is global warming harmful tohealth?hn2r/index_files/sciam.pdfsuch as malaria, dengue fever , yel-low...

50 Scientific American August 2000

Today few scientists doubt the atmo-sphere is warming. Most also agreethat the rate of heating is accelerat-ing and that the consequences of

this temperature change could become in-creasingly disruptive. Even high school stu-dents can reel off some projected outcomes:the oceans will warm, and glaciers will melt,causing sea levels to rise and salt water to in-undate settlements along many low-lyingcoasts. Meanwhile the regions suitable forfarming will shift. Weather patterns should alsobecome more erratic and storms more severe.

Yet less familiar effects could be equallydetrimental. Notably, computer models pre-dict that global warming, and other climatealterations it induces, will expand the inci-dence and distribution of many serious med-ical disorders. Disturbingly, these forecastsseem to be coming true.

Heating of the atmosphere can influencehealth through several routes. Most directly,it can generate more, stronger and hotter heatwaves, which will become especially treacher-ous if the evenings fail to bring cooling relief.Unfortunately, a lack of nighttime coolingseems to be in the cards; the atmosphere isheating unevenly and is showing the biggestrises at night, in winter and at latitudes higherthan about 50 degrees. In some places, thenumber of deaths related to heat waves isprojected to double by 2020. Prolonged heatcan, moreover, enhance production of smogand the dispersal of allergens. Both effectshave been linked to respiratory symptoms.

Global warming can also threaten humanwell-being profoundly, if somewhat less di-rectly, by revising weather patterns—particu-larly by pumping up the frequency and inten-sity of floods and droughts and by causingrapid swings in the weather. As the atmo-sphere has warmed over the past century,droughts in arid areas have persisted longer,

and massive bursts of precipitation have be-come more common. Aside from causingdeath by drowning or starvation, these disas-ters promote by various means the emergence,resurgence and spread of infectious disease.

That prospect is deeply troubling, becauseinfectious illness is a genie that can be veryhard to put back into its bottle. It may killfewer people in one fell swoop than a ragingflood or an extended drought, but once it takesroot in a community, it often defies eradica-tion and can invade other areas.

The control issue looms largest in the devel-oping world, where resources for preventionand treatment can be scarce. But the techno-logically advanced nations, too, can fall vic-tim to surprise attacks—as happened last yearwhen the West Nile virus broke out for thefirst time in North America, killing sevenNew Yorkers. In these days of internationalcommerce and travel, an infectious disorderthat appears in one part of the world canquickly become a problem continents away ifthe disease-causing agent, or pathogen, findsitself in a hospitable environment.

Floods and droughts associated with globalclimate change could undermine health inother ways as well. They could damage cropsand make them vulnerable to infection and in-festations by pests and choking weeds, there-by reducing food supplies and potentiallycontributing to malnutrition. And they couldpermanently or semipermanently displace en-tire populations in developing countries, lead-ing to overcrowding and the diseases connect-ed with it, such as tuberculosis.

Weather becomes more extreme and vari-able with atmospheric heating in part becausethe warming accelerates the water cycle: theprocess in which water vapor, mainly fromthe oceans, rises into the atmosphere beforecondensing out as precipitation. A warmedatmosphere heats the oceans (leading to faster

Computer models indicate that many diseases will surge as the earth’s atmosphere heats up.

Signs of the predicted troubles have begun to appear

by Paul R. Epstein

Is Global Warming Harmful to Health?

JEA

N-M

ARC

BO

UJU

AP

Phot

o (a

bove

an

dfa

r rig

ht);

KA

REL

PRIN

SLO

O A

P Ph

oto

(rig

ht)

Is Global Warming Harmful to Health?Copyright 2000 Scientific American, Inc.

52 Scientific American August 2000 Is Global Warming Harmful to Health?

BRYA

N C

HRI

STIE

;SO

URC

E:PI

M M

ART

ENS

Maa

stric

ht U

nive

rsit

yevaporation), and it holds more mois-ture than a cool one. When the extrawater condenses, it more frequentlydrops from the sky as larger downpours.While the oceans are being heated, so isthe land, which can become highlyparched in dry areas. Parching enlargesthe pressure gradients that cause windsto develop, leading to turbulent winds,tornadoes and other powerful storms.In addition, the altered pressure andtemperature gradients that accompanyglobal warming can shift the distribu-tion of when and where storms, floodsand droughts occur.

