Bioenergy Crops and Carbon Sequestration

Greenhouse gas (GHG) emissions constitute a global problem. The need for agricultural involvement in GHG mitigation has been widely recognized since the 1990s. The concept of C sinks, C credits, and emission trading has attracted special interests in herbaceous and woody species as energy crops and source of biofuel feedstock. Bioenergy crops are defined as any plant material used to produce bioenergy. These crops have the capacity to produce large volume of biomass, high energy potential, and can be grown in marginal soils. Planting bioenergy crops in degraded soils is one of the promising agricultural options with C sequestration rates ranging from 0.6 to 3.0 Mg C ha^?1 yr^?1. About 60 million hectares (Mha) of land is available in the United States and 757 Mha in the world to grow bioenergy crops. With an energy offset of 1 kg of C in biomass per 0.6 kg of C in fossil fuel, there exists a vast potential of offsetting fossil fuel emission. Bioenergy crops have the potential to sequester approximately 318 Tg C yr^?1 in the United States and 1631 Tg C yr^?1 worldwide. Bioenergy crops consist of herbaceous bunch-type grasses and short-rotation woody perennials. Important grasses include switchgrass (Panicum virgatum L.), elephant grass (Pennissetum purpureum Schum.), tall fescue (Fetusca arundinacea L.), etc. Important among short-rotation woody perennials are poplar (Populus spp.), willow (Salix spp.), mesquite (Prosopis spp.), etc. The emissions of CO₂ from using switchgrass as energy crop is 1.9 kg C Gj^?1 compared with 13.8, 22.3, and 24.6 kg C Gj^?1 from using gas, petroleum, and coal, respectively. Mitigation of GHG emissions cannot be achieved by C sinks alone, a substantial reduction in fossil fuel combustion will be necessary. Carbon sequestration and fossil fuel offset by bioenergy crops is an important component of a possible total societal response to a GHG emission reduction initiative.     

Greenhouse gas mitigation in agriculture

Agricultural lands occupy 37% of the earth's land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500-6000Mt CO2-eq.yr-1, with economic potentials of approximately 1500-1600, 2500-2700 and 4000-4300Mt CO2-eq.yr-1 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO2-eq.-1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000Mt CO2-eq.yr-1 at 0-20, 0-50 and 0-100 US$ t CO2-eq.-1, respectively.     

Determination of biogenic and fossil CO(2) emitted by waste incineration based on (14)CO(2) and mass balances

A field application of the radiocarbon ((14)C) method was developed to determine the ratio of biogenic vs. fossil CO(2) emissions from waste-to-energy plants (WTE). This methodology can be used to assign the Kyoto relevant share of fossil CO(2) emissions, which is highly relevant for emission budgets and emission trading. Furthermore, heat and electricity produced by waste incinerators might be labelled depending on the fossil or biogenic nature of the primary energy source. The method development includes representative on-site CO(2) absorption and subsequent release in the laboratory. Furthermore, a reference value for the (14)C content of pure biogenic waste (f(M,bio)) was determined as 1.130+/-0.038. Gas samples for (14)CO(2) analysis were taken at three WTEs during one month each. Results were compared to an alternative approach based on mass and energy balances. Both methods were in excellent agreement and indicated a fraction of biogenic CO(2) slightly above 50%.     

Cattle feed or bioenergy? Consequential life cycle assessment of biogas feedstock options on dairy farms

