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California’s coastal development: Sea-level rise and extreme events — where do we go from here?

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As sea level continues to rise at an accelerated rate, California’s intensive coastal development and infrastructure is coming under an increasing threat. Whether lowelevation shoreline areas that are subject to flooding at extreme tides and times of storm wave run-up, or construction on eroding bluffs or cliffs, the risks will continue to increase from extreme events but, over the longer term, from continuing sea-level rise. Future sea-level rise values under different greenhouse gas scenarios have recently been projected and adopted by the state to be used in coastal land use planning and decision making. While beach nourishment can provide very short-term protection, and seawalls and revetments can provide somewhat longer-term protection, they both come with significant costs and also environmental impacts. The era of routine armor emplacement is coming to an end in California, and whether designated as relocation or managed retreat, now is the time to make the difficult decisions on how this will be accomplished and what the trigger points will be to initiate the response.
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VOLUME 87 • NO. 2 • SPRING 2019
Journal of the American Shore & Beach Preservation Association
— IN THIS ISSUE —
California’s coastal development:
Sea-level rise and extreme events — where do we go from here?
The fate of beach nourishment sand placed on the Florida East Coast
Analysis and prediction of storm water levels in Delaware inland bays
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 1
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SECRETARY:
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Volume 87 • Number 2 n Spring 2019
A S  B
P A
On the cover:
Cliside development in Seascape Beach Park, Solana Beach, California, perches precariously
close to the cli edge in this 2002 photo. As sea levels continue to rise and cli retreat
proceeds, hard decisions will have to be made about the future of coastal development along
the state’s developed clis. Photo courtesy California Coastal Records Project (Copyright ©
2002 Kenneth & Gabrielle Adelman).
T  C
From the editor’s desk:
Sea level rise by the numbers
Lesley C. Ewing, editor-in-chief ..................................................................... 2
e fate of beach nourishment sand placed on the Florida East Coast
James R. Houston ........................................................................................... 3
California’s coastal development:
Sea-level rise and extreme events — where do we go from here?
Gary Griggs and Kiki Patsch ......................................................................... 15
Analysis and prediction of storm water levels in Delaware inland bays
Michele Strazzella, Nobuhisa Kobayashi, and Tingting Zhu ..................... 29
Technical note:
Simulating dune evolution on managed coastlines:
Exploring management options with the
Coastal Recovery from Storms Tool (CReST)
Peter Ruggiero, Nicholas Cohn, Bas Hoonhout, Evan Goldstein, Sierd
de Vries, Laura Moore, Sally Hacker, and Orencio Durán Vinent ............ 36
Coastal observations:
Beach and dune impacts due to Hurricane Florence
in Dare County, North Carolina
Elizabeth J. Sciaudone and Liliana Velasquez-Montoya ............................ 44
Coastal observations:
Coastal erosion eld trip at the Sea Grant’s Mid-Atlantic Regional
Meeting with North Carolina Sea Grant Specialist Spencer Rogers
Amy Williams, Kathleen Fallon, and Danielle Swallow ............................. 50
Coastal forum:
Where coasts and rivers meet:
Living on the edge requires us all to work together
Shannon E. Cunni ........................................................................................ 55
e ASBPAs 12th annual photography contest................... Inside back cover
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 15
The coast of California and, indeed,
the coastlines of nearly every state
and most nations around the
world, are facing a wicked challenge that
human civilization has never had to deal
with before. For the past approximately
7,000 years (virtually the entire period of
human civilization), sea level has been
nearly constant. In fact, the stabilization
of sea level and, therefore, the location
of the shoreline about 7,000 years ago,
may well have been one of the major
factors allowing for the evolution of
human civilization (Day et al. 2007).
ere are dierent ideas as to what initi-
ated or led to the transition from our
hunter-gatherer ancestors to farmers and
permanent settlements, among them the
climate changes that took place as the last
ice age came to a close and the modern
Holocene epoch began (usually dated
at about 11,700 years ago). Much of the
Earth became warmer and drier, which
favored annual plants that died back, but
produced seeds (grains) or tubers that
could be cultivated, harvested, and stored
for later consumption. is was a big step
forward for humans (Griggs 2017).
Another concept has been proposed
for a connection between the early devel-
opment of agriculture and the stabiliza-
tion of sea level. Sea level rose at an aver-
Californias coastal development: Sea-level rise
and extreme events — where do we go from here?
By
Gary Griggs1 and Kiki Patsch2
1) Department of Earth and Planetary Sciences,
University of California Santa Cruz 95064
2) Department of Environmental Science and Resource Management,
California State University, Channel Islands 93012
ABSTRACT
As sea level continues to rise at an accelerated rate, California’s intensive coastal
development and infrastructure is coming under an increasing threat. Whether low-
elevation shoreline areas that are subject to ooding at extreme tides and times of
storm wave run-up, or construction on eroding blus or clis, the risks will continue
to increase from extreme events but, over the longer term, from continuing sea-level
rise. Future sea-level rise values under dierent greenhouse gas scenarios have recently
been projected and adopted by the state to be used in coastal land use planning and
decision making. While beach nourishment can provide very short-term protection,
and seawalls and revetments can provide somewhat longer-term protection, they
both come with signicant costs and also environmental impacts. e era of routine
armor emplacement is coming to an end in California, and whether designated as
relocation or managed retreat, now is the time to make the dicult decisions on how
this will be accomplished and what the trigger points will be to initiate the response.
ADDITIONAL KEYWORDS: Coast-
al management, flooding, erosion,
coastal development, retreat, adapta-
tion.
Manuscript submitted 15 March 2019,
revised & accepted 7 May 2019.
age rate of about 12 mm per year or about
1 m per century between about 18,000
and 7,000 years ago. During this roughly
11,000-year period of warming, there
were also what are believed to have been
melt-water pulses when ice sheets and
glaciers retreated very rapidly, increas-
ing the rates of sea-level rise (Figure 1).
During these intervals, the oceans were
rising at nearly 25 mm a year or 2-3 m
per century. In low relief coastal plains or
river deltas, a meter of sea-level rise could
move the shoreline inland thousands of
meters or more. As a result, these areas
could not have supported permanent
agriculture or settlements.
