Net Reduction In Greenhouse Gas Emissions Research Articles

Evaluating the near- and long-term role of carbon dioxide removal in meeting global climate objectives

The 6th Assessment Report from the Intergovernmental Panel on Climate Change lacked sufficient land-sector scenario information to estimate total carbon dioxide removal deployment. Here, using a dataset of land-based carbon dioxide removal based on the scenarios assessed by the Intergovernmental Panel on Climate Change, we show that removals via afforestation and reforestation play a critical near-term role in mitigation, accounting for around 10% (median) of the net greenhouse gas emission reductions between 2020 and 2030 in scenarios that limit warming to 1.5 °C with limited overshoot. Novel carbon dioxide removal technologies such as direct air carbon capture and storage scale to multi-gigatonne levels by 2050 and beyond to balance residual emissions and draw down warming. We show that reducing fossil fuel and deforestation emissions (gross emissions) accounts for over 80% of net greenhouse gas reductions until global net zero carbon dioxide (CO2) independent of climate objective stringency. We explore the regional distributions of gross emissions and total carbon dioxide removal in cost-effective mitigation pathways and highlight the importance of incorporating fairness and broader sustainability considerations in future assessments of mitigation pathways with carbon dioxide removal.

A literature-based comparison of embodied GHG emissions of forced main sewer additives with potential reductions in methane generation

Abstract Fugitive emissions of methane (CH4) from force main sewers are of increasing concern. Dosing of additives into force main sewers could be employed to mitigate methane emissions. However, all additives will have embodied greenhouse gas (GHG) emissions. This study examined commonly employed additives in terms of modes of action and potential to mitigate methane generation. Typical dosing strategies reported in the literature for each chemical were compiled and their embodied GHG emissions were summarised from sources in the literature. The net emissions considering mitigated methane generation and embodied GHG emissions were calculated on the basis of typical usage reported in the literature. The results revealed that biofilm shocking strategies and addition of iron have the greatest net reduction in GHG emissions. There is, however, uncertainty associated with the mechanisms by which iron reduces CH4 generation in force mains. Furthermore, future changes in the sourcing of iron may increase its embodied emissions. A qualitative assessment of the impacts of additive use on downstream GHG emissions revealed that they are highly case specific.

Estimated Impacts of Smart Water Meter Implementation on Domestic Hot Water Consumption and Related Greenhouse Gas Emissions from Case Studies

This study investigates the water–energy–carbon (WEC) nexus in cities across four countries, namely the United Kingdom (UK), the United States of America (USA), Australia (AUS), and South Korea (KOR), over a decade, from 2011 to 2021. The primary objective is to assess the impact of smart water metering (SWM) implementation on the WEC nexus, with a specific focus on domestic hot water (DHW) consumption and associated greenhouse gas (GHG) emissions. The analysis of the collected data reveals diverse patterns among cities with varying levels of SWM implementation. Notably, cities with higher SWM implementation demonstrated significant reductions in water consumption, indicating the effectiveness of the efficient water consumption and demand management achieved through SWM. The study emphasizes the importance of addressing GHG emissions related to water heating, with the carbon intensity of water heating identified as a critical factor in this context. To achieve net reductions in GHG emissions, intensive efforts are required to simultaneously decrease both DHW consumption and the carbon intensity of water heating. The research findings highlight the potential for substantial GHG emissions reductions by combining SWM implementation with the decarbonization of water heating. By recognizing the interdependencies within WEC systems, this study underscores the significance of SWM in advancing toward a carbon-neutral society. In conclusion, this study contributes valuable insights into the WEC nexus and emphasizes the role of SWM in achieving sustainability goals. It advocates for integrated policies to effectively address the interconnected issues of the WEC nexus for effective climate change mitigation.

