Climate Change and...
Effects of Climate Change
- Climate Variability
- Climate Models
Effects of Climate Change
Energy, Alternative Energy, Biofuels and Biomass
ABSTRACT: Corn (Zea mays L.) stover is considered one of the prime lignocellulosic feedstocks for biofuel production. While producing renewable energy from biomass is necessary, impacts of harvesting corn stover on soil organic carbon (SOC) sequestration, agricultural productivity, and environmental quality must be also carefully and objectively assessed. We conducted a 2 1/2 year study of stover management in long-term (> 8 yr) no-tillage (NT) continuous corn systems under three contrasting soils in Ohio to determine changes in SOC sequestration, CO2 emissions, soil physical properties, and agronomic productivity. These measurements were made on a Rayne silt loam (RSL) (fine-loamy, mixed, active, mesic Typic Hapludult) with 6% slope, Celina silt loam (CSL) (fine, mixed, active, mesic Aquic Hapludalfs) with 2% slope, and Hoytville clay loam (HCL) (fine, illitic, mesic Mollic Epiaqualfs) with < 1% slope. Stover treatments consisted of removing 0, 25, 50, 75, and 100% of corn stover following each harvest. At the start of the experiment in May 2004, these percentages of removal corresponded to 5, 3.75, 2.5, 1.25, and 0 Mg ha−1 yr−1 of stover left on the soil surface, respectively. Annual stover removal rate of > 25% reduced SOC and soil productivity, but the magnitude of impacts depended on soil type and topographic conditions. Stover removal rate of 50% reduced grain yield by about 1.94 Mg ha−1 , stover yield by 0.97 Mg ha−1 , and SOC by 1.63 Mg ha−1 in an unglaciated, sloping, and erosion-prone soil (P < 0.05). The initial water infiltration rates were significantly reduced by > 25% of stover removal on a RSL and CSL. Plant available water reserves and earthworm population were significantly reduced by 50% of stover removal at all soils. Increases in soil compaction due to stover removal were moderate. Stover removal impacts on SOC, crop yield, and water infiltration for HCL were not significant. Results from this study following 2 1/2 yr of stover management suggest that only a small fraction (≤ 25%) of the total corn stover produced can be removed for biofuel feedstocks from sloping and erosion-prone soils.
ABSTRACT: The promise of low-input high-diversity prairies to provide sustainable bioenergy production has recently been emphasized. This review article presents a critical discussion of some controversial points of using grasslands to produce bioenergy. The following issues are addressed: proteins versus biofuels; reactive nitrogen emissions; biodiversity; and effective land use. Two major disadvantages in deriving bioenergy from grasslands are identified: (i) marginal lands are displaced from their fundamental role of producing meat and milk foods, in contrast with the rising worldwide demand for high-quality food; and (ii) the combustion of N-rich grassland biomass, or by-products, results in emission of reactive N into the atmosphere and dramatically reduces the residence time of biologically-fixed nitrogen in the ecosystems. Nitrogen oxides, released during atmospheric combustion of fossil fuels and biomass, have a detrimental effect on global warming. Since intensively managed crops on fertile soils need to be cultivated to fulfil the dietary needs of populations, the potential role of inedible cereal crop residues in providing bioenergy merits consideration. This might spare more marginal land area for forage production or even for full natural use, in order to sustain high levels of biodiversity. Owing to the complexity of terrestrial systems, and the complexity of interactions, a modeling effort is needed in order to predict and quantify outcomes of specific combination of land use at higher integration levels.
ABSTRACT: Full greenhouse gas (GHG) life-cycle analysis of bio-energy production chains is often constrained by a lack of information on pre-harvest GHG costs and emissions during production of the energy crop. In this paper, we assessed pre-harvest GHG costs of production of short rotation coppice (SRC), Miscanthus and oil seed rape (OSR: for liquid bio-fuel production) when compared to a range of former land-use baselines.
It was found that GHG costs are very low for Miscanthus and SRC but higher for OSR production, determined mainly by the need for nitrogen fertilisation. Compared to baseline land uses, SRC and Miscanthus have much lower GHG costs than arable cropping or intensively managed grasslands, with OSR production having similar GHG costs to arable cropping. Establishing broadleaved forests have low GHG costs, but 5-year GHG costs of Miscanthus and SRC are similar to forest.
