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CHAPTER 16

POTENTIAL CONSEQUENCES OF CLIMATEVARIABILITY AND CHANGE ON COASTALAREAS AND MARINE RESOURCESJohn C. Field1, Donald F. Boesch2, Donald Scavia1, Robert Buddemeier3,Virginia R.Burkett4,5, Daniel Cayan6, Michael Fogarty2, Mark Harwell7, Robert Howarth8, CurtMason1, Leonard J. Pietrafesa10, Denise Reed11,Thomas Royer12,Asbury Sallenger4,Michael Spranger13, James G.Titus14

Contents of this Chapter

Chapter Summary

Introduction

Context

Climate and Coastal Environments

Key Issues

Shoreline Systems,Erosion and Developed Coastal Areas

Threats to Estuarine Health

Coastal Wetland Survival

Coral Reef Die-Offs

Stresses on Ocean Margins and Marine Fisheries

Adaptation Strategies

Crucial Unknowns and Research Needs

Literature Cited

Acknowledgments

1National Oceanic and Atmospheric Administration,2University of Maryland, 3University of Kansas, 4U.S.Geological Survey, 5Coordinating author for the National Assessment Synthesis Team, 6Scripps Institution ofOceanography, 7University of Miami, 8Eco-Modeling, 10North Carolina State University, 11University of NewOrleans, 12Old Dominion University, 13University of Washington, 14 U.S.Environmental Protection Agency

Climate of the Past Century

• Sea level has risen by 4 to 8 inches (10-20 cm) inthe past century.

• Ocean temperatures have risen over the last 55years,and there has been a recent increase in thefrequency of extreme ocean warming events inmany tropical seas.

• Sea ice over large areas of the Arctic basin hasthinned by 3 to 6 feet (1 to 2 meters),losing 40%of its total thickness since the 1960s;it continuesto thin by about 4 inches (10 cm) per year.

• Marine populations and ecosystems have beenhighly responsive to climate variability.

Climate of the ComingCentury

• Sea level is projected to rise an additional 19inches (48 cm) by 2100 (with a possible range of5 to 37 inches [13 cm to 95 cm]) along most ofthe US coastline.

• Ocean temperatures will continue to rise,but therate of increase is likely to lag behind tempera-ture changes observed on land.

• The extent and thickness of Arctic sea ice isexpected to continue to decline. All climatemodels project large continued losses of sea ice,with year-round ice disappearing completely inthe Canadian model by 2100.

• Increased temperature or decreased salinitycould trigger abrupt changes in thermohalineocean circulation.

CHAPTER SUMMARY

Context

The US has over 95,000 miles of coastline andapproximately 3.4 million square miles of oceanwithin its territorial sea,all of which provide a widerange of essential goods and services to human sys-tems. Coastal and marine ecosystems supportdiverse and important fisheries throughout thenation’s waters,hold vast storehouses of biologicaldiversity, and provide unparalleled recreationalopportunities. Some 53% of the total US populationlives on the 17% of land in the coastal zone,andthese areas become more crowded every year.Demands on coastal and marine resources are rapid-ly increasing,and as coastal areas become moredeveloped,the vulnerability of human settlementsto hurricanes,storm surges,and flooding events alsoincreases. Coastal and marine environments areintrinsically linked to climate in many ways. Theocean is an important distributor of the planet’sheat,and this distribution could be strongly influ-enced by changes in global climate. Sea-level rise isprojected to accelerate in the 21st century, with dra-matic impacts in those regions where subsidenceand erosion problems already exist.

Potential Consequences of Climate Variability and Change

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Chapter 16 / Coastal Areas and Marine Resources

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Key Findings

• Climate change will increase the stresses alreadyoccurring to coastal and marine resources as aresult of increasing coastal populations,develop-ment pressure and habitat loss, overfishing,excess nutrient enrichment,pollution,and inva-sive species.

• Marine biodiversity will be further threatened bythe myriad of impacts to all marine ecosystems,from tropical coral reefs to polar ecosystems.

• Coral reefs are already under severe stress fromhuman activities,and have experienced unprece-dented increases in the extent of coral bleaching,emergent coral diseases,and widespread die-offs.

• The direct impact of increasing atmospheric car-bon dioxide on ocean chemistry will possiblyseverely inhibit the ability of coral reefs to growand persist in the future.

• Globally averaged sea level will continue to rise,and the developed nature of many coastlinesmakes both human settlements and ecosystemsmore vulnerable to flooding and inundation.

• Barrier islands are especially vulnerable to thecombined effects of sea-level rise and uncon-trolled development that hinders or prevents nat-ural migration.

• Ultimately, choices will have to be made betweenthe protection of human settlements and theprotection of coastal ecosystems such as beach-es,barrier islands,and coastal wetlands.

• Human development and habitat alteration willlimit the ability of coastal wetlands to migrateinland as sea levels rise,however, if sedimentsupplies are adequate,many wetlands may sur-vive through vertical adjustments.

• Increases in precipitation and runoff are likely tointensify stresses on estuaries in some regions byintensifying the transport of nutrients and con-taminants to coastal ecosystems.

• As rivers and streams also deliver sediments,which provide material for soil in wetlands andsand in beaches and shorelines,dramatic declinesin streamflows could have negative effects onthese systems.

• Changes in ocean temperatures,currents,andproductivity will affect the distribution, abun-dance,and productivity of marine populations,with unpredictable consequences to marineecosystems and fisheries.

• Increasing carbon dioxide levels could triggerabrupt changes in thermohaline ocean circula-tion,with massive and severe consequences forthe oceans and for global climate.

• Extreme and ongoing declines in the thicknessand extent of Arctic sea ice will have enormousconsequences for Arctic populations,ecosystems,and coastal evolution.


INTRODUCTIONHuman caused alterations and impacts to coastaland marine environments must be considered in thecontext of evaluating the health and viability ofthese resources. In many instances,it is difficult toassess the effects of climate variability and changesbecause human activities are often responsible forthe greatest impacts on coastal and marine environ-ments. Such disturbances often reduce the capacityof systems to adapt to climate variations and climatestress,and often mask the physical and biologicalresponses of many systems to climate forces. Forexample,naturally functioning estuarine and coastalwetland environments would typically be expectedto migrate inland in response to relative sea-levelrise,as they have responded to sea-level variationsthroughout time. When this natural migration isblocked by coastal development,such habitat isgradually lost by “coastal squeeze”as rising sea levelspush the remaining habitat against developed orotherwise altered landscapes. Similarly, estuariesalready degraded by excess nutrients could recovermore slowly from droughts or floods.

CONTEXTThe US has over 95,000 miles of coastline andapproximately 3.4 million square miles of oceanwithin its territorial sea,all of which provide a widerange of essential goods and services to society.These include overlapping and often competinguses,including but not limited to tourism,coastaldevelopment,commercial and recreational fisheries,aquaculture,biodiversity, marine biotechnology, navi-gation,and mineral resources.

The coastal population of the US is currently grow-ing faster than the nation’s population as a whole, atrend that is projected to continue. Currently some53% of the total population of the US live in 17% ofthe land area considered coastal (Culliton,1998).Over the next 25 years,population gains of approxi-mately 18 million people are projected to occur inthe coastal states of Florida,California,Texas,andWashington alone (Figure 1) (NPA,1999). With this

growth,as well as increased wealth andaffluence,there are rapidly increas-ing demands on coastal and marineresources for both aesthetic enjoy-ment and economic benefits.

This large and growing populationpressure in coastal areas is responsi -ble for many of the current stresses tocoastal resources. For example,theEPA (1996) estimated that nearly 40%of the nation’s surveyed estuarieswere impaired by some form of pollu-tion or habitat degradation. Some 30to 40% of shellfish-growing waters inthe nation’s estuaries are harvest pro-hibited or restricted each year, primari-

ly due to bacterial contaminationfrom urban and agricultural

runoff and septic systems(Alexander, 1998). Additionally,

over 3,500 beach advisories andbeach closings occurred in the

United States in 1995,primarily due to storm-waterrunoff and sewage overflows (NOAA,1998).

POTENTIAL CONSEQUENCES OF CLIMATEVARIABILITY AND CHANGE ON COASTAL AREAS AND MARINE RESOURCES

Population Distribution across the US

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Figure 1: Over the next 25 years, population gains of some 18 mil-lion people are projected to occur in the coastal states of Florida,California, Texas, and Washington (NPA, 1999). See color figureappendix.


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in the US, representing the second largest employerin the nation (after health care) and employingsome 6 million people (NOAA,1998). It has beenestimated that the US receives over 45% of thedeveloped world’s travel and tourism revenues,andoceans,bays,and beaches are among the most popu-lar tourist destinations in the nation (Houston,1996). As many as 180 million people visit the coasteach year for recreational purposes in all regions ofthe country, and many regions depend upon tourismas a key economic activity. For example one studyestimated that in the San Francisco Bay area alonetourism has been estimated to generate over $4 bil-lion a year (EPA,1997). Clean water, healthy ecosys-tems,and access to coastal areas are critical to main-taining tourism industries;ironically, however, theseindustries themselves often pose additional impactsto coastal environments and local communities(Miller and Auyong,1991).

As coastal populations increase,the vulnerability ofdeveloped coastal areas to natural hazards is simulta-neously expanding. Disaster losses are currentlyestimated at about $50 billion annually in the US,compared to just under $4.5 billion in 1970. Asmuch as 80% of these disasters were meteorological-ly related storms,hurricanes,and tornadoes (asopposed to geologically related disasters such asearthquakes and volcanoes) and many of these hadtheir greatest impacts on coastal communities. Thepotential increase in such events related to climatechange will pose an even greater threat to coastalpopulation centers and development in the future.However, the ongoing trends of population growthand development in coastal areas alone will ensurethat losses due to hurricanes,storms,and other dis-asters in coastal areas will continue to increase.