Around 7,000 years ago, however,
climate change slowed and the rate of
sea-level rise declined dramatically. Un-
til about 150 years ago, global sea levels
were relatively stable, rising less than 1
mm (0.04 inches) per year, or less than
10 cm or 4 inches per century) (NRC
2012). This created shoreline stability
and the opportunity for early humans to
begin to occupy and settle these fertile
coastal environments (Day et al. 2007).
e deltas and alluvial plains adjacent
to coastlines provided at fertile land
and fresh water that made agricultural
production possible. e mild climate
made life easier and more comfortable,
and the coastal waters provided an ad-
ditional food supply as well as access to
the sea. Over time, trade and commerce
would develop. ere were some long
steps for early humans, however, from
the grasslands of Africa to the Nile Delta
or the Fertile Crescent of the Middle East
and beyond, but over thousands of years
these areas were gradually settled.
e benets of living in the coastal
zone became increasingly apparent as
settlements grew and civilizations ad-
vanced globally. Many of the large cities
of Europe and Asia, and later the Ameri-
cas, developed along or near coastlines
as trade and commerce expanded. is
trend continued; today, 12 of the world’s
15 megacities (over 10 million people) are
located on coastlines.
Regardless of how we define “the
coast” or “the coastal zone,” it has become
substantially more crowded globally than
inland regions over the last two hundred
years, and all indications are that this
trend will continue. e total population
inhabiting coastal regions is dicult to
quantify and the numbers vary depend-
ing upon dierent references or studies:
approximately three billion people living
within 125 miles of the shoreline”; “40
percent of world population living within
100 kilometers”; or “three billion living
within 100 miles” (McGranahan et al.
2006 and 2007). You can take your pick,
but whatever the actual number, it’s big
and it’s growing.
In the lower 48 states, less than 10% of
the nation’s land area is in coastal coun-
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 16
Figure 1. Coastal sea level rose about 125 m (~400 ft.) between ~20,000 years
ago when the last ice age ended and ~7,000 years ago.
Figure 2. The greater San Francisco Bay area at night with light patterns
delineating the bay shoreline. While this portion of the California coast is not
intensively developed, the lights paralleling the shoreline to the left outline
the main highway corridor.
ties (those with a shoreline), but 39%, or
124 million people, live in these counties
(NOAA, 2013). Although Californias 19
coastal counties (including those border-
ing San Francisco Bay) make up just 22%
of the state’s area, they are home to 68
percent of its people, 80% of its salaries
and wages, and 80% of its Gross Domestic
Product (Sievanen et al. 2018). e coast
is more than just the beach or shoreline,
however, and what happens in coastal re-
gions aects far more of the state’s popula-
tion than just those who live in shoreline
counties. Sacramento, for example, while
100 miles from the Golden Gate, is a port
for ocean-going ships.
THREATS TO COASTAL
DEVELOPMENT AND
INFRASTRUCTURE
It is evident from the numbers above
that coastal areas are desirable places to
live and work, and in fact, the land clos-
est to the shoreline is the most coveted,
usually the most expensive, and the
most intensively developed (Figure 2).
Whether homes, condominiums, apart-
ments, hotels, restaurants or other private
development, or the public infrastructure
needed to support that development (e.g.
streets and highways, railways, airports,
power plants, water and wastewater lines,
pump stations and sewage treatment
plants), the coast represents a massive
investment of public and private money,
but also a huge economic engine. Califor-
nia has the largest ocean economy of any
state at about $46 billion/year (Eastern
Research Group 2015), of which the two
biggest contributors are tourism and
recreation ($17.6 billion or 38%) and
marine transportation/ports/harbors
($14.1 billion or 31%).
Much of the states shoreline and
coastal development, whether along the
back beach or on dunes, blus, or clis,
took place during a relatively calm period
in California’s coastal climate history. is
period has now been recognized as a cool
or negative Pacic Decadal Oscillation
(PDO) cycle, which extended from about
the mid-1940s to about 1977 (Figure 3).
ese three decades were characterized
by relatively calm coastal conditions
with few large El Niño events and storms
and little shoreline damage (Griggs et al.
2005). is same roughly three-decade
long period was precisely the era when
California’s population grew rapidly and
many coastal areas were developed. e
state’s population grew from 9.3 million
in 1945 to 22.8 million in 1978, or a 240%
increase.
In 1978, however, the climate over the
North Pacic and along California’s coast
transitioned rather abruptly to a warm
or positive PDO period characterized by
larger and more frequent El Niño events
with elevated sea levels and more damag-
ing coastal storms, which took their toll
on coastal development and infrastruc-
ture (Griggs et al. 2005). In particular, the
El Niño winters of 1977-1978, 1982-1983,
1997-1998, and 2014-2016 (Figure 4)
inicted heavy damage and led to a sig-
nicant increase in the number of permit
applications for seawalls and revetments
from coastal homeowners, followed by
the construction of additional armor. In
1971, just 2.5% (43.4 km) of California’s
entire 1760 km shoreline was armored,
although 7.3% (27.2 km) of the coastline
of the four southernmost counties (Ven-
tura, Los Angeles, Orange and San Diego)
had already been protected (Runyan and
Griggs 2003; Griggs 2005).
By 1998, 27 years later, aer the dam-
aging El Niño events of the 1978-1998
period, 176.5 km or 10.3% of the coast of
California had been protected. Along the
four most developed southern California
counties, the total extent of armor had
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 17
Figure 3. Pacic Decadal Oscillation Index from 1900 to 2018. Red indicates
positive or warm periods, and blue represents negative or cool periods.
Figure 5. Total kilometers and percentage of each of California’s coastal
counties armored as of 2018.
grown to 124.2 km or 33.4% of the entire
shoreline. A decade later in 2018, seawall
and revetment totals had reached 239.3
km or 13.9% of the state’s coastline, and
141.8 km or 38% of southern California’s
entire 373 km shoreline (Figure 5). is
represents a 5.5-fold increase in shore
protection over 47 years for the entire
state of California (Griggs and Patsch
in press).