We show that former land use is of critical importance when determining if energy crops are a net source or sink of GHGs. Converting to SRC and Miscanthus are the most favourable energy crops in terms of GHG savings. Converting to OSR from arable cropping results in either small increases or decreases in GHG emissions, depending upon the former tillage practice on the arable land, but replacing either broadleaved woodland with OSR (mainly due to soil carbon loss and increased fertiliser-related N2O emissions), or grassland with OSR (mainly due to loss of soil carbon), greatly increases emissions. Policies to maximise GHG benefits from energy crops.
ABSTRACT: We estimate the contributions from biomass burning (summer wildfires, other fires, residential biofuel, and industrial biofuel) to seasonal and annual aerosol concentrations in the United States. Our approach is to use total carbonaceous (TC) and non-soil potassium (ns-K) aerosol mass concentrations for 2001–2004 from the nationwide IMPROVE network of surface sites, together with satellite fire data. We find that summer wildfires largely drive the observed interannual variability of TC aerosol concentrations in the United States. TC/ns-K mass enhancement ratios from fires range from 10 for grassland and shrub fires in the south to 130 for forest fires in the north. The resulting summer wildfire contributions to annual TC aerosol concentrations for 2001–2004 are 0.26μg C m−3 in the west and 0.14μg C m−3 in the east; Canadian fires are a major contributor in the east. Non-summer wildfires and prescribed burns contribute on an annual mean basis 0.27 and 0.31μg C m−3 in the west and the east, highest in the southeast because of prescribed burning. Residential biofuel is a large contributor in the northeast with annual mean concentration of up to 2.2μg C m−3 in Maine. Industrial biofuel (mainly paper and pulp mills) contributes up to 0.3μg C m−3 in the southeast. Total annual mean fine aerosol concentrations from biomass burning average 1.2 and 1.6μg m−3 in the west and east, respectively, contributing about 50% of observed annual mean TC concentrations in both regions and accounting for 30% (west) and 20% (east) of total observed fine aerosol concentrations. Our analysis supports bottom-up source estimates for the contiguous United States of 0.7–0.9 Tg C yr−1 from open fires (climatological) and 0.4 Tg C yr−1 from biofuel use. Biomass burning is thus an important contributor to US air quality degradation, which is likely to grow in the future.
ABSTRACT: In decision making about the use of residues from annual crops for ethanol production, alternative applications of these residues should be considered. Especially important is the use of such residues for stabilizing and increasing levels of soil organic carbon. Such alternative use leads to a limited scope for residue removal from the field. Scope for removal of residues from annual crops can however, ceteris paribus, be increased when such crops generate relatively large amounts of biomass. Also selecting residues that contain relatively high levels of available cellulose and hemicellulose for removal or returning suitable ‘waste’ from processing crop residues that is rich in refractory compounds such as lignin to the field may increase scope for removal of crop residues for ethanol production.
ABSTRACT: Switchgrass (Panicum virgatum L.) has been identified as a model herbaceous energy crop for the USA. In this review, we selectively highlight current USDA-ARS research on switchgrass for biomass energy. Intensive research on switchgrass as a biomass feedstock in the 1990s greatly improved our understanding of the adaptation of switchgrass cultivars, production practices, and environmental benefits. Several constraints still remain in terms of economic production of switchgrass for biomass feedstock including reliable establishment practices to ensure productive stands in the seeding year, efficient use of fertilizers, and more efficient methods to convert lignocellulose to biofuels. Overcoming the biological constraints will require genetic enhancement, molecular biology, and plant breeding efforts to improve switchgrass cultivars. New genomic resources will aid in developing molecular markers, and should allow for marker-assisted selection of improved germplasm. Research is also needed on profitable management practices for switchgrass production appropriate to specific agro-ecoregions and breakthroughs in conversion methodology. Current higher costs of biofuels compared to fossil fuels may be offset by accurately valuing environmental benefits associated with perennial grasses such as reduced runoff and erosion and associated reduced losses of soil nutrients and organic matter, increased incorporation of soil carbon and reduced use of agricultural chemicals. Use of warm-season perennial grasses in bioenergy cropping systems may also mitigate increases in atmospheric CO2 . A critical need is teams of scientists, extension staff, and producer-cooperators in key agro-ecoregions to develop profitable management practices for the production of biomass feedstocks appropriate to those agro-ecoregions.