I will address the worrisome healtheffects of global warming and disruptedclimate patterns in greater detail, but Ishould note that the consequences maynot all be bad. Very high temperaturesin hot regions may reduce snail popula-tions, which have a role in transmittingschistosomiasis, a parasitic disease. Highwinds may at times disperse pollution.Hotter winters in normally chilly areasmay reduce cold-related heart attacksand respiratory ailments. Yet overall,the undesirable effects of more variableweather are likely to include new stress-es and nasty surprises that will over-shadow any benefits.

Mosquitoes Rule in the Heat

Diseases relayed by mosquitoes—such as malaria, dengue fever, yel-

low fever and several kinds of encepha-litis—are among those eliciting thegreatest concern as the world warms.Mosquitoes acquire disease-causing mi-croorganisms when they take a blood

meal from an infected animal or per-son. Then the pathogen reproduces in-side the insects, which may deliver dis-ease-causing doses to the next individu-als they bite.

Mosquito-borne disorders are project-ed to become increasingly prevalent be-cause their insect carriers, or “vectors,”are very sensitive to meteorological con-ditions. Cold can be a friend to humans,because it limits mosquitoes to seasonsand regions where temperatures stayabove certain minimums. Winter freez-ing kills many eggs, larvae and adultsoutright. Anopheles mosquitoes, whichtransmit malaria parasites (such asPlasmodium falciparum), cause sus-tained outbreaks of malaria only wheretemperatures routinely exceed 60 de-grees Fahrenheit. Similarly, Aedes ae-gypti mosquitoes, responsible for yel-low fever and dengue fever, conveyvirus only where temperatures rarelyfall below 50 degrees F.

Excessive heat kills insects as effec-tively as cold does. Nevertheless, withintheir survivable range of temperatures,mosquitoes proliferate faster and bitemore as the air becomes warmer. At thesame time, greater heat speeds the rateat which pathogens inside them repro-duce and mature. At 68 degrees F, theimmature P. falciparum parasite takes26 days to develop fully, but at 77 de-grees F, it takes only 13 days. The An-opheles mosquitoes that spread this ma-laria parasite live only several weeks;warmer temperatures raise the oddsthat the parasites will mature in timefor the mosquitoes to transfer the infec-tion. As whole areas heat up, then, mos-

quitoes could expand into formerly for-bidden territories, bringing illness withthem. Further, warmer nighttime andwinter temperatures may enable themto cause more disease for longer periodsin the areas they already inhabit.

The extra heat is not alone in encour-aging a rise in mosquito-borne infec-tions. Intensifying floods and droughtsresulting from global warming can eachhelp trigger outbreaks by creating breed-ing grounds for insects whose dessicat-ed eggs remain viable and hatch in stillwater. As floods recede, they leave pud-dles. In times of drought, streams canbecome stagnant pools, and people mayput out containers to catch water; thesepools and pots, too, can become incu-bators for new mosquitoes. And the in-sects can gain another boost if climatechange or other processes (such as al-terations of habitats by humans) reducethe populations of predators that nor-mally keep mosquitoes in check.

Mosquitoes on the March

Malaria and dengue fever are twoof the mosquito-borne diseases

most likely to spread dramatically asglobal temperatures head upward. Ma-laria (marked by chills, fever, aches andanemia) already kills 3,000 people,mostly children, every day. Some mod-els project that by the end of the 21stcentury, ongoing warming will have en-larged the zone of potential malariatransmission from an area containing45 percent of the world’s population toan area containing about 60 percent.That news is bad indeed, considering

DECREASE

NO SIGNIFICANT RISK

NO CHANGE

AREAS NEWLY AT RISK

1.1 TO 1.4

1.4 TO 1.7

1.7 TO 2.0

>2

RISK OF MALARIA TRANSMISSION will have risen in many parts of theworld by 2020 (relative to the average risk in the years 1961 to 1990), accordingto projections assuming a temperature increase of about two degrees Fahrenheit.The analysis was based solely on temperature threshold and did not assess otherfactors that could influence malaria’s spread.

