Global Warming’sIncreasingly Visible Impacts

Global Warming’s IncreasinglyVisible Impacts

AUTHORS

Dr. James Wang

Dr. Bill Chameides

AcknowledgmentsWe would like to thank Dr. Michael Oppenheimer (Princeton Univ.), Dr. Tim Male,Annie Petsonk, Peter Goldmark and Melissa Carey for reviewing this report. EricaRowell, Allan Margolin and Elizabeth Thompson provided helpful comments andsuggestions. Lauren Sacks, Deepali Dhar, Valentin Bellassen and Alena Herklotzprovided valuable assistance with researching and drafting parts of the report. Thanksgo to Miriam Horn for the editing work, Bonnie Greenfield for the design and pro-duction, and Sarah Stevens, Jennifer Coleman and Tim Connor for assistance inobtaining images.

Cover images: Ray Berkelsman, CRC Reef, Townsville (bleached corals), BryanDahlberg/FEMA News Photo (wildfire), U.S. Fish and Wildlife Service (Arctic fox)

Our missionEnvironmental Defense is dedicated to protecting the environmental rights of allpeople, including the right to clean air, clean water, healthy food and flourishingecosystems. Guided by science, we work to create practical solutions that win lastingpolitical, economic and social support because they are nonpartisan, cost-effectiveand fair.

©2005 Environmental Defense

The complete report is available online at www.environmentaldefense.org.

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Signs of global warming in the United States, region by region iv

Executive summary v

Introduction 1

Part I: Extreme events 3Killer heat waves 3Torrential rains and flooding 4Drought 5Forests and wildfires 7

Part II: Sea level rise and coastal flooding 10

Part III: Snow, land ice and sea ice 13Shrinking snowpack 13Vanishing glaciers 13Polar ice disintegration 16Melting permafrost and damage to infrastructure 17

Part IV: Ecological impacts 19Damage to coral reefs 19Shifting species ranges and yearly cycles 20Declining Arctic animal populations 20Declining amphibian populations 22

Part V: Outbreaks of vector-borne diseases 24

Conclusion 26

References 27

Contents

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Southeast/South-Central/Caribbean Islands• Smoke from record wildfires in Mexico

triggers health alert in Texas, 1998.Part I, “Forests and wildfires,” page 7.

• Loss of nearly 1 million acres ofwetlands in Louisiana due in part tosea-level rise. Part II, page 10.

• Coral bleaching in consecutive yearsobserved for the first time in FloridaKeys 1997–1998. Part IV, “Damage tocoral reefs,” page 19.

Northeast/Mid-Atlantic• Loss of large areas of wetlands in

Chesapeake Bay. Part II, page 10.

Midwest/Plains• Deadly Chicago heat wave, 1995.

Part I, “Killer Heat Waves,” page 3.

Rocky Mountains/Southwest• One of the worst droughts in 500 years

in the West, 1999-2004. Part I,“Drought,” page 5.

• Worst wildfire season in 50 years inthe West, 2000. Part I, “Forests andwildfires,” page 7.

• 16% decline in snowpack in theRockies; Spring snow melt beginsnine days earlier. Part III, “Shrinkingsnowpack,” page 13.

• Dramatic shrinkage of glaciers inGlacier National Park. Part III,“Vanishing glaciers,” page 13.

• Outbreaks of hantavirus in the pastdecade linked to heavy rains. Part V,page 24.

Pacific Coast/Hawaii/Pacific Islands• 29% decline in snowpack in the

Cascades; streamflow throughout

Signs of global warming in the United States, region by region

Sierra Nevada peaks 3 weeks earlier.Part III, “Shrinking snowpack,” page 13.

• South Cascade Glacier in Washingtonat smallest size ever in the last 6,000years. Part III, “Vanishing glaciers,”page 13.

• Decline in populations of mountainamphibians in Pacific Northwest.Part IV, “Declining amphibian popu-lations,” page 22.

• First large-scale coral bleaching eventever documented in Hawaii in 1996.Part IV, “Damage to coral reefs,” page 19.

Alaska• World's largest recorded outbreak of

spruce bark beetles, 1990s. Part I,“Forests and wildfires,” page 7.

• Worst fire season in 2004; record levelsof unhealthful smoke particles. Part I“Forests and wildfires,” page 7.

• Shrinkage and thinning of sea iceaffecting traditional hunting. Part III,“Polar ice disintegration,” page 16.

• Damage to houses, roads, and villagesand disruption of mining activities bymelting permafrost. Part III, “Meltingpermafrost and damage to infrastructure,”page 17.

• Decline in caribou populations due toearlier spring. Part IV, “Declining Arcticanimal populations,” page 20.

Nationwide• Increase in frequency of intense

precipitation events. Part I, “Torrentialrains and flooding,” page 4.

• Sea level rise averaging 4 to 8 inchesover 20th century. Part II, page 10.

• Migrations and shifts in yearly cyclesof plants and animals, including manybutterfly species. Part IV, “Shiftingspecies ranges and yearly cycles,” page 20.

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Global warming will not only be felt manydecades from now—it is already happen-ing and its impacts are clearly visible. Thispaper gathers examples from the peer-reviewed scientific literature of recentimpacts around the world. These includeincreases in extreme weather events, risingsea level, disappearing glaciers and polarice, damaged coral, changes in wildlifedistributions and health, and increasedactivity and abundance of disease vectors.Although a direct link to global warmingis difficult to establish for some of thesephenomena in isolation, the multitude ofchanges collectively provide clear evidenceof the immediate and growing danger thatglobal warming poses to the economy,human health, and the ecosystems uponwhich humans and other species depend.Since greenhouse gas pollution stays inthe atmosphere for decades or centuries,humanity may have no more than a dec-ade left to begin stabilizing the climate toavert devastating and irreversible impacts.Such an achievement will require a con-certed effort among all nations.

The following are highlights of theglobal warming impacts described inthis report. For readers particularlyinterested in the United States, weinclude, preceding this Executive Sum-mary, a listing of domestic impacts byregion. (For a comprehensive rebuttal ofskeptics’ claims regarding the science ofglobal warming, see our earlier report,The Latest Myths and Facts on GlobalWarming, available at http://www.undoit.org/what_is_gb_myth.cfm.)

In brief, this is what the scientificstudies show:

• Killer heat wavesHuman-caused global warming mayhave already doubled the chance of“killer” heat waves like the one that hit

Executive summary

Europe in July and August of 2003. Thatsummer was very likely the continent’shottest in 500 years. The relentless heatkilled at least 27,000 people, breakingall records worldwide for heat-inducedhuman fatalities. The heat and associateddrought and wildfires cost Europeaneconomies more than $14.7 billion(13 billion euros) in losses in the agricul-ture, forestry, and electric power sectors.

Records have been shattered in otherparts of the world as well in recent years.In April-June 1998, 3,028 people diedin the most disastrous heat wave to everhit India. In 1995, a five-day heat wavecaused 525 deaths in Chicago, with the106°F (41°C) reading on July 13 thewarmest July temperature ever measured.

• Torrential rains and floodingAccording to the available data, globalwarming has increased the intensity ofprecipitation events over recent decades.In December 1999, for instance, Vene-zuela saw its highest monthly rainfall in100 years, with massive landslides andflooding that killed approximately 30,000people. On two days in the city of Mai-quetia, rains fell with an intensity nor-mally experienced just once in 1,000 years.

• Drought, forest pests, and wildfires From 1998 to 2002, below-normalprecipitation and high temperaturesresulted in droughts covering wideswaths of North America, southernEurope, and southern and central Asia.Drought continued in some regionsthrough 2004, including the westernU.S., which endured the most severedrought in 80 years and one of the mostsevere in 500 years. The worldwidedrought has been linked to unusuallywarm waters in the Indian Ocean andwestern Pacific, which many scientists

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believe to be caused in part by globalwarming.

Insect pests are spreading to forestspreviously too cold for their survival;Alaska, for instance, had in the 1990sthe world’s largest recorded outbreak ofspruce bark beetles.

Drought, heat, and insect attackspromote severe forest fires. In 2004,Alaska had its warmest and third driestsummer, resulting in its worst fire yearon record, with fires consuming an areaof forest the size of Maryland. All told,over the past 30 years, the area burnedannually by wildfires in the Arctic regionof western North America has doubled.In Russia, the area of forest burned annu-ally more than doubled in the 1990scompared to the previous two decades.

• Rising sea levelSea-level rise is one of the most certainimpacts of global warming. During the20th century, sea levels around the worldrose by an average of 4 to 8 inches (10 to20 cm), ten times the average rate over thelast 3,000 years. That rise is projected tocontinue or accelerate further, with pos-sible catastrophic increases of many metersif the ice sheets on Greenland and/orAntarctica collapse. Already, one-third ofthe marsh at Blackwater National Wild-life Refuge in the Chesapeake Bay hasbeen submerged under the sea, and theedges of mangrove forests in Bermuda arelined with recently drowned trees. If sealevel continues to rise, thousands of squaremiles of land in densely populated areassuch as the eastern U.S. and Bangladeshmay be lost, and flooding during stormsurges will worsen. Construction ofphysical barriers such as seawalls would beexpensive and in some cases unfeasible.

