Climate Change and Managed Ecosystems - Chapter 11 doc

Biomass can also be used to provide an energy resource that can complement our existing fossil energy streams, thereby reducing net GHG emissions so long as the biosphere carbon stocks a

to Biosphere

Greenhouse Gas

Management

D.B Layzell and J Stephen

CONTENTS

11.1 Introduction 218

11.2 Biosphere Solutions 218

11.2.1 Reduce Biosphere GHG Emissions 218

11.2.2 Sequester Atmospheric CO2 218

11.2.3 Complement Fossil Energy Streams 219

11.2.4 Adapt Our Biosphere to a Changing Atmosphere and Climate 219

11.3 The Bioenergy Challenge 219

11.4 Sustainable Sources of Biomass 220

11.4.1 Municipalities 221

11.4.2 Agriculture 221

11.4.3 Forestry 222

11.5 Case Study: Accessing Biomass from Disturbed Forest Sites 222

11.5.1 Option 1 Harvest Biomass for Fiber Markets 223

11.5.2 Option 2: Leave the Biomass to Decompose 224

11.5.3 Option 3: Harvest for Bioenergy 224

11.6 Case Study: Impact of Various Feedstock-to-Product Threads 224

11.6.1 Biopower 224

11.6.2 Bioethanol 227

11.6.3 Biodiesel 227

11.6.4 Conclusion 228

11.7 Socioeconomics of Biomass Energy 228

11.8 Conclusions 229

Acknowledgment 230

References 230

11.1 INTRODUCTION

Plants have been in the business of managing greenhouse gases (GHGs) and solar energy for hundreds of millions of years Therefore, in a world where there are concerns about climate change and energy supply, it is not unreasonable to look to biological systems and the biosphere both for solutions to these challenges and for

a better understanding of the processes regulating atmospheric levels of greenhouse gases and the Earth’s climate

This is especially true for Canada, a nation with a vast biosphere and a relatively small population In Canada, the annual flux of carbon into and out of biological systems is more than ten times the nation’s emissions of CO2 from fossil fuel energy use The biosphere is also a large natural source and sink for the other greenhouse gases, nitrous oxide (N2O) and methane (CH4)

This chapter provides a brief overview of the role that the biosphere could play

in helping Canada address the challenges of climate change and energy supply It also explores the potential for using biomass to meet Canada’s energy demands, and the relevance of doing so on biosphere management in a climatically different future

11.2 BIOSPHERE SOLUTIONS

Biosphere solutions to the challenges of climate change and energy supply can be classified into four options for action

Agricultural systems in Canada are responsible for 8 to 10% of the nation’s annual GHG emissions Approximately half of these agricultural emissions are associated with N2O production from cropping systems, whereas the remainder involve N2O and CH4 production associated with animal production and manure management.1 Through improved management practices for cropping systems, animal produc-tion, or manure management,2 it is possible to reduce these emissions Such “ben-eficial management practices” may also reduce input costs, water pollution, soil degradation, or farm odors, so there can be benefits that are additional to GHGs and climate change

New technologies may also play a role in reducing GHG emissions Precision farming2 could ensure more efficient use of fertilizers, new fertilizer formulations could reduce the nitrification and denitrification processes that lead to N2O emis-sions, and new crops could be selected or engineered for improved N use, which may also reduce N2O emissions Similarly, improved feed formulations or antime-thanogenic feed additives can reduce CH4 production and manure production in ruminants,3 and a range of improved manure-handling technologies will reduce GHG emissions.4

Through photosynthesis, plants use the energy of the sun to remove CO2 from the atmosphere and sequester it into energy-rich biomass Initially, this biomass is living,

Linking Biomass Energy to Biosphere Greenhouse Gas Management 219

but when it dies, it can enhance soil carbon stocks before it eventually returns to the atmosphere through either respiration or fire Increases in carbon stocks, be it the living biomass in trees and perennial crops or the organic carbon in soils, could

be used to remove CO2 from the atmosphere

Improved land management strategies and a range of technologies are well known to build or preserve biosphere carbon stocks and could play a major, albeit temporary role in offsetting fossil fuel emissions Examples in the forest sector include afforestation, fire and pest control in forests, use of faster-growing tree genotypes, selective harvest, rapid replanting after harvest and pre-commercial thin-ning In agriculture, reduced tillage, crop rotation, incorporation of char, the culti-vation of perennial biomass crops, or the development of new crops that build soil carbon pools have all been proposed as strategies for biosphere sequestration of atmospheric CO2

