Global Climate Changes, Natural Disasters, and Travel Health Risks

James H. Diaz MD, DrPH
DOI: 361-372 First published online: 1 November 2006


Whether the result of cyclical atmospheric changes, anthropogenic activities, or combinations of both, authorities now agree that the earth is warming from a variety of climatic effects, including the cascading effects of greenhouse gas emissions to support human activities. To date, most reports of the public health outcomes of global warming have been anecdotal and retrospective in design and have focused on heat stroke deaths following heat waves, drowning deaths in floods and tsunamis, and mosquito‐borne infectious disease outbreaks following tropical storms and cyclones. Accurate predictions of the true public health outcomes of global climate change are confounded by several effect modifiers including human acclimatization and adaptation, the contributions of natural climatic changes, and many conflicting atmospheric models of climate change. Nevertheless, temporal relationships between environmental factors and human health outcomes have been identified and may be used as criteria to judge the causality of associations between the human health outcomes of climate changes and climate‐driven natural disasters. Travel medicine physicians are obligated to educate their patients about the known public health outcomes of climate changes, about the disease and injury risk factors their patients may face from climate‐spawned natural disasters, and about the best preventive measures to reduce infectious diseases and injuries following natural disasters throughout the world.

With the documented increase in average global surface temperatures of 0.6°C since 1975, there is now uniform agreement in the international scientific community that the earth is warming from a variety of climatic effects, most notably the cascading effects of greenhouse gas emissions to support human activities. 1–5 Invited editorial reviews by academics often echo the prevailing scientific consensus on climate change and seek causal associations between global warming and public health outcomes. 4,5 Nevertheless, accurate scientific predictions of the true human health outcomes of global climate change are significantly confounded by several effect modifiers that cannot be adjusted for analytically including (1) the absence of linear dose–response relationships between climate change and human health; (2) the balancing effects of human acclimatization and adaptation; (3) the contributions of natural, cyclical climate changes; (4) the conflicting models of climate change that disagree on how rapidly, how regionally, how asymmetrically, and to what extent the earth will warm, and last (5) the extent to which global warming will influence the occurrence and severity of natural disasters. Exemplifying such conflicting scientific positions, the US National Weather Service, an agency of the US National Oceanographic and Atmospheric Administration (NOAA), has concluded that the current increase in tropical cyclone activity in the South Atlantic has resulted from normal climate cycles, such as the Multi‐Decadal Oscillation, and not from anthropogenic climate changes, such as global warming from greenhouse gas emissions.

Most reports to date of the public health impact of global warming have been anecdotal and retrospective in design and have focused on the increase in heat stroke deaths following heat waves and on airborne and mosquito‐borne disease outbreaks following ocean temperature–spawned tropical storms and cyclones. Although vastly beyond the scope of this article, malaria, notably that caused by chloroquine‐resistant Plasmodium falciparum, remains the most common cause of arthropod‐borne infectious disease deaths worldwide, especially in travelers and expatriates. Due to combinations of global warming and increasing precipitation, the geographic range of malaria endemicity has now extended to higher altitudes and to new regions in formerly malaria‐free areas of the tropics, subtropics, and, even temperate locales with competent anopheline vectors.

The ultimate effects of global warming on rainfall and drought, tropical cyclone and tsunami activity, and tectonic and volcanic activity will have far‐reaching human health impacts, not only on environmentally associated disease outbreaks but also on world food supplies and mass population movements. International travelers need to be informed by their physicians of all potential human health risks they may face from regional natural disasters that may be the result of natural weather cycles, anthropogenic climatic changes, or both.


To better define regional risks to international travelers, the MEDLINE search engine, 1966 to 2004, was queried with the key words “climate change” and “natural disasters,” and used to link consistent and temporal associations between known outbreaks of human illnesses and prior climate changes or natural disasters. Since the outcomes of climate change demonstrated no linear or strength of association relationships, only consistent and temporal associations were used as suitable criteria to judge the causality of any associations between the human health outcomes of climate changes and climate‐driven natural disasters. Temporal relationships between environmental factors and human health outcomes occur frequently and are often used to demonstrate associations in human health outcomes, such as food‐borne disease outbreaks, drowning deaths in floods, and mosquito‐borne disease outbreaks following heavy rains.

Measuring the mechanisms of climate change

Since the 1980s, the outcomes of climatic change on human health have received more attention; climate change–induced infectious disease outbreaks have been investigated; and two climate prediction models have been selected by the Intergovernmental Panel on Climate Change (IPCC) to assess future global weather patterns: (1) the Canadian Centre for Climate Modeling and Analysis model and (2) the British Hadley Centre for Climate Prediction and Research model. 1–4 The IPCC is a respected international scientific organization composed of delegates from many countries and disciplines who meet in periodic summits to study and to report on global climate changes, whether due to natural variabilities or as consequences of anthropomorphic activities. 4 The major meteorological models of global climate change are compared in Table 1. Combining the differing climate change models and accounting for some successes in current efforts to limit greenhouse gases, scientists now share a forecast consensus of global warming within a range of 1.4ºC to 5.8ºC by 2100. 1–4 The primary mechanisms of climate change include the ocean temperature oscillations and, more importantly, the cascading greenhouse gas effects of global warming, increasing precipitation, polar meltdown, and rising sea levels. The secondary and mediating mechanisms of global climate change include stratospheric ozone depletion, increasing volcanic activity, and increasing tectonic activity with its associated tsunami effects.