• Shrinking snowpack andvanishing glaciersMountain snowpack constitutes a criti-cal reservoir of fresh water, as well as the

basis for the four-and-a-half billiondollar U.S. ski industry. Over the past50 years, spring snowpack has dimin-ished by 16% in the Rocky Mountainsand 29% in the Cascade Range, duemainly to rising temperatures. Further-more, springtime snowmelt in thewestern U.S. now begins 9 days earlieron average, lowering stream levelsduring the dry summer months. It willbe extremely difficult to solve the prob-lem of crippling, long-term water short-ages in the West without addressingglobal warming.

In almost every mountainous regionacross the world, glaciers are retreatingin response to the warming climate. Theshrinkage of glaciers is already creatingwater shortages, and threatening tour-ism in scenic parks. In one basin inGlacier National Park in Montana, forinstance, two-thirds of the ice has dis-appeared since 1850; with uncontrolledwarming, the remaining glaciers coulddisappear by 2030. In the EuropeanAlps, ice that had hidden and preservedthe remains of a Stone Age man meltedfor the first time in 5,000 years. Vene-zuela had six glaciers in 1972, but nowhas only two; these too will melt awayin the next ten years. In the PeruvianAndes, glacial retreat has acceleratedsevenfold over the past four decades.In Africa, 82 percent of the ice onMt. Kilimanjaro has disappeared since1912, with about one-third meltingin just the last dozen years. In Asia,glaciers are retreating at a record pace inthe Indian Himalaya, and two glaciersin New Guinea will be gone in a decade.

• Disintegrating polar ice andmelting permafrostSince 1950, the Antarctic Peninsulahas warmed by 4°F (2°C), four timesthe global average increase. In 2002,a Rhode Island-sized section of theLarsen B ice shelf, which sits offshore

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of the Peninsula, disintegrated in only35 days. The ice shelf acts as a dam forglaciers on land; its break-up is causinga worrisome speed-up of glacier flowinto the ocean, which could raise globalsea level.

In 2003 the Ward Hunt Ice Shelf,the largest in the Arctic, broke in two,draining a unique freshwater lake thatwas home to a rare microbial ecosystem.Since the 1950s, the surface area of theArctic’s sea ice has shrunk by 10 to 15%in spring and summer, and the ice hasthinned by about 40% in late summerand early autumn. In a turn for theworse, the years 2002–2005 have allseen record or near-record low icecoverage. The Hudson Bay has beenparticularly hard hit, with the sea-iceseason shortened by three weeks. Thereduced time for hunting ice-dwellingseals is seriously damaging the health ofthe bay’s polar bears and causing themto have 15% fewer cubs. At present ratesof shrinkage, Arctic sea ice could soonpass a point of no return, disappearingcompletely each summer by the endof this century and pushing polar bearsto the brink of extinction everywhere.Shrinking and thinning ice has alsomade hunting of seals and other foodsources more challenging and accident-filled for humans. Continued warmingcould destroy traditional societies.

Because the permafrost on whichthey are built is melting, buildings androads in Alaska have been sinking andbreaking up. The 4,000 year-old Eskimovillage of Shishmaref has been so severelyeroded by ocean waves that the entirecommunity was forced to relocate.

• Damage to coral reefsThe past 25 years have witnessed ahigher incidence around the world oflarge-scale coral “bleaching” events, whichcan lead to coral death. In 1997–98alone, the largest bleaching event on

record seriously damaged 16% of thereefs in the world and killed 1,000-year-old corals. Mass bleachings are usuallycaused by excessively high temperatures.Scientists therefore attribute the increasein bleaching events to the rise in averagesurface ocean temperatures in manytropical regions by almost 2°F (1°C)over the past century. Within the nextfew decades, continued warming couldcause mass bleachings to become anannual event, wiping out some reefspecies and ecosystems along with thefood, tourism income, and coastlineprotection they provide. Corals are alsodirectly threatened by increasing atmo-spheric concentrations of carbon dioxide,which is acidifying seawater and makingit more difficult for corals to build theircalcium carbonate skeletons.

• Shifting species ranges and yearlycyclesOf over 1,400 species analyzed, rangingfrom fish and mammals to grasses andtrees, over 80% are migrating to higherlatitudes or higher elevations andaltering their annual routines inresponse to global warming. Over time,this could cause disruptive ecologicaland economic changes, such as thedisappearance of entire fisheries.Amphibians have shown particularvulnerability: In mountains aroundthe globe, many species, including thegolden toad and most of the 70-oddspecies of harlequin frogs, have vanishedor declined because of diseases spurredby climatic changes.

• Disease outbreaksHigher temperatures accelerate thematuration of disease-causing agentsand the organisms that transmit them,especially mosquitoes and rodents.Higher temperatures can also lengthenthe season during which mosquitoes areactive, as has already been observed in

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Canada. Warming has also been linkedto the recent spread of tropical diseases,including malaria, dengue fever andyellow fever, into high-altitude areas inColombia, Mexico, and Rwanda thathad never seen the diseases before.

The increase in El Niño events sincethe mid-1970s—a change consistentwith global warming model predic-

tions—has also contributed to newoutbreaks of disease. In the past decade,heavy rains associated with El Niñoevents have caused explosive populationgrowth in the rodents that transmithantavirus, which can lead to severe andoften fatal illness in humans. As a con-sequence, record outbreaks of hantavirushave been occurring in the U.S.

1

Global warming is no longer just a pre-diction—it is actually happening. It isundisputed that the average temperatureat the surface of the Earth has increasedover the past century by about 1°F(0.6°C), with both the air and theoceans warming.1 Since 1880, whenpeople in many locations first began tokeep temperature records, the 25 warm-est years have all occurred within thelast 28 years.2 Scientists know withabsolute certainty that the observeddramatic increase in the atmosphericconcentrations of greenhouse gases sincepre-industrial times (to levels higherthan at any other time in at least thelast 420,000 years) has been caused byhuman activities, mostly the burningof fossil fuels (coal, oil, and natural gas),and to a lesser extent, deforestation.3

The ability of greenhouse gases, suchas carbon dioxide, methane, and nitrousoxide, to trap heat at the Earth’s surfaceis also scientifically well understood.While it has not yet been preciselydetermined how much of the recentwarming was caused by human activi-ties, the consensus among climatescientists is that most of the warmingover the past 50 years was probablycaused by human-produced greenhousegases. (See statements issued by theNational Academy of Sciences, theAmerican Meteorological Society, theAmerican Geophysical Union, theIntergovernmental Panel on ClimateChange, and the national academiesof eleven countries.)4 Recent precisemeasurements of the heat content ofthe world’s oceans, which show anincrease close to the amount expectedfrom warming by greenhouse gases,strengthen the consensus view.5,6

Many among the public may havethe misconception that global warming

Introduction

is a distant threat, with consequencesthat will only be felt many decades fromnow. The fact is, many widely accepted,peer-reviewed scientific studies havefound evidence that global warming hasalready had major impacts on eco-systems and societies across the world.Glaciers all around the world andArctic sea ice have been shrinking anddisappearing; sea level has been risingand flooding low-lying areas; life-threatening heat waves, flooding rain-storms, droughts, and forest fires havebecome more intense and frequent overrecent decades; corals are “bleaching”and dying in response to higher oceantemperatures; and numerous animal andplant species are migrating away fromthe higher temperatures, toward thepoles and higher elevations. While adirect causal link to global warming hasbeen established for some observedchanges, such as sea-level rise andworldwide glacial retreat, such a linkis difficult to definitively establish forother changes, such as the increasedincidence of droughts or the migrationof a particular species. However, themultitude of changes collectively pro-vides a consistent and clear body ofevidence of the immediate and growingdanger that global warming brings.Using the terminology of those taskedwith protecting public health, “the weightof the evidence,” or information com-piled from all available studies, pointsstrongly to global warming as a forcebehind the observed changes. At riskare the health of the global economy,of human individuals and communities,and of the ecosystems upon which wedepend for food, clean water, otherresources, and spiritual sustenance.

Carbon dioxide and other greenhousegases stay in the atmosphere for a

2

century or longer after being emitted.7

The greenhouse gases we have alreadyadded to the atmosphere since theIndustrial Revolution have thereforecommitted the globe to a certainamount of continued warming over thecoming decades no matter what we dowith future emissions.8,9,10 Humanitymay have only a narrow window of timeleft, perhaps a decade or so, to begin thelong process of stabilizing greenhousegas concentrations at a level that canavert devastating and irreversible im-pacts from climate change.11,12

This report summarizes some ofthe major impacts that global warminghas already had across the world,including some that have been observedsince the publication of major assess-ments by the Intergovernmental Panelon Climate Change (IPCC) and theNational Academy of Sciences in2001.13 Our goal is to provide policy-makers, journalists, and the public withfacts so that they can make informeddecisions on the measures needed tostem the global-warming tide. We havemade every effort to ensure that thedocument is scientifically rigorous,noting where the link between aparticular phenomenon and globalwarming may not be fully established

or where other causative factors maybe involved. We have relied almostexclusively on information from peer-reviewed scientific publications andgovernment websites; the few exceptionsinclude a Munich Re company report, aNational Geographic article, and a BBCNews article.

