1
Introduction

Climate scientists are projecting changes in the global climate with potentially profound impacts on agriculture and forest productivity, ecosystems, water resources, and energy, as well as related socioeconomic effects.1 Increases in annual globally averaged mean temperatures, in the number of warm days and nights over mid- and high-latitude land areas, and in temperature and precipitation extremes all are projected to occur with a high degree of confidence2 during the 21st century. These changes will bring about the retreat of sea ice and the thawing of glaciers and ice caps, particularly at high northern latitudes; rising sea levels; and greater flooding and higher storm surges along vulnerable coastal and riverine areas. The finer the geographic resolution and the longer the temporal projections, the greater are the uncertainties surrounding estimates of future climate change. The respective roles of human and natural causes in these changes have now been well established (IPCC 2007b).

Numerous studies have examined the link between climate change and the transportation sector. These studies have been conducted primarily

1

 Climate change refers to a statistically significant variation in either the mean state of the climate or its variability over an extended period, typically decades or longer, that can be attributed to either natural causes or human activity (IPCC 2007a). This definition is drawn from the Intergovernmental Panel on Climate Change (IPCC), which was jointly established by the World Meteorological Organization and the United Nations Environment Programme in 1988 to assess the available scientific and socioeconomic information on climate change and its impacts and on options for mitigating those impacts and developing adaptive responses.

2

 Climate scientists express uncertainty in a variety of ways. To encourage greater uniformity in communicating uncertainty, lead authors of the IPCC Fourth Assessment Report were provided guidance on how to treat issues of uncertainty and statistical confidence in a consistent manner (IPCC 2005). The term “high degree of confidence” means consistency across model projections and/or consistency with theory and/or changes in the mean. See Chapter 2 for a more detailed discussion of uncertainty.



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1 Introduction C limate scientists are projecting changes in the global climate with potentially profound impacts on agriculture and forest productivity, ecosystems, water resources, and energy, as well as related socioeconomic effects.1 Increases in annual globally averaged mean temperatures, in the number of warm days and nights over mid- and high-latitude land areas, and in temperature and precipitation extremes all are projected to occur with a high degree of confidence2 during the 21st century. These changes will bring about the retreat of sea ice and the thawing of glaciers and ice caps, particularly at high northern latitudes; rising sea levels; and greater flooding and higher storm surges along vulnerable coastal and riverine areas. The finer the geographic resolution and the longer the temporal pro- jections, the greater are the uncertainties surrounding estimates of future climate change. The respective roles of human and natural causes in these changes have now been well established (IPCC 2007b). Numerous studies have examined the link between climate change and the transportation sector. These studies have been conducted primarily Climate change refers to a statistically significant variation in either the mean state of the climate 1 or its variability over an extended period, typically decades or longer, that can be attributed to either natural causes or human activity (IPCC 2007a). This definition is drawn from the Intergovernmental Panel on Climate Change (IPCC), which was jointly established by the World Meteorological Organization and the United Nations Environment Programme in 1988 to assess the available scientific and socioeconomic information on climate change and its impacts and on options for mitigating those impacts and developing adaptive responses. 2 Climate scientists express uncertainty in a variety of ways. To encourage greater uniformity in communicating uncertainty, lead authors of the IPCC Fourth Assessment Report were provided guidance on how to treat issues of uncertainty and statistical confidence in a consistent manner (IPCC 2005). The term “high degree of confidence” means consistency across model projections and/or consistency with theory and/or changes in the mean. See Chapter 2 for a more detailed discussion of uncertainty. 21