Biomass can also be used to provide an energy resource that can complement our existing fossil energy streams, thereby reducing net GHG emissions so long as the biosphere carbon stocks are not depleted This option is considered in more detail below

AND C LIMATE

If Canada is to manage its biosphere to reduce GHG emissions, sequester more carbon into biomass, and use a portion of that biomass to provide an energy resource,

we will need to do this in a future in which the atmospheric CO2 is higher and the climate is changed from what it has been in the past Such a future will have both positive and negative effects on the health and vitality of the biosphere, and in the case of the negative impact, human intervention in the form of new management strategies and technologies will be needed to help the biosphere adapt

Examples include replanting after forest harvest or natural disturbance with genotypes or species that are better suited to future climate and the stresses associated with climate change, the establishment of north–south corridors to facilitate the movement of plant and animal species, or the selection or engineering of crops so they can take better advantage of a high-CO2 future

11.3 THE BIOENERGY CHALLENGE

Canada’s primary energy consumption in 2000 was about 12.6 exajoules (EJ), with approximately 8.24 EJ yr–1 coming from the combustion of fossil fuels.5,6 In Canada, the CO2 emissions from these fossil fuels are about 150 Mt C yr–1

Because biomass has lower energy content than fossil fuels,6 providing the same energy output requires more of the feedstock This is especially the case with wet biomass being processed thermochemically because energy must be expended to dry the biomass before processing In addition, the carbon content of most biomass

is typically lower than that of fossil fuels, so to provide a given amount of energy about 1.5 to 2 times the weight of biomass is required compared to that of coal Assuming that biomass has 50% water, the effective energy content would be about 30 GJ per tonne of biomass carbon.6 Therefore, to provide the 8.24 EJ of energy that Canada now derives from fossil fuels would require about 275 Mt yr–1 biomass carbon The aboveground carbon content of Canada’s forests has been estimated at 15,800 Mt C,7 equivalent to approximately 57 years of our current energy demand from fossil fuels

Perhaps a more relevant reference point is that currently biomass has been estimated to provide about 6% of Canada’s energy needs,6 a sink for about 16 Mt

C yr–1, primarily through home heating and power generation The total annual agriculture and forest harvest in Canada is about 143 Mt biomass C,7 a value equivalent to 50% of the biomass needed to meet the nation’s current fossil fuel energy demand Not all of this harvested biomass makes its way into products; recent estimates7 suggest that up to 50 Mt C yr–1 is residual, some of which could be used

as a bioenergy resource Economic and environmental concerns are key factors in determining the proportion that is accessible, and to date no consensus exists whether this proportion is as low as 20% (10 Mt C yr–1) or as high as 70% (35 Mt C yr–1) Even considering this resource, for Canada to meet its entire fossil fuel demand would require a threefold increase in the size of the forestry and agricultural harvest, with two thirds of the total harvest directed to bioenergy It is difficult to imagine

an increase in harvest of this magnitude, especially if it were to be done with minimal environmental impact Nevertheless, as discussed in the next section, there is capacity for a significant increase in the forestry and agricultural harvest in Canada, and when this is coupled with waste or residual carbon coming from municipalities, agriculture, and forestry, it is clear that biomass energy could complement our fossil energy streams, while helping the nation meet its climate change commitments Of course,

to do this, biomass resources in the range of many tens of megatonnes of biomass

C must be identified and directed toward bioenergy

11.4 SUSTAINABLE SOURCES OF BIOMASS

If Canada is to expand its use of biomass energy, it will be very important to ensure that the effort is sustainable, not only in economic and social terms, but in environ-mental terms For example, maintaining or enhancing biodiversity and minimizing environmental damage from pesticides and fertilizers are key issues Also, to address concerns about climate change, it will be imperative that biosphere carbon stocks are maintained in the face of an increased harvest and removal of biomass from ecosystems Because biomass has a lower energy content than coal or other fossil fuels and because biomass C stocks are more likely than fossil fuels to provide habitat for other organisms, the use of biomass energy in a way that depletes C stocks would be less sustainable, and have a greater climate change impact, than the use of any fossil fuel resource

New and improved biomass processing technologies will also be important, as

it will be necessary to avoid the particulate emissions and other environmental

Linking Biomass Energy to Biosphere Greenhouse Gas Management 221

impacts associated with simple combustion and other traditional biomass energy technologies