Temporal and Spatial Distribution, Utilization Status, and Carbon Emission Reduction Potential of Straw Resources in China

Temporal and Spatial Distribution, Utilization Status, and Carbon Emission Reduction Potential of Straw Resources in China

Spatiotemporally explicit pathway and material-energy-emission nexus of offshore wind energy development in China up to the year 2060

The temporal dynamics (e.g., pace and scale) and spatial heterogeneity (e.g., turbine location and wind speed) of offshore wind power systems (WPS) are critical to maximize the carbon gains from wind energy development and avoid trade-offs among climate, resources, and waste targets. However, such a spatiotemporally refined understanding of WPS development and the associated material cycle, energy use, and greenhouse gas (GHG) emissions is largely missing from the current research. In this study, we deployed a spatialized, technology-specific, stock-driven material flow analysis model to reveal the spatiotemporally explicit pathway of China's offshore WPS development and the associated material-energy-emission nexus up to the year 2060. Our results indicate a cumulative raw material requirement of 96–140 Mt, waste generation of 6.5–48 Mt, net energy payback of 2.9–12 PWh, and net reduction in GHG emissions of 2.9 – 9.7 Gt when substituting coal power until 2060 under different scenario combinations. Specifically, China's future offshore WPS development will need to address the increasing demand for critical materials (e.g., 3.8–5.2 Mt of copper and 55–140 kt of permanent magnets cumulatively until 2060) and challenges for end-of-life management (e.g., 0.3–2 Mt spent blades generated cumulatively until 2060). The spatiotemporally refined results that consider, among other key parameters, water depth and capacity factor at a 1 × 1 km resolution, revealed low values in the northern provinces (e.g., Hebei and Tianjin) and high values in the southern provinces (e.g., Guangdong and Fujian) for material flows, energy payback, and net GHG emission reduction. This combination of spatial and dynamic material flow analyses can also be applied to WPSs in other countries and regions.

Food Security and Climate Stabilization: Can Cereal Production Systems Address Both?

There is abundant evidence that greenhouse gas (GHG) emissions of cereal products, expressed per ton of grain output, have been trending downward over the past 20 years. This has largely been achieved through agricultural intensification that has concurrently increased area-based GHG emissions. The challenge is for agriculture to increase grain yields to meet the food demands of a growing world population while also contributing to climate stabilization goals by reducing net GHG emissions. This study assessed yield-based and area-based emissions and efficiencies for the winter wheat–summer maize (WWSM) rotation system over the period 1996 to 2016 using long-term, longitudinal, farm survey data and detailed soil emission data in Huantai county, Shandong Province, which is an archetype for cereal production across the North China Plain (NCP). In this region, yields have been increasing over time. However, nitrogen fertilizer inputs have decreased substantially with greater adoption of soil nutrient testing. In addition, there has been widespread adoption of residue incorporation into soils. As such, since 2002, the product carbon footprints of wheat and maize have reduced by 25% and 30%, respectively. Meanwhile, area-based carbon footprints for the rotation system have reduced by around 15% over the same period. These findings demonstrate the importance of detailed assessment of soil N2O emissions and rates of soil organic carbon sequestration. They also show the potential for net reductions in GHG emissions in cropping without loss of grain yields.

Climate change mitigation in British Columbia\u2019s forest sector: GHG reductions, costs, and environmental impacts

BackgroundThe potential contributions from forest-based greenhouse gas (GHG) mitigation actions need to be quantified to develop pathways towards net negative emissions. Here we present results from a comparative analysis that examined mitigation options for British Columbia’s forest sector. Mitigation scenarios were evaluated using a systems perspective that takes into account the changes in emissions and removals in forest ecosystems, in harvested wood product (HWP) carbon stocks, and in other sectors where wood products substitute for emission-intensive materials and fossil fuels. All mitigation activities were assessed relative to a forward-looking ‘business as usual’ baseline for three implementation levels. In addition to quantifying net GHG emission reductions, we assessed economic, and socio-economic impacts as well as other environmental indicators relating to forest species, age class, deadwood availability and future timber supply. We further considered risks of reversal for land-based scenarios, by assessing impacts of increasing future wildfires on stands that were not harvested.ResultsOur spatially explicit analyses of forest sector mitigation options demonstrated a cost-effective portfolio of regionally differentiated scenarios that directed more of the harvested wood to longer-lived wood products, stopped burning of harvest residues and instead produced bioenergy to displace fossil fuel burning, and reduced harvest levels in regions with low disturbance rates. Domestically, net GHG emissions were reduced by an average of -9 MtCO2e year−1 over 2020–2050 for a portfolio of mitigation activities at a default implementation level, with about 85% of the GHG emission reductions achieved below a cost of $50/tCO2e. Normalizing the net GHG reduction by changes in harvested wood levels permitted comparisons of the scenarios with different ambition levels, and showed that a 1 MtCO2 increase in cumulative harvested stemwood results in a 1 MtCO2e reduction in cumulative emissions, relative to the baseline, for the Higher Recovery scenario in 2070.ConclusionsThe analyses conducted in this study contribute to the global understanding of forest sector mitigation options by providing an integrated framework to synthesize the methods, assumptions, datasets and models needed to quantify mitigation activities using a systems approach. An understanding of economically feasible and socio-economically attractive mitigation scenarios along with trade offs for environmental indicators relating to species composition and age, helps decision makers with long-term planning for land sector contributions to GHG emission reduction efforts, and provides valuable information for stakeholder consultations.

