Regional Impacts of Climate Change: Four Case Studies in the United States

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Regional Impacts of Climate Change: Four Case Studies in the United States

Prepared for the Pew Center on Global Climate Change
December 2007 

Kristie L. Ebi, ESS
Gerald A. Meehl, National Center for Atmospheric Research
Dominique Bachelet, et al., Oregon State University
Robert R. Twilley, Louisiana State University
Donald F. Boesch, et al., University of Maryland Center for Environmental Science

Press Release

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Foreword Eileen Claussen, President, Pew Center on Global Climate Change

In 2007, the science of climate change achieved an unfortunate milestone: the Intergovernmental Panel on Climate Change reached a consensus position that human-induced global warming is already causing physical and biological impacts worldwide. The most recent scientific work demonstrates that changes in the climate system are occurring in the patterns that scientists had predicted, but the observed changes are happening earlier and faster than expected—again, unfortunate. Although serious reductions in manmade greenhouse gas emissions must be undertaken to reduce the extent of future impacts, climate change is already here and some impacts are clearly unavoidable. It is imperative, therefore, that we take stock of current and projected impacts so that we may begin to prepare for a future unlike the past we have known. 

The Pew Center has published a dozen previous reports on the environmental effects of climate change in various sectors across the United States. However, because climate impacts occur locally and can take many different forms in different places, Regional Impacts of Climate Change:Four Case Studies in the United States examines impacts of particular interest to different regions of the country. Although sections of the report examine different aspects of current and projected impacts, a look across the sections reveals common issues that decision makers and planners are likely to face in learning to cope with climate change. 

Kristie Ebi and Gerald Meehl find that Midwestern cities are very likely to experience more frequent, longer, and hotter heatwaves. According to Dominique Bachelet and her coauthors, wildfires are likely to increase in the West, continuing a dramatic trend already in progress. Robert Twilley explains that Gulf Coast wetlands provide critical ecosystems services to humanity, but sustaining these already fragile ecosystems will be increasingly difficult in the face of climate change. Finally, Donald Boesch and his colleagues warn that the Chesapeake Bay may respond to climate change with more frequent and larger low-oxygen “dead zone” events that damage fisheries and diminish tourist appeal. These authors are leading thinkers and practitioners in their respective fields and provide authoritative views on what must be done to adapt to climate change and diminish the threats to our environmental support systems. 

A key theme emerges from these four case studies: pre-existing problems caused by human activities are exacerbated by climate change, itself mostly a human-induced phenomenon. Fortunately, manmade problems are amenable to manmade solutions. Climate change cannot be stopped entirely, but it can be limited significantly through national and international action to reduce the amount of greenhouse gases emitted to the atmosphere over the next several decades and thereafter, thus limiting climate change impacts. Managing those impacts requires that we adapt other human activities so that crucial resources, such as Gulf Coast wetlands or public emergency systems, continue to function effectively. The papers in this volume offer insights into how we can adapt to a variety of major impacts that we can expect to face now and in decades to come. 

This report benefited from technical assistance, editing, and peer review. The Pew Center and the authors thank Joel Smith for project coordination as well as Ray Drapek, Anthony Janetos, BonnieNevel, James Morris, Steven Running, Don Scavia, Scott Sheridan, Peter Stott, Elizabeth Strange,Margaret Torn, Eugene Turner, John Wells, and Gary Yohe. 



The Pew Center on Global Climate Change has published many reports that address the impacts of climate change in a number of sectors and ecosystems across the United States, including agriculture, forests, coastal resources, water resources, and others. Results of previous studies in this series are summarized in a synthesis report (Smith, 2004).  