There are many more examples ofglobal warming impacts than can fitinto an easily digestible report like this.For more comprehensive information,the reader may want to refer to otherrecent reports, such as the 2004 ArcticClimate Impact Assessment; Status ofCoral Reefs of the World: 2004; the 2000National Assessment of Climate ChangeImpacts on the United States; and theIPCC Third Assessment Report.14 Fora comprehensive rebuttal of skeptics’claims regarding the science of globalwarming, see an earlier report of ours,The Latest Myths and Facts on GlobalWarming, available at http://www.undoit.org/what_is_gb_myth.cfm. Occasionalupdates to the present report areplanned. Suggestions for improvementsand additions are welcome. Pleasesend suggestions to: Dr. James Wang,Environmental Defense, 257 ParkAvenue South, New York, NY 10010;jwang@environmentaldefense.org

Humanity mayhave only a narrowwindow of time left,perhaps a decadeor so, to begin thelong process ofstabilizing green-house gas concen-trations at a levelthat can avertdevastating andirreversible impactsfrom climatechange.

3

It is difficult to blame a particularextreme weather event (such as aheat wave, flood-producing storm,or drought) on global warming, sinceweather fluctuates naturally. However,climate theory and models predictthat global warming will increase thefrequency and/or intensity of sometypes of extreme events. A warmedworld, in other words, is like a loadeddie that comes up “Heat Wave” or“Intense Rainstorm” more often thanan unperturbed world.15 Thus, scientistscan estimate the fraction of the riskof a particular kind of event for whichhumans are responsible. This section ofthe report presents examples of extremeevents observed during recent decadesthat are consistent with the effects ofglobal warming and may be harbingersof greater changes to come if we allowglobal warming to continue unabated.

Killer heat wavesHuman-caused global warming mayhave already doubled the chance of“killer” heat waves like the one thatscorched Europe in July–August2003.16 Strong evidence indicates thatthe summer was the hottest in Europein at least the past 500 years.17 All-timehigh temperature records were brokenin many countries. In the United King-dom, the mercury hit 100.6°F (38.1°C)at Gravesend-Broadness, Kent onAugust 10, exceeding 100°F for thefirst time in that country since recordsbegan.18 In Germany, an all-timerecord of 104.4°F (40.2°C) was seton August 8.19

At least 27,000 people died as a resultof the relentless heat, breaking allrecords worldwide for heat-inducedhuman fatalities.20 (The figure refers to

PART I

Extreme events

the number of deaths in excess of thetypical number during the summerperiod.) In France alone, over 14,000people died. In addition to the emo-tional trauma and medical costs, theheat and associated drought and wild-fires cost European economies over$14.7 billion (13 billion euros)* in lossesin the agriculture, forestry, and electricpower sectors.21 Specific damagesincluded a 60% reduction in fodderproduction in France, an 18% decreasefor wine in Italy, an 11% fall in grainproduction for Europe as a whole,livestock deaths (for example, millionsof chickens died in France and Spain,reducing the flock by 15–20% inSpain),22 and cuts in power generationdue to shortages of river water for cool-ing the plants. France, Europe’s mainelectricity exporter, cut its power exportsby more than half to preserve an ade-quate domestic supply. By the 2040s, therisk of a similar heat wave could increase100-fold if civilization doesn’t restrainthe growth of greenhouse gases, withone out of every two years being hotterthan 2003 (as compared to the currentone out of every 200).23

India was also hit in 2003 by a severeheat wave. Temperatures reached ashigh as 122°F (50°C) in May across theworst hit areas and over 1,200 peopledied.24 Just five years earlier, the mostdisastrous heat wave to ever hit Indiatook place during April–June of 1998,with an estimated 3,028 fatalities.25 Thetemperature rose as high as 113–121.6°F(45–49.8°C) in several Indian states.Disruptions to the electricity supply dueto excessive demand wreaked havoc on

* We obtained the U.S. dollar value from thevalue in euros by applying the 2003 con-version rate.

A warmed world,in other words, islike a loaded diethat comes up“Heat Wave” or“Intense Rainstorm”more often thanan unperturbedworld.

4

hospital services and on refrigeratedsupplies of vaccines and medicines.26

In the United States, Chicago experi-enced one of the worst weather-relateddisasters in Illinois history when a heatwave resulted in 525 deaths during a5-day period in July of 1995.27 The 106°F(41°C) reading on July 13 set a recordfor the warmest July temperature sincemeasurements began. The combinationof high humidity and high nighttimetemperatures meant little respite fromthe heat could be found, especially forsuch vulnerable populations as theelderly and people with low incomes.Studies indicate that the increase indeath rate from more frequent heatwaves in the future will probably out-weigh any decrease in death rate dueto less severe winter cold in the U.S.,because cold-related mortality is morecomplex and not so strongly tied to theseverity of the cold.28,29

Torrential rains and floodingAccording to the available data, asignificant increase in the intensity of

precipitation events occurred over thesecond half of the 20th century.30 Thisincrease is consistent with the predictedeffects of global warming, since highertemperatures speed up evaporation andincrease the amount of water vapor inthe air, leading to heavier downpours.Heavier rainfall in turn increases therisk of flooding.

Another factor contributing to moreintense precipitation in some regions isthe increase in frequency and intensityof El Niño events since the mid-1970s.An El Niño is a phase of warmer-than-average waters in the eastern Pacificand weaker-than-average tropical tradewinds, usually lasting around a year andoccurring once every two to seven years.El Niños typically bring unusually heavyrains to the southern tier of the U.S. andPeru, while causing below-normal pre-cipitation in the northwestern U.S.,northeastern Brazil, Southeast Asia,Australia, and southern Africa. Severalrecent El Niños may have been moreintense or long-lasting than any in thelast three centuries.31 Some climatesimulations have indicated that further

A ship on the river Rhine in Duesseldorf, Germany, July 25, 2003, during the extreme heat wave thatscorched Europe for much of the summer. Low water levels meant bigger ships could transport only30 to 50 percent of their normal cargo. (AP Photo/Martin Meissner)

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warming of the planet will produce morefrequent and longer-lasting El Niños inthe future, thus causing extreme floodsand droughts to occur more often.

One of many extreme flooding eventsthat may have been exacerbated byglobal warming occurred in December1999, when Venezuela experienced itshighest monthly rainfall in 100 years,with massive landslides and floodingthat killed approximately 30,000people.32 Total December rainfall in thecoastal city of Maiquetia, near Caracas,was almost 4 feet (1.2 m), more than5 times the previous December record.During one particularly intense period,2.8 inches (72 mm) of rain fell in onehour. Rainfall on two of those Decemberdays were “1,000-year events”—in otherwords, that daily amount of rainfall isexpected to occur in that location onaverage only once in 1,000 years. Rain-fall amounts in the neighboring moun-tains are estimated to have been twice ashigh, or around 8 feet over the month.

The rainfall was unusual not only forits intensity, but also because it occurredoutside of the normal rainy season (May

to October) and was not produced by ahurricane or other tropical cyclone. Theensuing flows of mud and boulders arethought to have been among the largestworldwide in at least a century. It isworth noting that the high death tollwas partly due to the building of largenumbers of homes on steep slopes proneto landslides and low-lying areas suscept-ible to floods. Discouraging developmentin these kinds of vulnerable locations, inaddition to reducing worldwide green-house gas pollution, would help mitigatefuture damages from global warming.

DroughtParadoxically, although flooding eventsare very likely to increase with globalwarming, droughts are also expected tobe more frequent and severe. Highertemperatures tend to increase the rateof evaporation; if precipitation doesn’tsoon replenish the lost moisture, soilsgrow drier. In drier soils, less solarenergy is used up in evaporating water,meaning more energy is available toraise the temperature of the soil and the

Devastation in coastal Venezuela caused by the December 1999 flows of mud and rocks. (LawsonSmith, U.S. Army Corps of Engineers)

6

overlying air, leading to even moredesiccating conditions; this kind of self-amplifying cycle can lead to a lengthyand severe drought.33 Dry soils can driveanother kind of self-amplifying cycle aswell: when there is less evaporation tothe air because soil moisture is depleted,there can be less moisture in the atmo-sphere locally to form precipitation,potentially resulting in yet drier soils.34

The drought that accompanied thedevastating heat waves of 2003 in Europe,for instance, is thought to have beenintensified by global warming.35 (See thesection “Killer Heat Waves” in Part I.)Models predict that the vulnerability tosummer droughts will be especially highin many mid-continental areas, whichare often important grain-producingand/or grazing regions. The reasons fortheir vulnerability are that their climateisn’t cooled by the ocean and that a largeportion of their precipitation is derivedfrom continental moisture.36

In addition to increasing evaporationand prolonging periods with deficientrainfall, a warmer climate can reducewater supplies in arid and semi-aridregions (such as the western U.S.) by

decreasing the proportion of precipi-tation that falls as snow rather than rainin the mountains, and by acceleratingthe rate of snow melt in the spring.A reduced snowpack and earlier andquicker melts make for lower streamflows in the summer, when water canbe in short supply. (See “DisappearingSnowpack” in Part III.)