AMOUNTTHE RISK

WILLMULTIPLY

PREDICTED CHANGEIN RISK OF MALARIA

TRANSMISSION

Copyright 2000 Scientific American, Inc.

that no vaccine is available and that thecausative parasites are becoming resist-ant to standard drugs.

True to the models, malaria is reap-pearing north and south of the tropics.The U.S. has long been home to An-opheles mosquitoes, and malaria circu-lated here decades ago. By the 1980smosquito-control programs and otherpublic health measures had restrictedthe disorder to California. Since 1990,however, when the hottest decade onrecord began, outbreaks of locally trans-mitted malaria have occurred during hotspells in Texas, Florida, Georgia, Michi-gan, New Jersey and New York (as wellas in Toronto). These episodes undoubt-edly started with a traveler or stow-away mosquito carrying malaria para-sites. But the parasites clearly foundfriendly conditions in the U.S.—enoughwarmth and humidity, and plenty ofmosquitoes able to transport them tovictims who had not traveled. Malariahas returned to the Korean peninsula,parts of southern Europe and the for-mer Soviet Union and to the coast ofSouth Africa along the Indian Ocean.

Dengue, or “breakbone,” fever (a se-vere flulike viral illness that sometimescauses fatal internal bleeding) is spread-ing as well. Today it afflicts an estimat-ed 50 million to 100 million in thetropics and subtropics (mainly in urbanareas and their surroundings). It hasbroadened its range in the Americasover the past 10 years and had reacheddown to Buenos Aires by the end of the1990s. It has also found its way to north-ern Australia. Neither a vaccine nor aspecific drug treatment is yet available.

Although these expansions of malar-ia and dengue fever certainly fit the pre-dictions, the cause of that growth cannotbe traced conclusively to global warm-ing. Other factors could have been in-volved as well—for instance, disruptionof the environment in ways that favormosquito proliferation, declines in mos-quito-control and other public healthprograms, and rises in drug and pesti-cide resistance. The case for a climaticcontribution becomes stronger, howev-er, when other projected consequencesof global warming appear in concertwith disease outbreaks.

Such is the case in highlands aroundthe world. There, as anticipated, warmthis climbing up many mountains, alongwith plants and butterflies, and summitglaciers are melting. Since 1970 the ele-vation at which temperatures are al-ways below freezing has ascended al-

most 500 feet in the tropics. Marchingupward, too, are mosquitoes and mos-quito-borne diseases.

In the 19th century, European colo-nists in Africa settled in the cooler moun-tains to escape the dangerous swampair (“mal aria”) that fostered disease inthe lowlands. Today many of those ha-vens are compromised. Insects and in-sect-borne infections are being reportedat high elevations in South and CentralAmerica, Asia, and east and central Af-rica. Since 1980 Ae. aegypti mosquitoes,once limited by temperature thresholdsto low altitudes, have been found aboveone mile in the highlands of northernIndia and at 1.3 miles in the ColombianAndes. Their presence magnifies the risk

that dengue and yellow fever may fol-low. Dengue fever itself has struck atthe mile mark in Taxco, Mexico. Pat-terns of insect migration change faster inthe mountains than they do at sea level.Those alterations can thus serve as indi-cators of climate change and of diseaseslikely to expand their range.

Opportunists Like Sequential Extremes

The increased climate variability ac-companying warming will proba-

bly be more important than the risingheat itself in fueling unwelcome out-breaks of certain vector-borne illnesses.For instance, warm winters followed byhot, dry summers (a pattern that could

Is Global Warming Harmful to Health? Scientific American August 2000 53

BRYA

N C

HRI

STIE

Computer models have predicted that global warming would produce sever-al changes in the highlands:summit glaciers (like North Polar sea ice) would

begin to melt, and plants, mosquitoes and mosquito-borne diseases would mi-grate upward into regions formerly too cold for them (diagram).All these predic-tions are coming true.This convergence strongly suggests that the upward ex-pansion of mosquitoes and mosquito-borne diseases documented in the past 15years ( list at bottom) has stemmed,at least in part, from rising temperatures.