In addition to direct economic benefits,coastal andmarine ecosystems,like all ecosystems,have charac-teristic properties or processes which directly orindirectly benefit human populations. Costanza etal.(1997) have attempted to estimate the economicvalue of sixteen biomes,or ecosystem types,andseventeen of their key goods and services,includingnutrient cycling,disturbance regulation, waste treat-ment, food production, raw materials, refugia forcommercially and recreationally important species,genetic resources,and opportunities for recreationaland cultural activities. For example,the societalvalue per hectare of estuaries,tidal marshes,coralreefs,and coastal oceans were estimated at $22,832,$9,990,$6,075,and $4,052 per hectare, respectively.On a global basis,the authors suggested that theseenvironments were of a disproportionately higher

Population pressures from further inland can alsohave detrimental impacts on coastal resources.Effluent discharges as well as agricultural runoffhave caused significant nutrient over-enrichment inmany coastal areas. Sewage and siltation are signif i-cant contributors to coral reef degradation inHawaii,Florida,and US-affiliated islands of thePacific and Caribbean. Dams,irrigation projects,andother water management activities have furtherimpacted coastal ecosystems and shorelines bydiverting or otherwise altering the timing and flowof water, sediments,and nutrients.

As population and development in coastal areasincrease,many of these stresses can be expected toincrease as well,further decreasing the resilience ofcoastal systems. This,in turn,increases the vulnera-bility of coastal communities and economies whichdepend upon healthy, functioning ecosystems. Theinteraction of these ongoing stresses with theexpected impacts imposed by future climate changeis likely to greatly accentuate the detrimentalimpacts to coastal ecosystems and communities(Reid and Trexler, 1992,Mathews-Amos andBernston,1999).

Despite these ongoing stresses to coastal environ-ments,the oceans and coastal margins provideunparalleled economic opportunities and revenues.One estimate suggests that as many as one out ofevery six jobs in the US is marine-related,and nearlyone-third of the gross domestic product (GDP) isproduced in coastal areas (NOAA,1998;NRC,1997).In 1996,approximately $590 billion worth of goodspassed through US ports, over 40% of the total valueof US trade and a much larger percentage by vol-ume. The US is also the world’s fifth largest fishingnation and the third largest seafood exporter;totallandings of marine stocks have averaged about 4.5million metric tons over the last decade. Ex-vesselvalue (the amount that fishermen are paid for theircatch) of commercial fisheries alone was estimatedat approximately $3.5 billion in 1997,and the total(direct and indirect) economic contribution ofrecreational and commercial fishing has been esti-mated at over $40 billion per year (NRC,1999). Thegrowing field of marine biotechnology has also gen-erated substantial opportunities; for example recentresearch has yielded five drugs originating frommarine organisms with a cumulative total potentialmarket value of over $2 billion annually (NOAA,1998).

Coastal tourism also generates enormous revenues.Travel and tourism are multi-billion dollar industries


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value,covering only some 6.3% of the world’s sur-face area but responsible for some 43% of the esti-mated value of the world’s ecosystem services.These results suggest that the oceans and coastalareas contribute the equivalent of some $21 trillionper year to human activities globally (Costanza,1999). The approach of Costanza et al.(1997) to val-uation is not universally accepted,and the authorsthemselves agree that ecosystem valuation is diffi-cult and fraught with uncertainties. However, themagnitude of their estimates,and the degree towhich coastal and marine ecosystems rank asamongst the most valuable to society, serve to placethe importance of the services and functions ofthese ecosystems in an economic context.

CLIMATE AND COASTALENVIRONMENTSSea-level Change

Global sea levels have been rising since the conclu-sion of the last ice age approximately 15,000 yearsago. During the last 100 years,globally averaged sealevel has risen approximately 4 to 8 inches (10-20cm,or about 1 to 2 millimeters per year). This rep-resents “eustatic”sea-level change,the change in ele-vation of the Earth’s oceans that has been deter-mined from tidal stations around the globe. Most of

Figure 2 : Projected rise in global average sea level based on theHadley and Canadian General Circulation Model (GCM) scenarios.See color figure appendix.

Global Average Sea Level Rise

Spatial Distribution Around North America in Sea Level Rise

Figure 3 : Projections of the regional pattern of global sea level rise by the year 2100 based on the Canadian(left) and Hadley (right) scenarios. These estimates do not include contributions to sea-level change due to verti-cal movement of coastal lands. See color figure appendix.


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the observed global sea-level change is accountedfor by two major variables:the thermal expansion ofseawater in the oceans with rising ocean tempera-tures and changes in the amount of the Earth’swater that is locked up in glaciers and ice sheets.The vast majority of landlocked water, enough toraise global sea levels by some 80 meters,is found inthe Greenland and Antarctic Ice sheets. Of these,there has been considerable concern regarding thestability of the West Antarctic Ice Sheet (WAIS).Oppenheimer (1998) suggested that the probabilityof mass wasting (melting) of this ice sheet over thenext 100 years is relatively low, but the probabilityof wasting after 2100 will be considerably greater.Over the next 100 years,most studies predict thatthe majority of observed sea-level change is expect-ed to come as a result of thermal expansion of theoceans (Gornitz,1995).

In addition to global changes in mean sea level,there are large regional variations in sea level asmeasured at the shoreline due to changes in coastalland masses such as subsidence (sinking),isostatic(glacial) rebound and tectonic uplift. The combinedeffects of eustatic and land mass factors contributeto relative sea-level change in each locality. Forexample,within the US,portions of the Gulf Coastare experiencing a relative sea-level rise of nearlyhalf an inch (approximately 10 mm) per year due tosubsidence. Concurrently, some portions of thesoutheastern Alaska coastline are experiencing upliftassociated with tectonic activity, causing a local rela-tive sea-level fall of slightly less than one half inch(approximately 8 mm) per year.

Finally, there are also regional changes in mean sealevel that result from dynamic changes to the oceangeoid,or the “topography”of the sea surface. Theseresult from changes in ocean circulation,wind andpressure patterns,and ocean-water density (IPCC,1996). The result is that sea-level rise will affect var-ious coastal regions differently, independent of theland motion that contributes to sea-level change.Figures 2 and 3 show the results of Hadley andCanadian General Circulation Model (GCM) projec-tions for regional changes in sea level,independentof land movement. In general,the Hadley modelpredicts a greater sea-level rise for the Pacific coastthan for the Atlantic and Gulf coasts as a result ofcurrent and wind patterns. By contrast,theCanadian model predicts a more complex pattern ofsea-level rise but with increases relatively similaralong all US coasts.

The Hadley climate model projects that sea levelwill rise between 8 and 12 inches (20 to 30 cen-

timeters) by 2100 for the Atlantic and Gulf Coasts,and 13 to 16 inches (33 cm to 41 cm) for the PacificCoast (Figure 3). The Canadian model projects a sig-nificantly greater estimate of 20 to 24 inches (51 cmto 61 cm) along parts of the US coast (Figure 3).These results are very similar to those found by theIntergovernmental Panel on Climate Change (IPCC,1996),which estimated that sea levels would mostlikely increase by approximately 19 inches (48 cm)by 2100,with a range of 5 to 37 inches (13 to 95cm). Most additional studies conducted since thenyield similar estimates, generally projecting increasesof about one foot above current trends over the 21st

century, for a total sea-level rise of approximately 18to 20 inches (45 to 52 cm) above their current levelby the year 2100 (Titus and Narayanan,1996;Wigley,1999). In addition,sea-level rise will continue tooccur, even accelerate,beyond 2100 as a result ofthe long time frame necessary for oceans and icesheets to approach equilibrium under the long-termperturbations anticipated with climate change.

Hurricanes and Non-TropicalStorms

Storm flooding, wave forces,and coastal erosion arenatural processes that pose hazards only when theyaffect people,homes,and infrastructure that areconcentrated in coastal areas. During the 20th cen-tury, loss of life and threats to human health duringhurricanes has decreased substantially because ofimproved tracking and early warning systems;how-ever, property losses have increased greatly (Herbertet al.,1996). Yet even if storm intensity and frequen-cy remain the same in the future,continued acceler-ation in property losses is likely as the increasedconcentration of people and infrastructure alongthe coasts continues. This acceleration in propertylosses will be amplified should global climatechange increase storm activity, although the currentrelationship between climate change and hurricanefrequency and intensity is not clear.

Historical records of hurricanes suggest strongannual to decadal variability. For example,the num-ber of hurricanes occurring per year can vary by afactor of three or more for consecutive years,andduring El Niño years,hurricanes are less prevalent inthe Atlantic Basin (Pielke and Landsea,1999).Furthermore,during the 25-year period from 1941to 1965,there were seventeen Category 3 hurri-canes landfalling on the US East Coast or peninsularFlorida, yet between 1966 and 1990 there were onlytwo (Figure 4). The mid-1990s have seen a recur -rence of large numbers of hur ricanes in the NorthAtlantic,perhaps suggesting a return to an active


regime,although the long term implications are notyet clear (Landsea et al.,1996). Globally, the histori-cal record shows “no discernible trends in tropicalcyclone number, intensity, or location”(Henderson-Sellers et al.,1998). However, regional variability,such as observed in the North Atlantic,can be large.