ABSTRACT: Biofuels derived from low-input high-diversity (LIHD) mixtures of native grassland perennials can provide more usable energy, greater greenhouse gas reductions, and less agrichemical pollution per hectare than can corn grain ethanol or soybean biodiesel. High-diversity grasslands had increasingly higher bioenergy yields that were 238% greater than monoculture yields after a decade. LIHD biofuels are carbon negative because net ecosystem carbon dioxide sequestration (4.4 megagram hectare–1 year–1 of carbon dioxide in soil and roots) exceeds fossil carbon dioxide release during biofuel production (0.32 megagram hectare–1 year–1 ). Moreover, LIHD biofuels can be produced on agriculturally degraded lands and thus need to neither displace food production nor cause loss of biodiversity via habitat destruction.
ABSTRACT: Increased production of biomass for energy has the potential to offset substantial use of fossil fuels, but it also has the potential to threaten conservation areas, pollute water resources and decrease food security. The net effect of biomass energy agriculture on climate could be either cooling or warming, depending on the crop, the technology for converting biomass into useable energy, and the difference in carbon stocks and reflectance of solar radiation between the biomass crop and the pre-existing vegetation. The area with the greatest potential for yielding biomass energy that reduces net warming and avoids competition with food production is land that was previously used for agriculture or pasture but that has been abandoned and not converted to forest or urban areas. At the global scale, potential above-ground plant growth on these abandoned lands has an energy content representing 5% of world primary energy consumption in 2006. The global potential for biomass energy production is large in absolute terms, but it is not enough to replace more than a few percent of current fossil fuel usage. Increasing biomass energy production beyond this level would probably reduce food security and exacerbate forcing of climate change.
ABSTRACT: This paper summarizes reports prepared for the U.S. Environmental Protection Agency (EPA) by researchers at the U.S. Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL). It also presents conclusions from a Biomass Energy Strategies Workshop conducted at ORNL. The Biofuels Feedstock Development Program (BFDP) has largely concentrated on the development of dedicated biomass feedstocks, referred to as energy crops. Two general types of energy crops have received the most attention—short-rotation woody crops (SRWC) and herbaceous energy crops (HEC). These cropping systems use traditional food production technologies as a means of maximizing the production of biomass per unit of land. Research focuses on the development of new crops and cropping technologies. The reports prepared for EPA and summarized by this article include discussions of crop production technologies, available land, economic considerations and environmental trade-offs. The discussion of other sources of biomass occurs only in the context of the workshop on biomass energy strategies.
K. A. Vogt, D. J. Vogt, T. Patel-Weynand, R. Upadhye, D. Edlund, R. L. Edmonds, J. C. Gordon, A. S. Suntan, R. Sigurdardottir, M. Miller, P. A. Roads, M. G. Andreu (2009). Bio-methanol: How energy choices in the western United States can help mitigate global climate change. Renewable Energy 34 (1): 233-241
ABSTRACT: Converting available biomass from municipal, agricultural and forest wastes to bio-methanol can result in significant environmental and economic benefits. Keeping these benefits in mind, one plausible scenario discussed here is the potential to produce energy using bio-methanol in five states of the western United States. In this scenario, the bio-methanol produced is from different biomass sources and used as a substitute for fossil fuels in energy production. In the U.S. West, forest materials are the dominant biomass waste source in Idaho, Montana, Oregon and Washington, while in California, the greatest amount of available biomass is from municipal wastes. Using a 100% rate of substitution, bio-methanol produced from these sources can replace an amount equivalent to most or all of the gasoline consumed by motor vehicles in each state. In contrast, when bio-methanol powered fuel cells are used to produce electricity, it is possible to generate 12–25% of the total electricity consumed annually in these five states.
