Share this article on:

Identifying Vulnerable Subpopulations for Climate Change Health Effects in the United States

Balbus, John M. MD, MPH; Malina, Catherine AB

Journal of Occupational & Environmental Medicine: January 2009 - Volume 51 - Issue 1 - pp 33-37
doi: 10.1097/JOM.0b013e318193e12e
Original Articles: Special Section on Climate Change and Health

Climate change can be expected to have differential effects on different subpopulations. Biological sensitivity, socioeconomic factors, and geography may each contribute to heightened risk for climate-sensitive health outcomes, which include heat stress, air pollution health effects, extreme weather event health effects, water-, food-, and vector-borne illnesses. Particularly vulnerable subpopulations include children, pregnant women, older adults, impoverished populations, people with chronic conditions and mobility and cognitive constraints, outdoor workers, and those in coastal and low-lying riverine zones. For public health planning, it is critical to identify populations that may experience synergistic effects of multiple risk factors for health problems, both related to climate change and to other temporal trends, with specific geographic factors that convey climate-related risks.

From the Environmental Defense Fund, Washington, DC.

Address correspondence to: John M. Balbus, MD, MPH, Environmental Defense Fund, 1875 Connecticut Avenue, NW, Suite 600, Washington, DC 20009; E-mail:

Like other environmental stressors, climate change can be expected to have differential effects on different subpopulations, depending on a variety of susceptibility factors. Biological sensitivity, socioeconomic factors, and geography may each contribute to heightened risk for climate-sensitive health outcomes, which include heat stress, air pollution health effects, extreme weather event health effects, water-, food-, and vector-borne illnesses. The term “vulnerability” connotes the balance between susceptibility factors and factors that increase the resilience of populations to environmental stressors. Particularly vulnerable subpopulations include children, pregnant women, older adults, impoverished populations, people with chronic conditions and mobility and cognitive constraints, outdoor workers, and those in coastal and low-lying riverine zones. For public health planning, it is critical to recognize those populations that may experience synergistic effects of multiple risk factors for health problems, both related to climate change and to other temporal trends.

Back to Top | Article Outline

Identifying Vulnerable Subpopulations

In adapting the IPCC's definitions1 to considerations of public health, “vulnerability” can be defined as the summation of all risk and protective factors that ultimately determine whether an individual or subpopulation experiences adverse health outcomes, and “sensitivity” can be defined as an individual's or subpopulation's increased responsiveness, primarily for biological reasons, to a given exposure. Thus, specific subpopulations may experience heightened vulnerability for climate-related health effects for a wide variety of reasons. Biological sensitivity may be related to the developmental stage; pre-existing chronic medical conditions (such as the sensitivity of people with chronic heart conditions to heat-related illness); acquired factors (such as immunity); and genetic factors (such as metabolic enzyme subtypes that play a role in sensitivity to air pollution effects). Socioeconomic factors also play a critical role in altering vulnerability and sensitivity to environmentally-mediated factors. They may increase likelihood of exposure to harmful agents, interact with biological factors that mediate risk (such as nutritional status), and/or lead to differences in the ability to adapt or respond to exposures or early phases of illness and injury.

Populations living in certain regions of the United States may also experience increased risks for specific climate-sensitive health outcomes due to their regions' baseline climate, abundance of natural resources such as fertile soil and fresh water supplies, elevation, dependence on private wells for drinking water, and/or vulnerability to coastal surges or riverine flooding. Some regions' populations may in fact experience multiple climate-sensitive health problems simultaneously. One approach to identifying such areas is to map regions currently experiencing increased rates of climate-sensitive health outcomes or other indicators of increased climate risk, as illustrated in Fig. 1.

Back to Top | Article Outline

Specific Subpopulations at Risk

Vulnerable subpopulations may be categorized according to specific health endpoints (Table 1). Although this is typically the way scientific literature reports risk factors for adverse health affects, this section discusses vulnerability for a variety of climate-sensitive health endpoints one subpopulation at a time.

