Global Warming and Extreme Weather

8/8/2019 Global Warming and Extreme Weather

1/53

Hurricanes SnowstormsTropical Storms DroughtWildfre Coastal Storms

Flooding Heat WavesExtreme Rainall WildfreHurricanes SnowstormsFire Drought Hurricanes

Global Warming andExtreme Weather

The Science, the Forecast, and the Impacts on America


2/53

Global Warming andExtreme WeatherThe Science, the Forecast,

and the Impacts on America

Environment AmericaResearch & Policy Center

Tony Dutzik,Frontier Group

Nathan Willcox,Environment America

Research & Policy Center

September 2010


3/53

Acknowledgments

Environment America Research & Policy Center thanks Kevin Trenberth, head o the Climate

Analysis Section at the National Center or Atmospheric Research; Amanda Staudt, climatescientist with the National Wildlie Federation; Paul Epstein, associate director o the Centeror Health and the Global Environment at Harvard Medical School; and Brenda Ekwurzel,assistant director o climate research and analysis or the Climate and Energy Program o theUnion o Concerned Scientists or their review o drats o this document, as well as their insightsand suggestions. Thanks also to Clair Embry and Kurt Walters or their research assistanceand Susan Rakov and Travis Madsen o Frontier Group or their editorial assistance.

The authors express sincere gratitude to the many scientists and researchers working to helpsociety understand the causes and likely impacts o global warming.

Environment America Research & Policy Center thanks the Energy Foundation, Oak Founda-tion and New York Community Trust or making this report possible.

The authors bear responsibility or any actual errors. The recommendations are those oEnvironment America Research & Policy Center. The views expressed in this report are thoseo the authors and do not necessarily reect the views o our unders or those who providedreview.

2010 Environment America Research & Policy Center

Environment America Research & Policy Center is a 501(c)(3) organization. We are dedicatedto protecting Americas air, water and open spaces. We investigate problems, crat solutions,educate the public and decision makers, and help Americans make their voices heard in local,state and national debates over the quality o our environment and our lives. For more inor-mation about Environment America Research & Policy Center or or additional copies o thisreport, please visit www.environmentamerica.org/center.

Frontier Group conducts independent research and policy analysis to support a cleaner, healthierand more democratic society. Our mission is to inject accurate inormation and compellingideas into public policy debates at the local, state and ederal levels. For more inormation aboutFrontier Group, please visit www.rontiergroup.org.

Cover: bocky, Shutterstock.comDesign and layout: Harriet Eckstein Graphic Design


4/53

Table o Contents

Executive Summary 1

Introduction 6

Global Warming: The Scientifc Consensus 8Americas Changing Climate 9

Extreme Weather and Why it Matters 11What Is Extreme Weather? 11Why Care About Extreme Weather? 12

Extreme Weather: The Trends, The Impacts,and Predictions or the Future 14Hurricanes and Tropical Storms 14Coastal Storms and Sea Level Rise 18Flooding and Extreme Rainall 24Snowstorms 30Drought, Wildfre and Heat Waves 32

Conclusions and Recommendations 38

Notes 40


5/53


6/53

Executive Summary 1

Executive Summary

Patterns o extreme weather are chang-ing in the United States, and climatescience predicts that urther changes

are in store. Extreme weather events lead tobillions o dollars in economic damage andloss o lie each year. Scientists project thatglobal warming could aect the requency,timing, location and severity o many typeso extreme weather events in the decadesto come.

Over the last ive years, science hascontinued to make progress in exploringthe connections between global warm-ing and extreme weather. Meanwhile, theUnited States has experienced a string oextreme eventsincluding massive oodsin the Midwest, Tennessee and Northeast,intense hurricanes in Florida and alongthe Gul Coast, drought and wildfre inthe Southeast and Southwestthat serveas a reminder o the damage that extremeweather can cause to people, the economy

and the environment. This report reviews recent trends in

several types o extreme weather, the im-pacts caused by notable events that haveoccurred since 2005, and the most recentscientifc projections o uture changes inextreme weather.

To protect the nation rom the damageto property and ecosystems that resultsrom changes in extreme weather pat-ternsas well as other consequences oglobal warmingthe United States mustmove quickly to reduce emissions o globalwarming pollutants.

The worldwide scientifc consensusthat the earth is warming and that hu-

man activities are largely responsiblehas solidifed in recent years.

A recent report published by the U.S.National Academy o Sciences statedthat the conclusion that the Earth sys-tem is warming and that much o thiswarming is very likely due to humanactivities is so thoroughly examinedand tested, and supported by so manyindependent observations and results,that its likelihood o subsequently being

ound to be wrong is vanishingly small.

The national academies o scienceso 13 leading nations issued a jointstatement in 2009 stating that climatechange is happening even aster thanpreviously estimated.


7/53

2 Global Warming and Extreme Weather

A 2009 study o the work o morethan 1,300 climate researchersactively publishing in the feldound that 97 to 98 percent othose researchers agree with thecentral theories behind global

warming.

The consequences o global warmingare already beginning to be experiencedin the United States, and are likely togrow in the years to come, particularlyi emissions o global warming pollut-ants continue unabated.

Average temperature in the UnitedStates has increased by more than2 Fahrenheit over the last 50 years.Temperatures are projected to rise byas much as an additional 7 F to 11 Fon average by the end o the century,should emissions o global warmingpollutants continue to increase.

The United States has experienced anincrease in heavy precipitation events,with the amount o precipitationalling in the top 1 percent o rainallevents increasing by 20 percent over

the course o the 20th

century. Thetrend toward extreme precipitation isprojected to continue, even as highertemperatures and drier summers in-crease the risk o drought in much othe country.

Snow cover has decreased over thepast three decades in the NorthernHemisphere, and the volume o springsnowpack in the Mountain West andPacifc Northwest has declined signif-

cantly since the mid-20th century.

Sea level has risen by nearly 8 inchesglobally since 1870. Global sea level iscurrently projected to rise by as muchas 2.5 to 6.25 eet by the end o thecentury i global warming

pollution continues unabated. Parts othe northeastern United States couldexperience an additional 8 inches osea-level rise due to changes in oceancirculation patterns.

Several types o extreme weatherevents have occurred more requentlyor with greater intensity in recent years.Global warming may drive changes inthe requency, timing, location or sever-ity o such events in the uture.

Hurricanes

The strongest tropical cyclones havebeen getting stronger around theglobe over the last several decades,with a documented increase in thenumber o severe Category 4 and 5hurricanes in the Atlantic Ocean since1980. (See page 14.)

Scientists project that globalwarming may bring ewerbut moreintensehurricanes worldwide, andthat those hurricanes will bring in-creased precipitation. The number ointense Category 4 and 5 hurricanes

in the Atlantic may nearly double overthe course o the next century. (Seepage 16.)

Estimated total damages rom theseven most costly hurricanes tostrike the United States since thebeginning o 2005 exceed$200 billion. (See page 16.) Thatincludes damages rom HurricaneKatrina, which was not only themost costly weather-related disaster

o all time in the United States, butwhich also caused major changesto important ecosystems, includ-ing massive loss o land on barrierislands along the Gul Coast. (Seepages 12-13.)


8/53

Executive Summary 3

Sea Level Rise and Coastal Storms

Sea level at many locations along theEast Coast has been rising at a rateo nearly 1 oot per century due tothe expansion o sea water as it has

warmed and due to the melting oglaciers. Relative sea level has risenaster along the Gul Coast, whereland has been subsiding, and less alongthe northern Pacifc Coast.

In addition to sea-level rise, waveheights have been rising along thenorthern Pacifc coast in recent years,possibly indicating an increase in theintensity o Pacifc winter storms. Inthe 1990s, scientists estimated that theheight o a 100-year wave (one ex-pected to occur every 100 years) o thecoast o the Pacifc Northwest was ap-proximately 33 eet; now it is estimatedto be 46 eet. (See page 20.)

Projected uture sea-level rise o 2.5to 6.25 eet by the end o the centurywould put more o the nations coast-line at risk o erosion or inundation byeven todays typical coastal storms.

oIn the mid-Atlantic region alone,between 900,000 and 3.4 millionpeople live in areas that would bethreatened by a 3.3 oot (1 meter)rise in sea level. (See page 18.)

oAlong the Gul Coast rom Galves-ton, Texas, to Mobile, Alabama,more than hal the highways,nearly all the rail miles, 29 airportsand almost all existing port inra-

structure are at risk o ooding inthe uture due to higher seas andstorm surges.

oHad New York City experienced a20-inch (0.5 meter) rise in sea levelover the 1997 to 2007 period (at

the low end o current projectionsor sea level rise by the end o thecentury), the number o moderatecoastal ooding events would haveincreased rom zero to 136theequivalent o a coastal ood warn-

ing every other week.

Rainall, Floods and Extreme Snow-storms

The number o heavy precipitationevents in the United States increasedby 24 percent between 1948 and 2006,with the greatest increases in NewEngland and the Midwest. In mucho the eastern part o the country, astorm so intense that once it wouldhave been expected to occur every 50years can now be expected to occurevery 40 years. (See page 25.)