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Table 1

The major meteorological models of climate change

ModelsCanadianHadley (UK)*
TemperatureFaster warmingSlower warmingUneven warming: troposphere > stratosphere, land > sea, higher > lower latitudes, night > day
DroughtWidespread increase: eastern > western hemisphereRegional increase: eastern > western hemisphereRegional increase: eastern > western hemisphere, southern > northern hemisphere
PrecipitationLimited increase: rainfall > snowfallRegional increase: rainfall > snowfallUneven increase: rainfall > snowfall, coastal > interior, northern > southern hemisphere, western > eastern hemisphere
StormsIncreasing: Pacific > AtlanticIncreasing: Atlantic > PacificIncreasing: Both Atlantic and Pacific Oceans
  • * The International Intergovernmental Panel on Climate Change (IPCC). The IPCC recommendations are simply consensus statements and not true independent climate change models.

Ocean temperature oscillations

Climatologists and oceanographers have now identified four major ocean surface and subsurface temperature oscillations that influence land weather patterns—the North Atlantic Oscillation and the three Pacific Oscillations. The North Atlantic Oscillation is created by the unstable confluence of warm Gulf Stream surface waters with cold North Atlantic waters. The North Atlantic Oscillation influences storm patterns in the Northeast Atlantic Ocean, the Gulf Stream, the US east coast, and the Canadian Maritimes. The unpredictable North Atlantic Oscillation lasts 1 to 2 years, often combines with hurricanes spawned in the South Atlantic to create megastorms, and frequently disrupts commercial fishing in the Northeast Atlantic and Outer Banks. The North Atlantic Oscillation is influenced by powerful ocean currents, including the Gulf Stream and the North Atlantic “conveyor belt” current that circulates cold Arctic waters southward and warm Gulf Stream waters northward to Northern Europe and the British Isles.

The El Niño Southern (Pacific) Oscillations (ENSOs), that is, the alternating El Niño and La Niña thermal equatorial current cycles, consistently affect regional variations in precipitation, temperature, and hurricane, or more precisely, tropical cyclone activity over most of the midlatitude areas of the world (Table 2). 2 Although the ENSOs have received the most recent attention with satellite and ocean surface buoy monitoring, the Pacific Decadal Oscillation (PDO), or Multi‐Decadal Oscillation, has the greatest global influence on world weather patterns. 1

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Table 2

The El Niño Southern (Pacific) Oscillations (ENSOs)

The ENSOsEl NiñoLa Niña
CycleEvery 1–2 years, formerly 3–7 yearsSame, but alternating
LocationEastern equatorial Pacific OceanSame, but alternating
OscillationIncreasing local sea surface temperatures, widening thermoclineDecreasing local sea surface temperatures, thinning thermocline
TemperatureIncreasing along entire Eastern Pacific Rim from Alaska to ChileDecreasing along entire Eastern Pacific Rim from Alaska to Chile
DroughtIncreasing in India, Asia, Africa, Australia, Southeast United States, with longer bush, brush, and forest fire seasonsIncreasing in Western United States and Latin America with longer brush and forest fire seasons
PrecipitationIncreasing in dry areas (Eastern Pacific Rim) with more flooding, mudslides, storm, and tidal surges and decreasing in wet areas (tropics)Decreasing in dry areas (Eastern Pacific Rim) and increasing in wet areas (tropics) with prolonged monsoon seasons in India, Asia, and Africa
StormsFewer hurricanes, typhoons, and tornadoes worldwideMore hurricanes, typhoons, and tornadoes worldwide

In the PDO, warmer‐than‐normal sea surface temperatures in the Western Pacific encircle cooler‐than‐normal temperatures in the Eastern Pacific. 1 The PDO was active in the 1940s to 1960s, lasts for 10 to 30 years, and restarted in the late 1990s. 1 The PDO will again cause harsher fluctuating weather patterns with more rainstorms, snowstorms, tropical storms, and hurricanes over the next decade or, even, longer. Thus, sea surface and subsurface temperature oscillations in the Pacific Ocean, the world’s largest ocean, have the greatest impact on global temperatures and climatic changes, and this impact will have far‐reaching effects on both contiguous and distant oceans, particularly with regard to ocean volume, ocean weight, and ocean plate tectonic activity.

Greenhouse gases

The greenhouse gases include carbon dioxide, methane, nitrous oxide, chlorofluorocarbons (CFCs), perfluorocarbons, and sulfur hexafluoride. 3,4 Greenhouse gases act together to absorb the earth’s infrared radiation and solar heat and limit radiant heat loss, warming the earth’s surface and increasing surrounding tropospheric temperatures. The continuing combustion of fossil fuels since the industrial revolution has contributed more than 75% of the carbon dioxide, the major greenhouse gas, to the atmosphere, with the remainder due to intentional cropland and rainforest burning. 4 The atmospheric concentrations of carbon dioxide have increased significantly over recent time from 300 ppm in 1850 to 370 ppm in 2000, with projected increases to 500 ppm by 2050. 3,4 More than half of all carbon dioxide produced since 1750 remains in the atmosphere; the rest has been absorbed by vegetation and phytoplankton for photosynthesis or is dissolved in seawater. 3,4