Back to Top | Article Outline


Children's small body mass to surface area ratio and greater susceptibility to dehydration make them more vulnerable to heat-related morbidity and mortality (Kovats and Hajat, 2008).2 In an analysis of warm season mortality in California, children under 5 and infants under 1 year of age suffered higher mortality with increasing daily temperatures (Basu and Ostro, 2008).3 Infant mortality increased 4.9% for a 10 degree increase in mean daily apparent temperature and children under five experienced a 4.2% increase, although the latter finding failed to achieve statistical significance. This study did not analyze temperature associations with specific causes of death in children. Epidemiologic analyses of heatwave events, however, have generally failed to find significantly increased mortality among children and infants (Kovats and Hajat, 2008).4

Children's increased breathing rates relative to body size, greater amount of time spent outdoors, and developing respiratory tracts heighten their sensitivity to harm from ozone air pollution.5 They are also susceptible to developing atopy and allergies related to aeroallergen exposures, which are anticipated to increase with increasing CO2 concentrations and longer pollen seasons (Bunyanavich et al, 2003).6–8

Children are especially vulnerable to a variety of infectious diseases. Their relatively naïve immune systems increase the risk of serious consequences from water- and food-borne diseases.9 Specific developmental factors make them more vulnerable to complications from severe infections like E. Coli O157:H7.10 Children's lack of immunity also plays a role in higher risk of mortality from malaria11; conversely, maternal antibodies to dengue in infants convey increased risk of developing dengue hemorrhagic syndromes. A second peak of greater risk of complications from dengue appears in children between the ages of 3 and 5 (Guzman and Khouri, 2002).12

Children may also be more vulnerable to psychological complications of extreme weather events related to climate change. Following two floods in Europe in the 1990 seconds, children demonstrated moderate to severe stress symptoms and long-term post-traumatic stress disorder (PTSD), depression, and dissatisfaction with ongoing life.13

Back to Top | Article Outline

Pregnant Women

Pregnant women are likely to be vulnerable to adverse health effects in the aftermath of extreme weather events, as they may have exposure to environmental toxins, limited access to safe food and water, psychological stress, and disrupted health care access. One review suggested an increased incidence of adverse reproductive outcomes after Hurricane Katrina.14

Studies of increased risk of adverse reproductive outcomes associated with air pollutants such as particulate matter and associated polycyclic aromatic hydrocarbons suggest that pregnant women constitute a vulnerable subpopulation for climate or climate change policy-associated changes in these types of air pollutants (Perera, 2008; Makri and Stilianakis, 2007).15,16

Pregnancy also confers increased susceptibility to a variety of climate-sensitive infectious diseases, including malaria and food-borne infections.9,17

Back to Top | Article Outline

Older Adults

Health effects associated with climate change pose significant risks for the elderly. Older adults are more sensitive to temperature extremes, particularly heat18,19; individuals 65 years of age and older comprised 72% of the heat-related deaths in the 1995 Chicago heatwave (Whitman et al, 1997).20 The elderly are also more likely to have preexisting medical conditions, including cardiovascular and respiratory illnesses as well as limited mobility, which may put them at greater risk of severe morbidity or mortality from climate-related events or conditions. For example, a 2004 rapid needs assessment of older adults in Florida found that Hurricane Charley exacerbated preexisting, physician-diagnosed medical conditions in 24% to 32% of elderly households.21

The elderly have been demonstrated to be more susceptible to adverse effects of air pollution. A recent study found people over 65 experienced a 1.1% additional increase in mortality for each 10 ppb increase in 8 hour daily mean ozone concentration.22 Effects of ambient particulate matter on daily mortality also tend to be greatest in older age groups.23

Back to Top | Article Outline

Impoverished Populations

In the US, as around the globe, the greatest health burdens related to climate change are likely to fall on those with the lowest socioeconomic status.24 Most affected are individuals with inadequate shelter or resources to find alternative shelter in the event their community is disrupted. Although quantitative methods to assess the increase in risk related to these social and economic factors are not well-developed, qualitative insights can be gained by examining risk factors for mortality and morbidity from recent weather-related extreme events such as the 1995 heatwave in Chicago and Hurricane Katrina in 2005 (Box 1).

Back to Top | Article Outline

Box 1: Hurricane Katrina

In 2005, Hurricane Katrina caused more than 1500 deaths along the Gulf Coast, and many of these victims were members of vulnerable subpopulations, such as hospital and nursing-home patients, older adults who required care within their homes, and individuals with disabilities.31 According to the Louisiana Department of Health and Hospitals, more than 45% of the state's identified victims were 75 years of age or older; 69% were above age 60.32 In Mississippi, 67% of the victims whose deaths were directly, indirectly, or possibly related to Katrina were 55 years of age or older.33

