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Sea-Level Rise and Its Impact on Coastal Zones


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Global sea levels have risen through the 20th century. These rises will almost certainly accelerate through the 21st century and beyond because of global warming, but their magnitude remains uncertain. Key uncertainties include the possible role of the Greenland and West Antarctic ice sheets and the amplitude of regional changes in sea level. In many areas, nonclimatic components of relative sea-level change (mainly subsidence) can also be locally appreciable. Although the impacts of sea-level rise are potentially large, the application and success of adaptation are large uncertainties that require more assessment and consideration.
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Sea-Level Rise and Its Impact on
Coastal Zones
Robert J. Nicholls
*and Anny Cazenave
Global sea levels have risen through the 20th century. These rises will almost certainly accelerate
through the 21st century and beyond because of global warming, but their magnitude remains uncertain.
KeyuncertaintiesincludethepossibleroleoftheGreenland and West Antarctic ice sheets and the
amplitude of regional changes in sea level. In many areas, nonclimatic components of relative sea-
level change (mainly subsidence) can also be locally appreciable. Although the impacts of sea-level rise
are potentially large, the application and success of adaptation are large uncertainties that require
more assessment and consideration.
The Fourth Assessment Report (AR4) of
the Intergovernmental Panel on Climate
Change (IPCC) projected that global sea
level will rise by up to ~60 cm by 2100 in re-
sponse to ocean warming and glaciers melting
(1). However, the recently identified accelerated
decline of polar ice sheet mass (25)raisesthe
possibility of future sea-level rise (SLR) of 1 m
or more by 2100 (6,7). Today, low-elevation
coastal zones below 10-m elevation contain ~10%
of the world population (8). Here, nonclimate-
related anthropogenic processes (such as ground
subsidence due to oil and groundwater extrac-
tion, or reduced sediment supply to river deltas
caused by dam building) often amplify local
vulnerability associated with climate-related
SLR. The extent of future SLR, the resulting im-
pacts on low-elevation coastal zones, and the
ability of society to cope via adaptation remain
uncertain. Here, we review current knowledge on
the magnitude and causes of contemporary SLR,
examine future projections and their uncertain-
ties, and discuss SLR impacts. These impacts
are sensitive to how societies prepare for and
adapt to SLR.
What Are the Causes of Contemporary
Sea-Level Rise?
Although mean sea level remained nearly stable
since the end of the last deglaciation [~3000 years
ago; e.g., (9)], tide gauge measurements available
since the late 19th century indicate that sea level
has risen by an average of 1.7 ± 0.3 mm/year
since 1950 (10). Since the early 1990s, SLR has
been routinely measured by high-precision al-
timeter satellites. From 1993 to 2009, the mean
rate of SLR amounts to 3.3 ± 0.4 mm/year (Fig. 1)
(11), suggesting that SLR is accelerating.
Two main factors contribute to SLR: (i) ther-
mal expansion of sea water due to ocean warm-
ing and (ii) water mass input from land ice melt
and land water reservoirs (1). Ocean temperature
data collected during the past few decades in-
dicate that ocean thermal expansion has signifi-
cantly increased during the second half of the
20th century [e.g., (12)]. Thermal expansion ac-
counts for about 25% of the observed SLR since
1960 (13) and about 50% from 1993 to 2003 (1).
Since then, upper-ocean warming has been smaller
[e.g., (12,14)], and on average over the satellite
altimetry era (1993 to 2009), the contribution of
ocean temperature change to the global mean sea
level may be ~30% (15).
Numerous observations have reported world-
wide retreat of glaciers and small ice caps during
recent decades, with an appreciable acceleration
of this retreat during the 1990s (1,16). The gla-
cier contribution to SLR from 1993 to 2009 may
be ~30% (1,17). Change in land water storage,
due to natural climate variability and human ac-
tivities (e.g., underground water mining, irriga-
tion, urbanization, and deforestation), contributes
little (<10%) to current sea-level change (18).By
contrast, intensive dam building along rivers dur-
ing the second half of the 20th century lowered
sea level by ~ 0.5 mm/year (19).
Since the early 1990s, different remote-
sensing tools [airborne and satellite radar and
laser altimetry; synthetic aperture radar interfer-
ometry (InSAR); and, since 2002, space gravimetry
from the Gravity Recovery and Climate Exper-
iment (GRACE) mission] have provided good
data on the mass balance of the polar ice sheets.
These data indicate that Greenland and West
Antarctica mass loss is accelerating [e.g., (2)].
Between 1993 and 2003, <15% of the global SLR
was due to the ice sheets (1). However, since
about 2003, their contribution has nearly doubled
(35,20); increasing glacier and ice sheet mass
loss has compensated for reduced ocean thermal
School of Civil Engineering and the Environment and the
Tyndall Centre for Climate Change Research, University of South-
ampton, Southampton SO17 1BJ, UK.
Laboratoire dEtudes
en Géophysique et Océanographie Spatiales LEGOS-CNES,
Observatoire Midi-Pyrénées, 18 Av. E. Belin, 31401 Toulouse
cedex 9, France.
