Robert R. Twilley

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

Prepared for the Pew Center on Global Climate Change
December 2007 

By:
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

Download full report (pdf) or individual case studies:

• The Heat is On: Climate Change & Heatwaves in the Midwest (pdf)
• The Importance of Climate Change for Future Wildfire Scenarios in the Western United States (pdf)
• Gulf Coast Wetland Sustainability in a Changing Climate (pdf)
• Ramifications of Climate Change for Chesapeake Bay Hypoxia (pdf)

Foreword

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. 

Introduction

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
STRATUS CONSULTING  

Jay Gulledge
PEW CENTER ON GLOBAL CLIMATE CHANGE 

References

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.

Coastal and Marine Ecosystems & Global Climate Change: Potential Effects on U.S. Resources

Prepared for the Pew Center on Global Climate Change
August 2002

By:
Victor S. Kennedy, University of Maryland
Robert R. Twilley, University of Louisiana at Lafayette
Joan A. Kleypas, National Center for Atmospheric Research
James H. Cowan, Jr., Louisiana State University
Steven R. Hare, International Pacific Halibut Commission

Press Release

Download Entire Report (pdf)

Foreword

Eileen Claussen, President, Pew Center on Global Climate Change

The world’s oceans cover approximately 70 percent of the Earth’s surface, indicating their importance to the global environment. In addition to having a large influence on global heat transport and precipitation, the oceans are comprised of diverse habitats that support a wealth of marine wildlife. They also provide humans with a wide variety of goods and services including foods, recreational opportunities, and transportation corridors. Based upon current scientific evidence, emissions of greenhouse gases from human activities are projected to cause significant global climate change during the 21st century. Such climate change will create novel challenges for coastal and marine ecosystems that are already stressed from human development, land-use change, environmental pollution, and over-fishing.

“Coastal and Marine Ecosystems & Global Climate Change” is the eighth in a series of Pew Center reports examining the potential impacts of climate change on the U.S. environment. It details the likely impacts of climate change over the next century on U.S. coastal and marine ecosystems, including estuaries, coral reefs, and the open ocean. Report authors, Drs. Victor Kennedy, Robert Twilley, Joan Klepas, James Cowan, Jr., and Steven Hare find:

Temperature changes in coastal and marine ecosystems will influence organism metabolism and alter ecological processes such as productivity and species interactions. Species are adapted to specific ranges of environmental temperature. As temperatures change, species’ geographic distributions will expand or contract, creating new combinations of species that will interact in unpredictable ways. Species that are unable to migrate or compete with other species for resources may face local or global extinction.

Changes in precipitation and sea-level rise will have important consequences for the water balance of coastal ecosystems. Increases or decreases in precipitation and runoff may respectively increase the risk of coastal flooding or drought. Meanwhile, sea-level rise will gradually inundate coastal lands. Coastal wetlands may migrate inland with rising sea levels, but only if they are not obstructed by human development.

Climate change is likely to alter patterns of wind and water circulation in the ocean environment. Such changes may influence the vertical movement of ocean waters (i.e., upwelling and downwelling), increasing or decreasing the availability of essential nutrients and oxygen to marine organisms. Changes in ocean circulation patterns can also cause substantial changes in regional ocean and land temperatures and the geographic distributions of marine species.

Critical coastal ecosystems such as wetlands, estuaries, and coral reefs are particularly vulnerable to climate change. Such ecosystems are among the most biologically productive environments in the world. Their existence at the interface between the terrestrial and marine environment exposes them to a wide variety of human and natural stressors. The added burden of climate change may further degrade these valuable ecosystems, threatening their ecological sustainability and the flow of goods and services they provide to human populations.

The authors and the Pew Center gratefully acknowledge the input of Drs. Richard Beamish, Michael Fogarty, and Nancy Rabalais on this report. The authors would also like to thank Andrea Belgrano, Jay Blundon, Lou Codispoti, Victoria Coles, Raleigh Hood, Richard Kraus, Thomas Malone, Ray Najjar, Roger Newell, Michael Pace, Frieda Taub, and Peter Vogt for comments on early drafts. The Pew Center would also like to thank Joel Smith of Stratus Consulting for his assistance in the management of this Environmental Impacts Series.