As a gasoline substitute, bio-methanol can optimally reduce vehicle C emissions by 2–29 Tg of C (23–81% of the total emitted by each state). Alternatively, if bio-methanol supported fuel cells are used to generate electricity, from 2 to 32 Tg of C emissions can be avoided. The emissions avoided, in this case, could equate to 25–32% of the total emissions produced by these particular western states when fossil fuels are used to generate electricity. The actual C emissions avoided will be lower than the estimates here because C emissions from the methanol production processes are not included; however, such emissions are expected to be relatively low. In general, there is less carbon emitted when bio-methanol is used to generate electricity with fuel cells than when it is used as a motor vehicle fuel.
In the state of Washington, thinning “high-fire-risk” small stems, namely 5.1–22.9 cm diameter trees, from wildfire-prone forests and using them to produce methanol for electricity generation with fuel cells would avoid C emissions of 3.7–7.3 Mg C/ha. Alternatively, when wood-methanol produced from the high-fire-risk wood is used as a gasoline substitute, 3.3–6.6 Mg C/ha of carbon emissions are avoided. If these same “high-fire-risk” woody stems were burned during a wildfire 7.9 Mg C/ha would be emitted in the state of Washington alone. Although detailed economic analyses of producing methanol from biomass are in its infancy, we believe that converting biomass into methanol and substituting it for fossil-fuel-based energy production is a viable option in locations that have high biomass availability.
Hillier, J., C. Whittaker, G. Dailey, M. Aylott, E. Casella, G.M. Richter, A. Riche, R. Murphy, G. Taylor, P. Smith (2009). Greenhouse gas emissions from four bioenergy crops in England and Wales: Integrating spatial estimates of yield and soil carbon balance in life cycle analyses. Global Change Biology - Bioenergy 1 (4): 267-281
ABSTRACT: Accurate estimation of the greenhouse gas (GHG) mitigation potential of bioenergy crops requires the integration of a significant component of spatially varying information. In particular, crop yield and soil carbon (C) stocks are variables which are generally soil type and climate dependent. Since gaseous emissions from soil C depend on current C stocks, which in turn are related to previous land management it is important to consider both previous and proposed future land use in any C accounting assessment. We have conducted a spatially explicit study for England and Wales, coupling empirical yield maps with the RothC soil C turnover model to simulate soil C dynamics. We estimate soil C changes under proposed planting of four bioenergy crops,Miscanthus (Miscanthus×giganteus ), short rotation coppice (SRC) poplar (Populus trichocarpa Torr. & Gray ×P. trichocarpa , var. Trichobel), winter wheat, and oilseed rape. This is then related to the former land use – arable, pasture, or forest/seminatural, and the outputs are then assessed in the context of a life cycle analysis (LCA) for each crop. By offsetting emissions from management under the previous land use, and considering fossil fuel C displaced, the GHG balance is estimated for each of the 12 land use change transitions associated with replacing arable, grassland, or forest/seminatural land, with each of the four bioenergy crops. Miscanthus and SRC are likely to have a mostly beneficial impact in reducing GHG emissions, while oilseed rape and winter wheat have either a net GHG cost, or only a marginal benefit. Previous land use is important and can make the difference between the bioenergy crop being beneficial or worse than the existing land use in terms of GHG balance.
ABSTRACT: A 10-year US Department of Energy-sponsored research program designed to evaluate and develop switchgrass (Panicum virgatum), a native perennial warm-season grass, as a dedicated energy crop is reviewed. The programmatic objectives were to identify the best varieties and management practices to optimize productivity, while developing an understanding of the basis for long-term improvement of switchgrass through breeding and sustainable production in conventional agroecosystems. This research has reduced the projected production cost of switchgrass by about 25% ($8–9 Mg−1 ) through yield increases of about 50% achieved through selection of the best regionally adapted varieties; through optimizing cutting frequency and timing; and by reducing the level (by about 40%) and timing of nitrogen fertilization. Breeding research has made further gains in productivity of switchgrass that exceed the historical rate of yield improvement of corn. Studies of soil carbon storage under switchgrass indicate significant carbon sequestration will occur in soils that will improve soil productivity and nutrient cycling and can substantially augment greenhouse gas reductions associated with substituting renewable energy for fossil energy. Collaborative research with industry has included fuel production and handling in power production, herbicide testing and licensing, release of new cultivars, and genetic modifications for chemical coproduct enhancement. Economically based life cycle analyses based on this research suggest that switchgrass produced for energy will compete favorably both as an agricultural crop and as fuel for industry.