*To whom correspondence should be addressed. E-mail: (R.J.N.); anny.cazenave@legos.obs- (A.C.)
1900 1950 2000 2050 2100
Time (year)
Sea level (cm)
Date (years)
Trend = +3.26 mm/year
Mean sea level (mm)
Fig. 1. Global mean sea level evolution over the 20th and 21stcenturies.Theredcurveisbasedontide
gauge measurements (10). The black curve is the altimetry record (zoomed over the 19932009 time
span) (15). Projections for the the 21st century are also shown. The shaded light blue zone represents IPCC
AR4 projections for the A1FI greenhouse gas emission scenario. Bars are semi-empirical projections [red
bar: (32); dark blue bar: (33); green bar: (34)]. SCIENCE VOL 328 18 JUNE 2010 1517
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expansion, such that SLR continues at almost the
same rate (Fig. 1). Although not monotonic
through time, we estimate that on average over
the altimetry era (1993 to 2009), total land ice
mass loss explains ~60% of the rate of SLR (15).
Accelerated loss of ice sheet mass partly re-
sults from rapid outlet glacier flow along some
margins of Greenland and West Antarctica where
the grounding line is below sea level, and further
iceberg discharge into the surrounding ocean [e.g.,
(2123)]. Recent observations suggest that warm-
ing of subsurface ocean waters triggers coastal ice
discharge (22,24,25). Although
surface mass processes (snow ac-
cumulation versus surface melt-
ing) also contribute to Greenland
mass loss (26), in West Antarctica
mass loss essentially results from
ice dynamics [e.g., (2,3)].
Satellite altimetry shows that
sea level is not rising uniformly
(Fig. 2). In some regions (e.g.,
western Pacific), sea level has ris-
en up to three times faster than the
global mean since 1993. Spatial
patterns in sea-level trends mainly
result from nonuniform ocean
warming and salinity variations
(1,27), although other factors al-
so contribute, including the solid
Earth response to the last degla-
ciation and gravitational effects
and changes in ocean circulation
due to ongoing land ice melting
and freshwater input (28,29). Spa-
tial patterns in ocean thermal ex-
pansion are not permanent features:
They fluctuate in space and time
in response to natural perturbations
of the climate system (1); as a
result, we expect that the sea-
level change patterns will oscil-
late on multidecadal time scales. IPCC AR4
projections suggest appreciable regional variabil-
ity around the future global mean rise by 2100 in
response to nonuniform future ocean warming
(1), but agreement between the models is poor.
However, accurate estimates of future regional
sea-level changes are required for coastal impact
and adaptation assessment.
How Much Will Global Sea-Level Rise
in the 21st Century?
The rapid changes observed in polar regions sug-
gest that the ice sheets respond to current warm-
ing on much shorter time scales than previously
anticipated [e.g., (1)]. However, it is unknown
whether these processes will continue into the
future, resulting in a partial collapse of the ice sheets
after a few centuries, or whether a new equilib-
rium will be reached (30,31). For the near term
(next decades), the largest unknown in future SLR
is the behavior of the ice sheets. Although IPCC
AR4 projections did not account for dynamical
changes of large ice sheets, simple kinematics
and observations of current velocities of marine-
terminated glaciers in Greenland and West Ant-
arctica suggest that future ice-dynamics discharge
could lead to SLR of about 80 cm by 2100 (6).
Several groups have developed semi-empirical ap-
proaches in which a simple relation between past
sea-level rate and temperature or radiative forcing
is determined, and then extrapolated through the
21st century using IPCC temperature or forcing
projections [e.g., (3234)]. Depending on some
model variants, these studies yield SLR between
~30 and 180 cm by 2100 (Fig. 1). The upper limit
of these estimates is well above IPCC AR4 SLR
projections [of ~60 cm for the business-as-usual
A1FI greenhouse gas emissions scenario (1)].
What Are the Main Impacts of Sea-Level Rise?
The physical impacts of SLR are well known
(35). The immediate effect is submergence and
increased flooding of coastal land, as well as
saltwater intrusion of surface waters. Longer-term
effects also occur as the coast adjusts to the new
conditions, including increased erosion and salt-
water intrusion into groundwater. Coastal wet-
lands such as saltmarshes and mangroves will
also decline unless they have a sufficient sedi-
ment supply to keep pace with SLR. These phys-
ical impacts in turn have both direct and indirect
socioeconomic impacts, which appear to be
overwhelmingly negative (35). Although climate-
induced SLR is important, coastal impacts also
result from relative (or local) SLR (e.g., from geo-
logical processes such as subsidence). For exam-
ple, relative sea level is presently falling where
land is uplifting considerably, such as the north-
ern Baltic and Hudson Baythe sites of large
(kilometer-thick) glaciers during the last glacial
maximum. In contrast, relative sea level is rising
more rapidly than climate-induced trends on subsid-
ing coasts. In many regions, human activities are
exacerbating subsidence on susceptible coasts,
including most river deltas [e.g., the Ganges-
Brahmaputra, Mekong, and Changjiang deltas
(36,37)]. The most dramatic subsidence effects
have been caused by drainage and groundwater
fluid withdrawal; over the 20th century, coasts
have subsided by up to 5 m in Tokyo, 3 m in
Shanghai, and 2 m in Bangkok (38). To avoid
submergence and/or frequent flooding, these
cities now all depend on a substantial flood de-
fense and water management infrastructure. South
of Bangkok, subsidence has led to substantial
shoreline retreat of more than 1 km, leaving tele-
graph poles standing in the sea.