PAST, PRESENT, AND
FUTURE SEA-LEVEL RISE
AND CALIFORNIA’S COAST
In addition to damaging short-term
extreme events (El Niños with elevated
sea levels, large storm waves coincident
with very high tides), a rising sea has
become an additional concern along
California’s shoreline. Specically, coastal
land use managers are actively asking
what sea level is likely to be reached at
dierent points in the future and what
risks this poses for California’s coastal
development and infrastructure.
While sea-level rise has been docu-
mented at Californias 12 NOAA coastal
tide gauges for decades, these instru-
ments all record local sea level change,
or the combined effects of global sea
level and land motion at each site. Aver-
aging tide gauge records globally led to
values ranging from about 1.2-1.7 mm/
yr. (4.7-6.8 in./century) over much of the
20th century. Tide gauges are not evenly
distributed, however, with most of these
in northern hemisphere sites (USA and
Europe).
In 1993, two satellites were placed
in orbit (Topex and Poseidon) with the
objective of measuring global or absolute
sea level accurately and precisely from
space. The average sea-level rise rate
from these satellite measurements over
their 25 years of operation is 3.34 mm/yr.
(13.1 in./century), and it is now evident
that this rate is accelerating (Nerem et al.
2018; Figure 6).
e combination of: 1) the connection
between greenhouse gas concentrations
in the atmosphere and a warming planet;
2) the continuing global increase in car-
bon dioxide emissions; 3) the increasing
rate of sea-level rise reflecting global
warming; and 4) the increasing incidents
and areas aected by tidal ooding and
gradual sea-level rise, led to two recent
studies on the future of sea-level rise
along the California’s coastline.
Figure 4. El Niño Southern Oscillation (ENSO) index for the period 1950-2018.
Red indicates warmer El Niño condition while blue indicates cooler La Niña
conditions.
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 18
Figure 6. Global sea-level rise determined using satellite altimetry.
Figure 7. Future sea-level rise projections at San Francisco for dierent
future dates and emission scenarios based on probability of occurrence
(from Griggs et al. 2017).
While signicant state-level attention
is focused on the impacts of sea-level rise
on the state’s coast, there were two studies
by the California Coastal Commission as
early as 1989 and again in 1991 that dealt
with the implications of sea-level rise for
coastal development (summarized in
Lester and Matella 2016).
In 2010, the governors of California,
Oregon, and Washington requested an
assessment of probable future sea levels
by the National Research Council. A
committee was appointed and a report
released (NRC 2012), which projected
sea level for 2030, 2050, and 2100, as
well as the potential coastal impacts of a
continuing rise in sea level. e median
(and range) of future sea levels in the NRC
report for the coast of California, south of
Cape Mendocino (a plate tectonic bound-
ary), at three dierent future times were
projected as:
• 2030: ~14 cm. (5-30 cm.) or ~6 in.
(2-12 in.)
• 2050: ~29 cm. (14-60 cm.) or ~12 in.
(5-24 in.)
• 2100: ~94 cm. (20-170 cm.) or ~35 in.
(16-66 in.)
Following a benchmark study by De-
Conto and Pollard (2016) on the potential
for ice sheet collapse in Antarctica and a
rapid rise in sea level, California’s next
governor asked for an update on what
this new science meant for the state’s
shoreline. A committee was established
by the California Ocean Sciences Trust
(OST) and the Ocean Protection Coun-
cil Science Advisory Team (OPC-SAT),
which prepared a report that updated
future sea-level rise values for California
(Griggs et al. 2017). e key ndings of
the report include:
1. Scientic understanding of sea-level
rise is advancing at a rapid pace.
2. e direction of sea level change
is clear.
3. e rate of ice loss from the Green-
land and Antarctic ice sheets is increas-
ing.
4. New scientic evidence has high-
lighted the potential for extreme sea-level
rise.
5. Probabilities of specic sea level
increases can inform decisions.
6. Current policy decisions are shaping
our coastal future.
7. Waiting for scientic certainty is
neither a safe nor a prudent option.
is report also includes future sea-
level rise projections for three of Califor-
nia’s 12 NOAA tide gauges spanning the
state’s coast (Crescent City, San Francisco,
and La Jolla), including sea level values
for 2030, 2050, 2100, and 2150 at dif-
ferent greenhouse gas emission levels
(Representative Concentration Pathways:
RCP 2.6, 4.5, and 8.5). e projections
also broke the future sea levels down by
probabilities: median, likely range, 1-in-
20 chance, 1-in-200 chance, and then an
extreme value (H++) that is considered
to be theoretically possible, but with an
as yet uncertain probability of occurring
(Figure 7).
is report was followed a year later by
a sea-level rise guidance document (Cali-
fornia Ocean Protection Council 2018),
which employed the same methodology
used in Griggs, et al. (2017) and projected
future sea levels for all of Californias 12
coastal tide gauges. e report provides
a step-by-step approach for state agencies
and local governments to evaluate these
projections and related hazard informa-
tion in their decision-making (Figure
8). It also spelled out preferred coastal
adaptation approaches. Using the same
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 19
Figure 8. Steps for determining and responding to future sea-level rise
vulnerability (from California Ocean Protection Council 2018).
Figure 9. Future sea-level rise projections at San Francisco for dierent
future dates and emission scenarios designated by risk level based on
probability of occurrence (from California Ocean Protection Council 2018).
future sea-level rise projections included
in Griggs et al. (2017) the guidance
document took these one step further
and designated the dierent probabili-
ties as Low Risk Aversion, Medium-High
Risk Aversion, and Extreme Risk Aversion
(Figure 9) in order to provide a risk per-
spective or context for each sea-level rise
value included.
e California Coastal Commission,
the state’s primary and nal permitting
authority for all signicant coastal devel-
opment or land-use decisions, produced
comprehensive sea-level rise guidance for
coastal land use in 2015 using projections
of the 2012 NRC report, and updated this
guidance in 2018 with the new projec-
tions (CCC 2018). is document used
the values determined in the 2017 Rising
Seas Report but took a more conserva-
tive approach. For each of the state’s tide
gauge sites the report presented only the
high emission scenario sea level value for
each future year included, and if a range
of values was given, this document listed
only the higher value (Figure 10). e sea
level values included were listed under
Low Risk Aversion, Medium-High Risk
Aversion, and Extreme Risk Aversion, the
same as the Ocean Protection Council
Policy Guidance.