Executive Summary

The predicted changes may have a significant effect on coastal ecosystems, especially estuaries and coral reefs, which are relatively shallow and currently under stress because of human population growth and coastal developments. Significant environmental factors that affect the structure (e.g., plant and animal composition) and function (e.g., plant and animal production, nutrient cycling) of estuarine and marine systems and that are expected to be part of global climate change include temperature, sea-level rise, the availability of water and associated nutrients from precipitation and runoff from land, wind patterns, and storminess. Temperature, in particular, influences organism biology, affects dissolved oxygen concentrations in water, and plays a direct role in sea-level rise and in major patterns of coastal and oceanic circulation.

Predictions of the effects of climate change on coastal and marine ecosystems are associated with varying degrees of confidence. There is some confidence in predictions of how increases in temperature will affect plant and animal physiology, abundances, and distributions; aquatic oxygen concentrations; and sea level. There is also some confidence in predictions of the effects of sea-level rise on shallow continental margins, including flooding of wetlands, shoreline erosion, and enhanced storm surges. There is less confidence regarding temperature’s influence on interactions among organisms, and even less as to its effects on water circulation patterns. It is also difficult to predict the effects of climate change on precipitation, wind patterns, and the frequency and intensity of storms.

Many species are sensitive to temperatures just a few degrees higher than those they usually experience in nature. A rise in temperature as small as 1oC could have important and rapid effects on mortality of some organisms and on their geographic distributions. Given that temperature increases in the coming century are predicted to exceed 1oC, the major biological change resulting from higher temperatures in U.S. coastal waters may be altered distributions of coastal organisms along the east and west coasts. The geographic ranges of heat-tolerant species such as commercial shrimp on the East Coast may expand northward, while the southern range boundaries of heat-intolerant organisms such as soft clams and winter flounder may retreat northward. The more mobile species should be able to adjust their ranges over time, but less mobile species may not. Such distributional changes would result in varying and novel mixes of organisms in a region, leaving species to adjust to new predators, prey, parasites, diseases, and competitors. Some species would flourish and others would not, and we have no way of predicting at present which species would prevail. Fisheries would also be affected as some species are lost from a region or as others arrive. Warmer conditions would support faster growth or a longer growing season for aquacultured species, but might become too warm for some species in a particular region, requiring a change in the species being cultured.

Because water expands and glaciers melt as temperatures warm, higher temperatures would raise sea levels, inundating coastal lands and eroding susceptible shores. In salt marsh and mangrove habitats, rapid sea-level rise would submerge land, waterlog soils, and cause plant death from salt stress. If sediment inputs were limited or prevented by the presence of flood-control, navigational, or other anthropogenic structures, marshes and mangroves might be starved for sediment, submerged, and lost. These plant systems can move inland on undeveloped coasts as sea levels rise on sedimentary shores with relatively gentle slopes, but seaside development by humans would prevent inland migration. Marshes and mangroves are critical contributors to the biological productivity of coastal systems and function as nurseries and as refuges from predators for many species. Thus their depletion or loss would affect nutrient flux, energy flow, essential habitat for a multitude of species, and biodiversity. Some organisms might thrive (e.g., shrimp, menhaden, dabbling ducks, some shorebirds), at least over the short term as marshes break up and release nutrients or become soft-bottom habitat. Other organisms would be lost from affected areas if their feeding or nesting grounds disappeared and they could not use alternative habitats (e.g., Black and Clapper Rails, some terns and plovers).

Climate change may decrease or increase precipitation, thereby altering coastal and estuarine ecosystems. Decreased precipitation and delivery of fresh water alters food webs in estuaries and affects the amount of time required to flush nutrients and contaminants from the system. Although reduced river flow would decrease nutrient input in estuaries with relatively uncontaminated watersheds, there could be different effects in polluted watersheds that contain point sources of nutrients and contaminants that are not a function of river flow. The combined effects of human development and reduced river flow would degrade water quality conditions, negatively affecting fisheries and human health through such changes as increased presence of harmful algal blooms and accumulation of contaminants in animals and plants. Increased rainfall and resultant freshwater runoff into an estuary would increase stratification of the water column, leading to depleted oxygen concentrations in estuaries with excess nutrients. It would also change the pattern of freshwater runoff in coastal plain watersheds, such as along the southern Atlantic coast and in the Gulf of Mexico. In those regions where water resources are managed by humans, the effects of increased flooding would depend on how managers controlled regional hydrology.

Wind speed and direction influence production of fish and invertebrate species, such as in regions of upwelling along the U.S. West Coast. If upwelling is slowed by changes in wind and temperature, phytoplankton production could be lowered. Where upwelling increases as a result of climate change, productivity should also increase. In some coastal regions, alongshore wind stress and buoyancy-driven density differences help produce water movements that transport larval fish and invertebrates to nurseries, such as in estuaries. Climate-related changes in these circulation patterns that hinder such transport might alter the species composition of coastal ecosystems.

