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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop DEVELOPING NARRATIVES FOR NEXT-GENERATION SCENARIOS FOR CLIMATE CHANGE RESEARCH AND ASSESSMENT98 Richard Moss99 Joint Global Change Research Institute The implications of anthropogenic climate change for the environment and society depend not only on the response of the Earth system to changes in atmospheric composition and land cover, but also on human responses. These responses are often classified into “adaptation”—changes in activities, infrastructure, or systems tailored to new climate conditions—and “mitigation”—actions to reduce net greenhouse gas emissions. Increasingly, analysts and researchers are examining adaptation and mitigation together, as both will involve changes in technology, economies, lifestyles, and policy that will interact in important ways geographically and sectorally. All of these processes—across socioeconomic, environmental, and climatic domains—are subject to extensive uncertainties. Scenarios are used by researchers and other analysts to evaluate how human choices about mitigation and adaption to future climate change will fare under uncertain future socioeconomic and climate conditions. Scenarios used in climate research and analysis cover a wide range of topics including human activities and systems, emissions of greenhouse gases and other pollutants, land use change, future climate conditions, environmental factors such as sea level rise and air/water quality, and attributes of society that influence vulnerability and resilience to climate change. This paper provides a brief overview of a new “parallel process” for developing and applying scenarios for climate change research and assessment. This parallel process was developed through a series of meetings and research papers from 2006-2010 and is described in the report of an expert meeting of the Intergovernmental Panel on Climate Change (IPCC) and a research article.100, 101 The new process is still evolving but is already improving research on interactions between climate change and human choices about responses. It begins with a broad range of potential future radiative forcing—a measure of human impact on the climate system—not with detailed socioeconomic narratives or projections, as in the past. The new process is intended to provide greater flexibility in analysis of socioeconomic dimensions of mitigation and adaptation, specifically to encourage exploration of alternative socioeconomic futures that could give rise to different levels of climate change. The paper briefly reviews the new process and points to resources for additional information on the current status of a range of related modeling activities. It focuses on challenges in developing socioeconomic scenarios for exploring future mitigation of net emissions and the interactions of mitigation with adaptation to changing climate conditions. The paper highlights a research need to develop narratives of potential institutional, demographic, eco 98 Prepared for “Modeling the Economics of Greenhouse Gas Mitigation,” National Research Council, the National Academies, Washington, DC, April 15-16, 2010. Comments by workshop participants are gratefully acknowledged. 99 This paper is based on a presentation given at a workshop on “Modeling the Economics of Greenhouse Gas Mitigation,” National Research Council, the National Academies, Washington, DC, April 15-16, 2010. It draws on an article that appeared in the February 11, 2010 issue of Nature on the next generation of scenarios for climate change research and assessment, as well as on results from a meeting on socioeconomic scenarios convened jointly by the Climate Research Committee and the Committee on the Human Dimensions of Global Environmental Change of the National Research Council on February 4-5, 2010. I am indebted to the co-authors of the Nature article and the presenters and participants in the joint workshop on socioeconomic scenarios. Comments by workshop participants are gratefully acknowledged. Information release: PNNL-SA-75225. 100 Moss, R.H., Mustafa Babiker, Sander Brinkman, Eduardo Calvo, Tim Carter, Jae Edmonds, Ismail Elgizouli, Seita Emori, Lin Erda, Kathy Hibbard, Roger Jones, Mikiko Kainuma, Jessica Kelleher, Jean Francois Lamarque, Martin Manning, Ben Matthews, Jerry Meehl, Leo Meyer, John Mitchell, Nebojsa Nakicenovic, Brian O’Neill, Ramon Pichs, Keywan Riahi, Steven Rose, Paul Runci, Ron Stouffer, Detlef van Vuuren, John Weyant, Tom Wilbanks, Jean Pascal van Ypersele, and Monika Zurek. Towards New Scenarios for Analysis of Emissions, Climate Change, Impacts, and Response Strategies. IPCC Expert Meeting Report, 19-21 September, 2007, Noordwijkerhout, The Netherlands. Intergovernmental Panel on Climate Change, Geneva, Switzerland (2008). 101 Moss, R.H. Jae A. Edmonds, Kathy Hibbard, Martin Manning, Steven K. Rose, Detlef P. van Vuuren, Timothy R. Carter, Seita Emori, Mikiko Kainuma, Tom Kram, Gerald Meehl, John Mitchell, Nebojsa Nakicenovic, Keywan Riahi, Steven J. Smith, Ronald J. Stouffer, Allison Thomson, John Weyant, and Tom Wilbanks. “The Next Generation of Climate Scenarios.” Nature 463, 11 February 2010 doi:10.1038/nature08823.