While interdecadal and intera n nual va ri ability ofh u rricane frequency and strength is like ly to domi-nate ch a n ges in hurricanes for at least the fi rs thalf of the next century, i n c reases in hurri c a n ewind strength could result from future eleva t e dsea surface tempera t u res over the next 50 to 100ye a rs . A recent model investigation shows thati n c reases in hurricane wind strength of 5 to 10%a re possible with a sea surface wa rming of 4˚F(2.2˚C) (Knutson et al., 1 9 9 8 ) . Other re s e a rchs u p p o rts the possibility that tropical cycl o n e scould become more intense (Ke rr, 1 9 9 9 ) . For a

m o d e rate hurri c a n e ,s u ch an increase in winds t rength would translate into approx i m a t e ly a 25%i n c rease in the destru c t i ve power of the winds;thus the resulting increase in wave action ands t o rm surge would be greater than the perc e n t agei n c rease in wind speed. S i m i l a r ly, wave height ands t o rm surge would have a greater perc e n t agei n c rease than wind speed, p o t e n t i a l ly yieldingi n c reased impacts to coasts.

H oweve r, it should be noted that recent global cl i-mate model investigations have shown that ElN i ñ o / S o u t h e rn Oscillation (ENSO) ex t remes couldbecome more frequent with increasing gre e n h o u s egas concentra t i o n s . For ex a m p l e , wo rk byTi m m e rmann et al. ( 1 9 9 9 ) , using a GCM with suffi-cient re s o l u t i o n ,s u g gests that the tropical Pa c i fic isl i ke ly to ch a n ge to a state similar to pre s e n t - d ay ElNiño conditions. Since fewer hurricanes occur in

the Atlantic during El Niño ye a rs ,t h e i rresults suggest that Atlantic hurricanes willl i ke ly decrease in frequency in the future .I n t e re s t i n g ly, d u ring seve re El Niño eve n t ss u ch as those in 1982-83 and 1997-98, the jets t ream over the North Pa c i fic brought win-ter storms fa rther south causing ex t e n s i vecoastal erosion and flooding in Califo rn i a .H e n c e , a pro l o n ged El Niño state shouldd e c rease the occurrence of hurricanes inthe Atlantic but lead to an increase in coastalimpacts by winter storms on the West Coast.On the other hand, the results ofTi m m e rmann et al. (1999) also sugge s ts t ro n ger intera n nual va ri ab i l i t y, with re l a t i ve-ly strong cold (La Niña) events becomingm o re fre q u e n t . Although these La Niñaevents would be superimposed upon a high-er mean tempera t u re , this could sugge s tm o re intera n nual va ri ability in Atlantic hurri-canes with more intense activity during thes t ro n ger cold eve n t s .

Even if storm magnitudes and frequenciesof occurrence remain the same,an impor-tant impact of future storms,whether tropi-cal or extratropical,will be their superposi-tion on a rising sea level. This has recentlybeen demonstrated by examining historicalstorm surge magnitudes calculated from sea-level records (Zhang et al.,1997). Theserecords included surges induced by bothwinter storms and hurricanes but weredominated by the more frequent winterstorms. No significant long term trendswere found in storm frequency or severity.When considering that the storms were

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Figure 4: Loss of life and property from hurricanes making landfallin the continental U.S. over the past 20th century Source: NationalHurricane Center: NOAA. See color figure appendix.

Hurricanes and their Impacts in the 20th Century(1900-1995)


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strong effects on biotic distributions,life histories,and geochemistry. Coastal runoff also affects circu-lation in estuaries and continental shelf areas,andincreases in runoff have the potential to increasethe vertical stratification and decrease the rate ofthermohaline circulation by adding more freshwaterto the system.

In the event that increased river flows result fromclimate change,more suspended sediments could betransported into the coastal regions,increasing theupper layer turbidity and potentially reducing avail-able light to both plankton and submerged aquaticvegetation. Changes in sediment transport couldalso alter the amount of sediment available for soilaggradation (accumulation) in wetlands and sandsfor littoral systems. Increased sediment transportwill provide needed material for accretion to coastalwetlands threatened by sea-level rise,whereas adecrease in sediment transport will concurrentlydiminish the ability of some wetlands to respond tosea-level rise.

Increased river flows could also increase the flux ofnutrients and contaminants into coastal systems,which influence eutrophication and the accumula-tion of toxins in marine sediments and livingresources. Both increased temperatures anddecreased densities in the upper layers might alsoreduce the vertical convection enough to preventoxygenation of the bottom waters,further contribut-ing to anoxic conditions in the near-bottom waters(Justic´ et al.,1996). Decreased freshwater inflowsinto coastal ecosystems would be likely have thereverse effect, reducing flushing in estuaries,increasing the salinity of brackish waters,and possi-bly increasing the susceptibility of shellfish to dis-eases and predators.

Ocean Temperatures

The oceans represent enormous reservoirs of heat;their heat capacity is such that the upper 16 to 33feet (5 to 10 meters) of the water column generallycontain as much heat as the entire column of airabove it. The oceans work to distribute heat global-ly, and atmospheric and oceanic processes worktogether to control both pelagic and coastal oceantemperatures.

Strong evidence for ocean warming was recentlypublished by Levitus et al.(2000),who evaluatedsome five million profiles of ocean temperaturetaken over the last 55 years. Their results indicatethat the mean temperature of the oceans between 0and 300 meters (0 and 984 feet) has increased by

superimposed on a rising sea level (0.15 inch/yearor 3.9 mm/year at Atlantic City),there is an inferredincrease in storm impact over an 82-year record.For example,the number of hours of extreme waterlevels per year increased from less than 200 in theearly 1900s to abnormally high values of up to 1200hours (averaging typically 600 hours) in the 1990s.Thus sea-level rise will increase impacts to the coastby a storm of a given magnitude.

Freshwater Runoff

Hydrological cycles are fundamental components ofclimate,and climate change is likely to affect bothwater quality and water availability. In general,theconsensus is that the hydrologic cycle will becomemore intense,with average precipitation increasing,especially at high latitudes. Extreme rainfall condi-tions,already demonstrated to have increased overthe 20th century, are likely to become more com-mon,as could droughts and floods (Karl et al.,1995a;Karl et al.,1995b). Changes in freshwaterrunoff will result both from climate-related factorsand changes in population and land use patternsrelating to supply and demand. While the reader isreferred to the Water Sector chapter for further dis-cussion of both climatic and human-inducedchanges in hydrological cycles,the close relation-ship between precipitation,streamflow, and coastalecosystems is a topic of special interest to coastalresearchers,managers,and planners.

The Canadian and Hadley climate models have beenused in concert with hydrology models to estimatethe changes in freshwater runoff for three portionsof coastline:the Atlantic,the Gulf of Mexico,and thePacific. In contrast to GCM scenarios of tempera-ture changes under the influence of increased CO2,the estimates of runoff vary widely. Wolock andMcCabe (1999) determined that for some regionsthe Hadley and Canadian climate models produceopposite results. For the Atlantic coast,the Hadleymodel projects an increase of more than 60% by the2090s,whereas the Canadian model projects arunoff decrease of about 80%. The large differencesare attributed to the projected increases in precipi-tation in the Hadley model, versus small changes tosignificant decreases in precipitation in theCanadian model during the 21st century.

Freshwater runoff affects coastal ecosystems andcommunities in many ways. The delivery of sedi -ment, nutrients,and contaminants is closely linkedto both the strength and timing of freshwaterrunoff. Salinity gradients are driven by freshwaterinputs into estuaries and coastal systems,and have

0.31˚C (0.56˚F) over that same period,which corre-sponds to an increase in heat content of approxi-mately 1 x 1023 Joules of energy. Furthermore,thewarming signal was obser vable to depths of some3000 meters (9843 feet),and the total heat contentbetween 300 and 3000 meters increased by an addi-tional 1 x 1023 Joules of energy (see Figure 5).Although Levitus et al.(2000) could not concludethat the signal was primarily one of climate change,as opposed to climate variability, they note that theirresults are in strong agreement with those projectedby many general circulation models. Earlier workdone by Cane et al.(1997) also suggest thatobserved patterns of change in ocean temperatureare consistent with warming scenarios.

Understanding how future ocean temperatures willbe affected by climate variability and change willdepend on improved understanding of the couplingbetween atmospheric and oceanic processes,andpredicting future variations in the forcing functions.The coupling between these processes is regionally


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or locally controlled,whereas the climate changemodels are usually more global. As these physicalstructures and processes,along with their naturalmodes of variability, have important implications foroverall levels of biological productivity in the ocean,an accurate assessment of potential changes inocean dynamics will necessarily be speculative untilGCMs with finer resolution of ocean processes aredeveloped.

The ecosystem responses to increased ocean tem-p e ra t u res can ch a n ge productivity both dire c t ly andi n d i re c t ly. Ocean tempera t u re ch a n ges will affe c tnot only the metabolic rate of organisms but alsosea leve l ,c u rre n t s ,m ovement of larva e ,e ro s i o nra t e s ,s u b s t rate stru c t u re s ,t u r b i d i t y, water columns t ra t i fi c a t i o n , nu t rient cycl i n g , and subsequentlyp roduction (McGowa n , et al., 1 9 9 8 ;R i c e ,1 9 9 5 ) .With population ch a n ge s ,c o m munity dynamics willch a n ge ,a l t e ring such things as pre d a t o r - p rey re l a-t i o n s h i p s . Ocean tempera t u re increases will affe c tthe distribution of marine species, l i ke ly with ap o l ewa rd migration of tropical and lower latitudeo rg a n i s m s . The result could be major ch a n ges inthe composition, f u n c t i o n , and productivity ofm a rine ecosystems, i n cluding potential impacts tom a rine biodive rs i t y. For ex a m p l e ,o b s e rvabl ech a n ges in the distribution and abundance of inter-tidal species along the Califo rnia coast have beendocumented by Sag a rin et al. (1999) which are con-sistent with wa rming tre n d s . S i m i l a r ly, l a rge inter-a n nual and interdecadal tempera t u re ch a n ges in theN o rth Pa c i fic have alre a dy been associated withch a n ges in the mixed layer depth over the Nort hPa c i fic and diminished biological pro d u c t i v i t y( M c G owan et al., 1 9 9 8 ).

