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KEY ISSUES

he US has over 95,000 miles of coastline and over 3.4 million square miles of

ocean within its territorial waters.These areas provide a wide range of essential goods and services to society. Some 53% of the total US population live on the

17% of land in the coastal zone,and these areas become more crowded every year.

Because of this growth,as well as increased wealth and affluence,demands on

coastal and marine resources for both aesthetic enjoyment and economic benefits

are rapidly increasing.

Coastal and marine environments are intrinsically linked to climate in many ways.

The ocean is an important distributor of the planet's heat,with major ocean currents moving heat toward the poles from the equator. There is some chance that

this distribution of heat through the ocean's "conveyor belt" circulation would be

strongly influenced by the changes projected in many global climate models. Sealevel rise is another climate-related phenomenon with a major influence on coastlines. Global sea level has already risen by 4 to 8 inches (10-20 cm) in the past century and models suggest this rise is very likely to accelerate. The best estimate is

that sea level will rise by an additional 19 inches (48 cm) by 2100,with an uncertainty range of 5 to 37 inches (13-95 cm). Geological forces (such as subsidence,in

which the land falls relative to sea level) play a prominent role in regional sea-level

change. Accelerated global sea-level rise is expected to have dramatic impacts in

those regions where subsidence and erosion problems already exist.

Key Issue: Shoreline Erosion and Human Communities

oastal erosion is already a widespread problem in much of the country and

has significant impacts on undeveloped shorelines as well as on coastal development and infrastructure. Along the Pacific Coast,cycles of beach and cliff erosion

have been linked to El Niño events that raise average sea levels over the short term

and alter storm tracks that affect the coastline. For example,during the 1982-83 El

Niño and the 1997-98 El Niño,erosion damage was widespread along the Pacific

Coastline. If increases in the frequency or intensity of El Niño events occur, they

would likely combine with long-term sea-level rise to exacerbate these impacts.

Atlantic and Gulf Coast shorelines are especially vulnerable to long term sea-level

rise as well as any increase in the frequency of storm surges

or hurricanes. Most erosion events on these coasts are the

result of storms,and the slope of these areas is so gentle that

a small rise in sea level produces a large inland shift of the

shoreline. When buildings, roads,and seawalls block this natural shift,the beaches and shorelines erode,especially during storm

events. This increases the threats to coastal development,transportation

infrastructure,tourism,freshwater aquifers,and fisheries (which are already stressed

by human activities). Coastal cities and towns,especially those in storm-prone

• Shoreline Erosion and

Human Communities

• Threats to Estuarine

Health

• Coastal Wetland Survival

• Coral Reef Die-offs

• Stresses on Marine

Fisheries

C

COASTAL AREAS AND MARINE RESOURCES

T

Coastal Vulnerabilty

The preliminary results shown on this

map illustrate the relative vulnerability

to sea-level rise along the New York

and New Jersey coastline.
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regions such as the Southeast,are particularly vulnerable to extreme events.

Intensive residential and commercial development in such regions puts life and

property at risk.

Key Issue: Threats to Estuarine Health

stuaries are extremely productive ecosystems that are affected in numerous ways by climate. Winter temperatures are projected to continue to

increase more than summer temperatures, resulting in a narrowing of the annual water temperature range of many estuaries. This is likely to cause species'

ranges to shift and increase the vulnerability of some estuaries to

non-native invasive species. Either increases or decreases in

runoff would very likely create impacts to estuaries. Increased

runoff would likely deliver increased amounts of nutrients such as

nitrogen and phosphorous to estuaries,while simultaneously increasing

the stratification between freshwater runoff and marine waters. Both nutrient additions and increased stratification would increase the potential for

blooms of algae that deplete the water of oxygen,increasing stresses on sea

grasses,fish,shellfish,and other living things on the bottom of lakes,streams,

and oceans. Decreased runoff would likely reduce flushing,decrease the size

of estuarine nursery zones,and allow predators and pathogens of shellfish to

penetrate further into the estuary.

Winter temperatures are projected to continue to increase

more than summer temperatures, resulting in a narrowing of the annual water temperature range of many estuaries. This is likely to cause

species' ranges to shift

and increase the vulnerability of some

estuaries to non-native

invasive species.

The ocean plays a major role in the distribution of the planet's heat through deep sea circulation. This simplified

illustration shows this "conveyor belt" circulation which is driven by differences in heat and salinity. Records of

past climate suggest that there is some chance that this circulation could be altered by the changes projected in

many climate models, with impacts to climate throughout lands bordering the North Atlantic.

Ocean Circulation Conveyor Belt

E

Sea-to-Air

Heat Transfer

Solar Warming

of Ocean Waters
Coastal Wetland Survival

oastal wetlands (marshes and mangroves) are highly productive ecosystems that are strongly linked to fisheries productivity.They provide

important nursery and habitat functions to many commercially important fish

and shellfish populations. Dramatic losses of coastal wetlands have already

occurred on the Gulf Coast due to subsidence, changes caused by dams and levees that alter flow and reduce sediment supply, dredge and fill activities,and

sea-level rise. Louisiana alone has been losing land at rates between 24 and 40

square miles per year during the last 40 years,accounting for as much as 80% of

the total US coastal wetland loss.

