Sea Level
                                   SEA LEVEL RISE FACT SHEET
                                   MARYLAND’S SHORELINES

                                            Sea Level Rise - At a Glance
                                             Sea levels have lowered and raised with each passing ice age. This
                                          process influences and shapes shorelines. During an ice age, a great
                                          portion of the Earth’s oceans become frozen as ice masses and result in
                                          low sea levels. At the peak of the last great ice age, sea levels were
                                          estimated to be about 100-meters lower than current levels (see blue line
                                          in Figure 1). As those masses melt during periods of warming, the Earth’s
                                          oceans gain volume. Evidence suggest that sea levels have been much
                                          higher than current levels (see red line in Figure 1).
                                              About 15,000 years ago, the Earth began emerging from its last ice
                                          age. During this period, eustatic (global) sea level has been steadily on
                                          the rise. Eustatic sea level changes
                                          arise from the thermal expansion of
                                          water due to global warming, and the
                                          increase in total volume of ocean
                                          water from the melting of glaciers.
                                          Over the past century, global sea
                                          levels have risen an average of 10-
                                          15 centimeters (4-6 inches)
 Figure 1. Sea levels during different        Relative sea level rise is the
 glacial periods. Source: USGS, Coasts    measured change at a particular
 in Crisis.                               location. It reflects the sum of
                                          changes in global sea level and local
vertical land movements. Changes in relative sea level result from tectonic
processes (the movement of Earth plates and ocean basins), the extraction
of subsurface resources (groundwater, oil, etc.), and post-glacial rebound.
During an ice age, the weight of ice sheets push down on land masses (see Figure 2. Post-glacial rebound. Top:
top illustration of Figure 2). As these ice sheets melt, the land begins to        ice sheet pushes down on land mass.
spring back up (see bottom illustration of Figure 2). This is referred to as       Bottom: ice sheet melts and land
post-glacial rebound (sometimes called continental rebound, isostatic              rebounds. Source: Geological Survey
                                                                                   of Canada
rebound or isostatic adjustment).

                                              Maryland’s Changing Shorelines
                                                 Maryland’s shoreline characteristics have changed drastically
                                              throughout the years. During the last ice age, the coastline along the
                                              Atlantic Ocean extended about 200 miles further seaward (east) and the
                                              Chesapeake Bay did not exist (illustrated by yellow area in Figure 3).
                                              Under these conditions, the Susquehanna, Potomac and other rivers
                                              flowed directly to the Atlantic Ocean. As the ice sheets and glaciers
                                              melted, rising sea levels flooded the lower valley of the Susquehanna
                                              River and created North America’s largest estuary—the Chesapeake
                                              Bay. Sea level rise continues to alter Maryland’s shorelines today.

 Figure 3. The exposed continental shelf (in
 yellow) along the Atlantic Ocean during the last
 ice age. Source:

                                 MARY LAND
                            Chesapea ke & Coastal Program
                                                                                     Sea Level Rise Fact Sheet, Page 2

Anticipated Sea Level Rise in Maryland
    Sea level rise rates in Maryland are currently between 3-4 mm per year. That
translates into about 1 foot per century, nearly twice the global average.
According to geologists, Maryland’s coastal areas are experiencing land
subsidence (sinking). These areas are settling down after a period of postglacial
rebound. Also, increased development in coastal areas increases the demand on
groundwater resources.
    Global climate change coupled with continued glacier melting and land sinking
are causing sea level rise to accelerate. Sea levels along Maryland’s shores are
expected to rise another 2 - 3 feet by the year 2100. Each one-foot-vertical rise in
sea level is more significant than it sounds: along low-lying areas such as
Maryland’s Eastern Shore, some tributaries and the coastal barrier islands, this
scant 1 foot/century rise could swamp 1,000 feet horizontally (Figure 4). Figure 5
                                                                                     Figure 4. Illustration of sea level
shows the regions in Maryland, based on elevation, that are anticipated to be        rise inundation along low-lying
flooded by a 0-2 ft , 2-5 ft, and 5-10 ft rise in sea level.                         shores. Source: MD Coastal
                                               0-2 ft Inundation Area
                                                                          What are the regional impacts of
                                               2-5 ft Inundation Area     rising sea levels?
                                               5-10 ft Inundation Area       Sea level rise increases the inland reach
                                                                          of coastal flooding and shoreline erosion:
                                                                          daily high tides reach further inland; waves
                                                                          and storm surges from severe weather can
                                                                          flood and erode land further inland; salt
                                                                          water intrusion can change ground water
                                                                          salinity making it unfit to drink. Salt water
                                                                          intrusion can also effect the near shore
                                                                          ecosystem: some brackish tolerant wetland
                                                                          vegetation may not be able to live with
                                                                          higher levels of salinity; the landward retreat
                                                                          of wetland vegetation may not be able to
                                                                          keep pace with rapidly rising sea levels—this
Figure 5. Land in the Chesapeake Bay region considered to be
                                                                          may mean a loss of important wetland
vulnerable to sea level rise (shown in shades of blue). Source:
MD Shoreline Changes Online.                                              habitats.

Rising sea levels may ultimately begin to determine where and how
people live and continue to develop in Maryland. Why? Because
land that was previously safe will become exposed to greater
flooding and erosion risks. A 1991 report by the Federal
Emergency Management Agency (FEMA) estimated that a one foot
rise in sea level would increase the size of the 100-year floodplain
nearly 20% and increase flood damages (and hence flood
insurance rates) by 36-58%. This begs the question: should we
continue to build and live so close to low-lying shorelines knowing
that some of this land will not exist in the near future? For more on
information on the effects of rising sea levels, refer to the Coastal
Hazards Lessons, Sea Level Rise.
                                                                         Figure 6. Flooding in downtown Annapolis, MD
                                                                         from Tropical Storm Isabel. Photo credit: MD

                                 MARY LAND
                            Chesapea ke & Coastal Program

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