So what are the sustainable sources of biomass and how much carbon could be obtained from each? At the present time, this information can only be estimated (Table 11.1), and very little work has been done to explore the costs and feasibility

of accessing these biomass energy streams for use in power, transportation fuels, or heavy industry Consequently, the analysis presented below explores only the bio-mass energy resources, not the feasibility of accessing these carbon streams, eco-nomically or otherwise

Municipal solid wastes (MSW) that are currently discarded (rather than recycled) have been estimated to contain about 6 Mt C yr–1 Together with industrial waste, biosolids, and landfill gases, a waste carbon stream of up to 15 Mt C could be made available.7

Of the 55 Mt C that are harvested from agricultural lands every year, about 33 Mt

C are in the primary products for which the crops were grown.7 There are other uses for the crop residues, including the maintenance of soil carbon stocks, but when the surplus is combined with animal waste, a bio-based carbon stream of up to 10 Mt

C yr–1 or more should be available

In addition, Canada has more than 7 million hectares of unused agricultural land,

a significant portion of which could be brought into production for biomass crops Such crops are typically fast-growing perennials, and can produce lignocellulosic

TABLE 11.1

A Summary of the Magnitude of Possible Sources of

Biomass That Could Be Used as a Sustainable

Bioenergy Resource

Mt C yr –1 Municipalities

Municipal solid waste, landfill gas, industrial waste 5 to 15

Agriculture

Waste (animal and crop), residues 2 to 10

Fast-growing species on unused lands 10 to 20

Forestry

Unused harvest and mill residues 10 to 30

Enhanced forest management 20 to 40

Harvest remaining carbon stock after severe disturbance 5 to 30

carbon at two to four times the average carbon accumulation rate of Canada’s current food crops (∼1.7 tC ha–1 yr–1)7 Assuming 7 million hectares producing lignocellu-losic biomass at a conservative 3 tC ha–1 yr–1, there would be an annual biomass carbon stream of more than 20 Mt C

Each year Canada’s forest industry harvests about 88 Mt C on 1 million of the 245 million hectares of timber productive forest Approximately 48 Mt C are removed from the site, and some of the remaining 40 Mt C are needed to maintain soil carbon stocks, other nutrients, and biodiversity.7 Unfortunately, there is no consensus regard-ing how much of this could be removed sustainably and at an acceptable cost In

Table 11.1, we have provided an estimated range of 10 to 30 Mt C yr–1

Enhanced forest management could be used to build biomass carbon stocks to provide a biomass energy resource Pre-commercial thinning, replanting after har-vest, improved pest or fire control, or the judicious use of fertilizers could all contribute to the health and vitality of forests, making it possible to increase the harvest of biomass on a landscape or regional scale with little or no negative impact

on net carbon stocks or biodiversity Assuming current forest management practices are sustainable from the perspective of carbon stocks and energy input, improvements

in management practices could increase forest growth and yield by 25 to 80%.8,9 This could provide a bioenergy resource of 20 to 40 Mt C yr–1 (Table 11.1) Large natural disturbances, such as those caused by fire, insect, wind, or floods, could also provide a source of forest biomass to support a bioenergy future for Canada Given that an actively growing Canadian forest accumulates carbon at a rate of 1 to 2 tC yr–1,10 the fact that Canada has 240 M ha of timber productive forest, and that disturbance plays a major role in determining the net carbon balance

of our forest ecosystems, a conservative estimate of biomass carbon that could flow

to bioenergy from disturbed sites is 5 to 30 Mt C yr–1 (Table 11.1) A case study exploring options for the possible use of this biomass from natural disturbance follows

11.5 CASE STUDY: ACCESSING BIOMASS FROM

DISTURBED FOREST SITES

In developing strategies for mitigating climate change through biosphere greenhouse gas management, it is also important to recognize and plan effective responses to the predicted effects of a future world with high atmospheric CO2 and a different climate The International Panel on Climate Change11 has predicted significant climate impacts on North American forests over the next 50 years, including greater frequency and impact of “catastrophic events (e.g fire, insect outbreaks, pathogens, storms) that have marked effects on ecosystem structure … leading to changes in composition as forests regenerate under altered conditions.”