Spatial and life cycle assessment of bioenergy-driven land-use changes in Ireland

Bioenergy crops are forecast to play a significant role if Ireland is to reach the 2020 and beyond targets set by the European Union's Renewable Energy Directive (RED). The aim of this study is to evaluate the environmental impacts associated with the cultivation of bioenergy crops in Ireland including land-use change (LUC) emissions by using geographical information systems (GIS) and Life Cycle Assessment (LCA). In this study, GIS is used to identify, and measure LUC changes associated with cultivation of Miscanthus and Short Rotation Coppice (SRC) willow. An LCA study was carried out to estimate the greenhouse gas (GHG) emissions from the LUC caused by the cultivation of bioenergy crops. The results find that miscanthus caused 86% of all LUC with SRC Willow accounting for 14%. The LCA results identify two major processes that contribute to total GHG emissions; field operations and loss of soil organic carbon (SOC) stocks. Land preparation, harvesting and the production of synthetic fertiliser are found to be the most significant contributors to field emissions. SOC emission for the conversion of pasture to SRC willow accounts for a large proportion of the overall GHG emissions. Conversion of arable land to miscanthus and SRC willow both cause a net reduction of GHG emissions. Sensitivity analysis on the type of fertilisers used and the inclusion of indirect land-use changes (iLUC), highlight the impacts that these have on the overall system performance. The replacement of synthetic fertiliser with biogenic fertiliser reduced overall GHG emissions. The inclusion of general iLUC data results in a large increase in total GHG emissions because of displaced food crops that must be grown elsewhere. The study shows that conversion of arable to miscanthus and SRC willow is preferable when cultivating bioenergy crops while conversion of pasture to SRC willow should be avoided.

Consequential life cycle assessment of automotive material substitution: Replacing steel with aluminum in production of north American vehicles

The substitution of aluminum for steel in vehicle body and closure components is a common strategy for reducing fuel consumption. In order to assess the greenhouse gas (GHG) consequences of this decision, the system must be examined using a life cycle approach. Furthermore, attributional life cycle assessment (ALCA) does not suffice for a number of reasons, including the fact that ALCA does not model the incremental system and that allocating the benefits of recycling inhibits the modelling of system-wide consequences caused by the decision studied. This study thus uses a consequential life cycle assessment (CLCA) framework. We examine the physical and economic processes that guide the North American light-duty vehicle fleet from its initial state in 2012 to a state in 2050. Industry projections are used to model the production and use phases. The system is expanded to include the scrap and material markets. This generates new insights regarding the environmental consequences of changes in scrap generation and recycling in automotive material substitution. The method is applied to the fleet in order to forecast if and when aluminum intensification constitutes net GHG reduction under various conditions. Using baseline parameter values compiled from public and industry data; we calculate a GHG payback period of 25 years, i.e. before a net reduction in emissions relative to a no change counterfactual is achieved. A local sensitivity analysis is performed, showing that the net GHG reduction may be achieved in a period as short as 12 years, or never be achieved at all. A global sensitivity analysis is performed using Monte Carlo simulation, where 16% of trials never reach a net reduction in GHG emissions. We also estimate which parameters contribute the most to variance in the model outcomes. The material replacement coefficient, or the amount of aluminum it takes to functionally replace one kilogram of steel, is the top contributor to the variance (29.8%). Overall, the results are most sensitive to parameters governing the amount of mass that can be replaced by each kilogram of additional aluminum, the GHG intensity of additional aluminum production, and the response of the aluminum scrap and material markets to additional aluminum scrap generation. We conclude that given the current lack of understanding of key parameters and their underlying uncertainties, it is not possible to definitively state that substituting aluminum for steel results in a net reduction in GHG emissions from a fleet of vehicles.

Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China?

To increase energy security and reduce emissions of air pollutants and CO2 from coal use, China is attempting to duplicate the rapid development of shale gas that has taken place in the United States. This work builds a framework to estimate the lifecycle greenhouse gas (GHG) emissions from China's shale gas system and compares them with GHG emissions from coal used in the power, residential, and industrial sectors. We find the mean lifecycle carbon footprint of shale gas is about 30-50% lower than that of coal in all sectors under both 20 year and 100 year global warming potentials (GWP20 and GWP100). However, primarily due to large uncertainties in methane leakage, the upper bound estimate of the lifecycle carbon footprint of shale gas in China could be approximately 15-60% higher than that of coal across sectors under GWP20. To ensure net GHG emission reductions when switching from coal to shale gas, we estimate the breakeven methane leakage rates to be approximately 6.0%, 7.7%, and 4.2% in the power, residential, and industrial sectors, respectively, under GWP20. We find shale gas in China has a good chance of delivering air quality and climate cobenefits, particularly when used in the residential sector, with proper methane leakage control.

Comparative life cycle assessment of biowaste to resource management systems – A Danish case study

Waste to Energy combustion plants currently process most of the organic fraction of the household waste. This study presents an assessment of the environmental performance of an increased circular bioresource management system obtained by reallocating the organic fraction of the household waste from combustion (Reference Scenario) to biogas and fertilizer production (Alternative Scenario). The goals defined in the Danish National resource action plan for waste management, i.e. 33% reduction of organic fraction household waste dry weight, is taken as a case study. A comparative life cycle assessment of the diverting of the organic fraction of the household waste away from a Waste to Energy combustion plant towards sludge- and manure-based biogas plants in North Zealand (Denmark) shows a net increase in renewable electricity production of 39% at the expense of a reduction in heat production of 8%. Moving up the waste hierarchy results in a net greenhouse gas emission reduction of 100 kg CO2eq. per ton of dry weight biowaste treated, corresponding to a 10% of reduction in CO2 emission. The latter accompanied by a net reduction in depletion of fossil resources of 11% and a reduction in the impacts on Freshwater and Marine Eutrophication of 4.8 t P eq. and 3.6 t N eq., respectively. As such, the modelled increased circular bioresource management indicates significant improvement of the efficiency in use of resources in biowaste. However, trade-offs occur due to the presence of micropollutants in the natural fertilizers that results in future increased damage cost on terrestrial ecosystems and human health exists.

Life cycle greenhouse gas analysis of bioenergy generation alternatives using forest and wood residues in remote locations: A case study in British Columbia, Canada

Utilization of forest and wood residues as bioenergy feedstock in some remote communities could reduce environmental burdens and increase development opportunities. In a thorough bioenergy project planning, in addition to the economic performance, the potential greenhouse gas (GHG) emissions from investment alternatives should be considered. We present an economic assessment and a life cycle analysis of GHG emissions of alternative bioenergy systems, which include four combustion and gasification technologies with different capacities (0.5MW, 2MW and 5MW), in two remote communities in British Columbia, Canada. In the analysis, all stages from harvesting to energy production are included, and the GHG emissions of the baseline system in each community (the current situation with all the products and services it provides) are used as the reference for comparison. Results of this study show that for small scale alternatives (0.5MW and 2MW), cogenerating plants using boiler/steam turbines generate the cheapest electricity, while for larger scale alternatives (5MW), the most economical plant alternative is a gasification cogeneration system. In the community where all energy needs are currently satisfied using fossil fuels, and all biomass residues (forest and sawmill residues) are currently disposed by burning, net reductions of up to 40,909t of CO2 equivalent GHG emissions could be achieved with the installation of a 5MW boiler/steam turbine cogenerating heat and electricity. In the community where the current energy mix is mostly supplied from other renewable sources (i.e. hydro), and where forest residues are disposed by burning and sawmill residues are landfilled, the net GHG emission reductions that can be achieved with a bioenergy system are considerably lower (2535t of CO2 equivalent emissions with a 5MW cogenerating gasification system) or null, since the carbon capture of current biomass disposal in landfill outweighs the carbon emission reduction of most bioenergy alternatives.