But differences in climate, topography, land use, and infrastructure result in different climate change impacts at the regional and local scales. As a complement to earlier the Pew Center reports focusing on the United States in general, this report presents four case studies of specific climate change impacts in different regions of the country:

  • The Heat is On: Climate Change & Heatwaves in the Midwest by Kristie L. Ebi of ESS and Gerald A. Meehl of the National Center for Atmospheric Research;
  • The Importance of Climate Change for Future Wildfire Scenarios in the Western United States by Dominique Bachelet of Oregon State University, and James M. Lenihan and Ronald P. Neilson of the U.S. Forest Service;
  • Gulf Coast Wetland Sustainability in a Changing Climate by Robert R. Twilley of Louisiana State University; and
  • Ramifications of Climate Change for Chesapeake Bay Hypoxia by Donald F. Boesch, Victoria J. Coles, David G. Kimmel and W. David Miller of the University of Maryland Center for Environmental Science.

Each case study focuses on a specific type of impact that is of particular concern for a region, but is not unique to that region. Each study also considers non-climatic factors, such as development and management practices, that are likely to interact with climate change. Consequently, cross-cutting themes emerge that are relevant to a wide array of regional and local climate change impacts beyond those examined here.


A. Individual Case Studies

Midwestern heatwaves. In coming decades heatwaves in the Midwest are likely to become more frequent, longer, and hotter than cities in the region have experienced in the past. This trend will result from a combination of general warming, which will raise temperatures more frequently above thresholds to which people have adapted, and more frequent and intense weather patterns that produce heatwaves. Studies projecting future mortality from heat foresee a substantial increase in health risks from heatwaves. Several factors contribute to increasing risk in Midwestern cities, including demographic shifts to more vulnerable populations and an infrastructure originally designed to withstand the less severe heat extremes of the past. The elderly living in inner cities are particularly vulnerable to stronger heatwaves; other groups, including children and the infirmed, are vulnerable as well. Adaptations of infrastructure and public health systems will be required to cope with increased heat stress in a warmer climate.  

Fire in the West. Wildfire is a natural part of the western landscape and is very sensitive to climate variability. In recent decades, a trend toward earlier spring snowmelt and hotter, drier summers has already increased the number and duration of large wildfires in the West (Westerling et al., 2006). Although total annual precipitation may increase in the Northwest, climate projections generally foresee less precipitation throughout the West during the summer when risk of fire is greatest. In Alaska and Canada, warming has accelerated the reproduction and increased the winter survival and geographic range of insect pests that may make forests more vulnerable to fire by killing more trees (Berg et al., 2006; Volney and Fleming, 2000). Development in the West has placed more people and assets in fire-prone areas, increasing the need to suppress wildfires (McKinley and Johnson, 2007). Ironically, suppression increases the risk of catastrophic fire by allowing vegetation to build up, providing more fuel for fires when they ignite. Humans have also introduced invasive plant species that consume limited soil moisture and burn readily. Careful attention to development decisions and human-induced ecosystem stressors may help with adapting to increased risk from fire in the West resulting from climate change.  

Gulf Coast wetlands. The coastline of the Gulf of Mexico offers a prototypical example of how human development patterns and climate change can interact to create high risks to human and natural systems. The combination of intense development in low-lying coastal areas, building levees along major rivers such as the Mississippi, high pollution levels, and extreme weather events, have degraded economically and culturally valuable coastal wetlands and made many human settlements in the Gulf region more vulnerable to rising seas and coastal storms. Accelerated sea-level rise and more intense hurricanes resulting from climate change would increase these risks. Therefore, plans to restore Gulf Coast wetlands and make them resilient to human activities and climate variability require careful consideration of how future climate change and human activities will degrade or enhance the natural processes that build and maintain coastal wetlands.  

Chesapeake Bay hypoxia. Hypoxia (inadequate levels of oxygen that can lead to dead zones) in the Chesapeake Bay is another example of a natural phenomenon made substantially worse by human development and that could also be exacerbated by climate change. Hypoxia occurs when nutrient runoff from land stimulates biological oxygen demand, reducing oxygen levels in the Chesapeake Bay. This condition adversely affects the bay ecosystem, including its fisheries, and recreational opportunities in the bay. Development within the Chesapeake Bay watershed has resulted in runoff of nutrients from farms and settlements, increasing the incidence and intensity of hypoxia in the bay. Increased regional rainfall, which washes nutrients into the bay, and higher summer temperatures, which accelerate oxygen depletion, are likely to increase the incidence and intensity of hypoxia in the Chesapeake Bay. These changes could alter the current assessment of nutrient reductions needed to meet water quality objectives.