Because the California Coastal Com-
mission has the ultimate permit authority
along California’s 1,760 km coastline,
these values are likely the ones that any
requests for coastal development permits
will need to evaluate and consider. In ad-
dition, many of the state’s 61 coastal cities
and 15 coastal counties are now updating
their individual Local Coastal Programs
(LCPs), which provide guidance and set
standards for coastal land use and devel-
opment, using the Coastal Commission
Sea-level rise Policy Guidance Document.
is process is ongoing as of 2019.
e Coastal Commission’s Guidance
Document also recommends: “taking a
long-term view when analyzing sea-level
rise impact because land use decisions
made today will aect what happens over
the long-term. For example, development
constructed today is likely to remain in
place over the next 75-100 years, or longer.
In practice, many jurisdictions have com-
pleted assessments that look at sea-level
rise vulnerabilities through approximately
2100.” Additional guidance includes:
Determine the full range of sea-level rise
projections from the best available sci-
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 20
Figure 10. Future
sea-level rise
projections at
San Francisco
for dierent
future dates
based on level of
risk (California
Coastal
Commission
2018).
Figure 11. Beach Drive in Rio Del Mar, northern Monterey Bay, was ooded in
January 1983 by a combination of elevated ENSO sea level, very high tides
and large storm waves. This coincidence of events led to some water and
sand entering the homes on the inland side of the road.
Figure 12. The southern portion of the Great Highway along San Francisco’s
Ocean Beach has repeatedly been threatened by large waves, high tides, and
elevated sea levels, and will now be relocated further inland.
ence…currently the OPC SLR Guidance…
determine the range of sea-level rise for the
planning horizons of concern.
RISKS TO DIFFERENT
COASTAL ENVIRONMENTS
Different coastal environments in
California face distinct hazards, the sim-
plest breakdown being: 1) those low-lying
and low-relief shoreline areas subject
to flooding and wave damage during
El Niño conditions and/or large waves
arriving simultaneously with very high
tides, as well as higher sea levels of the
future (Figure 11); and 2) those developed
areas on dunes, blus, or clis, where
coastal erosion or retreat from wave at-
tack at times of high tides is the process
that will create the greatest impacts. e
risk will increase with higher sea levels
simply because large waves will reach
the base of the cli, blu, or dunes more
frequently, thereby increasing erosion
rates (Figure 12).
ese issues have come into clear fo-
cus along virtually the entire California
coast over the past 40 years. Public and
private losses during the 1978 El Niño,
the rst serious storm in several decades,
amounted to $194 million (in 2018 dol-
lars). Five years later in 1983, another
major El Niño hit the coast. e com-
bined impacts of elevated sea levels and
the concurrent arrival of large waves and
very high tides inicted $469 million (in
2018 dollars) in damages to oceanfront
properties. Damage was not restricted
to broken windows and ooding of low-
lying shoreline areas, however. irty-
three oceanfront homes were completely
destroyed and over 3,000 homes were
damaged. Dozens of businesses, state and
county park improvements, roads, and
other public infrastructure were heavily
damaged as well (Griggs et al. 2005; Fig-
ure 13). In mid-January 1988, very large
waves struck the southern California
coastline and le behind $58 million in
property damage.
For low-lying shoreline areas, there are
now two essentially identical tools that
can be used to determine which areas
would be inundated at dierent future sea
levels. ese are based on the most up-to-
date LiDAR elevations and both utilize a
simple bathtub model with no additional
storm surge or wave-runup. Climate
Central has developed the Surging Seas
website (http://sealevel.climatecentral.
org/maps) and NOAA has the Sea Level
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 21
Figure 13. Elevated sea levels and repeated storms arriving coincident with
high tides during the rst three months of 1983 led to failure of timber and
concrete bulkheads, followed by loss of ll and collapse of beach-level
homes along the northern Monterey Bay shoreline at Rio Del Mar.
Figure 14. San Francisco International Airport with 0.3
meters (1 ft.) of sea-level rise above high tide. Areas in
light gray are below 0.3 m but separated from the bay by
a feature of higher elevation; dark gray areas would be
inundated (NOAA Sea Level Rise Viewer).
Figure 15. San Francisco International Airport with 0.9 m
(3 ft.) of sea-level rise above high tide (NOAA Sea Level
Rise Viewer).
Figure 16. San Francisco International Airport with 1.5 m
(5 ft.) of sea-level rise above high tide (NOAA Sea Level
Rise Viewer).
Figure 17. San Francisco International Airport with 3
meters (10 ft.) of sea-level rise above high tide (NOAA Sea
Level Rise Viewer).
Rise Viewer (https://coast.noaa.gov/
digitalcoast/tools/slr). Both of these data
visualizations are accessible, easy to use,
and allow the user to select a location on
a map and input any sea level elevation
up to 3 m (10 .) above the present to see
what would be inundated. In addition to
these simple models, the United States
Geological Survey provides a dynamic
model called the Coastal Storm Model-
ing System (CoSMoS), (https://www.
usgs.gov/centers/pcmsc/science/coastal-
storm-modeling-system-cosmos) which
accounts for coastal ooding due to fu-
ture sea-level rise while integrating waves,
tides, storms and storm surge as well as
long-term coastal evolution including
beach change, and cli/blu retreat, and
in some regions, integrates management
strategies such as “Hold the Line” and
“Beach Nourishment.” CoSMos allows for
the prediction of ooding under multiple
storm scenarios and sea-level rise pre-
dictions (up to a 5 m scenario) to allow
users to view multiple future condition
variables. Currently, the CoSMos model
projections are available for the north-
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 22
Figure 18. High tide overtopping the low seawall on Balboa island (photo
courtesy City of Newport Beach).
Figure 19. Balboa Island and Peninsula with 0.3 m (1 ft.)
of sea-level rise (NOAA Sea Level Rise Viewer).
Figure 20. Balboa Island and Peninsula with 0.9 m (3 ft.) of
sea-level rise (NOAA Sea Level Rise Viewer).
Figure 21. Balboa Island and Peninsula with 1.5 m (5 ft.) of
sea-level rise (NOAA Sea Level Rise Viewer).
