Task XV: Greenhouse Gas Balances of Bioenergy Systems
30 – 31 May 1997 – Westin Bayshore Hotel, Vancouver, Canada
Jointly organized by
|NATURAL RESOURCES CANADA
Edmonton, Alberta, Canada
FRIDAY, 30 MAY 1997
Welcome and Introduction
Mike Apps (Department of Natural Resources Canada, Canadian Forest Service, Edmonton, Canada)
Josef Spitzer (Joanneum Research, Graz, Austria)
Recent developments regarding renewable energy in Canada
John Legg (Department of Natural Resources Canada, Canadian Forest Service, Ontario, Canada)
Carbon budget update for Canada
Mike Apps and Werner Kurz (Department of Natural Resources Canada, Canadian Forest Service, Edmonton, Canada;
Essa Technologies Ltd., Vancouver, Canada)
Forest and bioenergy mitigation options: the issue of credits and debits
Gregg Marland (Oak Ridge National Laboratory, Oak Ridge, TN, USA)
Large-scale biomass for power generation / large-scale forestry for C-sequestration
Bill Ormerod and Paul Freund (IEA Greenhouse Gas R&D Programme, Cheltenham, UK)
Report from the climate change task force of the Canadian Pulp and Paper Assoc.
(Canadian Pulp and Paper Association, Canada)
Survey of bioenergy and greenhouse gas emissions in Brazil
Luiz Pinguelli Rosa (Energy Planning Program, COPPE/UFRJ, Brazil)
Using the model GORCAM for sensitivity analyses of carbon sequestration in forestry projects
Neil Bird (Woodrising Consulting Inc., Ontarion, Canada)
Recent development of the forest carbon balance in Finland
Timo Karjalainen, Ari Pussinen and Seppo Kellomäki
(European Forest Institute, Joensuu, Finland; University of Joensuu, Faculty of Forestry, Joensuu, Finland)
Standard methodology for greenhouse gas balances of bioenergy systems in comparison with fossil energy systems: status of working group manuscript
Bernhard Schlamadinger (Joanneum Research, Graz, Austria)
Future production and utilisation of biomass in Sweden: potentials and CO2 mitigation
Leif Gustavsson (Lund University, Department of Environmental and Energy Systems Studies, Sweden)
Wood construction alternatives in Finland: carbon sink and substitution for energy intensive materials
K. Pingoud and A.-L. Perälä (VTT-Energy, Espoo, Finland)
SATURDAY, 31 MAY 1997
IPCC Guidelines for National GHG Inventories, Land-Use Change and Forestry: “GHG emissions from harvested wood products”
(Chairs: Bo Lim and Sandra Brown)
Working Group paper: Standard methodology for greenhouse gas balances of bioenergy systems in comparison with fossil energy systems
|Apps Mike||Department of Natural
Canadian Forest Service
|5320 – 122 Street,
T6H 3S5 CANADA
|+1 403 435 7305||+1 403 435 firstname.lastname@example.org|
|Bird D. Neil||Woodrising Consulting Inc.||132 Main Street,
N0B 1T0 CANADA
|+1 519 833 1031||+1 519 833 email@example.com|
Board for Industrial and
|+46 8 681 9388||+46 8 681 firstname.lastname@example.org|
|Bradley Doug||E.B. Eddy Forest Products Ltd.||1600 Scott St.
700 Ottawa, Ontario,
K1Y 4N7 CANADA
|+1 613 725 6854||+1 613 725 6858||dbradley@
|Bradley Mike||Canfor||2900, 1055 Dunsnuir St.
Box 49420, Bentall Port,
V7X 1B5 CANADA
|+1 604 661 5264||+1 604 661 email@example.com|
|Brown Sandra||US Environmental
Western Ecology Division
|200 SW 35th St.
|+1 541 754 4346||+1 541 754 firstname.lastname@example.org|
|Clark Robin||Robin B. Clark Inc.||3431 West 21st Ave
|+1 604 737 1112||+1 604 737 email@example.com|
|Energy Planning Programm
|Centro de Tecnologia,
Bloco C, Sala 211,
Rio de Janeiro, BRAZIL
|+55 21 560 8995||+55 21 290 firstname.lastname@example.org|
Forest Research Institute
|Private Bag 3020,
Rotorua, NEW ZEALAND
|+64 7 347 5660||+64 7 347 email@example.com|
|Freund Paul||IEA Greenhouse Gas
|Cheltenham GL52 4RZ
|+44 1242 680 753||+44 1242 680 758||paul@
|Gustavsson Leif||Department of
Energy System Studies,
S-223 62 Lund
|+46 46 222 8641||+46 46 222 8644||leif.gustavsson@
|Jaques Art||Environment Canada||351 St. Joseph Blud.