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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop nomic, cultural, and other factors that are essential for understanding the potential to reduce emissions and adapt to changed climate conditions. These factors are currently underrepresented in integrated assessment models of emissions and consequences of climate change and mitigation policies. Scenarios Scenarios are tools for analyzing situations in which outcomes are uncertain. The goal of working with scenarios is not to predict the future but to better understand uncertainties in order to reach decisions that are robust under a wide range of possible futures. Space constraints do not allow a full review of scenario development, but such reviews exist in the literature.102 In climate change research, scenarios describe plausible trajectories of different aspects of the future that are constructed to investigate the potential consequences of anthropogenic climate change. Over time, an increasingly broad array of scenarios has been developed to address different components of the issue. Scenarios currently represent major driving forces, processes, impacts, and potential responses important for informing climate change policy. See Box C.1 for a detailed description of types of scenarios used in climate change research. A variety of techniques have been used in developing scenarios. For climate scenarios, these approaches include analogues of anticipated future conditions (both temporal and spatial), and model-based scenarios produced with general circulation models (GCMs—both global and regional) “forced” with scenarios of emissions.103 Emissions scenarios are developed primarily using integrated assessment models (IAMs), which are comprehensive representations of quantifiable socioeconomic (e.g., demographic, economic, and technological) and environmental (e.g., land use) drivers of emissions and, increasingly, impacts. 104 A variety of environmental scenarios (e.g., sea level rise, hydrology, land cover, air quality) are produced with specialized hydrological, agricultural, ecological, and other models that incorporate both human and environmental processes—these, along with climate scenarios and socioeconomic assumptions are commonly used in evaluating potential consequences of climate change for a variety of human and natural systems. 105 Quantitative approaches to scenarios do not adequately account for political, cultural, and institutional influences that are important in understanding innovation, technological change, and the ability of societies to effectively implement policies. These factors are most often represented in qualitative narratives or storylines, which are used by analysts in a variety of ways to coordinate scenarios across scales or subject matters.106, 107 Many different groups have used scenarios at different spatial scales. At a global scale, the IPCC has used emissions and climate scenarios as a central component of its work of assessing climate change research. The IPCC has commissioned several sets of emissions scenarios for use in its reports, convening authors and modelers, providing terms of reference, and approving the scenarios through an intergovernmental process that took several 102 Parson, E.A. et al. Global Change Scenarios: Their Development and Use (Sub-report 2.1B of Synthesis and Assessment Product 2.1, U.S. Climate Change Science Program and the Subcommittee on Global Change Research, Department of Energy, Office of Biological and Environmental Research, Washington DC (2007). 103 Mearns, L.O. et al. Climate Scenario Development. In Climate Change 2001: The Physical Science Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, eds J.T. Houghton, Y. Ding, and D.J. Griggs. Cambridge University Press, Cambridge, UK. 739-768 (2001). 104 For an excellent review of emissions scenario methods and literature, see Nakicenovic, N., et al. Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge Univ. Press, 2000). 105 For an overview of the use of different types of scenarios in assessment of impacts, adaptation, and vulnerability, see Carter, T.R. et al. Developing and Applying Scenarios. In Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change Eds J.J. McCarthy, O.F. Canziani, N.A. Leary, D.J. Dokken, and K.S. White. Cambridge University Press, Cambridge, UK. 145-190 (2001). 106 National Research Council. Describing Socioeconomic Futures for Climate Change Research and Assessment: Report of a Workshop. Panel on Socio-Economic Scenarios for Climate Change Research and Assessment, Committee on the Human Dimensions of Global Change, Division of Behavioral and Social Science and Education. Washington, DC: The National Academies Press (2010). 107 Arnell, N.W. et al. Climate and socio-economic scenarios for global-scale climate change impacts assessments: Characterising the SRES storylines. Global Environmental Change 14, 3-20 (2004).