Figure 22. Balboa Island and Peninsula with 3 m (10 ft.) of
sea-level rise (NOAA Sea Level Rise Viewer).
central California Coast, San Francisco
Bay, and southern California.
While it is easy to talk about these
future sea level projections, it is quite
another to actually visualize these on a
map using one of the above data visualiza-
tion models and see what is highly likely
to be inundated in the not too distant
future. We selected two low-lying areas
with very dierent types of development
(and without any signicant wave runup
issues) as case studies to illustrate the
challenges we will face in the very near fu-
ture: San Francisco International Airport
in San Francisco Bay and Balboa Island
in Newport Bay in southern California.
San Francisco International Airport
generates nearly 43,000 jobs and $8.4 bil-
lion in business activity on site annually
(Economic Development Research Group
2017). Looking at the larger San Fran-
cisco Bay area, the airport is responsible
for a total of more than 300,000 jobs and
has an economic impact of $62.5 billion
annually. e original airport was built
in the early 1930s on a low-lying cow
pasture on the margin of San Francisco
Bay. Fill was added to raise the site to its
present elevation. It grew in subsequent
years, and by 2017 it served 51.4 million
total passengers. However, the runways
and most of the airport today are only a
little more than a foot above the highest
tides. Sea-level rise was not a concern or
a consideration 50 or 60 years ago. Using
Climate Central’s Surging Seas sea-level
rise visualizer, a simple bathtub model,
we selected sea levels of 0.3 m (1 .), 0.9
m (3 .), 1.5 m (5 .), and 3 m (10 .)
above high tide to document what would
be inundated in future years as these sea
levels are progressively reached.
Surprisingly, at just 0.3 m (1 .) above
the present highest tides a significant
portion of the airport runways would
be ooded (Figure 14). With 0.9 m (3
.) of sea-level rise, almost the entire
airport is inundated including adjacent
portions of State Highway 101 — the
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 23
Figure 23: The oceanfront city of Del Mar in northern San Diego County has made the decision that they are not
going to consider managed retreat (photo courtesy California Coastal Records Project).
major thoroughfare through the South
San Francisco Bay area — in the vicinity
of the airport (Figure 15). One meter
is the mean sea-level rise projection by
2100 determined in the most recent as-
sessments (Griggs et al. 2017; CA OPC
2018). At 1.5 m (5 .) of sea-level rise the
entire airport, more of State Highway 101,
and commercial and industrial facilities
on both sides of the highway would be
inundated (Figure 16), and at 3 m (10 .),
the situation gets signicantly worse; yet
3m of additional rise (Figure 17), while
having an uncertain probability, is poten-
tially possible by 2100 (CA OPC 2018).
e impacts and ramications of even
1 m of additional sea-level rise will be
very signicant and problematic for San
Francisco International Airport.
Balboa Island in Newport Bay in
Orange County was originally built on
sand and silt dredged from Newport Bay
and actually sits below the high tide line;
it is protected from the rising sea by a
low seawall. e island is home to about
2,800 people and 2,015 housing units
with a mean value of $2 million. High
tides along with a slowly rising sea are
now overtopping the island’s low seawall
under storm and extreme high tide con-
ditions (Figure 18). e Newport City
Council recently approved $2 million to
add a nine-inch cap to the top of the old
seawall to buy a little more time. Local
planners pushed for an 18-inch high
cap, but residents argued that this would
ruin their waterfront views. Raising the
entire island, including homes, streets,
and seawalls is also being discussed. An
additional 0.3 m (1 .) of sea level oods
portions of the western end and northern
side of Balboa Island (Figure 19); at 0.9 m
(3 .), the entire island is inundated, as is
much of the development on the Balboa
Peninsula (Figure 20). One and a half
meters (5 .) of sea-level rise makes the
situation dire (Figure 21), and the Coastal
Commission is asking coastal communi-
ties to plan for 3 m (10 .) of sea-level
rise (Figure 22). A simple calculation of
the total home value on Balboa Island
alone (2,015 housing units with a mean
value of $2 million) reaches just over $4
billion, without counting the homes on
the Balboa peninsula; both of these neigh-
borhoods go underwater at 0.9 meters (3
.) of additional sea level, which could be
reached within 50 years.
The San Francisco International
Airport and Balboa Island in Newport
Bay are just two examples of large and
valuable infrastructure and expensive
coastal homes that were originally built
less than a meter above high tide and are
now threatened. ere are many other ex-
amples of coastal development and infra-
structure, both private and public, which
are in similar settings along Californias
coastline and elsewhere. is situation
didn’t arise from negligence, but simply
because throughout virtually the entire
~7,000 years of human civilization sea
level has been essentially constant. is
is changing and the rate of change is in-
creasing, leaving California, and coastal
areas around the United States and the
planet, with the greatest challenge they
have ever faced: How to respond to a
rising sea that, regardless of all of the
mitigation eorts we might be able to
agree on to reduce greenhouse gas emis-
sions — and we aren’t even close — that
sea level is going to continue to rise for
a century or more because of all of the
heat already baked into the atmosphere
(Meehl et al. 2005). is is truly a very
challenging problem to resolve.
LOOKING TO THE FUTURE —
WHERE DOES CALIFORNIA
GO FROM HERE?
As each new coastal development,
redevelopment, or protection proposal
moves forward, there will be input, re-
quirements, conditions or questions put
forward by the California Coastal Com-
mission as well as local government plan-
ning departments, on how the proposed
project intends to respond to future sea
levels. Such an assessment will include:
1) e projected lifetime of the proposed
project and, therefore, how far into the
future sea-level rise must be considered;
and 2) What risk aversion or sea-level rise
value must be used or considered? For
example, is the proposal for a parking lot
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 24
Figure 24. Nearly all of this original group of 23 blutop homes along the seaward side of State Highway One in
Sonoma County have been destroyed by ongoing cli erosion.
or organic approaches that are capable
of signicantly reducing the impacts of
storm waves, high tides, and long-term
sea-level rise.
e phrase “building resilient coastal
communities” — or something similar
— appears oen and has been the subject
of many conferences, workshops, and
meetings. Yet, what does this mean for
the 1,760 km (1,100 mile) exposed coast
of California? Are there actual examples
of resilient coastal developments or com-
munities?
e combination of the El Niño storm
damage of the last four decades, the im-
ages of low-lying shoreline areas ooded
by extreme high tides each year, the dam-
ages to or destruction of blu top homes,
and the projections of future sea-level
rise discussed above, have given many
(including state and local agency sta
and elected ocials) the clear message
that we need to begin developing adapta-
tion plans and timelines for relocation or
managed retreat from the shoreline for
the most vulnerable structures and facili-
ties. Understandably, this is not a process
that coastal property owners want to
contemplate, and also not one that many
or any local government ocial is ready
to initiate, yet.