Hull, P.Q., CANADA
|+1 819 993 3098||+1 819 993 firstname.lastname@example.org|
|Karjalainen Timo||European Forest Institute||Torikatu 34,
|+358 13 252020||+358 13 124393||timo.karjalainen@
|Kurz Werner||Esssa Technologies Ltd.||Suite 300,
1765 West 8th Avenue,
V6J 5C6 CANADA
|+1 604 733 2996||+1 604 733 email@example.com|
|Heuristic Engineering Inc.||5189 Maple Street,
V6M 3T4 CANADA
|+1 604 263 8005||+1 604 263 0786||mlefcort@
|Legg John F.||Office of Energy R&D,
Natural Resources Canada
|580 Booth Street,
K1H 0E4 CANADA
|+1 613 995 0968||+1 613 995 firstname.lastname@example.org|
|Lim Bo||OECD Environment Directorate||2 rue Andre-Pascal,
75016 Paris, FRANCE
|+33 1 4524 7894||+33 1 4524 email@example.com|
|Marland Gregg||Environmental Sciences Division,
Oak Ridge National Laboratory
|+1 423 241 4850||+1 423 574 firstname.lastname@example.org|
|McCloy Brian||Council of Forest Industries
|1200-55 Burrard Street,
V7X 1S7 CANADA
|+1 604 684 0211||+1 604 684 email@example.com|
|Moore Patrick||Forest Alliance of B.C.||4068 West 32nd Ave,
V6S 1Z6 CANADA
|+1 604 221 1990||+1 604 221 firstname.lastname@example.org|
|Ormerod Bill||IEA Greenhouse Gas
|Cheltenham GL52 4RZ,
|+44 1242 680 753||+44 1242 680 758||paul@
|Pingoud Kim||Technical Research
Centre of Finland
|P.O. Box 1606,
|+358 9 456 5074||+358 9 456 email@example.com|
|Federal University of
Rio de Janeiro
|Centro de Tecnologia,
Bloco H, Sala H.106,
Cidade Universitaria BRAZIL
|+55 21 560 4697||+55 21 290 firstname.lastname@example.org|
|Energy Planning Program
|Centro de Tecnologia,
Bloco C, Sala 211,
Rio de Janeiro, BRAZIL
|+55 21 560 8832||+55 21 290 email@example.com|
Institute of Energy Research
A-8010 Graz, AUSTRIA
|+43 316 876 1340||+43 316 876 1320||bernhard.schlamadinger@
|Spitzer Josef||JOANNEUM RESEARCH
Institute of Energy Research
A-8010 Graz, AUSTRIA
|+43 316 876 1338||+43 316 876 1320||josef.spitzer@
|Wellisch Maria||MWA Consultants||300-6388 Marlborough Avenue,
V5H 4P4 CANADA
|+1 604 431 7280||+1 604 431 firstname.lastname@example.org|
The carbon storage of the tree biomass in Finland was approximately 543 Tg C (24.8 Mg C/ha) in the early 1950s when calculated from the results of the 3rd national forest inventory (Figure 1) . Since then it has grown to 660 Tg C (28.8 Mg C/ha) according to the data provided by the 8th national forest inventory, or even to 680 Tg C (29.5 Mg C/ha) if the latest inventory results from southern Finland are taken into account. The uptake of carbon has increased at the same time from 19.7 Tg C (0.90 Mg C/ha/a) to 27.3 Tg C (1.16 Mg C/ha/a). The total drain in Finnish forestry, which includes timber harvesting and natural mortality, has been approximately 19.3 Tg C/a. The net carbon sequestration (i.e. the difference between uptake and total drain) of the tree biomass was negative in the early 1960s when total drain exceeded the uptake. Since then, the net carbon sequestration has increased, and amounted to 8.3 Tg C (0.36 Mg C/ha/a) in 1990. The uptake of carbon has, however, decreased slightly since 1990, which is the base year for the United Nations Framework Convention on Climate Change. At the same time, the total drain has increased due to an increasing demand for wood by the Finnish forest industries, and as a consequence net sequestration has decreased to 4.6 Tg C (0.17 Mg C/ha/a) in 1995. In addition to the increased use of domestic raw material, wood imports have also increased, representing some 15% of the industrial consumption of roundwood in 1995 (7% in 1970). Carbon dioxide emissions in Finland have increased from 19.3 Tg C in 1990 to 20.7 Tg C in 1995, and the tendency is for them to increase unless major changes take place in energy generation and consumption.