These and other human-induced changes in
coastal areas (such as coastal defenses, destruction
of wetlands, port and harbor works, and reduced
sediment supply due to dams) obscure the im-
pacts of climate-induced SLR during the 20th
century (39,40). The nonclimate components of
SLR receive much less attention than climate com-
ponents, because they are considered a local issue.
However, they are so widespread that they amount
to a global problem warranting more systematic
-20.0 -17.5 -15.0 -12.5 -10.0 -7.5 -5.0 -2.0 -1.0 0.0 1.0 2.0 5.0 7.5 10.0 12.5 15.0 17.5 20.0
80° 180° 270°
360° 90° 80°
Fig. 2. Regional sea-level trends from satellite altimetry (Topex/Poseidon, Jason-1&2, GFO, ERS-1&2, and Envisat
missions) for the period October 1992 to July 2009 (48).
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study, including appropriate
mitigation (of human influ-
ence) as well as adaptation
As the magnitude of climate-
induced SLR increases, the
impacts will become more ap-
parent (35), especially in certain
low-elevation coastal zones
(Fig. 3). Most countries in South,
Southeast, and East Asia ap-
pear to be highly threatened
because of the widespread oc-
currence of densely populated
deltas, often associated with large
growing cities (Fig. 3). Africa
also appears highly threatened
owing to the low levels of de-
velopment combined with ex-
pectations of rapid population
growth in coastal area: Egypt
and Mozambique are two hot-
spotsfor potential impacts.
However, the small island states
experience the largest relative
increase in impacts, including
regions of high islands like the Caribbean. Low
islands such as the Maldives or Tuvalu face the
real prospect of submergence and complete
abandonment during the 21st century (41).
Can Adaptation Help?
Many impact studies do not consider adaptation,
and hence determine worst-case impacts [e.g.,
(42)]. Yet, the history of the human relationship
with the coast is one of an increasing capacity to
adapt to adverse change [e.g., (43)]. In addition,
the worlds populated coasts became increasingly
managed and engineered over the 20th century
(35). The subsiding cities discussed above all
remain protected to date, despite large relative
SLR. Analysis based on benefit-cost methods
show that protection would be widespread as
well-populated coastal areas have a high value
and actual impacts would only be a small fraction
of the potential impacts [e.g., (44)], even assum-
ing high-SLR (>1 m/century) scenarios (45).
This suggests that the common assumption of a
widespread forced retreat from the shore in the
face of SLR is not inevitable. In many densely
populated coastal areas, communities advanced
the coast seaward via land claim owing to the
high value of land (e.g., Singapore). Yet, pro-
tection often attracts new development in low-
lying areas, which may not be desirable, and
coastal defense failures have occurred, such as New
Orleans in 2005. Hence, we must choose between
protection, accommodation, and planned retreat
adaptation options (35). This choice is both tech-
nical and sociopolitical, addressing which mea-
sures are desirable, affordable, and sustainable in
the long term. Adaptation remains a major un-
certainty concerning the actual impacts of SLR.
In one of the few strategic plans to respond to
SLR, the Netherlands is planning to upgrade
protection both for SLR and to provide higher
levels of safety (to a nominal chance of failure of
1 in 100,000) by building their North Sea coast
seaward using beach nourishment (46). The plan
stresses how adaptation to SLR must be integrated
into wider coastal management and development
plans. It also explicitly recognizes that adaptation
will continue beyond 2100 (35). In most develop-
ing countries, the issues are more challenging,
and the limits to adaptive capacity will be a key
constraint. National development plans will need
to address the growing risks of coastal occupancy
and identify the most appropriate approaches to
coastal management.
The extent of future SLR remains highly
uncertainmore so than in 2007, when the IPCC
AR4 was published. A two-track solution is
required to advance the scientific understanding
of observed and future climate-induced SLR and
develop pragmatic impact and adaptation scenar-
ios that capture the uncertainties of future SLR.
The former analysis should focus on understand-
ing the processes that control SLR (e.g., ice sheet
instabilities), whereas the latter analysis requires a
range of plausible scenarios, including the low
probabilityhigh consequence part of the possible
SLR range where our understanding is weaker
(7). More attention must also focus on the non-
climate components of SLR, especially for coasts
more susceptible to subsidence, such as deltas. Non-
climate processes tend to be larger where there
are high concentrations of people and economic
activity, and hence have a high impact potential.