ABSTRACT: Energy outputs from ethanol produced using corn, switchgrass, and wood biomass were each less than the respective fossil energy inputs. The same was true for producing biodiesel using soybeans and sunflower, however, the energy cost for producing soybean biodiesel was only slightly negative compared with ethanol production. Findings in terms of energy outputs compared with the energy inputs were: • Ethanol production using corn grain required 29% more fossil energy than the ethanol fuel produced. • Ethanol production using switchgrass required 50% more fossil energy than the ethanol fuel produced. • Ethanol production using wood biomass required 57% more fossil energy than the ethanol fuel produced. • Biodiesel production using soybean required 27% more fossil energy than the biodiesel fuel produced (Note, the energy yield from soy oil per hectare is far lower than the ethanol yield from corn). • Biodiesel production using sunflower required 118% more fossil energy than the biodiesel fuel produced.
ABSTRACT: This paper discusses the contribution of biomass in the future global energy supply. The discussion is based on a review of 17 earlier studies on the subject. These studies have arrived at widely different conclusions about the possible contribution of biomass in the future global energy supply (e.g., from below 100 EJ yr−1 to above 400 EJ yr−1 in 2050). The major reason for the differences is that the two most crucial parameters—land availability and yield levels in energy crop production—are very uncertain, and subject to widely different opinions (e.g., the assessed 2050 plantation supply ranges from below 50 EJ yr−1 to almost 240 EJ yr−1 ). However, also the expectations about future availability of forest wood and of residues from agriculture and forestry vary substantially among the studies.
The question how an expanding bioenergy sector would interact with other land uses, such as food production, biodiversity, soil and nature conservation, and carbon sequestration has been insufficiently analyzed in the studies. It is therefore difficult to establish to what extent bioenergy is an attractive option for climate change mitigation in the energy sector. A refined modeling of interactions between different uses and bioenergy, food and materials production—i.e., of competition for resources, and of synergies between different uses—would facilitate an improved understanding of the prospects for large-scale bioenergy and of future land-use and biomass management in general.
ABSTRACT: Estimates of world regional potentials of the sustainable use of biomass for energy uses through the year 2050 are presented. The estimated potentials are consistent with scenarios of agricultural production and land use developed at the International Institute for Applied Systems Analysis, Austria. They thus avoid inconsistent land use, in particular conflicts between the agricultural and bioenergy land use. As an illustration of the circumstances under which a large part of this potential could be used in practice, a global energy scenario with high economic growth and low greenhouse gas emissions, developed by IIASA and the World Energy Council is summarised. In that scenario, bioenergy supplies 15% of global primary energy by 2050. Our estimation method is transparent and reproducible. A computer program to repeat the calculation of the estimates with possibly changed assumptions is available on request.
M.D.A. Rounsevell, I. Reginster, M.B. Araújo, T.R. Carter, N. Dendoncker, F. Ewert, J.I. House, S. Kankaanpääc, R. Leemans, M.J. Metzger, C. Schmit, P. Smith, G. Tuck (2005). A coherent set of future land use change scenarios for Europe. 114 (1): 57-68
ABSTRACT: This paper presents a range of future, spatially explicit, land use change scenarios for the EU15, Norway and Switzerland based on an interpretation of the global storylines of the Intergovernmental Panel on Climate Change (IPCC) that are presented in the special report on emissions scenarios (SRES). The methodology is based on a qualitative interpretation of the SRES storylines for the European region, an estimation of the aggregate totals of land use change using various land use change models and the allocation of these aggregate quantities in space using spatially explicit rules. The spatial patterns are further downscaled from a resolution of 10 min to 250 m using statistical downscaling procedures. The scenarios include the major land use/land cover classes urban, cropland, grassland and forest land as well as introducing new land use classes such as bioenergy crops.
The scenario changes are most striking for the agricultural land uses, with large area declines resulting from assumptions about future crop yield development with respect to changes in the demand for agricultural commodities. Abandoned agricultural land is a consequence of these assumptions. Increases in urban areas (arising from population and economic change) are similar for each scenario, but the spatial patterns are very different. This reflects alternative assumptions about urban development processes. Forest land areas increase in all scenarios, although such changes will occur slowly and largely reflect assumed policy objectives. The scenarios also consider changes in protected areas (for conservation or recreation goals) and how these might provide a break on future land use change. The approach to estimate new protected areas is based in part on the use of models of species distribution and richness. All scenarios assume some increases in the area of bioenergy crops with some scenarios assuming a major development of this new land use.