The increase in the uptake of carbon has been a result of changes in the forest structure as affected by intensified forest management, draining of waterlogged sites, and intensive protection of forests against fires and insect epidemics. Moreover, increasing nitrogen deposition and carbon dioxide concentration, as well as a slightly warmer climate during the past few decades (especially warmer springs), may have enhanced the carbon uptake. Unproductive sites have been regenerated, but the single biggest impact on the increased uptake of carbon has been the draining of waterlogged areas; 5.4 million hectares have been drained since the early 1950s. Between 1950 and 1984, 2.7 million hectares of low-productive forestland (annual long term increment less than 1 m3/ha/a) have been converted to productive forestland (annual long term growth in excess of 1 m3/ha/a), which has meant an increase in area by 15%, to 20 million hectares. In addition, over 3 million hectares of forestland have been fertilised during the past 30 years. Both draining and fertilisation have almost ceased during the past few years.
The forest area treated annually with fellings has been approximately 430 000 ha during the past 25 years, i.e. 11.1 million hectares, which is nearly half of the total forested area of 23 million hectares. The area annually thinned has been 165 000 hectares, and 265 000 ha have been treated with regeneration felling (clear felling, removal of seed trees and shelterwood trees). The areas seeded and planted annually have been approximately 127 000 hectares and the area of tended seedling stands 297 000 hectares, over 3.3 and 7.7 million hectares during the past 25 years. As a result of intensified forest management, the age class structure of the forests has changed considerably. In the early 1950s, the distribution of forestland into different age classes followed the normal distribution in the southern Finland, and in the northern Finland the proportion of older age classes was greater than that of younger age classes. Currently, the proportions of the different age classes are fairly even. Fire suppression has been effective, as the average area burned annually since early 1950s has been 1695 hectares, but during the past 25 years less than 700 hectares.
In order for Finland to reduce the national net emissions of carbon dioxide and to fulfil international commitments, emissions from energy generation and consumption should decrease and/or net sequestration should increase. Latest developments in the forest carbon balance demonstrate that the carbon uptake by tree biomass does not necessarily increase as it has during the past few decades. If the forested area does not expand, maximum carbon uptake will probably be reached during the next 20-30 years. It could be possible to increase net sequestration by decreasing the level of timber harvesting. This would, however, have drastic consequences for the national economy since a large proportion of Finland’s net export income is based on exports of forest products. Approximately 80% of the wood products manufactured in Finland are exported. Moreover, a decreasing level of timber harvesting would lead to decreasing net carbon uptake in the longer run. A sustainable way to decrease net emissions would therefore be to step up the use of forest biomass for energy generation (currently at 17%) and thereby replace fossil fuels (currently at 52%). Bioenergy has to be generated in large-scale plants ( e.g. as a by- product of pulp production or in power plants) in order to have a significant role. There is potential for increased use of bioenergy, since the age-class structure of Finnish forests is such that large areas require pre-commercial and first commercial thinning, and also the use of forest residues could be increased. Increased level of felling would also provide energy, since a substantial proportion of the raw material is used in pulp mills, which generate more energy than they need. Some potential exists also in biomass production on abandoned farming land (0.5 million hectares). Moreover, there is a limited potential for sequestering more carbon by increasing the use of wood as construction material in place of concrete, steel or other non-renewable materials.
The Swedish biomass production potential could be significantly increased if new production methods, such as optimised fertilisation, where to be used. Optimised fertilisation on 25% of Swedish forest land could almost double the biomass potential from forestry, compared with no fertilisation, as not only logging residues but also large quantities of excess stem wood not needed for industrial purposes could be used for energy purposes. Together with energy crops and straw from agriculture, the total Swedish biomass potential with estimated production conditions around 2015 would be about 230 TWh/yr, or half the current Swedish energy supply, if the demand for stem wood for building and industrial purposes were the same as today. The new production methods discussed here are assumed not to cause any significant negative impact on the local environment. An increased biomass production with optimised fertilisation on some forest sites with low biodiversity could, on the contrary, make available other forest sites with high biodiverstiy for protection. A high intensity in biomass production, compared with low intensity, would also reduce biomass transportation demands. Time-related constrains have not been employed regarding, for example, the plantation of energy crops on large areas of arable land, fertilisation of large amounts of forest land, or the long rotation period of the stands in Swedish forestry.