Changes Are Already Under Way

Cold temperaturescaused freezing at highelevations and limitedmosquitoes, mosquito-borne diseases andmany plants to low altitudes

Some mosquitoes,mosquito-borne diseases and plants have migrated upward

MOSQUITOESDENGUE FEVEROR MALARIA

PLANTS

BEFORE 1970 TODAYIncreased warmth has

caused mountain glaciersto shrink in the tropics and

temperate zones

Aedes aegypti mosquitoes(can spread dengue

fever and yellow fever)Eastern Andes Mountains,

ColombiaNorthern highlands of India

MalariaHighlands of Ethiopia, Rwanda,

Uganda and Zimbabwe Usamabara Mountains,Tanzania Highlands of Papua New Guinea

and West Papua (Irian Jaya)

Dengue feverSan Jose,Costa Rica

Taxco,Mexico

WHERE DISEASES OR THEIR CARRIERS HAVE REACHED HIGHER ELEVATIONS


become all too familiar as the atmo-sphere heats up) favor the transmissionof St. Louis encephalitis and other in-fections that cycle among birds, urbanmosquitoes and humans.

This sequence seems to have abettedthe surprise emergence of the West Nilevirus in New York City last year. Noone knows how this virus found its wayinto the U.S. But one reasonable expla-nation for its persistence and amplifica-tion here centers on the weather’s effectson Culex pipiens mosquitoes, which ac-counted for the bulk of the transmis-sion. These urban dwellers typically laytheir eggs in damp basements, gutters,sewers and polluted pools of water.

The interaction between the weather,the mosquitoes and the virus probablywent something like this: The mild win-ter of 1998–99 enabled many of themosquitoes to survive into the spring,which arrived early. Drought in springand summer concentrated nourishingorganic matter in their breeding areasand simultaneously killed off mosquitopredators, such as lacewings and lady-bugs, that would otherwise have helpedlimit mosquito populations. Droughtwould also have led birds to congregatemore, as they shared fewer and smallerwatering holes, many of which were fre-quented, naturally, by mosquitoes.

Once mosquitoes acquired the virus,the heat wave that accompanied thedrought would speed up viral matura-tion inside the insects. Consequently, asinfected mosquitoes sought blood meals,they could spread the virus to birds at arapid clip. As bird after bird became in-fected, so did more mosquitoes, whichultimately fanned out to infect humanbeings. Torrential rains toward the endof August provided new puddles for thebreeding of C. pipiens and other mos-quitoes, unleashing an added crop of po-tential virus carriers.

Like mosquitoes, other disease-con-veying vectors tend to be “pests”—op-portunists that reproduce quickly andthrive under disturbed conditions unfa-vorable to species with more specializedneeds. In the 1990s climate variabilitycontributed to the appearance in hu-mans of a new rodent-borne ailment:the hantavirus pulmonary syndrome, ahighly lethal infection of the lungs. Thisinfection can jump from animals to hu-mans when people inhale viral particleshiding in the secretions and excretionsof rodents. The sequential weather ex-tremes that set the stage for the first hu-man eruption, in the U.S. Southwest in

1993, were long-lasting drought inter-rupted by intense rains.

First, a regional drought helped to re-duce the pool of animals that prey onrodents—raptors (owls, eagles, prairiefalcons, red-tailed hawks and kestrels),coyotes and snakes. Then, as droughtyielded to unusually heavy rains early in1993, the rodents found a bounty offood, in the form of grasshoppers andpiñon nuts. The resulting populationexplosion enabled a virus that had beeneither inactive or isolated in a smallgroup to take hold in many rodents.When drought returned in summer, theanimals sought food in human dwellingsand brought the disease to people. Byfall 1993, rodent numbers had fallen,and the outbreak abated.

Subsequent episodes of hantaviruspulmonary syndrome in the U.S. havebeen limited, in part because early-warn-ing systems now indicate when rodent-control efforts have to be stepped up and

because people have learned to be morecareful about avoiding the animals’droppings. But the disease has appearedin Latin America, where some ominousevidence suggests that it may be passedfrom one person to another.

As the natural ending of the first han-tavirus episode demonstrates, ecosys-tems can usually survive occasional ex-tremes. They are even strengthened byseasonal changes in weather conditions,because the species that live in change-able climates have to evolve an ability tocope with a broad range of conditions.But long-lasting extremes and very widefluctuations in weather can overwhelmecosystem resilience. (Persistent oceanheating, for instance, is menacing coralreef systems, and drought-driven forestfires are threatening forest habitats.)And ecosystem upheaval is one of themost profound ways in which climatechange can affect human health. Pestcontrol is one of nature’s underappreci-


Scientists often gain insight into the work-ings of complicated systems by studying

subsystems. In that spirit, investigatorsconcerned about global warm-ing’s health ef-fects are assess-ing outcomes of the El Niño/Southern Oscillation(ENSO), a climate process thatproduces many of the same me-teorological changes predictedfor a warming world. The find-ings are not reassuring.