Increases in temperature will also result in furthermelting of sea ice in polar and subpolar regions.Recent observations in the Arctic have alreadyshown significant declines in ice extent,which hasbeen shrinking by as much as 7% per decade overthe last 20 years (Johannessen et al.,1999) as well asice thickness,with Arctic sea ice thinning (and sub-sequently decreasing in volume) by as much as 15%per decade (Rothrock et al.,1999). Additionally,record low levels of ice extent occurred in theBering and Chukchi seas during 1998,the warmestyear on record (Maslanik et al.,1999). While a possi-ble mechanism could be related to the ArcticOscillation,a decadal scale mode of atmosphericvariability in the Arctic,some comparisons withGCM outputs strongly suggest that these observeddeclines in sea ice are related to anthropogenicallyinduced global warming (Vinnikov et al.,1999). Thereduction and potential loss of sea ice has enormous

Figure 5: A comprehensive analysis of over 5 million temperatureprofiles by Levitus, et al. (2000) reveals a pattern of warming inboth the surface and the deep ocean over the last 40 years. Thelargest warming has occurred in the upper 300 meters (984 feet),which have warmed by an average of 0.31°C (0.56°F), with addition-al warming as deep as 3000 meters (9843 feet). See Color FigureAppendix

Ocean Heat Content in the 0-3000 m Layer

feedback implications for the climate sys-tem as well;ice and snow are highlyreflective surfaces that reflect the vastmajority of the Sun’s incoming radiativeheat back to outer space. By contrast,open oceans reflect only 10 to 20% of theSun’s energy. Thus,the conversion of theArctic ice cap to open ocean could greatlyincrease solar energy absorption,and actas a positive feedback to global warming.

Ocean Currents

Major ocean current systems play a signifi-cant role in the dispersal of marine organ-isms and in the production characteristicsof marine systems. These current systemsare likely to be affected in critical ways bychanges in global and local temperatures,precipitation and runoff, and wind fields.Similarly, oceanic features such as frontsand upwelling and downwelling zoneswill be strongly influenced by variations in tempera-ture,salinity, and winds. These changes will be man-ifest on scales ranging from the relatively small spa-tial and temporal scales characteristic of turbulentmixing processes to very large scales characteristicof the deep water “conveyor belt”circulation,withpotentially dramatic feedback influences on climatepatterns. Changes occurring on this spectrum ofspatial and temporal scales have important implica-tions for overall levels of biological productivity inthe ocean,and are critical to understanding theimplications of global climate change on livingmarine resources.

Research suggests that the processes of formationand circulation of deep-water through the so-calledconveyor-belt circulation (see Figure 6) could bestrongly influenced by changes in temperature andsalinity, with significant implications for the NorthAtlantic region and global ocean circulation(Broecker et al.,1999;Taylor 1999). Generallywarm,saline surface waters are transported north-wards by the Gulf Stream,ultimately feeding theNorwegian,East Greenland,and West Greenland cur-rents. Here winter air-sea interactions cool thealready highly saline water masses, resulting in arapid increase in density. This rapid increase in den-sity drives convection,in which the heavier, denserwater sinks and flows away from the polar regionsto fill the deep ocean basins,driving deep sea ther-mohaline circulation.

Increased temperature or decreased salinity (result-ing from changes in precipitation patterns or melt-

ing ice sheets) at high latitudes could result in areduction in the deep-water formation by decreas-ing the density of surface waters,with importantconsequences for this convective system(Schmittner and Stocker, 1999;Broecker, 1997).Hadley Centre models have suggested a decline inthe strength of deep-water circulation of approxi-mately 25% under some scenarios (Wood et al.,1999). Such a decline could lead to a general cool-ing throughout the North Atlantic region, resultingfrom a reduction in transport of warmer watersfrom lower latitudes (Driscoll and Haug,1998).Additionally, a complete cessation of the conveyorbelt circulation is possible,which could cause win-ter temperatures throughout the North Atlantic tofall abruptly by as much as 9˚F (5˚C). Sedimentaryrecords in the northern Atlantic suggest that pastcirculation shutdowns have occurred in extremelyshort time intervals,associated with abrupt climateshifts and dramatic cooling in Europe. Ironically, theresult would likely be further acceleration of globalwarming trends as a result of a decrease in theoceanic uptake of carbon dioxide that would followweakening or cessation of thermohaline circulation(Sarmiento and Le Quere,1996).


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Figure 6: The ocean plays a major role in the distribution of theplanet's heat through deep sea circulation. This simplified illustra-tion shows this "conveyor belt" circulation which is driven by dif-ferences in heat and salinity. Records of past climate suggest thatthere is some chance that this circulation could be altered by thechanges projected in many climate models, with impacts to climatethroughout lands bordering the North Atlantic (Modified fromBroecker, 1991).See color figure appendix.

The Global Ocean Conveyor Belt


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KEY ISSUES1. Shoreline Systems,Erosion,and Developed

Coastal Areas2. Threats to Estuarine Health3. Coastal Wetland Survival4. Coral Reef Die-offs5. Stresses on Ocean Margins and Marine Fisheries

Coastal and marine resources are uniquely influ-enced by the long-term climate dynamics describedabove. For the purposes of this Assessment,thepotential impacts on five principal ecosystem typeswere evaluated:shorelines,estuaries,coastal wet-lands,coral reefs,and ocean margins/marine fish-eries. While there is significant overlap betweensome of these ecosystem types,and also further divi-sions that could be made within these ecosystems,this breakdown provides a methodology for under -standing what may be the most significant genericimpacts on ecological systems. These are conse-quences which are either ongoing or could be rea-sonably expected on the basis of past climate vari-ability, forcing scenarios,and change thresholds. Inaddition,individual case studies were conducted inorder to provide specific examples of the complexset of interactions between the effects of climateand human activities; results from several of thesecase studies have been incorporated here.

1. Shoreline Systems, Erosion, andDeveloped Coastal Areas

Storms,hurricanes,typhoons,and similarly extremeatmospheric phenomena along coasts produce highwinds that in turn generate large waves and cur-rents. Storms and hurricanes produce storm surgesthat temporarily raise water levels by as much as 23feet (7 meters) above normal. Although theseevents are sporadic,they are a primary cause ofbeach erosion and shoreline impacts throughout theUS. Hurricanes account for far more insured lossesof property than do other hazards such as earth-quakes and wildfires. Sea-level rise increases thevulnerability of shorelines and floodplains to stormdamage by increasing the baseline water level forextreme storms and coastal flooding events. In addi-tion to storm and flooding damages,specificimpacts associated with sea-level rise could includeincreased salinity of estuaries and freshwateraquifers,altered tidal ranges in rivers and bays,changes in sediment and nutrient transport whichdrive beach processes,and the inundation of wastedisposal sites and landfills which could reintroducetoxic materials into coastal ecosystems.

Individual hurricanes have resulted in enormouseconomic impacts,particularly to the Southeast.Hurricane Hugo in 1989 caused an estimated $9 bil-lion in damages;Hurricane Andrew in 1992 causedan estimated $27 billion in damages;and HurricaneGeorges in 1998 caused an estimated $5.9 billion indamages (Source:National Climatic Data Center).However, hurricanes are not the only storm threatto coastal inhabitants and property owners.Extratropical winter storms have significant impactsas well,such as the Halloween “nor’easter”of 1991which caused damages amounting to over $1.5 bil-lion along the Atlantic Coast. Along the PacificCoast, extratropical storms battered California caus-ing an estimated $500 million in damage during the1997-98 El Niño (Griggs and Brown,1999). Ascoastal population and property constructionincreases,the economic vulnerability of humandevelopments in coastal areas to hurricane andstorm activity will continue to rise,and will beaggravated by any climate-induced changes in thefrequencies or intensities of these events.

Coastal erosion is already a widespread problemthroughout much of the country (Figure 7),and hassignificant impacts to both undeveloped shorelinesand coastal development and infrastructure. In addi-tion to storms and extreme events,interannualmodes of variability such as ENSO have been shownto impact many shorelines. For example,along thePacific Coast,cycles of beach and cliff erosion havebeen linked to El Niño events,which elevate aver-age sea levels over the short term and alter the fre-quency, intensity, and direction of storms impactingthe coastline. During the 1982-83 and the 1997-98El Niños,impacts were especially severe alongshorelines throughout California,Oregon,andWashington (Komar, 1999;Kaminsky et al.,1999).Good (1994) has shown that along the centralOregon coast,a rapid buildup of seawalls and revet-ments routinely followed major El Niño events ofthe last two decades,as coastal property ownersattempted to protect their shorelines from increas-ing erosion.

Atlantic and Gulf coastlines are especially vulnerabl eto sea-level ri s e , as well as to ch a n ges in the fre q u e n-cy and seve rity of storms and hurri c a n e s . Most of theEast and Gulf coasts are rimmed by a series of barri e risland and bay systems which separate the ge n t lysloping mainland coastal plains from the continentals h e l f. These islands bear the brunt of fo rces fro mwinter storms and hurri c a n e s ,p rotecting the main-land from wave action. H oweve r, these islands andcoastlines are not stable but are instead highlydynamic systems that are highly sensitive and re s p o n-

s i ve to the rate of re l a t i ve sea-level rise as well as thef requency and seve rity of storms and hurri c a n e s .