Optimised fertilisation with a nutrient content balanced to suit the trees could increase the volume increment in coniferous stands from 2 to 4 times, without causing negative environmental effects such as nutrient leaching. When such fertilisation is combined with irrigation, the volume increment could increase further. Here, optimised fertilisation is defined as fertilisation with commercial fertilisers leading to an increased volume increment of 75 to 150%. Thus, optimised fertilisation as defined here is not the same as the maximum biological increment in Swedish forests, which could be much higher.
The future demand for stem wood for building and industrial purposes is uncertain as several factors influence the demand for paper and wood products. Therefore, estimates of the future biomass potential of stem wood for energy purposes are also uncertain. For example, if the demand for stem wood for industrial purposes where to increase by 2% yearly, the total Swedish biomass potential for energy purposes around 2015 would be reduced from about 230 to 170 TWh/yr.
Economic considerations have not been included in this paper. The cost of utilising stem wood produced with optimised fertilisation for energy purposes must be further analysed. The commercial market for logging residues for energy purposes has, however, grown steadily in Sweden since the mid 1970s. The price of logging residues has also decreased by 70% in real terms since then, and is now per energy unit around the same, or somewhat lower, than for oil and NG when taxes are excluded.
The two major uncertainties in estimating future biomass potential from agriculture are the amount of land available for energy crop production and future yield increases through improved cultivation methods and plant breeding. For example, if only 7% of current Swedish arable land is used for energy crop production and no productivity increases have been achieved, the biomass potential from agriculture will be up to six times lower than if 30% arable land is used and hectare yields have increased by 50%.
Waste water treatment in energy crop cultivation has several benefits. Compared with conventional treatment plants, this purification system is cost-efficient and will increase the nitrogen removal, thus reducing marine eutrophication. The amount of sewage sludge will also be reduced. Using municipal waste water in energy crop cultivation will satisfy, not only the demand for water, but also the demand for most nutrients, giving significant yield increases compared with conventional fertilisation methods. The cost of biomass produced could thus be reduced.
An increased utilisation of biomass by around 200 TWh/yr could reduce Swedish CO2 emissions by about 65%. If optimised fertilisation were to be practised and the demand for stem wood were the same as today, around 30 TWh electricity could be produced yearly from excess biomass through cogeneration using district heating systems in densely populated regions, together with black liquid gasification in pulp plants in forest regions. Alcohols for transportation and stand-alone power production are preferably produced in less densely populated regions with excess biomass. If biomass is produced with high intensity using optimised fertilisation, and the potential of wind power were to be utilised, the energy system in Sweden could become mainly renewable in the future. Improvements in energy efficiency reducing the total energy demand would facilitate the transition to a renewable energy system as the demand for such energy sources would be reduced.
The prospect of global climate change has focussed attention on C sequestration from the atmosphere by forests and other managed ecosystems. The goal of such programs is to maximise the removal of atmospheric C or to reduce net emissions due to human activities. This is a goal of global proportions but which requires a series of management actions that, in case of forestry offset programs, are typically implemented at the scale of forest stands. How this global policy objective may be effectively accomplished is a non-trivial task. It has been referred to as the “down-scaling problem” – how does the global society promote and encourage activities at the local scale that are locally acceptable and beneficial to society at that scale while still contributing to the global target? Achieving the goal of reduced atmospheric CO2 burden does not mean maximising C storage in each indicidual stand. There are a number of reasons why such a simple-minded approach will not result in the desired result. These are of two types: spatial and temporal. Focussing only on forest ecosystem C storage would be in conflict with other essential services provided by these forest ecosystems, such as wildlife habitat and fibre supply to name but two. The loss of some of these services would lead to increased emissions elsewhere (an example of this is the replacement of wood building products with other material requiring high energy inputs in their production). In more general terms this is referred to as ‘leakage’: the securing of storage at one point may result on increased losses (or reduced storage) at another. The other problem is the need to recognise that carbon sequestration is a dynamic process. In forest ecosystems, maximum C storage and maximum C uptake rate occur at different phases of stand development and cannot be simultaneously attained. This is a fact not widely appreciated.