In general,coastal wetlands will survive if soil buildup equals the rate of

relative sea-level rise or if the wetland is able to migrate inland.

However, if soil accumulation is unable to keep pace with high rates

of sea-level rise,or if wetland migration is blocked by bluffs,

coastal development,or shoreline protective structures

(such as dikes,sea walls,and jetties),the wetland

will be excessively inundated and eventually lost.

The projected increase in the current rate of sealevel rise will very likely exacerbate coastal wetland losses nationwide,although the extent of

impacts will vary among regions.

110

COASTAL AREAS AND MARINE

RESOURCES KEY ISSUES

US Coastal Lands at Risk from a 

20-inch Sea-Level Rise 

CO2 and Temperature Stresses on Coral Reefs 

This graph shows a simulation of the effect of increased atmospheric

CO2 on percent change in coral reef calcification. Rising atmospheric

CO2 harms coral directly by making surface waters less alkaline, reducing corals' calcification and making their skeletons smaller and weaker.

Warmer ocean temperatures will be another significant added stress,

causing corals to expel the algae that live inside them and are crucial to

their survival. Because these algae also give coral its color, this process

is called "coral bleaching." Coral can recover after a short episode of

warmer water, but if the warming persists the coral die. Under these

combined stresses in addition to the existing stresses posed by human

activities, corals may not survive in many areas.

These bars show the square miles of coastal land at risk from a 20-

inch rise in sea level, for seven areas of the US. Coastal wetlands

projected to be inundated are shown in yellow while drylands projected to be inundated are shown in blue.

C

The rate of sealevel rise is projected

to accelerate 2-5 fold over

the next 100 years. The delivery

of sediments to coastal wetlands is

extremely important in determining the

potential of these systems to maintain

themselves in the face of current and

future sea-level changes.

Subsidence

Marsh

Plant Processes

Soil Volume

Sedimentation Hydrology Rising Sea-level

Processes Affecting 

Marsh Elevation
Coral Reef Die-offs

oral reefs play a major role in the environment and economies of two

states (Florida and Hawaii) as well as most US territories in the Caribbean

and Pacific. Coral reefs are valuable economic resources for fisheries, recreation,tourism,and coastal protection. In addition, reefs are one of the largest

global storehouses of marine biodiversity, with untapped genetic resources.

Some estimates of the global cost of losing coral reefs run in the hundreds of

billions of dollars each year. The demise or continued deterioration of reefs

could have profound implications for the US.

The last few years have seen unprecedented declines in the health of coral

reefs. The 1998 El Niño was associated with record sea-surface temperatures

and associated coral bleaching (when coral expel the algae that live within

them and are necessary to their survival);in some regions,as much as 70% of

the coral may have died in a single season. There has also been an upsurge in

the variety, incidence,and virulence of coral diseases in recent years,with

major die-offs in Florida and much of the Caribbean region. In addition,increasing atmospheric CO2

concentrations could possibly decrease the calcification

rates of the reef-building corals, resulting in weaker skeletons, reduced growth

rates and increased vulnerability to erosion. Model results suggest that these

effects would likely be most severe at the current margins of coral reef distribution.

111

C

Calcium Carbonate Saturation in Ocean Surface Waters

>4.0 Optimal

3.5 - 4 Adequate

3 - 3.5 Marginal

<3.0 Extremely 

Low

Preindustrial (~1880) Current (2000)

Projected (~2050)

Corals require the right combination of temperature, light, and

calcium carbonate saturation. At higher latitudes, there is

less light and lower temperatures than nearer the equator.

The saturation level of calcium carbonate is also lower at

higher latitudes, in part because more CO2, an acid, can be

dissolved in colder waters. As the CO2level rises, this effect

dominates, making it more difficult for corals to form at the

poleward edges of their distribution. These maps show model

results of the saturation level of calcium carbonate for preindustrial, present and future CO2

concentrations. The dots

indicate present coral reefs. Note that under model projections of the future, it is very unlikely that calcium carbonate

saturation levels will provide fully adequate support for coral

reefs in any US waters. The possibility of this future scenario

occurring demands continued research on effects of increasing CO2

on entire coral reef systems.

There has also been an

upsurge in the variety, incidence, and virulence of coral

diseases in recent years, with

major die-offs in Florida and

much of the Caribbean region.

