67322 Paper number 122 E N V I R O N M E N T D E PA R T M E N T PA P E R S Climate Change Series Black Carbon and Climate Change Considerations for International Development Agencies Michael Levitsky December 2011 Sustainable Development Vice Presidency The World Bank Environment Department Black Carbon and Climate Change Considerations for International Development Agencies Michael Levitsky December 2011 Papers in this series are not formal publications of the World Bank. They are circulated to encourage thought and discussion. The use and citation of this paper should take this into account. The views expressed are those of the authors and should not be attributed to the World Bank. This book is available on-line from the Environment Department of the World Bank at: www.worldbank.org/environmentaleconomics © The International Bank for Reconstruction and Development/THE WORLD BANK 1818 H Street, N.W. Washington, D.C. 20433, U.S.A. Manufactured in the United States of America First published December 2011 Design: Jim Cantrell Cover photos: Burning sugarcane fields, Africa. © Shutterstock, LLC Contents Preface v Acknowledgments vii Acronyms and Abbreviations ix Executive Summary 1 Chapter 1 — Introduction 7 Chapter 2 — Black Carbon and Climate Change 11 Description of Black Carbon 11 Effects of Black Carbon on Climate Change 12 Chapter 3 — Sources of Black Carbon and Their Impact on Climate Change 17 Coal 18 Diesel Fuel 18 Gas Flaring 19 Residential Biomass 19 Open Burning of Biomass 21 Chapter 4 — Global Volumes of Black Carbon Emissions 23 Chapter 5 — Black Carbon Mitigation Policies and Costs 27 Coal 27 Diesel 27 Biomass 28 Costs of Mitigation 30 Chapter 6 — Black Carbon and Global Climate Change Policy 33 Climate Change Series iii Black Carbon and Climate Change — Considerations for International Development Agencies Chapter 7 — Considerations for Development Agencies 35 Mainstreaming Consideration of Black Carbon in Development Work 35 Supporting Projects that Reduce Black Carbon to Yield Climate and Health Co-benefits 36 Filling the Knowledge Gaps 37 Exploring Global and Regional Policy Options to Include Black Carbon in Climate Change Policy 38 References 39 Boxes 1. Effects of Black Carbon Emissions on the Arctic 13 2. Impact of Black Carbon on Clouds and Resulting Climate Change 15 3. Impact of Particulate Matter Emissions from Residential Biomass on Climate 20 4. Control of Black Carbon from Diesel Fuels 29 Figures 1. The Impact of Black Carbon on the Global Climate 12 2. Estimates of Radiative Forcing for Greenhouse Gases and Black Carbon 14 3. Global Sources of Black Carbon Emissions, 2000 23 4. Black Carbon Emissions from the Energy Sector by Region, 2000 24 5. Historical Emissions of Black Carbon by Fuel and Region 25 Table 1. Sources of Black Carbon and Their Impact on Climate 17 iv Environment Department Papers Preface O ver the past decade black carbon has come inhibit policy preparation and consideration of black to be seen as a major agent contributing to carbon in development work. global warming. Emissions of black carbon come from all countries, but developing This paper aims to provide an overview of this countries play a particular role since some emissions important topic for development practitioners, and are closely associated with poverty and with the process suggests some considerations for integrating the impact of economic development. These include black carbon of black carbon on climate into broader development from the transport sector and from use of biomass policy. It is not a detailed scientific review, nor does it and coal in the rural residential sector. As an element cover all aspects of this multifaceted issue. The aim is to of particulate matter pollution black carbon has introduce the topic to development specialists working already attracted much attention from development in climate change policy, and in the many sectors where practitioners, due to the severe effects of such pollution black carbon is an issue, including transport, energy, on public health. Climate change thus brings a new urban development, rural development, and public global environmental dimension to a well-known local health. environmental and health problem. As evidence of the mounting importance of this topic, The scientific understanding of the role of black carbon the link between black carbon and climate change is in climate change has lagged behind that for carbon the subject of a rapidly growing number of publications dioxide and other greenhouse gases. The gap appears to among climate change research and policy groups. be closing as research is expanding rapidly. Yet as this While this paper focuses on material published until basic paper seeks to describe, the scientific challenges to the end of 2010, it makes note of further key reports quantifying the contribution of black carbon to climate released prior to publication. change remain significant. However, this should not Climate Change Series v Acknowledgments T his paper was prepared by Michael Levitsky Specialist, SEG), Ian Noble (Lead Environmental (ENV Climate Change Team, and SEG Specialist, ENV), Nataliya Kulichenko (Senior Energy Oil, Gas and Mining Division). The author Specialist, SEGEN), Alan Miller (Principal Project is grateful for support and comments from Officer, CBGSM), Xiadong Wang (Senior Energy Kseniya Lvovsky (Country Manager, Albania, formerly Specialist, EASIN), Masami Kojima (Lead Energy Program Manager, ENV Climate Change Team), Jane Specialist, SEGOM), Sonu Jain (Consultant, ENV), Ebinger (Program Manager, ENV Climate Change and other World Bank staff. Michael MacCracken Team), and Sameer Akbar (Senior Environmental (Chief Scientist for Climate Change Programs, the Specialist, ENV). The paper also benefited greatly from Climate Institute) provided valuable advice on climate comments from Daniel Kammen (Chief Technical science and policy. Climate Change Series vii Acronyms and Abbreviations ABC Atmospheric brown cloud BC Black carbon CH4 Methane CNG Compressed natural gas CO2 Carbon dioxide DPF Diesel particulate filter GHG Greenhouse gas GWP Global warming potential IEA International Energy Agency IMO International Maritime Organization IPCC Intergovernmental Panel on Climate Change LPG Liquified petroleum gas OECD Organisation for Economic Co-operation and Development PM Particulate matter RF Radiative forcing SLCF Short-Lived Climate Forcers SO2 Sulfur dioxide ULSD Ultra-low sulfur diesel UNFCCC United Nations Framework Convention on Climate Change USAID United States Agency for International Development W/m 2 Watts per square meter Climate Change Series ix Executive Summary T his report is intended to inform the a significant fraction of CO2 emissions. Hence BC, international development community about unlike CO2, does not accumulate from year to year; the links between black carbon and climate instead it is constantly replenished by the human and change. With growing scientific clarity on the natural activities of the previous few weeks. contribution of black carbon to climate change, the benefits of limiting its emissions are becoming more What is Known About the Impact of Black evident. This report reviews the existing knowledge on Carbon on the Climate? the subject and identifies relevant considerations for development organizations. BC warms the atmosphere differently than greenhouse gases (GHGs). It is highly effective in absorbing energy from the sun, which the particles then convey to the What is Black Carbon? atmosphere. It also darkens snow and ice, causing Black carbon (BC) consists of extremely small particles them to warm and melt more rapidly. The melting that result from the incomplete combustion of fossil usually reveals darker land or sea, making the Earth’s fuels and biomass. Commonly known as soot, it is one surface less reflective, which amplifies global warming. of the many types of particulate matter (PM, also called Increasing evidence indicates that BC is a major cause aerosols) that influence the climate; the others include of the rapid warming and melting of snow and ice in sulfates and volcanic ash. Over the past decade, BC has the Arctic and the Himalayas. In addition to the direct come to be recognized as one of the principal agents effect on atmospheric warming, BC and other aerosols of global warming. Climate science now views BC as have large indirect effects on the global climate through the second or third largest warming agent after carbon their complex influence on clouds and precipitation. dioxide (CO2), alongside methane. Moreover, particles undergo chemical changes after they are emitted. Calculation of the net impact of these The primary emissions sources of BC include burning direct and indirect effects must take into account their of agricultural land and forests (both human-induced interactions and various feedback mechanisms. Such burning and natural burning), use of biomass for fuel calculations are done using global climate models of (wood, charcoal, and so forth), coal use in households increasing sophistication. Scientific understanding of and industry, and use of diesel for transportation and how the multiple actions of BC affect the climate is far stationary power generation. In large power stations from complete and is less comprehensive than for the using coal, the PM is almost always filtered out from GHGs. Considerable research is being carried out in emissions. this area, with rapid progress being made. The average lifetime of BC particles in the atmosphere BC is emitted with organic carbon particles, which is one to two weeks, compared with millennia for tend to condense into gray or white PM (that is, Climate Change Series 1 Black Carbon and Climate Change — Considerations for International Development Agencies smoke) that can reflect sunlight back into space, thus growth is likely to decline as incomes rise further in the exerting a cooling influence on the climate. While coming decades. black smoke has a high proportion of BC and exerts a strong warming influence, white smoke contains mostly Why Reduce Emissions of Black Carbon? organic carbon and so exerts a cooling influence. For example, open burning of biomass creates near-white Since its substantial role in global warming is becoming smoke and thereby exerts a large net cooling influence. clearer, BC is becoming more prominent in global Use of biomass for cooking creates varieties of gray strategies to address climate change. Climate models smoke that may have either a net warming or net show that a rapid reduction in BC emissions would cooling influence. In contrast, diesel engines and coal reduce their warming influence over the ensuing combustion create almost black smoke that is strongly months roughly in proportion to the amount of BC in warming. the atmosphere. In theory, the elimination of all BC emissions from the global atmosphere could postpone Because it consists largely of BC, cutting PM from exceeding the threshold of dangerous warming by one diesel and coal is highly likely to reduce global or two decades. In practice, however, it is not possible warming; however, in the case of open burning and to reduce BC emissions selectively; any policy cutting biomass from cooking stoves, cutting PM may not BC emissions would also reduce emissions of cooling always lead to a net reduction in global warming, organic carbon. It should be emphasized that tackling because cooling from lower BC emissions is offset by BC emissions alone will not solve the basic problem the reduction in cooling (that is, increase in warming) of climate change, which is caused by the long-term from lower emissions of organic carbon. When looking accumulation and persistence of the climate effects of at the net climatic impact of changing an activity, such CO2 and other GHGs. as biofuels burning, all of the co-emissions of gases and PM from the activity need to be considered. In addition to causing global warming, BC has substantial effects on the regional climate. In areas with Along with other aerosols and short-lived gases (for high emissions of BC, the resulting extensive brown example, ozone), BC was not included in the Kyoto haze can affect temperature and precipitation. Early Protocol. This is partly because of the limited scientific evidence is suggesting that large BC emissions in India understanding at the time of the contribution of BC and China have caused shifts in the Indian monsoon to climate change. In addition, estimating the volumes and in Chinese rainfall patterns. The impact of BC of emissions of BC is difficult, as they come from a on ice and snow, and hence on water accumulation, very large number of sources and processes. Due to is becoming increasingly important in assessing the its short atmospheric lifetime, BC is not uniformly total effect of climate change in the Arctic and the mixed in the atmosphere, and its concentrations can Himalayas. In these regions, the specific local effects vary regionally, preventing the straightforward global of BC add to the impact of global warming, causing atmospheric sampling done for measuring the volumes temperatures to rise much more rapidly than the global of GHGs. Moreover, the impacts of BC are regional as average. At the regional level, organic carbon does not well as global, unlike the Kyoto gases where the impacts offset the effects of BC, and all sources of BC emissions, are almost entirely global. Emissions estimates indicate including biomass burning, contribute to BC’s net that the mass of BC emitted from developed countries climatic impacts. has been decreasing as burning of biomass has declined and coal and diesel emissions controlled. In developing The adverse health impacts of inhaling BC, which are countries, BC emissions are rising, although the rate of similar to those caused by other small PM, are well 2 Environment Department Papers Executive Summary understood. The widespread use of biomass and coal for produce ultra-low sulfur diesel (ULSD) that permits cooking in developing countries makes PM, including removal of PM from vehicle emissions. Even when such BC, one of the leading causes of death and disease, with diesel is available, vehicles must possess the advanced about 2 million premature deaths a year from damage technology to cut PM emissions, such as vehicle to the respiratory organs. PM from diesel engines and particle traps. Introducing advanced biomass cookstoves industrial coal use also damages health significantly. To to poor rural households in developing countries in date all interventions that reduce BC have been done order to cut PM