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22 Potential Impacts of Climate Change on U.S. Transportation from the perspective of transportation’s contribution to global warming through the burning of fossil fuels, which releases carbon dioxide (CO2) and other greenhouse gases (GHGs) into the atmosphere.3 CO2 from com- bustion of fossil fuels is the largest source of U.S. GHG emissions. In 2005, the most recent year for which data are available, the transportation sector accounted for 33 percent of U.S. CO2 emissions from fossil fuel combus- tion,4 exceeded only by electricity generation by the electric power industry at 41 percent (USEPA 2007, Table 3-7).5 CO2 emissions from U.S. trans- portation activities are expected to increase over the next several decades, primarily as a result of growth in road travel, fueled by population and eco- nomic growth (World Business Council for Sustainable Development 2004). However, these emissions are likely to be regulated. In a landmark decision in April 2007 (Massachusetts et al., Petitioners, v. Environmental Protection Agency et al.), the U.S. Supreme Court ruled that the U.S. Environmental Protection Agency has the authority under the Clean Air Act to regulate GHG emissions and that CO2 can be construed as an air pollutant under the statute. Far less attention has been paid to the consequences of potential climate changes for U.S. transportation infrastructure and operations.6, 7 For exam- ple, projected rising sea levels, flooding, and storm surges could swamp marine terminal facilities, airport runways near coastlines, subway and rail- road tunnel entrances, and roads and bridges in low-lying coastal areas. CO2 and other GHGs allow sunlight to enter and prevent heat from leaving the earth’s atmosphere— 3 the so-called greenhouse effect, loosely analogous to the operation of a greenhouse window. Higher concentrations of CO2 and other GHGs than occur naturally trap excess heat in the atmosphere and warm the earth’s surface (Staudt et al. 2005). 4 Emissions from combustion of both aviation and marine international bunker fuels (i.e., fuel loaded on transport vehicles in the United States but consumed in international operations) are excluded from this total. See Appendix B for a more detailed discussion of the transportation sector’s contribution in general, and the U.S. contribution in particular, to worldwide GHG emissions, particularly emissions of CO2 from fuel combustion. 5 The total is larger if emissions from the extraction, production, and distribution of transport fuels and from the manufacture, distribution, and disposal of transportation vehicles are summed to produce a total life-cycle emissions estimate (see the discussion in Appendix B). 6 In this report, infrastructure refers to both transportation networks (e.g., road and rail systems) and facilities (e.g., bridges, tunnels, ports). 7 In fact, a recent assessment of the U.S. Climate Change Science Program (CCSP) found that the scientific community is not well structured to develop information that would enable adaptive response for any sector in the United States (NRC 2007). The CCSP integrates federal research on climate and global change, as sponsored by 13 federal agencies.

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Introduction 23 Across the northern portions of the contiguous United States, warmer tem- peratures and reduced lake ice will likely lead to increased evaporation from bodies of water and their surrounding watersheds, potentially lower- ing lake and river levels and reducing vessel-carrying capacity. Shipping across the Great Lakes and the Upper Midwest river system would thereby be impaired, although a longer shipping season would offset some of the adverse economic effects. Thawing permafrost in Alaska is already creating settlement and land subsidence problems for roads, rail lines, runways, and pipelines. Greater temperature extremes (mainly heat waves) in some U.S. regions could lead to buckling of pavements and misalignment of rail lines. More intense precipitation could increase the severity of flooding events, such as the storms that plagued the Midwest during the flooding of the Mississippi River in 1993 and the Chicago area in 1996. More intense tropical storms, like Hurricanes Katrina and Rita, which ravaged the Gulf Coast in 2005, are likely to become more frequent. However, no significant increases in the annual number of Atlantic tropical storms are projected. The vulnerability8 of the transportation sector to these impacts has not been thoroughly studied, nor has it been widely considered by transporta- tion planners and decision makers in planning, designing, constructing, retrofitting, and operating the transportation infrastructure. Many trans- portation professionals are unaware of the problems climate change could create. Others are hesitant to take action in view of the uncertain outcomes and long time frames involved and the lack of clear guidelines and stan- dards for addressing the effects of climate change and related hazards. STUDY CHARGE, SCOPE, AND AUDIENCE The Executive Committee of the Transportation Research Board (TRB) requested and provided funding for this study, which was undertaken jointly with the Division on Earth and Life Studies of the National 8 One in-depth assessment of impacts in the Gulf Coast region, entitled Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study, was ongoing during the course of this study. It became available for public comment only after the committee had completed its deliberations. The public review version of the Gulf Coast study can be accessed at www.climatescience.gov/Library/sap/sap4-7/public-review-draft/default.htm.