The impacts of SLR can also be divided into
two distinct issues: impacts for climate policy, which
usually focus on the effects of climate-induced SLR
and the incremental benefits of different climate
mitigation policies, and impacts for coastal manage-
ment policy, which must consider all relevant cli-
mate and nonclimate coastal drivers. An improved
understanding of adaptation is fundamental,
because it is one of the biggest determinants of
actual rather than potential impacts. Studies such
as the World Bank assessment of adaptation costs
in developing countries (47) are useful starting
points to address these problems.
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highest risk are coastal zones with dense populations, low elevations, appreciable rates of subsidence, and/or inadequate
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How Do Polar Marine Ecosystems
Respond to Rapid Climate Change?
Oscar Schofield,
*Hugh W. Ducklow,
Douglas G. Martinson,
Michael P. Meredith,
Mark A. Moline,
William R. Fraser
Climate change will alter marine ecosystems; however, the complexity of the food webs,
combined with chronic undersampling, constrains efforts to predict their future and to optimally
manage and protect marine resources. Sustained observations at the West Antarctic Peninsula
show that in this region, rapid environmental change has coincided with shifts in the food web,
from its base up to apex predators. New strategies will be required to gain further insight into
how the marine climate system has influenced such changes and how it will do so in the future.
Robotic networks, satellites, ships, and instruments mounted on animals and ice will collect
data needed to improve numerical models that can then be used to study the future of polar
ecosystems as climate change progresses.
How does a changing physical ocean en-
vironment affect regional and local ma-
rine food webs? Many regions, especially
polar seas (1,2), are experiencing changes in
atmospheric/ocean circulation (3), ocean prop-
erties (4,5), sea ice cover (6,7), and ice sheets
(8,9). These rapid climatic changes are trigger-
ing pronounced shifts and reorganizations in
regional ecosystems and biogeochemical cycles
(10,11). However, it remains difficult to link
these ecosystem changes to shifts in the physical
system. Overcoming this gap is a critical step in
establishing any level of predictive skill.
The West Antarctic Peninsula (WAP), north-
western North America, and the Siberian Pla-
teau are exhibiting rapid regional warming (1),
but only the WAP has a maritime climate.
Thus, the WAP is an ideal location to monitor
and understand the impacts of rapid climate
change on marine ecosystems. Other regions
of Antarctica are exhibiting much smaller rates
of warmingand some, such as the Ross Sea
(12), are even experiencing trends in the oppo-
site directionbut climate models predict strong
warming and circumpolar sea ice retreat around
Antarctica over the next century (13). Under-
standing the response of the WAP ecosystems to
climate change will thus help to predict further
changes in the polar ecosystem as a whole and
will provide insight into the planetary-scale
changes that are likely as greenhouse gasdriven
warming continues.
Physical Changes in the WAP
Changes in the WAP are profound (Fig. 1). Mid-
winter surface atmospheric temperatures have
increased by 6°C (more than five times the global
average) in the past 50 years (14,15). Eighty-
seven percent of the WAP glaciers are in retreat
(16), the ice season has shortened by nearly 90
days, and perennial sea ice is no longer a feature
of this environment (17,18). These changes are
accelerating (19,20).
Ocean warming has been implicated as a
major driver for this deglaciation (21). The ocean
has become warmer in the WAP (17). Most of this
heat comes from the warm, saline Upper Circum-
polar Deep Water (UCDW) that penetrates onto
the WAP shelf from the Antarctic Circumpolar
Current (ACC) in the adjacent deep ocean. The
increased supply of heat from the UCDW is
believed to be associated with the strengthening
of winds over the Southern Ocean (22,23). En-
hanced upwelling of heat to the WAP is comple-
mented by rising summertime surface-ocean
heating (24), which is associated with the strong
retreats in the seasonal sea ice cover (7,18).
This atmosphereocean-ice interplay at the
WAP results in a positive feedback that amplifies
and sustains atmospheric warming. Understand-
ing these feedbacks will require better knowledge
of the processes at the shelf edge and in the adja-
cent deep ocean to determine where and when the
UCDW intrudes from the ACC onto the WAP
shelf. Although the ACC is a major current in the
Coastal Ocean Observation Laboratory, Institute of Marine
and Coastal Sciences, School of Environmental and Biolog-
ical Sciences, Rutgers University, New Brunswick, NJ 08901,
The Ecosystems Center, Marine Biological Laboratory,
Woods Hole, MA 02543, USA.
Department of Earth and
Environmental Sciences, Columbia University, NY 10964,
British Antarctic Survey, Madingley Road, Cambridge
CB3 0ET, UK.
Biological Sciences Department and Center
for Coastal Marine Sciences, California Polytechnic State
University, San Luis Obispo, CA 93407, USA.
Polar Oceans
Research Group, Post Office Box 368, Sheridan, MT 59749,
*To whom correspondence should be addressed. E-mail:
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... Coastal areas concentrate intensive physical and socialeconomic resources, which are threatened by global change, primarily due to forces including land use change and climate change, especially sea level rise (Gutiérrez et al., 2016;Nicholls and Cazenave, 2010). The global sea levels rose by 19 cm from 1901 to 2010 (IPCC, 2013), and the rise will almost certainly accelerate through the 21st century (Nicholls and Cazenave, 2010), which is drawing more focus on potential impacts and strategies research (Cozannet et al., 2014;Hallegatte, 2012;Hinkel et al., 2010Hinkel et al., , 2013Mimura, 2013;Nicholls and Cazenave, 2010). ...