B. Cross-cutting Themes

The case studies provide but a few diverse examples of potential climate change impacts. Many other impacts will occur far and wide and will affect many sectors in all regions of the country and the world in different ways. However, several key themes emerge from these studies that are likely to cut across many distinct impacts in many different regions:  

Impacts from climate change are already apparent. In all four of the case studies, there is growing evidence that climate change may already be increasing risks. To be sure, attribution of particular events either wholly or partially to climate change is a difficult process that can be controversial. But the literature linking climate change with the events discussed in this report is growing. Westerling et al. (2006) found that climate change over the 20th century is a key factor explaining the increase in fires in the American West after accounting for human settlements and fire management. Extreme heat events in the United States are on the rise. DeGaetano and Allen (2002) found that minimum and maximum temperatures increased in the latter half of the 20th century, with particularly large increases in urban areas. Multi-day extreme heat events are also increasing. Global sea levels have been rising for centuries, but recently the rate of sea-level rise has accelerated (IPCC, 2007). This rise is likely contributing to some loss of wetlands in places such as the Gulf of Mexico and the Chesapeake Bay. Finally, there is growing evidence that the intensity and possibly the number of hurricanes in the Atlantic have increased in recent decades as a result of rising sea surface temperatures (Emanuel, 2005; Hoyos et al., 2006).  

Multiple stressors exacerbate climate change impacts on natural systems. Enlarged pest populations, invasive species, and fire suppression all increase the vulnerability of ecosystems to fire. Nutrient inputs from farms and settlements increase the potential for hypoxia in coastal estuaries. Canals, flood-control structures, and pollution decrease the resilience of wetlands to rising sea levels and powerful storms. In many cases stressors that limit the ability of natural systems to resist stress from climate change are under human control, either directly (e.g., development) or indirectly (e.g., invasive species). Successful adaptation to climate change will likely require close attention to the many ways that human activities can be altered to increase ecosystem resilience to climate change.

Development patterns affect vulnerability to climate change impacts. In the four studies presented here, development and associated planning decisions and management practices exacerbate the impacts of climate change. The concentration of infrastructure and housing along with dense populations of the poor and elderly make inner cities more vulnerable to heatwaves than less developed areas. Increased population, building of impervious surfaces, and agriculture in the Chesapeake Bay watershed increase runoff of nutrients and risk of hypoxia. Development in low-lying coastal areas of the Gulf and Atlantic coasts places more people and property along the coastline and degrades buffering wetlands, putting people at greater risk from faster sea-level rise and more intense coastal storms. More development in wilderness areas in the West also increases the number of people and amount of property facing wildfire risk, as climate change increases the frequency and intensity of large fires. Adaptation to climate change will require closer attention to the implications of development patterns and land use decisions for climate change impacts.  

There are likely to be increasing risks and costs from future climate change. The impacts of future climate change are likely to become greater as climate continues to change. There will likely be more loss of wetlands, higher risk to human life and property from stronger storms and hurricanes in the Gulf of Mexico and the Atlantic, more potential for hypoxia in the Chesapeake Bay and other coastal waters, more frequent and more intense heatwaves with greater risks to human health, and more frequent and intense wildfires. Many impacts not examined here would likely follow similar trends. Droughts and flash floods, for example, will likely increase in the future, presenting greater risks in areas that are already prone to such events (IPCC, 2007).  