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24 Potential Impacts of Climate Change on U.S. Transportation Academies. The expert committee formed to conduct the study was charged9 to • Provide federal, state, and local transportation officials in the United States with an overview of the scientific consensus regarding climate change, including uncertainty about its nature and extent; • Summarize previous work on strategies for reducing transporta- tion’s impact on climate change; • Summarize possible impacts on transportation, such as those due to rising sea levels, higher mean temperatures with less extreme low temperatures and more heat extremes, and more frequent intense precipitation events; • Analyze options for adapting to these impacts, including the possi- ble need to alter assumptions about infrastructure design and operations, the ability to incorporate uncertainty into long-range decision making, and the capability of institutions to plan and act on mitigation and adaptation strategies at the state and regional levels; • Identify critical areas for research; and • Suggest policies and actions for preparing for the potential impacts of climate change. The committee’s charge can be viewed more broadly as a risk manage- ment problem with hazards to address (potential impacts of climate change) and vulnerable10 assets to protect (transportation infrastructure). Seen in this framework, the objective is to minimize risk by reducing the hazards (i.e., identify mitigation measures to reduce the potential effects of climate change) and protecting the assets (i.e., identify adaptation mea- A more detailed statement of task is included as Appendix A. 9 In this report, the term “vulnerability” is defined as “the degree to which a system is susceptible 10 to, and unable to cope with, adverse effects of climate change, including climate variability and extremes. Vulnerability is a function of the character, magnitude, and rate of climate change and variation to which a system is exposed, its sensitivity, and its adaptive capacity” (IPCC 2007a, 21). The committee notes that there is a large literature on vulnerability as it relates to many hazards and cites Turner et al. (2003) as an example of a broad vulnerability framework and its application to several different types of hazards and affected communities in case studies.

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Introduction 25 sures11 to strengthen the infrastructure and increase its resilience to changing climate conditions through more stringent design standards and construction codes and retrofitting or relocation of at-risk facilities).12 The primary focus of this report is on adaptation strategies rather than on strategies to mitigate transportation-related GHG emissions. The topic of adaptation, particularly as it relates to transportation, has not received the attention or research effort devoted to the issue of mitigation. In- vestigating both topics fully was beyond the resources available for this study. In fact, at the time of this writing, TRB had initiated a new study focused entirely on mitigation.13 Nevertheless, in response to its charge and drawing heavily on existing studies, committee member George Eads, with the consensus of the full committee, summarized current and pro- jected contributions of the transportation sector to GHG emissions and examined numerous technological and nontechnological mitigation strategies (see Appendix B). The analysis did not attempt to pick winners and losers by comparing the costs and benefits of alternative mitigation approaches. Indeed, the data for doing so were not available. That level of analysis would require a separate study or even a series of studies. The committee was mindful of the potential interaction between miti- gation and adaptation strategies as shown in Figure 1-1. For example, if the fuel consumption and CO2 emissions and concentrations of transportation vehicles could be substantially reduced by the introduction of new tech- nologies, this would lessen the human-caused contribution to climate change and its impacts on transportation infrastructure. Reductions in travel demand or shifts to less GHG-emitting travel modes (e.g., public transit for personal travel and rail for freight travel) would operate in a sim- ilar fashion. The summary of Appendix B notes, however, that a common 11 Adaptation strategies refer to human attempts to protect or adapt systems so as to reduce the risks and moderate the potential harm from and exploit the beneficial opportunities of the impacts of climate change. Mitigation strategies refer to human intervention to reduce the sources of GHGs that contribute to climate change. 12 Until researchers can quantify both the severity of expected outcomes and their probabilities, however, a full risk assessment is not possible. 13 The study on potential energy savings and GHG reductions will review policies and strategies to affect behavior and improve fuel economy for passenger and freight vehicles across all modes; develop scenarios to illustrate potential savings over a 25- to 50-year time horizon for the United States; and analyze the safety, economic, transportation finance, and environmental consequences of energy-saving measures.

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26 Potential Impacts of Climate Change on U.S. Transportation Adaptation Strategies Reduce Impacts Greenhouse Gas Climate Mediating Impacts on U.S. Policies/ Emissions and Changes Environmental Transportation Actions Concentrations Effects Infrastructure Mitigation Reduce greenhouse gas emissions and concentrations Measures FIGURE 1-1 Role of mitigation measures and adaptation strategies in addressing climate change impacts on U.S. transportation infrastructure. (Bolded areas denote the primary focus of this study.) characteristic of these mitigation measures is the considerable time they would take to be fully effective14 and the fact that they would affect only future GHG emissions and concentration levels. Complementary adapta- tion strategies are thus essential if the transportation sector is to address the consequences of GHG emissions and concentration levels that have already occurred. The report begins with an overview of the current state of knowledge about climate change and its potential impacts, with a particular focus on North America, to set the stage for assessing the consequences for the transportation sector and identifying prudent adaptation strategies. The objective of this review is not to advance the state of climate science but 14 The appendix notes that the time required to develop, commercialize, and disseminate new vehicle technologies is probably shorter than the time required to alter the fundamental drivers of demand for personal and freight transport—growth in real income, population growth, urbanization, and changes in urban form. Nevertheless, both new technology and shifts in demand are needed if future levels of transportation-related GHG emissions—a major source of total GHG emissions— are to be significantly reduced.