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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop BOX C.1 Types of Scenarios in Climate Research and Assessment Emissions Scenarios Emissions scenarios describe future releases to the atmosphere of greenhouse gases, aerosols, and other pollutants and, along with information on land use and land cover, provide inputs to climate models. They are based on assumptions about driving forces such as patterns of economic and population growth, technology development, and other factors. In addition to their use as inputs to climate models, emissions scenarios are used in research on mitigation to explore the economic, environmental, and climatic implications of alternative energy and technology futures. For example, numerous studies evaluate the changes in technologies, economic development, policy, or other factors that would be required to shift emissions from a baseline to a lower path, for example keeping greenhouse gas concentrations (or global average surface air temperature increases) below a specified level (see, for example, Clarke, L. et al. Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations). They do not track “short-term” fluctuations such as business cycles or oil market price volatility but instead focus on long-term (e.g., decades to centuries) trends. Climate Scenarios Climate scenarios are plausible representations of future climate conditions (temperature, precipitation, and other climatological phenomena).They can be produced using a variety of approaches including: incremental techniques where particular climatic (or related) elements are increased by plausible amounts; spatial and temporal analogues in which recorded climate regimes that may resemble the future climate are used as example future conditions; other techniques such as extrapolation and expert judgment; and techniques that use a variety of physical climate and earth system models including regional climate models. There is a notable increase in interest in regional-scale climate scenarios and scenarios of climate extremes and surprises, which are especially for impact and adaptation assessment. Environmental Scenarios These scenarios focus on changes in environmental conditions other than climate that may occur regardless of climate change. Such factors include water availability and quality at basin levels (including human uses), sea level rise incorporating geological and climate factors, characteristics of land cover and use, and local atmospheric and other conditions affecting air quality. The potential impact of climate change and effectiveness of adaptation options cannot be examined without understanding these interactions. Vulnerability Scenarios Scenarios of demographic, economic, policy, cultural, and institutional characteristics are needed for different types of impact modeling and research. This information is crucial for evaluating the potential to be affected by changes in climate, as well for examining how different types of economic growth and social change affect vulnerability and the capacity to adapt to potential impacts. Many of the same socioeconomic factors that affect emissions also affect vulnerability and adaptive capacity of different societies, and thus the underlying socioeconomic modeling must be coordinated. Narratives While some socioeconomic factors affecting emissions and vulnerability are modeled quantitatively, political, institutional, cultural and other qualitative factors are not effectively incorporated into quantitative model-based scenarios. For this reason, qualitative narratives (also referred to in the literature as “storylines”) are developed to describe developments in these factors and how they could influence future forcing and responses.Narratives can be used as the foundation for quantitative scenarios, describing the general logic and developments underlying a particular quantitative set of scenarios. For example, the IPCC SRES scenarios were based on a set of four narratives that described a range of different development pathways for the world. Narratives can also facilitate coordination across spatial scales and substantive domains.