... Coastal areas concentrate intensive physical and socialeconomic resources, which are threatened by global change, primarily due to forces including land use change and climate change, especially sea level rise (Gutiérrez et al., 2016;Nicholls and Cazenave, 2010). The global sea levels rose by 19 cm from 1901 to 2010 (IPCC, 2013), and the rise will almost certainly accelerate through the 21st century (Nicholls and Cazenave, 2010), which is drawing more focus on potential impacts and strategies research (Cozannet et al., 2014;Hallegatte, 2012;Hinkel et al., 2010Hinkel et al., , 2013Mimura, 2013;Nicholls and Cazenave, 2010). China is severely affected by sea level rise and related coastal hazards. ...
... Coastal areas concentrate intensive physical and socialeconomic resources, which are threatened by global change, primarily due to forces including land use change and climate change, especially sea level rise (Gutiérrez et al., 2016;Nicholls and Cazenave, 2010). The global sea levels rose by 19 cm from 1901 to 2010 (IPCC, 2013), and the rise will almost certainly accelerate through the 21st century (Nicholls and Cazenave, 2010), which is drawing more focus on potential impacts and strategies research (Cozannet et al., 2014;Hallegatte, 2012;Hinkel et al., 2010Hinkel et al., , 2013Mimura, 2013;Nicholls and Cazenave, 2010). China is severely affected by sea level rise and related coastal hazards. ...
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Li, W.; Xiang, W.; Wang, H.; Dong, J.; Xu, H.; Zhang, J.; Zuo, C.; Liu, Q.; Lv, J., and Xie, Q., 0000. Preliminary coastal vulnerability assessment for Guangdong province, Southeast China. Journal of Coastal Research, 00(0), 000-000. Charlotte (North Carolina), ISSN 0749-0208. Accelerating sea level rise and intensifying extreme marine and weather events pose unprecedented challenges to coastal areas in the context of climate change. As a hotspot of marine disasters, Guangdong has been suffering from severe marine disasters including storms, flooding, coastal erosion, and saltwater intrusion in the last decades. It is essential for coastal management authorities to distinguish vulnerable areas and optimize coastal planning. To help identify the coastal vulnerability patterns of the Guangdong coast, the coastal vulnerability index was used based on integrated physical and socioeconomic indicators including relative sea level rise, mean tide range, significant wave height, coastal slope, geomorphology, population, land use, and coastal gross domestic product. Each indicator was assigned five vulnerability classifications from very low to very high (1-5). Results show that about 36.7% of the coastline in Guangdong is highly vulnerable, of which 18.3% of the coastline is very highly vulnerable. About 63.3% of the coastline is in moderate to low vulnerability. In particular, the coastal areas in east of Zhanjiang, Maoming, Yangjiang, Zhuhai, Zhongshan, Guangzhou, west of Shenzhen, east Shanwei, and Chaozhou are more vulnerable to sea level rise, which calls for urgent planning and protective measures. ADDITIONAL INDEX WORDS: Sea level rise, coastal vulnerability index, physical indicators, socioeconomic indicators.
... Moreover, due to the distribution of the most vulnerable communities along the Ionian coastal sector, research development could be carried out by applying a multi-risk analysis procedure and taking into account also the hazard distribution of other marine-and climaterelated processes (i.e., coastal retreat, coastal flooding, and coastal inundation) and their combination [103][104][105][106][107][108]. In fact, interest in the multi-risk assessment increased in the last decades at the international level [109,110] especially for the analysis of coastal areas, which are potentially exposed to different processes, such as storms, coastal erosion, saltwater intrusion, and sea level rise [9,17,[111][112][113][114]. ...
... In order to mitigate the threat of storms and sea level rise caused by global climate change [43,44], humans have implemented synthetic engineering structures, such as sea dikes, breakwaters, and spur dams, leading to an increase in the proportion of the boundary length of the protective dams in the Bohai Sea of 7.8% from 2003 to 2018. However, in the process of constructing these marine constructions, the natural ecosystems, including grasses, trees and biological communities of the ocean and land, were destroyed, and the potential loss of ecological benefits was difficult to estimate. ...
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The coastal reclamation, as one of the most extreme transformations of the ocean space by humans, still lacks scientific quantitative evaluating methods to a large extent, compared with the evolution of land use patterns. A cumulative ecological impacts of reclamation (RCEI) was established in our study based on ecological influence characteristics of different reclamation types, and the attenuation effect of reclamation on adjacent areas. It was characterized by spatio-temporal features in decades. Here, we estimated that the cumulative reclamation area in the Bohai Sea from 1985 to 2018 was 5839.5 km2. Under the influence of human activity, proportions of the industrial and urban boundary, marine construction boundaries (e.g., ports, wharves, and bridges), and protective dams were increased significantly, which led to a sharp increase of the RCEI. In addition, spatio-temporal changes of reclamation were affected by the combination of population growth, economic development, urbanization, industrialization, and marine industry development in coastal cities. These results provided an important historical reference for tracking future development of the Bohai Sea by humans and provided basic data support for the development and protection of the ocean.