The United States contributes 25% of the world’s greenhouse gases, primarily through fossil fuel burning for energy and transportation needs. As rapidly growing populations in developing nations, especially in Asia, consume more goods and services, however, a further 5‐ to 10‐fold increase in energy output will be required just to bring the level of consumption in the developing world up to that in the developed world. 4,6

Global warming

Global average surface temperature has increased significantly since 1861, with most of the warming occurring during two periods in the 20th century—1910 to 1945 and 1976 to 2001. 4 The 1990s were the warmest decade, and 1998 was the warmest year since 1861. 4 Between 1900 and 1970, the earth’s surface temperature rose by 1.5ºC. 4 Summertime mean high temperatures are now 1.7ºC to 3.2ºC higher than in 1970, and mean wintertime low temperatures are now 2.3ºC to 4.5ºC higher than in 1970. 4 Although tropospheric temperatures have increased 0.1ºC per decade since 1861, satellite and weather balloon data have confirmed little stratospheric warming. 4 The stratosphere has been further insulated from global warming by shielding aerosols from greatly increased volcanic activity since 1880 and by CFC depletion of heat‐retaining ozone since the 1960s. 4 Although tropospheric temperatures may vary widely due to seasonal changes, and natural (volcanic eruptions) and man‐made (crop burning, nuclear weapons testing) events, stratospheric temperatures always remain relatively constant, ranging from –45ºC to –74ºC. In combination with natural cyclical climate changes, the constancy of stratospheric temperatures is one of the most common arguments used to counter the reality of global warming.

Precipitation effects

Global warming has a significant influence on rainfall as rising temperatures cause more ocean evaporation and trap more moisture in the atmosphere, increasing both summertime rainstorms and wintertime precipitation. More wintertime precipitation now falls as rain or ice rather than as snow, decreasing watershed snowpack levels and promoting quicker freshwater runoff with more wintertime flooding and less springtime snowmelt to refill reservoirs. Satellite data have documented a 10% decrease in global snow cover since the 1960s, and ground observations have documented a 2‐week reduction in the annual duration of lake and river ice pack in the mid‐ and higher latitudes of the northern hemisphere over the 20th century, particularly in the Northern United States, Alaska, Canada, Greenland, Iceland, and Russia. 4,7 The net result is that more watersheds and reservoirs cannot meet summertime water needs, forcing Western United States and Australian municipalities to ration outdoor water use. 7

Polar meltdown

Since the 1940s, the mean annual temperature on the Western Antarctic Peninsula has risen by 1.4ºC to 1.8ºC and the mean wintertime temperature has risen by 3.2ºC to 4.1ºC. 4 More than 1,000 square miles of the Larsen Ice Shelf on the Western Antarctic Peninsula have melted. 4,8,9 In the Arctic, spring and summer sea ice packs have contracted 10% to 15% since the 1950s, and there has been a 40% reduction in sea ice thickness. 4,9 Melting Arctic glaciers and sea ice now contribute more cold freshwater to the North Atlantic conveyor belt current, slowing the system that bathes Northern Europe and the British Isles with warm Gulf Stream waters. 9,10 Such a current shift could result in warmer ocean waters in the South Atlantic and Gulf of Mexico with greater hurricane‐fueling capacity and cooler environmental temperatures for Northern Europe. Further continuous monitoring of conveyor current temperatures and flow rates will be necessary to determine if current slowing is the result of anthropogenic climate changes or natural thermal oscillation cycles, as in the Atlantic and Pacific Ocean current temperature oscillations.

Since 1970, annual mean temperatures in Alaska have risen by 2ºC, shifting homes constructed on permafrost, thinning sea ice, and creating more coastal open water for storm surges. 8,9 The coastal village of Shishmaref, Alaska, recently voted to move inland at a cost of $100 million to escape coastal flooding and erosion. 8 On September 20, 2002, the southern Russian town of Karmadon was obliterated in an ice avalanche caused by the melting Kolka Glacier in the Caucasus Mountains, burying more than 200 townspeople and a documentary film crew. 10

Rising sea levels

Tidal gauge data have documented a global mean sea level rise of 10 to 20 cm during the 20th century. 4 Approximately 70% of the world’s population live within 100 miles of seacoasts, and nearly 50 million people now live at risk of coastal flooding and displacement by tidal and storm surges. 11 Sea levels are anticipated to rise by another 7.6 to 91.4 cm by 2020 due to a combination of polar ice cap and glacial meltdown, increased precipitation, coastal land erosion and subsidence, and thermal expansion form rising seawater temperatures. 9,12,13 A 100 cm (1 m) rise in sea levels would flood 34% of Bangladesh, the Marshall Islands, the Florida Keys, and many other islands and coastal areas. 3,4 If the entire Western Antarctic ice sheet were to melt, sea levels would rise by another 6.1 m. 11 Flooding is now the most common type of natural disaster worldwide, and flash flooding, usually associated with tropical storms and hurricanes, is among the leading causes of weather‐related deaths in the United States, along with heat wave‐related deaths. As a result of climate changes, more frequently alternating Pacific Ocean surface and subsurface temperature oscillations, as NOAA asserts, or synergistic combinations, hurricanes of category 3 or greater now strike the continental United States approximately every 18 months. 12

Ozone depletion

A secondary and mediating mechanism of global climate change is stratospheric ozone depletion by CFCs. The CFCs, formerly used as refrigerants and aerosol propellants, and nitrous oxide, primarily from microbial, not anesthetic, activity, rise to the stratosphere and deplete ozone in a series of photolytic reactions. In 1985, a hole in the stratospheric ozone layer first opened over Antarctica near the south pole, and in 1988, a second hole developed over the Arctic near the north pole.