In recent decades, 2.8 million hectares of forested lands have been burned every year in Canada, representing approximately 27 Mt C.12 Large fires of greater than

1000 ha in size account for only 1.4% of forest fires in Canada, but represent 93.1%

Linking Biomass Energy to Biosphere Greenhouse Gas Management 223

of the total area burned.8 These statistics account for the fact that there is a large year-to-year variability in losses to fires, ranging from 3 Mt C to over 115 Mt C.13 Fire activity, including land area and total biomass burned, has been increasing

in Canada over the past three decades On average, increased fire activity is the result of decreased moisture conditions, brought about by increased temperatures and reductions in rain/snow fall.14 An earlier start date to the fire season and an increase in the area under high to extreme fire risk have already been seen as temperatures have risen in recent years.15 Based on general circulation models (set

to two times pre-industrial atmospheric CO2), the trend is expected to continue.15 Insect infestations are the single largest cause of losses in Canada’s forests, accounting for 1.4 to 2 times that lost to fire Since climate change over the next 50 years has been predicted to accelerate insect development, expand current ranges (particularly northward), and raise overwinter survival rates,16 losses due to insect infestation may increase For example, stresses put on trees by climate, such as unusually high temperatures or drought conditions, make them more susceptible to attack An earlier spring enhances the likelihood of synchronous development between insects and buds of their host, leading to increased survival rates.16 Insect infestations cause changes in ecosystem carbon and nutrient cycling and increase rates of decomposition, due to tree mortality In addition, they significantly increase the risk of wildfires.10

Approximately 6.3 million hectares of forest (at a conservative 25 t C ha–1, this would be equivalent to 160 Mt C) are currently infected by insects, and tree mortality rates on these sites can reach 85%.16,17 Insect infestation is a leading cause of pathogen infection, and fungi play the most important role in enhancing death rates Storms and extreme weather events, such as the 1998 ice storm in eastern Ontario and Quebec,10 are also likely to increase in occurrence and intensity12 and may be

a third source of adverse climate impacts on Canada’s forests In future decades, there may be significant forest death due to temperature and water stress linked directly to climate change.18

There are several options for the excess timber that will be generated as a result of climate change and the associated impacts of temperature, fire, infestation, and disease

This is currently done with some of the dead biomass, especially that left from insect infestation However, if the harvest is not carried out reasonably soon after distur-bance, there is a decline in the suitability of the timber for higher-value wood products This fact, coupled with the sheer magnitude of supply from heavily dis-turbed ecosystems, means that the biomass supply from disturbance is likely to swamp either the processing capacity in the region of the disturbance or the regional and global markets for the forest products, especially in a climate-different future

On the basis of climate models, higher-latitude timber producers are expected

to be the hardest hit by climate change because of a large predicted increase in the availability of timber, but a relatively low predicted growth in demand for wood products.19 An increase in harvest scope to include more damaged and “at-risk” trees would only widen this difference between supply and demand

11.5.2 O PTION 2: L EAVE THE B IOMASS TO D ECOMPOSE

This strategy is currently being used in many situations involving major disturbances

On the positive side, the nutrients are being left in the field to be recycled, and the carbon will remain for perhaps a few years or decades where it will continue to act

as a carbon sink However, the biomass carbon will eventually decompose or be burned, and in the latter case, the fire will take with it much of the biomass carbon that has regrown in the meantime Even though fire-affected sites provide an oppor-tunity for forest managers to replant them with tree species that are better adapted

to the climate-different future in which they must grow, it seems likely that there would be an overall decline in carbon stocks on affected lands over time, and it could be many decades or centuries before this trend would be reversed

Once a tree is dead, it will no longer gain carbon, but it begins to decompose or it will burn in a forest fire Either way, the carbon and the energy it contains will be released to the atmosphere By harvesting the biomass and processing it to extract its energy content, the biomass could replace fossil fuels in the energy streams, thereby providing energy for human needs and reducing the associated greenhouse gas emissions This strategy would reduce forest fire risk, remove diseased or infected trees that might reinfect others, and make it possible for forest managers

to better manage the affected area to ensure rapid forest regrowth, thereby rebuilding carbon stocks Recent studies have calculated that, in the long run, managed bioen-ergy systems will have a much greater impact on reducing greenhouse gas emissions than forest management practices focused solely on building carbon stocks.20

11.6 CASE STUDY: IMPACT OF VARIOUS

FEEDSTOCK-TO-PRODUCT THREADS

Compared to other developed nations, Canada has very large biomass reserves, and has the capacity to produce more biomass that could feed into human energy systems Indeed, Table 11.1 identifies potential sources of 52 to 145 Mt biomass carbon If this magnitude of biomass were to be used for energy production in Canada, bioen-ergy would make a significant and lasting contribution to Canada’s enbioen-ergy needs and the challenges of climate change

To illustrate this point, we present below three case studies of feedstock-to-product threads For each, we explore what could be achieved with 10 Mt biomass carbon in terms of Canada’s energy demands and GHG benefits