... Sea level rise is an important result of climate change as the global mean temperature increases. It has been driving and intensifying the coastal hazards that could bring damages and losses to the coastal zones (Kron 2013;Nicholls and Cazenave 2010;Sweet et al. 2014;Woodruff et al. 2013). Both frequency and magnitude of coastal flooding are expected to increase due to sea level rise (Vitousek et al. 2017) with some regions (e.g., the tropics) facing a doubling of frequency of extreme water-level events as early as 2030. ...
... Such temporal changes in water masses will not only modulate the transport of water properties such as heat or CO 2 , but can also produce a signature in steric sea level, which in the long-term will be associated to climate warming trends (Silvy et al. 2020). Understanding future mean sea level rise in the Caribbean Sea is of main importance, due to the large expected impacts in the low-lying coastal areas (Nicholls and Cazenave 2010). ...
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The study of water masses is important as they transport water properties affecting the biosphere and ocean dynamics. In this study, we revisit water masses in the Caribbean Sea using climatology and 11 months of observations at different depths from 3 moorings placed in the Guajira upwelling region, providing some new findings. The Caribbean Surface Water (CSW) seasonal variability is studied at the mixed layer depth. Salinity differences between CSW and the saltier North Atlantic Subtropical Underwater (SUW) determine static stability spatial and temporal variations, with implications for regional ocean dynamics. Besides, we assess the climatologic distribution of water masses below the salinity maximum using the optimum multiparameter analysis and the Thermodynamic Equation of Seawater 2010, defining their source water indices when entering the Caribbean Sea. The SUW, with its core at ~ 150 m depth, occupies 16% of the Caribbean Sea volume, complemented by 38% of Antarctic Intermediate Water, with its core at ~ 700 m depth and North Atlantic Deep Water, which as bottom water occupies 46% of the volume. Hydrographic observations do not differ from climatology, regardless of their large sub-annual variations decreasing with depth. Daily time series of dominant water fractions at different depths correlate at each mooring, indicating a common forcing. Besides, rotated wind stress, which is an indicator of the Guajira upwelling, correlates regularly with water mass fractions down to 700 m depth. However, during strong wind shifts, upwelling seems to affect them down to 1450 m depth.
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Coastal environments are highly recognized for their spectacular morphological features and economic activities, such as agriculture, maritime traffic, fishing, and tourism. In the context of climate change and the evolution of physical processes, the occurrence of intense natural phenomena adjacent to populated coastal areas may result in natural hazards, causing human and/or structural losses. As an outcome, scientific interest in researching and assessing multi-hazard susceptibility techniques has increased rapidly in an effort to better understand spatial patterns that are threatening coastal exposed elements, with or without temporal coincidence. The islands of Milos and Thira (Santorini Island) in Greece are prone to natural hazards due to their unique volcano-tectonic setting, the high number of tourist visits annually, and the unplanned expansion of urban fabric within the boundaries of the low-lying coastal zone. The main goal of this research is to analyze the onshore coastal terrain’s susceptibility to natural hazards, identifying regions that are vulnerable to soil erosion, torrential flooding, landslides and tsunamis. Therefore, the objective of this work is the development of a multi-hazard approach to the South Aegean Volcanic Arc (SAVA) islands, integrating them into a superimposed susceptibility map utilizing Multi-Criteria Decision-Making (MCDM) analysis. The illustrated geospatial workflow introduces a promising multi-hazard tool that can be implemented in low-lying coastal regions globally, regardless of their morphometric and manmade characteristics. Consequently, findings indicated that more than 30% of built-up areas, 20% of the transportation network, and 50% of seaports are within the high and very high susceptible zones, in terms of the Extended Low Elevation Coastal Zone (ELECZ). Coastal managers and decision-makers must develop a strategic plan in order to minimize potential economic and natural losses, private property damage, and tourism infrastructure degradation from potential inundation and erosion occurrences, which are likely to increase in the foreseeable future
South Korea's east coast is facing several issues related to coastal erosion because of sea-level rise, typhoon-induced storm surges, and various coastal development projects. In recent decades, high storm waves have frequently appeared on the east coast, causing casualty, beach erosion, and coastal infrastructure damage, drawing significant public attention. Thus, we analyzed the multi-decadal shoreline changes to understand the coastal dynamics and the forces responsible for the spatio-temporal changes along the 173 km coastline. The shorelines covering 38 years between 1984 and 2022 were derived from Landsat images and the change statistics, i.e., linear regression rate (LRR), endpoint rate (EPR), weighted linear regression (WLR), and net shoreline movement (NSM), were calculated at a 100 m alongshore intervals using Digital Shoreline Analysis System (DSAS), revealed several distinct behaviors of shoreline position. The long-period (1984-2022) assessment showed an average shoreline change rate (LRR) of 0.17 m/year with an estimated mean erosion and deposition rate of -0.57 and 2.07 m/year, respectively. The long-term surface gain and loss of the backshore region exhibited that the net surface gain of the east coast is 421.13 ha, and the net loss is 181.82 ha. The assessment of decadal shoreline changes showed a cyclic pattern of erosion (from 1984-1990 and 1999-2010) and accretion (from 1990-1999 and 2010-2022). Furthermore, a secondary level of investigation was conducted to address a wider variety of coastal behaviors by segmenting shoreline change rates based on coast types and average slopes along coastlines. It was observed that the frequent coastal deformation is associated with a flatter beach compared to a steep one. This study found that the artificial structures constructed along the east coast have not completely solved or stopped the erosion issues but shifted it from one location to another. The analysis of local and regional shoreline changes had shown that typhoon-induced storm surges, high storm waves, and anthropogenic activities like encroachment and the development of artificial coastal structures were the primary drivers of coastline changes along the east coast. Finally, we proposed a decision-making classification scheme that can be used to determine the mechanism of decision for protective and preventive measures against further coastal deterioration.
