Compelling observations have led most scientists to agree that the global climate is changing due to human-induced warming (e.g., Intergovernmental Panel on Climate Change [IPCC] reports released in 2001 and 2007, IPCC, 2001 and IPCC, 2007). The predicted consequences are highly variable, but two that will greatly affect coastal regions are sea-level rise and the potential for more frequent and energetic storms. In the United States, the U.S. Climate Change Science Program (CCSP; http://www.climatescience.gov/) has undertaken a synthesis and assessment of the state-of-science regarding climate change and its impacts. As part of this effort, scientists from the USGS, EPA, and NOAA have been tasked with reviewing potential sea-level rise impacts to coastal regions (see http://www.climatescience.gov/Library/sap/sap4-1/SAP4-1prospectus-final.pdf.). The CCSP synthesis and assessment products (SAP) are typically framed to answer a set of key questions about specific topics relating to climate change and its impacts. For this SAP, the USGS was asked to address several "key questions." The subject of this report is key question 2:

How does sea-level rise change the coastline? Among those lands with sufficient elevation to avoid inundation, which land could potentially erode in the next century? Which lands could be transformed by related coastal processes? (key question 2, page 5 of SAP 4.1 Prospectus)

Sea-level changes over geological time scales have driven large changes in shoreline position, particularly on low-gradient margins lacking significant fluvial systems (e.g., Muhs and others, 2004). While it is widely believed that changes in sea-level over the last century have had some role in shoreline change and land-loss along the coast, it has been difficult to quantify this relationship. The difficulty is due to the range of processes that affect coastal areas, the frequency at which coastal changes occur, and the closely coupled links between sea-level rise and the other processes driving coastal change. For example, over time periods of a century or less, changes in shoreline position have been linked closely to the availability of sand to the coastal sediment transport system (Carter and Woodroffe, 1994; Wright, 1995). In addition, shoreline changes caused by large storms can cause changes in shoreline position that persist for weeks to a decade or more (Morton and others, 1994; Zhang and others, 2004; List and others, 2006; Riggs and Ames, 2007). Shoreline position and beach morphology can vary by tens of meters over periods of a few months to several decades in response to these factors (Morton and others, 1994; Honeycutt and others, 2001; Zhang and others, 2002). Complex interactions with nearshore sand bodies and/or underlying geology (the geologic framework), the mechanics of which are not yet clearly understood, also influence the behavior of beach morphology over a range of time scales (Riggs and others, 1995; Honeycutt and others, 2003; Schuup and others, 2006; Miselis and McNinch, 2006).

Existing shoreline-change prediction techniques such as the Bruun Rule (Bruun, 1962), extrapolation of historic shoreline change rates (NRC, 1987; Leatherman, 1990), and simple inundation of a static topography (Najjar and others, 2000; Titus and Richman, 2001) are based on assumptions that are either difficult to validate or too simplistic to account for the complex processes driving coastal change to be reliable for many real-world applications (Pilkey and Davis, 1987; Wells, 1995; Bird, 1995). As a result, the usefulness of these predictive approaches, and whether it is possible to quantify the link between sea-level rise and shoreline change, has been debated in the coastal science community (Pilkey and others, 1993; Thieler and others, 2000; Leatherman and others, 2000a; 2000b; Pilkey and others, 2000; Sallenger and others, 2000; Cooper and Pilkey, 2004). Recently, more complex coastal process-based models like the Advanced Circulation Model (ADCIRC) (Luettich and Westerink, 1995), Regional Ocean Modeling System (ROMS) (Shchepetkin and McWilliams, 2005), Delft3D (e.g., Vitousek and others, 2007), Shoreface Translation Model (Cowell and others, 1995) and the Geomorphic Model of Barrier, Estuarine, and Shoreface Translations (GEOMBEST) (Stolper and others, 2005) have sought to incorporate important factors such as the sediment budget and geologic framework into predictions of coastal evolution. Research with these models is underway to advance our understanding of past and present coastal behavior. However, much additional research and testing against both the geologic record and present-day processes are needed to advance scientific understanding and inform management.

A different technique for assessing the potential for future coastal changes, the Coastal Vulnerability Index, uses physical characteristics of the coastal system to classify the potential effects of sea-level rise on open coasts. This approach combines the coastal system's susceptibility to change with its natural ability to adapt to changing environmental conditions, yielding a quantitative, although relative, measure of the shoreline's natural vulnerability to the effects of sea-level rise. The method has been applied in the U.S. (Gornitz and White, 1992; Thieler and Hammar-Klose, 1999; 2000a; 2000b; Pendleton and others, 2004a; 2004b; 2005), Canada (Shaw and others, 1998), and elsewhere (Argentina -- Diez and others, 2007), and is presently used by the U.S. National Park Service as a planning tool for coastal park units (Thieler and others, 2002). While a rank-based vulnerability assessment allows scientists and decision makers to identify portions of the coast at higher risk, it is not a predictive tool.

Because of the difficulties involved in long-term coastal change projections and the general lack of consensus among coastal scientists regarding appropriate methodologies, the USGS authors of the CCSP SAP 4.1 (Anderson, Cahoon, Gutierrez, Thieler, Williams; see Appendix A) chose to convene a committee of coastal scientists to address key question 2. Given the limited time and resources available to conduct this assessment, more formal group consensus approaches such as expert panel methods (e.g., Fink and others, 1984; Cooke, 1991; Aspinall and Cooke, 1998) were not pursued. In this effort, USGS authors convened a committee of 13 coastal scientists (see Appendix A) to discuss the potential changes that might occur to the ocean shores of the U.S. mid-Atlantic coast in response to predicted accelerations in sea-level rise over the next century. The resulting assessment that is synthesized in this document is based upon the professional judgement of the committee members who participated in this process.

In this report, the results of the two-day meeting are summarized and reviewed. The details of the meeting process are presented in Section C. Section D reviews the geological characteristics of the mid-Atlantic coast. Section E reviews the current understanding of relative sea-level rise for the Atlantic Coast of the United States. Section F summarizes the important factors and processes of shoreline change discussed by the committee. Section G provides a brief summary of assessment and prediction techniques that could be used to assess shoreline changes in response to sea-level rise. Section H summarizes the coastal landforms of the mid-Atlantic coast. Section I describes the potential landform response to sea-level rise, and Section J presents the assessment of coastal changes that may occur due to the future sea-level rise scenarios that were considered in this effort.