In response to rising sea levels,these islands typical-ly “roll over”towards the mainland,through aprocess of beach erosion on their seaward flank andoverwash of sediment across the island. Humanactivities block this natural landward migrationthrough the construction of buildings, roads,andseawalls;as a result,shorelines erode,increasing thethreat to coastal development and infrastructure.Subsequent impacts include the destruction of prop-erty, loss of transportation infrastructure,increasedcoastal flooding,negative effects on tourism,saltwa-ter intrusion into freshwater aquifers,and impactsto fisheries and biodiversity. Such impacts willunquestionably further modify the functioning ofbarrier islands and inland waters that have alreadybeen impacted by pollution,physical modification,sediment starvation by dams,and material inputsrelated to human activities.

B a rrier islands are cert a i n ly not the only coastlinesat ri s k . P ri vate pro p e rty on mainland and estuari n es h o re l i n e s , harbor installations, other wa t e r - d e p e n d-ent activities and infra s t ru c t u re ,t ra n s p o rt a t i o ni n f ra s t ru c t u re , re c reational are a s , and agri c u l t u ra la reas are all part i c u l a r ly vulnerable to inu n d a t i o nand increased erosion as a result of climate ch a n ge ,e s p e c i a l ly in low - lying are a s . Assessing the total


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economic impacts from sea-level rise on coastala reas and on a national scale is still somewhat spec-u l a t i ve . N eve rt h e l e s s , a study by Yohe et al. ( 1 9 9 6 )q u a n t i fied the economic costs (protection plusabandonment) to coastal stru c t u res with a onemeter sea-level ri s e . This analysis estimated costs ofas mu ch as $6 billion (in 1990 dollars) betwe e n1996 and 2100. H oweve r, this number re p re s e n t sm a rke t - valued estimates only, w h i ch are deri ve df rom pro p e rt y - value appre c i a t i o n ,m a rket adapta-t i o n , and protection costs. As such , this is a mini-mum cost estimate, as it does not include the lostecosystem services value of non-market re s o u rc e s ,s u ch estuaries and tidal we t l a n d s , or the costs toc o m munities resulting from reductions in coastaleconomic activities such as fi s h i n g ,t o u ri s m ,a n dre c re a t i o n . A compre h e n s i ve rev i ew of the poten-tial cost of sea-level rise to developed coastlineswas re c e n t ly completed by Neumann et al. ( 2 0 0 0 ) ;and should be re fe rred to for a wider ra n ge of esti-mates of the potential economic consequences ofs e a - l evel rise to developed are a s .

Many coastal structures were designed with the100- year flood as their basis. This flooding leveldetermines the elevations to which the federal proj-ects are built,such as the Army Corps of Engineers

Figure 7: A general classification scheme of shoreline erosionrates throughout the US. (modified from Dolan et al., 1985). SeeColor Figure Appendix

climate va ri ability and ch a n ge . Wa rmer spri n gand fall tempera t u res will alter the timing ofseasonal tempera t u re tra n s i t i o n s , w h i ch affe c ta number of ecologi c a l ly important pro c e s s e sand will thus impact fi s h e ries and marine pop-u l a t i o n s . As re fe renced ab ove in the sectionon fre s h water fo rc i n g , the amount and timingof fre s h water f l ow into estuaries gre a t ly inf l u-ence salinity, s t ra t i fi c a t i o n , c i rc u l a t i o n , s e d i-m e n t , and nu t rient inputs. T h u s , i n c reases inw i n t e r - s p ring disch a rges in particular couldd e l i ver more excess nu t rients as well as con-taminants to estuari e s , while simu l t a n e o u s lyi n c reasing the density stra t i fi c a t i o n . Both ofthese would increase the potential for algalblooms (including potentially harmful species)and the development of hy p oxic (low ox y ge n )c o n d i t i o n s , w h i ch could in turn incre a s es t resses on sea grasses and affect commerc i a lfishing and shellfish harve s t i n g .

Currently, nutrient over-enrichment is one of thegreatest threats to estuaries in the US,with over halfthe nation’s estuaries having at least some of thesymptoms of moderate to high states of eutrophica-tion (Bricker et al.,1999). Eutrophication has multi-ple impacts to estuaries,as well as other coastal

levees that protect New Orleans. It is also the levelto which coastal structures must be built to qualifyfor flood insurance through the Federal EmergencyManagement Agency’s (FEMA) Flood InsuranceProgram. If sea level rises,the statistics used todesign these structures change. For example,whatwas once considered a 50-year flood could becomeas severe as a 100-year flood following an increasein sea level (Pugh and Maul,1999). Coastal insur-ance rates would have to be adjusted to reflect thechange in risk. Furthermore,FEMA has estimatedthat the number of households in the coastal flood-plain could increase from 2.7 million currently tosome 6.6 million by the year 2100,as a result of thecombination of sea-level rise and rapidly growingcoastal populations and development (FEMA,1991).Again,it is clear that the vulnerability of coastaldeveloped areas to natural disasters can be expect-ed to rise throughout the 21st century, even inde-pendent of climate-induced changes in risk.

2. Threats to Estuarine Health

E s t u a ries are among the most pro d u c t i vecoastal ecosystems, c ritical to the health of agreat many commercial and re c reational fi s h-e ri e s , and are affected in nu m e rous ways by


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South Florida Case Study

The natural South Florida ecosystem was largely defined by a high degree of variability in rainfall both withinand across years. The region originally supported a mosaic of multiple interactions among many differentecosystem types,including freshwater, wetland,mangrove,estuarine,and coral habitats all intimately coupledby the regional hydrology. All of these ecosystems now severely impacted by a large and very rapidly growinghuman population perched along a very narrow strip of coastal land. Tourism in South Florida is a multibil-lion-dollar-a-year industry, and the existence of the Everglades,Biscayne National Park and the Florida KeysNational Marine Sanctuary illustrate the high value society places on this unique environment.

The South Florida region is vulnerable to multiple climate change stresses,as sea-level rise, changes in the fre-quency of freezing events,hurricanes,droughts and associated fires,sea surface temperatures and many oth-ers all affect the full diversity of ecosystems. The responses of all of these ecosystems will be significantlymodified or constrained by human development. In particular, South Florida has developed one of theworld's largest water management systems with the primary objectives of dampening hydrological variability,providing flood protection,and supplying water to urban and agricultural systems (Harwell,1998;US COE1994). This alteration of hydrological functions has caused serious degradation to the ecosystems,whichwere formerly adapted to natural modes of variability but have been made more vulnerable as a result ofhuman disturbance and development.

Any significant change to the precipitation regime could have major consequences to coastal ecosystems;already the Everglades and associated systems are not considered sustainable due to regional hydrologic alter-ations. While a massive and costly restructuring of the water management system is currently underway, areduced precipitation regime could further increase multi-year droughts,increase fire frequency and intensity,reduce water supply to urban users,and increase estuarine hypersalinity. Thus, global climate change can beexpected to exacerbate the effects of natural and anthropogenic stresses on South Florida,making the currentchallenge of restoring and sustaining its ecosystems even greater.

ecosystems,including more frequent and longer last-ing harmful algal blooms,degradation of seagrassbeds and coral reefs,alteration of ecological struc-ture,decreased biological diversity, and the loss offishery resources resulting from low oxygen events.In this instance, climate change is only one aspect ofhuman-accelerated global environmental change,and particularly for estuaries,the broader effects ofglobal change have to be considered. Specifically,human activities have altered the biological availabil-ity of nitrogen through the production of inorganicfertilizer, the combustion of fossil fuel,and the man-agement of nitrogen-fixing agricultural crops. As aresult,since the 1960s the world has changed fromone in which natural nitrogen fixation was the dom-inant process to a situation in which human-con-trolled processes are at least as important in makingnitrogen available on land.

This increased availability has led to an increase inthe delivery of nitrogen to coastal marine systems,particularly estuaries (Vitousek et al.,1997). Thedelivery of nutrients has been closely linked to vari-ability in streamflow; for example,in the Gulf ofMexico,increases in freshwater delivery from theMississippi River are closely linked with increases innutrient delivery and the subsequent developmentof hypoxia. The spring floods of 1993 resulted inthe greatest nitrogen delivery ever recorded in theGulf of Mexico (Rabalais et al.,1999),and the arealextent of the resulting hypoxic zone was twice aslarge as the average for the preceding eight years.However, the response of individual estuaries tochanges in freshwater and nutrient delivery will dif-fer significantly as related to variation in water resi-dence times,stratification,and the timing and mag-nitude of inputs. Yet because the solubility of oxy-gen in warmer waters is lower than in coolerwaters,any additional warming of estuaries duringsummer months would be likely to aggravate theproblems of hypoxia and anoxia that already plaguemany estuaries.

With few exceptions,the potential consequences ofclimate change to estuarine ecosystems are not yetbeing considered in long-term estuarine and coastalzone management. In the Mid-Atlantic,estuaries arealready in a degraded environmental condition,butare currently the subject of substantial societal com-mitments for their restoration through pollutionreduction,habitat rehabilitation,and more sustain-able use of living resources. An increase in winter-spring precipitation that delivers additional nutri-ents to estuaries such as the Chesapeake Bay wouldmake achieving the management goals of reducingnutrient inputs and improving dissolved oxygen lev-

els more difficult. More efficient nutrient manage-ment practices and more extensive restoration ofriparian zones and wetlands would be required tomeet current nutrient goals in seasonally wetterwatersheds. However, it should be recognized thatclimate change is expected to bring about alter-ations to many estuaries for which mitigatingresponses may not exist.