Climate change could have important consequences for the private insurance industry and for public disaster management and response. Many of the impacts discussed in these studies could affect lives and property, and therefore, are likely to affect insurance claims as well as government response to (and perhaps preparation for) disasters. For example, greater loss of life from more intense heatwaves and property damage from hurricanes and fires could well result in higher insurance payouts and insurance companies refusing coverage to more individuals and businesses. This effect would likely have further consequences for insurance rates, deductibles, and profits, which could affect other parts of the economy. Public disaster management and response will require increased resources and more funding in a future with more frequent and bigger fires, floods, and heatwaves.  

Adaptation will be important in determining future vulnerability. The climate is already changing and affecting society and nature. Significant reductions in greenhouse gas emissions leading to lower atmospheric concentrations would reduce the magnitude of climate change and its impacts. Nonetheless, even with the most optimistic emissions reductions, there will still be substantial additional climate change. Thus, adaptation is an important component of a response to climate change. Reducing the level of pollution in the Chesapeake Bay will most likely reduce the risks of hypoxia. Adoption of heatwave early warning systems and other measures such as improving access to air conditioning have been shown to reduce risks from extreme heat events (Ebi et al., 2004). Wisely managing development patterns and vegetation can reduce the risks of fire (Platt et al., 2006). Evacuation planning, adoption of certain building designs, and limiting development in coastal areas can reduce risks from hurricanes. Furthermore, limits on certain types of development can also reduce destruction of wetlands, which are important for their ecosystem services. 

C. Final Thoughts

Although climate change is a global problem, its impacts vary widely and are felt locally. With this report, the Pew Center on Global Climate Change endeavors to provide not just useful information about particular impacts in particular regions, but also a more general perspective on the types of challenges decision-makers everywhere will face in developing sustainable responses to varied climate impacts. Historically, risk management strategies have relied on the past as a guide to the future. But with global climate change, the future will no longer resemble the past. As illustrated by the four regional studies that follow, new strategies for developing resilience to climate variability and extreme weather events will be needed. Well-considered assumptions about regional climate change should be incorporated into development and management plans. Studying regions with different vulnerabilities will provide insights and methods for conducting assessments in other regions and sectors.    

Joel B. Smith

Jay Gulledge


Berg, E.E., J.D. Henry, C.L. Fastie, A.D. De Volderd, and S.M. Matsuoka. 2006. Spruce beetle outbreaks on the Kenai Peninsula, Alaska, and Kluane National Park and Reserve, Yukon Territory: Relationship to summer temperatures and regional differences in disturbance regimes. Forest Ecology and Management 227:219-232.

DeGaetano, A.T. and R.J. Allen. 2002. Trends in twentieth-century temperature extremes across the United States. Journal of Climate 15:3188-3205.

Ebi, K.L., T.J. Teisberg, L.S. Kalkstein, L. Robinson, and R.F. Weiher. 2004. Heat watch/warning systems save lives: estimated costs and benefits for Philadelphis 1995-1998. Bulletin of the American Meteorological Society 85:1067-1073.

Emanuel, K. 2005. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436:686-688.

Hoyos, C.D., P.A. Aguidelo, P.J. Webster, and J.A. Curry. 2006. Deconvolution of the factors contributing to the increase in global hurricane intensity. Science 312:94-97.

IPCC (Intergovernmental Panel on Climate Change). 2007. 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, NY, USA.

McKinley, J. and K. Johnson. 2007. On fringe of forests, homes and wildfires meet. New York Times, June 26.

Platt, R.V., T.T. Veblen, and R.L. Sherriff. 2006. Are wildfire mitigation and restoration of historic forest structure compatible? A spatial modeling assessment. Annals of the Association of American Geographers 96:455-470.

Smith, J.B. 2004. A Synthesis of the Potential Impacts of Climate Change on the United States. Pew Center on Global Climate Change, Arlington, VA.

Volney, W.J.A. and R.A. Fleming. 2000. Climate change and impacts of boreal forest insects. Agriculture, Ecosystems & Environment 82:283-294.

Westerling, A.L., H.G. Hidalgo, D.R. Cayan, and T.W. Swetnam. 2006. Warming and earlier spring increases western U.S. forest wildfire activity. Science 313:940-943.