Nonetheless, relocation or managed
retreat will become more and more com-
mon as sea levels continue to rise and
or pedestrian path, a single family dwell-
ing, coastal armoring, or a large industrial
facility such as a power plant, wastewater
treatment facility or desalination plant?
While the Coastal Commission Policy
Guidance Document doesn’t specifi-
cally require that a proposal for a Coastal
Development Permit must evaluate and
plan for a sea-level rise of 3 m (10 .) by
2100, the language included suggests that
this what is still considered to be an
extreme value should be considered.
e original Coastal Act did include lan-
guage, however, that all new development
shall minimize risks to life and property
in areas of high geologic hazards.
California is taking future sea-level
rise very seriously (in contrast to some
states where climate and sea level science
has been undermined or disregarded),
although the issue of how state agencies
and local governments will respond to
the long-term risks posed by this chal-
lenge has only relatively recently been
put on the table for serious consider-
ation and planning. What is obvious is
that there are massive investments in
California’s coastal development and in
the supporting infrastructure, and that
the oceanfront or shoreline homes and
other structures provide very large annual
property tax revenues to local govern-
ments. It is also becoming clear that the
historic responses to coastal hazards and
shoreline retreat along the high energy
ocean coast (e.g. armor for the most part
in California, beach nourishment in a few
cases) will not provide long-term solu-
tions for the impacts of future sea-level
rise. e options implemented to date
for the outer coast of California are very
limited: denial, do nothing or sell, more
armor, or very short-term beach nourish-
ment (Griggs and Kinsman 2016).
In addition, there have been a number
of recent studies and reports proposing
or evaluating the use of living shorelines
as alternatives to hard protection struc-
tures (Judge et al. 2017). is living or
natural shoreline infrastructure includes
things like salt marsh or wetland build-
ing, mangroves, coral reefs or other
similar approaches that can provide some
protection from sea-level rise, extreme
tides, hurricanes, storm wave attack
and erosion. Some of these ecosystems
are restricted to particular latitudes and
energy conditions, however, and are
therefore limited in their distribution.
Mangroves and coral reefs, for example,
can only ourish in tropical latitudes.
Salt marshes and similar wetland ecosys-
tems require ne-grained sediment and
cannot tolerate or survive high wave en-
ergy environments like Californias ocean
coastline. While dunes can be restored,
and salt marshes and other wetlands can
be rebuilt and nourished, for the 1,760
km of exposed, high-energy outer coast
of California, there are no living, green,
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 25
Figure 25. Nearly $16 billion in coastal property value has been lost from
2005-2017 due to tidal ooding from Maine to Mississippi (courtesy First
Street Foundation).
risks and damages are amplied through
short-term events such as extreme tides
and large storm waves with their associ-
ated run-up. If we do not manage the
inevitable retreat, it will be become un-
managed retreat resulting in greater losses
and more devastation (Griggs 2015).
Although relocation, managed re-
treat, or moving back from high-risk
or already impacted coastal sites may
be viewed favorably by coastal planners
and policy and decision makers, as well
as some coastal geologists and engineers,
it is understandably far less palatable to
those who own homes or property along
the shoreline. Retreat is oen ruled out
before any serious discussion or cost-
benet analysis has taken place, for sev-
eral reasons (Young 2018). Landowners
are concerned that even the mention of
retreat can negatively aect property val-
ues. e city of Del Mar in northern San
Diego County is a good example, where
many very expensive homes are located
directly on the beach and where the city
has taken a formal position of no retreat
(Figure 23). Even when proposed by a
government entity, to date it has rarely
been implemented as too unpopular and
too costly, with no source of funds to buy
out property owners or cover the inevi-
table costs. ere are also two key aws
in arrangements whereby government
acquires threatened coastal properties at
pre-hazard prices: it acts as a distorting
eect on the market and it incentivizes
increased risk exposure as homeowners
know there is a guaranteed solution down
the road (Young 2018).
The title of a recent report by the
Union of Concerned Scientists (2018),
Underwater: Rising Seas, Chronic Floods,
and the Implications for U.S. Coastal
Real Estate, states it clearly. is com-
prehensive assessment explains that the
consequences of a rising sea level will
strain many coastal real estate markets —
abruptly or gradually, but some eventually
to the point of collapse — with potential
reverberations throughout the national
economy. As sea levels rise, continued
high tide ooding of homes, streets, and
business districts in low-lying shoreline
areas (see Figure 11) will begin to render
many properties unlivable and neighbor-
hoods — even entire communities —
nancially unattractive and potentially
unviable. Store owners in some low-lying
cities along the South Atlantic coast of the
U.S. are already seeing lost revenues as the
number of days each year of coastal ood-
ing are rendering these areas unreachable
due to high water. Yet property values in
most vulnerable coastal communities
do not currently reect this risk. Many
homeowners, communities, and investors
are either not fully aware or are disregard-
ing the nancial losses they may soon face
(UCS 2018).
While managed retreat from the
shoreline hasn’t yet been implemented
in California in any significant way,
there has been unmanaged retreat along
the state’s coast for decades (Griggs et
al. 2005). Coastal homes, apartments,
and entire neighborhoods have been de-
stroyed by coastal erosion or demolished
from Humboldt County in the north to
San Diego County in the south (Griggs
2015; Figure 24). As the risks of damage
from storm waves, high tides, and rising
waters have been more widely publicized,
coastal property prices are beginning to
be more frequently aected, particularly
along the Atlantic coast of the U.S. A
recent study reported that rising seas in
Massachusetts have already cost home-
owners more than a quarter of a billion
dollars in lost property value with more
severe losses on the horizon (Logan
2019). e same study determined that
tidal ooding caused by sea-level rise
has contributed to a loss of $70 million
in waterfront real estate values in Maine
over the past 12 years. A larger scale as-
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 26
sessment of 17 coastal states extending
from Maine to Mississippi indicates that
nearly $16 billion in relative property
value was lost between 2005 and 2017
because of tidal ooding, which is wors-
ened by sea-level rise (Figure 25; First
Street Foundation 2019).