3. Coastal Wetland Survival

Coastal wetlands are some of the most va l u abl eecosystems in the nation as well as some of the mostt h re a t e n e d . By providing hab i t a t , re f u ge , and fo rageo p p o rtunities for fishes and inve rt e b ra t e s ,m a rs h e sand mangroves around the coastal US are the basisof many commu n i t i e s ’ economic live l i h o o d s(Costanza et al., 1 9 9 7 ;M i t s ch and Gosslink, 1 9 9 3 ) .The role of wetlands in nu t rient uptake ,i m p rov i n gwater quality, and reducing nu t rient loads to thecoastal ocean is widely re c o g n i z e d , as is their va l u ein providing re c reational opportunities and pro t e c t-ing local communities from flooding — either bydampening storm surges from the ocean or prov i d-ing storage for ri ver fl o o dwa t e rs . Climate va ri ab i l i t yand ch a n ge compound existing stresses from humanactivities (Mark h a m ,1 9 9 6 ) ,s u ch as dre d ging and/orfilling for deve l o p m e n t ,n avigation or mineral ex t ra c-t i o n ,a l t e red salinity and water quality, and the dire c tp re s s u res of increasing nu m b e rs of people living andre c reating in close prox i m i t y.

These ecosystems are sensitive to a number of cli-mate related variables. Changes in atmospherictemperatures and carbon dioxide concentrationsgenerally result in increased plant production,although the response varies considerably amongspecies. Increases in freshwater discharge wouldgenerally benefit many coastal wetlands,anddecreases might result in salinity stress for somecommunities,particularly in the western Gulf ofMexico where already limited freshwater inputs areexpected to decrease dramatically. For coastal wet-lands facing current or future relative sea-level rise,increased sediment delivery will be necessary forvertical accumulation of the substrate.

Coastal wetlands can cope with changes in sea levelwhen they are capable of remaining at the same ele-vation relative to the tidal range,which can occur ifsediment buildup equals the rate of relative sea-levelrise or if the wetland is able to migrate. Migrationoccurs when the wetland moves upslope alongwith the tidal range,with the seaward edge of thewetland drowning or eroding and the landwardedge invading adjacent upslope communities


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lands become extremely difficult to restore. Theremaining 3.5 million acres of wetlands in SouthLouisiana provide critical nursery areas for finfishesand crustaceans,particularly shrimp and crabs,which make up the bulk of the state’s multimilliondollar seafood industry. Additionally, these coastalwetlands serve as important buffers against stormsurges,protecting inland residential and commercialinfrastructure from severe flooding. Thus,if climatechange exacerbates the current rate of sea-level rise,those regions of coastal Louisiana where marshesare on the margin of survival will suffer, and evenmore extensive land loss will result.

4. Coral Reef Die-Offs

Although coral reefs might seem exotic to many re s i-dents of the US, these ecosystems play a major ro l ein the env i ronment and economies of two states( F l o rida and Hawaii) as well as most US terri t o ries inboth the Cari bbean and the Pa c i fi c . C o ral reefs areva l u abl e , if often ove r - u t i l i z e d , economic re s o u rc e sfor many tropical coastal re gi o n s ,p roviding nu m e r-ous fi s h e ries opport u n i t i e s , re c re a t i o n ,t o u ri s m ,a n dcoastal protection (Wilkinson and Buddemeier,1 9 9 4 ) . It is widely recognized that reefs and re l a t e dc o m munities are also some of the largest store h o u s-es of marine biodive rs i t y, with untapped re s o u rces ofgenetic and biochemical materi a l s , and of scientifi ck n ow l e d ge (Ve ro n ,1 9 9 5 ) . F u rt h e r, the living re e fc o m munities are not isolated dots on a map, but partof an interacting mosaic of oceanic and terre s t ri a l

h abitats and commu n i t i e s , and many of the org a n-isms and processes found on reefs are impor-

tant in a mu ch wider sphere of related env i-ronments (Buddemeier and Smith,

1 9 9 9 ) . In many important way s ,the condition and re s p o n s e s

of coral reef commu n i-ties can be seen as diag-nostic of the conditionof the wo r l d ’s low - l a t i-tude coastal oceans.

Degradation of reefcommunities has been

increasing worldwide over thepast few decades,and the last few years

have seen a dramatic increase in the extent ofcoral bleaching,new emergent coral diseases andwidespread reef die-offs. Coral bleaching,whichoccurs when symbiotic algae that live in the coralsthemselves are expelled from their hosts due tohigh sea surface temperatures,has been occurringwith increasing frequency in the last severaldecades,notably during El Niño events. The 1998 El

(Figure 8). However, if wetlands are unable to keeppace with relative sea-level change,or if their migra-tion is blocked by bluffs,coastal development,orshoreline protection structures,then the wetlandwill become immersed and eventually lost as risingseas submerge the remaining habitat.

Currently, many US coastlines are areas of coastalsubsidence where both natural and human-inducedprocesses strongly influence wetlands. CoastalLouisiana has experienced the greatest wetland lossin the nation,where a combination of anthro-pogenic (human-caused) and natural factors havedriven losses between 24 and 40 square miles peryear during the last 40 years. As approximately 25%of the nation’s brackish and freshwater coastal wet-lands are found in Louisiana,this constitutes asmuch as 80% of the total loss of these wetlands inthe US (Boesch et al.,1994). Changes have occurredso rapidly in the many bald cypress forests nearNew Orleans that they have been converted directlyto open water rather than being gradually overtakenby salt marsh. Once lost to open water, these wet-


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Figure 8: The rate of sea-level rise is projected to accelerate 2 to 5fold over the next 100 years. The delivery of sediments to coastalwetlands is extremely important in determining the potential ofthese systems to maintain themselves in the face of current andfuture sea-level changes (based on Reed, 1995). See Color FigureAppendix

Processes Affecting Wetland Migration

Niño in particular was associated with unprecedent-ed high sea surface temperatures and thus the mostwidespread coral bleaching ever observed (Stronget al.,2000;Wilkinson et.al.,1999;Hoegh-Guldberg,1999). In many past bleaching events,both thealgae and the corals are capable of recovery;howev-er, warming events in 1998 resulted in unusuallyhigh levels of mortality from which many reefs haveyet to recover. In addition to bleaching ef fects,there has been an upsurge in the variety, incidence,and virulence of coral diseases in recent years,withmajor die-offs reported,particularly in Florida andthe Caribbean region. The causes of these epi-zootics are not known,but they suggest that coralecosystems and organisms are weakened and vul-nerable.

One of the most significant unanticipated directconsequences of increased atmospheric carbondioxide concentration is the reduction of carbonateion concentrations in seawater. Carbon dioxide actsas an acid when dissolved in seawater, causing sea-water to be less alkaline. A drop in alkalinity subse-quently decreases the amount of calcium carbonate(aragonite) which can be dissolved in seawater,which in turn decreases the calcification rates ofreef-building corals and coraline algae (Figure 9)(Kleypas et al.,1999a;Gattuso,1999). The impactson coral reefs are weaker skeletons, reduced growthrates,and an increased vulnerability to erosion,witha wide range of impacts on coral reef health andcommunity function. Additionally, the effects ofincreasing atmospheric carbon dioxide on the con-centration of carbonate ions is greatest at the mar-gins of coral distributions,due to the fact that car-bon dioxide is more soluble in cooler waters. Thus,these effects will be most severe at high latitudes,socoral reefs at the margins of their distribution arenot expected to expand their ranges as might other-wise be predicted by some ocean warming scenar-ios (Figure 10).

Human-induced disturbances have already taken asignificant toll on coral reef systems,from activitiessuch as over-fishing,the use of destructive fishingtechniques, recreational activities,ship groundings,anchor damage,sedimentation,pollution,andeutrophication. Thus,the future for many coral reefsappears bleak. The synergy of stresses and theresponse time scales involved to restore reefs makeintegrated management essential but dif ficult. Giventrends already in motion,some of the more marginalreef systems will almost certainly continue to deteri-orate,making allocation of resources an importantpolicy issue. The demise or continued deteriorationof reef communities will have profound social and

economic implications for the US,as well as seriouspolitical and economic implications for the world.

5. Stresses on Ocean Margins andMarine Fisheries

Projected changes in the marine environment haveimportant implications for marine populations andfisheries resources. In addition to their economicvalue,marine fisheries hold a special social and cul-tural significance in many coastal communities.However, over-fishing and habitat loss have alreadytaken serious tolls on the nation’s fisheries and thecommunities that depend upon them. Currentlysome 33% of the stocks for which trends are knownare either over-fished or depleted (NMFS,1998),andfor the vast majority of stocks,an accurate assessmentof their status is unknown. The possible effects of cli-mate change range from shifts in distribution to


477

Figures 9: Increasing levels of atmospheric CO2 are projected todecrease carbonate ion concentrations in seawater, which willdecrease the calcification rates of many coral building species andimpact coral reef health (Gattuso et al., 1999).

Bleached coral.

Effects of CO2 on Coral


478

changes in survival and growth rates,with directimplications for fishery yields.

Changes in climate forcing will have importanteffects in ocean margin ecosystems through expect-ed changes in the distribution and abundance ofmarine organisms and in fundamental changes inthe production characteristics of these systems.Changes in temperature,precipitation,wind fields,and sea level can all be expected to affect oceano-graphic conditions in the ocean margins with directramifications for marine life in these areas.Physiological effects of temperature and salinitychanges can also be expected with potentiallyimportant consequences for growth and mortalityof marine species (Jobling,1996). Impacts tomarine ecosystems and fisheries associated with ElNiño events illustrate the extent to which climateand fisheries can interact. For example,the high sea

surface temperatures and anomalous conditionsassociated with the 1997-98 El Niño had a tremen-dous impact on marine resources off of Californiaand the Pacific Northwest. Landings of marketsquid,California’s largest fishery by volume and sec-ond largest in value, fell from over 110,000 metrictons in the 1996-97 season to less than 1000 metrictons during the 1997-98 El Niño season (Kronman,1999). Amongst the many other events associatedwith this El Niño were high sea lion pup mortalitiesin California (Wong,1997),poor reproductive suc-cess in seabirds off of Oregon and Washington,andunexpected catches of warm-water marlin off of theWashington coast (Holt,1997). Even further northwere rare coccolithophore blooms,massive seabirddie-offs along the Aleutian Islands,and poor salmonreturns in Alaska’s Bristol Bay sockeye salmon fish-ery (Macklin,1999).