emissions has taken much longer than as part of a program to limit health damage from PM. expected, due to the difficulty of overcoming a range of Because the environmental consequences of emissions local economic, social, and technical barriers. Cooking of BC are both local (health) and global (climate with clean petroleum fuels is not affordable for most change), dealing with BC can provide a good example low-income households, and the priority has been to of co-benefits from environmental policies. Reducing introduce improved cookstoves, of which a wide range PM from diesel and coal clearly benefits health, reduces are available. perturbations in regional climates, and reduces global warming; reducing PM from biomass burning clearly Many studies have detailed the costs and benefits on benefits health, reduces perturbations in regional health grounds of reducing emissions of PM, which climates, and may also reduce global warming. includes BC. However, there has been limited analysis that also takes into account the climate impact of BC and organic carbon emissions. Calculating the Challenges Ahead overall economic costs and benefits of mitigating BC The policy priorities for dealing with the effects of involves assessing impacts in multiple areas, including human-induced BC emissions on climate require health, and both regional and global climate impacts. careful consideration. These need to address both the Much work remains to be done in this area and there challenges of reducing PM emissions overall and the is significant potential for advancing understanding. different impacts of lower PM emissions from various Improved data on BC and organic carbon emissions is activities. Thus, cutting PM from diesel and coal will much needed, particularly for biomass cooking. reduce global warming due to the high proportion of BC in emissions. But cutting PM from biomass Considerations for the Future burning (open burning and cooking) will have less certain impacts on climate because of the need to take Development agencies deal with activities that can into account the offsetting impact of BC and organic generate or reduce BC in developing countries, directly carbon. Climate science is still evolving, and its or indirectly. Since BC has significant environmental messages for policy may change. consequences, understanding these is important for the agencies’ operations and policies. In the short run, large-scale global mitigation of BC emissions is still challenging in many respects. The Agencies could consider addressing BC emissions in a technologies to reduce PM, including BC, are well number of ways: known. They are being introduced in high-income • Mainstream consideration of BC in development countries, where they will eventually lead to reduced work: The current investments and policies sup- BC emissions. The introduction of these technologies ported by development agencies have impacts on in developing countries will require new policy emissions of BC and organic carbon. The agencies initiatives and substantial investment. For diesel, large could consider describing the climate effects of capital expenditures will be needed in refineries to Climate Change Series 3 Black Carbon and Climate Change — Considerations for International Development Agencies these emissions alongside other project impacts, explored if projects are to go beyond conventional initially in qualitative terms. A key aspect for agen- development finance. cies is the cross-cutting nature of BC emissions, • Fill the knowledge gaps: Improved analysis can be which can be affected by activities in a number of done on the economic costs and the health and sectors. These include the energy, environment, climate co-benefits of mitigating BC and other transport, industry, rural, health, and urban PM emissions. Agencies’ knowledge base in project sectors. Projects and policies in which the impact economics, pollution control, and climate mitiga- of BC and organic carbon could be considered tion strategies could give them an advantage in include those involving diesel use in transport and addressing the problem. Agencies could consider power, coal use in industry and the residential sec- supporting efforts to improve knowledge of the tor, biomass use in the residential sector, and open magnitude, sources, and effects of BC emissions burning of biomass. Where relevant, the impact in developing countries. Data on emissions from on regional climate, through atmospheric brown biomass cooking should be a priority. Further clouds (ABCs) and snow and ice melting, could research may be needed into policies and projects also be described. for introducing clean transport fuels and corre- • Support projects that reduce BC to yield climate sponding advanced vehicle technology in develop- and health co-benefits: Assessment would be ing countries, including ULSD and compressed needed of the combined costs and benefits of natural gas (CNG). Other measures to reduce such projects. Several areas merit consideration PM from diesel could also receive more analyti- for support. Policies and projects that promote a cal attention from a climate change perspective, reduction in PM emissions from diesel (both in including modal shifts in transport, introduction transport and power generation) should probably of more effective vehicle inspection, retrofitting of be strongly encouraged from a climate change high-emitting vehicles, and less reliance on diesel perspective. The scientific evidence that lower in power generation. emissions of PM from diesel reduce global warm- • Explore global and regional policy options to ing is strong, as is evidence of the harm to health. include BC in climate change policy: In the context Projects that substitute cleaner fuels (primarily of global climate policy, BC is considered along natural gas, biogas, and liquefied petroleum gas) with other short-lived climate forcers, such as for industrial and residential coal in urban and ozone. BC and non-Kyoto gases are primarily a rural areas should be encouraged from both global climate issue, not specific to developing climate and health perspectives. Policies concern- countries. Nonetheless, development agencies ing residential biomass emissions will continue to can take a role in addressing the nature of BC be driven mainly by considerations of public health emissions from developing countries, within the as well as by other local environmental and social context of low-carbon development and green factors. However, evolving evidence of the impacts growth options. Development agencies could of PM from biomass on global climate should be consider how to include BC in the formulation closely monitored. Development agencies could of climate change policies and strategies, taking introduce BC emissions into discussions with into account the policies of the United Nations the private sector. Since BC is not included in Framework Convention on Climate Change the Kyoto Protocol, and hence is not linked to (UNFCCC). Agencies should keep abreast of the carbon markets or low-carbon financing, innova- rapid progress of research and policy in this area. tive financial and policy solutions may need to be “Low carbon� growth strategies for countries could 4 Environment Department Papers Executive Summary consider, in a qualitative manner, the impact of BC policies concerning the regional impacts of BC. and other aerosol emissions on global warming, Development agencies could reach out to regional and assess measures for reducing emissions of partner organizations, including those dealing with BC where possible. More focus could be given to the Himalayas and the Arctic. Climate Change Series 5 1 Introduction B lack carbon (BC) consists of particulate matter warming the climate. This work is part of a broader (PM) emitted from the combustion of biomass effort to clarify the role of PM (or aerosols) in the and fossil fuels. It is widespread in all regions, climate system, which poses major scientific challenges. and is associated with certain activities in both While the research effort is expanding rapidly, many developed and developing countries, including use of questions remain. Although having important climatic biomass and coal for cooking and heating, and diesel influences, BC and other aerosols were not included use in transport and power generation. Development in the Kyoto Protocol, in part because of the limited agencies thus deal with activities that generate or understanding of their influences on the climate. In its reduce BC, either directly or indirectly. Since BC 2007 report, the Intergovernmental Panel on Climate has significant environmental consequences, an Change (IPCC) stated that the level of scientific understanding of these is important for the agencies’ understanding of the climatic impact of BC and other operations and policies. aerosols was between “medium-low� and “low�1 (Forster and others 2007). It is possible that by the time of the Over the past decade, BC has come to be recognized next major report in 2014, the IPCC will conclude as one of the principal causes of global warming. In that the understanding of these questions has improved part because BC loading varies so much by location, sufficiently to consider whether BC and aerosols this understanding has developed much more slowly can enter more directly into international climate than for the roles of GHGs such as carbon dioxide discussions. (CO2) and methane, which have been the main focus of research. Recent research suggests that BC may be The widespread use of biomass for cooking in the second or third largest global warming agent. There developing countries makes emissions of PM, is also evidence that BC changes the climate in regions including BC, one of the leading causes of premature such as South and East Asia and is a principal cause death and disease, mainly through damage to the of ice and snow melting in the Arctic. PM emissions, respiratory organs. PM emitted from automotive including BC, are extremely harmful to health when vehicles, primarily those using diesel, is also a key factor inhaled. Thus it is now clear that the environmental in damage to health from urban pollution in both consequences of emissions of BC are both local developed and developing countries. This has prompted (health and environment) and global (climate change). long-running programs to reduce such emissions—for BC, which has long been a concern of national example, by improving the quality of cooking stoves in environmental health policy, now needs to be seen also developing countries, and reducing PM emissions from as an element in global climate policy. transport. A considerable body of scientific research has been 1. For CO2, and the other long-lived greenhouse gases covered by the Kyoto Protocol, the level of understanding was conducted to understand better the role of BC in “high.� Climate Change Series 7 Black Carbon and Climate Change — Considerations for International Development Agencies A key consideration when examining the effects Climate modeling shows that a large reduction in the of BC on the climate is the impact of aerosols that global amounts of BC emissions, without changes are co-emitted with BC—mainly organic carbon. in emissions of organic carbon, would lead to a BC emissions alone unequivocally exert a warming sharp onetime decrease in the warming influence of influence on the climate; however, organic carbon human activities. A rapid reduction in BC emissions emissions exert a cooling influence. Thus, taking has thus been proposed as a way to partially offset action to reduce warming from BC may mean the projected increase in temperatures in coming reducing emissions of cooling aerosols, making the net decades2. This would not solve the long-term problem effect uncertain. Much needs to be done to improve of climate change, which is caused by the GHGs, but understanding of the composition and quantity of PM it could extend the limited time that is available to emissions from the main sources, particularly from reduce emissions of GHGs aggressively, before global residential biomass use. temperatures reach dangerous levels. Proposals to reduce BC emissions also often address the need to Many actions to reduce emissions of BC also involve reduce emissions of several other short-lived gases (such reducing CO2 emissions. However, not all actions as ozone) that are mostly not covered by the Kyoto to reduce CO2 emissions also reduce BC emissions. Protocol. One example is the replacement of vehicles using gasoline with more efficient diesel vehicles that emit This paper is designed to inform development agencies, less CO2. The diesel vehicles emit more BC, because in a brief, simplified, and non-technical manner, about emissions of BC from diesel are generally higher than the links between BC and climate change, and how from gasoline. In assessing the costs and benefits of these could relate to development policy. The paper actions to reduce CO2 emissions, the impact on BC describes: (a) what is known about the impact of BC and aerosol emissions also needs to be determined. In and related aerosols on climate, (b) the sources and order to preserve a clear focus on BC and aerosols, this importance of BC emissions, (c) possible actions and report does not deal with the joint effects of BC and policies to mitigate emissions, and (d) considerations greenhouse gases (GHGs). for agencies in light of these issues. 