Warmer ocean temperatures dueto global warming may also increasethe severity of droughts. The IndianOcean and the western Pacific wereexceptionally warm between 1998 and2002,* in part because of the overallwarming trend in the world’s oceans.37

In the same period, unusually persistentatmospheric flow patterns resultedin below normal precipitation, hightemperatures, and drought conditionsacross wide swaths of North America,southern Europe, and southern andcentral Asia. Drought continuedthrough 2004 in some areas, includingthe western U.S., where according tostream flow records and tree ring studiesthe drought was the most severe in80 years and one of the most severein 500 years.38,39,40 During the peak,more than 50% of the area of the co-terminous U.S. suffered from moderateto severe drought, with much of the areaexperiencing record or near-record lowprecipitation.41 The average annual flowof the Colorado River at Lees Ferry,Arizona during the 2001–2003 periodwas 5.4 million acre feet (6.7 cubickilometers), just half of the 10.2 million

Lowering water level during severe drought atLake Powell on the Colorado River, at the con-fluence with the Dirty Devil River (entering fromleft). Top: June 29, 2002. Bottom: December 23,2003. (John C. Dohrenwend, USGS files)

* While the geographic pattern of the warmthcan be explained by a La Niña event (theopposite of an El Niño, or in other words,a phase of warmer-than-average waters inthe western Pacific and cooler-than-averagewaters in the eastern Pacific), scientists study-ing the 1998–2002 event believe that anoverall warming trend in the world's oceansover the past few decades contributed to theunusual extremeness of the warmth.

7

acre feet (12.6 cubic kilometers)* thatflowed during the Dust Bowl years(1930–1937).42

A number of researchers have usedclimate models to examine the under-lying causes of the recent drought.43,44

Their model simulations produced aclimate pattern very similar to that ob-served, and suggested that the warmthin the Indian Ocean and western Pacificcaused the persistent atmospheric flowpatterns, which in turn produced thedrought conditions across the wide ex-panse of mid-latitude regions. In short,there is mounting evidence that globalwarming contributed to the vast extentand severity of the recent drought.

Forests and wildfiresScientists expect global warming tocontribute to an increase in wildfire inseveral ways. As discussed in the pre-vious section, droughts are expected tobecome more common and severe insome regions. Desiccating heat and lackof precipitation create ideal conditionsfor major wildfires. In addition, longerwarm seasons often translate into longerfire seasons. Warmer temperatures alsopromote outbreaks of insects that feedon trees, killing many of the hosts andcreating large amounts of dry fuel forforest fires. Insects are even spreadingto areas that until recently were too coldfor their survival. In south-centralAlaska in the 1990s, the world’s largestrecorded outbreak of spruce bark beetlesdamaged more than 4 million acres(1.6 million hectares) of forest, an areanearly the size of the state of New Jersey.45

Since 1994, Canada has been afflictedwith its largest and most northerlyspruce bark beetle outbreak ever, affect-ing 750,000 acres (300,000 hectares) inthe Yukon.46

* This comparison of streamflow is adjustedfor changes caused by the Glen Canyon Dam,which was constructed in the early 1960s.The streamflow figures are not corrected forincreases in water consumption upstream ofLees Ferry over time; but even after applyingan extremely large correction, the estimatedflow during the recent period would still be1.3 million acre feet (1.6 cubic kilometers)lower than during the Dust Bowl.

Example of a recent severe wildfire in the West: In Glenwood Springs, Colorado, on June 8, 2002, theevening sun barely penetrates the smoke and ash as evacuees flee West Glenwood because of thespreading wildfires in Garfield County. (Bryan Dahlberg/FEMA News Photo)

8

With this combination of heat,drought and pests, wildfires have becomeincreasingly destructive in recent dec-ades. Among the regions hit hard arethe huge tracts of Arctic spruce andpine forest spanning Alaska, northernCanada, Scandinavia, and Siberia(which despite their northerly latitudeare susceptible to fires in the summer-time, especially during warm, dry years).In the Arctic region of western NorthAmerica, the area burned annually hasdoubled over the past thirty years.47 Inthe Russian Arctic, fire damage increasedsharply in the 1990s, with the area offorest burned annually being more thantwice as large as during the previoustwo decades.48 The risk of catastrophicfires has been exacerbated in the Arcticas well as other parts of the world bydecades of fire suppression by humans,which has allowed dead, flammableplant material to accumulate. But evenremote parts of the Arctic, which haveseen little fire suppression, have experi-enced an increase in wildfire, suggestingthat suppression by itself cannot com-pletely explain the increase in wildfire

around the world, and that globalwarming has played an important role.49

The summer of 2004 was particularlyfierce: Alaska’s warmest and third driestsummer on record made for its worstfire year ever.50,51 A total of 703 firesconsumed 6,517,200 acres (2.6 millionhectares) of forest, an area the size ofMaryland. Evacuations of threatenedcommunities reached record levels,and for the first time ever, fire engineswere shipped from the lower 48 statesto deal with the conflagration. Becauseof the fires, air quality in the interiorand the northeast of the state wasreported as unhealthy or hazardouson 52 days. On June 28 in Fairbanks,health-threatening airborne particulatesregistered 1,000 micrograms per cubicmeter, the highest ever recorded inAlaska; normal is 65.

Regions outside of the Arctic haveseen many severe fires in recent decadesas well. For example, severe drought andhigh temperatures in the western U.S.in 2000 resulted in over 122,000 fires,which burned approximately 8.5 millionacres (3.44 million hectares), the worst

Aerial view of a white spruce forest severely damaged by spruce bark beetles, Canada. (Courtesy ofNatural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre/Luc Jobin)

9

wildfire season in the last 50 years.52 Thefirst seven months of that year were thewarmest in 106 years of records in NewMexico, Utah, and Texas, while Arizona,Colorado, Nevada, Wyoming, and Idahohad their 2nd or 3rd warmest January–July. In 1998, Mexico experienced itsworst fire season ever, when 1.25 millionacres (506,000 hectares) burned duringa severe drought.53 Smoke reachingTexas triggered a statewide health alert.

As with drought, wildfire can set off aself-amplifying cycle. If, as climate modelspredict, wildfires continue to increase infrequency and intensity,54 the amountof carbon dioxide released into the atmo-sphere from burning vegetation andsoil organic matter could outstrip theamount absorbed by regrowing forests,strengthening the greenhouse effect andglobal warming and possibly leading toeven more fires in a worsening cycle.

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Sea-level rise is one of the most certainimpacts of global warming. Sea level rosearound the world by an average of 4 to8 inches (10 to 20 cm) over the courseof the 20th century, ten times the averagerate over the previous three thousandyears.55 The rise in sea level is due to theexpansion of ocean water as it warms,and to the addition of water from melt-ing glaciers and ice sheets, both of whichare consequences of global warming.

The effects of global sea-level riseare amplified in some places due to localgeologic and man-made factors. Forexample, about one-third of the marshat Blackwater National Wildlife Refugein the Chesapeake Bay in the easternU.S. has become submerged since 1938.Half of the marsh loss is attributed tothe sinking of land due to groundwaterextraction, and the rest is attributedto global warming.56 Elsewhere in theChesapeake Bay, Bloodsworth Island is590 acres (235 hectares) smaller than itwas in 1942, a loss of more than 10% ofits original land area.57

In Louisiana, nearly a million acres(400,000 hectares) of biologically-richmarsh, 28% of the original marsh area inthe state, has been lost to the encroach-ing sea since 1932. Many factors havecontributed, including the sinking ofland along geologic fault-lines, com-paction of loose soil, and a decrease inthe supply of soil-replenishing sedi-ments due to the construction of damsand levees. However, global sea-levelrise has contributed at least one-eighthof the flooding, even at the sites that aresinking most rapidly.58 In Bermuda,rising sea level is leading to saltwaterinundation of coastal mangrove forests.59

The edges of the forests are now linedwith trees that have recently drowned orwhose roots have been exposed due to

PART II

Sea level rise and coastal flooding

erosion, making them susceptible tobeing blown over by the wind. Mangroveforests provide habitat for many birdsand economically important marinespecies including shrimp, oysters, andfish; these forests also filter the water,keeping it clean and clear, and protectthe coast from storm surges and waves.(A storm surge is a sharp, localized risein sea level lasting hours or days, causedby a storm.) These forests, like othercoastal ecosystems, are not able to buildup sediment fast enough to keep upwith the current rate of sea-level rise,and could completely disappear in placeswhere natural or man-made barriersprevent landward migration.