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In this study, we couple an integrated flood damage and agent-based model (ABM) with a gravity model of internal migration and a flood risk module (DYNAMO-M) to project household adaptation and migration decisions under increasing coastal flood risk in France. We ground the agent decision rules in a framework of subjective expected utility theory. This method addresses agent’s bounded rationality related to risk perception and risk aversion and simulates the impact of push, pull, and mooring factors on migration and adaptation decisions. The agents are parameterized using subnational statistics, and the model is calibrated using a household survey on adaptation uptake. Subsequently, the model simulates household adaptation and migration based on increasing coastal flood damage from 2015 until 2080. A medium population growth scenario is used to simulate future population development, and sea level rise (SLR) is assessed for different climate scenarios. The results indicate that SLR can drive migration exceeding 8000 and 10,000 coastal inhabitants for 2080 under the Representative Concentration Pathways 4.5 and 8.5, respectively. Although household adaptation to flood risk strongly impacts projected annual flood damage, its impact on migration decisions is small and falls within the 90% confidence interval of model runs. Projections of coastal migration under SLR are most sensitive to migration costs and coastal flood protection standards, highlighting the need for better characterization of both in modeling exercises. The modeling framework demonstrated in this study can be upscaled to the global scale and function as a platform for a more integrated assessment of SLR-induced migration.
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Many of the world’s largest deltas are densely populated and heavily farmed. Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean. The vulnerability is a result of sediment compaction from the removal of oil, gas and water from the delta’s underlying sediments, the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level. Here we present an assessment of 33 deltas chosen to represent the world’s deltas. We find that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of 260,000 km2. We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas.
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We provide estimates of the warming of the world ocean for 1955-2008 based on historical data not previously available, additional modern data, correcting for instrumental biases of bathythermograph data, and correcting or excluding some Argo float data. The strong interdecadal variability of global ocean heat content reported previously by us is reduced in magnitude but the linear trend in ocean heat content remain similar to our earlier estimate. Citation: Levitus, S., J. I. Antonov, T. P. Boyer, R. A. Locarnini, H. E. Garcia, and A. V. Mishonov (2009), Global ocean heat content 1955-2008 in light of recently revealed instrumentation problems, Geophys. Res. Lett., 36, L07608, doi: 10.1029/2008GL037155.
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Settlements in coastal lowlands are especially vulnerable to risks resulting from climate change, yet these lowlands are densely settled and growing rapidly. In this paper, we undertake the first global review of the population and urban settlement patterns in the Low Elevation Coastal Zone (LECZ), defined here as the contiguous area along the coast that is less than 10 metres above sea level. Overall, this zone covers 2 per cent of the world's land area but contains 10 per cent of the world's population and 13 per cent of the world's urban population. A disproportionate number of the countries with a large share of their population in this zone are small island countries, but most of the countries with large populations in the zone are large countries with heavily populated delta regions. On average, the Least Developed Countries have a higher share of their population living in the zone (14 per cent) than do OECD countries (10 per cent), with even greater disparities in the urban shares (21 per cent compared to 11 per cent). Almost two-thirds of urban settlements with populations greater than 5 million fall, at least partly, in the zone. In some countries (most notably China), urbanization is driving a movement in population towards the coast. Reducing the risk of disasters related to climate change in coastal settlements will require a combination of mitigation, migration and settlement modification.