The ozone layer and its bipolar holes re‐configure their sizes and shapes frequently in response to rising tropospheric aerosols and particulates, especially volcanic ash, that may temporarily trap or inactivate ozone‐depleting CFCs. 4 By 1992, however, stratospheric ozone loss was greater than predicted, with losses increasing in the summertime when more solar ultraviolet (UV) radiation reaches the earth. In Montreal in 1987, 135 nations agreed to ban CFC production by 2000. Nevertheless, ozone layer depletion is not anticipated to stop until 2050.

The ozone layer forms a physical barrier in the stratosphere shielding all living organisms from UV radiation. Prolonged UV exposure has been associated with sunburn, senile elastosis, skin aging, skin cancers, and cataracts and has contributed to the increasing worldwide incidences of malignant melanoma and macular degeneration of the retina. 3,4 Increasing levels of UV radiation, particularly UV‐A and UV‐C, impair immunocompetency, increasing susceptibility to respiratory droplet–transmitted (eg, measles, smallpox, influenza, severe acute respiratory syndrome) and waterborne (eg, cholera, cryptosporidiosis) infectious diseases. 3 UV‐B kills phytoplankton and could disrupt seafood chains and commercial fisheries that provide 40% of the world’s dietary protein. 3

The combination of malnutrition from drought‐induced crop failures and impaired immunity from UV irradiation could increase epidemics of measles, mumps, rubella, polio, influenza, and pertussis in unimmunized populations in developing nations and refugee camps. 3 After diabetic retinopathy, UV‐induced cataracts and macular degeneration are leading causes of blindness in the world. Nonmelanoma skin cancer is the most commonly occurring cancer in man, so common that its incidence is not even reported in annual cancer statistics. Over 1 million new skin cancers occur annually in the United States with 10,000 deaths/y, mostly from melanomas (7,600). Melanomas occur even more commonly per capita in Australia, in white races, and, especially, in whites living in the southern hemisphere. Darker skinned individuals, however, are not immune from melanomas and may develop melanomas on non–sun exposed areas of the palms, soles, genitalia, and, rarely, the retina.

Increasing tectonic and volcanic activity

Global tectonic and volcanic activities have increased significantly since 1880 due to a combination of polar meltdown from global warming and increasing ocean weight from rising sea levels. 10,13,14 In Iceland, a thinning ice pack has caused abrupt reductions in capping pressures over prehistoric volcanoes. 10,14 Freed of overlying ice weight, subglacial volcanoes have now resurfaced decompressing molten mantles below, which erupt precipitously in magma geysers. 10

Increasing tectonic and volcanic activity results from a combination of coastal tectonic plate undermining by the seawater‐weighted Northern Pacific plate and wintertime sinking of the north pole from ice melt. 14 As winter water and ice weights increase, these seasonal geophysical changes will be accentuated, exerting greater influences on tidal surges, tectonic plate movements, and geothermal activities, especially in the northern hemisphere and along the Pacific Rim. 14 These powerful combined geophysical forces will generate more molten magma in the earth’s mantle, which expands to uncork dormant volcanoes or burst through thinning ice packs. 10,14 Case fatality rates for earth‐centered natural disasters, such as earthquakes, earthquake‐spawned tsunamis, and volcanic eruptions, often significantly exceed case fatalities from more predictable water‐centered disasters, such as tropical cyclones and floods.

Over 36,000 deaths were reported in the Krakatoa eruption in Indonesia in 1883, 30,000 deaths in the Pelée eruption on Martinique in 1902, 57 deaths (mostly backpackers and campers) in the eruption of Mount St. Helens in rural southern Washington in 1980, and 40 deaths in the eruptions of 1995 and 1997 eruptions of the Soufrière Hills volcano on Montserrat. After nearly 400 years of dormancy, Soufrière Hills has been erupting almost continuously since July 1995, devastating Montserrat’s capital of Plymouth, forcing multiple evacuations, and reducing the island’s population from over 11,000 inhabitants to 4,000.

Linking anticipated outcomes of climate change with the observed human health consequences

The anticipated outcomes of global climate change include heat waves, tropical cyclones or hurricanes, mudslides, earthquakes, tsunamis, wildfires, volcanic eruptions, air pollution, water wars, crop failures, emerging (mostly zoonotic) infectious diseases, environmental refugees, coral reef destruction, and commercial fishery disruption. Overall, heat waves will cause more heat and heart‐related morbidity and mortality than move focal natural disasters, such as floods and tornadoes. Infants and the elderly, especially elderly women, will remain at increased risks of thermal stress due to several physiological factors including poor central and peripheral thermoregulation, increased body surface areas, increased body surface area to mass ratios, and reduced muscle mass. A paralyzing summer heat wave in Western Europe in 2003 caused temperatures to top 104°F (40°C) in parts of France, killing over 14,000 people, mostly cardiac‐related deaths among infants, the disabled, and the elderly, with poor thermoregulatory capabilities.

Although not as frequent, younger populations, especially athletes, honeymooners, soldiers, and emergency response and rescue workers, are also at greater risk of thermal stress from a variety of unique, and not uncommon, conditions including fatal ventricular arrhythmogenesis from left ventricular hypertrophy, prolonged Q‐T syndrome, and R‐on‐T phenomenon; malignant hyperthermia; and undiagnosed familial myopathies and neuromuscular diseases. These are all preexisting, often congenital, medical conditions that pose less common risks for younger people; yet, are common causes of heat‐induced cardiovascular deaths outdoors and on athletic courts and fields and parade grounds.