Several technical and conceptual difficulties in developing future land use change scenarios are discussed. These include the problems of the subjective nature of qualitative interpretations, the land use change models used in scenario development, the problem of validating future change scenarios, the quality of the observed baseline, and statistical downscaling techniques.
ABSTRACT: The paper reviews analytical challenges for assessing the environmental impact of bioenergy production in the context of global greenhouse gas emissions and global biofuel production targets. The main environmental issues associated with bioenergy production are briefly explained and used to describe different analytical approaches for assessing the environmental effects of bioenergy production. The paper discusses the relevance of suitable system boundaries in analysing the sustainability of bioenergy production. This includes the need for achieving coherence between several policy areas such as agriculture and food, energy and transport, climate and environment as well as international development. The review concludes with a range of research and policy challenges in the bioenergy field.
A. L. Cowie, P. Smith, D. Johnson (2006). Does soil carbon loss in biomass production systems negate the greenhouse benefits of bioenergy?. Mitigation and Adaptation Strategies for Global Change 11 (5-6): 979-1002
ABSTRACT: Interest in bioenergy is growing across the Western world in response to mounting concerns about climate change. There is a risk of depletion of soil carbon stocks in biomass production systems, because a higher proportion of the organic matter and nutrients are removed from the site, compared with conventional agricultural and forestry systems. This paper reviews the factors that influence soil carbon dynamics in bioenergy systems, and utilises the model FullCAM to investigate the likely magnitude of soil carbon change where bioenergy systems replace conventional land uses. Environmental and management factors govern the magnitude and direction of change. Soil C losses are most likely where soil C is initially high, such as where improved pasture is converted to biomass production. Bioenergy systems are likely to enhance soil C where these replace conventional cropping, as intensively cropped soils are generally depleted in soil C. Measures that enhance soil C include maintenance of productivity through application of fertilisers, inclusion of legumes, and retention of nutrient-rich foliage on-site.
Modelling results demonstrate that loss of soil carbon in bioenergy systems is associated with declines in the resistant plant matter and humified soil C pools. However, published experimental data and modelling results indicate that total soil C loss in bioenergy systems is generally small. Thus, although there may be some decline in soil carbon associated with biomass production, this is negligible in comparison with the contribution of bioenergy systems towards greenhouse mitigation through avoided fossil fuel emissions.
Hellebrand, H. J., M. Strähle, V. Scholz, J. Kern (2009). Soil carbon, soil nitrate, and soil emissions of nitrous oxide during cultivation of energy crops. Nutrient Cycling in Agroecosystems Online First
ABSTRACT: Carbon (C) sequestration and soil emissions of nitrous oxide (N2 O) affect the carbon dioxide (CO2 ) advantage of energy crops. A long-term study has been performed to evaluate the environmental effects of energy crop cultivation on the loamy sand soil of the drier northeast region of Germany. The experimental field, established in 1994, consisted of columns (0.25 ha each) cultivated with short rotation coppice (SRC:Salix andPopulus ) and columns cultivated with annual crops. The columns were subdivided into four blocks, with each receiving different fertilization treatments. The soil C content was measured annually from 1994 until 1997, and then in 2006. Soil N2 O levels were measured several times per week from 1999 to 2007. Water-filled pore space (WFPS) and soil nitrate measurements have been performed weekly since 2003. Increased C stocks were found in SRC columns, and C loss was observed in blocks with annual crops. The soil from fertilized blocks had higher levels of C than the soil from non-fertilized blocks. SRC cropping systems on dry, loamy sand soils are advantageous relative to annual cropping systems because of higher C sequestration, lower fertilized-induced N2 O emissions, and reduced background N2 O emissions in these soils. SRC cropping systems on dry, loamy sand soils have a CO2 advantage (approximately 4 Mg CO2 ha−1 year−1 ) relative to annual cropping systems.