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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop years.108, 109, 110The World Energy Council and the International Energy Agency, among other groups, have both commissioned scenarios that include greenhouse gas emissions and their interactions with socioeconomic and environmental systems as a way of analyzing the potential implications of different economic, industrial, energy, and research and development policies for future levels of emissions. 111, 112 The Energy Modeling Forum has played a substantial role in shaping the development of socioeconomic and emissions scenarios, convening a variety of intercomparisons of the results of IAM-based projections.113 The Millennium Ecosystem Assessment, building on work in the IPCC, created a comprehensive set of scenarios covering a range of human, climate, and environmental changes relevant to assessing potential future changes in ecosystem goods and services.114 There is increasing interest in developing scenarios at finer spatial scales, for example focusing on states/provinces or even metropolitan regions. Approaches for developing finer scale scenarios that are coupled to global or national scenarios to varying degrees are under development.115 A challenge is representing the different socioeconomic and environmental processes at work at different scales, and nesting these scenarios in a way that adequately incorporates cross-scale interactions.116 Further research on this issue is essential. A New Process Scenarios were typically developed and applied sequentially, in a linear causal chain that extended from the socioeconomic factors that influence greenhouse gas emissions to atmospheric and climate processes to impacts. This sequential process involved developing emissions scenarios based on different socioeconomic futures, estimating concentrations and radiative forcing from emissions and land use change, projecting the ensuing climate, and then using the resulting climate scenarios in impact research. As a result of this sequential process, there were frequently long delays in handing off information on emissions to climate modelers, and scenarios of climate change to researchers investigating impacts. This complicated the synthesis of results on issues such as costs and benefits and created challenges when comparing feedbacks across different types of models. In addition, climate futures appeared to be tied to only a single socioeconomic future when in fact a single climate future could result from a wide variety of development pathways (varying demographic, economic, technological, institutional, policy, and cultural conditions). A new process and new scenarios were developed by researchers working on integrated assessment modeling, climate modeling, and modeling and analysis of impacts to respond to a variety of needs and opportunities. These included: A decade of new data on socioeconomic, environmental, and technological trends; New information needs of users, including a need for more information on the feasibility and implications of very low emissions scenarios and “overshoot” scenarios in which radiative forcing peaks and then declines to a target level; An increasing interest in scenarios which focus on the next two to three decades with higher spatial and temporal resolution and improved representation of extreme events to support adaptation studies; 108 Response Strategies Working Group. in Climate Change: The IPCC Scientific Assessment (eds Houghton, J. T., Jenkins, G. J. and Ephraums J. J.) 329-341 (Cambridge Univ. Press, 1990). 109 Leggett, J., Pepper, W. J. and Swart, R. J. in Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment (eds Houghton, J. T., Callander, B. A. and Varney, S. K.) 69-95 (Cambridge Univ. Press, 1992). 110 Nakicenovic, N., et al., op. cit. 111 Deciding the Future: Energy Policy Scenarios to 2050 (World Energy Council, 2007). 112 World Energy Outlook (International Energy Agency, Paris, 2009). 113 See http://emf.stanford.edu/. 114 Millennium Ecosystem Assessment. Ecosystems and Human Well-being: Scenarios, Vol. 2 (eds Carpenter, S. R. et al.) xix-551 (Island Press, 2005). 115 The U.S. National Park Service is developing capacity for application of scenarios at a variety of spatial scales. See http://www.nps.gov/climatechange/docs/ScenarioPlanningBrief.pdf for an overview of this approach. 116 Zurek, M., and Henrichs, T. Linking scenarios across geographical scales in international environmental assessments. Technological Forecasting and Social Change Volume 74, Issue 8, (2007) 1282-1295, doi 10.1016/j.techfore.2006.11.005.
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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop More information to support analysis of factors that affect vulnerability and resilience, which requires a process that promotes linked but flexible analysis across geographical scales; Scientific advances including advances in climate modeling (incorporation into climate models of the oceanic and terrestrial carbon cycle, aerosols, atmospheric chemistry, ice sheets, and dynamic vegetation); Increasing overlap in the substantive domains of climate, impact, and integrated assessment models which creates increased demand for harmonization of assumptions and data. In addition to responding to these new information needs and opportunities, a new process for developing scenarios was stimulated by the IPCC’s decision not to commission another set of emissions scenarios but instead to limit its role to assessing scenarios developed in the literature. The new parallel process developed in response to these factors is shortening the time to develop different types of scenarios and transfer them from one set of researchers to another. Conceptually, the process begins with pathways