On‐farm anaerobic digestion (AD) of wastes and crops can potentially avoid greenhouse gas (GHG) emissions, but incurs extensive environmental effects via carbon and nitrogen cycles and substitution of multiple processes within and outside farm system boundaries. Farm models were combined with consequential life cycle assessment (CLCA) to assess plausible biogas and miscanthus heating pellet scenarios on dairy farms. On the large dairy farm, the introduction of slurry‐only AD led to reductions in global warming potential (GWP) and resource depletion burdens of 14% and 67%, respectively, but eutrophication and acidification burden increases of 9% and 10%, respectively, assuming open tank digestate storage. Marginal GWP burdens per Mg dry matter (DM) feedstock codigested with slurry ranged from –637 kg CO₂e for food waste to +509 kg CO₂e for maize. Codigestion of grass and maize led to increased imports of concentrate feed to the farm, negating the GWP benefits of grid electricity substitution. Attributing grass‐to‐arable land use change (LUC) to marginal wheat feed production led to net GWP burdens exceeding 900 kg CO₂e Mg^?1 maize DM codigested. Converting the medium‐sized dairy farm to a beef‐plus‐AD farm led to a minor reduction in GWP when grass‐to‐arable LUC was excluded, but a 38% GWP increase when such LUC was attributed to marginal maize and wheat feed required for intensive compensatory milk production. If marginal animal feed is derived from soybeans cultivated on recently converted cropland in South America, the net GWP burden increases to 4099 kg CO₂e Mg^?1 maize DM codigested – equivalent to 55 Mg CO₂e yr^?1 per hectare used for AD‐maize cultivation. We conclude that AD of slurry and food waste on dairy farms is an effective GHG mitigation option, but that the quantity of codigested crops should be strictly limited to avoid potentially large international carbon leakage via animal feed displacement.     

Plant roots and GHG mitigation in native perennial bioenergy cropping systems

Native perennial bioenergy crops can mitigate greenhouse gases (GHG) by displacing fossil fuels with renewable energy and sequestering atmospheric carbon (C) in soil and roots. The relative contribution of root C to net GHG mitigation potential has not been compared in perennial bioenergy crops ranging in species diversity and N fertility. We measured root biomass, C, nitrogen (N), and soil organic carbon (SOC) in the upper 90 cm of soil for five native perennial bioenergy crops managed with and without N fertilizer. Bioenergy crops ranged in species composition and were annually harvested for 6 (one location) and 7 years (three locations) following the seeding year. Total root biomass was 84% greater in switchgrass (Panicum virgatum L.) and a four‐species grass polyculture compared to high‐diversity polycultures; the difference was driven by more biomass at shallow soil depth (0–30 cm). Total root C (0–90 cm) ranged from 3.7 Mg C ha^?1 for a 12‐species mixture to 7.6 Mg C ha^?1 for switchgrass. On average, standing root C accounted for 41% of net GHG mitigation potential. After accounting for farm and ethanol production emissions, net GHG mitigation potential from fossil fuel offsets and root C was greatest for switchgrass (?8.4 Mg CO2e ha^?1 yr^?1) and lowest for high‐diversity mixtures (?4.5 Mg CO2e ha^?1 yr^?1). Nitrogen fertilizer did not affect net GHG mitigation potential or the contribution of roots to GHG mitigation for any bioenergy crop. SOC did not change and therefore did not contribute to GHG mitigation potential. However, associations among SOC, root biomass, and root C : N ratio suggest greater long‐term C storage in diverse polycultures vs. switchgrass. Carbon pools in roots have a greater effect on net GHG mitigation than SOC in the short‐term, yet variation in root characteristics may alter patterns in long‐term C storage among bioenergy crops.     

Implications of land class and environmental factors on life cycle GHG emissions of Miscanthus as a bioenergy feedstock

Replacement of fossil fuels with sustainably produced biomass crops for energy purposes has the potential to make progress in addressing climate change concerns, nonrenewable resource use, and energy security. The perennial grass Miscanthus is a dedicated energy crop candidate being field tested in Ontario, Canada, and elsewhere. Miscanthus could potentially be grown in areas of the province that differ substantially in terms of agricultural land class, environmental factors and current land use. These differences could significantly affect Miscanthus yields, input requirements, production practices, and the types of crops being displaced by Miscanthus establishment. This study assesses implications on life cycle greenhouse gas (GHG) emissions of these differences through evaluating five Miscanthus production scenarios within the Ontario context. Emissions associated with electricity generation with Miscanthus pellets in a hypothetically retrofitted coal generating station are examined. Indirect land use change impacts are not quantified but are discussed. The net life cycle emissions for Miscanthus production varied greatly among scenarios (?90–170 kg CO₂eq per oven dry tonne of Miscanthus bales at the farm gate). In some cases, the carbon stock dynamics of the agricultural system offset the combined emissions of all other life cycle stages (i.e., production, harvest, transport, and processing of biomass). Yield and soil C of the displaced agricultural systems are key parameters affecting emissions. The systems with the highest potential to provide reductions in GHG emissions are those with high yields, or systems established on land with low soil carbon. All scenarios have substantially lower life cycle emissions (?20–190 g CO₂eq kWh^?1) compared with coal‐generated electricity (1130 g CO₂eq kWh^?1). Policy development should consider the implication of land class, environmental factors, and current land use on Miscanthus production.     