Accomodating these spatial and temporal concerns requires a systems approach whose spatial and temporal boundaries include all components that are influenced by management interventions and which contribute to the global atmospheric C burden. One way of breaking down such a formidable task into workable pieces is to view the system as a hierarchical set of systems which span the scales from the action element to the global result: i.e., stand to forest to region to national and thence to global. These nested systems are open systems, not closed, and each provides a context for the system below and a component of the system above. Critical to this hierarchical approach are the identification, estimation, and predicted response for a set of indicators of C storage and sequestration as well as other goods and services. In addition, values (social and economic) must be attached to these indicators. The weight assigned to the various indicators at any given scale depends on both the specific nature of that scale and the context (social, economic and environmental) provided by the scale above. Changes over time – the temporal issue – has traditionally dealt with by taking some form of average, either over time or over a large enough area. This poses its own problem however if, as believed by many, large-scale changes are occuring in the environment. How do we ensure that a given management intervention designed to achieve some local carbon sequestration is performing appropiately? From a monitoring or compliance point of view, what is the appropriate baseline against which the project performance is to be assessed? Results for Canada suggest that large-scale forest carbon budgets are surprisingly dynamic and the Canadian boreal forest has gone from being a net sink of atmospheric CO2 to a source in the last two decades. This change is not due to direct human interventions by Canadians but rather due to changes in the natural disturbance regime. While it is uncertain how much of the changes in this regime are due to indirect human influence (e.g., climate change), it is very certain that any such influence is global in origin. If such a situation is true for other forested countries of the world as well, defining the reference baseline for offset programs must be thought through with care, maintaining always a focus of attention on the global objective. One way of doing this is to use a running baseline in which the reference case is the no-intervention scenario. Such a “with and without” comparison presents significant, but not insurmountable challenges for the scientific community (to estimate and predict the appropriate indicators) and for the policy community (to ensure that the final sums add up to the needed result). These challenges will be foaced at each scale where management decisions are made: from local up to national and international.
1 – Introduction
First of all I would like to acknowledge in behalf of COPPE- the Graduate Institute of Engineering of Federal University of Rio de Janeiro the invitation to make this presentation in the seminar of this working group of IEA here in Vancouver. In the case of Brazil, environmental questions made the country the center of various international discussions, especially in relation to the devastation of the Amazon forest through burning, cattle raising and mining or the construction of large hydroelectric plants. This was an important point raised and discussed at UNCED – 92 in Rio de Janeiro, in the context of the negotiations over the Climate Change Convention. Meanwhile, CO2 emission to the atmosphere from the use of petroleum natural gas, coal, firewood and charcoal, in the Brazilian Energy Sector, has a relatively little impact. The country’s electricity generation is predominantly hydro. The subject of this paper is the biomass and GHG emission in Brazil, including firewood, alcohol and sugar cane bagasse, which are important to avoid emissions from fossil fuels, but we would like to refer also to the problem of CO2 and CH4 emission through the decomposition of the biomass submerged by the dams of the hydroelectric plants in the Amazon. With respect to the ongoing international discussions, there are two noteworthy Brazilian programs for reducing CO2 emissions: the fuel alcohol program and the use of hydroelectric plants instead of plants using fossil oil for the generation of electricity. However, both are undergoing crises because the disturbing consequence of deregulation and free market international forces, which are pushing Brazil towards an increasing use of fossil fuels, which are CO2 emitters, in place of endogenous renewable energy, such as hydro and biomass, which are not. Energy use in Brazil contributes but slightly for the intensification of the greenhouse effect. Considering only CO2 emissions, COPPE’s study (Rosa and Cecchi, 1994 and Rosa and Santos, 1995) estimates 73 Mt C/year for 1990. This corresponds to a bit over 1% of the world emissions. The relatively low contribution of energy use for CO2 emissions can be explained by the large share of hydroelectricity and of renewable biomass in the Brazilian energy matrix. More than 90% of the electricity consumed in the country is generated by hydroelectric plants. Fuel alcohol is responsible for supplying about half the energy used by Brazilian cars. Sugar cane bagasse accounts for more than 6% of the total national energy consumption. According to the above mentioned study of COPPE, in 1990, CO2 emissions in Brazil were distributed as follows by sources: Petroleum 58%; Firewood 16%; Charcoal 10%; Coal 12%; Natural gas 4% (Rosa, Schechtman and Cecchi, 1995). A common mistake is to consider firewood as being completely non-renewable, produced through deforestation and which leads to exaggerating its share in CO2 emissions. Conversely, when the influence of firewood is not taken into account, another problem arises, found in prospective projections and in the elaboration of scenarios, i.e., the sectorial distortion and that of energy sources when analyzing the impact of the Brazilian energy system on the greenhouse effect.