The largest increases in heavy rainallevents in the United States are pro-jected to occur in the Northeast andMidwest. The timing o overall pre-cipitation is also projected to change,with increases in precipitation duringthe winter and spring in much o the

north, but drier summers across mosto the country. (See page 26.)

Global warming is projected to bringmore requent intense precipitationevents, since warmer air is capable oholding more water vapor. Changingprecipitation patterns could lead toincreased risk o oods. What is now a100-year ood in the Columbia Riverbasin could occur once every threeyears by the end o the 21st century

under an extreme global warming sce-nario, due to the combination o wet-ter winters and accelerated snowmelt.This change is projected to occur evenas the region experiences an increasein summer drought due to reducedsummer precipitation and declining


9/53


availability o snowmelt in the sum-mer. (See page 27.)

Flooding is the most commonweather-related disaster in the UnitedStates. Recent years have seen a string

o incredibly destructive oods, in-cluding the 2008 Midwest ood thatinundated Cedar Rapids, Iowa, andcaused an estimated $8 to $10 bil-lion in damage, and the massive 2010oods in New England and Tennes-see. (See pages 28 and 29.)

Projections o more requent heavyprecipitation apply to both rain andsnow storms (although warming willbring a shit in precipitation rom snowto rain over time). The 2010 recordsnowalls in the mid-Atlantic region(dubbed Snowmageddon) are ullyconsistent with projections o increasedextreme precipitation in a warmingworldand with the string o massiveooding events elsewhere in the coun-try during 2010. (See page 30.)

Heat Waves, Drought and Wildres

Over the past century, drought hasbecome more common in parts o thenorthern Rockies, the Southwest andthe Southeast. Periods o extreme heathave also become more common since1960. (See page 32.)

Large wildfres have become more re-quent in the American West since themid-1980s, with the greatest increasesin large wildfres coming in the north-ern Rockies and northern Caliornia.

Heat waves are projected to be morerequent, more intense, and last longerin a warming world. Much o the Unit-ed Statesespecially the Southwestisprojected to experience more requentor more severe drought. (See page 34.)

Scientists project that a warmerclimate could lead to a 54 percentincrease in the average area burnedby western wildfres annually, withthe greatest increases in the PacifcNorthwest and Rocky Mountains.

(See page 35.)

Heat waves are among the most lethalo extreme weather events. A 2006heat wave that aected the entire con-tiguous United States was blamed orat least 147 deaths in Caliornia andanother 140 deaths in New York City.(See page 36.)

Wildfre is capable o causing greatdamage to property, while the cost ofghting wildfres is a signifcant drainon public resources. In 2008, Cali-ornia spent $200 million in a singlemonth fghting a series o wildfresin the northern part o the state. (Seepage 36.)

Avoiding the potential increased risksrom extreme weather eventsandtheir costs to the economy andsocietyis among the reasons the

United States and the world shouldreduce emissions o global warmingpollution.

The United States and the worldshould adopt measures designed toprevent an increase in global averagetemperatures o more than 2 C (3.6F) above pre-industrial levelsa com-mitment that would enable the worldto avoid the most damaging impacts oglobal warming.

The United States should commit toemission reductions equivalent to a 35percent reduction in global warmingpollution rom 2005 levels by 2020and an 83 percent reduction by 2050,with the majority o near-term


10/53

Executive Summary

emission reductions coming rom theU.S. economy. A variety o policymeasures can be used to achieve thisgoal, including:

oA cap-and-trade system that puts a

price on emissions o global warm-ing pollutants.

oA renewable energy standard topromote the use o clean renewableenergy.

oA strong energy efciency resourcestandard or utilities that maximiz-es the use o cost-eective energyefciency improvements.

oEnhanced energy efciency stan-dards or appliances and vehiclesand stronger energy codes or newor renovated commercial and resi-dential buildings.

oInvestments in low-carbon trans-portation inrastructureinclud-ing transit and passenger railand

support or a transition to plug-inand other alternative uel vehicles.

oRetention o the EPAs author-ity to require reductions in globalwarming pollution at power plants,

as well as retention o state author-ity to go beyond ederal minimumstandards in reducing global warm-ing pollution.

State and local governments shouldadopt similar measures to reduce glob-al warming pollution and encourage atransition to clean energy.

In addition, ederal, state and localofcials should take steps to betterprotect the public rom the impact oextreme weather events. Governmentofcials should explicitly actor thepotential or global warming-inducedchanges in extreme weather patternsinto the design o public inrastruc-ture and revise policies that encourageconstruction in areas likely to be atrisk o ooding in a warming climate.


11/53


On August 29, 2005, Hurricane Ka-trina made landall along the GulCoast. Katrina was the most expen-

sive natural disaster in U.S. history and oneo the most deadly. Its landallespeciallyin the context o a 2005 season that shat-tered all previous records or hurricane re-quency, intensity and damagelaunched avigorous discussion among the public andin the media about the role global warming

may play in extreme weather trends.That discussion is renewedoten

heatedlyvirtually every t ime an extremeweather event occurs in the United States,whether it is an unprecedented string osnowstorms in the nations capital, massiveooding in Nashville, Tennessee, or a sea-son o rampant wildfres in Caliornia.

Five years ater Hurricane Katrina,it is worthwhile to take a step back andreview what we know about the connec-tion between global warming and extreme

weather and why it matters. The irst thing we know is that the

worlds climate has changed. The evidenceis now unequivocal that air and oceantemperatures have increased globally, snowand ice cover has decreased, and globalaverage sea level has risen.1

We also know rom the worlds lead-ing scientifc authorities that much o thewarming that has occurred is very likelythe result o human activities, especiallythe release o global warming pollution.

We know that the climate has not justchanged on average, but also that therehave been changes at the extremessuchas an increase in the requency o extremelyhot days and heavy precipitation events

worldwide.2 We also understand, with ahigh degree o confdence, why some othese changes in extremes are occurring.We know, or example, that warmer air iscapable o holding more water vapor, andthat water vapor content in the atmospherehas in act increased over timeand thatthese changes would be expected to lead toan increase in heavy precipitation events.

For other types o extreme weatheres-pecially rare or complex events that arecaused or made more severe by the conu-

ence o several weather phenomenadis-cerning long-term trends and attributingcauses is much more difcult. Yet, the re-cent increase in the severity and requencyo some o these events is troubling. To beconcerned that the apparent changes insome extreme events may have something

Introduction


12/53

Introduction

to do with the broader changes humanshave made in the climate is not hyste-riait is simple common sense.

Ultimately, however, we may neverknow i global warming is the cause otrends such as the recent uptick in extreme

hurricanes or severe Western wildfres.That is because every weather event nowreects both natural variability and hu-man-induced climate change.

It is important or us to know, as a soci-ety, how the changes that have taken placein the climate are likely to aect patternso extreme weather and how these eventswill change in the uture. Many criticaldecisionswhich crops to plant, where tobuild homes, how to manage and preserveecosystemsdepend on that knowledge,some o them with lie-or-death conse-quences.

When it comes to predicting the uture,science again gives us good tools to un-derstand the broad changes in the climatethat will occur i global warming pollu-tion continues unabated. It is very likelythat the world will continue to warm, andthe degree o warming will exceed that which has already taken place.3 Futurechanges are also likely to take place at the

extremesextremely hot days, heat waves,and heavy precipitation events can all beexpected to become more requent globallyin a warming world.4

Complex weather events are, again,harder to predictas is the exact degreeto which the world will warm or a givenlevel o global warming pollution in theatmospherebut scientists continue tomake remarkable strides in this direction.

All o the abovethe knowledge thatthe climate has changed, the strength o

the scientiic evidence predicting con-tinued warming i emissions continue

unabated, the understanding that climatewill change not only on average but also atthe extremes, and the scientifc evidenceon the links between global warming andspecifc extreme weather eventsis reasonor alarm.

Avoiding increases in the requencyor severity o extreme weather events isnot the only reason to take action againstglobal warming. But it isan extremely goodone. Americas ecosystems and built envi-ronment are designed or a particular cli-mateincluding the expected boundarieso extreme events. That climate has alreadychanged and will change urther. But thedegree o change that could occur i global warming pollution continues unabatedcould outstrip the ability o human andnatural systems to react and adaptwithmassive consequences to lie, property,critical ecosystems and our economy.

Coming to grips with what thosechanges might meanboth in the up-coming decades and or the lives o uturegenerationsis difcult. As anyone whohas lived through, or volunteered in thewake o a natural disaster can attest, theimpacts transcend any measure o dollarsand cents.

The profles o extreme weather eventsincluded in this reportall o which haveoccurred since 2005are intended to illus-trate the impacts o major extreme weatherevents. Their inclusion in this report isnot an assertion that these events werecaused by global warming. Rather, thesestories are intended to remind usjust asHurricane Katrina did in 2005that thepotential or damage rom extreme weatheris worth avoiding. One important way toprotect our uture is by switly reducing

emissions o pollutants that are changingour climate.