On the other side of the Atlantic,the Thames Flood Barrier, whichprotects the city of London from stormsurges coming up from the mouth ofthe river, was used less than once a yearin the 1980s; in the 1990s it was usedon average more than six times a year.60

Although this increase is attributablemainly to a combination of naturalvariations in storm surge intensity andincreased occurrence of high runofffrom rainstorms, it illustrates a potentialimpact of rising global sea level. Ifthe barrier were to break during a flood,the resulting damage to London couldcost about $54 billion in 2004 dollars(30 billion pounds), roughly 2% ofthe current U.K. GDP. In addition tothe Thames, more frequent and extremeflooding due to sea-level rise threatenslow-lying areas near the mouths ofthe Nile in Egypt, the Mekong inVietnam and Cambodia, the Gangesand Brahmaputra in Bangladesh, andother rivers around the world.61

Scientists project that sea level willcontinue to rise as a result of human-produced greenhouse gas pollution and

11

could reach an additional 3.5 inches to3 feet (9–88 cm) by the end of the cen-tury, with even further rises in subse-quent centuries as sea level graduallyadjusts to the warmer climate.62 (Thelarge range for projected sea level risereflects differences among models andemission projections, with the lower endreflecting possible growth in ice sheetsin parts of Antarctica due to increased

precipitation.) Some studies have evensuggested the possibility that warmingover the next several centuries wouldlead to the complete, irreversible dis-appearance of the Greenland ice sheet,which would raise sea level by an extra23 feet (7 m); there is also a slight chancethat the West Antarctic Ice Sheet couldcollapse, further raising sea level by13–20 ft (4–6 m).63,64

This map highlights the areas along the U.S. Atlantic and Gulf coasts that are vulnerable to inundationresulting from sea-level rise. This is a simple elevation map and does not include additional futureimpacts from erosion and local sinking of land. Altogether, 22,400 square miles (58,000 squarekilometers) of land, an area more than twice the size of Maryland, lie within 5 feet (1.5 m) of sea level;sea level could rise by this amount within the next few centuries. More than 80% of this low land isfound in just four states: Louisiana, Florida, Texas, and North Carolina. (Source: Titus, J.G. and C.Richman. 2001. Maps of lands vulnerable to sea level rise: modeled elevations along the U.S. Atlanticand Gulf coasts, Climate Research. Available at http://yosemite.epa.gov/oar/globalwarming.nsf/content/ResourceCenterPublicationsSLRMapsIndex.html)

200 miles

� below 1.5 meters� 1.5–3.5 meters� above 3.5 meters

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In the absence of expensive man-made physical barriers such as seawalls,even a moderate sea-level rise wouldsubmerge large portions of islandnations and densely populated coastalareas, displacing millions of people.(See the accompanying figures forexamples of vulnerable areas in theeastern U.S. and Bangladesh.) Adapta-tion to sea-level rise could cost severalpercent of GDP for certain developingcountries, and for many small islandnations would simply be infeasible.65

Sea-level rise not only inundates land,but also causes additional land loss dueto erosion by ocean waves. A foot of sealevel rise would result in approximately50-1000 feet of horizontal shorelineretreat in many parts of the U.S., vary-ing according to location.66 In addition,higher sea levels would exacerbate theflooding risk associated with stormsurges during hurricanes and otherstorms.67 Increased loss of coastal prop-

erty due to shoreline retreat and flood-ing could be costly to taxpayers as wellas property owners in the U.S., since thefederal government subsidizes floodinsurance for much coastal property.68

Another impact of rising sea level iscontamination of fresh surface waterand groundwater supplies by salty water.Communities that obtain water fromsections of rivers that are currently justupstream from the point where thewater becomes salty include Phila-delphia, New York City (as an emer-gency supply during droughts) andmuch of California’s Central Valley.69

It takes even more time to stabilizerising sea levels than it does to stabilizerising atmospheric temperatures, due tothe slow rate at which water is circulatedand heat distributed throughout the depthof the ocean.70 We need to put the brakeson rising greenhouse gas concentrationsnow to avoid an increasingly disastrousrise in sea-level down the road.

This graphic, based on an analysis conducted in 1989, illustrates the potential impact of sea-level rise onBangladesh, a low-income nation with a very large population living within a few feet of sea level. With a5 feet (1.5 m) sea-level rise, approximately 8,500 square miles (22,000 square km), or 16% of the country’sland area, would be submerged, displacing 17 million people. That figure is based on the estimatedpopulation in 1989. Given that the nation’s population has grown rapidly since 1989 and is projectedto continue growing, a much higher number of people could actually be affected. (Source: UNEP/GRIDGeneva; University of Dacca; JRO Munich; The World Bank; World Resources Institute. Washington,D.C. http://www.grida.no/climate/vital/33.htm.)

Potential impact of sea-level rise on Bangladesh

Sea-level rise of 1.5 m impactTotal population affected: 17 million (15%)Total land area affected: 22,000 km2 (16%)

1989Total population: 112 millionTotal land area: 134,000 km2

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Shrinking snowpack Over the past 30 years, scientists aroundthe world have recorded a steady declinein mountain snowpack, an importantreservoir of fresh water, as well as thebasis for the ski industry and otherwinter tourism. In the western UnitedStates, where water is scarce, 75% of thewater in streams and rivers comes fromsnowmelt, providing a crucial supplyfor farms, hydroelectric power plants,aquatic life, and 60 million people—one-fifth of the U.S. population.71 Springsnowpack has been decreasing in theregion: measurements recorded declinesin three-quarters of the mountainousareas between 1950 and 1997.72 In theRockies, snowpack decreased an averageof 16%; the Cascades lost an average of29%, with many sites in Washington,Oregon, and Northern California losingmore than 50%. Model simulations in-dicate that temperature increases are themain culprit in the snowpack decline.Even precipitation increases in someareas have generally not been sufficientto overcome the impact of strong regionalwarming. In the Swiss Alps, risingnighttime temperatures and an increasein the percentage of precipitation fallingas rain rather than as snow were toblame for a reduction in snowpack of12–45% between the 1960s and the1990s at low- to mid-elevation sites.73

Assessments of global warming im-pacts on ski resorts in North America,Europe, and Australia all project nega-tive consequences.74 Assuming currentsnowmaking technology, the ski seasonin the province of Ontario in Canadais projected to shorten by 0–16% in the2020s (11–50% in the 2080s), even withan increase in snowmaking of 36–144%in the 2020s.75 Snowmaking is expensive;for example, it currently makes up 20%

PART III

Snow, land ice and sea ice

of the operating costs of the AttitashMountain resort in New Hampshire.76

Warming thus threatens the ability ofski resorts to stay in business and remaina vital contributor to regional econo-mies. U.S. ski resorts bring in approxi-mately $4.5 billion in revenues annually(including tickets, rentals, retail, andfood and beverages).77

Records also show that the spring-time pulse, when a large amount ofsnow suddenly begins to melt and fillstreams, has shifted over the last twodecades across the western U.S., begin-ning 9 days earlier on average than itdid 40 years ago.78 Earlier snowmeltmeans that streamflow reaches its max-imum earlier in the season; throughoutCalifornia’s Sierra Nevada it now peaks3 weeks earlier than it did in 1948.79

Capturing higher streamflows earlierin the year is difficult in places such asCalifornia and the Columbia RiverBasin. Existing man-made reservoirs arenearly filled to capacity at that time;to avoid flooding, extra runoff mustbe allowed to drain into the ocean.80 Bythe time summer arrives, streamflow hasgreatly diminished, reducing the watersupply all through the hottest, driestmonths. The West already faces watershortages in times of drought: it will beextremely difficult to prevent still morecrippling water shortages withoutaddressing global warming.

Vanishing glaciersGlaciers are slow-moving “rivers” ofice formed over many years from com-pacted snow on sloping land. In almostevery mountainous region across theworld, long-term monitoring has re-vealed that the vast majority of glaciersare retreating upslope in response to a

14

warming climate;81 the glaciers’ lowerreaches are melting faster than iceflowing down from above can replenishthem. Since glaciers, like snowpack,serve to store water and release itsteadily over the year, their continueddisappearance will have a severe impacton water supplies in some regions.

In Montana’s Glacier National Park,the retreat of the glaciers has beendramatic. Between 1850 and 1979,glaciers in the Blackfoot-JacksonGlacier Basin decreased in area by about65%, from 8.3 square miles (21.6 squarekilometers) to 2.8 square miles (7.4square kilometers).82 More recentobservations show that the retreat andthinning of glaciers in the parkcontinues: For example, between 1979and 1993, Grinnell Glacier shrank by22% and Sperry Glacier by 11%.83 Theshrinkage has been driven by both an

increase in regional temperatures and adecrease in precipitation. Using climatemodels, scientists project that all theglaciers in Glacier National Park coulddisappear completely by 2030,eliminating one of the park’s maintourist attractions.84

The Pacific Northwest is witnessingsimilarly rapid retreats. The SouthCascade Glacier in Washington Statemay currently be at its smallest size everin the last 6,000 years. Between 4000 BCand A.D. 1958, its length had alwaysstayed within the range of 2.24 to 2.88miles (3.60 to 4.63 km). By 1995, it haddropped to 1.81 miles (2.92 km).85

Across the Atlantic, in the EuropeanAlps, glacial retreat has exposed well-preserved remains, including the 5,000-year-old Stone Age Oetzal “ice man.”Having survived in the ice for so longdue to the absence of ice flow in the flat

Grinnell Glacier in Glacier National Park, Montana, viewed from the top of Mount Gouldduring late summer 1938 (left) and 1981 (right). In just 43 years, a dramatic response towarming is evident, including loss of volume and formation of a lake at the foot of theglacier. Between 1850 and 1993, the glacier shrank 63% in area and the foot receded about0.7 miles (1.1 km). Debris marks the 1850 glacier boundary, right. (Courtesy of Carl H. Key(originally published in Key et al., 1998. Glacier retreat in Glacier National Park, Montana.In R.S. Williams and J.G. Ferrigno, eds. Satellite image atlas of glaciers of the world,Chapter J, Glaciers of North America. U.S. Geological Survey Professional Paper 1386-J.)