2 – Comparative Advantage of Hydro and Biomass Energy in Brazil
The Brazilian case is interesting for electricity generation and transport, because hydro and sugar-cane alcohol are used. Neither of these energy products contributes to CO2 emissions (or their contribution is so insignificant that it can be neglected for practical purposes). Energy substitution can decrease and efficiency improvement increases. Among fossil fuels, coal has the largest, while the natural gas has the smallest. Oil has an intermediate position. Combined cycle plants with gas turbines give efficiency values higher than conventional thermoelectric plants. But hydro and sugar-cane products, as well as nuclear energy, has zero emission. Assuming an average value for the CO2 emission by all energy forms with net CO2 emission we can do a rough approximation for emission calculation. For electricity generation in Brazil, the following energy sources are used: hydro (89,9%); nuclear (4.9%); oil products (2.2%); coal (1.8%); biomass (1.1%); renewable biomass (bagasse) (0.3%); natural gas (0,1%). The fraction of energy with emission in Brazil corresponds to nearly 5%, while in the USA, it amounts to almost 75%. Using the approximation above refered Brazil is therefore more efficient than the USA in respect of CO2 emissions per unit of electric energy generated (t C/MWh) by the factor: 0.75 / .05 = 15. In car transport, Brazilian fuel consumption is approximately half alcohol and gasoline, while in the USA, it /is almost 100% gasoline. So the relation between CO2 per gigajoule in the USA and Brazil is: 1.0 / 0.5 = 2. The above rough calculations provide only an order of magnitude. Energy policy in Brazil is changing to satisfy the present orientation of multilateral and international organizations, with the goal of reducing the state’s role in the economy. The outcome is proposals for deregulating the electric energy generation and fuel supply. A World Bank Report of 1990 has recommended that Brazil must change from hydro to thermoelectric energy, using coal, oil products and natural gas in the new plants. There are two different reasons for this recommendation. Hydro power has the inconvenience of causing environmental impacts when large dams are constructed in the Amazon, where the major part of the still unused Brazilian hydro potential is concentrated. Brazil presently uses only about 20% of this hydro potential, which amounts to 213 GW. On the other hand thermoelectricity is much more attractive to private investment in electricity generation. Although the investment cost is low, the energy price is high, depending on the cost of the fuel. It depends on the international oil price, which also exhibits strong uncertainty. A revision of the Brazilian electric energy plan, brought about by the economic and political crisis of the Brazilian state electricity companies, has decided to delay the construction of 49 hydroelectric projects for a long time span. Meanwhile, three thermoelectric plants using oil have been substituted, and four coal plants were retained in the revision (Rosa and Tolmasquim, 1993). In the same way, the use of alcohol in transport is also endangered, because it costs more than gasoline. With no government protection, the free market must induce a progressive elimination of alcohol, substituting it with gasoline. As a concrete result of the policy of weak state intervention in the fuel market, the participation of alcohol fueled vehicles in total car sales has been decreasing. It was 96% in 1985, 88% in 1988, 55% in 1989 and about 20% in 1990. In 1989-90, there was a shortage in alcohol supply, due to the government no long stimulating sugar-cane production. So deregulation and privatization of energy in LDCs could have a negative consequence for global warming since pure market forces will push out biomass and hydro. There will therefore be an increase of CO2 emission per unit of energy used if the present tendency continues.