Systematic Exploration of Efficient Strategies to Manage Solid Waste in U.S. Municipalities: Perspectives from the Solid Waste Optimization Life-Cycle Framework (SWOLF)

Solid waste management (SWM) systems must proactively adapt to changing policy requirements, waste composition, and an evolving energy system to sustainably manage future solid waste. This study represents the first application of an optimizable dynamic life-cycle assessment framework capable of considering these future changes. The framework was used to draw insights by analyzing the SWM system of a hypothetical suburban U.S. city of 100 000 people over 30 years while considering changes to population, waste generation, and energy mix and costs. The SWM system included 3 waste generation sectors, 30 types of waste materials, and 9 processes for waste separation, treatment, and disposal. A business-as-usual scenario (BAU) was compared to three optimization scenarios that (1) minimized cost (Min Cost), (2) maximized diversion (Max Diversion), and (3) minimized greenhouse gas (GHG) emissions (Min GHG) from the system. The Min Cost scenario saved $7.2 million (12%) and reduced GHG emissions (3%) relative to the BAU scenario. Compared to the Max Diversion scenario, the Min GHG scenario cost approximately 27% less and more than doubled the net reduction in GHG emissions. The results illustrate how the timed-deployment of technologies in response to changes in waste composition and the energy system results in more efficient SWM system performance compared to what is possible from static analyses.

Evaluation of the Effect of Agricultural Management on Energy Yield and Greenhouse Gas Emission Reduction of Bioenergy Production Chains

The role of energy crops in reducing fossil energy use and greenhouse gas emission is much debated. To improve decision making on the use of crops for producing bioenergy, a tool (Energy Crop Simulation Model or E-CROP) has been developed to calculate 1) sustainable crop dry matter yield levels as function of agricultural inputs, and 2) gross and net energy yield and greenhouse gas emission reduction, covering the entire bioenergy production chain from sowing to distribution of bioenergy. E-CROP can be applied to a wide range of crops, soils, climatic conditions, management choices, and conversion technologies. This paper describes E-CROP and focuses on its application on four arable crops, as cultivated on two contrasting sites in the Netherlands (potato and sugar beet for bioethanol, winter oilseed rape for biodiesel and silage maize for bioelectricity) and on the effect of crop management (viz. irrigation and nitrogen fertilisation). In all situations, gross energy output exceeded total energy input. Calculated for an average situation, net energy yield ranged from 45 to 140 GJ.ha-1. Lowering irrigation and/or fertilisation input levels generally resulted in a reduction of net energy yields. The net reduction of greenhouse gas emissions in the average situation ranged from 0.60 to 6.5 t CO2-eq.ha-1. In general, N2O emission from nitrogen fertiliser caused large variations in the net reduction of greenhouse gas emission, which even became negative in some situations. Lowering nitrogen fertilisation to levels that are suboptimal for net energy yields enhanced the net reduction in greenhouse gas emission, implicating that both goals cannot be optimised simultaneously. Agricultural knowledge is important for optimising the outputs of bioenergy production chains.

Energy cost and greenhouse gas emissions of a Chinese solar tower power plant

It is commonly assumed that the application of solar power system can save energy and relief global climate change. Presented in this study is the account of energy performance and greenhouse gas emissions of a planned solar tower power plant in China based on the life cycle analysis method. The conservative estimation of energy cost for the concerned plant is 1.21 times of the electricity output, which is a relatively decent performance amongst power generation technologies. In order to analyze the greenhouse gas performance, a comparison is carried out between the solar tower power plant and conventional coal-fired power plant in China. Results show the application of this solar system obtains a net greenhouse gas emission reduction of 0.31E+06 ton CO2 equivalent, during its operating period of twenty years. It is believed that this successful example can lend solid support to a future wide use of solar power in China.