The question of whether flooding or heat waves cause more climate change‐related natural disaster deaths remains to be answered conclusively. Kalkstein has repeatedly asserted that there is a direct causal relationship between a warming climate and heat wave‐related mortality, especially during summers in large cities. 15,16 However, in an observational study in Europe in 1999 to 2000, Keatings and colleagues 17 demonstrated that warmer European regions (Greece, Italy) did not have statistically significant higher annual heat‐related mortality per million population than colder European regions (England, Finland, Netherlands). The authors concluded that Europeans had indeed adjusted successfully to higher mean summer temperatures and could be expected to further acclimatize to global warming with little‐to‐no sustained increase in heat‐related mortality, even in warmer Mediterranean regions. 17 Nevertheless, without effective early warning systems directing timely coastal evacuations, flooding disasters during heavy rains, hurricanes, and tsunamis will continue to claim many lives, unrelated to human adaptation and acclimatization, as recently evidenced by the Indian Ocean tsunami on December 26, 2004.

Drier and hotter summers following milder winters with less snowmelt will empty reservoirs and fuel lightning‐ignited and intentionally set brush and forest fires destroying timberlands, displacing residents, and causing more smoke inhalation injuries and deaths. Greater tropospheric trapping of primary pollutants from fossil fuel consumption and secondary pollutants from photochemical smog reactions will cause the continuing deterioration of air quality and visibility. Air pollution will cause more seasonal allergic asthma and other respiratory diseases, defoliate alpine forests, and contaminate surface freshwater with acid rain. Annual US hospital admission rates for acute asthma in children have now increased from 19 per 10,000 children in 1979 to 35 per 10,000 children in 2001. 18 Droughts will provoke water rights disputes between upstream and downstream populations. Litigation over water rights has started between California and other western slope US states, between Georgia and Florida, and between the United States and Mexico. Droughts will also cause crops to fail, triggering malnutrition and famine in developing nations.

Tidal flooding will increase salinity of water tables, coastal marshes, and alluvial deltas, destroying shellfish beds, contaminating freshwater aquifers, and rendering deltas unfit for agriculture. Warmer and wetter conditions will spawn more airborne fungal and viral respiratory illnesses.18,19 Greater hurricane and tropical storm activity will also create ideal conditions for food‐, water‐, and arthropod‐borne, particularly mosquito‐borne, disease outbreaks. 12,19,20 The heavier Pacific Ocean will drive the Pacific Ocean tectonic plates beneath the coastal continental plates, increasing tectonic and volcanic activity, even in geologically dormant inland areas. Coastal and subsea earthquakes will be associated with tidal and tsunami waves, as in the Indian Ocean tsunami of December 2004. Many anticipated and, later, observed public health consequences of global climate change might now be matched in temporal association with earlier climatic events (Table 3).

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Table 3

Recent climate change–associated infectious disease epidemics

YearsGeographic locationsAssociated climatic factors and/or confoundersInfectious disease epidemicsNo. of persons infected (no. of deaths)
1975Mississippi–Ohio River Basin, USA↑ Mild winters, ↑ hot summers, ↑ rainfall, ↓ mosquito vector control, ↑ emerging mosquito vectors, expanding insect–pathogen–host relationshipsSt. Louis encephalitis2,000 (150)
1980Montana, Western USA↑ Rainfall, ↓ drinking water filtrationGiardiasisSporadic case reports; no specific population‐based data
1993Four Corners (Arizona, Colorado, New Mexico, Utah), Western USA↑ Drought–rainfall cyclesPulmonary hantavirus syndrome100 (45)
1993Milwaukee, Wisconsin, USA↑ Rainfall, ↓ drinking water filtrationCryptosporidiosis200,000 (150)
1993–1995Costa Rica, El Salvador, Mexico; Texas and Louisiana, Southern USA↑ Rainfall, ↓ mosquito vector control, ↑ emerging domestic mosquito vectors, expanding insect– pathogen–host relationshipsDengue140,000 (4000)
1994Western India↑ Rainfall, ↓ rodent reservoir control, ↓ flea vector control, expanding insect–pathogen–host relationshipsPlague2,100 (170)
1997–1998East Africa↑ Drought–rainfall cyclesRift Valley fever10,000 (500)
1998–2001Arizona, New Mexico; Western USA↑ Drought, ↑ soil erosion, ↑ road–highway, commercial, and residential construction, ↑ susceptible hostsCoccidioidomycosis (pulmonary and extrapulmonary systemic mycoses)>5,000; no population‐based mortality data
2000–2002Sweden, Central Europe, Eastern Europe↑ Mild winters, ↑ rainfall, ↑ hot summers and falls, ↓ permafrost, ↑ outdoor activity, expanding insect–pathogen–host relationshipsTick‐borne diseases, particularly Lyme disease and tick‐ borne viral encephalidides, as tick vectors and their preferred vertebrate hosts shift their distribution ranges northwardNo specific population‐based data available
1999–2005Continental USA↑ Mild winters, ↑ rainfall, ↑hot summers and falls, ↓ mosquito vector control, ↑ new emerging mosquito vectors, expanding insect–pathogen–host relationshipsWest Nile virus4,007 (263)

