trophic cascades are textbook examples of predator indirect effects on ecological systems. Yet there is considerable debate about their nature, strength and overall importance. This debate stems in part from continued uncertainty about the ultimate mechanisms driving cascading effects. We present a synthesis of empirical evidence in support of one possible ultimate mechanism: the foraging‐predation risk trade‐offs undertaken by intermediary species. We show that simple trade‐off behaviour can lead to both positive and negative indirect effects of predators on plant resources and hence can explain considerable contingency on the nature and strength of cascading effects among systems. Thus, predicting the sign and strength of indirect effect simply requires knowledge of habitat and resource use by prey with regard to predators’ presence, habitat use and hunting mode. The synthesis allows us to postulate a hypothesis for new conceptualization of trophic cascades which is to be viewed as an ultimate trade‐off between intervening species. In this context, different predators apply different rules of engagement based on their hunting mode and habitat use. These different rules then determine whether behavioural effects persist or attenuate at the level of the food chain.     

Comparison of measured and EF5-r-derived N2O fluxes from a spring-fed river

There is considerable uncertainty in the estimates of indirect N₂O emissions as defined by the intergovernmental panel on climate change's (IPCC) methodology. Direct measurements of N₂O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N₂O budget. The objectives of this research were to measure the N₂O fluxes from a spring‐fed river, relate these fluxes to the dissolved N₂O concentrations and NO₃‐N loading of the river, and to try and define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N₂O L^?1. River NO₃‐N and dissolved N₂O concentrations ranged from 2.5 to 5.3 mg L^?1 and 0.4 to 1.9 μg N₂O‐N L^?1, respectively, with N₂O saturation reaching 404%. Floating headspace chambers were used to sample N₂O fluxes. N₂O‐N fluxes were significantly related to dissolved N₂O‐N concentrations (r²=30.6) but not to NO₃‐N concentrations. The N₂O‐N fluxes ranged from 38–501 μg m^?2 h^?1, averaging 171 μg m^?2 h^?1 (±SD 85) overall. The measured N₂O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N₂O present in the groundwater that fed the river.     

The greenhouse gas intensity and potential biofuel production capacity of maize stover harvest in the US Midwest

Agricultural residues are important sources of feedstock for a cellulosic biofuels industry that is being developed to reduce greenhouse gas emissions and improve energy independence. While the US Midwest has been recognized as key to providing maize stover for meeting near‐term cellulosic biofuel production goals, there is uncertainty that such feedstocks can produce biofuels that meet federal cellulosic standards. Here, we conducted extensive site‐level calibration of the Environmental Policy Integrated Climate (EPIC) terrestrial ecosystems model and applied the model at high spatial resolution across the US Midwest to improve estimates of the maximum production potential and greenhouse gas emissions expected from continuous maize residue‐derived biofuels. A comparison of methodologies for calculating the soil carbon impacts of residue harvesting demonstrates the large impact of study duration, depth of soil considered, and inclusion of litter carbon in soil carbon change calculations on the estimated greenhouse gas intensity of maize stover‐derived biofuels. Using the most representative methodology for assessing long‐term residue harvesting impacts, we estimate that only 5.3 billion liters per year (bly) of ethanol, or 8.7% of the near‐term US cellulosic biofuel demand, could be met under common no‐till farming practices. However, appreciably more feedstock becomes available at modestly higher emissions levels, with potential for 89.0 bly of ethanol production meeting US advanced biofuel standards. Adjustments to management practices, such as adding cover crops to no‐till management, will be required to produce sufficient quantities of residue meeting the greenhouse gas emission reduction standard for cellulosic biofuels. Considering the rapid increase in residue availability with modest relaxations in GHG reduction level, it is expected that management practices with modest benefits to soil carbon would allow considerable expansion of potential cellulosic biofuel production.     

Transporting stochastic direct and indirect effects to new populations

Transported mediation effects may contribute to understanding how interventions work differently when applied to new populations. However, we are not aware of any estimators for such effects. Thus, we propose two doubly robust, efficient estimators of transported stochastic (also called randomized interventional) direct and indirect effects. We demonstrate their finite sample properties in a simulation study. We then apply the preferred substitution estimator to longitudinal data from the Moving to Opportunity Study, a large‐scale housing voucher experiment, to transport stochastic indirect effect estimates of voucher receipt in childhood on subsequent risk of mental health or substance use disorder mediated through parental employment across sites, thereby gaining understanding of drivers of the site differences.     

GHG emissions and other environmental impacts of indirect land use change mitigation

The implementation of measures to increase productivity and resource efficiency in food and bioenergy chains as well as to more sustainably manage land use can significantly increase the biofuel production potential while limiting the risk of causing indirect land use change (ILUC). However, the application of these measures may influence the greenhouse gas (GHG) balance and other environmental impacts of agricultural and biofuel production. This study applies a novel, integrated approach to assess the environmental impacts of agricultural and biofuel production for three ILUC mitigation scenarios, representing a low, medium and high miscanthus‐based ethanol production potential, and for three agricultural intensification pathways in terms of sustainability in Lublin province in 2020. Generally, the ILUC mitigation scenarios attain lower net annual emissions compared to a baseline scenario that excludes ILUC mitigation and bioethanol production. However, the reduction potential significantly depends on the intensification pathway considered. For example, in the moderate ILUC mitigation scenario, the net annual GHG emissions in the case study are 2.3 MtCO₂‐eq yr^?1 (1.8 tCO₂‐eq ha^?1 yr^?1) for conventional intensification and ?0.8 MtCO₂‐eq yr^?1 (?0.6 tCO₂‐eq ha^?1 yr^?1) for sustainable intensification, compared to 3.0 MtCO₂‐eq yr^?1 (2.3 tCO₂‐eq ha^?1 yr^?1) in the baseline scenario. In addition, the intensification pathway is found to be more influential for the GHG balance than the ILUC mitigation scenario, indicating the importance of how agricultural intensification is implemented in practice. Furthermore, when the net emissions are included in the assessment of GHG emissions from bioenergy, the ILUC mitigation scenarios often abate GHG emissions compared to gasoline. But sustainable intensification is required to attain GHG abatement potentials of 90% or higher. A qualitative assessment of the impacts on biodiversity, water quantity and quality, soil quality and air quality also emphasizes the importance of sustainable intensification.