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Introduction 27 to inform transportation professionals about climate change—including uncertainty as to its precise timing and geographic locations—so they can begin to consider appropriate responses. The report encompasses all modes of transportation—highways (including bridges and tunnels), rail (including private rail lines and public transportation), marine and air transportation, and pipelines. Its primary focus is on the direct impacts of climate change on transporta- tion infrastructure and system operating performance, although indirect impacts are noted (e.g., potential shifts in the location of economic activ- ities and use of transportation modes, pollution impacts). These indirect impacts are highly uncertain because they depend on assumptions about population and economic growth, the rate of technological innovation, and policy decisions (e.g., government regulations and controls on coastal land use and development, private-sector decisions about business oper- ations and logistics). The geographic scope of the study is confined to the United States but extends beyond the contiguous 48 states to include Alaska, Hawaii, and the U.S. territories.15 The range of weather and climate conditions16 embraced by this area is broad—from the permafrost conditions of Alaska to the tropical conditions of Puerto Rico and Hawaii. Thus, the United States can expect a wide range of climate changes and their impacts. International studies were reviewed for techniques and approaches that might be appro- priate to the United States. However, the committee found few studies that address the impact of climate change on transportation and adaptation strategies. The audience for this report is the transportation community broadly defined. The overall goal of the report is to demonstrate to decision makers responsible for transportation infrastructure—both public and private—why they should plan for climate change. At the same time, an attempt is made to moderate expectations about the level of precision with which the report can provide guidance on specific impacts of cli- mate change and their time frames. 15 Information on climate change effects and impacts, however, is not always available for smaller geographic areas. 16 Climate change refers to a statistically significant variation in either the mean state of the climate or its variability over an extended period, typically decades or longer, that can be attributed to either natural causes or human activity. Weather refers to the familiar hour-by-hour, day-by-day changes in temperature, cloudiness, precipitation, and other atmospheric phenomena.

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28 Potential Impacts of Climate Change on U.S. Transportation WHY CLIMATE CHANGE MATTERS When asked to consider climate change, transportation professionals fre- quently protest that dealing with a problem whose time horizon is decades and centuries and whose effects are uncertain is impractical. Moreover, they maintain, resources are insufficient to address day-to-day mainte- nance problems, much less to make investments on the basis of changes that may or may not occur years or even generations into the future. So why should transportation professionals take note of climate change? First, it is not just a problem for the future. Recent changes, such as global warming and resulting sea level rises, reflect the effects of GHG emissions that were released into the atmosphere over the past century. What appears to be new is the greater certainty of scientists that human activity is already warming the climate and that the rate of change is likely to be greater than at any time in modern history (IPCC 2007b). Second, climate change will not necessarily occur gradually. Climate scientists expect that higher temperatures will be amplified by normal vari- ability in climate, leading to new extremes far outside current experience [e.g., the heat wave in Europe in 2003 (Stott et al. 2004) and the near record heat of 2006 in the United States (Hoerling et al. 2007)]. Higher tempera- tures are also likely to trigger surprises, such as more rapid than expected melting of Arctic sea ice and rising sea levels. Third, although transportation professionals typically plan 20 to 30 years into the future, many decisions taken today, particularly about the location of infrastructure, help shape development patterns and mar- kets that endure far beyond these planning horizons. Similarly, decisions about land use, zoning, and development often create demand for long- lived transportation infrastructure investments. Thus, it is important for transportation decision makers to consider potential impacts of climate change now in making these investment choices because those impacts will affect how well the infrastructure adapts to climate change. Fourth, professionals in many fields—among them finance, building (where protecting against earthquakes, wildfires, or wind risk is a concern), nuclear power, and water resources (in the design of dams and canals)— are continually making decisions in the face of uncertain information about risks and outcomes. In fact, the highway and bridge engineering community, through the auspices of the American Association of State Highway and Transportation Officials, has developed design guidelines and