13/53


In 2007, the Intergovernmental Panel onClimate Change (IPCC)the worldsoremost scientiic authority on the

subjectcompleted its ourth assessmento the science o global warming. Thereport, which reected the work o thou-sands o scientists worldwide, concludedthat warming o the climate system is un-equivocal and that [m]ost o the observedincrease in global average temperatures

since the mid-20th century is very likely dueto the observed increase in anthropogenic[greenhouse gas] concentrations.5

In the years since publication o theFourth Assessment Report, the consen-sus surrounding the basic science behindglobal warming has urther crystallized.The worlds leading scientifc authoritieshave concluded that the planet is warmingand emissions o global warming pollutantsare very likely to blame.

A recent report published by the U.S.

National Academy o Sciences concluded:

Some scientifc conclusions or theo-ries have been so thoroughly exam-ined and tested, and supported byso many independent observationsand results, that their likelihood o

subsequently being ound to bewrong is vanishingly small. Suchconclusions and theories are thenregarded as settled acts. This is thecase or the conclusion that the Earthsystem is warming and that much othis warming is very likely due to hu-man activities.6 (emphasis added)

Similarly, 13 national academies o sci-

ences rom around the world produced ajoint statement in 2009 concluding:

[C]limate change is happening evenaster than previously estimated;global CO

2emissions since 2000 have

been higher than even the highestpredictions, Arctic sea ice has beenmelting at rates much aster thanpredicted, and the rise in sea levelhas become more rapid. The need

or urgent action to address climate

change is now indisputable.7(empha-sis added)

The scientifc consensus behind globalwarming is underscored by a recent studyo more than 1,300 climate researchers ac-tively publishing in the feld, which ound

Global Warming:The Scientifc Consensus


14/53

Global Warming: The Scientifc Consensus 9

that 97 to 98 percent o those researchersagree with the central theories behindglobal warming as laid out by the Inter-governmental Panel on Climate Change.8

There remain many unanswered ques-tions about the specifc impacts o global

warming, but in the worlds most respectedscientifc institutions, the issues o whetherglobal warming is occurring, and whetherhuman activities are playing a role, arelargely settled. Global warming is alreadychanging Americas climate, and will leadto even greater changes in the decadesto comeparticularly i human-causedemissions o global warming pollutantscontinue unchecked.

Americas Changing ClimateGlobal warming will bring major changesto Americas climate over the comingdecades. Some o those changes have al-ready begun to occur and are projected toaccelerate i emissions o global warmingpollutants continue unabated.

Temperature: Average temperature

in the United States has increased bymore than 2 F over the last 50 years.9Temperatures are expected to rise byas much as an additional 7 F to 11 Fon average by the end o this centuryunder a high-emission scenario.10 Heatwaves have become more common andmore intense in recent years.11

The heat content o the ocean has alsoincreased since the mid-20th century.12Sea surace temperatures in the Gul

o Mexico and Atlantic Ocean have in-creased over the last 100 years duringthe July to September period, whenmany hurricanes orm.13

Precipitation: Precipitation hasincreased on average in the United

States over the last 50 years. However,the increase in precipitation has notbeen uniorm around the country,with the Northeast and upper Mid-west receiving more precipitation onaverage since the late 1950s and the

Southeast and parts o the Southwestreceiving less.14 In addition, a greatershare o precipitation is alling inheavy rainstorms and snowstorms, andthere have been shits in the seasonaldistribution o precipitation. Scientistsproject that global warming will resultin an increase in the share o precipi-tation that comes in heavy events andwill cause important seasonal shits.Virtually the entire United States,or example, may experience driersummers by the end o the century iglobal warming pollution continues toincrease unabated.15

Figure 1. Decline in Northern

Hemisphere Spring Snow Cover16

Snow cover: Snow cover has de-creased over the Northern Hemi-sphere over the past three decades,with the greatest reductions in spring

and summer.17 The volume o earlyspring snowpack in the mountainWest and Pacifc Northwest hasdeclined signifcantly on average sincethe mid 20th century, with the greatestlosses in more temperate areas subjectto earlier spring snowmelt.18


15/53


Sea level rise: Sea level has risen bynearly 8 inches (20 cm) globally since1870, with the rate o sea level riseincreasing in recent years. Sea levelrise is occurring both because o thethermal expansion o sea water as it

warms and by the melting o glaciersand ice caps.19 Relative sea level hasrisen along U.S. shorelines (with ex-ceptions in parts o the Pacifc North-west and Alaska) since early in the 20thcentury, with the greatest relative risein the mid-Atlantic and Gul Coastregions. (See page 19.) A recent studysuggests that global sea level could riseby an average o between 2.5 and 6.25eet (0.75 and 1.9 meters) by the endo the century, depending on uturetrends in global warming pollution.20Changes in ocean circulation patternscould result in some areassuch asthe northeastern U.S. coastline

experiencing greater increases in sealevel than the global average. (Seepage 22.)

Shits in species and ecosystems:Global warming has already had

signifcant eects on ecosystems, withshits in the timing o spring events,the observed migration o plant andanimal species northward and tohigher elevations, and the spread oinestations by insect pests and inva-sive species.21

In addition to these changes, climate sci-ence projects that there will be changes inthe timing, requency, severity and impactso extreme weather events, both in theUnited States and worldwide.


16/53

Extreme Weather and Why it Matters 11

What Is Extreme Weather?Extreme weather is a term potentiallyraught with ambiguity. According tothe Intergovernmental Panel on ClimateChange:

An extreme weather event is an eventthat is rare at a particular place andtime o year. Deinitions o rare

vary, but an extreme weather eventwould normally be as rare as or rarerthan the 10th or 90th percentile othe observed probability densityunction. By defnition, the char-acteristics o what is called extreme

weather may vary rom place toplace in an absolute sense.22

The IPCC defnition reinorces thatextreme is a relative term, one that onlyhas meaning when compared with a par-

ticular historical record (or other reerencepoint) at a particular place. For instance, astorm that brought 12 inches o snow in a24-hour period would hardly be extremetoday in Bualo, New York, but it would behighly unusual in Washington, D.C.

However, it is important to remember

that extremes in meteorological mea-surementstemperature, rainall, windspeedare mainly meaningul becauseo the impact they have on people and theenvironment. Changes brought about byglobal warming, as well as decisions madeby humans, can make humans and eco-systems more vulnerable to the impacts oeven routine weather events. Sea levelrise, or example, magnifes the danger o

damage to property, human lie, and theenvironment o both extreme storms andstorms that would be considered normaltoday.

In addition, there is a blurry linebetween what the IPCC calls extremeweather events, which are o short dura-tion, and extreme climate events, whichtake place over a longer period o time(or example, droughts or extremely rainyseasons).23 I an area that has experiencedmonths o above-normal rainall receives

a sudden downpour that triggers a ood,or an area locked in a dry spell experiencesa severe thunderstorm that sparks a fre,is the resulting disaster attributable to aclimate event or a weather event?

In this report, we will use the term ex-treme weather broadly to describe weather

Extreme Weather and Why it Matters


17/53


events that would be considered rare whencompared to the modern historical record,events that create extreme impacts on hu-mans or the environment (particularly ithose impacts are likely to be exacerbatedby global warming), as well as longer-term

events that might otherwise be describedas extreme climate events.

Why Care AboutExtreme Weather?Changes in the requency and severity oextreme weather events are among manyprojected impacts o global warming.

Extreme weather events tend to attractgreat notice by the public and the media,leading television news coverage andgrabbing headlines. But other impacts oglobal warming that occur slowly over along period o time, or are less amenable tomedia coverage, may also cause tremendousdamage to human health and well-being orto treasured ecosystems.

Extreme weather events, however, are vitally important. By defnition, extreme

weather tests the boundaries o human-built and natural systems. Extreme weatherevents are capable o inicting massivedamage on human lie, the economy, andthe environment in a variety o ways:

Property and crop damage: Count-less private and public investmentdecisionsrom the location o roadsand buildings to the design o bridgesand ood control systemsare madebased on assumptions about the prob-

ability and likely maximum severityo extreme weather events. Whenextreme weather events dey thoseexpectations, massive damage toproperty can result. According to theNational Oceanic and AtmosphericAdministration, insured property

losses rom weather-related disastersin the United States in 2008 totaledmore than $30 billion.24 Because manylosses are not covered by insurance,the total cost o damages rom natu-ral catastrophes is likely to be much

higher.

Death and injury: Improvements inweather orecasting and communica-tions now enable early warning omany extreme weather events, givingmany vulnerable people the opportu-nity to escape rom harms way. Evenwith these advances, however, extremeweather events cause signifcant losso lie in the United States each year.In 2008, or example, weather-relatedevents killed 568 Americans and in-jured more than 2,000 people.25

Permanent changes to ecosys-tems: Extreme weather events canalso result in permanent changes toecosystems.The storm surge createdby Hurricane Katrina, or example,permanently converted 118 squaremiles o wetlands and dry land alongthe Gul Coast to open water, remov-

ing an important protection or theLouisiana coast.26 The ChandeleurIslands o the Louisiana coastparto the nations second-oldest nationalwildlie reuge and an important birdhabitatlost 84 percent o their landarea ollowing Hurricane Katrina.27Similarly, persistent drought, unusual-ly hot temperatures, and pest inesta-tion in the southwestern United Stateshave led to the widespread die-o opion pine treesan event described

byNational Geographic Newsin 2005 asarguably the most extensive die-o otrees ever documented by modern sci-ence.28 The economic costs o thesechanges wrought by extreme weatherevents are rarely tabulated or includedin estimates o storm damage.