Increases in the severity of coastal storms and storm surges would have serious implications for the well-being of fishery and aquaculture industries, as has been demonstrated by the effects of recent intense hurricanes along the U.S. East Coast. Most ecosystems can recover rapidly from hurricanes, but the anthropogenic alteration of coastal habitats may increase the ecological damage associated with more severe storms.

The immense area and the modest extent of our knowledge of the open ocean hamper predictions of how ocean systems will respond to climate change. Nevertheless, it is clear that increased temperature or freshwater input to the upper layers of the ocean results in increased density stratification, which affects ocean productivity. Coupled physical/biogeochemical models predict a net decrease (~5 percent) in global productivity if atmospheric concentrations of carbon dioxide (CO2) reach a doubling of pre-industrial levels, increasing oceanic thermal stratification and reducing nutrient upwelling. Because productivity varies regionally, simple extrapolation to particular U.S. marine waters is difficult, although some high-latitude areas might benefit from warmer temperatures that lengthen the growing season. Open ocean productivity is also affected by natural interannual climate variability associated with large-scale climate phenomena such as the El Niño-Southern Oscillation. Climate-driven changes in the intensity or timing of any of these phenomena could lead to marked changes in water column mixing and stratification and, ultimately, a reorganization of the ecosystems involved, for better or worse.

Increased CO2 concentrations lower ocean pH, which in turn changes ocean carbonate chemistry. This may have negative effects on the myriad planktonic organisms that use calcium carbonate to build their skeletons. Some of these organisms appear to play important roles in ocean-atmosphere interactions, but we cannot yet predict any effects that might arise from their diminishment.

Finally, coral reefs, which are already threatened by multiple stressors such as abusive fishing practices, pollution, increased disease outbreaks, and invasive species, would also be at risk from changes in seawater chemistry, temperature increase, and sea-level rise. Lower ocean pH and changed carbonate chemistry would decrease the calcification necessary for building coral reef material. Increased warming would lead to coral bleaching, the breakdown in the symbiotic relationship between the coral animal and the unicellular algae (zooxanthellae) that live within coral tissues and allow corals to thrive in nutrient-poor waters and to secrete massive calcium carbonate accumulations. If sea levels were to rise at a pace faster than corals could build their reefs upward, eventually light conditions would be too low for the zooxanthellae to continue photosynthesis. On reefs near low-lying coastal areas, sea-level rise would likely increase coastal erosion rates, thus degrading water quality and reducing light penetration necessary for photosynthesis and increasing sedimentation that smothers and stresses coral animals. Losses of coral reefs would mean losses in the high biodiversity of these systems as well as the fisheries and recreational opportunities they provide.

About the Authors

Dr. Victor S. Kennedy
University of Maryland Center for Environmental Science

Dr. Kennedy is a marine ecologist who has spent over 30 years working as a research scientist on the ecology and physiology of aquatic animals. His early training included studying the effects of temperature on survival and physiology of estuarine species. His research in the 1960s helped convince the State of Maryland to revise its regulations governing discharge of heated water from power plants and other industrial facilities into Chesapeake Bay. Beginning in 1989, he used his experience with the effects of temperature on aquatic organisms to write papers and make presentations at scientific meetings on the possible effects of climate change. He is a co-author of the recent assessment for the mid-Atlantic coastal region that appeared in Climate Research and is the lead author of the Center's report, "Coastal and Marine Systems and Global Climate Change."

Dr. Kennedy is a Professor at the Horn Point Laboratory of the University of Maryland Center for Environmental Science, where he performs research, directs the Multiscale Experimental Ecosystem Research Center, and teaches graduate students. In addition to his research activities in Chesapeake Bay, he has worked as a marine ecologist in the coastal waters of New Zealand and in the coastal and offshore waters of Newfoundland, Canada. He has had extensive experience as a science editor, spending five years as the Editor of the Transactions of the American Fisheries Society, as well as editing or co-editing six technical books. He served as president of two scientific organizations.