Potential microbial agents and transmission vectors of climate change–induced infectious disease outbreaks

The food‐, water‐, and vector‐borne microbial agents that will cause climate change–induced infectious disease outbreaks have now independently identified themselves as having low infective doses and high virulence, and being environmentally stable and salt, chlorine, and iodine resistant. Water‐ and food‐borne diseases will include gastroenteritis caused by the coccidian protozoans (Cryptosporidium parvum, Cyclospora cayetanensis, Isospora belli), hepatitis A virus, astroviruses, caliciviruses, Giardia lamblia, the non‐cholera marine vibrios (Vibrio vulnificus, Vibrio parahaemolyticus), Campylobacter jejuni, Shigella species, and the typhoidal and non‐typhoidal Salmonella species.

Campylobacter jejuni and many Salmonella species are natural commensals that live in the gastrointestinal (GI) tracts of birds, amphibians, and reptiles. Following natural disasters, man may be exposed to these bacteria following the consumption of contaminated drinking water or food exposed to animal or human carriers, or to contaminated fomites, such as cutting boards and carving knives. Rarely, human beings can become chronic asymptomatic carriers (especially in female gall bladders) and fecal super‐shedders of Salmonella typhi. These bacteria are very heat sensitive and can be killed by boiling drinking water and thoroughly cooking meat, especially poultry. Following natural disasters, particularly floods and tropical cyclones, reptiles are often displaced from their dens and can contaminate food preparation surfaces with non‐typhoidal Salmonella species, particularly outdoor surfaces on which fresh fruits are later sliced for eating or squeezed or tapped for juices. On the other hand, the Vibrio bacteria, including Vibrio cholera, are natural seawater‐dwelling organisms that often contaminate human drinking water reservoirs following storm surges and can also contaminate open wounds and shellfish, later consumed raw. Cholera‐induced watery diarrhea is treated with rehydration only, with antibiotics reserved for dysentery and prolonged or complicated infections. The non‐cholera vibrios (V parahaemolyticus, V vulnificus) are much more ubiquitous and virulent pathogens than cholera vibrios, require antibiotic therapy in addition to rehydration, and can cause systemic septicemia and Ecythema gangrenosa (V vulnificus) with high case fatality rates, especially in those patients with preexisting liver diseases, chronic alcoholism, hemochromatosis, or on iron supplementation.

Arthropod‐borne viral disease outbreaks will include St. Louis encephalitis, LaCrosse encephalitis, and West Nile Virus in North America; dengue, malaria, and yellow fever in the subtropical and tropical Americas; dengue and Japanese encephalitis in Asia, Indonesia, and Micronesia; and Ross River fever in Australia. As noted, malaria caused by chloroquine‐resistant P falciparum will occur at higher altitudes throughout Latin America, Africa, Asia, and the Middle East.

Outbreaks of plague caused by Yersinia pestis and transmitted from rodents to man by fleas will continue to occur in regions where the organism is endemic in prairie dogs and other rodents, such as the US Four Corners (shared state boundaries of Arizona, Colorado, New Mexico, and Utah) and the southern Himalayas. Leptospirosis caused by the spirochete, Leptospira interrogans, and transmitted to man via rodent urine–contaminated surface waters will occur in coastal and other waterside municipalities. The large rodent populations in these cities will be frequently displaced by heavy rainfall, flash flooding, and tidal and storm surges. Pulmonary hantavirus syndrome, another rodent zoonosis, transmitted by rodent fecal aerosols, will occur in dry areas following heavy rainfalls that force domestic deer mice from their underground burrows into vacant homes, garages, and crawl spaces. All the tick‐transmitted diseases, including the spirochetal diseases, such as the Lyme disease, babesiosis, ehrlichioses (primarily human granulocytic ehrlichiosis), and tick‐borne viral encephalitides, will shift their continental distributions northward by several latitudes and their altitude distributions higher by tens of meters.

The descriptive epidemiology of human health outcomes following tropical storms and cyclones (hurricanes)

Water‐centered disasters, such as floods, rainstorm‐spawned tornadoes, tropical storms, tropical cyclones or hurricanes, and earthquake‐spawned tidal waves or tsunamis, now occur more often than geological disasters; occur more commonly in the Americas, Asia, and Africa; often cause more deaths by drowning than other disasters; and cause more serious injuries overall, primarily through falls and falling objects, motor vehicle accidents (MVAs), and chain saw injuries during storm debris cleanup than deaths.20–22 Increased endemic infectious disease risks, especially acute GI illnesses, and mass population movements are more common after water‐centered disasters than after geological disasters, such as earthquakes and volcanic eruptions. 20–22

Storm surge is the greatest threat to human life during hurricanes and tsunamis, and storm tide is the greatest threat to property during hurricanes and tsunamis. 20–23 A storm surge is a massive wall of seawater 50 to 100 miles wide that sweeps across the coastline near hurricane or tsunami landfall. A storm tide is the combination of the storm surge and the astronomical high tide. The storm tide sweeps along coastlines at hurricane or tsunami landfall for much longer distances (over 100 miles) and penetrates much deeper inland than the storm surge.