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Introduction 29 standards for earthquake resistance on the basis of probabilistic seismic haz- ard assessments that take many uncertainties into account. Similarly, addressing climate change requires more quantitative assessments, such as the development of probabilistic climate change scenarios at the level of geographic and modal specificity needed by transportation planners and engineers, which can be incorporated into planning forecasts and engi- neering design guidelines and standards. Finally, transportation professionals already consider weather- and climate-related factors in designing and operating the transportation infrastructure. For example, many transportation networks and facilities are designed with adequate drainage and pumping capacity to handle a 100-year storm.17 Materials and maintenance cycles are geared to assump- tions about temperature and precipitation levels. Evacuation plans and routes have been identified in hurricane- and other storm-prone locations on the basis of current elevations and assumptions about storm surges and wave action. But what if the 100-year storm were to become the 50- or 30-year storm, or design thresholds were frequently to be exceeded, or evacuation routes themselves were to become vulnerable (see Box 1-1)? Such changes could necessitate different design criteria, asset management policies, maintenance cycles, and operating strategies. Recent severe weather events—such as the Mississippi River floods of 1993, Category 3 or greater hurricanes (e.g., Ivan, Katrina, Rita), the California wildfires of 2003— provide ample opportunities for transportation professionals to observe the vulnerabilities of the infrastructure to shocks to the system that could become more commonplace in the future. They also illustrate the dilemma facing transportation decision makers of whether to rebuild, rebuild differently, or relocate critical transportation infrastructure. STUDY APPROACH AND KEY ISSUES A wide range of climate changes could affect transportation infrastruc- ture and result in changes in the way U.S. transportation professionals plan, design, operate, and maintain the infrastructure. The committee adapted a figure from a workshop conducted by the U.S. Department of 17 A 100-year storm is defined as the amount of rainfall during a specified length of time that has a 1 percent chance of being equaled or exceeded in any given year or, put another way, has a recurrence interval of 100 years.

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30 Potential Impacts of Climate Change on U.S. Transportation BOX 1-1 What If? • What if design lives for infrastructure and return periods were to be exceeded routinely? Many facilities are built to withstand a 100-year storm. The design of other facilities, such as bridges, assumes a 50-year storm and does not take into account the effect of wave action, vividly illustrated by Hurricane Katrina (Meyer 2006). What if the 50-year storm, or even the 100-year storm, were to be exceeded routinely, reducing pro- jected recurrence periods to much below one in 50 or one in 100 years? • What if multiple severe weather events were to occur? Each year, Florida and the Gulf Coast brace for hurricanes, and California prepares for wild- fires or heavy rains. Emergency personnel are generally able to handle these events, and transportation managers find alternative routes to keep freight moving, largely because the events occur sequentially and at rel- atively infrequent intervals. But consider the impact of a Category 4 or 5 hurricane directed at Houston and its critical petrochemical infrastruc- ture at the same time that torrential rains and mudslides prevent access to the Port of Los Angeles. How would emergency responders and the economy fare in the face of multiple and simultaneous intense storms that climate change could bring with greater frequency? • What if critical evacuation routes were themselves to become sub- merged by rising seas and storm surge? Population increases in coastal areas are projected to more than double in the next 20 years. Many sea- side communities count on coastal highways for evacuation in a major storm. Some of these highways also act as flood barriers. What if the current accelerating rate of sea level rise were to continue into the fore- seeable future? Highways in low-lying areas that provide a vital lifeline could themselves become compromised by encroaching seas and storm surge. Some communities could be cut off in a severe storm or would be forced to evacuate well in advance of the storm’s known trajectory to avoid that risk. In the longer term, it may be possible to relocate some coastal highways farther inland and still provide a means of egress for vulnerable communities.