2. In practice it would be necessary to avoid a large associ- ated decrease in organic carbon emissions, which could be achieved only through addressing certain activities, such as diesel use. 8 Environment Department Papers Introduction Messages froM: Integrated assessment of Black Carbon and Tropospheric ozone (UNeP and WMo 2011) A small number of emission reduction measures targeting black carbon and ozone precursors could immediately begin to protect climate, public health, water and food security, and ecosystems. Measures include the recovery of methane from coal, oil and gas extraction and transport, methane capture in waste management, use of clean-burning stoves for residential cooking, diesel particulate filters for vehicles and the banning of field burning of agricultural waste. Widespread implementation is achievable with existing technology but would require significant strategic investment and institutional arrangements. Full implementation of the identified measures by 2030 would reduce future global warming by 0.5˚C (within a range of 0.2–0.7˚C). The rate of regional temperature increase would also be reduced. Full implementation of the identified measures would have substantial benefits in the Arctic, the Himalayas, and other glaciated and snow-covered regions. This substantially decreases the risk of changes in weather patterns and amplification of global warming resulting from changes in the Arctic. Regional benefits of the black carbon measures, such as their effects on snow- and ice-covered regions or regional rainfall patterns, are largely independent of their impact on global mean warming. Both near-term and long-term strategies are essential to protect climate. Implementing both reduction strategies is needed to improve the chances of keeping the Earth’s global mean temperature increase to within the UNFCCC 2˚C target. At national and sub-national scales many of the identified measures could be implemented under existing policies designed to address air quality and development concerns. Improved cooperation within and between regions would enhance widespread implementation and address transboundary issues. International policy and financing instruments to address the co-benefits of reducing emissions of short-lived climate forcers need development and strengthening. There is confidence that immediate and multiple benefits will be realized upon implementation of the identified measures. The degree of confidence varies according to pollutant, impact, and region. For example, there is higher confidence in the effect of methane measures on global temperatures than in the effect of black carbon measures, especially where these relate to the burning of biomass. Given the scientific complexity of the issues, further research is required to optimize near-term strategies in different regions and to evaluate the cost-benefit ratio for individual measures. Messages froM: abatement opportunities for Non-Co2 Climate forcers (Climate Works foundation, european Climate foundation 2011) While there is still much uncertainty around the emissions and abatement opportunities for black carbon and methane, nitrous oxide, and fluorinated gases, enough is now known to inform action. These non-CO2 climate forcers collectively cause at least one quarter of global warming and accelerate the rate of temperature change. Emissions from the four non-CO2 climate forcers can be reduced by over 20 percent by 2030 using available methods: fugitive emissions capture, efficient agricultural practices, combustion optimization, diesel particulate controls, and alternative cooling technologies. Reducing non-CO2 emissions is essential to limit global warming during this century, slow the rate of temperature increase, and reduce the risk of adverse climate feedbacks. On top of the positive climate effects, 80 percent of the measures also improve public health and half come at a net savings to society. While a large share of the measures is relatively straightforward to implement, capturing the remainder will be challenging, as millions of people would need to take action, some of whom are the world’s poorest. In developed countries, the principal abatement opportunities lie in waste management, air conditioning and refrigeration, and diesel engines. Opportunity areas for developing countries are diesel engines, natural gas production, waste management, and traditional combustion technologies. Climate Change Series 9 2 Black Carbon and Climate Change B lack carbon exerts a large effect on the climate, BC is often referred to as soot, as seen in smoke, and but it does so in a very different way from is the principal component of black soot. BC consists the greenhouse gases. This chapter explains of light-absorbing particles of pure carbon that appear the nature of BC, provides an overview of its black to the naked eye. In practice BC is usually complicated interaction with the climate, and describes released together with other particles that consist of some of the challenges being addressed by science in compounds of carbon with other elements (hydrogen, this important area. nitrogen, oxygen, and so forth). This combination of carbon with other elements constitutes “organic carbon� Description of Black Carbon PM.4 Organic carbon particles usually reflect some Black carbon differs from the other key anthropogenic sunlight back into space.5 Smoke emitted from the substances affecting the climate in that it consists of burning of different substances will vary greatly in the particulate matter, rather than being a gas such as proportion of BC to organic carbon (Jacobson 2010). carbon dioxide or methane. BC is emitted from the Smoke with a low proportion of BC relative to organic burning of biomass and fossil fuels that contain carbon carbon will appear lighter to the eye than smoke with a and is a product of the incomplete combustion of these high content of BC, which can appear black when the fuels.3 BC proportion is very high. Once emitted, both BC and organic carbon particles undergo chemical changes On average, BC particles have a residence time in that will affect how they interact with the atmosphere, the atmosphere of at most two weeks, before they are and hence how they will affect the climate. washed down or fall to the ground. This compares with the millennia that the elevated CO2 concentration An important characteristic of PM, including BC, is persists in the atmosphere and continues to exert the size of the particles. There is no single definition a warming influence on the climate. This is a key of BC in terms of particle size. The literature is based difference between BC (and other aerosols) and the upon particle sizes of 2.5 micron6 or smaller, known “long lived� Kyoto gases: these gases accumulate in the as PM2.5. Because they have the largest radiative atmosphere from one year to the next, but BC does not, influence, most work deals with particles of 1 micron it is constantly being removed from the atmosphere and (PM1) and smaller, with particles being as small as 0.1 replenished. Another difference is that BC does not mix 4. There are thousands of organic carbon compounds emitted uniformly throughout the atmosphere, tending to be as PM, which is a challenge to assessing their impact on climate change. found in some regions more than others. 5. It has recently been recognized that some organic carbon particles consist of “brown carbon� which can absorb heat 3. Emission of soot is a sign of inefficient use of fuels, since radiation (Ramanathan 2010). the carbon thus emitted could have provided energy when 6. A micron is one millionth of a meter (one thousandths of a burned in the presence of oxygen. millimeter). Climate Change Series 11 Black Carbon and Climate Change — Considerations for International Development Agencies micron. These small particles tend to have the greatest These warmed air molecules tend to travel farther effect on climate, in part because larger particles than the BC particles, spreading the heat to the generally do not stay aloft in the atmosphere long surrounding air. enough to have a significant impact (Bond 2004). Most • BC absorbs (then re-emits) solar infrared radiation measurements of PM are taken because of concerns that is radiated from the Earth’s surface. about local health consequences; these also concentrate • BC deposited on snow and ice reduces the albedo (reflectivity) of the Earth’s surface. on the smallest particles, which are more likely to • BC interacts with clouds and with other PM to penetrate deep into the lungs to cause damage. affect regional and global weather patterns. GHGs interact with the atmosphere differently than Effects of Black Carbon on Climate Change BC particles and they do not tend to darken the Earth’s The physical behavior of BC, and its mode of action in surface. The gases warm the atmosphere by absorbing affecting climate, is fundamentally different from that infrared light (that is, heat) radiation from the sun that of GHGs. BC affects climate in several ways (see is re-emitted upward mainly by the Earth’s surface, and Figure 1): re-radiating half of the energy back toward the surface, adding to the normal warming by solar radiation. • BC absorbs solar radiation that it then gives off as heat, warming the surrounding air molecules. Figure 1. The Impact of Black Carbon on the Global Climate Source: World Bank 2011. 12 Environment Department Papers Black Carbon and Climate Change This heat-trapping effect is commonly known as the feedback is particularly effective in the Arctic because greenhouse effect.7 the seasonal snow cover and sea ice are relatively thin, so that accelerating the springtime melting leads to The impact of deposition of BC particles onto the greater solar absorption all summer long (see Box 1). surface is especially significant. When these particles Most BC in the Arctic comes from surrounding regions land on snow or ice, they darken the surface, which of Europe and North America; however, some of it has been transported from South Asia and China (Quinn causes more solar radiation to be absorbed and increases 2008). BC from the latter regions also affects the ice the rate of melting. This acceleration of melting both and snow of the nearby Himalayas. The reduction of has a marked local effect and contributes to global snow and ice in the Arctic and Himalayas due to BC warming, because the melting exposes darker surfaces has been estimated to be as significant as that due to (rock, soil, or water) and this leads to even greater absorption of solar energy (Hansen and Nazarenko global warming (Ramanathan 2010). As is shown in 2004). This amplification of the natural albedo Figure 2, the albedo effect of BC on snow and ice is significant, if relatively small, at the global level. 7. This is not a full or precise definition of the greenhouse ef- fect. For a concise description see: Intergovernmental Panel An important distinction between BC and GHGs on Climate Change Fourth Assessment Report, Working Group 1, Chapter 1: “What is the Greenhouse Effect?�. is that the impact of the former on global warming Box 1. effects of Black Carbon emissions on the arctic BC emissions have a disproportionate influence on the warming of the Arctic. Temperatures in the Arctic have risen twice as fast as the global average over the past 100 years, and BC may be a major contributor to this excess warming. This warm- ing has been accompanied by earlier melting of sea ice in the spring, a longer melting season, and faster melting of the Greenland ice sheet. The total area covered by summer sea ice decreased by 40 percent between 1979 and 2007. The trend toward warming and melting has been attributed primarily to human-induced climate change (Pew 2009). The impacts of ice loss include an important amplifying climate feedback—the reduction of the Earth’s albedo (the ability to reflect sunlight back into space). BC landing on snow or ice absorbs heat and reduces its reflectivity, promoting melting. As warming causes greater amounts of snow to melt, bare land and dark ocean water are exposed, which absorb more solar radiation. This positive feedback leads to further warming and is one of the reasons that the Arctic is highly sensitive to BC. It has been estimated that a given amount of BC causes twice as much warming in the Arctic as it does in the rest of the world (Hansen and Nazarenko 2004). The changes in the Arctic climate have significant consequences for the land, ice, and aquatic ecosystems in the Arctic. Moreover, melting of Arctic land-based glaciers contributes to global sea-level rise. Most of the BC received by the Arctic comes from activities in Northern Europe and North America; however, studies have shown that large quantities also come from regions below 40° N, particularly from South and East Asia. Pollution from these regions tends to be lofted to high altitudes and then carried for long distances. Further study will be needed to assess with precision the sources of Arctic BC (Quinn, 2008). The melting of Arctic sea ice will effectively unlock the Arctic Ocean, leaving it increasingly open to human activity— particularly shipping and oil and gas production. The trends indicate an Arctic Ocean with longer seasons of less sea-ice cover of reduced thickness, implying that there will be improved accessibility to ships around the margins of the Arctic Basin. Until recently, seaborne transport of cargo in these waters has been very limited, and reported ship emissions have been low. Taking the Northern Sea Route via the Barents Sea between Europe and the North Pacific Region can reduce travel time by up to 50 percent, compared to the sea routes in use today. Increased shipping in Arctic waters will produce significant amounts of BC that will settle on Arctic snow and ice (IMO 2009). Climate Change Series 13 Black Carbon and Climate Change — Considerations for International Development Agencies Figure 2. Estimates of Radiative Forcing for Greenhouse Gases and Black Carbon Source: World Bank (based on Pew Center on Global Climate Change. 