About the Authors


Heatwaves in the Midwest. Dr. Kristie L. Ebi is an independent consultant (ESS, LLC) and has studied connections between climate change and human health for more than ten years. She is working with the World Health Organization, UN Development Program, and USAID on adaptation measures for developing countries, and with the Center for Climate Strategies on adaptation options for U.S. states. She is a Lead Author for the Human Health chapter of the Fourth Assessment Report of the Nobel Peace Prize-winning IPCC, and Lead Author for Human Health for the U.S. Climate Change Science Program’s assessment of global change effects on human health and welfare.  She has edited three books on climate change and health, and has more than 75 publications.  Dr. Ebi earned the M.S. degree in toxicology from MIT, and the Ph.D. and MPH degrees in epidemiology from the University of Michigan.

Dr. Gerald A. Meehl is a Senior Scientist in the Climate and Global Dynamics Division at the National Center for Atmospheric Research, where he has worked in various capacities since 1973, including his involvement in several large international climate experiments. He specializes in modeling climate dynamics, including the possible effects of increased carbon dioxide, sulfate aerosols, and other natural and manmade drivers of global climate. He was a Coordinating Lead Author for the Global Climate Projections chapter in the Fourth Assessment Report of the Nobel Peace Prize-winning IPCC. He also contributed to all of the previous IPCC assessment reports. Among other committee appointments, he is a member of National Research Council’s Climate Research Committee. He has published more than 150 peer-reviewed articles and contributed to several textbooks. Dr. Meehl earned the Ph.D. in climate dynamics from the University of Colorado in Boulder.

Fire in the West. Dr. Dominique Bachelet is an associate professor in the Department of Biological and Ecological Engineering at Oregon State University and Director of Climate Change Science at The Nature Conservancy. She uses models to study complex ecological systems and how they respond to climate variability and change. Over the past decade, she has worked with colleagues at Oregon State University, Colorado State University, and the U.S. Forest Service to develop the MC1 dynamic vegetation model which uses global climate model scenarios to project, among other things, future wildfire characteristics resulting from climate change. She has published more than 20 peer-reviewed scientific articles. Dr. Bachelet earned the Ph.D. from Colorado State University in 1983 and subsequently worked at the University of California Riverside, New Mexico State University, and the US Environmental Protection Agency.

Gulf Coast wetland sustainability. Dr. Robert R. Twilley is Distinguished Professor in Louisiana Environmental Studies and Associate Vice Chancellor of Research and Economic Development at Louisiana State University. He directs the Shell Coastal Environmental Modeling Laboratory and heads the Coastal Louisiana Ecosystem Assessment and Restoration program, which develops ecosystem models coupled with engineering designs to forecast the rehabilitation of coastal and wetland ecosystems. He edited a 64-author, two-volume report that is Louisiana’s official coastal restoration plan. Before moving to LSU, Dr. Twilley founded the Center for Ecology and Environmental Technology at University of Louisiana at Lafayette. He has published more than 80 peer-reviewed articles and co-edited the 1999 book, The Biogeochemistry of Gulf of Mexico Estuaries. Dr. Twilley received his PhD in plant and systems ecology from the University of Florida in 1982 and conducted postdoctoral research at University of Maryland on the Chesapeake Bay.

Chesapeake Bay Hypoxia. Dr. Donald F. Boesch is professor of marine science and President of the University of Maryland Center for Environmental Science. He has studied marine ecosystems of the Atlantic and Gulf coasts of the U.S. and in Australia and the East China Sea. He serves on the National Research Council’s Ocean Studies Board and the Board of Trustees of the Consortium for Ocean Leadership. He was a lead author on the U.S. National Assessment of the Potential Consequences of Climate Variability and Change, and is leading an impacts assessment for the Maryland Commission on Climate Change. He recently testified in the Senate on the impacts of global warming on the Chesapeake Bay and improving the Federal climate change research and information program. He has published two books and more than 85 research articles. He received his Ph.D. in marine science from the College of William and Mary in 1971.