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Introduction 31 Transportation (USDOT 2003) on the potential impacts of climate change on transportation (Potter and Savonis 2003) to provide a concep- tual framework for this study (Figure 1-2). The first task is to identify potential climate change effects, focusing on those of greatest relevance for transportation (see Column 1). This task also includes indicating what is known from climate scientists about the certainty of these effects, particularly at the regional and local levels, and the time frame over which they are likely to unfold. The second task (see Column 2) involves describing the impacts of the effects of climate change on transportation. These impacts can be consid- ered in several different ways—by type of climate change effect (e.g., sea level rise, temperature extremes), by transportation mode, by geographic area, and by type of impact. With regard to the latter, impacts on trans- portation can be direct (i.e., affecting the physical infrastructure as well as 1. Potential Climate 2. Impacts on U.S. 3. Possible Change Effects Transportation Adaptation Strategies • Effects of greatest • By climate change • Identification of relevance for effect critical infrastructure transportation potentially at risk • By transportation • Geographic scale at • Monitoring of mode which effect can be changing climate projected with conditions and • By geographic area confidence impacts on where the infrastructure infrastructure is • Degree of certainty located • Changes in with which effect is known operating and • By type of impact maintenance – Direct, indirect practices • Time frame over – Infrastructure, which effect is likely operations • Changes in to unfold infrastructure design and redesign • Relocation of vulnerable infrastructure FIGURE 1-2 Potential impacts of climate change on transportation infrastructure. [Note in Column 2 that the impacts of climate change on U.S. transportation infrastructure will be influenced by the environment in which the infrastructure is located (e.g., soil moisture, stream flow), which will vary from region to region.] (Source: Adapted from Potter and Savonis 2003, 29.)

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32 Potential Impacts of Climate Change on U.S. Transportation the operating performance of the system) or indirect (e.g., affecting the location of economic activities or levels of pollution). Finally, these impacts will be influenced by changes in the environment in which the infrastruc- ture is situated. For example, changes in temperature and precipitation will affect soil moisture and runoff, which in turn will affect peak stream flows, sediment delivery to coasts, and the sustainability of the landforms upon which the infrastructure is built, with considerable regional variability. The tasks listed in Columns 1 and 2 require good communication among cli- mate scientists, transportation professionals, and other relevant scientific disciplines. The final task (see Column 3) requires developing possible adaptation strategies. A range of approaches is suggested—from the identification of at-risk critical infrastructure, to the monitoring of conditions (both climate and infrastructure), to changes in operating and maintenance practices, to changes in infrastructure design and redesign, to relocation of vulnerable infrastructure. The strategies listed in this column require action primar- ily by transportation decision makers—planners, designers, engineers, and operating and maintenance personnel. Figure 1-2 links together potential climate change effects, impacts on U.S. transportation infrastructure, and possible adaptation strategies, but it does not fully address several key points. First, issues of scale affect the certainty with which the effects of climate change on transportation infra- structure can be examined at present. Climate change projections are most accurate at the global level, but transportation infrastructure is largely local and regional. Nevertheless, the ability to predict climate change at the local and regional levels is improving. Furthermore, the effects of climate change are not point specific; their impacts may differ even within a region, depending on location. For example, sea level rise will affect coastal regions, but the seriousness of the impact will depend on the elevation, the amount of land subsidence, and the extent of protection (e.g., levees) provided and the redundancy of vulnerable infrastructure in the affected areas. The network character of transportation infrastructure adds another layer of complexity. Adverse impacts of climate change on transportation facilities in one region, for example, may shift activity to another location or route, either temporarily, as was the case for freight movement in the wake of Hurricane Katrina, or in the longer term (e.g., shifts in port activ- ity resulting from new shipping routes opening as a result of warming and deepening seas), with net effects that may be positive or negative.

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Introduction 33 Differences in time frames are another complicating factor. Some cli- mate changes will unfold over decades and centuries, ostensibly allowing time for transportation decision makers to plan and respond. Others are likely to increase the sensitivity of the climate system and could bring surprises and abrupt changes that would make planning difficult.18 The lifetime of transportation infrastructure can be as little as 10 to 20 years (e.g., some pavement surfaces), allowing engineers to adapt to some cli- mate changes as they unfold. Many other transportation networks and facilities are longer-lived. Major bridges and pipelines, for example, have lifetimes of 50 to 100 years, while the right-of-way of major transportation networks (e.g., rail lines, roads) is easily that long-lived. Thus, many of the investment decisions made by transportation professionals today will have a significant effect on how well the infrastructure adapts to climate change. Finally, like so many other problems, climate change will not be experienced in isolation. It will manifest itself in the context of other demographic, social, and economic trends, often aggravating existing con- ditions. For example, many coastal areas are likely to experience increased development pressures as a result of population growth, greater affluence, and tourist demands. Many of these areas are already vulnerable to erosion and storm damage. As sea levels rise with global warming, coastal storms with higher tides and storm surges are likely to create the conditions for more severe coastal flooding and erosion, placing more people in harm’s way and increasing the difficulty of evacuating in an emergency. ORGANIZATION OF THE REPORT The remainder of this report addresses the committee’s charge. Chapter 2 reviews the current state of knowledge about climate change, including projected changes over the next century, and those factors of particular relevance to U.S. transportation. Chapter 3 is focused on the potential impacts of climate changes on transportation infrastructure. The chapter begins with an overview of the vulnerability of the infrastructure to these changes; it then examines the likely impacts of the most critical climate changes by transportation mode, reviews the handful of studies that have examined the impacts of climate change on transportation, and draws a 18 Evidence exists for abrupt climate changes that can occur within a decade. The Dust Bowl drought of the 1930s is a good example (NRC 2002).