2009). can vary significantly by region. In areas where BC important as their “direct� warming and cooling effects concentrations are high, the warming effect of BC (see Box 2). These interactions are highly complex can be comparable to that of the main GHGs. BC and not fully understood (Forster and others 2007). As contributes to the formation of atmospheric brown the scientific understanding of the effects of the Kyoto clouds (ABCs), which can have climate impacts over Protocol gases on climate grows, the complications large regions. These ABCs are widespread loadings of introduced by BC and aerosols have become an PM in the atmosphere that cause visible dimming of important factor in the remaining uncertainties in sunlight; by changing the local climate energy balance, climate model projections (CCSP 2008). This is one they affect precipitation patterns and temperature of the reasons for the rapidly growing scientific interest gradients. ABCs have been implicated in such regional in aerosols and BC among climate scientists in recent weather alterations as shifts in the South Asian years. monsoon and changes in the rain distribution over eastern China (Ramanathan and Carmichael 2008). Despite the additional scientific research over the past decade, uncertainty remains about the scale of The interaction of BC and organic carbon particles with the contribution of BC to climate change. There is water vapor causes changes in the nature and behavior no doubt that BC contributes to global warming, of clouds. Given the importance of clouds in the the debate is about the size of its contribution. This dynamics of global warming, the effect of BC and other uncertainty is due primarily to limited information aerosols on climate via changes in clouds may be as about BC’s activity in the atmosphere and on the 14 Environment Department Papers Black Carbon and Climate Change Box 2. Impact of Black Carbon on Clouds and resulting Climate Change Aerosols such as BC affect the climate both directly, by absorbing or reflecting light, and indirectly, through their interaction with clouds, snow, and ice. Aerosols can influence clouds in several ways. As the humidity of the atmosphere goes up (for example, by the air moving up, expanding and therefore cooling), the small particles take up water vapor to form small cloud droplets—with properties that are determined by the characteristics of the particles. The more the particles, the smaller the droplets and the more they reflect sunlight, thus cooling the atmosphere (the “cloud albedo effect�). Other indirect effects operate through changes in the intensity and type of precipitation, and by affecting the height and lifetime of clouds. These effects are significant, but are both complicated (involving feedback effects) and not yet well understood. Because of the variety and variability of clouds, the effects are difficult to observe and quantify. The RF of the cloud albedo effect has been estimated through global climate models that incorporate aerosols and other climate factors. Figures quoted by the IPCC range from -0.2 to -1.8 (that is, of the same order of magnitude as the direct RF of greenhouse gases and BC). Most of this variation is due to the different assumptions and mechanism of the models, and the need to simplify a very complex system. The effects of BC, through warming and possibly reducing planetary albedo (which can occur if the BC layer is above the cloud), are quite different from the influences of cooling aerosols. However, since all the aerosols exist in a mixed state, at varying concentrations by location and season, it is the combined effect that is important for climate. Source: Forster and others 2007. Earth’s surface, questions about how BC interacts with balance of incoming sunlight and outgoing infrared other aerosols and clouds, and uncertainties about radiation caused by a gas or aerosol, relative to pre- the global quantity and distribution of BC. The 2007 industrial levels (a.d. 1750).8 Amounts of RF for key IPCC analysis estimated BC to be the third largest gases and aerosols are shown in Figure 2. global warming agent, substantially behind CO2 and methane (see Figure 2). However, a more recent widely As can be seen in Figure 2, global RF is dominated by cited analysis concluded that BC is the second largest CO2 and methane (CH4). The combined RF of these contributor to global warming after CO2 (Ramanathan and the other Kyoto gases is +2.6 W/m2. The impact of and Carmichael 2008). organic carbon and most other aerosols (except BC)9 is negative and offsets some of the warming from gases. The measure used to estimate the impact of the effect of gases and aerosols on global temperatures is “radiative 8. It is measured in watts per square meter (W/m2) averaged over the globe. forcing� (RF). This is a measure of the change in the 9. Primarily sulfates, nitrates, and dust. Climate Change Series 15 Black Carbon and Climate Change — Considerations for International Development Agencies These substances reflect Sunlight back into space and accumulate. The amount of BC in the atmosphere is thus cool the planet. The offset for organic carbon is approximately the amount emitted during one to two about -0.2 W/m2. BC occupies an unusual position weeks (the time over which the BC in the atmosphere in that it is both an aerosol and a major positive is “recycled�). In addition, the impact of BC is regional contributor to global warming. The IPCC estimate of as well as global, which means that its effect on global RF for BC was +0.34 W/m2 with a range of +/- 0.25 warming (hence GWP) can vary according to where it W/m2. A further forcing of +0.10 W/m2 is attributed is emitted (Forster and others 2007). to BC on ice and snow. Ramanathan and Carmichael (2008) suggest that the RF for BC is much greater, Despite its short atmospheric lifetime, the global being as high as +0.9 W/m2, which would make warming effect of a quantity of BC is huge relative to it the second largest cause of global warming after an emission of the same mass of CO2. Over roughly CO2.10 Attention should be paid to the error bars in its two-week lifetime, one ton of BC can absorb over the diagram which are proportionately much larger a million times more radiative energy than a ton of for aerosols than for long-lived GHGs such as CO2 CO2. The climatic importance of CO2 arises from the and methane, reflecting the lower level of scientific fact that (a) global emissions of CO2 are some 3,000 understanding of their effects on climate. times higher than BC, and (b) the average atmospheric lifetime of CO2 is thousands of times longer than The “standard� measures of climate change impacts BC (USAID 2010). At the global level the impact of developed for long-lived greenhouse gases do not work BC on global warming is strong but short-lived and well for BC and other aerosols. The main estimate BC is scarce, whereas the impact of CO2 is weak and of global warming impact is the “global warming prolonged and CO2 is plentiful. potential� (GWP). This is an estimate of the total cumulative radiative forcing of one ton of a substance The large difference between the warming process of emitted today over a period of 100 years, or GWP100 BC and that of CO2 means that where an activity is (sometimes 20 years is used). GWPs are measured in adjusted to lower emissions of both CO2 and BC (for relation to CO2. With the CO2 level calibrated as 1, the example, reduction in coal burning), the latter will 100-year GWP of methane is 25, while halocarbons often have the greater impact on climate change over have GWPs of 1,000 or more. International climate the next few years to decades. policies generally refer to the GWP100. The GWP for BC has been estimated at 680 over a Because the GWP100 is a measure of the ratio of the 100-year period, and 2,200 for a 20- year period.11 cumulative warming influence of a unit mass of a There are very large ranges of uncertainty around these substance as compared to the warming influence of a mean estimates, reflecting the continued uncertainty unit mass of CO2 over a century, it can be a poor metric about the atmospheric effects of BC (Bond and Sun for representing the effects of BC on climate. Except 2005).12 These estimates do not include the impact on for the effects of BC on snow and ice, the warming ice and snow, which would raise the GWP of BC but effects of BC occur during the one or two weeks that also add to the uncertainty about BC’s overall impact the particles stay aloft in the atmosphere. This contrasts on climate. with the hundreds of years to millennia during which CO2 continues to affect the climate. CO2 accumulates 11. Since all of BC’s impact is during the first one or two weeks, in the atmosphere, with each year’s emissions being the amount of forcing is the same over a 100- or 20-year added to those from previous years, while BC does not period. The impact of CO2 however, is considerably less over 20 years than over 100 years. 12. The ranges are 210 to 1,500 over 100 years, and 690 to 10. With a range of +0.4 to +1.2 W/m2. 4,700 over 20 years. 16 Environment Department Papers Sources of Black Carbon and Their 3 Impact on Climate Change T he main sources of BC are the burning of in the levels of emissions relative to raw material biomass and fossil fuels. Activities that generate consumption and in the co-emissions of organic BC emissions include: use of coal in the carbon. As stated earlier, the greater the proportion industrial and residential sectors, diesel and fuel of BC emitted relative to organic carbon, the greater oil use in engines, residential biomass use for cooking the net impact of an activity on global warming. and heating, and open burning of biomass (see Table 1). This means that measurements of both BC and organic carbon are needed for each source, which While all of the sources listed in Table 1 generate makes estimation of emissions extremely challenging. significant amounts of BC, there are large variations Differences in emissions can be ascribed to generic Table 1. Sources of Black Carbon and Their Impact on Climate Ratio: BC/ Fuel type organic carbon Climate impact Emissions estimates Key features Mitigation policies Residential High Net warming – Volumes and trends – Mostly in China – Substitution by and industrial known cleaner fuels – Very harmful to coal (PM not – Composition health – Emission controls contained) relatively uniform (industry) Diesel High Net warming – Volumes and trends – Present in all – Regulate vehicle known countries emissions – Composition uniform – Growing fastest in – Introduce ULSD developing countries and particle traps – Harmful to health in – Substitute urban areas cleaner fuels Gas flaring High Net warming – Volumes partly – Varies by flare – Effective flaring estimated efficiency and gas regulations composition – Market structure Residential Moderate Uncertain – Volumes and trends – Mostly in – Introduction biomass use somewhat uncertain developing countries of improved cookstoves, cleaner – Wide variation in – May be harmful to fuels (for example, composition health LPG) Open Burning of Low Net cooling – Volumes and trends – Both natural and – Policies on crop biomass very uncertain anthropogenic burning and wildfires – Wide variation in composition Climate Change Series 17 Black Carbon and Climate Change — Considerations for International Development Agencies sources (biomass, diesel, and so forth), but there are Diesel Fuel also major variations within sources, depending on the Use of petroleum fuels is a very substantial source specific nature of the material input (for example, type of BC emissions in many parts of the world. Most of wood), the technology used for combustion (type of emissions come from the middle distillates and heavy stove or boiler), and the way in which the technology is oil products. Of these the largest is from diesel use used. To this must be added the unfortunate fact that in three categories: on-road vehicles (trucks, cars, for many BC and organic carbon emission sources, buses, and so forth), off-road vehicles (agricultural there are limited data on the scale of activities on which and construction machinery), and stationary sources to base aggregate estimates of emissions.13 (power generators). The heavy forms of diesel and fuel oil are used in ships and larger power generation units. Coal Diesel use emits few organic carbons and it is thus a major source of net warming from BC (see Box 4). Coal use in households and industries is a significant However, there is a variation in the intensity of BC source of BC. Households use coal for both cooking emissions from diesel between countries, depending and heating. Industries use coal as a basic energy source. upon whether they have implemented fuel and vehicle While the main use of coal is in the power sector, large standards to contain emissions of PM. Emissions from power stations are equipped with filters that remove use of gasoline in vehicles are usually much lower than nearly all direct emissions of PM. Coal use does from diesel, and those from the lightest petroleum increase other aerosols in the atmosphere, particularly products, butane and propane, are minimal.14 through emission of sulfur dioxide (SO2) that creates sulfates. Ash may also have an effect. These latter BC emissions from diesel vary considerably between aerosols generally have a cooling effect. individual vehicles and types of vehicles. Off-road vehicles and stationary engines generally have higher Coal burning emits BC and very little organic carbon. BC emissions than cars and trucks. Shipping is also Coal use in the residential sector is less widespread than a significant source of BC, accounting for about 3 biomass. It occurs almost exclusively in areas where percent of worldwide emissions. BC emissions from local sources of low-cost coal are available and access to shipping have a larger warming effect when they occur cleaner fuels is restricted by economic circumstances. at northern latitudes and impact the snow and ice cover The largest concentration of use is in China, which of the Arctic (see Box 1). Hence emissions of BC from also has the largest uncontained emissions from coal in shipping, like emissions from most other sources, will industry; however, in recent years the government has have a strong regional component that then affects the targeted emissions from both household and industrial global environment through induced changes in the coal use for reduction, with considerable success. In the local weather (Quinn and others 2008). Among cars industrial sector the worst problems with coal emissions and trucks a proportion of vehicles can be classified as are from smaller and poorly regulated plants in major “smoke-belchers� or “super-emitters� with BC output sectors such as iron and steel and cement. These plants 5 to 10 times that of average vehicles (due to poor are uncompetitive with large modern facilities and maintenance and other deficiencies). Such vehicles can sector restructuring is thus reducing BC emissions. make up 15 to 20 percent of all vehicles in developing Small industries, such as brick kilns, are more difficult countries, and thus account for a large proportion of to control and represent a major source of BC in some total BC emissions. urban areas in Asia. 13. This section uses information from Bond and others (2004) 14. Gasoline vehicles can emit more significant quantities of BC and Bond and others (2007). and other PM when very poorly maintained. 