The role of N2O derived from crop-based biofuels, and from agriculture in general, in Earth's climate

In earlier work, we compared the amount of newly fixed nitrogen (N, as synthetic fertilizer and biologically fixed N) entering agricultural systems globally to the total emission of nitrous oxide (N(2)O). We obtained an N(2)O emission factor (EF) of 3-5%, and applied it to biofuel production. For 'first-generation' biofuels, e.g. biodiesel from rapeseed and bioethanol from corn (maize), that require N fertilizer, N(2)O from biofuel production could cause (depending on N uptake efficiency) as much or more global warming as that avoided by replacement of fossil fuel by the biofuel. Our subsequent calculations in a follow-up paper, using published life cycle analysis (LCA) models, led to broadly similar conclusions. The N(2)O EF applies to agricultural crops in general, not just to biofuel crops, and has made possible a top-down estimate of global emissions from agriculture. Independent modelling by another group using bottom-up IPCC inventory methodology has shown good agreement at the global scale with our top-down estimate. Work by Davidson showed that the rate of accumulation of N(2)O in the atmosphere in the late nineteenth and twentieth centuries was greater than that predicted from agricultural inputs limited to fertilizer N and biologically fixed N (Davidson, E. A. 2009 Nat. Geosci. 2, 659-662.). However, by also including soil organic N mineralized following land-use change and NO(x) deposited from the atmosphere in our estimates of the reactive N entering the agricultural cycle, we have now obtained a good fit between the observed atmospheric N(2)O concentrations from 1860 to 2000 and those calculated on the basis of a 4 per cent EF for the reactive N.     

Ecosystem-Service Tradeoffs Associated with Switching from Annual to Perennial Energy Crops in Riparian Zones of the US Midwest

Integration of energy crops into agricultural landscapes could promote sustainability if they are placed in ways that foster multiple ecosystem services and mitigate ecosystem disservices from existing crops. We conducted a modeling study to investigate how replacing annual energy crops with perennial energy crops along Wisconsin waterways could affect a variety of provisioning and regulating ecosystem services. We found that a switch from continuous corn production to perennial-grass production decreased annual income provisioning by 75%, although it increased annual energy provisioning by 33%, decreased annual phosphorous loading to surface water by 29%, increased below-ground carbon sequestration by 30%, decreased annual nitrous oxide emissions by 84%, increased an index of pollinator abundance by an average of 11%, and increased an index of biocontrol potential by an average of 6%. We expressed the tradeoffs between income provisioning and other ecosystem services as benefit-cost ratios. Benefit-cost ratios averaged 12.06 GJ of additional net energy, 0.84 kg of avoided phosphorus pollution, 18.97 Mg of sequestered carbon, and 1.99 kg of avoided nitrous oxide emissions for every $1,000 reduction in income. These ratios varied spatially, from 2- to 70-fold depending on the ecosystem service. Benefit-cost ratios for different ecosystem services were generally correlated within watersheds, suggesting the presence of hotspots – watersheds where increases in multiple ecosystem services would come at lower-than-average opportunity costs. When assessing the monetary value of ecosystem services relative to existing conservation programs and environmental markets, the overall value of enhanced services associated with adoption of perennial energy crops was far lower than the opportunity cost. However, when we monitized services using estimates for the social costs of pollution, the value of enhanced services far exceeded the opportunity cost. This disparity between recoverable costs and social value represents a fundamental challenge to expansion of perennial energy crops and sustainable agricultural landscapes.     