In addition, increasing atmospheric CO2

concentrations

could possibly decrease the

calcification rates of the reefbuilding corals, resulting in

weaker skeletons, reduced

growth rates and increased

vulnerability to erosion.
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COASTAL AREAS AND MARINE

RESOURCES KEY ISSUES

Stresses on Marine Fisheries

n the US,the total economic contribution of recreational and commercial fishing

has been estimated at approximately $40 billion per year, with total marine landings averaging about 4.5 million metric tons over the last decade. Climate change is

very likely to substantially alter the distribution and abundance of major fish stocks,

and have important implications for marine populations and ecosystems.Changes

over the long term are likely to include poleward shifts in distribution of marine

populations.With changing ocean temperatures and conditions,shifts in the distribution of commercially important species are likely. For example,models suggest

that several species of Pacific salmon are likely to have reduced distribution and

productivity, while species that thrive in warmer waters,such as Pacific sardine and

Atlantic menheden,are likely to have increased distribution.

Along the Pacific Coast,impacts to fisheries related to the El Niño/Southern

Oscillation illustrate how climate directly affects marine fisheries on short time

scales. For example,elevated sea-surface temperatures associated with the 1997-98

El Niño had a tremendous impact on the distribution and abundance of market

squid,California’s largest fishery by volume. Landings fell to less than 1,000 metric

tons in the 1997-98 season,down from a record-breaking 110,000 tons in the 1996-

97 season. Many other unusual events occurred during this same El Niño as a result

of elevated sea-surface temperatures. Examples include widespread sea lion pup

deaths in California,catches of warm-water marlin in the usually frigid waters off

Washington State,and poor salmon returns in Bristol Bay, Alaska.

I

Sea-level Rise Projections Sea-level Rise Projections - 2080-2099

Hadley Model Canadian Model

The Canadian model projects

a more complex pattern of

sea-level rise by 2100.

Because of its larger warming

estimate, sea level is projected to rise 20 to 24 inches (50

to 60 cm) along parts of the

US Atlantic and Pacific coastlines. The orange peak in the

Labrador Sea is the result of

shifts in the location and

intensity of ocean currents.

Historic and projected changes in sea level based on the

Canadian and Hadley model simulations. The Canadian model

projection includes only the effects of thermal expansion of

warming ocean waters. The Hadley projection includes both

thermal expansion and the additional sea-level rise projected

due to melting of land-based glaciers. Neither model includes

consideration of possible sea-level changes due to polar ice

melting or accumulation of snow on Greenland and Antarctica. 

The Hadley model projects that

ocean warming and melting of

mountain glaciers will cause

between 8 to 12 inches (20 to 30 cm)

of sea-level rise by 2100 for much of

the Atlantic and Gulf coasts of the

US, depending on changes in winds

and ocean current patterns.

Projections for the Northeast US and

the Pacific coast range from 13 to 16

inches (32 to 40 cm). Any effects of

the rising or sinking of the coastal

lands must be added to these numbers.

Canadian Model (Thermal Expansion)

Hadley Model (Thermal Expansion)

Hadley Model (Thermal Expansion and glacial melt)

Sea-level Rise (inches)

0 10 20 30 40

Atlantic and Gulf Coast

shorelines are especially vulnerable to long term sealevel rise as well as any

increase in the frequency of

storm surges or hurricanes.

Most erosion events on these

coasts are the result of

storms and extreme events,

and the slope of these areas

is so gentle that a small rise

in sea level produces a large

inland shift of the shoreline. 
113

Adaptation Strategies

t is difficult to assess the potential effects of climate change over the next

few decades on coastal and marine resources,especially as climate variability

is a dominant factor in shaping coastal and marine systems. The effects of

future change will vary greatly in the diverse coastal regions of the nation.

Additionally, human-induced disturbances also influence coastal and marine systems,often reducing the ability of systems to adapt,so that systems that might

ordinarily be capable of responding to variability and change are less able to do

so. In this context, climate change is likely to add to the cumulative impact of

both natural and human-caused stresses on ecological systems and resources.

This makes devising adaptation strategies particularly challenging.

With few exceptions,the potential consequences of climate change are not yet

being considered in coastal management. It is especially urgent to begin adaptation now with regard to development of land in the coastal zone. In areas

where beaches or wetlands must migrate inland to survive,it has been shown

that implementing protection or retreat strategies for coastal developments can

substantially reduce the economic impacts of inundation and shoreline movement. For example,coastal management programs in Maine,Rhode Island,

South Carolina,and Massachusetts have implemented various forms of "rolling

easement" policies to ensure that wetlands and beaches can migrate inland as

sea level rises,and coastal landowners and conservation agencies can purchase

the required easements. However,some regulatory programs continue to permit structures that may block the inland shift of wetlands and beaches.

Additionally, allowing for such shoreline movement is only feasible in some

locations due to the high degree of development on many coastlines.

I

With few exceptions, the

potential consequences

of climate change are not

yet being considered in

coastal management. It

is especially urgent to

begin adaptation now

with regard to development of land in the

coastal zone.

This map is a preliminary Annual Shoreline Change

classification of annual

shoreline erosion

throughout the US, in

coarse detail and resolution. The areas most vulnerable to future

sea-level change are

those with low relief

which are already experiencing rapid erosion

rates, such as the

Southeast and Gulf Coast.