Biomass for power, or biopower, is a technology that already exists and is being implemented, especially by forestry companies using their mill wastes Canada produces 576 TWhr of electricity each year (Table 11.2, Item 1a), only 15 of which

is from biomass, whereas 19% comes from coal combustion that leads to significant

Linking Biomass Energy to Biosphere Greenhouse Gas Manag

TABLE 11.2

Comparison of the Contribution that 10 Mt Biomass Carbon Could Make to Canada’s Energy Demand for Electrical Power

and Liquid Fuels, and the Calculated Net Impact on Greenhouse Gas Emissions

1 Biopower

a Current Cdn Power Consumption TW hr 576 100% From Cdn Electrical Association (www.canelect.ca)

Resource Potential of 10 Mt C

b 10 Mt C yr –1 at 16% conversion efficiency TW hr 10Mt C –1 13.3 2.3% Assumes 100% energy conversion would yield 8.33 MWhr tC –1 (30 GJ t

C –1 and 3.6 GJ MWhr –1 ) [22]

c 10 Mt C yr –1 at 40% conversion efficiency TW hr 10Mt C –1 33.3 5.8% Assumes 100% energy conversion would yield 8.33 MWhr tC –1 (30 GJ t

C –1 and 3.6 GJ MWhr –1 ) [22]

d GHG emissions from coal power generation g CO2e KW hr –1 1042 [23]

GHG Mitigation Potential Assuming Coal Displacement

e 10 Mt C yr –1 at 16% conversion efficiency Mt CO2e yr –1 13.9 Calculated as (1d) × (1b) 1000 –1

f 10 Mt C yr –1 at 40% conversion efficiency Mt CO2e yr –1 34.7 Calculated as (1d) × (1c) 1000 –1

2 Bioethanol

a Current Canadian gasoline use GL yr –1 40.3 100% [24]

Resource Potential of 10 Mt C

b Starch crop: 10 Mt C yr –1 at 844 l tC –1 GL yr –1 8.4 21% Assumes 380 l ethanol t –1 biomass at 45% C [25]

c Lignocellulose crop: 10 Mt C yr –1 at 620 l tC –1 GL yr –1 6.2 15% Assumes 310 l ethanol t –1 biomass at 50% C [25]

d Canadian GHG emissions from gasoline Mt CO2e yr –1 111 Assumes Item 2a × 2.75 kg CO 2 l –1 [1]

© 2006 by Taylor & Francis Group, LLC

Climate Chang

TABLE 11.2 (continued)

Comparison of the Contribution that 10 Mt Biomass Carbon Could Make to Canada’s Energy Demand for Electrical Power and Liquid Fuels, and the Calculated Net Impact on Greenhouse Gas Emissions

GHG Mitigation Potential Assuming Gasoline Displacement (per km traveled)

e Starch crop: 10 Mt C yr –1 at 844 l tC –1 Mt CO2e yr –1 8.1 Calculated as (2d) * (2b%) × Life cycle factor [F(LCA)], where F(LCA)

= 35% [22]

f Lignocellulose crop: 10 Mt C yr –1 at 620 l tC –1 Mt CO2e yr –1 13.6 Calculated as (2d) * (2c%) × Life cycle factor [F(LCA)], where F(LCA)

= 80% [26]

3 Biodiesel

a Current Canadian petroleum diesel use GL yr –1 26.6 100% [24]

Resource Potential of 10 Mt C

b Oil seed crop: 10 Mt C yr –1 at 813 l tC –1 GL yr –1 8.1 31% Assumes 528 l t –1 seed at 65% C [27]

c Lignocellulose crop: 10 Mt C yr –1 at 300 l tC –1 GL yr –1 3.0 11% Assumes 150 l t –1 biomass at 50% C [28]

d Canadian GHG emissions from diesel Mt CO2e yr –1 73 Assumes Item 2a × 2.75 kg CO 2 l –1 [1]

GHG Mitigation Potential Assuming Diesel Displacement (per km traveled)

e Oil seed crop: 10 Mt C yr –1 at 813 l tC –1 Mt CO2e yr –1 11.2 Calculated as (3d) * (3b%) × Life cycle factor [F(LCA)], where F(LCA)

= 50% [25]

f Lignocellulose crop: 10 Mt C yr –1 at 300 l tC –1 Mt CO2e yr –1 8.3 Calculated as (3d) * (3c%) × Life cycle factor [F(LCA)], where F(LCA)

= 100% [29]

© 2006 by Taylor & Francis Group, LLC