Reduction in greenhouse gas emissions due to the use of bio-ethanol from wheat grain and straw produced in the south-eastern USA

SUMMARYBiofuels can reduce greenhouse gas (GHG) emissions by replacing fossil fuels. However, the energy yield from agronomic crops varies due to local climate, weather and soil variability. A variation in the yield of raw material used (feedstock) could also cause variability in GHG reductions if biofuels are used. The goal of the present study was to determine the net reduction of GHG emissions if ethanol from wheat produced in different regions of the south-eastern USA is used as an alternative to gasoline from fossil fuel sources. Two scenarios were investigated; the first included ethanol produced from grain only, and the second included ethanol produced from both grain and wheat straw. Winter wheat yield was simulated with the Cropping System Model (CSM)-CERES-Wheat model for climate, soil and crop management representing six counties in the following USA states: Alabama, Florida and Georgia. Ethanol production was determined from the simulated grain and straw yields together with fixed grain and straw yield ethanol ratios. Subsequently, net reductions in GHG emissions were determined by accounting for the emissions from the replaced gasoline, and by animal feed and electricity that were replaced by ethanol processing co-products. Greenhouse gases that were emitted in the ethanol production chain were also taken into account. Across all locations, the reduction in GHG emissions was 187 g CO2-equivalents/km in the grain-only scenario and 208 g CO2-equivalents/km in the grain and straw scenario. The reductions in GHG emissions varied significantly between locations and growing seasons within the two scenarios. Similar approaches could be applied to assess the environmental impact of GHG emissions from other biofuels.

Primary energy and greenhouse gas implications of increasing biomass production through forest fertilization

In this study we analyze the primary energy and greenhouse gas (GHG) implications of increasing biomass production by fertilizing 10% of Swedish forest land. We estimate the primary energy use and GHG emissions from forest management including production and application of N and NPK fertilizers. Based on modelled growth response, we then estimate the net primary energy and GHG benefits of using biomaterials and biofuels obtained from the increased forest biomass production. The results show an increased annual biomass harvest of 7.4 million t dry matter, of which 41% is large-diameter stemwood. About 6.9 PJ/year of additional primary energy input is needed for fertilizer production and forest management. Using the additional biomass for fuel and material substitution can reduce fossil primary energy use by 150 or 164 PJ/year if the reference fossil fuel is fossil gas or coal, respectively. About 22% of the reduced fossil energy use is due to material substitution and the remainder is due to fuel substitution. The net annual primary energy benefit corresponds to about 7% of Sweden's total primary energy use. The resulting annual net GHG emission reduction is 11.9 million or 18.1 million tCO 2equiv if the reference fossil fuel is fossil gas or coal, respectively, corresponding to 18% or 28% of the total Swedish GHG emissions in 2007. A significant one-time carbon stock increase also occurs in wood products and forest tree biomass. These results suggest that forest fertilization is an attractive option for increasing energy security and reducing net GHG emission.

Potential of Municipal Solid Waste for Renewable Energy Production and Reduction of Greenhouse Gas Emissions in South Korea

Energy from waste (EfW) for nonrecyclable wastes is a suitable method of waste management and is important for renewable energy production. South Korea currently recycles 57% of household waste and landfills 26%. The remaining 17% is incinerated, mainly for heat production. In this study, the potential for energy production and reduction of corresponding greenhouse gas (GHG) emissions from municipal solid waste (MSW) in Korea was estimated without accounting for the lifecycle impact of waste management. The properties of the MSW were established from data available in national-scale waste surveys and reports. The potential of EfW for GHG emission reduction was calculated considering (1) the direct release of anthropogenic carbon, nitrous oxide (N2O), and methane (CH4); and (2) the reduction in indirect GHG emissions by fossil fuel displacement. CH4 emissions from landfilling were also estimated from biogenic carbon in waste. Applying the resulting emission factors to various EfW cases suggests that the current level of GHG emissions is significant but can be substantially reduced by increased use of EfW. A net reduction in GHG emissions can be achieved only by EfW with combined heat and power (CHP).

Miscanthus and willow heat production—An effective land-use strategy for greenhouse gas emission avoidance in Ireland?