18 Environment Department Papers Sources of Black Carbon and Their Impact on Climate Change The Organisation for Economic Co-operation and in the poorest parts of cities as well. A wide variety of Development (OECD) countries account for the fuels is used: wood (either gathered as “dead wood� majority of global diesel use, but demand has been or taken from living plants), charcoal (manufactured growing most rapidly in developing countries. As with from wood, usually harvested from standing forests), biomass, the PM emitted by diesel is extremely harmful agricultural wastes (including rice stalks, wheat, and to human health. This is a major environmental issue in maize), and animal waste (dried dung). cities where PM concentrations are high, as is the case in many large cities in developing countries. The direct Given the large number of poor households exposed and indirect impacts of diesel on health are the prime to PM from biomass cooking, the burning of biomass reasons why there has been a shift to cleaner diesel is a critical issue for development policy (Barnes and technology in high-income countries. The beneficial others 2011). Despite the importance of the health and effects of this move on climate change, through a large climate change issues involved, there is surprisingly reduction in BC, have until now been incidental to little concrete scientific data on emission factors for policy. Policy in developing countries also aims to biomass use, such as the total PM emissions and the reduce PM in cities, but as is explained below this has ratio of BC to organic carbon. Like open burning not yet led to large reductions in BC emissions. As with of biomass, use of wood for cooking in traditional coal, the reduction in SO2 emissions from diesel has led stoves (which account for the vast majority) produces to a reduced cooling effect from sulfate aerosols. substantial amounts of organic carbon alongside BC. However, since the combustion of biomass in residential fuels is contained, and more efficient than Gas Flaring in open burning, the ratio of organic carbon to BC is A likely source of significant BC emissions is the flaring much lower (see Box 3). of natural gas from production and processing facilities. The net influence on climate of PM emissions from This practice, although increasingly controlled in many residential biomass will depend in large part upon countries, persists in many regions, the most notable the ratio of BC to organic carbon. Research has being the Niger Delta in Nigeria and West Siberia in shown that within reasonable ranges of this ratio, Russia (GGFR 2011). While burning of pure methane it is possible for emissions from residential biomass emits almost no BC, “rich gas� contains much heavier to have either a small net warming or a small net hydrocarbons including natural gas liquids. When cooling effect on climate (see Box 3). It thus cannot flared, rich gas can emit very large volumes of BC. In be asserted with confidence that reducing emissions of the case of flaring, an important consideration is the PM from biomass cookstoves will, in all cases, reduce efficiency of the flare—how much of the total volume global warming. Some mitigation strategies, such as of gas and liquids is burned. Improving the efficiency introducing cookstoves designed to reduce PM, could of flaring may be one way to reduce BC emissions from both reduce the emissions of PM and affect their flares until they are eliminated by the processing and composition. This adds to the uncertainties in this area use of the gas. The global volumes and characteristics of (Ramanathan 2010). PM from flaring have not been estimated. This judgment takes account of both the “direct� Residential Biomass effects of BC and organic carbon on climate (that is, through heating and cooling due to the particles in Biomass is the most widely used fuel for cooking in the atmosphere), and the “indirect� effects through rural areas of developing countries; it is extensively used the impacts on clouds and the deposition of BC Climate Change Series 19 Black Carbon and Climate Change — Considerations for International Development Agencies Box 3. Impact of Particulate Matter emissions from residential Biomass on Climate Residential biomass burning emits both BC and organic carbon; however, their proportion is such that neither has an over- whelmingly dominating effect when compared with emissions from open burning, diesel, and coal use. Rough estimates of the ratio of BC to organic carbon for residential biomass range around 0.2 to 0.3, compared with around 0.1 for open burning and 3.0 for diesel. In other words, if the fossil fuels stand at one end of the scale with a large predominance of BC, and open burning stands at the other end with a predominance of organic carbon, residential biofuels sit somewhere in the area between them. The RF estimates for residential biomass emissions are derived from global climate models. Results from these depend upon a large number of variables in addition to the levels of BC and organic carbon emissions. Important parameters for the PM itself include the size ranges of particles, mixing state of the particles, and chemical evolution of BC particles after emission. These models estimate both the direct effect on climate of BC and organic carbon, and the indirect effects. The direct effects exclude influences through clouds (see Box 2), while the indirect effects measure the influence from interac- tions of aerosols with clouds. The total effect of PM on climate is the sum of the direct and indirect effects. The direct effect of biofuels use on climate is generally seen to be slightly warming, with the influence of BC being dominant over organic carbon. However, the indirect effect may be cooling. Since the RF of the indirect effect is of the opposite sign to the net direct effect and of the same order of magnitude, climate models cannot yet ascertain with a high degree of confidence whether the total effect of biofuels use on climate is cooling or warming. Studies that have specifically used global climate models to assess the influence of residential biomass emissions on the climate have come to differing conclusions: (a) Unger (2008 and 2009) concluded that the RF from residential biomass use had a small positive sign, (b) Aunan (2009) concluded that the best estimate for the RF was zero (with very large uncertainty), (c) Jacobson (2010) concluded that household biomass had a warming impact on climate, (d) Bauer (2010) came to the conclusion that the net influence of biomass use was cooling, and (e) Koch (2011) came to the conclusion that the indirect effect may dominate the direct effect for biofuels, resulting in overall negative RF. All of these models concluded that the absolute level of the RF from residential biomass was probably small, whether positive or negative. This level was in all cases significantly smaller than the positive RF due to emissions from diesel and coal use. The different studies used different models and assumptions, and their varying results demonstrate the considerable uncertainties in this area and the need for continued research. As in other areas relating to BC, the absence of widely applicable physical data on actual volumes and types of emissions remains a major constraint. Even the simple ratio of BC to organic carbon, which is key to results, is roughly assumed. A wide range of improved biomass cookstoves is available, but little is known about the impact of these on BC and organic carbon emissions. Since the ratio of BC to organic carbon is likely to vary between locations and types of biofuels, field measurements may find that biomass use in some localities would tend to have a warming influence on the global climate, while in others it could have a cooling influence. From the perspective of policy, the scientific uncertainty about the net warming impact on climate of the use of biomass for fuel would counsel caution in making assumptions in this area. The impact of biomass use on health is so clear and pressing that it will continue to be the main justification for urgent action to replace traditional cooking stoves with cleaner stoves and clean fuels. However, it should be noted that while the impact of biomass use on global climate may be uncertain, it has definite impacts on regional climate and resources, through snow and glacier melting, and formation of atmospheric brown clouds. 20 Environment Department Papers Sources of Black Carbon and Their Impact on Climate Change on snow and ice. The indirect effects on clouds are In addition to PM and CO2, biomass burning emits generally considered to be cooling, and of similar other gases that contribute to global warming, orders of magnitude to the direct effects. The impact including methane, carbon monoxide, nitrogen oxide on snow and ice is warming, though relatively small in and other non-methane hydrocarbons. Accounting global terms, and will strengthen the warming effect for these gases may increase the warming impact of residential biomass burning. Additional factors to of emissions from biomass burning on the climate. be taken into account include the size distribution However, improved stoves also have a different GHG of particles, their concentration at various heights in emissions profile from traditional stoves. Policies that the atmosphere, and the evolution of their chemical reduce PM emissions from biomass use will also tend properties after they are emitted (Bauer and others to reduce the emission of such GHGs, and alter their 2010). Research in this area requires use of large global relative composition.15 climate models and is continuing with increasingly sophisticated models incorporating all of these factors. Open Burning of Biomass The impact of BC from biomass may vary regionally due to its contribution to ABCs (Ramanathan and A range of sources contributes to BC emissions from others 2008). open burning of biomass. These include both naturally occurring wildfires and sources due to specific human There are formidable difficulties in obtaining data on activities. The latter category includes (a) regular BC and organic carbon emissions for the major part burning of field crop residues after harvest, which is of biomass use. Emissions will vary greatly by location a common agricultural practice in many parts of the and time. Each village or group of urban users will world, and (b) forest fires set deliberately in order to have their characteristic fuel use patterns, and there clear land for agricultural uses. may even be large variations within this group. In the case of charcoal, emissions of BC and organic Open burning of biomass produces far more organic carbon will occur both during manufacture and in carbon than BC. Estimates of emissions from various final use. There is far less uniformity in the emission types of burning put the mean ratio of BC to organic characteristics of residential biomass use than in any carbon at around 0.1, compared with about 3.0 for other area of energy use. An additional consideration is diesel transport. Within the central ratio there are that current policy initiatives emphasize replacement of very wide variations, but organic carbon will tend traditional stoves by a wide variety of improved stoves to dominate. This means that open burning has on (Barnes and others 2010). The effect of these stoves balance a cooling effect in the atmosphere. However, on the relative emissions of BC and organic carbon is the BC from open burning of biomass still affects snow not well understood. When suitably designed such and ice, hence smoke from open burning that reaches stoves greatly reduce indoor PM concentrations, with Arctic areas and snow and glaciers elsewhere could corresponding benefits for health. If BC is reduced have a warming effect. This is the case with much of much more than organic carbon, the resulting new the open burning in Northern Europe and Northern composition of PM will be less warming than the Eurasia, which has a large impact on the Arctic original composition, and vice versa. Much more (Box 1). Open burning also contributes substantially to concrete data are needed about the overall composition the formation of regional ABCs. of emissions from contained biomass burning in order to reach conclusions about its impact on climate. 15. Kerosene, one of the main substitutes for biomass in poor rural areas, may also emit BC if not burned cleanly. Climate Change Series 21 Black Carbon and Climate Change — Considerations for International Development Agencies It should be noted that open burning differs from Climate change and the rising CO2 concentration can other sources of BC in that a large proportion of the also affect the return period of natural wildfires. An emissions are not anthropogenic—that is, they existed increase in the CO2 concentration, and the increase in naturally before human intervention, as wildfires. This water use efficiency that this causes, tends to increase presents challenges in measuring the additional impact the growth rate of plants. Thus a critical fire mass builds of human activities in the total. up faster. As summer heat becomes hotter and plants and soil become dryer, fire risk increases. 22 Environment Department Papers Global Volumes of Black Carbon 4 Emissions O nly one estimate of global emissions of BC Estimates of total emissions of BC, derived from the and organic carbon has been attempted using sole current global estimate available, are shown in engineering parameters based upon bottom-up Figure 3. As can be seen, the largest contribution is activity levels (Bond and others 2004). This from open burning (35 percent), followed by the estimate is derived from an extremely comprehensive residential and transport sectors. Figure 4 shows that and rigorous analysis of hundreds of different sources the pattern of emission sources differs substantially and technologies. While there can be confidence that between developed and developing countries, with the the global estimates are of the right order of magnitude, latter producing most emissions from the residential the research suggests that the overall estimates are and industry sectors and the former from the transport correct within a factor of two. Uncertainties about the sector.16 volumes, sources, types, and regional distribution of PM necessarily limit the accuracy with which global Global emissions of BC from energy use have grown climate models can incorporate BC and organic carbon significantly, but less so than total energy demand, into climate projections. Uncertainty also complicates due primarily to improved pollution controls. The identification and assessment of mitigation strategies estimated annual output from fossil fuels has risen from to deal with the impact of BC on climate. More measurement and research are needed before global Figure 3. Global Sources of Black Carbon volumes of BC and organic carbon can be estimated Emissions, 2000 with significant accuracy. However, remaining Other uncertainties should not detract from developing 7% Transport 22% policies based upon the clear messages of climate science and of extensive analysis and surveys already completed. Open burning Industry Assessment of BC and organic carbon levels by satellite 10% 35% may be possible; however, there are technical challenges in distinguishing between BC and organic carbon, and in arriving at comprehensive global figures. Ground or air monitoring can also measure point concentrations Residential of PM, but these are too few to provide reliable data Grand total: 26% over large regions, and also do not cover all altitudes at 7.5 million tonnes which PM may be present (CCSP 2008). Source: Bond 2010. 