Since hurricane Hugo in 1989, several surveillance investigations and needs assessments following tropical storms and hurricanes have been conducted by the US Centers for Disease Control and Prevention (CDC) and by local US and Latin American public health departments and ministeries. 21–23 Over the 2 weeks following hurricane Hugo (North Carolina, 1989), 2,090 patients were treated in local hospital emergency departments (EDs) for injuries and illnesses related to the hurricane. 21 Injuries were responsible for 88% of patient encounters, with half of the injuries due to lacerations and insect bites or stings. 21 More than 50% of the lacerations were caused by chain saw injuries during the cleanup of fallen trees and limbs; 26% of the insect bites or stings were associated with systemic reactions, including anaphylaxis, wheezing, and hives. 21

Following hurricane Andrew (Miami and Dade County, FL, USA, 1992), 25,000 homes were destroyed; 200,000 people were left homeless; 66% of the remaining households lost electricity; but most households had sewer service and nonpotable running water. 22 Six index conditions accounted for the most visits to civilian free‐care sites: injuries 15.7%, miscellaneous infections (not upper respiratory or GI infections) 9.6%, nonspecific rash 5.4%, cough 4.7%, diarrhea 4.7%, and animal bites 1.2%. 22 Five index conditions accounted for the most civilian visits to military free‐care sites: chronic disease conditions 24.4%, injuries 23.7%, dermatological conditions 12.4%, respiratory illnesses 9.9%, and diarrhea 5.3%. 22 During the 5 weeks after hurricane Andrew, the proportional morbidity from injuries decreased, proportional morbidity from respiratory illnesses increased, and proportional morbidity from diarrheal diseases remained stable. 22 No infectious disease outbreaks occurred. 22 The investigators concluded that injuries and exacerbations of chronic diseases were the most common causes of morbidity immediately after hurricanes and that infectious diseases were uncommon, presented weeks after hurricanes, and were not associated with communicable disease outbreaks. 22

Following hurricane Opal (Navarre, FL, USA, 1995), 1,135 patients were treated in the two local EDs during the first 6 days after the hurricane and were compared to 996 patients treated by the same EDs during a prehurricane period. 23 For both periods, the proportion of ED visits were similar for lacerations, puncture wounds, musculoskeletal injuries, rashes, and GI and respiratory illnesses. 23 During the posthurricane period, however, the proportion of visits for insect bites and stings increased from 0.2% to 1.7% (p < 0.05). 23

In a descriptive analysis of the 27 hurricane Opal–related deaths, the CDC reported that the mean age of the decedents was 52.4 years, with most deaths in males (n= 21), and due to accidental injuries (n= 24) and three deaths from acute exacerbations of chronic illnesses. 23 A ranking of the causes of accidental deaths included falling and fallen trees (n= 13); MVAs not involving falling or fallen trees (n= 3); carbon monoxide (CO) poisoning from candle‐started house fires (n= 3), unventilated propane cooking tanks (n= 1), and unventilated gas‐powered electrical generators (n= 1); drowning (n= 1); electrocution of a utility worker (n= 1); and massive chest trauma after a tractor overturned (n= 1). 23 The three deaths related to exacerbations of chronic diseases included two fatal myocardial infarctions in patients with coronary artery disease and one respiratory failure in a patient with chronic obstructive pulmonary disease. 23

Early reports indicated that the most common causes of the 29 deaths during hurricane Isabel, a category 2 hurricane that made landfall on the North Carolina Outer Banks on September 18, 2003, pushing 6‐foot storm surges and 12‐foot storm tides north into Chesapeake Bay, included (1) MVAs (n= 16), (2) blunt injuries from falling tree limbs and utility poles (n= 7), (3) drowning (n= 3); carbon monoxide poisoning from electrical power generator use in unventilated living spaces (n= 2); and (4) electrocution (n= 1 electrical utility worker). 23

Atmospheric and climate scientists have now been able to measure the impact of sea surface temperatures on the intensification and direction of tropical storms and hurricanes (tropical cyclones) using a worldwide network of ocean temperature buoys. Other continuous measurements in assessing ENSO activity and tropical cyclone intensification and landfall prediction have also been identified now and include ocean subsurface temperatures, thermocline depths and thicknesses, and storm‐steering current barometric pressures. Armed with these new measurements, forecasters will be better able to make earlier and more accurate predictions of hurricane intensity and landfall, permitting local authorities to order timely population evacuations prior to landfall.

Conclusions and recommendations

Higher summer and winter temperatures and increased rainfall have now been significantly associated with emerging arthropod‐borne infectious disease epidemics, including West Nile virus in the United States, Rift Valley fever virus in Africa, Ross River fever virus in Australia, and plague in India (Table 3).2,20 Cycles of drought and flooding have been associated with outbreaks of pulmonary hantavirus syndrome in the desert US Southwest and of pulmonary coccidioidomycosis in Southern California and the desert Southwest. El Niño events have been associated with a significant increase in hospitalizations in women for viral pneumonia in California. 19 Filtration deficiencies and sewage contamination of municipal drinking water treatment facilities by animal or human fecal wastes have been associated with urban outbreaks of waterborne diarrheal diseases, particularly cryptosporidiosis (Milwaukee, WI, USA) and giardiasis (Aspen, CO, USA). As a result of these and other recognized associations between climate change and public health consequences, many of which have been confounded by deficiencies in public health infrastructures, the active responses to progressive climate change must include a combination of economic, environmental, legal, regulatory, and, most importantly, public health measures.