“El Niño” refers to an oceanicphenomenon that materializesevery five years or so in the trop-ical Pacific. The ocean off Perubecomes unusually warm andstays that way for months be-fore returning to normal or go-ing to a cold extreme (La Niña).The name “Southern Oscillation”refers to atmospheric changesthat happen in tandem with thePacific’s shifts to warmer or cool-er conditions.

During an El Niño,evaporationfrom the heated eastern Pacificcan lead to abnormally heavyrains in parts of South Americaand Africa; meanwhile other ar-eas of South America and Africa

and parts of Southeast Asia and Australia suf-fer droughts.Atmospheric pressure changesover the tropical Pacific also have ripple ef-fects throughout the globe, generally yield-ing milder winters in some northern regions

El Niño’s Message

Disease Outbreaks Accompanying Extreme

Weather during the1997–98 El Niño

Abnormally wet areas

Abnormally dry areas

Extreme Weather


ated services to people; well-functioningecosystems that include diverse specieshelp to keep nuisance organisms incheck. If increased warming and weath-er extremes result in more ecosystemdisturbance, that disruption may fosterthe growth of opportunist populationsand enhance the spread of disease.

Unhealthy Water

Beyond exacerbating the vector-borneillnesses mentioned above, global

warming will probably elevate the inci-dence of waterborne diseases, includingcholera (a cause of severe diarrhea).Warming itself can contribute to thechange, as can a heightened frequencyand extent of droughts and floods. Itmay seem strange that droughts wouldfavor waterborne disease, but they canwipe out supplies of safe drinking waterand concentrate contaminants that mightotherwise remain dilute. Further, the

lack of clean water during a drought in-terferes with good hygiene and safe re-hydration of those who have lost largeamounts of water because of diarrheaor fever.

Floods favor waterborne ills in differ-ent ways. They wash sewage and othersources of pathogens (such as Crypto-sporidium) into supplies of drinking wa-ter. They also flush fertilizer into watersupplies. Fertilizer and sewage can eachcombine with warmed water to triggerexpansive blooms of harmful algae.Some of these blooms are directly toxicto humans who inhale their vapors; oth-ers contaminate fish and shellfish, which,when eaten, sicken the consumers. Re-cent discoveries have revealed that algalblooms can threaten human health inyet another way. As they grow bigger,they support the proliferation of variouspathogens, among them Vibrio cholerae,the causative agent of cholera.

Drenching rains brought by a warmed

Indian Ocean to the Horn of Africa in1997 and 1998 offer an example of howpeople will be affected as global warm-ing spawns added flooding. The down-pours set off epidemics of cholera aswell as two mosquito-borne infections:malaria and Rift Valley fever (a flulikedisease that can be lethal to livestockand people alike).

To the west, Hurricane Mitch stalledover Central America in October 1998for three days. Fueled by a heated Carib-bean, the storm unleashed torrents thatkilled at least 11,000 people. But thatwas only the beginning of its havoc. Inthe aftermath, Honduras reported thou-sands of cases of cholera, malaria anddengue fever. Beginning in February ofthis year, unprecedented rains and a se-ries of cyclones inundated large parts ofsouthern Africa. Floods in Mozambiqueand Madagascar killed hundreds, dis-placed thousands and spread both chol-era and malaria. Such events can also


BRYA

N C

HRI

STIE

;SO

URC

ES:N

OA

A C

LIM

ATE

PRED

ICTI

ON

CEN

TER;

htt

p://

chg

e2.m

ed.h

arva

rd.e

du

/en

so/d

isea

se.h

tml

of the U.S. and western Canada. During a LaNiña, weather patterns in the affected areasmay go to opposite extremes.