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34 Potential Impacts of Climate Change on U.S. Transportation series of findings. Chapter 4 describes how the transportation sector is organized and explains why climate change poses a difficult challenge to decision makers. It concludes with some suggestions for a more strategic, risk-based approach to investment decisions. Chapter 5 considers adap- tation strategies—both engineering and operational measures, as well as changes in transportation planning and land use controls, development of new technologies, improved data and analysis tools, and organiza- tional changes. In the sixth and final chapter, the committee offers its recommendations for policies and actions to address the impacts of cli- mate change on transportation and for needed research. REFERENCES Abbreviations IPCC Intergovernmental Panel on Climate Change NRC National Research Council USDOT U.S. Department of Transportation USEPA U.S. Environmental Protection Agency Hoerling, M., J. Eischeid, X. Quan, and T. Xu. 2007. Explaining the Record U.S. Warmth of 2006. Geophysical Research Letters, Vol. 34, No. 17, L17704. IPCC. 2005. Guidance Notes for Lead Authors of the IPCC Fourth Assessment Report on Addressing Uncertainties, July. ipcc-wg1.ucar.edu/wg1/Report/AR4_Uncertainty GuidanceNote.pdf. Accessed Jan. 30, 2008. IPCC. 2007a. Summary for Policymakers. In Climate Change 2007: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (M. L. Parry, O. F. Canziani, J. P. Palutikof, P. J. van der Linden, and C. E. Hanson, eds.), Cambridge University Press, Cambridge, United Kingdom. IPCC. 2007b. Summary for Policymakers. In Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, eds.), Cambridge University Press, Cambridge, United Kingdom, and New York. Meyer, M. D. 2006. Design Standards for U.S. Transportation Infrastructure: The Implications of Climate Change. Georgia Institute of Technology, Dec. 18. NRC. 2002. Abrupt Climate Change: Inevitable Surprises. National Academies Press, Washington, D.C. NRC. 2007. Evaluating Progress of the U.S. Climate Change Science Program: Methods and Preliminary Results. National Academies Press, Washington, D.C. Potter, J. R., and M. J. Savonis. 2003. Transportation in an Age of Climate Change: What Are the Research Priorities? TR News, Vol. 227, July–Aug., pp. 26–31.

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Introduction 35 Staudt, A., N. Huddleston, and S. Rudenstein. 2005. Understanding and Responding to Climate Change: Highlights of National Academies Reports. National Academies Press, Washington, D.C., Oct. Stott, P. A., D. A. Stone, and M. R. Allen. 2004. Human Contribution to the European Heatwave of 2003. Nature, Vol. 432, pp. 610–614. doi: 10.1038/nature03089. Turner, B. L., P. A. Matson, J. J. McCarthy, R. W. Corell, L. Christensen, N. Eckley, G. K. Hovelsrud-Broda, J. X. Kasperson, R. E. Kasperson, A. Luers, M. L. Martello, S. Mathiesen, R. Naylor, C. Polsky, A. Pulsipher, A. Schiller, H. Selin, and N. Tyler. 2003. Illustrating the Coupled Human–Environment System for Vulnerability Analysis: Three Case Studies. Proceedings of the National Academy of Sciences, Vol. 100, No. 14, July 8, pp. 8080–8085. USDOT. 2003. The Potential Impacts of Climate Change on Transportation, Summary and Discussion Papers. Federal Research Partnership Workshop, Brookings Institution, Washington, D.C., Oct. 1–2, 2002. USEPA. 2007. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2005. EPA 430-R-07-002. Washington, D.C., Apr. 15. World Business Council for Sustainable Development. 2004. Mobility 2030: Meeting the Challenges to Sustainability. Sustainable Mobility Project. National Academies Press, Washington, D.C.