of radiative forcing (the change in the balance between incoming and outgoing radiation to the atmosphere caused primarily by changes in atmospheric composition), not detailed socioeconomic narratives or scenarios. Central to the process is the concept that any single radiative forcing pathway can result from a diverse range of socioeconomic and technological development scenarios.117 Among other issues, the new process facilitates exploration of the question “What are the ways in which the world could develop in order to reach a particular radiative forcing pathway?” To jump start the process, four RCPs were selected, defined by their total radiative forcing in 2100. The selection process for the RCPs was based on a detailed set of criteria and included an open peer review.118 The RCP data and information on their intended uses and limits is freely available elsewhere.119 In the “parallel phase” of the new process, climate and integrated assessment modelers will work simultaneously rather than sequentially. Climate modelers will conduct new climate model experiments using the time series of emissions and concentrations from the four RCPs. These experiments will explore carbon cycle feedbacks, atmospheric chemistry interactions, and the response of the climate system, including a set of short-term experiments to 2035 at higher resolution in an effort to provide more information for adaptation studies.120 Further information on these research activities, which are coordinated through the Climate Model Intercomparison Project, Phase 5 (CMIP5) is available.121 Integrated assessment modelers will develop an ensemble of new socioeconomic and emissions scenarios that explore a variety of issues including alternative baselines and approaches to reach the various radiative forcing targets. IAM researchers will also work with researchers interested in impacts and adaptation to develop new socioeconomic narratives and scenarios to inform research on these topics. Many of these activities are being conducted through a newly-formed Integrated Assessment Modeling Consortium.122 This paper will now turn to examining development of socioeconomic scenarios in some greater detail. Development of Socioeconomic Scenarios There are a variety of techniques and approaches for creating and applying socioeconomic scenarios that have been used in research and assessments. These have been developed to meet the needs of various user communities. Two major groups can be distinguished: (1) modelers and researchers who need the scenario outputs of one type of research as inputs to their analysis; and (2) resource managers, urban planners, or decision makers who need to incorporate climate change concerns into their decision processes. In the traditional sequential approach, most of the focus has been on serving the needs of modelers and researchers, particularly the climate modeling community, which has required emissions scenarios as inputs to model experiments. The substantive focus of this work was primarily on developing centennial scale projections of 117 Ibid. 118 Moss, R.H., et al., (2008), op. cit. 119 http://www.iiasa.ac.at/web-apps/tnt/RcpDb. 120 Hibbard, K.A., Meehl, G.A., Cox, P. and Friedlingstein, P. A strategy for climate change stabilization experiments. EOS 88, 217, 219,EOS 88, 217, 219, 221 (2007). 121 http://cmip-pcmdi.llnl.gov/cmip5/. 122 Further information is available at http://iamconsortium.org/.
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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop emissions based on analysis of trends in fields as diverse as demography, economic development, and a full range of energy and agricultural technologies. Previous scenario efforts such as the SRES performed extensive reviews of the current state of science on scenario “driving forces” in relevant fields of socioeconomic research and used IAMs to develop quantitative projections for an increasingly comprehensive set of atmospheric constituents at the global scale.123 The significant achievements of this approach notwithstanding, there were limits to its ability to serve the needs of impacts-oriented researchers as well as resource managers, urban planners, or decision makers who focus on impacts, adaptation, and vulnerability and evaluating the robustness of potential decisions under uncertainty. These end users would benefit from improved approaches to develop locally or sectorally oriented scenarios embedded within broader climate and socioeconomic scenarios. Initial efforts at developing such nested scenarios were carried out using the SRES, and these were facilitated by use of the narratives of storylines that served as the foundation for the SRES.124 However, the initial focus on emissions, coupled with the time pressure to produce the scenarios relatively quickly so that climate modelers could apply them, meant that issues important to vulnerability assessments were not incorporated systematically into the global scenarios themselves. One of the motivations behind the new scenarios process is to provide more time and flexibility to develop storylines that are relevant to a broader range of concerns including vulnerability assessment. There is also the potential to develop mitigation-oriented narratives and scenarios at the scale of the globe or large regions (e.g., continents) that are broadly consistent with the RCPs but that are oriented toward needs for analysis of specific sectoral or regional issues. Taking advantage of the potential in the new scenarios process will require advances in research methods and process. These include: Coupling specific decision support scenarios relevant to regions/sectors to global scenarios: This is an issue that is particularly important for large scale assessments such as the IPCC and the U.S. National Climate