The incidence of vector-borne and water-borne diseases climbs during El Niño and La

Niña years,especially in areas hit by floods ordroughts. Long-term studies in Colombia,Venezuela, India and Pakistan reveal, for in-stance, that malaria surges in the wake of ElNiños. And my colleagues and I at Harvard

University have shown that regions strickenby flooding or drought during the El Niño of1997–98 (the strongest of the century) oftenhad to contend as well with a convergenceof diseases borne by mosquitoes, rodents

and water (map). Addition-ally, in many dry ar-eas, fires raged outof control, pollut-ing the air for miles

around.ENSO is not merely a

warning of troubles to come;it is likely to be an engine for

those troubles. Several climatemodels predict that as the atmo-sphere and oceans heat up,El Niñosthemselves will become more com-mon and severe—which means thatthe weather disasters they produceand the diseases they promote could

become more prevalentas well.

Indeed, the ENSOpattern has alreadybegun to change.Since 1976 the inten-sity, duration andpace of El Niños haveincreased. And dur-ing the 1990s, everyyear was marked by

an El Niño or La Niña ex-treme. Those trends bode ill for

human health in the 21st century.—P.R.E.

Mosquito-borne: Dengue fever

Encephalitis

Malaria

Rift Valley fever

Rodent-borne: Hantavirus pulmonary syndrome

Waterborne: Cholera

Noninfectious: Respiratory illness resultingfrom fire and smoke

Disease Outbreaks


greatly retard economic development,and its accompanying public health ben-efits, in affected areas for years.

Solutions

The health toll taken by globalwarming will depend to a large ex-

tent on the steps taken to prepare forthe dangers. The ideal defensive strate-

gy would have multiple components.One would include improved surveil-

lance systems that would promptly spotthe emergence or resurgence of infec-tious diseases or the vectors that carrythem. Discovery could quickly triggermeasures to control vector proliferationwithout harming the environment, toadvise the public about self-protection,to provide vaccines (when available) for

at-risk populations and to deliver prompttreatments.

This past spring, efforts to limit theWest Nile virus in the northeastern U.S.followed this model. On seeing that thevirus had survived the winter, publichealth officials warned people to cleartheir yards of receptacles that can holdstagnant water favorable to mosquitobreeding. They also introduced fish that


BRYA

N C

HRI

STIE

MILD WINTER

DRY SPRING AND SUMMER

JULY HEAT WAVE

VICIOUS CYCLEBEGAN

More mosquitoes than usual survived the winter in sewers, damp basements

and other sources of still water

Many birds congregated at dwindling water sources

Lack of rain killedpredators of mosquitoes

(frogs, lacewings, ladybugs)

MOSQUITOPOPULATIONGREW LARGE

Once mosquitoes infected with the West Nile virus

appeared, the heat caused the virus to proliferate

rapidly inside them

DRENCHING AUGUST RAINS

INFECTION SPREAD TO PEOPLE

Downpours formed new breeding sites for mosquitoes, yielding

a new crop of the insects

Mosquito population flourished in spring

and summer

As water in breeding sites evaporated, organic compounds

became concentrated, nourishing mosquito larvae

1

2

3

4

Infected mosquitoes transmitted the virus to initially uninfected birds

Initially uninfected mosquitoes picked up the virus from infected birds

As more and more mosquitoes became infected, they spread the virus to still more birds and ultimately to people

This diagram offers a possible explanation for how awarming trend and sequential weather extremes helped

the West Nile virus to establish itself in the New York City area

in 1999. Whether the virus entered the U.S. via mosquitoes,birds or people is unknown. But once it arrived, interactionsbetween mosquitoes and birds amplified its proliferation.

INFECTED MOSQUITO

UNINFECTED MOSQUITO

Weather and the West Nile Virus


eat mosquito larvae into catchbasins and put insecticide pel-lets into sewers.

Sadly, however, comprehen-sive surveillance plans are notyet realistic in much of theworld. And even when vaccinesor effective treatments exist,many regions have no meansof obtaining and distributingthem. Providing these preven-tive measures and treatmentsshould be a global priority.

A second component wouldfocus on predicting when cli-matological and other envi-ronmental conditions couldbecome conducive to diseaseoutbreaks, so that the riskscould be minimized. If climate modelsindicate that floods are likely in a givenregion, officials might stock shelterswith extra supplies. Or if satellite im-ages and sampling of coastal waters in-dicate that algal blooms related tocholera outbreaks are beginning, offi-cials could warn people to filter con-taminated water and could advise med-ical facilities to arrange for additionalstaff, beds and treatment supplies.