To improve the estimate of economic costs of future sea-level rise associated with global climate change, this report generalizes the sea-level rise cost function originally proposed by Fankhauser, and applies it to a new database on coastal vulnerability developed as part of the Dynamic Interactive Vulnerability Assessment (DIVA) tool. An analytic expression for the generalized sea-level rise cost function is obtained to explore the effect of various spatial distributions of capital and nonlinear sea-level rise scenarios. With its high spatial resolution, the DIVA database shows that capital is usually highly spatially concentrated along a nation’s coastline, and that previous studies, which assumed linear marginal capital loss for lack of this information, probably overestimated the fraction of a nation’s coastline to be protected and hence protection cost. In addition, the new function can treat a sea-level rise scenario that is nonlinear in time. As a nonlinear sea-level rise scenario causes more costs in the future than an equivalent linear sea-level rise scenario, using the new equation with a nonlinear scenario also reduces the estimated damage and protection fraction through discounting of the costs in later periods. Numerical calculations are performed, applying the cost function to the DIVA database and socioeconomic scenarios from the MIT Emissions Prediction and Policy Analysis (EPPA) model. The effect of capital concentration substantially decreases protection cost and capital loss compared with previous studies, but not wetland loss. The use of a nonlinear sea-level rise scenario further reduces the total cost because the cost is postponed into the future.
Finding a climate change signal on coasts is more problematic than often assumed. Coasts undergo natural dynamics at many scales, with erosion and recovery in response to climate variability such as El Niño, or extreme events such as storms and infrequent tsunamis. Additionally, humans have had enormous impacts on most coasts, overshadowing most changes that one can presently attribute directly to climate change. Each area of coast is experiencing its own pattern of relative sea-level change and climate change, making discrimination of the component of degradation that results from climate change problems. The best examples of a climate influence are related to temperature rise at low and high latitudes, as seen by the impacts on coral reefs and polar coasts, respectively. Observations through the twentieth century demonstrate the importance of understanding the impacts of sea-level rise and climate change in the context of multiple drivers of change; this will remain a challenge under a more rapidly changing climate. Nevertheless, there are emerging signs that climate change provides a global threat—sea ice is retreating, permafrost in coastal areas is widely melting. Reefs are bleaching more often, and the sea is rising—amplifying widespread trends of subsidence and threatening low-lying areas. To enhance the sustainability of coastal systems, management strategies will also need to address this challenge, focusing on the drivers that are dominant at each section of coast. Global warming through the twentieth century has caused a series of changes with important implications for coastal areas. These include rising temperatures, rising sea level, increasing CO2 concentrations with an associated reduction in seawater pH, and more intense precipitation on average.
Estimates of regional patterns of global sea level change are obtained from a 1° horizontal resolution general circulation model constrained by least squares to about 100 million ocean observations and many more meteorological estimates during the period 1993-2004. The data include not only altimetric variability, but most of the modern hydrography, Argo float profiles, sea surface temperature, and other observations. Spatial-mean trends in altimetric data are explicitly suppressed to isolate global average long-term changes required by the in situ data alone. On large scales, some regions display strong signals although few individual points have statistically significant trends. In the regional patterns, thermal, salinity, and mass redistribution contributions are all important, showing that regional sea level change is tied directly to the general circulation. Contributions below about 900 m are significant, but not dominant, and are expected to grow with time as the abyssal ocean shifts. Estimates made here produce a global mean of about 1.6 mm yr1, or about 60% of the pure altimetric estimate, of which about 70% is from the addition of freshwater. Interannual global variations may be dominated by the freshwater changes rather than by heating changes. The widely quoted altimetric global average values may well be correct, but the accuracies being inferred in the literature are not testable by existing in situ observations. Useful estimation of the global averages is extremely difficult given the realities of space-time sampling and model approximations. Systematic errors are likely to dominate most estimates of global average change: published values and error bars should be used very cautiously.
An analysis of the steric and ocean mass components of sea level shows that the sea level rise budget for the period January 2004 to December 2007 can be closed. Using corrected and verified Jason-1 and Envisat altimetry observations of total sea level, upper ocean steric sea level from the Argo array, and ocean mass variations inferred from GRACE gravity mission observations, we find that the sum of steric sea level and the ocean mass component has a trend of 1.5 +/- 1.0 mm/a over the period, in agreement with the total sea level rise observed by either Jason-1 (2.4 +/- 1.1 mm/a) or Envisat (2.7 +/- 1.5 mm/a) within a 95% confidence interval.
We investigate the transient response of the global ocean circulation to enhanced freshwater forcing associated with melting of the Greenland and Antarctic ice sheets. Increased freshwater runoff from Greenland results in a basin-wide response of the North Atlantic on timescales of a few years, communicated via boundary waves, equatorial Kelvin waves, and westward propagating Rossby waves. In addition, modified air-sea interaction plays a fundamental role in setting up the basin-scale response of the Atlantic circulation in its subpolar and subtropical gyres. In particular, the modified ocean dynamics and thermodynamics lead to a depression in the central North and South Atlantic that would not be expected from linear wave dynamics. Moreover, the heat content increases on basin and global scales in response to anomalous freshwater forcing from Greenland, suggesting that the ocean's response to enhanced freshwater forcing would be a coupled problem. Other parts of the world ocean experience a much slower adjustment in response to Greenland freshwater forcing, communicated via planetary waves, but also involving advective/diffusive processes, especially in the Southern Ocean. Over the 50 years considered here, most of the sea level increase associated with freshwater input from Greenland remains in the Atlantic Ocean. In contrast, ice melting around Antarctica has a much reduced effect on the global ocean. In both cases, none of the basins came to a stationary state during the 50-year experiment.