16. The estimated emissions from open burning are very dif- ficult to attribute to regions at present. Climate Change Series 23 Black Carbon and Climate Change — Considerations for International Development Agencies Figure 4. Black Carbon Emissions from the Energy Sector by Region, 2000 Source: Bond 2010. 1.0 million to 4.6 million tons/year between 1850 uncontrolled coal use in industry—toward cleaner fuels. and 2000 (Bond and others 2007; see Figure 5). By Developed countries that have introduced ultra-low comparison, total fossil fuel use has risen by a factor sulfur diesel, along with vehicle emissions standards, of ten over the same period. The 20th century saw a will see a fairly rapid decline in emissions from diesel shift in BC sources away from coal toward petroleum, as the vehicle fleet turns over. ULSD simplifies the despite the rapid growth of coal use. This reflects the use of particle traps in vehicles that remove BC from installation of emission controls (for all PM including emissions (see Box 4). One area of rapid growth for BC) in power stations, while emissions from diesel BC in coming decades will be in emissions from diesel (middle distillates) remained largely uncontrolled. BC in developing countries where the introduction of output in OECD countries has fallen in recent decades ULSD, along with stringent emissions standards, is due to greatly improved controls over coal emissions, not yet a firm policy in most countries. However, these and more recently from stricter standards for diesel improvements will take place over coming decades as combustion. Emissions in developing countries have incomes rise. continued to grow from all fuels. While it may be thought that the problem of BC Long-term trends in economic development and will eventually solve itself as global emissions from environmental controls are likely to lead to declining anthropogenic sources decline to relatively low levels— global BC emissions. Contrary to the case of CO2, BC perhaps between 2050 and 2100—this should not lead has tended to decline with economic development, to complacency in making emissions reductions, either particularly where a priority has been given to from the point of view of health or from the point of view controlling vehicle emissions. Rising incomes in of controlling climate change. As discussed in Chapter developing countries will bring a steady move away 6, accelerating the reduction in BC emissions can be an from residential biomass and coal use—as well as option to limit global warming in the near term. 24 Environment Department Papers Global Volumes of Black Carbon Emissions Figure 5. Historical Emissions of Black Carbon by Fuel and Region Source: Bond and others 2007. Climate Change Series 25 Black Carbon Mitigation Policies 5 and Costs M itigation of BC in order to reduce global million people still use coal for heating and cooking warming is new to the global policy agenda. (IEA 2010). This usage and resulting BC emissions To date nearly all policies that have reduced should be susceptible to further interventions. BC emissions have been motivated by factors other than global warming, usually control of local Uncontrolled coal use in industry presents two environmental and health impacts of PM. Options to aspects. One is the large-scale use in simple iron and further reduce BC emissions generally entail building steel furnaces, coke making, and similar substantial on those initial control policies. industrial facilities. These basic facilities are often uncompetitive in terms of costs, so their complete Practical technologies for eliminating BC from closure in the interests of economic efficiency has emissions are generally well known and are established tended to reduce BC emissions (Bond and others as standard in many parts of the world. Difficulties 2004). arise with implementing appropriate policies, including paying the cost of updating and replacing equipment. More difficult to address is the widespread use of coal A fundamental dilemma for controlling BC in the in small- and medium-sized enterprises, such as brick atmosphere is that approximately 60 percent of it is kilns. These industries are not regulated and operate emitted together with large proportions of organic many plants in a large range of localities, including carbon in open burning and residential biomass (see major urban areas. Options to cut PM emissions Figure 3). The only options for reducing BC with from such small-scale operations may involve either minimal effects on other types of PM occur for coal switching to a cleaner but more expensive fuel such as and diesel fuel use. Hence, while much literature dwells natural gas, or complete closure of the operation. Brick on policies for reducing BC from all sources in order to kilns are a large pollution problem, particularly in Asia. limit global warming, in practice only reductions from They consume not only coal but also other fuels with coal and diesel use could achieve this objective with any high BC emissions, such as used tires (USAID 2010). degree of certainty. Diesel Coal Control of BC from diesel is a relatively straightforward Residential coal use is confined to a few countries, with problem to address from a technical point of view, the largest use being in China. Relatively successful given experience with transition to cleaner fuels interventions in China have done much to reduce in high-income countries. It is also, in general, a the problem, but significant usage remains: some 400 relatively expensive option for reducing BC emissions. Eliminating BC emissions from diesel use requires Climate Change Series 27 Black Carbon and Climate Change — Considerations for International Development Agencies installation of diesel particulate filters (DPFs),17 but • Implementation of control policies and regulation in general this can only be done effectively with to reduce emissions from high-emitting vehicles ULSD. Removal of sulfur from diesel to this degree (“super-emitters�), which can present institutional calls for specialized facilities in oil refineries. The challenges motivation for introduction of ULSD and advanced • A modal shift in transport, in which total fuel vehicle specifications in high-income countries has use is reduced through provision of mass transit been the need to control urban pollution, rather than with low-emissions vehicles (for example, electric considerations of climate change impacts. It should be trains and trams) or with bus rapid transit systems noted that reduction of sulfur in fuels alone reduces (which may use CNG). sulfate PM formed from SO2, but it does not result in lower BC emissions. Hence introduction and use Two other major sources of BC are off-road diesel (for of ULSD will not reduce BC emissions from legacy example, power generation, construction vehicles) vehicles unless these are retrofitted with DPFs. and shipping. Off-road diesel emissions may be of the same order of magnitude as on-road emissions, but In the case of diesel it is not necessary to deal with are harder to control (Bond and others 2004). Use of the dispersed and differentiated supply-and-demand ULSD with particulate filters can largely eliminate BC profile of biomass fuels. Supplies usually come from a emissions from heavy construction and agricultural few large sources (refineries or import terminals), while equipment, although regulation in this area lags behind technical standards for oil products, and to a lesser that for road vehicles. Control of smaller stationary extent for vehicles, exist in most countries. Once ULSD sources, such as power generators, is challenging standards have been implemented, control of emissions because they are dispersed and hard to monitor (for depends upon the rate of introduction of new vehicles example, residential generators); given the widespread with DPFs, and the number of filters retrofitted to the use of small generators in developing countries, this legacy fleet. Because of the relatively slow turnover of is a considerable problem. Large diesel generators use the diesel vehicle fleet, the elimination of BC emissions lower-quality fuels and may present technical challenges from vehicles can take up to 25 years (Baum 2010). for BC control. Shipping similarly presents technical challenges in eliminating BC and other PM. While high-income countries have adopted ULSD standards, developing countries have been reducing the sulfur content of fuels more slowly and are generally Biomass some way from introducing ULSD (see Box 4). This The key policy issues for biomass use concern the would require significant additional investments in the elimination, or substantial reduction, of PM emissions refining system. In the absence of ULSD, the main as a whole, not only of BC. The largest reduction in strategies for reducing BC emissions from diesel in PM emissions occurs with a switch to fossil fuels such transport are the following: as kerosene and LPG. However, these fuels are at present not affordable to the major part of households • Fuel conversion by replacing diesel with LPG in low-income countries. A reduction in PM emissions or CNG, although CNG requires considerable can also be achieved with suitable improved cookstoves, investment in vehicle conversion and in supply and by moving from direct use of biomass to efficient infrastructure use of charcoal (Bailis and others 2005). Despite increasing penetration of more modern fuels, such 17. Diesel oxidation catalysts reduce PM emissions using as LPG and kerosene, the population of low-income chemical catalysts, but they are typically less effective. countries continues to rely primarily on biomass for 28 Environment Department Papers Black Carbon Mitigation Policies and Costs Box 4. Control of Black Carbon from Diesel fuels Most high-income countries have already mandated sale of ULSD and phased out higher sulfur grades of diesel. New ve- hicles are fitted with diesel particulate filters, and as a result virtually all PM emissions from diesel engines are expected to be eliminated as the fleet turns over. In the United States, almost complete elimination of BC from diesel trucks is expected by 2025 (Baum 2010). In certain cases, such as large trucks that meet required specifications, retrofitting of DPFs may be justified, possibly with public subsidies, given the large health and climate benefits. Developing countries also have been reducing the sulfur content of diesel, primarily as a way of reducing SO2 and related pollutants, but as yet with little impact on emissions of BC. While some countries still tolerate very high levels of sulfur (1,500 ppm or more), many countries have come down to 350 ppm or even 50 ppm. However, 50 ppm is still too high for full use of DPFs. Few developing countries are as yet planning to introduce ULSD (10–15 ppm). Costs for reducing sulfur tend to increase sharply in the transition from 50 ppm to 10 ppm, due to the high cost and difficulty of adapting refineries to produce ULSD. A study for the Asian Development Bank estimated the cost of introducing ULSD in Asia to be between 1.1 and 1.4 U.S. cents per liter of diesel. About half of this cost is to take standards to 50 ppm, and the rest from 50 ppm to 15 ppm (ADB 2008). The cost is equivalent to about 10 to 20 percent of total refining margins; therefore, while introduction of ULSD may increase retail fuel prices by only 1 to 2 percent, the absolute investments required are still large. In addition, older refineries may need to be closed. Countries struggling to build refining capacity to keep pace with oil product demand may be reluctant to increase the cost of refining in the short term by mandating ULSD. A problem for developing countries is control of emissions from specific vehicles. High-income countries tend to have strict codes that limit emissions from vehicles and may mandate regular testing, which greatly reduce the number of diesel super- emitters. In developing countries it is hard to enforce codes that prevent super-emitters from operating. Establishing an effective inspection and maintenance program for road vehicles to deal with super-emitters and other poorly maintained vehicles is a challenging task for countries with limited institutional and technical capacity. Problems include inadequately trained personnel, poor test equipment, lack of oversight and enforcement, and fraud and corruption. The problems can be addressed with careful design of an inspection and maintenance program and provision of adequate resources. The program can be made self-financing through inspection fees and the work can be contracted out to private operators (USAID 2010). Shipping accounts for about 1 to 2 percent of global BC emissions (Bond 2004). Ships have been subject to almost no restrictions on fuel use. Most of their consumption is in international waters and they therefore may lie beyond the reach of national regulations. The diesel engines on ships (low-speed diesels) use heavy grades of diesel and fuel oil. Such engines emit high volumes of BC as well as SO2. International standards for ship fuel use are in the process of being introduced. Regulations will require use of ultra-low sulfur fuels, which will reduce the large amounts of SO2 emissions from ships and thus volumes of cooling sulfate PM. The use of ultra-low sulfur fuels will not, however, reduce emissions of BC, and DPFs are not generally suitable for large marine engines (Schneider 2010). The net effect will be warming as fewer sulfate particles offset the warming from BC. BC emissions from shipping are a particular concern given the large amount of marine traffic in waters close to the Arctic. Pressures are growing in international forums to consider how to address the problem of marine transport BC emissions (IMO 2009). The example of fuel standards for ships illustrates the importance of taking account of the impact of PM on climate when making decisions about fuel quality and use. cooking and water heating. A total of 2.5 billion people • Difficulty of designing new low-cost durable live in households using biomass fuels in unimproved cookstoves that meet the needs of consumers while stoves (Barnes and others 2011). reducing PM substantially • Affordability of new stoves to poor households Reducing