Life cycle assessment of ethanol production from miscanthus: A comparison of production pathways at two European sites

Lignocellulosic ethanol represents a renewable alternative to petrol. Miscanthus, a perennial plant that grows on marginal land, is characterized by efficient use of resources and is considered a promising source of lignocellulosic biomass. A life cycle assessment (LCA) was performed to determine the environmental impacts of ethanol production from miscanthus grown on marginal land in Great Britain (Aberystwyth) and an average‐yield site in Germany (Stuttgart; functional unit: 1 GJ). As the conversion process has substantial influence on the overall environmental performance, the comparison examined three pretreatment options for miscanthus. Overall, results indicate lower impacts for the production in Stuttgart in comparison with the corresponding pathways in Aberystwyth across the analysed categories. Disparities between the sites were mainly attributed to differences in biomass yield. When comparing the conversion options, liquid hot water treatment resulted in the lowest impacts, followed by dilute sulphuric acid. Dilute sodium hydroxide pretreatment represented the least favourable option. Site‐dependent variation in biomass composition and degradability did not have substantial influence on the environmental performance of the analysed pathways. Additionally, implications of replacing petrol with miscanthus ethanol were examined. Ethanol derived from miscanthus resulted in lower impacts with respect to greenhouse gas emissions, fossil resource depletion, natural land transformation and ozone depletion. However, for other categories, including toxicity, eutrophication and agricultural land occupation, net scores were substantially higher than for the fossil reference. Nevertheless, the results indicate that miscanthus ethanol produced via dilute acid and liquid hot water treatment at the site in Stuttgart has the potential to comply with the requirements of the European Renewable energy directive for greenhouse gas emission reduction. For ethanol production at the marginal site, carbon sequestration needs to be considered in order to meet the requirements for greenhouse gas mitigation.     

Renewable Energy from Willow Biomass Crops: Life Cycle Energy,Environmental and Economic Performance

Short-rotation woody crops (SRWC) along with other woody biomass feedstocks will play a significant role in a more secure and sustainable energy future for the United States and around the world. In temperate regions, shrub willows are being developed as a SRWC because of their potential for high biomass production in short time periods, ease of vegetative propagation, broad genetic base, and ability to resprout after multiple harvests. Understanding and working with willow's biology is important for the agricultural and economic success of the system.

The energy, environmental, and economic performance of willow biomass production and conversion to electricity is evaluated using life cycle modeling methods. The net energy ratio (electricity generated/life cycle fossil fuel consumed) for willow ranges from 10 to 13 for direct firing and gasification processes. Reductions of 70 to 98 percent (compared to U.S. grid generated electricity) in greenhouse gas emissions as well as NO_x, SO₂, and particulate emissions are achieved.

Despite willow's multiple environmental and rural development benefits, its high cost of production has limited deployment. Costs will be lowered by significant improvements in yields and production efficiency and by valuing the system's environmental and rural development benefits. Policies like the Conservation Reserve Program (CRP), federal biomass tax credits and renewable portfolio standards will make willow cost competitive in the near term.

The avoided air pollution from the substitution of willow for conventional fossil fuel generated electricity has an estimated damage cost of $0.02 to $0.06 kWh^?1. The land intensity of about 4.9 × 10^?5 ha-yr/kWh is greater than other renewable energy sources. This may be considered the most significant limitation of willow, but unlike other biomass crops such as corn it can be cultivated on the millions of hectares of marginal agricultural lands, improving site conditions, soil quality and landscape diversity. A clear advantage of willow biomass compared to other renewables is that it is a stock resource whereas wind and PV are intermittent. With only 6 percent of the current U.S. energy consumption met by renewable sources the accelerated development of willow biomass and other renewable energy sources is critical to address concerns of energy security and environmental impacts associated with fossil fuels.     

China's bioenergy potential

Despite great enthusiasm about developing renewable energy in China, the country's bioenergy potential remains unclear. Traditional utilization of bioenergy through primarily household combustion of crop residue and fuelwood is still a predominant energy source for rural China. More efficient utilization of ～300 million tons of crop residues for bioelectricity generation could add a couple of percent of renewable energy to China's total energy production. With <9% of the world's arable land supporting ～20% of the world's population, China is already a net grain importer and has little extra farmland for producing a significantly additional amount of biofuels from first‐generation energy crops, such as maize, sugarcane, and soybean. Second‐generation energy crops hold the greatest potential for bioenergy development worldwide. Miscanthus, a native perennial C4 grass that produces high biomass across almost the entire climatic zone of China, is the most promising second‐generation energy crop to domesticate and cultivate. A reasonable near‐term goal is to produce 1 billion tons of Miscanthus biomass annually from ～100 million hectares of marginal and degraded land concentrated in northern and northwestern China. This can generate ～1458 TW h electricity and mitigate ～1.7 billion tons of CO₂ emission from power coal, which account for ～45% of China's electricity output and ～28% of CO₂ emission in 2007. Furthermore, growing perennial grasses on marginal and degraded land will contribute to the ongoing efforts in China to restore vast areas of land under serious threat of desertification. With this potential taken into account, bioenergy can play a major role in meeting China's rapidly growing energy demand while substantially reducing greenhouse gas emission.     