Dr. Robert R. Twilley
University of Louisiana at Lafayette

Dr. Twilley is the Director for Ecology and Environmental Technology at the University of Louisiana at Lafayette. Dr. Twilley received his B.S. and M.S. (Biology) from East Carolina University, and his Ph.D. (Botany/Systems Ecology) from the University of Florida, after which he completed a postdoctoral fellowship in coastal oceanography at the University of Maryland. His research interests include ecosystem ecology, estuarine and coastal ecosystems; biogeochemistry of mangroves and tropical estuarine ecosystems; and ecosystem management and restoration of coastal regions. Among his various professional activities, Dr. Twilley currently serves on the editorial boards for Mangroves and Salt Marches and Environmental Science and Policy, and he previously served as a guest editor for Ecology and as an associate editor for Estuaries. Dr. Twilley is an active member in several professional societies including the Ecological Society of America, Estuarine Research Federation, Society of Wetland Science, and the American Association for the Advancement of Science. In addition to serving on the Board of Directors for the Society of Wetland Scientists (1993-97), Dr. Twilley has contributed to 71 publications and received a Distinguished Professor award for the 1999-00 academic year at the University of Louisiana at Lafayette.

Joan A. Kleypas
National Center for Atmospheric Research

Joan Kleypas specializes in examining how environmental factors control coral reef development at the global scale. She has a bachelor's degree in Marine Biology (Lamar Univ., Texas), and a master's in Marine Ecology (Univ. of South Carolina). She obtained a Ph.D. from James Cook University, as a Fulbright scholar to Australia, where she conducted a reef coring program to examine the causes for differences in coral reef development in the southern Great Barrier Reef. From there she moved to the National Center for Atmospheric Research (NCAR) Boulder, Colorado, to examine not only how climate affects coral reefs, but also how coral reefs affect climate. Much of this work entailed modeling reef response to sea level and temperature changes since the last ice age. She is currently involved with issues relating to the direct effects of increasing atmospheric CO2 on coral reefs; i.e., how CO2-induced changes in seawater chemistry affect the rates at which reef-building coral and algae secrete their calcium carbonate skeletons. She continues to work at NCAR as an Associate Scientist with Scott Doney, in the broad field of ocean biogeochemistry and its role in the global carbon cycle. Dr. Kleypas has also taught numerous courses in geology, oceanography, and global change as a visiting professor at Colorado College.

Dr. James H. Cowan, Jr.
Louisiana State University

James H. Cowan, Jr. is a Professor in the Department of Oceanography and Coastal Sciences and the Coastal Fisheries Institute at the Louisiana State University. He received B.Sc. (Biology) and M.Sc. (Biological Oceanography) degrees from Old Dominion University, and M.Sc. (Experimental Statistics) and Ph.D. (Marine Sciences) degrees from the Louisiana State University. Among many other professional activities, he has thrice served on National Research Council study committees and technical review panels concerning fisheries issues, has twice served on the Ocean Sciences Division, Biological Oceanography Review Panel for the National Science Foundation, and has served as a U.S. delegate both to the International Council for the Exploration of the Sea (ICES) and the Pacific Marine Sciences Organization (PICES). He currently is Chairman of the Reef Fish Stock Assessment Panel and a member of the Standing Scientific and Statistical Committee for the Gulf of Mexico Fishery Management Council. He has served as President of the Early Life History Section, and on the Outstanding Chapter Award and Distinguished Service Award committees for the American Fisheries Society. He has almost 20 years of experience conducting fisheries research in marine and estuarine ecosystems, has authored more than 75 refereed publications in the primary fisheries literature, served four years as an associate editor for Estuaries, the journal of the Estuarine Research Federation, for 6 years as an associate editor for Gulf of Mexico Science, and currently is an associate editor for Transactions of the American Fisheries Society.

Dr. Steven R. Hare
International Pacific Halibut Commission

Dr. Steven Hare is a quantitative biologist with the International Pacific Halibut Commission in Seattle, Washington. His principal duties are to assess the status of the Pacific halibut resource, determine a sustainable harvest level and conduct life history investigations. Dr. Hare obtained his B.S. in Engineering at the University of Michigan and both his M.S. and Ph.D. at the University of Washington in Fisheries Science. His main area of research is fisheries oceanography, in particular the organizing influence of climate on marine resources of the North Pacific. Dr. Hare is a co-discoverer, and was responsible for naming, the Pacific Decadal Oscillation, an important mode of Pacific climate variability. In his 20 years as a fisheries biologist, Dr. Hare has worked for the University of Washington and National Marine Fisheries Service. He has also spent considerable time working overseas with stints in Oman and Guinea-Bissau and a tour of duty in the Peace Corps in the Solomon Islands.