18/53

Extreme Weather and Why it Matters 13

Emergency response expenses:Deaths, injuries and property damagerom extreme weather events wouldlikely be even greater were it not orthe work o emergency respondersfrefghters, workers stacking sandbags

alongside swollen creeks, and policeand National Guard troops calledupon to preserve public order. Thecosts o providing emergency responseor extreme weather events are signif-cant. The ederal government alone,or example, spends approximately $1billion per year on fre suppressioneorts.29

Economic disruption: Natural disas-ters also cause temporary economicdisruptions by reducing productivityor the duration o the storm, render-ing transportation systems and othertypes o inrastructure inoperable,and orcing workers and businesses toexpend time and resources recoveringrom dislocation and propertydamage.

Investments in preventive mea-sures: Another hidden cost o extreme

weather is the added cost o buildingstructures and settlements designed towithstand natural disasters. Adoptiono stronger building codes designedto ensure that buildings withstandhigh winds and oods, or relocationor ortifcation o public inrastruc-ture, such as roads and sewer systems,impose majori difcult to calcu-latecosts.

Broader and longer-term impacts:

The costs o extreme weather eventscan persist long ater buildings arerebuilt and things are seeminglyback to normal. During a disaster,

schools and health centers may close,and close-knit communities may betorn apart through relocation, all withlong-term implications or health, hu-man development and the economy.30

Changes in the severity or requency oextreme weather events can have massiveimpacts on the environment and society. Itis important, thereore, that decision-mak-ers and the public attempt to understandthe potential or global warming-drivenchanges in extreme weather.

Louisianas Chandeleur Islandsan important bird habi-tatwere greatly diminished between 2001 (top photo) andthe days ollowing the passage o Hurricane Katrina (bottom).Credit: U.S. Geological Survey.


19/53


Patterns o extreme weather eventsare already changing in the UnitedStates, and climate science predicts

that urther changes are in store. In thisreport, we review recent trends in severaltypes o extreme weather events, the im-pacts caused by notable events that haveoccurred since 2005, and the most recentscientifc projections o uture changes inextreme weather.

Hurricanes and TropicalStormsHurricanes are the most costly extreme weather events that aect the UnitedStates. Hurricane Katrina was, in nominalterms, the most costly single weather-re-lated disaster in American history, with

property damages estimated to be as muchas $125 billion.33 Hurricanes can unleashooding rains, violent winds, tornadoes,and massive coastal storm surges, inict-ing severe damage to property and naturalsystems over a wide area.

In recent decades, there has been a

trend toward stronger, more destructivehurricanes. Climate science projects thatglobal warming may bring about increasedhurricane activity, with changes in thenumber, intensity, duration or size o thosestorms.34

Recent TrendsThere has been a clear trend in recent

years toward stronger, more destructive

hurricanes in the Atlantic Ocean andworldwide.

The strongest tropical cyclones havebeen getting stronger around the globe inrecent decades.35 There has been an ob-served increase in the number o Category4 and 5 hurricanes in the Atlantic since1980.36 Measurements that aggregate thedestructive power o tropical stormsinterms o their intensity, duration and re-quencyover entire storm seasons haveshown a marked increase in the power o

hurricanes in the Atlantic since the 1970s.37Other research has ound that both the en-ergy o and amount o precipitation in trop-ical cyclones in the Atlantic have increasedin recent years, with an abrupt, step-wiseincrease in cyclone energy and precipita-tion occurring in the mid-1990s.38

Extreme Weather:The Trends, the Impacts, andPredictions or the Future


20/53

Extreme Weather: The Trends, the Impacts, and Predictions or the Future 1

The general trend toward increasesin hurricane strength is correlated withwarmer sea surace temperatures39 which,in turn, have been linked to the increase inthe concentration o global warming pol-lution in the atmosphere.40 However, thenumber, size and strength o hurricanesin any particular year vary dramaticallybased on a number o other actors, and

the relative importance o global warm-ing as a actor in recent trends remainsuncertain.41

Very recent records show an unmis-takable increase in hurricane activity inthe Atlantic during the 1995-2005 periodcompared with the average or the second

hal o the 20th centurya phenomenonthat has been linked to warmer sea watersduring the August-September period omaximum hurricane activity.42

While there has been a clear trendtoward stronger hurricanes in recentdecades, longer-term trendswhich areimportant or sorting out the potentialimpacts o global warming versus the

normal decade-to-decade variability inhurricane requency and strengthareless clear. Much o this uncertainty is dueto questions about the consistency o thehistorical hurricane record, given the vastimprovements in our ability to detect andtrack hurricanes since record-keeping on

A Focus on the Most Damaging ExtremeWeather Events

Not all extreme weather events are created equal. Floods, tornadoes andwildfres occur requently across the United States. The vast majority othe damage caused by extreme weather events, however, comes rom the ew

extreme events that are either so intense, or cover such a large geographic area, thatthey overwhelm the deenses and adaptive ability o human and natural systems.

For example, major hurricanesthose in Categories 3, 4 and 5 o the widelyused Safr-Simpson Scalepack a ar greater destructive punch than minor Cat-egory 1 or 2 hurricanes. Indeed, between 1990 and 2005, major hurricanes accountedor only 24 percent o landalling U.S. hurricanes, but were responsible or 85 per-cent o total hurricane damages.31 A reconstruction o historical damage estimatesrom oods shows a similar dynamic, with the estimated damages rom oodingevents in any given state typically dominated by a ew, very extreme events.32

At present, there is no single, reliable, consistent, and comprehensive source odata on economic or other damages rom extreme weather events. As such, in thisreport we will ocus on describing the damage inicted by several notable extremeweather events since the beginning o 2005either those that are the most deadlyor most costly in economic terms, or that are extremely unusual or their location.The estimates o damages and loss o lie used in this report are compiled romvarious sources, which include or exclude various costs associated with extremeweather events. The intention is not to provide defnitive estimates o the cost oparticular natural disasters where none likely exist, nor to compare the cost o oneevent to that o another, but rather to illustrate the severe impact that extremeweather events impose on the economy, society and the environment.


21/53


Atlantic hurricanes began in the 1850s. Asa result, scientists disagree about whetherthe number o hurricanes has increased43since the 19th century, or there has beenno change.44

Hurricanes in a Warming WorldGlobal warming is projected to lead to

an increase in the destructive power ohurricanes, with a likely increase in thenumber o extreme storms, but a possibledecrease in the overall number o hur-ricanes.45 Hurricanes, like all storms, areexpected to bring more precipitation in awarming world.

An expert team convened by the World Meteorological Organization (WMO)recently concluded that hurricane activitycould change in important ways by the endo this century i global warming continuesunabated:

The number o tropical cyclones isprojected to decrease globally, by anestimated 6 to 34 percent, but withgreat potential variation in trends orspecifc ocean basins.

Average maximum wind speeds are

projected to increase globally by 2 to11 percent.

The number o intense hurricanes isprojected to increase.46

Tropical cyclones are projected tobring more rainall, with a projectedaverage increase o about 20 percent.47

These global trends are likely to varyby region. Five o seven climate models in

one recent study pointed to an increase inthe aggregate power o hurricanes in the Atlantic by the end o the next century,with an average increase in power acrossall models o 10 percent.48 Another recentmodeling eort projected that the numbero severe Category 4 and 5 hurricanes could

be expected to double in the Atlantic overthe course o the 21st century as a result oglobal warming.49

Climate scientists have made greatprogress in improving their understand-ing o the links between global warming

and hurricanes over the past fve years, butthere remain areas o uncertainty about thetiming and degree o projected changes inhurricane activityparticularly when thescale o analysis is narrowed rom the entireglobe to particular ocean basins. Projectedtrends toward increasingly intense hurri-canes that bring more rainall, i they holdtrue along the Atlantic or Gul coasts, poseserious risks to coastal communitiespar-ticularly when coupled with rising sea level.(See page 18.)

Notable Recent Hurricanes andTheir ImpactsAccording to the National Oceanic andAtmospheric Administration, there havebeen seven hurricanes since the beginningo 2005 that inicted more than $1 billionin damages or costs.50 (It is likely that theseestimates, while the most comprehensiveavailable, still undercount the damageimposed by these disasters.) Collective

damage rom these storms exceeded $200billion. Major destructive hurricanes dur-ing this period include:

Katrina 2005 - $134 billion in esti-mated damages (normalized 2007dollars)51

Ike 2008 - $27 billion

Rita 2005 - $17.1 billion

Wilma 2005 - $17.1 billion

Gustav 2008 - $5 billion

Dennis 2005 - $2.2 billion

Dolly 2005 - $1.2 billion


22/53


Damages rom hurricanes extend arbeyond the destruction o property andloss o lie. Hurricanes are capable oinlicting permanent change to coastalecosystems (see page 12), triggering oilspills and the discharge o toxic chemicals

that can threaten public health, and caus-ing destructive inland ooding hundredso miles rom the point o landall. In ad-dition to Hurricane Katrina, the costliestweather-related disaster in U.S. history,several other hurricanes have caused majordamage in recent years.