Assessment (U.S. NCA) which need to coordinate assumptions and activities distributed across a wide range of specific regions and sectors. Processes affecting vulnerability and mitigation potential differ across geographic scales, and much work is required to better understand the key global determinants of mitigation and adaptation potential at finer scale in order to systematically include those factors in the design of scenarios. A second component of this work will examine the effects of local conditions and choices on vulnerability. A nested approach to scenario development links (i) global scenarios, which provide broad bounding conditions within which local/regional actors will have to operate and (ii) more specific decision support scenarios, which when coupled to global scenarios enable users to examine the robustness of specific options/decisions against a broad range of future conditions. Such an approach would enable users to tap into knowledge about global scale processes/conditions and relate that information to their own decision making. Work carried out by Robinson and colleagues focuses on approaches for relating stakeholder-driven concerns in the context of future levels of climate change and broader socioeconomic conditions.125 Relating qualitative narratives to quantitative scenarios: Scenarios of socioeconomic change need to focus not only on quantifiable factors such as demography, economic development, and emissions or cost characteristics of different technologies, but also on a variety of qualitative factors that are essential for understanding the potential for innovation and adaption. These include a variety of institutional factors such as intellectual property regimes, international agreements, the effectiveness of enforcement of legal agreements, the functioning of markets, and the quality of public health, education, and other public services. Additional research is required to understand how to characterize uncertainty in potential outcomes in these areas, and to evaluate how a typology of future qualitative conditions could influence mitigation and adaptation potential. Evaluating the plausibility of combinations of future socioeconomic conditions: this is an important input into identifying a small number of strategically-important global scenarios to inform mitigation and vulnerability 123 Nakicenovic, N., et al., op. cit., Chapter 3. 124 UK Climate Impacts Programme, Socio-economic scenarios for climate change impact assessment: a guide to their use in the UK Climate Impacts Programme. UKCIP, Oxford (2000). See http://www.ukcip.org.uk/images/stories/Pub_pdfs/socioeconomic_tec.pdf. 125 Alison Shaw, et al. Making local futures tangible—Synthesizing, downscaling, and visualizing climate change scenarios for participatory capacity building. Global Environmental Change 19 (2009) 447-463, doi:10.1016/j.gloenvcha.2009.04.002.
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Modeling the Economics of Greenhouse Gas Mitigation: Summary of a Workshop assessments. Initial statistical evaluation of population trends, economic development, and other factors indicate that a very wide range of socioeconomic conditions can be associated with any of the RCPs. Clearly, there are relationships among socioeconomic conditions (e.g., demographics are not independent of the other variables, for example rates of urbanization will depend on economic development paths) that will make some combinations of conditions unlikely to occur. The full range of potential conditions presents too broad an array of futures to consider systematically. Research is needed to develop characterizations of a smaller number of potential futures that represent plausible combinations of conditions but that span important uncertainties, for example futures that give rise to greater levels of vulnerability or in which mitigation is more difficult. The new process provides new opportunities to consider potentially undesirable futures (e.g., global pandemics, failure of development in some countries) that governments have been reluctant to consider. Delivering and supporting use of scenarios: scenario data are becoming increasingly available through a wide variety of websites. In many cases, the proper uses and limits of the information provided in scenarios is not acknowledged, potentially leading to misapplication of information. In addition, the new scenario process itself calls for creation of a scenario “library” with guidance for users on how to integrate climate, socioeonomic, and environmental scenarios in a consistent fashion. Support for users, especially in developing countries where access to scenario information can be limited, is especially important. Concluding Thoughts The new parallel scenario process presents opportunities but remains a still evolving and imperfect approach for coordinating across research communities and providing tools that meet the needs of various user communities. It has the potential to be more open and flexible, especially for socioeconomic scenario development; to increase collaboration across distinct research communities; and improve synthesis and coordination across multi-scale assessments. More attention to the development of socioeconomic scenarios that address both mitigation and adaptation can lead to improved understanding of the interactions of these distinct approaches in managing risks from anthropogenic climate change. Because of the inherent potential of scenario techniques to evaluate decision making under conditions of deep uncertainty, it is especially important to develop tools for a wider range of users that facilitate examination of regional or sectoral decisions in the context of a wide range of future climate and socioeconomic conditions.
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