Emission scenario of non-CO2 gases from energy activities and other sources in China

This paper gives a quantitative analysis on the non-CO2 emissions related to energy demand, energy activities and land use change of six scenarios with different development pattern in 2030 and 2050 based on IPAC emission model. The various mitigation technologies and policies are assessed to understand the corresponding non-CO2 emission reduction effect. The research shows that the future non-CO2 emissions of China will grow along with increasing energy demand, in which thermal power and transportation will be the major emission and mitigation sectors. During the cause of future social and economic development, the control and mitigation of non-CO2 emissions is a problem as challenging and pressing as that of CO2 emissions.This study indicates that the energy efficiency improvement, renewable energy, advanced nuclear power generation, fuel cell, coal-fired combined cycle, clean coal and motor vehicle emission control technologies will contribute to non-CO2 emissions control and mitigation.     

Emission scenario of non-CO2 gases from energy activities and other sources in China

This paper gives a quantitative analysis on the non-CO2 emissions related to energy demand, energy activities and land use change of six scenarios with different development pattern in 2030 and 2050 based on IPAC emission model. The various mitigation technologies and policies are assessed to understand the corresponding non-CO2 emission reduction effect. The research shows that the future non-CO2 emissions of China will grow along with increasing energy demand, in which thermal power and transportation will be the major emission and mitigation sectors. During the cause of future social and economic development, the control and mitigation of non-CO2 emissions is a problem as challenging and pressing as that of CO2 emissions. This study indicates that the energy efficiency improvement, renewable energy, advanced nuclear power generation, fuel cell, coal-fired combined cycle, clean coal and motor vehicle emission control technologies will contribute to non-CO2 emissions control and mitigation.     

Atmospheric impact of bioenergy based on perennial crop (reed canary grass,Phalaris arundinaceae,L.) cultivation on a drained boreal organic soil

Marginal organic soils, abundant in the boreal region, are being increasingly used for bioenergy crop cultivation. Using long‐term field experimental data on greenhouse gas (GHG) balance from a perennial bioenergy crop [reed canary grass (RCG), Phalaris arundinaceae L.] cultivated on a drained organic soil as an example, we show here for the first time that, with a proper cultivation and land‐use practice, environmentally sound bioenergy production is possible on these problematic soil types. We performed a life cycle assessment (LCA) for RCG on this organic soil. We found that, on an average, this system produces 40% less CO₂‐equivalents per MWh of energy in comparison with a conventional energy source such as coal. Climatic conditions regulating the RCG carbon exchange processes have a high impact on the benefits from this bioenergy production system. Under appropriate hydrological conditions, this system can even be carbon‐negative. An LCA sensitivity analysis revealed that net ecosystem CO₂ exchange and crop yield are the major LCA components, while non‐CO₂ GHG emissions and costs associated with crop production are the minor ones. Net bioenergy GHG emissions resulting from restricted net CO₂ uptake and low crop yields, due to climatic and moisture stress during dry years, were comparable with coal emissions. However, net bioenergy emissions during wet years with high net uptake and crop yield were only a third of the coal emissions. As long‐term experimental data on GHG balance of bioenergy production are scarce, scientific data stemming from field experiments are needed in shaping renewable energy source policies.     

LCA of energetic biomass utilization: actual projects and new developments—April 23, 2012, Berne, Switzerland

Introduction

In the last years, the use of biomass for energy purposes has been seen as a promising option to reduce the use of nonrenewable energy sources and the emissions of fossil carbon. However, LCA studies have shown that the energetic use of biomass also causes impacts on climate change and, furthermore, that different environmental issues arise, such as land use and agricultural emissions. While biomass is renewable, it is not an unlimited resource. Its use, to whatever purpose, must therefore be well studied to promote the most efficient option with the least environmental impacts. The 47th LCA Discussion Forum gathered several national and international speakers who provided a broad and qualified view on the topic.