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)Figure 10: Map of current and projected changes in calciumcarbonate saturation in ocean surface waters. Corals requirethe right combination of temperature, light, and calcium car-bonate saturation. At higher latitudes, there is less light andlower temperatures than nearer the equator. The saturationlevel of calcium carbonate is also lower at higher latitudes,in part because more CO2, an acid, can be dissolved in cold-er waters. As the CO2 level rises, this effect dominates,making it more difficult for corals to form at the polewardedges of their distribution. These maps show model resultsof the saturation level of calcium carbonate for pre-industri-al, present, and future CO2 concentrations. The dots indi-cate present coral reefs. Note that under model projectionsof the future, it is very unlikely that calcium carbonate satu-ration levels will provide fully adequate support for coralreefs in any US waters. The possibility of this future sce-nario occurring demands continued research on effects ofincreasing CO 2 on entire coral reef systems. Classificationintervals for saturation effects on reef systems are derivedfrom Kleypas et al. (1999b). See Color Figure Appendix


479

Climate change is likely to cause even greaterimpacts to marine populations. Poleward shifts indistribution of marine populations can be expectedwith increasing water temperatures (Murowski,1993). Species at the southern extent of their rangealong the East Coast can be expected to shift theirdistribution to the north with important overall con-sequences for ecosystem structure. Cod,Americanplaice,haddock,Atlantic halibut, redfish,and yellow-tail flounder all would be expected to experiencesome poleward displacement from their southerlylimits in the Gulf of Maine and off New Englandunder increasing water temperatures (Frank et al.,

1990). Thus,the loss of populations or sub-popula-tions due to shifts in temperature under these con-straints is likely, with regional impacts to communi-ties that depend on local populations. An expansionof species commonly occurring in the middleAtlantic region,such as butterfish and menhaden,into the Gulf of Maine could also be expected.

In the Pacific,Welch et al.(1998) suggest that pro-jected changes in water temperatures in the NorthPacific could possibly result in a reduction of suit-able thermal habitat for sockeye salmon. The mostsurprising prediction is that under scenarios of

Understanding Global Climate and Marine Productivity

The US Global Ocean Ecosystems Dynamics (US GLOBEC) research program is operated in collaborationbetween the NOAA/National Ocean Service (NOS) Coastal Ocean Program and the NSF BiologicalOceanography Program. GLOBEC is designed to address the questions of how global climate change mayaffect the abundance and production of marine animals. Two large marine regions have been the subjects ofintensive research,the Northwest Atlantic and the Northeast Pacific. In the Atlantic program,the overall goalis to improve the predictability and management of the living marine resources of the region. This is beingdone through improved understanding of ecosystem interactions and the coupling between climate change,the ocean's physical environment and the ecosystem components (Figure 11). Particularly crucial physicaldrivers are the North Atlantic Oscillation and the salinity variations derived from flows from the Labrador Sea.A major objective of this program is to apply the understanding of the physical processes that affect the dis-tribution, abundance and production of target species. This information will be used in the identification ofcritical variables that will support ecosystem-based forecasts and indicators as a prelude to the implementa-tion of a long-term ecosystem monitoring strategy.

Remarkable changes have been observed in recentdecades in the Northeast Pacific. Concurrentchanges in atmospheric pressure and ocean temper-atures indicate that in 1976 and 1977 the NorthPacific shifted from one climate state or regime toanother that persisted through the 1980s. Analysisof records of North Pacific sea surface temperatureand atmospheric conditions show a pattern of suchregime shifts lasting several years to decades.Although the important linkages are poorly under-stood,there is growing evidence that biological pro-ductivity in the North Pacific responds quite strong-ly to these decadal-scale shifts in atmospheric andoceanic conditions by alternating between periodsof high and low productivity. Some of the keyissues being addressed in this region concern theevaluation of life history patterns,distributions,growth rates,and population dynamics of highertrophic level species and their direct and indirectresponses to climate variability. Additionally, theprogram seeks to better understand complexecosystem interactions,such as how the NorthPacific ecosystem is structured and whether highertrophic levels respond to climate variability solely asa consequence of bottom-up forcing.

Figure 11: Biological processes in the ocean are related to climatein many ways, both directly and indirectly. Improvements in ourunderstanding of the direct and indirect effects of climate on bio-logical processes in the oceans are essential to predicting howmarine populations might respond to future change Source: USGLOBEC.

Climatic Pathways Affecting the AbioticEnvironment and Biological Processes


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For example, changes in the abundance of sardineand anchovy populations appear to be stronglylinked to global climate shifts (Lluch-Belda et al.,1992). The California sardine population wasrecently declared “recovered,” decades after its neardisappearance from Pacific waters. The recoveryhas in part been related to an increase in sea surfacetemperatures off the Pacific Coast observed over thelast 20 years (California Department of Fish andGame,1999). Sardines are once again found in large

future climate,none of the Pacific Ocean is project-ed to lie within the thermal limits that have definedthe distribution of sockeye salmon over the last 40years. Under such scenarios,the distribution of allspecies of salmonids could be restricted to marginalseas in the North Pacific region (see also the PacificNorthwest chapter and Mantua et al.1997 for moreinformation on interactions between salmon and cli-mate variability). Conversely, higher sea surfacetemperatures will be beneficial for other species.

Predicting Coastal Evolution at Societally-Relevant Time and Space Scales

One of the most important applied problems in coastal geology today is determining the response of thecoastline to sea-level rise. Prediction of shoreline retreat and land loss rates is critical to the planning offuture coastal zone management strategies,and assessing biological impacts due to habitat changes or destruc-tion. Presently, long-term (~50 years) coastal planning and decision-making has been done piecemeal,if at all,for the nation's shoreline. Consequently, facilities are being located and entire communities are being devel-oped without adequate consideration of the potential costs of protecting them from or relocating them dueto sea-level rise-related erosion, flooding and storm damage.

The prediction of future coastal evolution is not stra i g h t fo r wa rd . T h e re is no standard methodology, and eve nthe kinds of data re q u i red to make such predictions are the subject of mu ch scientific debate. A number of pre-d i c t i ve appro a ches could be used, i n cl u d i n g : 1) ex t rapolation of historical data, ( e .g . , coastal erosion ra t e s ) ,2 )i nundation modeling, 3) application of a simple ge o m e t ric model (e. g . , the Bruun Rule), 4) application of a sedi-

ment dy n a m i c s / b u d get model, or 5) MonteCarlo (pro b abilistic) simu l a t i o n . E a ch of thesea p p ro a ch e s ,h oweve r, has its shortcomings orcan be shown to be invalid for certain applica-t i o n s . S i m i l a r ly, the types of input datare q u i red va ry widely, and for a gi ven appro a ch( e .g . , sediment budge t ) , existing data may bei n d e t e rminate or simply not ex i s t .

The relative susceptibility of different coastalenvironments to sea-level rise,however, maybe quantified at a regional to national scale(e.g.,Gornitz et al.1994) using basic data oncoastal geomorphology, rate of sea-level rise,and past shoreline evolution (Figure 12). Apilot project is underway at the USGeological Survey, Coastal and MarineGeology Program to assess the susceptibilityof the nation's coasts to sea-level rise from ageologic perspective. The long-term goal ofthis project is to predict future coastalchanges with a degree of certainty useful tocoastal management, following an approach

similar to that used to map national seismic and vol-canic hazards. This information has immediateapplication to many of the decisions our society willbe making regarding coastal development in boththe short- and long-term.

Figure 12: These preliminary results illustrate the relative vulnera-bility to sea-level rise along the New York and New Jersey coastlineas assessed by ongoing USGS research. Note that the vulnerabilitymapped here is likely to change as methodologies in this pilot pro-gram are critically evaluated and improved (Source: USGS). SeeColor Figure Appendix

numbers as far north as British Columbia(Hargreaves et al.,1994),and their recovery has ledto a concurrent resurgence of the fishery long agoimmortalized in John Steinbeck’s Cannery Row.

ADAPTATION STRATEGIESAssessing the effects of climate variability andchange on coastal and marine resources is especiallydifficult given that human activities are generallyresponsible for the greatest impacts on coastal andmarine environments. The nature of climate effects— both detrimental and beneficial to resources inquestion — are likely to vary greatly in the diversecoastal regions of the US. Anthropogenic distur-bance often results in a reduction in the adaptivecapacity of systems to cope with change and stress,making the real or potential impacts of climate diffi-cult to observe. It is in this context that climatechange acts as an increased stress on coastal andmarine environments,adding to the cumulativeimpact of both natural and anthropogenic stress onecological systems and resources.

This is most abundantly clear in coral reef systems.Coral reefs,both in US waters and worldwide,areclearly stressed,and many are degraded to the pointof destruction. The prospects for the future are thatin many, if not most,instances,the levels of both cli -mate-related stress and local or regional stress result-ing from anthropogenic impacts will increase. Theimplication for coral reefs is that local and regionalreef protection and management efforts must beeven more effective in controlling local stresses,toprovide some compensation for large scale impacts.If local and regional anthropogenic stresses contin-ue or increase,many of the reefs that are heavilyused or affected by humans will be poor candidatesfor survival. This would result in substantial impactsto the communities and regional economies thatdepend upon healthy reefs for fisheries,subsistence,recreation,and tourism.