3 – CO2 and CH4 from Biomass Decomposition in Hydroelectric Reservoir in Amazon
In a previous work (Rosa and Schaeffer, 1994) we have shown that the traditional GWP index for CH4 is inappropriate for dealing with emissions from hydroelectric reservoirs when comparing them with greenhouse emissions from fossil fueled power plants. The original definition of GWP for CH4 is based on the ratio of the instantaneous radiative forcing of a pulse emission of CH4 and that of an equal and simultaneous emission of CO2 integrated up to an arbitrarily determined time horizon. However, it is obvious that the pattern of gas emissions from a hydroelectric reservoir is totally different from the pattern of emissions from a fossil fueled power plant. While CO2 emissions from the combustion of fossil fuels in a thermal power plant are released uniformly over the entire period of operation of the plant, the production of both CH4 and CO2 from the bacterial decomposition of flooded forest biomass in a hydroelectric reservoir is concentrated in time and decay over a period much shorter then the lifespan of the reservoir. Therefore, in order to compare the cumulative heating effects of emitted amounts of CH4 and CO2 with each other, three factors must be considered: a) the instantaneous radiative forcing due to a unit increase in the concentration of the gases; b) the decay time functions of the gases in the atmosphere and, last but not least; c) the emission patterns of the gases. In the case of hydroelectric reservoirs the magnitude and pattern of emissions will vary depending on biomass density and type of the flooded area, soil type, length of flooding (whether continuous or intermittent) and depth of flooding. There is some consensus that greenhouse gas emissions to the atmosphere from some hydroelectric reservoirs may be far from negligible (Oud, 1993; Rudd et al., 1993). There is less agreement, however, on the cumulative heating effects of those emissions over time per unit of energy produced compared to greenhouse gas emissions by fossil fueled electricity generation (Rosa and Schaeffer, 1994). It may be worthwhile, therefore, to investigate how hydroelectric reservoirs in the Amazon region in Brazil stand against fossil fueled power plants with respect to the cumulative heating effects of greenhouse gas emissions. We have made a comparison between the integrated radiative forcing from emissions from three hypothetical hydroelectric reservoirs similar (in terms of characteristics of reservoirs and extent and types of landscape flooded) to three real hydroelectric reservoirs in the Amazon region in Brazil (two existing and one projected) with low, medium and high ratios of energy produced to flooded area, and CO2 emissions from combined cycle natural gas and coal fired power stations over two different time horizons. The reason for assuming hypothetical, rather than real, hydroelectric power stations is to allow a wide range of estimates using different biomass densities (since forest biomass varies greatly in different parts of the region) as well as different rates for bacterial decomposition of forest biomass to CH4. By applying our generalized GWP inde we have been able to express the CH4 fluxes as “CO2 equivalents” and compare their warming effects with those from the CO2 fluxes. Results are strongly dependent on assumptions and on time horizons. For reservoirs with medium and high ratios of energy produced to flooded area, the estimated integrated radiative forcing per unit of energy produced were 0.22-1.50 (Mt C pa)/MWh and 0.04-0.25 (Mt C pa)/MWh equivalent units respectively over 100 years. These estimates are clearly much lower than the cumulative heating effects of electrical generation by fossil fueled power plants: 4.45- 10.23 ( Mt C pa) / MWh. For a reservoir with a low ratio of energy produced to flooded area , however, the estimated integrated radiative forcings per unit of energy produced were 0.91-6.27 (Mt C pa)/TWh equivalent units over 100 years. These estimates may be lower or similar in order of magnitude to the greenhouse effect of fossil fuelled electrical generation, depending on biomass density and CH4 production in the flooded area, fossil fuelled electrical generation technology and time horizon of concern. In any case, however, the longer the planning horizon the better hydroelectricity becomes and the worse thermoelectricity becames. This is a direct consequence of both the distinct pattern of emissions between hydroelectricity and thermoelectricity, and also a consequence of the different atmospheric lifetime of CH4 as compared to CO2.
In this paper, which was prepared as part of IEA Bioenergy Task XV (“Greenhouse Gas Balances of Bioenergy Systems”), we outline a standard methodology for comparing the greenhouse gas balances of bioenergy systems with those of fossil energy systems. Emphasis is on a careful definition of system boundaries. The following issues are dealt with in detail: time interval analysed and changes of carbon stocks; reference energy systems; energy inputs required to produce, process and transport fuels; mass and energy losses along the entire fuel chain; energy embodied in facility infrastructure; distribution systems; cogeneration systems; by-products; waste wood and other biomass waste for energy; reference land use; and other environmental issues. For each of these areas recommendations are given on how analyses of greenhouse gas balances should be performed. In some cases we also point out alternative ways of doing the greenhouse gas accounting. Finally the paper gives some recommendations on how bioenergy systems should be optimized from a greenhouse-gas-emissions point of view.