In the EuropeanAlps, glacialretreat hasexposed well-preserved remains,including the5,000-year-oldStone Age Oetzal“ice man.”

15

areas where they were found, theseremains only now have been exposedfor the first time in thousands of years—evidence that the recent glacial retreatis highly unusual.86

At the opposite end of the Earth,glaciers in the Patagonia region ofsouthern South America have beenretreating over the past several dec-ades.87 Chile’s San Rafael Glacier—aWorld Heritage Site and a popular tour-ist attraction where boats can pull rightup to the towering edge of the ice on thewater—has retreated 0.6 miles (1 km)in just the last decade.88 If this continues,the glacier will terminate over land in-stead of water in the near future.

Even in tropical mountain areas,where the climate is generally morestable than in high-latitude regions,glaciers are receding at an acceleratingrate.89,90 Venezuela had six glaciers in1972. Now it has only two and, if presenttrends continue, those too will be com-pletely melted in the next 10 years.91

Glacial retreat has accelerated seven-fold in the Peruvian Andes:92 The edgeof the Qori Kalis glacier retreated 13 feet(4.0 m) annually between 1963 and 1978;by 1995, the rate had stepped up to 99feet (30.1 m) per year. Shrinkage of theZongo Glacier in the Bolivian Andes

has created water shortages for down-stream communities.93

Tropical regions in Africa and South-east Asia are showing similar patterns.82% of the ice on Mt. Kilimanjaro hasdisappeared since 1912, with aboutone third melting in just the last dozenyears.94,95 Kilimanjaro’s remaining iceis projected to disappear by 2020. Aglacier on Mount Kenya has shrunk by40% since 1963. Two glaciers in IrianJaya (the Indonesian portion of theisland of New Guinea) are disappearingand should be gone in a decade.

In the subtropics, glaciers are also re-treating at a record pace. The DokrianiBamak Glacier in India retreated 66 ft(20.1 m) in 1998, and an annual averageof 54 ft (16.5 m) over the preceding5 years; the Gangotri Glacier is retreating98 ft (30 m) per year.96 Both are in theHimalayan range, which has the world’slargest concentration of glaciers outsideof the polar regions and has been calledthe “Water Tower of Asia.”97 Seven of thecontinent’s great rivers originate here andsupply water to hundreds of millions ofpeople: the Ganges, Indus, Brahmaputra,Salween, Mekong, Yangtze, and HuangHo. Initially, continued warming is pro-jected to swell those rivers with more ex-tensive melting of glaciers and snowpack

Left: In 1978, the Qori Kalis Glacier looked like this, flowing out from the Quelccaya Ice Cap in the Peruvian AndesMountains. Right: In 2002, the view of Qori Kalis has changed dramatically with a massive 10-acre lake forming at theice margin. (Courtesy of Professor Lonnie G. Thompson, Byrd Polar Research Center, The Ohio State University)

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and increased precipitation.98 This willworsen the already high flood risk. In afew decades, after the most vulnerableportions of the glaciers are gone, river flowwill get dangerously low in summer.99

The loss of glacial meltwater wouldreduce summer flows on the Ganges bytwo thirds, creating water shortages forseveral hundred million people and upto 37% of India’s irrigated farmland.100

Global warming skeptics have actuallyclaimed that the majority of glaciers acrossthe world are advancing rather than re-treating. In fact, in only a very few areas,specifically western Norway, Iceland,and New Zealand, have a significantfraction of the glaciers been expandingduring the past few decades.101,102 Thatexpansion is a result of regional increasesin storm frequency and snowfall amountsrather than colder temperatures, and istherefore compatible with a global warm-ing trend. But in all other regions of theworld, the retreat of glaciers has beenpronounced;103 the total net loss in vol-ume across all of the world’s glaciers be-tween 1961 and 1997 is about 3 billionacre feet (890 cubic miles, or 3,700cubic km).104 Skeptics have also arguedthat the glacial retreat is unconnected toglobal warming by focusing on the iso-lated case of Kilimanjaro, for which scien-tists have offered alternative explanations,including a drop in precipitation begin-ning in the late 1800s, a decrease in cloudcover, and the drying effect of regionaldeforestation.105 The consensus amongscientists remains, however, that risingair temperatures are the most importantfactor behind the retreat of glaciers on aglobal scale over long time periods.106,107

Polar ice disintegration Polar regions have two kinds of floatingice. Ice shelves are thick plates of ice thatform where glaciers flow into the sea.Sea ice forms when seawater gets cold

enough to freeze. Unlike land-basedglaciers and ice sheets, floating ice doesnot raise sea level when it melts. It does,however, have serious consequences.

One of the most dramatic meltingevents so far has occurred on the AntarcticPeninsula, the part of that continent thatjuts out towards South America. Whilea slight cooling occurred in the interiorof Antarctica over the past century, thePeninsula has warmed by around 4°F(2°C) since 1950, four times the globalaverage of 0.9°F (0.5°C).108 The retreatof ice shelves on both the eastern andwestern sides of the Peninsula since 1995has been attributed to this regional warm-ing.109 That retreat took a surprising turnin 2002, when the northern section of theLarsen B ice shelf, a large floating icemass on the eastern side of the Penin-sula, shattered and separated from thecontinent. In just 35 days, beginning onJanuary 31, 2002, a total of about 1,250square miles (3,250 square kilometers)of shelf, an area bigger than the state ofRhode Island, completely disintegrated.

An ice shelf acts as a dam for glacierson land. So although its break-up didnot directly contribute to sea-level rise,observations show that the removal ofthe Larsen B ice dam has caused a worri-some acceleration of glacier flow intothe ocean (as much as eight-fold), whichcould in time raise global sea level.110,111

A similar event occurred in the Arcticin the spring and summer of 2003, whenthe Ward Hunt Ice Shelf, the Arctic’slargest ice shelf, broke in two.112 The iceshelf had been acting as a dam for aunique freshwater lake, the largest of itskind in the northern hemisphere andhome to a rare microbial ecosystem thatwas only discovered in 1999. Researchersbelieve that rising temperatures causedthe weakening of the ice shelf. When itbroke, the lake drained and disappeared.

Sea ice has been faring no better. In2000 and again in 2001, people were

17

astounded by the appearance of a gapinghole of ice-free water at the North Pole,a stark demonstration that Arctic sea iceis no longer as extensive and solid as itused to be. Spring and summer Arcticsea ice has decreased in surface area by10 to 15% since the 1950s.113 Further-more, in late summer to early autumn,sea ice has thinned by about 40% in manyparts of the Arctic. (By comparing identi-cal parts of the year, these numbersaccount for seasonal fluctuations andtherefore represent real, long-termchanges.) While for much of the pastfew decades the downward trend fluctu-ated between record-low years and closer-to-normal years, the ice took a turn forthe worse from 2002 to 2005, whichhave all seen record or near-record lowice coverage.114 Like drought and otherclimatic changes, sea ice shrinkage setsin motion a worsening cycle, amplifyingglobal warming. Light colored ice reflectsa significant portion of the energy fromthe sun back into space. If that sea ice isgone, the darker water absorbs the solarenergy and the climate heats up faster.At present rates of shrinkage, Arctic seaice could soon pass a point of no return,disappearing completely each summer

by the end of this century; that situationwould be unprecedented in the last onemillion years.115

The implications for many inhabi-tants of the Arctic are grim. The shrink-ing of sea ice, especially during thewarmer part of the year, has resulted inpopulation declines among animals suchas polar bears and ice-dwelling seals,which require a sufficiently long sea-iceseason for hunting and rearing young.116

(A detailed discussion on Arctic wildlifecan be found in Part IV of this report.)This in turn makes it more difficult fornative peoples to hunt for seals andother food sources.117 Hunters’ lives arealso endangered by the increasing risk offalling through thin ice. If we allowglobal warming to continue, traditionalsocieties in the Arctic could be destroyed.

Melting permafrost and damageto infrastructureIn cold regions around the world,large reaches of land have been frozenyear-round. That permafrost is nowmelting rapidly in places like the Arcticof North America, Siberia, and theHimalayan/Tibetan region of Asia.118

Sudden break-up of the Larsen B ice shelf in Antarctica. Left: At the beginning of the break-up, January31, 2002; Right: At the end of the break-up, March 7, 2002. (Ted Scambos, National Snow and Ice DataCenter, University of Colorado, Boulder, based on data from MODIS. http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=8257)

Like drought andother climaticchanges, sea iceshrinkage sets inmotion a worsen-ing cycle, amplify-ing global warming.