For responding or adapting to sea-level rise,threegroups of strategies have been discussed,thesebeing:(planned) retreat,accommodation,and pro-tection (IPCC,1996). A retreat strategy would pre-vent or discourage major developments in vulnera-ble coastal areas and could include rolling ease-ments,which allow development but explicitly pre-vent property owners from preventing the uplandmigration of wetlands and beaches. An accommoda-tion strategy might elevate land surfaces or humanstructures,modify drainage systems,or otherwisechange land use practices,thus allowing many

coastal ecosystems to be maintained. A protectionstrategy could utilize beach nourishment and dunestabilization,as well as dikes,seawalls,bulkheads,and revetments,to form a barrier between waterand land. This might generally lead to a loss of natu-ral functions for beaches, wetlands,and other inter-tidal zones,but would be capable of roughly main-taining the coastline in place.

In areas where beaches or wetlands must migrateinland in response to sea-level change,it has beenshown that planning and implementing protectionor retreat strategies for coastal developments cansubstantially reduce the long-term economicimpacts of inundation and shoreline migration.While some regulatory programs continue to permitstructures that block the migration of wetlands andbeaches,others have tried to decrease economicmotivations for developing in vulnerable areas,orhave experimented with retreat strategies. Forexample,coastal management programs in Maine,Rhode Island,South Carolina,and Massachusettshave implemented various forms of rolling easementpolicies in an attempt to ensure that wetlands andbeaches can migrate inland as sea-level rises. Severalother states require coastal counties to consider sea-level rise in their coastal management plans.However, the difficulties and obstacles facing coastalmanagers in effectively implementing setback androlling easement policies are substantial. Many ofthe programs initiated to date are not mandatory,and the effectiveness of state coastal zone manage-ment programs often varies significantly.

While the potential impacts of sea-level rise havebegun to initiate concern and some discussion ofpotential response strategies,the broader ramifica-tions of changes in temperature,freshwater dis-charges,and the frequency and intensity of stormevents,have scarcely been assessed. For example,inestuaries such as Chesapeake Bay, a particular focusof restoration efforts is the reduction of nutrientover-enrichment,or eutrophication,from both pointdischarges and diffuse sources throughout thewatersheds draining into the estuaries. However,efforts to reduce eutrophication will have to con-tend with multiple climate change-related problemssuch as sea-level rise,increased winter-spring dis-charges but reduced summer runoff, warmer seasurface temperatures,and greater shoreline erosion.

For marine fisheries,adaptations to changes in theproduction characteristics of exploited populationswill include adjustments in the recommended har-vest levels and/or exploitation rates and in the sizeor age at which fish and invertebrate populations


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attempts to manage or mitigate the effects of cli-mate must be tightly coupled with management ofhuman behavior at all spatial and temporal scales.Most importantly, those who are or will likely beaffected by climate impacts must be made aware ofthe risks and potential consequences that futurechange will pose to their communities and theirlivelihoods.

CRUCIAL UNKNOWNS ANDRESEARCH NEEDSDirect human impacts dominate the changes occur-ring in most coastal areas,making it difficult to sepa-rate climatic effects from these direct stresses. Inmost areas,study of climate-related coastal impactsis only beginning. Consequently, for nearly allcoastal and marine ecosystems considered in thisAssessment,knowledge is inadequate to assesspotential impacts fully and to determine effectiveadaptations. The Assessment has identified siximportant areas for research related to climateimpacts on coastal and marine systems.

Coastal Hazards and the Physical Transformations ofCoastlines and Wetlands. The significant erosion ofbeach fronts,barrier islands,and coastal marshes,coupled with accelerated sea-level rise,increases thevulnerability of coastal life and property to stormsurge. Regardless of projected changes in the fre-quency and severity of coastal storms (hurricanesand nor’easters),storms will be riding on a highersea level in the future. Research and assessmentsare needed to fully evaluate the vulnerability ofhuman and natural coastal systems to the combinedeffects of sea-level rise,land subsidence,and stormsurge. This information is required for rationalresponses in coastal protection,setbacks,and mitiga-tion approaches to sustaining coastal wetlands.

Changes in Freshwater Loads to Coastal Ecosystems.Because of the importance of changes in land-usepatterns and freshwater inflow to coastal ecosys-tems,particularly estuaries and wetlands,and to keyspecies like Pacific salmon,considerable effort isneeded to improve assessments of the impact ofchanges in the extent and timing of freshwaterrunoff. While contemporary GCM estimates ofpotential runoff vary widely, it is clear that changesare likely to occur and that the impacts could besubstantial. Thus,new research is needed to assessthe consequences of changes in runoff and theattendant changes in nutrient,contaminant,and sed-iment supply, circulation,and biological processes.

are first harvested. The limiting level of exploitation(which is the rate at which the risk of populationcollapse is high) for a population is directly relatedto the rate of recruitment at low abundance levels.Thus,environmental changes that result in a reduc-tion in recruitment rates must be countered byreductions in exploitation rates. Conversely, somehigher levels of exploitation should be sustainablefor some stocks under favorable environmental con-ditions. Adaptation to changes in the compositionof fish stocks will also be necessary; regional mar-kets will undoubtedly have to adjust to shifts inspecies composition due to changes in the availabili-ty of different species. Additionally, changes in dis-tribution are likely to lead to more complex con-flicts regarding the management of transboundarystocks and species.

Although much remains to be learned in order toconfidently project impacts of climate change oncoastal areas and marine resources,the trends andrelationships already apparent suggest that the man-agers,decision makers,and the public must take cli-mate change impacts into account. To be success-ful,this will have to be done in the context ofcoastal and resource management challenges alreadybeing addressed, for example:

• Strategic adaptation of coastal communities (e.g.,barrier islands and other low-lying areas) to sea-level rise and increased storm surge.

• Adaptive management of coastal wetlands toimprove their prospects of soil building to keepup with sea-level rise and allow their migrationover adjacent lowlands.

• Comprehensive and forward-looking water useand management policies that factor in require-ments for coastal ecosystems,such as reducednutrient and pollutant delivery.

• Control procedures to reduce the risk of inva-sions by non-indigenous species.

• Fishery management regimes that incorporateknowledge of fluctuations in productivity andpopulations resulting from varying modes of cli-matic variability.

• Controls on impacts such as runoff from landand unsustainable fishing pressures that reducethe resilience of coral reef ecosystems.

In general,many of the strategies which might beappropriate for coping with future climate changehave been or are currently being discussed or imple-mented in response to current stressors on coastaland marine environments. The future impacts of cli-mate will be deeply integrated with the ongoingimpacts resulting from human activities;thus,


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Decline of Coral Ecosystems. The decline of coralecosystems is significant and global. Contributionsto this decline include changes in ocean tempera-tures,levels of atmospheric CO2, and a series ofmore direct anthropogenic stress (e.g., over-fishing,eutrophication,and sedimentation). Increased effortis needed to adequately understand and predict thecumulative effects of these multiple stresses oncoral ecosystems. It is important in this work to rec-ognize the significance of the full ecosystem(including e.g.,sand beds,sea grasses,and the watercolumn) associated with corals,and not only thecoral reefs alone.

Alterations and Geographic Shifts in MarineEcosystems. Changes in ocean temperature and cir -culation (e.g.,ENSO, PDO, and NAO),coupled withchanges in nutrient supplies (driven by changes infreshwater fluxes and arctic ice dynamics),are likelyto modify patterns of primary productivity, the dis-tribution and recruitment success of marine fish,thereproductive success of protected species,and theeconomic viability of marine fisheries. Whileresearch on environmental variability and marineecosystems is advancing (e.g.,in GLOBEC),the cur-rent effort is limited to relatively few importantregional ecosystems. More research is needed tounderstand and predict potential changes andregional shifts for all important coastal and USmarine ecosystems,including the socioeconomicimpacts to fishing communities.

Loss of Arctic Sea Ice. Loss of sea ice in Arcticre gions will have widespread re gional impacts oncoastal env i ronments and marine ecosystems.Recent dramatic reductions in the extent of sea icein the A rctic Ocean and Bering Sea have led tom o re seve re storm surges because the larger openwater areas are capable of ge n e rating mu ch large rwave s . This has led to unprecedented ero s i o np ro blems both for Native villages and for oil andgas ex t raction infra s t ru c t u re along the Beaufo rt Seac o a s t . Reductions in sea ice also result in a loss ofc ritical habitat for marine mammals such as wa l ru sand polar bears , and significant ch a n ges in the dis-t ribution of nu t rients supporting the base of thefood we b . R e s e a rch to better understand howch a n ging ice re gimes will affect the productivity ofpolar ecosystems, and to assess the long-term con-sequences of these impacts is essential, both tosustain marine ecosystems and to develop copings t ra t e gies for the Native communities that dependon hunting for their food and other aspects oftheir culture .


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ACKNOWLEDGMENTSSpecial thanks to:

Jim Allen,Paul Smith CollegeDonald Cahoon,US Geological SurveyBenjamin Felzer, National Center for Atmospheric

ResearchMichael MacCracken,US Global Change Research

ProgramLaShaunda Malone,US Global Change Research

ProgramMelissa Taylor, US Global Change Research Program Rob Thieler, US Geological SurveyElizabeth Turner, National Oceanic and Atmospheric

AdministrationJustin Wettstein,US Global Change Research

Program


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coastal areas and marine resources (chapter 16) of the ...€¦ · 461 chapter 16 potential...

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