Hurricane Ike (2008)

Texas, Louisiana, Arkansas, Tennessee,Ohio, Indiana, Illinois, Missouri, Ken-tucky, Michigan, Pennsylvania

Hurricane Ike, 2008s strongest Atlantichurricane, made landall on the north side

o Galveston Island as a Category 2 hurri-cane, but it packed a storm surge consistentwith a larger storm, inundating large partso Galveston Island, Texas Bolivar Penin-sula and nearby low-lying areas.52

The destruction o homes and busi-

nesses along the Gul Coast made nationalheadlines, but Ike brought other orms odamage as well. Ike hit the oil industryhard and caused signifcant environmen-tal damage, destroying 49 oshore oilplatorms,53 spilling hal a million barrelso oil into the Gul,54 and shutting down14 oil refneries accounting or 23 percento American capacity, causing gas pricesto rise fve cents per gallon.55 The stormknocked out power or 3 million residents.Houston saw Ike blow out windows andtear steel o the sides o skyscrapers.56 Theprospect o similar storms in the uturehas prompted Houston-area leaders topush or the construction o a 17-oot-tall

A lone house stands on a section o Texas Bolivar Peninsula that was inundated by the stormsurge rom 2008s Hurricane Ike. Credit: Adam T. Baker


23/53


Ike Dike that would stretch 60 miles andprotect the area rom oodwaters. I built,the structure would cost an estimated $2billion to $4 billion.57

Ike was responsible or 112 deaths in theUnited States and the Caribbean. While

the destruction along the Gul Coast at-tracted the bulk o the attention, oodingrains rom the storm aected large partso the Midwest and Canada. Authoritiesblamed at least 28 deaths in the Midwestand Appalachian regions on ooding romIke, and ranked the storm as one o thecostliest natural disasters in the historyo Ohio.58

Hurricane Wilma (2005)

FloridaBy the time Hurricane Wilma ormed inOctober 2005, the 2005 U.S. hurricaneseason had already tied or broken recordsor both the highest number o hurricanesand o Category 5 hurricanes, had alreadyregistered two o the fve strongest hurri-canes on record (Katrina and Rita), and hadseen the costliest hurricane ever in termso estimated damage (Katrina).59

Hurricane Wilma, however, showed

that records still remained to be brokenduring 2005, becoming the strongest Atlantic hurricane on record. Within a24-hour period, Wilma intensifed rom atropical storm to a Category 5 hurricane,a rate o intensifcation that sta at theNational Hurricane Center described asby ar the largest in the available records going back to 1851.60

Wilma weakened slightly to a Category4 hurricane beore striking Cozumel, Mex-ico. Ater crossing the Yucatan peninsula,

Wilma emerged into the Gul o Mexicoand restrengthened (to a Category 3) beoremaking landall in southwestern Florida.Wilma knocked out power to 98 percento South Florida and caused 23 deaths inall, fve o them in Florida.61 Wilmas stormsurge inundated the Florida Keys, putting

60 percent o Key West underwatertheworst storm surge ooding in the Keyssince 1965.62 The cost o damage rom thestorm was estimated at nearly $21 billion,making it (at the time) the third costliesthurricane in U.S. history.

Coastal Storms and SeaLevel RiseThe United States is the worlds third-largest country by land area, but much oour population and property is clusteredalong the coasts. Nearly three out o every10 Americans live in counties that abutthe Atlantic or Pacifc Oceans or the Gulo Mexico.63 The coasts are home to fveo the nations 10 largest cities as well asmuch o its economic productivity, keyinrastructure, culture and history. All inall, between 900,000 and 3.4 million peoplein the mid-Atlantic region alone live on cityblocks or land parcels with some land below3.3 eet (1 meter) in elevation.64

The images o widespread destructionalong the Gul Coast ater Hurricane

Katrina and Hurricane Ike reinorce theassociation o storm surge damages withhurricanes. But coastal ooding is not onlya problem in the southern states and notonly a result o hurricanes. In 2003, orexample, Hurricane Isabel pushed stormsurge waters ar up Chesapeake Bay, in-undating low-lying portions o Baltimore,Annapolis and other communities.65 In-tense winter storms along the East andWest coasts also cause ooding that dam-ages coastal property.

The U.S. coastline aces a double threatrom global warmingthe potential ormore intense storms that generate greaterstorm surge and wave action and theprojected rise in sea level that will enablecoastal storms to have a more destructiveimpact urther inland.


24/53


Recent TrendsSea level along the U.S. coast is on the rise

and there are indications o an increase inthe number o intense winter storms othe U.S. Pacic coast.

Rising sea level is not a weather event,

but it can play a major role in magniyingthe damage done by severe storms.

Sea level has risen by nearly 8 inches (20cm) globally since 1870, with the rate o sealevel rise increasing in recent years. Sealevel rise is occurring both because o thethermal expansion o sea water as it warmsand because o the melting o glaciers andice caps.66

Sea level rise is not experienced the sameway at all points along the coastline, or two

reasons. First, land along the coast is risingor alling as a result o long-term geologicalprocesses (and, in some cases, such as alongthe Gul Coast, by the drawdown o un-derground reserves o ossil uels or reshwater). Second, global warming is likely tocause sea level to rise more in some loca-tions than others, due to associated changesin ocean circulation patterns.

Figure 2 shows the relative rise in aver-age sea level at various points along thecoast rom the beginning o record-keep-ing at each station to 2006. Relative sealevel rise has been greatest in areas thatare experiencing simultaneous land sub-sidence, such as in the mid-Atlantic andalong the Gul Coast. Land subsidence and

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

MeanSeaLevelTrend(feet/

century)

Figure 2. Measured Rise in Mean Sea Level Along the U.S. Coast (from the beginning

of record-keeping at each station to 2006) in Feet per Century68


25/53


rising seas have been contributing actorsto the loss o 1,900 square miles o coastalwetlands in Louisiana.67

Sea level rise has the potential to in-crease the destructive capability o coastalstormsboth tropical storms and extra-

tropical storms such as the Noreastersthat requently hammer the East Coast andthe vicious winter storms that occur alongthe Pacifc Coast.

The storm tracks o extratropical cy-clones have shited toward the poles inrecent decades, coinciding with a declinein the number o such storms o the U.S.Atlantic and Pacifc coasts.69

Parts o the Pacifc o the U.S. WestCoast, however, have experienced increas-ing numbers o intense winter storms sincethe middle o the 20th century.70 One clueto the increase in the power o winterstorms has come rom the measuremento wave heights o the coast o the PacifcNorthwest. Researchers have ound thatwaves o the Oregon coast are higher thanthey were 35 years ago, with the greatestincrease coming in the largest waves.71 Asrecently as the early 1990s, scientists esti-mated that the height o a 100-year wave(one expected to occur only once every

century) was 33 eet; now it is estimated tobe 46 eet.72 The study also ound that theincreases in wave height have been greatesto the coast o Washington and northernOregon, and less in southern Oregon. Thestudy is consistent with other researchthat suggests an increase in the height othe highest waves along the West Coast,

particularly in the Pacifc Northwest.73(Similar research has ound an increasein maximum wave heights on the AtlanticCoast resulting rom hurricanes.74)

As described below, however, sea levelrise is likely to increase the destructive

power o even normal coastal storms.

Sea Level Rise and Coastal Stormsin a Warming WorldGlobal warming will bring higher seas as

glaciers and ice caps melt and sea watercontinues to expand as it warms. Rising

sea level will increase the damage that canbe inficted by coastal storms. The implica-tions o global warming or changes in thenumber and severity o non-tropical coastal

storms are less clear, though these stormswill likely bring more rainall.

A warmer world will bring higher seasas glaciers and ice caps continue to meltand sea water continues to expand as itwarms.

In 2007, the Intergovernmental Panelon Climate Change estimated that sea levelwould likely rise by 7 to 23 inches (18 to59 centimeters) by the end o the century. That estimate, however, (as the IPCC

acknowledged at the time) did not includethe potential or sea level change resultingrom the potential changes in the ow oice sheets in Greenland or Antarctica.75

Research conducted since publicationo the IPCCs Fourth Assessment projectsthat sea level rise will be signiicantlygreater than the IPCC estimate. The

Table 1. Land Area Less than One Meter in Elevation Above Spring High Water,Mid-Atlantic Region (sq. mi.)

NY NJ PA DE MD DC VA NC TOTAL

Dry Land 63 106 9 49 174 2 135 528 1,065

Non-Tidal Wetland 4 66 1 12 47 0 57 1,193 1,381

All Land 91 551 13 199 652 2 817 2,212 4,536


26/53


U.S. Climate Change Research Programconcluded in 2008 that, based on observedchanges in the behavior o the Greenland

and Antarctic ice sheets, including theseprocesses in models will very likely showthat IPCC AR4 [Fourth Assessment Re-port] projected sea level rises or the end othe 21st century are too low.76 One recentstudy projects that sea level rise by the endo the century could be more than doublethat predicted by the IPCCor between2.5 and 6.25 eet (75 centimeters and 1.9meters).77

What would such an increase mean or Americas coastline? In the mid-Atlantic

region rom New York to North Carolina,approximately 1,065 square miles o dryland, as well as vast areas o wetland, areless than 3.3 eet (1 meter) above the springhigh water mark. (See Table 1.)78

Rising sea level will increase thedestructive power o even routine coastal

storms by driving storm surge urtherinland. Under a high-emission scenario, a100-year coastal ood in New York City

(a ood o a size expected to occur once acentury based on historical recordsseethe text box on page 26), could happentwice as oten by the middle o this century,and 10 times as oten by the end o the cen-tury.79 Meanwhile, higher seas would raisethe water level o tidally inuenced rivers,creating greater risk o inland oodingduring heavy rainal l events.