Travel medicine physicians are obligated to educate their patients about the public health outcomes of climate change and about the potential disease and injury risks their patients may face from global warming and climate‐associated natural disasters. Although not an exhaustive listing, many of the major health risks faced by travelers from global warming and climate‐associated natural disasters and recommendations to reduce these travel risks are summarized in Table 4.

View this table:
Table 4

The major risks faced by travelers from global warming and climate change–associated natural disasters

Mechanisms of climate changeMajor travel risksRecommendations to reduce travel risks
Ocean surface temperature oscillations↑ Tropical storm activity, ↑ tropical cyclone (hurricane and typhoon) activity, ↑ winter snowstorm and spring mudslide and rockslide activityMonitor local weather forecasts and advisories; maintain wireless communications; evacuate early and immediately when ordered by local authorities; respect roadway mudslide and rockslide advisories; do not camp in floodplains (including arroyos and wadis), in mudslide‐ or rockslide‐prone areas, or in any areas where such disasters have occurred before
Accumulating greenhouse gases↑ Heat wave–related stress, worsening air quality, expanding arthropod vector–pathogen–human host interrelationships, especially for malaria, dengue, West Nile virus, St. Louis encephalitis, and all tick‐borne diseasesAvoid dehydration; carry bottled water; wear light‐colored, lightweight clothing with hats, long sleeves, and pants tucked into socks and shoes or boots; spray outer garments with pyrethroid‐containing insect repellants before trekking outdoors; spray exposed body areas with N,N‐diethyl‐m‐toluamide (DEET)‐containing insect repellants before trekking outdoors, with particular attention to any exposed areas, such as the neck, wrists, and ankles; maintain all infectious disease immunizations; consult travel medicine physicians for pretravel malaria prophylaxis; wear a Medic‐Alert® bracelet or similar tag identifying any food or medication allergies; carry all prescription drugs with clear dosage and direction labeling, prescription drugs also need to be identified by generic drug names; if allergic to hymenopterid venoms, carry injectable epinephrine; sleep indoors and in mosquito‐netted or protected areas; inspect skin and whole body daily for embedded ticks and/or insect bites
Melting polar ice caps and glaciersThinning polar and glacial ice caps, thinning river and lake surface ice packs, thinning permafrost subsurfaces, seasonally delayed surface water freezing, freeze–thaw‐related snow slides and mudslides, ↑ avalanche activityMonitor snow and ice depth and quality; heed avalanche and glacial melt‐and‐advance advisories; do not ice skate or snow ski, sled, or snowboard alone; carry a pocket satellite‐linked, global positioning system locator during all “back country” skiing and trekking activities; dress in layers with a waterproof exterior shell of bright‐colored clothing; carry hot, non‐ethanol‐containing liquids and high‐energy snacks; do not drink vasodilating and intoxicating ethanol‐containing beverages while outdoors in cold climates
Rising ocean and sea levels↑ Island and coastal flooding, ↑ tidal activity, ↑ storm and tidal surges, ↑ riptide activity, ↑ coastal marine life, eg, jellyfish and sharksDo not camp on beaches, deltas, marsh islands, or other tidal floodplains; swim only in designated areas; wear approved and tested personal floatation devices when boating, sailing, water skiing, or parasailing; do not swim alone; swim in areas with lifeguards and rescue capabilities; monitor and heed rough surf warnings; monitor and heed jellyfish and shark warnings; if caught by riptides, swim parallel to the beach with the prevailing currents until released; move to higher ground to avoid storm, tidal, and tsunami wave surges, whenever advised by local authorities
Ozone depletion↑UV‐A exposure, ↑ UV‐B exposure, ↑UV‐C exposureWear hats and long sleeves when outdoors in sunlight; apply appropriate sun protection factor–rated waterproof sunscreens; wear UV‐protected dark glasses while outdoors during daytime; if you have cataracts, intraocular lenses, or macular degeneration consult an ophthalmologist prior to travel regarding additional UV‐C retinal protection
Increasing tectonic activity↑ Earthquake activity, ↑ landslides, mudslides, and rockslides, ↑ avalanche activity, ↑ tsunami activityDo not camp at the base of slide‐prone hills or mountains, or in any areas with physical evidence of prior slide activity; if possible, exit buildings by stairwells during earthquakes; if exit is impractical, brace yourself tightly in a doorframe or door‐jamb during earthquakes; stay away from windows, file cabinets, vending machines, and bookshelves during earthquakes; move to higher ground to avoid earthquake‐spawned tidal and tsunami wave surges
Increasing volcanic activity↑ Active and dormant volcano activity, ↑ geothermal vent and geyser activityMonitor all local advisories and warnings regarding near volcanic activity; evacuate early and immediately by specified routes when ordered by local authorities; evacuate by automobile with windows closed and air conditioners on full fan and indoor air recirculate cycles; do not approach lava flows, lava vents, or lava tubes; do not walk on recently hardened lava beds or lava tubes; cover nose and mouth with a moistened handkerchief or, if available, a large particulate–filtering mask (N‐95 or HEPA‐rated masks) to filter volcanic ash during evacuation; wear appropriate wraparound eye protection whenever exposed to volcanic ash aerosols

Declaration of Interests

The author states that he has no conflicts of interest.


Financial support for J. H. D. was provided by departmental and institutional sources and by a state grant from the Health Education Fund of the Board of Regents, State of Louisiana, entitled The Assessment and Remediation of Public Health Impacts due to Hurricanes and Major Flooding Events.


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