emissions of PM, including BC, from • Problems maintaining condition and use of clean cooking in poor households has proved challenging. stoves after distribution Problems have included the following: • Inertia among households long accustomed to indoor smoke Climate Change Series 29 Black Carbon and Climate Change — Considerations for International Development Agencies • Limitations on distribution systems for new clean accelerate melting of ice and snow, disrupting regional fuels water supplies. Further effects occur from ABCs that • Affordability and availability of new fuels, particu- disrupt regional weather and precipitation patterns and larly for LPG consequently affect agriculture. As continuing research • Cultural factors favoring cooking styles using open clarifies the impacts of PM emissions from biomass use fires on climate change, these impacts could be considered more definitely as an aspect of policies on biomass use. These problems are substantial, but they can be overcome with well-designed policies, supplemented by appropriate funding where needed. Most governments, Costs of Mitigation however, have not placed reduction of biomass use and The cost-effectiveness of BC mitigation with respect associated emissions high on their list of energy sector to climate change impacts has just begun to be priorities. This may be changing with an increased investigated. The few estimates available are subject to focus on health indicators, such as in the Millennium a large number of uncertainties in terms of cost data, Development Goals, and rising income levels in many technical parameters, and assumed impact on global countries, such as India (Wilkinson and others 2009). warming. Much more work is needed in this area. By Another factor may be growing activity among private contrast, extensive work has been done on the costs and suppliers of clean stoves. benefits of options to mitigate GHG emissions. In spite of the overwhelming evidence of health benefits, international support for the reduction of In looking at the total costs and the climatic benefits PM from biomass use by households is generally of reducing BC, several factors need to be taken into felt to have been inadequate. To date, multilateral account: development banks and bilateral donors have not provided large resources for this purpose. Interventions • The direct impacts on global warming of lower BC have been small and isolated. It has proved difficult emissions to design and implement large-scale projects for • The offsetting impact on warming of reduced cookstove conversion. Some governments have also associated emissions of organic carbon given low priority to obtaining international assistance • The indirect impact of BC and other aerosols on in this area. Rural energy policies have focused more clouds on electrification than on provision of clean fuel for • Changes in net emissions of CO2 and other GHGs cooking and heating (Barnes and others 2011). • Health co-benefits of reductions in BC and associ- ated aerosols While the health benefits of reducing exposure to PM from residential biomass use are well known, the Two studies18 that have attempted to assemble estimates impacts of such reduced PM emissions on the global of mitigation costs looked at the relative costs and climate remain uncertain. Hence policies for the benefits of reducing BC through specific actions reduction of residential biomass use will most probably in several sectors. In order to compare the costs of continue to be based primarily on health grounds, reducing warming through reducing BC with the rather than on the need to reduce global warming. cost of doing so through GHGs, a conversion for the However, the regional climatic impacts of BC emissions warming impact from BC units to CO2 equivalent could factor into mitigation policies. The deposition of BC on snow in areas such as the Himalayas tends to 18. USAID 2010, Kandlikar and others 2009. 30 Environment Department Papers Black Carbon Mitigation Policies and Costs units is needed. This has been done using GWPs, could cut total BC emissions from the fleet by although this method has shortcomings (as noted about one third. This is a highly cost-effective above). In looking at BC mitigation, these studies means of reducing BC emissions and their impact have only taken into account the estimated global on climate. The net value of the health impact warming impact of BC, and have not considered the may also compare favorably with indoor pollution offsetting direct cooling effect of organic carbon, or reduction. indirect effects. Because of this, such studies could be misleading concerning the costs and benefits of actions Additional BC reduction options that have been looked related to residential biomass use. The calculations at include: (a) retrofitting DPF to light-duty vehicles, done for diesel and coal may be approximately correct, (b) an effective inspection and maintenance program to because BC dominates emissions. Preliminary ensure improved performance of all vehicles, and conclusions include the following: (c) changing to a new kiln type in low-tech coal-fired brick kilns. Of these, (b) and (c) may be the most • Replacing residential coal stoves with LPG stoves attractive in terms of the cost of emissions reduction. (in China): In terms of global warming, most of the benefits from such a switch come from Much more work needs to be done in this area, as the reducing the BC emitted by the coal. Substitution estimates available are limited, are based upon sparse of coal by LPG reduces, but does not eliminate, data, use uncertain climate impacts for BC, and do CO2 emissions. The cost of such substitution (an not take account of the direct and indirect impacts LPG stove and cylinder, cost of LPG fuel) is high of all PM. The effect of reducing BC emissions on for poor consumers. Costs for such an intervention climate needs to be combined more systematically can be as low as $10/ton CO2 equivalent. This with the benefits for health. Furthermore, measures intervention also has considerable health benefits. to reduce BC will involve changes in GHG emissions. • Switching of heavy-duty diesel vehicles (consuming A consistent basis is needed to combine the costs high-sulfur diesel) to CNG: This option is very and benefits of the climate and health impacts of effective in reducing BC, but capital costs are reducing BC emissions with those from changes in relatively high for vehicle conversion and new GHG emissions.19 Actions to reduce BC emissions infrastructure. The impact of this change on thus generate a range of potential costs and benefits for health will be greatest in urban areas. climate and health, including: (a) lower global warming • Retrofit of existing heavy-duty diesel vehicles from reduced BC emissions, (b) impacts on climate with particle traps: Such retrofits are relatively from PM emissions associated with BC (such as organic expensive and reduce fuel efficiency. They are carbon), (c) impacts on climate from changes in GHG usually only an option when ULSD is available emissions, and (d) effects on health of lower emissions and vehicles meet certain minimum technical of BC and other PM. The challenge in evaluating specifications. While BC emissions would be mitigation policies for BC is to assess all these costs reduced substantially, the overall cost could be high and benefits, and then to combine them in a consistent when compared to the economic benefits for both manner. climate and health. • Repair super-emitting diesel vehicles: Since such 19. See Bailis and others for an example of how reduction in vehicles typically make up about 15 to 20 percent PM can be integrated with large positive health outcomes of the fleet in developing countries, and may emit and changed GHG emissions from policies on biomass use. Such work could be supplemented by assessment of the net up to 10 times as much BC as the average vehicle, impacts on climate of emissions of BC and organic carbon, the repair of half of these high-emission vehicles as estimates of such impacts improve. Climate Change Series 31 Black Carbon and Global Climate 6 Change Policy T he possible role of BC in international climate BC and the short-lived gases could “buy time� for discussions has usually been examined along the world to act decisively to limit concentrations of with short-lived gases that were not included in GHGs to levels consistent with manageable increases the Kyoto Protocol, such as ozone.20 Methane is in temperatures. The overall cost of mitigation could also regarded as one of such “short-lived climate forcers� be reduced, as future CO2 reduction technologies will (SLCF), although it was included in the Protocol. The probably be more efficient than today’s. Delaying the positive RF of ozone and methane is estimated by the onset of higher temperatures also lessens the risk of IPCC to be of the same order of magnitude as BC. The catastrophic (runaway) global warming. It has been global warming effect of all the SLCF is high, making estimated that the reduction in global warming from them attractive targets for mitigation. Some have eliminating all BC emissions would be equivalent advocated a focus on eliminating BC and other SLCF to the continuing impact of 10 to 20 years of CO2 rapidly, as a way of delaying the temperature increase emissions (for a target of 450 ppm by 2100) (Bice that is already built into the levels of CO2 in the 2009). The world could live with a somewhat higher atmosphere. This would not be a substitute for urgent level of atmospheric CO2 before hitting key trigger action to reduce GHG levels, which are the drivers of points in terms of unmanageable increases in global global warming in the long term. temperatures, such as a rise in excess of 2ºC. The impact of eliminating BC from the atmosphere One suggested approach would be to widen global would be a onetime change in temperature levels. The climate agreements to include BC and short-lived short residence time of BC means that this change GHGs (MacCracken 2009). This approach would would take place within months. There is effectively require high-income countries to pursue aggressive no cumulative impact in the atmosphere from past policies to reduce emissions of CO2 and other GHGs. emissions21. In the case of CO2, climate change today Developing countries would, in a first phase lasting results from the cumulative emissions from the past several decades, focus on reducing short-lived warming century or more. A reduction in CO2 emissions will not agents (partcularly BC), on improving their carbon bring about an immediate lowering of temperatures. intensity, and on reversing deforestation. The intention would be that all countries should be brought into a It has been suggested that the onetime reduction in global framework for reducing global warming agents. global temperatures resulting from elimination of Under this framework, it is suggested that avoiding hard CO2 targets for developing countries over the next 20. Ozone is formed in the atmosphere by ozone precursor gases, including carbon monoxide, nitrogen oxides, and few decades would permit them to pursue economic methane. development that will almost inevitably entail some 21. The feedback effects from BC deposited on snow and ice increases in CO2 emissions. This would address the will be cumulative. In addition, the warming of the oceans due to the climate effect of BC emissions will take many point that dealing with the needs of developing years to dissipate. Climate Change Series 33 Black Carbon and Climate Change — Considerations for International Development Agencies countries for latitude in CO2 emissions has been one ignored the uncertain net warming impact of residential of the main difficulties in formulating a global climate biomass emissions, focusing on BC only, rather than on agreement. the combined effects of BC and organic carbon. This approach proposes changing the basis of climate To avoid the potential adversarial effects of introducing discussions by focusing on the fact that reducing BC BC into global climate discussions, it has been and short-lived gases is justified by the co-benefits for suggested that a focus on regional agreements may be health arising from eliminating (a) BC from cooking more productive (Wallack 2009). This also takes into smoke and diesel and (b) urban smog from gases such account the strong regional effects of BC emissions, as ozone. This reduction is a part of the economic as seen in the Himalayas and the Arctic. In such cases development process that could be accelerated to yield the impacts on countries may be more specific and substantial positive climate impacts as a co-benefit. evident—such as changes in regional water supplies and weather patterns—than those from generalized From a practical point of view, this approach needs to global warming. These direct impacts could create a consider that elimination of BC from the atmosphere short-term national incentive to participate that is more would necessarily also involve a large reduction in difficult to achieve when dealing with CO2. Precedents organic carbon concentrations as biomass emissions for such regional frameworks exist, for example in of PM are cut22. Hence, if the concern is about the UN Convention on Long-range Trans-boundary limiting short term warming, reducing emissions of Air Pollution, which brings together countries in the BC from biomass would not be the highest priority. European space (Bice 2009).23 This Convention is The principal activities to be addressed in reducing considering whether BC can be incorporated into its emissions of SLCF would be road transport as the provisions (UN ECE 2010). major emitter of BC, and large emitters of methane such as fermentation of organic matter, production of Prospects for introducing BC into global climate oil, gas and coal, and rice cultivation (Jackson 2009). policies are also affected by continuing uncertainties In policy terms, comprehensive implementation of an about the magnitude and mechanics of BC’s influence architecture for BC reduction on a global scale would on climate change (Bond 2007). This is an important seem very challenging given the well-known difficulties question, and it is one reason why substantial efforts in agreeing a global climate treaty. Moreover, attempts are being devoted to research into the climatic impacts to introduce BC into climate discussions have proved of aerosols, including BC. The conclusions of this work politically controversial. Developing countries often are expected to feature in the next IPCC report, due see a focus on BC as an attempt to divert attention in 2014. While the scientific case for reducing BC to from developed countries’ contributions to CO2 combat global warming is very strong, global policy emissions, which account for the bulk of global formulation requires more precise data. For example, warming. Since much BC is emitted from cooking if BC were to be introduced into carbon trading by the rural poor, these discussions can inadvertently, schemes, a sound and widely accepted CO2 equivalent and inaccurately, portray the poor as causing global value would have to be established. Moreover, actual warming. Unfortunately, policy discussions have often policies to cut BC emissions would require a more precise understanding of how much of BC’s warming 22. The assessment of the approach has usually been made effect is offset by the cooling effect from organic carbon with climate models that vary one atmospheric species at a time, such as removing BC without varying organic carbon. emissions. Models can vary more than one species (see Box 3), but the complexity of modeling and interpretation increases consid- 23. The Convention has helped coordinate action on reducing erably. emissions of sulfur dioxide. 