The risks to property and inrastructureposed by a combination o sea level rise andstrong storms are severe. In the portion o

the Gul Coast stretching rom Galveston,Texas, to Mobile, Alabama, more thanhal o the highways, nearly hal o therail miles, 29 airports and almost all portinrastructure are subject to ooding in theuture due to the combination o higher sealevels and hurricane storm surge. Much

Cost o Adaptation to Sea-Level Rise

The inundation o New Orleans ollowing Hurricane Katrina demonstrated theneed or eective systems to protect low-lying coastal cities rom storm surge.Should sea level continue to rise, the preservation o low-lying citiesinclud-

ing parts o major economic engines such as Miami, New York, and Bostoncouldcome to depend on engineered deensesdeenses that could cost tens o billionso dollars to build and maintain.

Engineered deenses against sea-level rise and associated storm surge oodingare expensive and, as the case o New Orleans showed, not inallible. Great Britainand the Netherlands have built ood barriers to deend against periodic storm surgeooding that is capable o causing major property damage and loss o lie. TheThames Barrier, which protects London rom storm surge ooding, was completedat a cost o $1.9 billion, while the Netherlands Oosterscheldekering barrier nearRotterdam cost about $3.4 billion.89

Other strategies to protect coastal property rom global warming-induced sealevel riseranging rom construction o seawalls to stronger building codes tothe relocation o people and businesses away rom the shorewould also imposeeconomic costs.


27/53


o this inrastructure is at risk even in theabsence o storm surge due to projectedsea-level rise.80

In the mid-Atlantic region, a one-metersea level rise could result in the breakup ormigration o barrier islands, and convert

vast areas o wetland to open water. In areassuch as the New York City metropolitanarea, sea-level rise coupled with stormsurge rom coastal storms could result insevere damage to transportation inra-structure, including airports, highways,tunnels, railroads, ports and public trans-portation systems. A review o past stormsurges in New York City estimated thata 20-inch (50 centimeter) rise in sea level(well below the current low-end estimateo sea level rise by the end o the centuryi global warming pollution continues un-abated), had it been present during theperiod between 1997 and 2007, would have

increased the number o moderate coastalooding events at Battery Park rom zeroto 136, or the equivalent o a coastal oodwarning every other week.81

Making matters worse or residents othe northeastern United States is evidence

suggesting that sea-level rise in that region will be greater than the global average,due to global warming-induced changesin ocean circulation patterns. The resultcould be an additional 8 inches o sea-levelrise in cities such as Boston, New York andWashington, D.C., atop the roughly threeeet that will occur globally, urther mag-niying the damage caused by even routinecoastal storms.82

There is less clarity regarding thepotential impacts o global warming onextratropical storms. Recent studies sug-gest that global warming will reduce thenumber o extratropical cyclones in the

Floodwaters washed out a rail line in the Pacic Northwest during the destructive December 1-3,2007 winter storms that pounded the Pacic Coast. Credit: National Weather Service


28/53


Northern Hemisphereconsistent withthe already-alling number o these stormsas shown by the historical data.83 The U.S.Climate Change Science Program conclud-ed that the number o strong extratropicalstorms in the Northern Hemisphere would

increase.84 Other research, however, sug-gests that there will be no intensifcation oextratropical storms on the whole.85

One clear conclusion o the research isthat global warming will likely result in apoleward shit o extratropical storm tracks,with the strength o those poleward-mov-ing storms increasing.86 Shiting tracks oautumn extratropical cyclones in the NorthAtlantic may move those storms closer tothe U.S. East Coast and the storms maycover a greater area.87

Another conclusion is that extratropicalstormslike tropical stormsare likely todeliver increased precipitation, leading toincreased potential or ooding rains (seepage 24) and major snowall (see page 30)rom those storms.88

Scientifc understanding o non-tropi-cal storms continues to evolve. It is clear,however, that sea level rise will increasethe danger posed by even routine storms,and that precipitation rom extratropical

storms can be expected to increase.

Notable Recent Coastal Storms andTheir ImpactsCoastal storms have multiple impacts,bringing large amounts o rainall thatcauses inland ooding, as well as snow-all and strong winds that cause coastalooding.

The most damaging extratropical stormin U.S. history was the 1993 Superstorm

or Storm o the Century, which ormedin the Gul o Mexico and swept up theEast Coast, bringing blizzard conditionsto much o the eastern United States,dropping snow rom the Deep South toMaine, closing every airport on the EastCoast, causing storm surge damage along

the Gul and Atlantic coasts, spawningdeadly tornadoes in Florida, and cuttingo power to millions o customers.90 Anestimated 270 people died in the storm,with property damages and other costsestimated at nearly $8 billion.91

More recent coastal storms have alsocaused major damage to property andlie.

Great Coastal Gale (2007)

Oregon, WashingtonThe coastline o Washington and Oregonis dotted with small communities that areno strangers to severe winter storms. Thestorms o December 1-3, 2007, however,are likely to go down in regional lore asamong the strongest and most destructivein memory.

A series o three powerul, tightly-spaced storms brought hurricane-orce winds, coastal looding, and record ornear-record rainall in many locations.High, persistent winds snapped trees anddowned power lines. In Washington state,trees were elled in an estimated 29,000acres o orestincluding areas in which75 percent or more o trees were blown

down.92

The storm cut o transportation,electricity and communications to partso the Oregon coast. Floodwaters (someoutside o the 500-year ood zone) andmudslides completely isolated Vernonia,Oregona logging town inland rom thecoastrom the rest o the state.93 (Seenote explaining the meaning o 500-yearood and similar terms on page 26.) TheChehalis River in southwest Washingtonexperienced double its previous recordrate o streamow, with major ooding

aecting the towns o Chehalis and Cen-tralia.94

The storm was the strongest to hit theregion in at least 45 years, causing an esti-mated $180 million in damage in Oregonand possibly more than a billion dollarsmore in Washington.95


29/53


Southwest Winter Storm (2010)

Caliornia, Arizona, Utah, NevadaThe winter o 2009-2010 will be bestremembered or the series o massivesnowstorms (dubbed Snowmageddon)

that smashed snowall records in Wash-ington, D.C., and the mid-Atlantic region.But January 2010 saw other records all inAmericas Southwest.

Strong winter storms are not uncommonin the Southwest during El Nio periods,but the January 2010 storm was truly epic,setting all-time records or low pressureacross 10 to 15 percent o the United States,including Los Angeles, Salt Lake City, LasVegas and Phoenix.96 The storm broughtheavy snowall to higher elevations, heavyrain elsewhere, and strong winds, alongwith severe thunderstorms and tornadoes.In Caliornia, which experiences an aver-age o six tornadoes a year, there wereunconfrmed reports o seven tornadoes inJanuary, which would make it the all-timebusiest January or tornadoes and the sixthbusiest o any month since 1950.97

In Arizona, Yuma and Flagsta experi-enced their wettest January days on record,with heavy rainall also recorded in Phoe-

nix and Tucson.98

Accumulation o heavy,wet snow collapsed the roos o buildings inFlagsta and heavy rains caused oodingthat led to the death o a six-year-old boyas well as evacuations o low-lying areas.99

Another potential calamity, however, wasaverted, when rainall ell short o projec-tions in Caliornia. Public ofcials orderedevacuations and warned residents o thepotential or mudslides in areas that hadbeen burned in wildfres the previous year. While some mudslides were reported in

areas aected by the 2009 Station wildfre,according to Susan Cannon, a researchgeologist at the U.S. Geological Survey, Ithe initial orecast had held, its likely somecatchment basins would have overowed,potentially sending rivers o ast-movingdebris into communities.100

Flooding and ExtremeRainallFlooding is a major cause o property dam-age and loss o lie in the United States.Major oods can devastate communities,

ruin crops, and bring transportation toa halt. The 1993 Midwestern ood, orexample, was the fth most-costly weather-related disaster since 1980, trailing onlyHurricane Katrina, heat waves and relateddroughts in 1980 and 1988, and 1992s Hur-ricane Andrew.101

Property damage rom ooding resultsin part rom human decisionssuch asthe location o houses and transporta-tion inrastructure in oodplains or thepaving-over o large areas o natural land with impervious suraces, which acceler-ates the ow o runo into waterways. Butprecipitationin the orm o rain or melt-ing snowis a key ingredient o any oodevent. And with the number o extremedownpours in the United States increasingin recent decadesand projected to con-tinue to increase in the utureoodingmay well become an even more importantconcern in the years to come.