Summary of the topics presented in DF 47

Several aspects of energetic biomass use from a range of projects financed by the Swiss Federal Office of Energy (SFOE) were presented in this Discussion Forum. The first session focused on important aspects of the agricultural biogas production like the use of high energy crops or catch crops as well as the influence of plant size on the environmental performance of biogas. In the second session, other possibilities of biomass treatment like direct combustion, composting, and incineration with municipal waste were presented. Topic of the first afternoon session was the update and harmonization of biomass inventories and the resulting new assessment of biofuels. The short presentations investigated some further aspects of the LCA of bioenergy like the assessment of spatial variation of greenhouse gas (GHG) emissions from bioenergy production in a country, the importance of indirect land use change emissions on the overall results, the assessment of alternative technologies to direct spreading of digestate or the updates of the car operation datasets in ecoinvent.

Conclusions

One main outcome of this Discussion Forum is that bioenergy is not environmentally friendly per se. In many cases, energetic use of biomass allows a reduction of GHG and fossil energy use. However, there is often a tradeoff with other environmental impacts linked to agricultural production like eutrophication or ecotoxicity. Methodological challenges still exist, like the assessment of direct and indirect land use change emissions and their attribution to the bioenergy production, or the influence of heavy metal flows on the bioenergy assessment. Another challenge is the implementation of a life cycle approach in certification or legislation schemes, as shown by the example of the Renewable Energy Directive of the European Union.     

The issues of energy and carbon cycle: new perspectives for assessing the environmental impact of animal waste utilization

This paper focuses on the benefits of an efficient use of animal waste from the standpoint of curbing the rise of anthropogenic carbon dioxide (CO(2)) in the atmosphere. An effective use of animal waste resources might provide a partial, but still important, contribution in reducing net CO(2) emissions. In particular: the fulfillment of nutrient requirements of crop plants growing in non-limiting conditions and thus sequestering CO(2) at their potential level; the chance of diminishing the use of fossil energy, and related CO(2) emissions, required for manufacturing industrial fertilizers; the possibility of enhancing carbon sequestration in agricultural soils by the application of farmyard manure. The future success of agriculture in providing these ecosystem services can only be achieved with a changed social awareness of the links between sustainable land use and global environmental change.     

Lifecycle climate impact and primary energy use of electric and biofuel cargo trucks

Heavy trucks contribute significantly to climate change, and in 2020 were responsible for 7% of total Swedish GHG emissions and 5% of total global CO₂ emissions. Here we study the full lifecycle of cargo trucks powered by different energy pathways, comparing their biomass feedstock use, primary energy use, net biogenic and fossil CO₂ emission and cumulative radiative forcing. We analyse battery electric trucks with bioelectricity from stand-alone or combined heat and power (CHP) plants, and pathways where bioelectricity is integrated with wind and solar electricity. We analyse trucks operated on fossil diesel fuel and on dimethyl ether (DME). All energy pathways are analysed with and without carbon capture and storage (CCS). Bioelectricity and DME are produced from forest harvest residues. Forest biomass is a limited resource, so in a scenario analysis we allocate a fixed amount of biomass to power Swedish truck transport. Battery lifespan and chemistry, the technology level of energy supply, and the biomass source and transport distance are all varied to understand how sensitive the results are to these parameters. We find that pathways using electricity to power battery electric trucks have much lower climate impacts and primary energy use, compared to diesel- and DME-based pathways. The pathways using bioelectricity with CCS result in negative emissions leading to global cooling of the earth. The pathways using diesel and DME have significant and very similar climate impact, even with CCS. The robust results show that truck electrification and increased renewable electricity production is a much better strategy to reduce the climate impact of cargo transport than the adoption of DME trucks, and much more primary energy efficient. This climate impact analysis includes all fossil and net biogenic CO₂ emissions as well as the timing of these emissions. Considering only fossil emissions is incomplete and could be misleading.     