Recent decoupling of EU direct payments from agricultural production, to land-area-based payments, has accelerated the national trend of declining livestock numbers, presenting opportunities for new agricultural products. This paper uses life-cycle analyses to quantify the national magnitude and area-based efficiency of greenhouse gas (GHG) emission reductions possible from utilising indigenously grown willow and Miscanthus as heating fuels in domestic/commercial premises. Willow and Miscanthus fuel-chain emissions were calculated at 0.045 and 0.062 kg CO 2 eq. kWh th, compared with 0.248, 0.331 and 0.624 kg CO 2 eq. kWh th for gas, oil and electric heat, respectively. Long-term soil C sequestration where willow and Miscanthus are grown on tillage land could exceed fuel-chain emissions, resulting in heat production better than C-neutral. Net GHG emission reductions ranged from 7671 kg CO 2 eq. ha −1 a −1 where willow displaced grassland and gas to 34,187 kg CO 2 eq. ha −1 a −1 where Miscanthus displaced set-aside and electric heat. A simple, indicative scenario assumed that energy-crops were grown on set-aside and destocked grassland in the ratio of 1:2, and displaced a total of 4728 GWh th combined gas, oil and electric heat. Consequent net GHG emission reductions arising from sole utilisation of either willow or Miscanthus equated to 2.6% or 2.5% of 2004 national emissions, and required just 2.9% or 2.1% of Ireland's agricultural land area. Net total emission reductions were relatively insensitive to variation in yield and cultivation emissions, but large reductions associated with electric-heat displacement will decline as electricity production becomes less GHG-intensive, and may not be representative of other countries. Energy-crop heat production offers considerably greater GHG emission reduction potential compared with agricultural destocking alone, and appears to represent an efficient land-use option for this purpose.

Estimated N2O and CO2Emissions as Influenced by Agricultural Practices in Canada

The Denitrification-Decompostion (DNDC) model was used to estimate the impact of change in management practices on N2O emissions in seven major soil regions in Canada, for the period 1970 to 2029. Conversion of cultivated land to permanent grassland would result in the greatest reduction in N2O emissions, particularly in eastern Canada wherethe model estimated about 60% less N2O emissions for thisconversion. About 33% less N2O emissions were predicted for a changefrom conventional tillage to no-tillage in western Canada, however, a slight increase in N2O emissions was predicted for eastern Canada. GreaterN2O emissions in eastern Canada associated with the adoption of no-tillage were attributed to higher soil moisture causing denitrification, whereas the lower emissions in western Canada were attributed to less decomposition of soil organic matter in no-till versus conventional tilled soil. Elimination of summer fallow in a crop rotation resulted in a 9% decrease in N2O emissions, with substantial emissions occurringduring the wetter fallow years when N had accumulated. Increasing N-fertilizer application rates by 50% increased average emissions by 32%,while a 50% decrease of N-fertilizer application decreased emissions by16%. In general, a small increase in N2O emissions was predicted when N-fertilizer was applied in the fall rather than in the spring. Previous research on CO2 emissions with the CENTURY model (Smith et al.,2001) allowed the quantification of the combined change in N2O andCO2 emissions in CO2 equivalents for a wide range of managementpractices in the seven major soil regions in Canada. The management practices that have the greatest potential to reduce the combined N2O andCO2 emissions are conversion from conventional tillage to permanent grassland, reduced tillage, and reduction of summer fallow. The estimated net greenhouse gas (GHG) emission reduction when changing from cultivated land to permanent grassland ranged from 0.97 (Brown Chernozem) to 4.24 MgCO2 equiv. ha−1 y−1 (BlackChernozem) for the seven soil regions examined. When changing from conventional tillage to no-tillage the net GHG emission reduction ranged from 0.33 (Brown Chernozem) to 0.80 Mg CO2 equiv. ha−1 y−1 (Dark GrayLuvisol). Elimination of fallow in the crop rotation lead to an estimated net GHG emission reduction of 0.43 (Brown Chernozem) to 0.80 Mg CO2 equiv.ha−1 y−1 (Dark Brown Chernozem). The addition of 50% more or 50% less N-fertilizer both resulted in slight increases in combined CO2 and N2O emissions. There was a tradeoff in GHG flux with greaterN2O emissions and a comparable increase in carbon storage when 50% more N-fertilizer was added. The results from this work indicate that conversion of cultivated land to grassland, the conversion from conventional tillage to no-tillage, and the reduction of summerallow in crop rotations could substantially increase C sequestration and decrease net GHG emissions. Based on these results a simple scaling-up scenario to derive the possible impacts on Canada's Kyoto commitment has been calculated.