18

The impacts on Alaskan infrastruc-ture have been particularly striking.Alaska has experienced the largestwarming trend of any state; since the1950s, temperatures have increasedabout 4°F (2.2°C) on an annual average,and as much as 7°F (3.9°C) in theinterior in winter.119 Climate modelsproject that Alaskan temperatures willrise by an additional 9–18°F (5–10°C)by 2100. In addition to the increase incatastrophic forest fires described earlier,Alaska’s warming has caused buildingsto sink and break into pieces and roadsto buckle, as the underlying permafrostliquefies.120 In the Mackenzie Basin,thawing permafrost has destabilizedslopes, causing landslides, erosion andlocal flooding, and threatening roadsand bridges. Meat stored in traditionalice cellars dug into the ground has begunto rot.121 The residents of Shishmaref,an Eskimo village that had existed for4,000 years on an island off the coast ofAlaska, were recently forced to relocatetheir entire community to the mainland.122

The ground under their feet had weak-ened as the permafrost melted and been

eroded by ocean waves, which are ampli-fied when disappearing sea ice is replacedby open water. Many other villages aredangerously close to a similar fate.

Beyond these immediate impacts,scientists are concerned that thawingpermafrost may increase atmosphericlevels of carbon dioxide and methane,which are both greenhouse gases. Becauseof the slow rates of decomposition ofdead plant material in the cold, water-logged environment, Arctic soils containvast stores of carbon. In fact, 25% ofthe global reservoir of soil carbon canbe found in this region.123 Permafrostalso contains large quantities of frozenmethane.124 With continued thawing,large amounts of carbon and methanecould be released, raising atmosphericlevels significantly and warming theplanet further.125 Ironically, the meltingof permafrost will also make oil andnatural gas exploration more difficult,since the heavy equipment requiredcan only be transported over solidlyfrozen ground.126 This could meanthe reduction of one source of green-house gases.

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Coastline next to the village of Shishmaref, Alaska, eroding as rising temperatures causethe permafrost underneath the land to melt.

19

Damage to coral reefsAround the world, the incidence oflarge-scale coral “bleaching” events hasincreased since 1979, and most evidenceindicates that this increase in mass bleach-ings is linked to global warming.127,128 Thenormally brilliant colors of corals areprovided by photosynthetic algae, calledzooxanthellae, which live inside thecorals in a mutually beneficial relation-ship. Under certain stressful conditions,especially when the surrounding watertemperature rises at least 1.8°F (1°C)above the long-term average summermaximum, corals cope by expelling theirzooxanthellae guests. This results in theloss of color that gives rise to the term“bleaching.” Prolonged bleaching oftenleads to death of the coral.

Average surface ocean temperaturesin many tropical regions rose by almost2°F (1°C) over the past century. Frommid-1997 to mid-1998, the warmest12-month period on record, the largestbleaching event on record affected everyregion of the world. About 16% of thereefs in the world were seriously dam-aged in that one event.129 Corals whichhad survived for as long as a thousandyears perished. In the Florida Keys,significant bleaching in consecutiveyears was observed for the first time; the

PART IV

Ecological impacts

damaged reefs have shown little recoverysince. A year earlier, in 1996, the firstbleaching event ever documented inHawaii occurred, affecting severalislands.130 Although bleaching events inHawaii may have occurred previously,no evidence has been found of such anextensive one across the island chain.

Continued warming could causemass bleachings to become an annualevent within the next few decades.While there is some evidence that coralscan cope with excessive heat by formingnew relationships with heat-tolerantzooxanthellae, it is currently unknownwhether this adaptation mechanismcould occur widely and rapidly enoughto prevent loss of some reef ecosystemsor species.131 The extensive loss of coralsduring the 1997–1998 bleaching eventand the projected further warming oftropical oceans by 1–3°C (1.8–5.4°F)over the next century do not bode well.

Increases in atmospheric carbondioxide pose a more direct danger tocorals as well. When carbon dioxide gasdissolves in seawater, it changes oceanchemistry, making it more difficult forcorals to produce calcium carbonate,the main building material in theirskeletons.132 Such a change in seawaterchemistry has in fact been observed.133

Left: Healthy corals (iStockphoto).Right: bleached corals (Ray Berkelsman, CRC Reef,Townsville).

20

Coupled with other human-inducedstresses, including water pollution, in-creased runoff of dirt from disturbedland areas, mining and blasting of reefs,and destructive fishing practices, coralreefs could soon be wiped out across manyparts of the world, an irreparable loss ofone of the world’s ecological treasures.

The loss of coral ecosystems wouldalso have severe economic repercussionsin regions that depend on reefs for foodand tourism income, and for the protec-tion of coastal land from destructivewaves. Coral reefs provide an estimated$3.1–4.6 billion (U.S.) in economic bene-fits to the Caribbean region each year.134

The Great Barrier Reef directly con-tributes around $1 billion to the economyof Australia each year. Saving thesebeautiful, wondrous ecosystems mayrequire rapid, worldwide cuts in green-house gas emissions, as well as mitigationof other human disturbances to reefs.

Shifting species ranges andyearly cyclesRecent research provides strong evidencethat global warming is already havingmeasurable impacts on many wild ani-mal and plant species worldwide. Twodifferent research groups, each of whomsynthesized numerous studies of shiftsin the geographic range and yearlycycles of over 1,400 species, found adiscernible “fingerprint” of global warm-ing on the web of life.135 Over 80% ofthe species, ranging from fish to mam-mals and from grasses to trees, arechanging in the direction expected fora warming climate.

In one strong indication of globalwarming, the researchers found an aver-age range shift of 3.8 miles (6.1 km) perdecade towards the poles, and 20 feet(6.1 m) per decade upward in altitude,across a large number of diverse species.Among 36 butterfly species in North

America and Europe, eight expandedtheir range northward while dying outat the southern end of their range; nospecies showed the opposite pattern.Of 36 species of fish in the North Sea(between Great Britain and Norway),the populations of 13 shifted northwardover the past 25 years in response towarming waters, while only 2 shiftedsouthward.136 The average distancemoved was a remarkable 107 miles(172 km). An additional 6 speciesmoved into deeper, cooler waters.Pressure from fishing does not appearto explain the shifts in distribution. It isprojected that two kinds of commercialfish could move completely out of theNorth Sea by 2050, with profound eco-logical and economic consequences.

In another indication of globalwarming, springtime events such asmigration of birds and butterflies, birdnesting, frog breeding, tree leafing, andflowering are starting an average of2.3–5.1 days earlier every decade acrossall observed species.137 The authors ofone analysis conclude that continuedrapid climate change combined withother man-made stresses, such as habitatdestruction, could result in numerousdisruptive changes to ecosystems, in-cluding extinctions.

Declining Arctic animalpopulationsThe disproportionate warming in theArctic has had detrimental effects onmany Arctic species. The health of polarbears, in particular, is declining due todecreasing ice coverage in the HudsonBay, at the southern end of the species’range.138 As the total area of Arctic seaice has declined by close to 6% over thelast 20 years, the sea ice season in theHudson Bay has shortened by threeweeks. Polar bears depend on sea icethick enough to walk on to travel

The loss of coralecosystems wouldalso have severeeconomic reper-cussions in regionsthat depend onreefs for food andtourism income,and for the protec-tion of coastal landfrom destructivewaves.

21

between their dens (which can be on theshore or out on the ice), and their mainfood source: ice-dwelling ringed seals.As the ice in the Bay forms later eachautumn and breaks up earlier each spring,polar bears have less time to hunt, andreturn to land at the end of the season inpoorer condition. Less accumulatedweight makes it more difficult forfemales to successfully give birth in thewinter, when they must hole up insidetheir dens and go for months withouteating. Insufficient sea ice in the springcan also prevent the mothers fromhunting food for their cubs. Scientistsfound a 15% decline in both the averageweight of adult bears and the number ofcubs born during the last 20 years.

Further jeopardy is posed to the bearsby increasingly frequent and intensespring rains— yet another consequence

of global warming— which causesome snow dens to collapse, killing themothers and cubs.139 In 2005, a scientificpetition was filed in the U.S. to listpolar bears as a threatened species underthe Endangered Species Act. Ongoingenvironmental changes due to globalwarming were cited as the primarythreat.140 If summer sea ice disappearsacross the entire Arctic, as is projectedfor the end of this century in the ab-sence of action to limit warming, polarbears are likely to be pushed to the brinkof extinction.

Other Arctic animals are also show-ing population declines in response towarming. For caribou, an earlier springmeans that their food plants havepassed their prime by the time thecaribou migrate back from their winterhome to the south.141 The range of the

A polar bear in its natural sea ice habitat. (NOAA Photo Library)

Left: Caribou (NOAA Photo Library. Photographer: Captain Budd Christman, NOAA Corps).Right: Arctic fox (U.S. Fish and Wildlife Service).

22

Arctic fox is shrinking as the animalsretreat toward the North Pole and arereplaced by more common red foxes,which are adapted to warmer climates.142

Declining amphibian populationsAmphibian populations in highlandareas around the globe are decliningstill more precipitously. In Centraland South America, many mountainamphibians, including the goldentoad and most of the 70-odd speciesof harlequin frogs, have vanished ordeclined markedly.143 In the PacificNorthwest of the United States,embryo mortality rates are increasingfor species like the western toad andthe Cascades frog, which lay their eggsin mountain lakes: fewer of those eggsever hatch.144

Research suggests that changingcloud and/or precipitation patternsassociated with global warming could beaffecting how amphibians respond todisease. In the mountains of the tropics,two specific climate-related causes ofamphibian declines have been identi-fied.145,146 First, amphibians typicallyescape the effects of a lethal fungalparasite of the skin that thrives in cool,moist conditions by basking temporarilyin sunny, warm microclimates. Globalwarming increases the amount of water

vapor in the atmosphere, producingmore clouds when moisture-laden tradewinds in the tropics are forced upwardagainst mountains and cooled. Theincreased cloud cover reduces theoccurrence of sunny microclimates,preventing the amphibians from riddingthemselves of the fungus.