Yet, in Miami, despite the predictions
of future sea-level rise and the reality that
the average elevation of the city is just 2 m
(6 .), developers continue to get permits
for, and then build and market, luxury de-
velopments along the water’s edge. Buyers
are still purchasing condominiums in
prime waterfront areas (with the most
expensive penthouse recently going on
the market for $68 million) that are not
immune from the projected two meters of
additional sea level by 2100. e general
perception from the real estate agents is
that this is too far out in the future to be
of concern to their buyers.
ere are many dierent stakeholders
in coastal real estate, including individual
home and business owners, realtors, de-
velopers, lenders, and insurers. Whether
a property market crashes, or property
values continue to decline in response to
more frequent ooding, all of these stake-
holders are going to sustain large collec-
tive losses (UCS 2018). e reduction or
complete loss of some of the most expen-
sive real estate in California will reduce
property tax income and therefore much
of the funding that local governments
depend on for their operations, whether
schools, re and police, public works, or
other local government services.
e risks will increase as sea levels
continue to rise along with the potential
economic costs and losses. If there were
simple or easy solutions, they would have
been adopted and implemented by now.
Inaction will only lead to increased costs
down the road. While probabilities for
dierent sea levels have been generated
for different future time periods (see
Figures 7 and 9), it is important to realize
that even if California’s shoreline doesn’t
experience 0.6 m (2 .) of sea-level rise by
2050, for example, it will eventually reach
that level because of the amount of green-
house gases already in the atmosphere
and those that we are continuing to add.
Unfortunately, sea-level rise cannot be
halted any time soon.
It is time to determine vulnerabilities
of individual coastal developments and
infrastructure based on either projected
sea-level rise values or historic blu/cli
retreat rates, and then develop response
or adaptation plans, along with trigger
points to implement those plans. e dif-
ferent physical or geomorphic settings as
well as the type and intensity of develop-
ment of individual coastal communities
or cities will require or lead to dierent
adaptation or relocation responses. ere
won’t be a “one size ts all” solution (Les-
ter and Matella 2016). Decisions will also
have to be made regarding what future
time frame to plan for. If a building,
structure, or facility was only planned or
engineered to function for 50 years, then
the solution may be to plan for the reloca-
tion or demolition of that structure at that
time, perhaps with the potential for short-
term protection to allow it to survive and
function for its designated useful lifetime.
If the facility is public infrastructure (e.g.
a highway, wastewater treatment plant, or
airport), this also provides for lead time
to develop plans and pursue replacement
funding options such as municipal or
state bonds. If it is a private home, busi-
ness, or larger structure, this could allow
for a signicant reduction of property
taxes and amortization of the losses that
will be incurred.
Gibbs (2016) concludes: “Despite the
burgeoning number of coastal adapta-
tion studies that have been performed,
it has been argued that there has been a
conspicuous lack of on-the-ground adap-
tation. ere is now a fairly widespread
acceptance of the main responses to
coastal climate adaptation in three broad
options: protect, manage/accommodation,
and retreat (Nicholls and Casenave 2010).
Retreat can be pre-emptive, just-in-time,
or reactionary (Gibbs 2016). Pre-emptive,
planned retreat or proactive abandonment
would involve the systematic relocation of
buildings or communities well before they
are impacted by major coastal ooding or
threatened by cli or blu erosion. Just-
in-time retreat involves delaying retreat as
long as possible but prior to major damage
or loss. is approach would take place
when many of the involved property own-
ers realize the risk is unacceptable or when
sea level reaches some threshold level that
has been established in advance. Reactive
retreat can be implemented following a
major ooding or disaster event, and could
be designated as unplanned retreat, where
this is the only option le. is would re-
quire local, state, or national government
legislation preventing reconstruction in
high-risk areas that have recently been
devastated and potentially implementing
some type of partial buyout program. e
tens of billions in losses following Super-
storm Sandy along the shorelines of New
York and New Jersey could have set the
stage for this approach.
While this article focuses primarily on
California, there are also some immediate
steps that the federal government can take
now with the lessons from Superstorm
Sandy and other extreme events in mind:
1. Terminate federal ood insurance
for coastal properties in hazardous loca-
tions with repeated insurance claims.
2. Raise federal ood insurance premi-
ums to reect the actual costs of coastal
ooding and other damage. e National
Flood Insurance Program continues to
borrow from the Department of the Trea-
sury to cover claims from the increasing
climate-related disasters. As of March
2017, FEMAs debt was $24.6 billion.
3. Assess risk to all government facili-
ties in coastal areas exposed to sea-level
rise and other coastal hazards and devel-
op response plans including adaptation
and relocation.
4. Require sea-level rise risk assess-
ment for any new government-funded or
subsidized construction or development
using the most up-to-date sea-level rise
values.
Any major policy initiative, change,
or legislation needs to be approved by
elected ocials at some level before being
implemented. Being subject to the next
election and voter approval, it is under-
standable that many elected ocials and
their supporting policy-makers until
now have given serious consideration to
the political impacts of major decisions
such as new policies on coastal reloca-
tion or managed retreat. To date, the
inability to nd eective ways to avoid
or mitigate this perceived or real political
risk appears to have been a major factor
hindering the implementation of timely
and eective on-the-ground adaptation
measures in California.
On the other hand, the California
Coastal Commission is in a very dierent
position and has statewide authority that
it is increasingly exercising as the threat
of future sea-level rise becomes more
apparent. e 12 voting commissioners
are appointed by several dierent state
Shore & Beach Vol. 87, No. 2 Spring 2019 Page 27
ocials and their decisions are therefore
not at the mercy of local voters. The
Coastal Commission is also backed by the
original legal document, the California
Coastal Act of 1976.