ABSTRACT: Scenarios, roadmaps and similar foresight methods are used to cope with uncertainty in areas with long planning horizons, such as energy policy, and research into the future of hydrogen energy is no exception. Such studies can play an important role in the development of shared visions of the future: creating powerful expectations of the potential of emerging technologies and mobilising resources necessary for their realisation.
This paper reviews the hydrogen futures literature, using a six-fold typology to map the state of the art of scenario construction. The paper then explores the expectations embodied in the literature, through the ‘answers’ it provides to questions about the future of hydrogen. What are the drivers, barriers and challenges facing the development of a hydrogen economy? What are the key technological building blocks required? In what kinds of futures does hydrogen become important? What does a hydrogen economy look like, how and when does it evolve, and what does it achieve?
The literature describes a diverse range of possible futures, from decentralised systems based upon small-scale renewables, through to centralised systems reliant on nuclear energy or carbon-sequestration. There is a broad consensus that the hydrogen economy emerges only slowly, if at all, under ‘Business as Usual’ scenarios. Rapid transitions to hydrogen occur only under conditions of strong governmental support combined with, or as a result of, major ‘discontinuities’ such as shifts in society's environmental values, ‘game changing’ technological breakthroughs, or rapid increases in the oil price or speed and intensity of climate change.
ABSTRACT: Forest and bioenergy strategies offer the prospect of reduced CO2 emissions to the atmosphere. Such strategies can affect the net flux of carbon to the atmosphere through 4 mechanisms: storage of C in the biosphere; storage of C in forest products; use of biofuels to displace fossil-fuel use; use of wood products which often displaces other products that require more fossil fuel for their production. We use the mathematical model GORCAM (Graz/Oak Ridge Carbon Accounting Model) to examine these mechanisms for 16 land-use scenarios. Over long time intervals the amount of C stored in the biosphere and in forest products reaches a steady state and continuing mitigation of C emissions depends on the extent to which fossil fuel use is displaced by the use of bioenergy and wood products. The relative effectiveness of alternative forest and bioenergy strategies and their impact on net C emissions strongly depend, for example, on the productivity of the site, its current usage, and the efficiency with which the harvest is used. When growth rates are high and harvest is used efficiently, the dominant opportunity for net reduction in C emissions is seen to be fossil-fuel displacement. At the growth rates and efficiencies of harvest utilization adopted in many of our base scenarios, the net C balance at the end of 100 years is very similar whether trees are harvested and used for energy and traditional forest products, or reforestation and forest protection strategies are implemented. The C balance on a plantation system that provides a constant output of biomass products can look different than the balance of a single parcel of land.
ABSTRACT: The Kyoto protocol has focused the attention of the public and policymakers on the earth's carbon (C) budget. Previous estimates of the impacts of vegetation change have been limited to equilibrium "snapshots" that could not capture nonlinear or threshold effects along the trajectory of change. New models have been designed to complement equilibrium models and simulate vegetation succession through time while estimating variability in the C budget and responses to episodic events such as drought and fire. In addition, a plethora of future climate scenarios has been used to produce a bewildering variety of simulated ecological responses. Our objectives were to use an equilibrium model (Mapped Atmosphere-Plant-Soil system, or MAPSS) and a dynamic model (MC1) to (a) simulate changes in potential equilibrium vegetation distribution under historical conditions and across a wide gradient of future temperature changes to look for consistencies and trends among the many future scenarios, (b) simulate time-dependent changes in vegetation distribution and its associated C pools to illustrate the possible trajectories of vegetation change near the high and low ends of the temperature gradient, and (c) analyze the extent of the US area supporting a negative C balance. Both models agree that a moderate increase in temperature produces an increase in vegetation density and carbon sequestration across most of the US with small changes in vegetation types. Large increases in temperature cause losses of C with large shifts in vegetation types. In the western states, particularly southern California, precipitation and thus vegetation density increase and forests expand under all but the hottest scenarios. In the eastern US, particularly the Southeast, forests expand under the more moderate scenarios but decline under more severe climate scenarios, with catastrophic fires potentially causing rapid vegetation conversions from forest to savanna. Both models show that there is a potential for either positive or negative feedbacks to the atmosphere depending on the level of warming in the climate change scenarios.
ABSTRACT: The carbon sequestered by restoring forests is greater than the emissions avoided by the use of the liquid biofuels.