Second, global warming may raisethe altitude at which clouds and mistform; with warmer temperatures,moisture-containing air must insome circumstances rise higher upthe mountains to cool sufficiently forcondensation to occur. That possibilityhas been demonstrated in climatemodels, especially for the winter dryseason, which is when tropical mountainforests are the most dependent for theirwater supply on direct contact withclouds and mist.147 A decrease in wateravailability can further promote fungalattack, since amphibians are forcedto spend prolonged periods in cool,moist spots in order to maintain bodymoisture. A decrease in the amountof mist, along with an increase in theoccurrence of higher clouds, has in factbeen observed since the early 1970s inCosta Rica in Central America.

In the Pacific Northwest, the rise inembryonic mortality may be linked tothe increase in El Niño events associ-ated with global warming.148 Years with

Left: Golden toads in the mountains of Costa Rica are believed to have gone extinct in recentyears. Right: Harlequin frog in the mountains of Costa Rica. (Michael and Patricia Fogden)

23

unusually low rainfall in the regionhave become more common in recentdecades, corresponding to the increasein El Niño events. (For more on ElNiño, see the section “Torrential Rainsand Flooding” in Part I.) As a resultlake levels have been low. Without water

sufficiently deep to filter out some sun-light, amphibian eggs in high-altitudelakes may be exposed to high levelsof UV radiation. The embryos withinexposed eggs, experiments have found,are more vulnerable to infection by adeadly fungus.

24

Many infectious diseases are spreadby organisms such as mosquitoes androdents, known as disease vectors, whosedistributions and behavior are sensitiveto temperature and moisture. Globalwarming can increase the risk of vector-borne disease in a number of ways:

1. Higher temperatures accelerate thematuration of certain disease-causingagents and their vectors. For example,the incubation period required for amosquito to be able to transmit denguefever virus after it has been infectedfalls from 12 days at 30°C to 7 days at32–35°C; this translates into a potentialthreefold increase in the transmissionrate of disease.149

2. Higher annual average temperaturescan lengthen the season during whichvectors are active. For example, inCanada, ecologists have found thatpresent-day mosquitoes wait nine daysmore than their ancestors did 30 yearsago before they begin their winter dor-mancy, with warmer autumns being themost likely cause.150

3. A warmer climate can expand thegeographic range of tropical mosquito-borne diseases, such as malaria, denguefever, and yellow fever, to higher alti-

PART V

Outbreaks of vector-borne diseases

tudes and latitudes. Especially vulner-able are less developed countries thathave fewer resources to combat disease.Malaria, the most prevalent vector-borne disease, kills 1 to 2 million peopleannually.151 The disease is generallylimited to areas with winter tempera-tures above 16°C, since the parasite isnot able to grow below this temperature.Dengue viruses are generally limited tothe tropics between the latitudes of 30°north and 20° south, since frosts or pro-longed cold weather kill the vector, adultAedes aegypti mosquitoes, as well as theiroverwintering eggs and larvae.152

Nighttime and winter temperaturesare increasing faster than daytime andsummer temperatures in many regionsof the world.153 This decrease in theoccurrence of cold weather means thatareas at high latitudes or altitudes thatwere previously unsuitable for thetransmission of tropical diseases maybecome suitable due to global warming.This has, apparently, already started tohappen. In the South American countryof Colombia, the mosquitoes that carrydengue fever and yellow fever viruseswere previously limited to altitudesbelow 3,300 ft (1,000 m), but have beenrecently found at 7,200 ft (2,200 m).154

To the north in Mexico, dengue feverhas spread above its former limitof 3,300 ft (1,000 m), appearing at5,600 ft (1,700 m).155 An ocean andhalf a continent away in Rwanda,malaria was unheard of above 5,600feet (1,700 m) until the early 1980s.156

Higher nighttime temperatures arestrongly correlated with the spikein malaria cases. The spread of thedisease to higher altitudes has alsobeen facilitated by heavy rainfall, whichcreates more pools of water in whichmosquitoes can breed.

Mosquito feeding on human hand. (Courtesyof Dr. Gary Alpert, Environmental Healthand Safety Dept., Harvard University)

25

There are factors in addition toglobal warming that can influence thespread of tropical diseases, as skepticsoften emphasize. For example, therehas been a resurgence of malaria allover the tropics since 1973, influencedmore by the appearance of insecticide-resistant mosquitoes and by the malariaparasite’s growing resistance to anti-biotics than by global warming.157 Butthe correlation between rising tempera-tures and the spread of diseases to high-altitude areas previously free of diseaseprovides strong evidence that globalwarming has actually expanded therange of tropical diseases.

4. Increasing climate variability associ-ated with global warming, especiallyincreases in the frequency of heavyprecipitation events and floods, canpromote explosive growth in the pop-

ulations of disease vectors. Outbreaksof hantavirus, which is carried by wildrodents and can lead to severe and oftenfatal illness in humans, have in the pastdecade been occurring in parts of theU.S. These record outbreaks appear tobe a result of episodes of unusuallyheavy precipitation associated withEl Niño events, which as noted in Part Imay increase in frequency and intensitywith global warming. In the Southwest,six years of drought followed by heavyspring rains in 1993 produced a burst ofvegetation growth that resulted in a ten-fold increase in the population of deermice, a known carrier of hantavirus.158

Despite public education campaignsafter an outbreak in 1993-1994 tospread awareness of the disease andpreventive measures, another outbreakhit the Southwest in the wake of the1997–1998 El Niño.

26

• Although individual events or phenom-ena may not always be easy to linkto global warming, the increase infrequency and intensity of suchphenomena, and their simultaneousoccurrence around the world, providesstronger evidence for such a linkage.

• Many of the recently observed eventshave been the worst or unprecedentedin 100, 500, 1,000 years or more. Thissuggests that something highlyunusual is happening to our planet.

• Many of the impacts we have seen sofar are likely just “the tip of the ice-berg”—scientists predict more dramatic,severe and, in some cases, irreversibleimpacts if we allow warming to con-tinue unabated in the future.

• Other effects of human activity, suchas the spread of homes and infrastruc-ture into vulnerable locations, sinkingof coastal land, and degradation ofwildlife habitat, can compound thedamage caused by global warming.

Conclusion

• Global warming has wide-rangingeffects on many aspects of human life.It threatens economies, lives andtraditional ways of life.

The facts gathered in this reportpresent society with a choice: We canmake no serious effort to combat globalwarming, and instead try to cope withits increasingly devastating impacts onour livelihoods and the natural world wecherish. Or we can act now to stabilizethe climate and mitigate future damages.

Progress in combating globalwarming has already been made at theinternational, state, and local levels. Butnational action by the U.S.—the world’smost powerful and technologicallyadvanced nation and its biggest emitterof greenhouse gas pollution—is urgentlyneeded as well. National legislation thatsets a mandatory cap on emissions, aswell as a renewed engagement by theU.S. with the international community,would be transformative steps towardssolving the problem of global warming.

27

1 IPCC. 2001. Climate Change 2001: TheScientific Basis. Contribution of WorkingGroup I to the Third Assessment Report ofthe Intergovernmental Panel on ClimateChange. Edited by J.T. Houghton, Y. Ding,D.J. Griggs, M. Noguer, P.J. van der Linden,X. Dai, K. Maskell, and C.A. Johnson.Cambridge and New York: CambridgeUniversity Press. (http://www.grida.no/climate/ipcc_tar/wg1/index.htm)

2 National Climatic Data Center. 2005.ftp://ftp.ncdc.noaa.gov/pub/data/anomalies/annual_land.and.ocean.ts

3 IPCC, 2001.4 National Academy of Sciences: http://www

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5 Hansen, J., et al. 2005. Earth’s energy im-balance: Confirmation and implications.Science, 308, 1431–1435. 10.1126/science.1110252. Published online 28 April 2005.

6 Barnett et al. 2005. Penetration of human-induced warming into the world’s oceans.Science, 309, 284–287. 10.1126/science.1112418. Published online 2 June 2005.

7 Ramaswamy, V., O. Boucher, J. Haigh, D.Hauglustaine, J. Haywood, G. Myhre, T.Nakajima, G.Y. Shi, and S. Solomon:Radiative Forcing of Climate Change. In:Climate Change 2001: The Scientific Basis.Contribution of Working Group I to the ThirdAssessment Report of the IntergovernmentalPanel on Climate Change [Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. vander Linden, X. Dai, K. Maskell, and C.A.Johnson (eds.)]. Cambridge UniversityPress, Cambridge, U.K., and New York, NY,U.S.A., 881 pp., 2001.

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9 Meehl, G.A., W.M. Washington, W.D.Collins, J.M. Arblaster, A. Hu, L.E. Buja,W.G. Strand, and H. Teng. 2005. Howmuch more global warming and sea levelrise? Science, 307, 1769-1772.

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