Whether low elevation shoreline areas
that are subject to temporary ooding at
extreme high tides and wave runup now,
or development on eroding bluffs or
clis, risks for both of these geomorphic
environments will continue to increase
from extreme short-term events, and
over time, from accelerating sea-level
rise. For the former, the Coastal Com-
mission could set an elevation for future
sea level (30 cm above present high tide,
for example) or designate a frequency
of ooding (perhaps twice a year), aer
which time local governments need to
have an approved retreat or relocation
plan to implement. At this point, ood
insurance would no longer cover these
properties or development.
For dune, blu, or cli development
where no new armoring is permitted,
the Commission could establish some
distance from the blu or cli edge to
the structure when the foundation will
be compromised and damage is inevitable
in the very near future under storm wave
and high tide conditions. is distance
will be specic to individual areas based
on cli or blu height, erosion rate, and
type of failure. Again, a relocation, retreat,
or removal plan must have been devel-
oped in advance and then initiated when
this distance is reached. While this may
seem today to homeowners to be an ex-
treme approach, the collapse and destruc-
tion of cli top homes and apartments
discussed earlier (Griggs 2015) indicates
that these losses have been occurring for
years already. e French government
took a very bold step in dealing with this
issue several years ago following the dam-
age and casualties from a massive storm
(Xynthia) that struck their Atlantic Coast
on 28 February 2010. is was the largest
storm in historic memory for most of the
local residents and led to the deaths of 53
people, some drowning while they slept,
with others trapped in their shoreline
homes (Chadenas et al. 2013). e vul-
nerability of this portion of the coastline
of France was well known. Several of the
towns had been built in an area that for-
merly had been a swamp and the towns
are 2-2.5 m below sea level. One seawall
was built in 1860, originally to protect
the land for agriculture, and a second was
Figure 26. The coastline of La Plage d’Aytre, France on 30 December 2006,
prior to the impact of Storm Xynthia in February 2010 (Image courtesy of
Google Earth).
Figure 27. The coastline of La Plage d’Aytre, France on 22 September 2017,
following the removal of a number of shoreline homes after Xynthia (Image
courtesy of Google Earth).
Shore & Beach Vol. 87, No. 2 Spring 2019
Page 28
built in 1929. e well-forecasted storm
swept across the coastline leaving a trail
of devastation. About half of the 53 deaths
were due to the breaching of the old and
substandard seawalls that allowed the sea
to ood the villages of La Faute-sur-Mer,
l’Aiquillon-sur-Mer and Plage d’Aytre.
e French government initiated a
program, which may have been the rst
in the world, directed at relocating build-
ings away from the shoreline (Figures
26 and 27). e French minister of the
environment set a precedent by stating:
We need to act now to save the coastline
of tomorrow.” rough close consultation
with coastal communities, the French
government identied communities at
high risk and then recommended actions
to be taken. ese included moving build-
ings back, demolition of buildings at risk,
prohibition of new building construction
in high risk areas, and in some areas, even
prohibiting modifications to existing
buildings. In addition, at least 30 beach-
front construction permits were revoked.
Four years aer the deadly storm, four
elected ocials and a real estate agent
went on trial for aggravated manslaughter
and the mayor of La Faute-sur-Mer was
sentenced to four years in jail for granting
construction permits in areas mapped
and identied as highly ood prone. e
sentence was subsequently overturned
in an appeals court, and the mayor only
received a two year suspended sentence,
but perhaps the message was heard.
The science is clear and the future
is, unfortunately, increasingly certain;
we need to act and we need to act now.
ere are no simple answers or solutions,
but there are some lessons and options
discussed above as well as some policy
proposals. It is time to implement change
and plan for the inevitable future. Local
and state government agencies need to
take the steps that will move California
forward in dealing with this inevitable
challenge. e longer we wait, the greater
the losses and the higher the costs will be.
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... This includes renewed focus on the original language in the Coastal Act of 1976, which sought to allow only shoreline protection for structures that were in existence at that time (California Coastal Commission 2018a;Lester 2005). Given this heightened regulatory concern, it may become increasingly difficult to get new armoring approved along the state's coastline (Griggs and Patsch 2019b). Additionally, with a continuing rise in sea level, the process of passive erosion will lead to progressive loss of sandy beaches in armored settings (Vitousek et al. 2017) with resultant reduction of beach visitation and the associated economic losses (Pendleton et al. 2012). ...
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Crowded into the beautiful, narrow strip at the edge of the ocean, the large number of people who live near California's dynamic coastline often have little awareness of the hazards-waves, tides, wind, storms, rain, and runoff-that erode and impact the coast and claim property on a regular basis. This up-to-date, authoritative, and easy-to-use book, a geological profile of the California coast from Mexico to the Oregon border, describes the landforms and processes that shape the coastline and beaches, documents how erosion has affected development, and discusses the options that are available for dealing with coastal hazards and geologic instability. A completely revised and updated edition of Living with the California Coast (1985), this book features hundreds of new photographs and the latest data on human activity on the coast, on climate change, on rising seas levels, and on coastal erosion and protection. With its dramatic photographs and mile-by-mile maps, Living with the Changing California Coast will be an essential resource for those intending to buy or build along the coast, those who need specific information about various coastal regions, and those who are seeking information about how this remarkable coastline has evolved.
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Coastal climate adaptation, as a response to managing the increasing risk of inundation of coastal settlements and infrastructure, is a global challenge. As a result, there is a burgeoning body of studies recommending adaptation options, pathways and strategies generated by the research and increasingly private consulting sector. However, recent reviews of global adaptation performance repeatedly highlight a lack of implementation of many adaptation studies and plans. It is suggested here that one of the reasons why many coastal adaptation plans have not been applied is due to inadequate consideration of the political risk, underpinned by lack of consideration of potential allocation and distributional impacts of adaptation strategies. The work presented here identifies the political risk of the most common coastal adaptation pathways and approaches (‘retreat’, ‘protect’ and ‘manage’). This work especially highlights the major political risk of pre-emptive planned retreat adaptation strategies, which may seem the most obvious adaptation approach from the perspective of minimising future risks to settlements and infrastructure. However, it carries the largest political risk and potential distributional impacts, which is likely to hinder the adoption of this adaptation strategy in the short term.
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Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics - including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs - that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.