Recent TrendsThe number o extreme rainall events hasincreased in the United States in recentdecades.

Over the last century, the amount oprecipitation alling over most o the Unit-ed States has increased, with the exceptiono the Southwest, which has received lessprecipitation.102

However, the increase in precipitationhas come largely in the orm o heavyprecipitation events. Research suggests

that there has either been no change or adecrease in the number o light or aver-age precipitation days during the last 30years.103 But, the amount o precipitationalling in the top 1 percent o rainall eventshas increased by 20 percent over the courseo the 20th century.104


30/53


A 2007 Environment America Research& Policy Center analysis ound that thenumber o extreme precipitation events hadincreased by 24 percent over the continen-tal United States between 1948 and 2006,with the greatest increases coming in New

England (61 percent) and the Mid-Atlanticregion (42 percent).105 (See Figure 3.) (Thedefnition o extreme precipitation eventsalso includes snowall, which is discussedurther on page 30.)

The increase in the number o heavyprecipitation events is leading to chang-ing expectat ions about the return timeo large rainstorms and snowstorms.Critical decisions about the locationso homes and public inrastructure aremade based on the expected requency oextreme eventse.g., 100-year storms.Across the United States, the amount orainall expected in 2-year, 5-year and10-year rainall events has increased,with the most signifcant changes in theNortheast, western Great Lakes, andPacifc Northwest regions.106 The studyestimated that the amount o rain in a100-year rainstorm in the Northeast

and western Great Lakes regions is in-creasing at a rate o between 4 percentand 9 percent per decade. In much othe northeastern United States, a stormthat would have been expected to occuronce every 50 years based on data rom

1950-1979 would be expected to occuronce every 40 years based on data romthe ull 1950-2007 period.107

The trend toward more days o heavyprecipitation has even held true in theSouthwest, which has experienced lessprecipitation overall.108

The heaviest prolonged precipitationeventsincluding precipitation measuredover 5-day, 10-day, and 90-day periods otimehave also become more requent.109This fnding is important since ooding omajor rivers oten occurs during periods oprolonged wet weather, rather than atershort but intense bursts o rainall.

Summarizing the evidence on extremerainall, the U.S. Climate Change Sci-ence Program concluded that it is highlylikely that the recent elevated requenciesin heavy precipitation in the United Statesare the highest on record.110

Figure 3. Trend in Frequency of Storms with Extreme Precipitation114


31/53


Flooding and Extreme Rainall ina Warming World

The trend toward more extreme rainallevents is expected to continue in a warm-ing climate, bringing with it an increased

risk o fooding.111 Warmer temperatures lead to greater

evaporation, and warmer air is capableo holding more water vapor. These twoactors will result in rainall events thatbring more requent heavy precipitationevents in a warmer world, even in locationswhere there is no overall increase in annualrainall.112

The greatest increase in intense pre-cipitation is projected or the Northeastand Midwest.113 As discussed earlier, bothhurricanes (see page 14) and extra-tropi-cal storms (see page 18) are also projected

to come with increased precipitation in awarming world.

The question o whether increases inheavy precipitation events will lead to in-creased ooding, however, is more compli-cateddepending not only on the number

and severity o extreme events, but alsoon their timing, as well as the eective-ness o human-built systems in managingstormwater. By the end o the century,precipitation is expected to increase duringthe winter months in much o the northernUnited States, with the greatest increasestaking place in the Northeast and North-west. The summer months are projected tobe drier over most o the nation.115

A good example o the complicatedconnections between precipitation andooding is the Columbia River basin oWashington and Oregon. Climate science

Return Time (e.g., The 100-Year Flood):Its Meaning and Signifcance

M

any engineering and planning decisions are made on assumptions aboutthe likely return time o extreme weather events. Calculations o return

time are typically based on the historical climate record and rest on theassumption that what has happened in the past provides us with useul inormationabout the likelihood o extreme events recurring in the uture.

Terms such as 100-year ood are commonly misunderstood to suggest that suchan event occurs only once every 100 years. The proper way to interpret returntime is as an estimate o the probability o an event occurring in any given year,based on the historical climate record. In other words, a 100-year ood would have anestimated 1 percent chance o occurring in any particular year. The occurrence o100-year events in back-to-back years would be improbable, but not impossible.

More importantly, because the climate is changing, the historical climate recordmay no longer be as useul in helping society to estimate how requently extremeevents will occur in the uture.

In this report, we make use o terms such as 100-year ood to illustrate the im-probability o specifc extreme weather events in the context o the historical climaterecord, but caution readers that what may have been judged to be a 100-year oodbased on historical climate records may nowdepending on the changes that havetaken place in the climate in that locationbe more or less likely to occur.


32/53


projects that spring snowmelt will occurearlier in the Paciic Northwest, whileprecipitation will increase in the winter butdecrease during the summer.116 The resultis projected to be a shit toward higherriver ows during the winter and spring

months.117 A 2008 study o the potential orooding in major river basins worldwideunder an extreme climate change scenarioprojected that the Columbia River couldexperience what is now a 100-year oodas requently as once every three years bythe end o the 21st century.118

However, the increased risk o majorooding in the Columbia basin is expectedto occur at the same time that the region

also becomes more susceptible to sum-mertime drought, due to reduced summerprecipitation, a reduction in the availabil-ity o water rom snowmelt, and higher

temperatures. Indeed, the same study thatprojected a dramatic increase in the re-quency o severe oods also projected thatthe Columbia basin will experience triplethe number o drought days and lower to-tal discharge rom the Columbia over the

course o the year under a scenario markedby dramatic increases in global warmingpollution.119 (See discussion o drought onpage 32.)

This same complex combination oactors will aect uture trends in oodingin other major river basins. A 2002 studyo the potential or great loods inriver basins worldwide projected that theOhio River would be more than twiceas likely to experience a 100-year loodollowing a quadrupling o atmosphericcarbon dioxide beyond pre-industriallevels (though the same study projected

Downtown Davenport, Iowa, was submerged under foodwaters during the Midwest foods o2008, which caused between $8 billion and $10 billion in damages in the state o Iowa alone.Credit: Kurt Ockelmann


33/53


a slightly lower probability o 100-yearoods in the upper Mississippi River, theonly river studied worldwide that exhibiteda negative extreme ooding trend.)120

On a more localized level, an increasein the number o heavy downpours could

be expected to increase the risk o ashooding and urban ooding, which arealso capable o inicting property damageand loss o lie.

Notable Recent Floods and ExtremeRainall Events and their Impacts

Historically, ooding has been the mostcommon natural disaster aecting theUnited States.121 Damaging oods can oc-cur in any region o the country, and majoroods can inict massive damage. In partso the countryparticularly those thathave experienced the greatest increase inextreme rainall eventsextreme oodingseems to be happening more requently,with two massive 500-year oods occur-ring in the Midwest over a 15-year periodand a pattern o increasingly requent majoroods in New England.

Midwest Floods (2008)

Iowa, Wisconsin, Illinois, Indiana, Mis-souri, Minnesota, NebraskaIn June 2008, abnormally heavy rains trig-gered the Midwests second 500-yearooding event in 15 years. The rains cameollowing an unusually wet winter andspring. During June, more than 1,000 newdaily precipitation records were set acrossthe Midwest, as were new all-time recordsor streamow on rivers such as the Cedar,Wisconsin and Des Moines rivers.122

Iowa was hit especially hard by theoods, which let 1,300 city blocks o Ce-dar Rapids under water and devastatedthe surrounding region.123 The ood wasdeemed to be the worst natural disasterever to hit the state o Iowa124 and 85 o thestates 99 counties were declared disaster

areas by the President.125 Damage to thestate was extensive, with 40,000 Iowansorced rom their homes and 3,000 homesdestroyed.126 Economic losses were monu-mental. Total job losses stemming romthe ood were estimated at 7,500,127 and

the American Farm Bureau estimated thatthere were $4 billion in agricultural lossesin Iowa,128 contributing to total damagesestimated by state ofcials at between $8billion and $10 billion.129 The oods werealso responsible or 24 deaths and 148injuries.130

Northeast Floods (2010)

Rhode Island, Massachusetts, New Hamp- shire, Maine, New York, New Jersey,Pennsylvania

In March, 2010, New England was struckby a series o extremely wet Noreastersthat dumped record rainall on much othe region. On March 13, a large stormdropped 6 to 10 inches o rain in parts oNew England and the mid-Atlantic region. Then, two weeks later, a second majorstorm deposited several more inches o rainon the regions already saturated ground.Rainall records throughout the region

were smashed, with New York, Boston andPortland, Maine, experiencing their raini-est March ever and Providence setting arecord or its all-time rainiest month sincerecords have been kept.131

The damage was most severe in RhodeIsland. Having just started to recover roma 100-year ooding event in mid-March,the late March rains created an even worse,500-year ooding event.132 The PawtuxetRiver crested at nearly 21 eet12 eethigher than its usual levelleaving homes,

businesses and transportation inrastruc-ture underwater.133 The oods damagedsewage treatment plants and created anenvironmental crisis as raw sewage owedinto Narragansett Bay. In addition to leav-ing 2,000 residents homeless or severalweeks,134 the storm prompted ofcials to