Meeting US biofuel goals with less land: the potential of Miscanthus

Biofuels from crops are emerging as a Jekyll & Hyde – promoted by some as a means to offset fossil fuel emissions, denigrated by others as lacking sustainability and taking land from food crops. It is frequently asserted that plants convert only 0.1% of solar energy into biomass, therefore requiring unacceptable amounts of land for production of fuel feedstocks. The C₄ perennial grass Miscanthus × giganteus has proved a promising biomass crop in Europe, while switchgrass ( Panicum virgatum ) has been tested at several locations in N. America. Here, replicated side-by-side trials of these two crops were established for the first time along a latitudinal gradient in Illinois. Over 3 years of trials, Miscanthus × giganteus achieved average annual conversion efficiencies into harvestable biomass of 1.0% (30 t ha⁻¹) and a maximum of 2.0% (61 t ha⁻¹), with minimal agricultural inputs. The regionally adapted switchgrass variety Cave-in-Rock achieved somewhat lower yields, averaging 10 t ha⁻¹. Given that there has been little attempt to improve the agronomy and genetics of these grasses compared with the major grain crops, these efficiencies are the minimum of what may be achieved. At this 1.0% efficiency, 12 million hectares, or 9.3% of current US cropland, would be sufficient to provide 133 × 10⁹ L of ethanol, enough to offset one-fifth of the current US gasoline use. In contrast, maize grain from the same area of land would only provide 49 × 10⁹ L, while requiring much higher nitrogen and fossil energy inputs in its cultivation.     

Effect of Change of Forest Carbon Storage on Net Carbon Dioxide Balance of Wood Use for Energy in Japan

This study analyzed the net carbon dioxide (CO₂) emission reductions between 2005 and 2050 by using wood for energy under various scenarios of forest management and energy conversion technology in Japan, considering both CO₂ emission reductions from replacement of fossil fuels and changes in carbon storage in forests. According to our model, wood production for energy results in a significant reduction of carbon storage levels in forests (by 46% to 77% in 2050 from the 2005 level). Thus, the net CO₂ emission reduction when wood is used for energy becomes drastically smaller. Conventional tree production for energy increases net CO₂ emissions relative to preserving forests, but fast‐growing tree production may reduce net CO₂ emissions more than preserving forests does. When wood from fast‐growing trees is used to generate electricity with gas turbines, displacing natural gas, the net CO₂ emission reduction from the combination of fast‐growing trees and electricity generation with gas turbines is about 58% of the CO₂ emission reduction from electricity generation from gas turbines alone in 2050, and an energy conversion efficiency of around 20% or more is required to obtain net reductions over the entire period until 2050. When wood is used to produce bioethanol, displacing gasoline, net reductions are realized after 2030, provided that heat energy is recovered from residues from ethanol production. These results show the importance of considering the change in carbon storage when estimating the net CO₂ emission reduction effect of the wood use for energy.     

Biofuels and other approaches for decreasing fossil fuel emissions from agriculture

Biofuels offer one method for decreasing emissions of carbon dioxide (CO2) from fossil fuels, thus helping to meet UK and EU targets for mitigating climate change. They also provide a rational option for land use within the EU that could be economically viable, provided that an appropriate financial and policy environment is developed. If 80% of current set‐aside land in the UK were used for production of biomass crops for electricity generation, about 3% of current UK electricity demand could be met from this source. Considering possibilities for increasing yields and land area devoted to such crops over the coming decades, this could possibly rise to 12%. These estimates exclude consideration of developments in electricity generation which should increase the efficiency of conversion. Also, the use of combined heat and power units at local level (e.g. on farms or in rural communities) gives additional energy saving. Dedicated biomass crops such as willow, poplar, miscanthus, switchgrass or reed canary grass are perennials: in comparison with annual arable crops they would be expected to deliver additional environmental benefits. The elimination of annual cultivation should give a more stable environment, beneficial for farmland biodiversity. Some increase in soil organic matter content is likely, leading to some sequestration of carbon in soil and long‐term improvements in soil quality. The impact on water quality may be positive as nitrate losses are small and a similar trend is expected for phosphate and pesticides. However, these crops may well use more water than arable crops so their impact on water resources could be negative – an issue for further research. Agricultural land can also be used to produce liquid fuels for use in transport. At present biodiesel can be produced from oilseed rape and ethanol from either sucrose in sugar beet or cellulose from virtually any plant material. In the short‐term, liquid biofuels are an easy option as they require little change to either agriculture or transport infrastructure. However, their benefits for CO2 emissions are much less than for biomass used for generating electricity. It is therefore necessary to debate the priorities for land use in this context.