Research reported in 1999 illustratesthe benefits of satellite monitoring. Itshowed that satellite images detectingheated water in two specific ocean re-gions and lush vegetation in the Hornof Africa can predict outbreaks of RiftValley fever in the Horn five months inadvance. If such assessments led to vac-cination campaigns in animals, theycould potentially forestall epidemics inboth livestock and people.

A third component of the strategywould attack global warming itself. Hu-

man activities that contribute to the heat-ing or that exacerbate its effects mustbe limited. Little doubt remains thatburning fossil fuels for energy is playinga significant role in global warming, byspewing carbon dioxide and other heat-absorbing, or “greenhouse,” gases intothe air. Cleaner energy sources must beput to use quickly and broadly, both inthe energy-guzzling industrial worldand in developing nations, which can-not be expected to cut back on their en-ergy use. (Providing sanitation, hous-ing, food, refrigeration and indoor firesfor cooking takes energy, as do thepumping and purification of water andthe desalination of seawater for irriga-tion.) In parallel, forests and wetlandsneed to be restored, to absorb carbondioxide and floodwaters and to filtercontaminants before they reach watersupplies.

The world’s leaders, if they are wise,will make it their business to find a way

to pay for these solutions. Climate, eco-logical systems and society can all re-coup after stress, but only if they arenot exposed to prolonged challenge orto one disruption after another. The Intergovernmental Panel on ClimateChange, established by the United Na-tions, calculates that halting the ongo-ing rise in atmospheric concentrationsof greenhouse gases will require awhopping 60 to 70 percent reductionin emissions.

I worry that effective corrective mea-sures will not be instituted soon enough.Climate does not necessarily changegradually. The multiple factors that arenow destabilizing the global climate sys-tem could cause it to jump abruptly outof its current state. At any time, theworld could suddenly become muchhotter or even much colder. Such a sud-den, catastrophic change is the ultimatehealth risk—one that must be avoidedat all costs.


The Author

PAUL R. EPSTEIN, an M.D. trainedin tropical public health, is associatedirector of the Center for Health andthe Global Environment at HarvardMedical School. He has served in med-ical, teaching and research capacitiesin Africa, Asia and Latin America andhas worked with the Intergovernmen-tal Panel on Climate Change, the Na-tional Oceanic and Atmospheric Ad-ministration, and the National Aero-nautics and Space Administration toassess the health effects of climatechange and to develop health applica-tions for climate forecasting and re-mote-sensing technologies.

Further Information

The Emergence of New Disease. Richard Levins, Tamara Auerbuch, Uwe Brinkmann, IrinaEckardt, Paul R. Epstein, Tim Ford, Najwa Makhoul, Christina dePossas, Charles Puccia, AndrewSpielman and Mary E. Wilson in American Scientist, Vol. 82, No. 1, pages 52–60; January/February 1994.

Climate Change and Human Health. Edited by Anthony J. McMichael, Andrew Haines,Rudolf Slooff and Sari Kovats. World Health Organization, World Meteorological Organiza-tion, United Nations Environmental Program, 1996.

The Regional Impacts of Climate Change: An Assessment of Vulnerability, 1997. Editedby R. T. Watson, M. C. Zinyowera and R. H. Moss. Cambridge University Press, 1997. Sum-mary from the Intergovernmental Panel on Climate Change available at www.ipcc.ch/pub/ reports.htm

Biological and Physical Signs of Climate Change: Focus on Mosquito-Borne Diseases.Paul R. Epstein, Henry F. Diaz, Scott Elias, Georg Grabherr, Nicholas E. Graham, Willem J. M.Martens, Ellen Mosley-Thompson and Joel Susskind in Bulletin of the American MeteorologicalSociety, Vol. 79, pages 409–417; 1998.

Other Web sites of interest: www.heatisonline.org and www.med.harvard.edu/chge

NA

SA (h

ttp

://p

ao.g

sfc.

nas

a.g

ov/g

sfc/

eart

h/r

valle

y/rv

alle

y.h

tm)

SA


is global warming harmful tohealth?hn2r/index_files/sciam.pdfsuch as malaria, dengue fever , yel-low...

Documents