34 Environment Department Papers Considerations for Development 7 Agencies B lack carbon has not been considered as an agent sectors. Awareness of the impacts of BC and organic of climate change by multilateral and bilateral carbon on climate thus needs to be present in many development agencies in the assessment of areas. Diesel use is affected by policies in the energy, projects and policies. Consideration has focused environment, transport, health, and urban sectors. on the local health aspects of PM, which include BC. Energy, environment, industrial, and urban policies all The growing evidence of the role of BC in climate affect use of coal by small industries and households. change suggests that agencies’ focus on PM arising from Use of biomass for energy and for cooking cuts health considerations could be supplemented by taking across the energy, rural policy, forestry, health, and into account the effects on climate change. Project environment sectors. evaluations could include describing their effects on BC and organic carbon emissions, and the corresponding As part of identifying the impact of project investments impacts on climate. Consideration could be given to on climate change, agencies could consider including promoting some projects that reduce BC substantially, a description of potential climate impacts from BC taking into account both health and climate co-benefits. and organic carbon resulting from projects. The Agencies could also make a contribution to expanding description would most likely be in qualitative terms, knowledge about BC and climate change, including given uncertainties over measurement and net climate improving the understanding of how to evaluate the impacts. Examples of projects where significant changes economic costs and benefits of BC reduction. Finally, in BC and organic carbon take place include the agencies could consider how the evolving knowledge following: about BC and climate change may affect policies in • Projects that have a significant impact on the level relation to climate change, at the regional and global of diesel use in transport: A reduction in urban levels. emissions of diesel PM may be brought about by public transport schemes, for example through Mainstreaming Consideration of Black bus rapid transit projects. They should reduce BC Carbon in Development Work emissions by cutting overall vehicle miles and using high-efficiency diesel engines. Such projects have The current investments and policies supported by been implemented in Egypt, Nigeria, Colombia, development agencies have impacts on emissions of and Peru. Some projects that encourage the use BC and organic carbon. The agencies could consider of heavy vehicles or shipping will increase BC describing the climate effects of these emissions emissions. alongside other project impacts. A key aspect for • Projects that involve power generation from diesel: agencies is the cross-cutting nature of BC emissions, Some projects may increase diesel use from genera- which can be affected by activities in a number of tors to meet urgent power needs, while others Climate Change Series 35 Black Carbon and Climate Change — Considerations for International Development Agencies will reduce diesel use where diesel generation is urban. There may be justification for a joint review of replaced with cleaner alternatives (for example, the climate and health impacts of BC and other PM from renewable power or natural gas) and private as a coordinated exercise among these sectors. Some diesel generation is curtailed as power supply agencies could build on a comparative advantage for reliability improves. tackling BC, arising from an ability to cover all the • Reduction in industrial PM emissions: This would relevant sectors and issues in an integrated manner. include reducing polluting emissions from brick kilns in urban areas (particularly in South Asia and Supporting Projects that Reduce Black China). Carbon to Yield Climate and Health • Substitution of rural residential coal use with Co-benefits cleaner alternatives: Alternatives to coal include LPG and biogas. Agencies could consider supporting projects that reduce • Reduction of local pollution through substitution BC emissions to yield climate and health co-benefits. of residential gas for coal in urban areas: This has Assessment would be needed of the combined costs been a feature of investments in urban gas distribu- and benefits of such projects (see below). Several areas tion in such countries as China and Turkey, where merit strong consideration for support. Since BC is not seasonal heating loads are significant. included in the Kyoto Protocol, and thus is not linked • Interventions that affect biomass use in rural and to carbon markets or low-carbon financing, innovative urban areas: Projects such as the introduction of financial and policy solutions may need to be explored advanced cookstoves, and substitution of LPG if projects are to go beyond conventional development for biomass in cooking, have significant effects on finance. both BC and organic carbon emissions. • Projects with a large impact on open burning of Policies and projects that encourage a reduction in agricultural wastes and forests: Some forestry and PM emissions from diesel probably should be strongly agricultural projects may lead to reduced open encouraged from a climate change perspective. The burning, with substantial reductions in organic scientific evidence that lower emissions of PM from carbon and BC emissions. diesel reduce global warming is sufficiently strong to be used as a guide to policy. Certain policies to cut When interventions lead to large reductions in BC emissions from diesel could result in relatively emissions of PM from the burning of biomass, the low-cost reductions in global warming. The reduction regional climate change impacts could be noted: (a) in PM from diesel also has significant health benefits, the lower BC emissions may reduce Arctic and regional especially in high-density urban areas. Policies of melting of snow and ice, with consequent impacts on interest include the following: the regional environment and on water supplies, and (b) lower BC emissions may limit formation of ABCs • Vehicle inspection regimes that can force the repair with significant regional climate effects. of the highest emitting vehicles • Replacement of diesel with CNG in vehicles, The agencies could consider greater coordination of where gas is readily available and the infrastructure activities relating to the health and climate-related cost can be kept low impacts of BC and other PM. Coordination could • Where the opportunity arises, analyzing and be established among the relevant sectors, including supporting introduction of ULSD in developing environment, energy, agriculture, transport, and countries 36 Environment Department Papers Considerations for Development Agencies • Targeting reduced use of diesel generators, mitigation strategies could give them an advantage particularly in urban areas. in addressing the problem. Better estimates of co- benefits would help in decision making on policies and Projects that substitute cleaner fuels (primarily natural investments. gas and LPG) for coal in urban and rural areas should be encouraged. To date these projects have been Agencies could consider supporting efforts to improve justified on the basis of health and energy policies, knowledge of the magnitude, sources, and effects of and to this can be added a consideration of the likely BC emissions in developing countries. Due to the mitigation of global warming from lower BC emissions. technical nature of much of this work, some agencies may consider using their development expertise and Policies and projects concerning residential biomass global networks to partner with specialist institutions. emissions will continue to be driven mainly by Improving information about emissions from biomass public health considerations, as well as by other local cooking would be a particularly strong priority, as may environmental and social factors. While projects are be seen from the foregoing discussion. A further area considered and implemented on health grounds, it is in which BC emissions data is currently lacking is gas important to the extent possible to take into account flaring; agencies engaged in this area24 could use their their potential impact on the global climate. To this end specialized knowledge to estimate the contribution of it would be essential to monitor evolving research and flaring to BC and other aerosol emissions. initiatives to improve the understanding of the effect of biomass emissions on climate change. Further research into policies and projects for the introduction of clean transport fuels and corresponding The development agencies that are suitably positioned advanced vehicle technology in developing countries could introduce BC emissions into discussions with may be called for. This could focus on progress the private sector, which has paid limited attention to toward introduction of ULSD and corresponding BC in developing countries. Most of the areas outlined vehicle technologies for cutting PM emissions. Other above include substantial private sector investment measures to reduce PM from diesel can also receive activity. While climate finance is not yet available more analytical attention from the climate change for projects specifically to reduce BC emissions, perspective, including modal shifts in transport, government policies that take BC emissions into introduction of more effective vehicle inspection, account could encourage private investment in this and repairing of high-emitting vehicles to reduce PM area. emissions. Further research may also be needed on the climate benefits of the use of CNG as a replacement for Filling the Knowledge Gaps diesel in transport. A considerable body of knowledge on the introduction of cleaner fuels, primarily with Further research is underway to clarify the impacts health considerations in mind, already exists. A climate on climate of emissions of BC and organic carbon. dimension could increase the priority of additional In parallel, improved analysis can be done on the work in this area. economic costs and benefits from climate change of mitigating BC and other PM emissions in developing countries. The work would need to be closely integrated with the analysis of the effects of PM on health in urban and rural contexts. Agencies’ knowledge base in project economics, pollution control, and climate 24. For example, the World Bank and its partners in the Global Gas Flaring Reduction Partnership (GGFR). Climate Change Series 37 Black Carbon and Climate Change — Considerations for International Development Agencies Exploring Global and Regional Policy diesel generators). This would need to be done Options to Include Black Carbon in initially at the qualitative level, given uncertainties of Climate Change Policy measurement and climate impacts. Including BC in the outlook for the energy sector would help to provide In the context of global climate policy, BC is usually a more comprehensive view of how growth policies considered along with other short-lived climate forcers, will impact climate. An example that can arise in this such as ozone. Like the Kyoto greenhouse gases, BC context is the perception of diesel as a transport fuel and non-Kyoto gases are a global issue, not specific with less climate impact than gasoline, in terms of to developing countries. Nonetheless, development CO2 emissions alone. This view may be altered if the agencies can take a role in addressing the specific nature unconstrained emissions of BC, which are higher for of BC emissions from developing countries within the diesel than for gasoline, are also taken into account. context of low-carbon development and green growth options. Development agencies could consider how More focus could be given to the regional impacts to include BC in their formulation of climate change of BC. This is particularly the case for the ABCs policies and strategies. In this they would usually be in India and China, the snow and glacier melt in guided largely by progress in dealing with BC at the the Himalayas, and the effect of BC on the Arctic. UNFCCC. Agencies should keep abreast of the rapid Development agencies could reach out to regional progress of research and policy in this area. partner organizations, including those dealing with the Himalayas and the Arctic. The likely impact of Low-carbon growth strategies for countries could BC emissions from developing countries on the Arctic consider the impact of BC and other PM emissions means that there may be a role for the agencies to help on global warming and assess measures for reducing Arctic nations address their concerns. emissions of BC where possible (for example, through introduction of ULSD and cutting the use of small 38 Environment Department Papers References Asian Development Bank. 2008. “A Road Map for Cleaner Bond, T. 2009. “What Is Black Carbon and Where Does It Fuels and Vehicles in Asia.� Manila, Philippines. Come From?� Presentation to ICCT Workshop on Black Carbon, Mexico City, October 19, 2009. Aunan, K. and others. 2009. “Radiative Forcing from Household Fuel Burning in Asia.� Atmospheric Bond, T. 2010. “Clearing the Smoke: Black Carbon Environment 43. 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