34/53


ask residents to not ush toilets becauseo the damaged treatment plants.135 Theooding led to over $200 million in dam-age, a signifcant setback to a state withunemployment over 13 percent.136

The 2010 oods were the ourth major

ooding event in New England in fveyears, ollowing oods in October 2005(which caused 10 deaths),137 May 2006(during which Boston experienced itssecond-highest our-day rainall in 125years o record-keeping),138 and April 2007(which recorded the third- to fth-high-est streamows since 1936 at numerouslocations in Massachusetts).139 Weatherexperts have noted a pattern o increas-ingly requent major oods since 1970 inthe region.140

Tennessee Floods (2010)

Tennessee, Kentucky, MississippiOn May 1 and 2, 2010, residents o Nash- ville, Tennessee, watched in shock asoodwaters ripped churches and homes

rom their oundations and carried themdown highways alongside cars and trucks.Nashville suered a two-day rainall o13.57 inchesmore than double the pre-vious two-day record and enough to makethe frst two days o Mayalonewetter than

any other May on record.141 According topreliminary estimates rom the NationalClimatic Data Center, more than 200 daily,monthly and all-time precipitation recordswere broken in Tennessee and neighboringstates by the storm.142

Property damage rom the loodwhich achieved 1,000-year ood statusacross a broad swath o Tennesseewasastounding. Nashville landmarks such asthe Country Music Hall o Fame and LPField, the home o the NFLs TennesseeTitans, were submerged. Property damagein the Nashville area alone was estimatedat greater than $1.5 billion.143 Surround-ing areas in Tennessee, Kentucky, andMississippi were also not spared, and atthe end o the ooding, the death tollstood at 30.144

A directional sign in East Nashville, submerged during the massive May 2010 foods in Tennessee.Credit: Debbie Smith


35/53


SnowstormsThe idea that global warming might uelmore extreme snowall events might seemcounter-intuitive. Ater all, common sensewould suggest that a warmer world will

bring less snow. And, on average, thatis trueclimate science suggests thatnorthern portions o the United States willexperience a greater share o precipitationalling as rain and less as snow in a warm-ing world.145

But, as with other weather events, mucho the damage caused by snow is causedby extreme snowall events, those withthe capability to collapse roos, impairtransportation, and shut down economicactivity. Global warming has the potential

to increase the risk o extreme snowallevents or areas that remain cold enoughto receive snow.

Recent TrendsTrends toward increases in extreme pre-cipitation events apply equally to snow andrain events. There has been a northward

shit in snowstorm occurrence over thepast century, along with an apparentincrease in lake eect snow.

The same conditions that lead to moreintense rainstormsincluding increasedevaporation rom oceans and the ability owarmer air to hold more water vaporcanalso be expected to contribute to an in-crease in extreme snowstorms. Indeed, astudy o snowstorms during the 20 th cen-tury ound that most snowstorms occurredduring warmer-than-normal years in mosto the United States.146

During the 20th century, there was nosignifcant trend in snowstorms nation-

wide, but there were signifcant changesat the regional level. Snowstorms becamemore requent over the course o the cen-tury in the upper Midwest and Northeast,and less requent in the lower Midwest andSouth.147

For dierent reasonsalso potentially

linked to global warmingthere hasbeen an apparent increase in lake-eectsnows. Lake-eect snows occur whencold air blows across the surace o theGreat Lakes, causing water evaporatedrom the lakes to be deposited on the ar

shore as snow.Lake-eect snow is not possible ater

ice has ormed on the lakesthis maybe one reason why areas downwind othe Great Lakes experience the greatestsnowstorm activity early in the winter,during December, compared with otherareas where snowstorm activity peaks laterin the season.148

Ice cover on the Great Lakes hasdeclined by roughly 30 percent on aver-age since the early 1970s as the result owarmer temperatures.149 As ice cover hasdeclined, lake-eect snows have appar-ently increased. A 2003 study ound thatthere had been a signifcant increase insnowall at sites receiving lake-eect snowsince the early 1930s, compared with notrend or comparable areas not receivinglake-eect snow. The study noted, orexample, that Syracuse, New Yorkalake-eect snow hot spotexperiencedits snowiest decade o the 20 th century

during the 1990s.150

Extreme Snowstorms in aWarming World

Projected increases in extreme precipita-tion events apply to both snow and rainevents, though, over time, the share o

precipitation alling as snow versus rainis expected to decrease.

The U.S. Global Change ResearchProgram projects that the strongest winter

storms are likely to become stronger andmore requent in the decades to come.151To the extent that certain areas o thecountry remain cold enough or snowallduring periods o the winter, this wouldsuggest increased requency o storms othe century in a warming world.


36/53


Climate models project that the north-ern United States will receive more pre-

cipitation in the winter and spring months,though, over time, an increasing share othis precipitation will come as rain, as op-posed to snow.152

In a warming world, the Great Lakesare projected to reeze later and less thor-oughly, allowing or more requent lake-e-ect precipitation events. Climate scienceprojects that, while lake-eect snowallwill increase over the next several decades,it is likely to decrease ater then as warmertemperatures more requently change lake-

eect snows into lake-eect rains.153

Notable Recent ExtremeSnowstorms and their ImpactsExtreme snowstorms generally do notcreate the same degree o direct property

damage as hurricanes or ooding rains,though they can cause loss o lie as

well as economic disruption over a widearea.

2010 Mid-Atlantic Snowmageddon

Maryland, Virginia, District o Colum-bia, Delaware, West Virginia, Pennsyl-vania, New Jersey, New York

Prior to 2009, Washington, D.C., hadonly received more than a oot o snow12 times since 1870.154 In the winter o

2009-2010, it happened twiceonce inDecember 2009 and once in February2010. The February storm, which waspaired with a second, less-intense stormjust a ew days later, brought Washington,D.C. and much o the mid-Atlantic regionto a standstill.

Washington, D.C., was paralyzed by two back-to-back snowstorms in February 2010part oa string o extreme precipitation events across the country during the rst hal o 2010. Credit:Tim Brown


37/53


Dubbed Snowmaggedon or theSnowpocalypse, the storms dropped 32inches155 o snow at Washington-Dulles Airport on February 5-6and nine moreinches o snow156 on February 10-11, virtu-ally paralyzing the nations capital.157 All

modes o transportation were aected asroads became impassable, transit serviceon all but the underground portions othe citys Metro system came to a halt,Amtrak canceled most service, and thevast majority o ights to and rom the citywere stopped.158 The U.S. Postal Servicedid not deliver mail on Saturday, Febru-ary 6the frst time in 30 years that thePostal Service canceled delivery.159

The economic costs o the storm wereestimated at more than $2 billion.160 Withthe roads blocked, ederal employees hadto take unplanned leave starting ourhours early on Friday and lasting into theollowing week, at an estimated cost totaxpayers o $100 million each day.161 Thesnow also caused the collapse o severalbuildings throughout the area, includinga jet hanger at Dulles International Air-port.162 While the massive snowall in thenations capital received the most mediaattention, seasonal snowall records were

also broken in Baltimore and Philadelphiaand economic disruption spread through-out the mid-Atlantic region.163

At the time, the February 2010Snowmageddon appeared to many tobe a reak occurrence, but it was actu-ally one o a series o damaging extremeprecipitation events in the United Statesduring the latter part o 2009 and early2010including the massive mid-Atlan-tic and eastern snowstorm o December2009, the 500-year ood event in New

England in March 2010 (see page 28), the1,000-year ood event in Tennessee inMay 2010 (see page 29), and massive ood-ing in Oklahoma in June 2010.164

Drought, Wildfre and HeatWavesExtended periods o drought have broadimpacts on the economy and the environ-ment. Crops ail, reservoirs dry up, cities

and towns scramble to fnd water to supplythe needs o residents and industry, andorests and grasslands become increasinglysusceptible to damaging wildfres. The sec-ond and third most costly weather disasterso the last 30 years were droughts and heatwaves that struck the eastern and centralUnited States in 1980 and 1988.165

Global warming threatens to increasethe occurrence o extreme drought worldwide, with the percentage o the globein extreme drought projected to increaserom 1 percent today to 30 percent by theend o the century i global warming emis-sions continue unabated.166 The UnitedStates is not immune, with global warmingprojected to increase drought in much othe country, which could contribute to anincrease in wildfre activity.

Heat waves do not create the same de-gree o direct physical damage to propertyand crops as other extreme weather events(not counting their contribution to drought

or wildfre), but they are oten ar more le-thal. The U.S. Centers or Disease Controland Prevention estimates that excessiveheat killed more than 8,000 Americansbetween 1979 and 2003.167

Recent TrendsOver the past century, drought hasbecome more common in parts o thenorthern Rockies, the Southwest and theSoutheast. Periods o extreme heat havebecome more common since 1960, and

large wildre activity in the AmericanWest has increased markedly since themid-1980s.

Heat waves, droughts and wildfres areoten related events. Heat waves occur overa span o days to weeks, while droughtstypically develop ollowing long periods

8/8/2019 Global Warming and Extreme Weath

Documents

Global Warming and Extreme Weather