At hurricane evacuation centers in Louisiana, Mississippi, Arkansas, and Texas, chronic illness was the most commonly reported health problem, accounting for 33% or 4786 of 14,531 visits.34 Six of the fifteen deaths indirectly related to the hurricane and its immediate aftermath in Alabama were associated with preexisting cardiovascular disease (CDC, 2006 days),35 and the storm disrupted an estimated 100,000 diabetic evacuees across the region from obtaining appropriate care and medication.36 One study suggested that the hurricane had a negative effect on reproductive outcomes among pregnant women and infants, who experienced exposure to environmental toxins, limited access to safe food and water, psychological stress, and disrupted health care.14 Other vulnerable individuals included those without personal means of transportation and poor residents in Louisiana and Mississippi who were unable to evacuate in time.31

The tragic loss of life that occurred after Hurricane Katrina underscores the increased vulnerability of special populations and demonstrates that, in the wake of extreme weather events, particularly those that disrupt medical infrastructure and require large-scale evacuation, treating individuals with chronic diseases is of critical concern.37

Studies of heatwaves identify poor housing conditions, including lack of access to air conditioning and living spaces with fewer rooms, as significant risk factors for heat-related mortality.18,25 Higher heat-related mortality has been associated with socioeconomic indicators, such as lacking a high school education and living in poverty.26 Financial stress plays a role, as one study of the 1995 Chicago heatwave found that concern about the affordability of utility bills influenced individuals to limit air conditioning use.27 The risk for exposure and sensitivity to air pollution is also elevated among groups in a lower socioeconomic position.28

Another area of concern for impoverished populations is the impact that climate change may have on food systems and food supply. In the US, food insecurity is a prevalent health risk among the poor and poor children in particular (Cook et al 2007).29 On a global scale, studies suggest that climate change is likely to contribute to food insecurity by reducing crop yield, most significantly at lower latitudes, due to shortened growing periods and decreases in water availability (Parry et al, 2005).30 In the US, changes in the price of food would be likely to contribute to food insecurity to a greater degree than frank scarcity.

Back to Top | Article Outline

People with Chronic Conditions and Mobility and Cognitive Constraints

People with chronic medical conditions have an especially heightened vulnerability for the health impacts of climate change. Extreme heat poses a great risk for individuals with diabetes,38 and extreme cold has an increased effect on individuals with chronic obstructive pulmonary disease.38 People with mobility and cognitive constraints may be at particular risk during heat waves and other extreme weather events (EPA, 2006).39 As noted above, those with chronic medical conditions are also at risk of worsened status as the result of stressors and limited access to medical care during extreme events.

Back to Top | Article Outline

Occupational Groups

Certain occupational groups, primarily by virtue of spending their working hours outdoors, are at greater risk of climate-related health outcomes. Outdoor workers in rural or suburban areas, such as electricity and pipeline utility workers, are at increased risk of infection with Lyme Disease, although evidence is lacking for greater risk of clinical illness (Piacentino and Schwartz, 2002).40,41 They and other outdoor workers have increased exposures to ozone air pollution and heat stress, especially if work tasks involve heavy exertion.42

Table 2 summarizes the climate-related vulnerability of specific US subpopulations, based on age, underlying medical conditions, and socioeconomic status. Recognition of combined effects will aid efforts at public health intervention and disease prevention.

Back to Top | Article Outline


Assessing vulnerability for climate change related health effects entails combining epidemiologic information on the specific health effects anticipated in a given region, consideration of the unique geography and ecosystems of a region, which will mediate climate-related health effects, and an assessment of the resilience or adaptive capacity of specific subpopulations in a given region. Although there are studies that provide assessments of population and individual risk factors for specific health outcomes, very few associate these health risk factors with geographic risk factors. To date, these assessments have been conducted in a fairly qualitative manner, relying on analogy and fragmented data sources. For the future, improvements in integrated modeling and ongoing research on climate-related health effects will facilitate the development of more quantitative indices for vulnerability that will assist public health planning. In the interim, increased identification of synergies between geography, socioeconomic status, and underlying medical conditions in specific US subpopulations is essential to protecting public health in the face of accelerating climate change.

Back to Top | Article Outline


1.IPCC. IPCC Second Assessment. Climate Change 1995. Available at: Accessed November 12, 2007.
2.Climatic heat stress and the exercising child and adolescent. American Academy of Pediatrics. Committee on Sports Medicine and Fitness. Pediatrics. 2000;106(1 Pt 1):158–159.
3.Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health. 2008;29:41–55.
4.Basu R, Ostro BD. A multicounty analysis identifying the populations vulnerable to mortality associated with high ambient temperature in California. Am J Epidemiol. 2008;168:632–637.
5.American Academy of Pediatrics. Ambient air pollution: health hazards to children. Pediatrics. 2004;114:1699–1707.
6.Bunyavanich S, Landrigan CP, McMichael AJ, Epstein PR. The impact of climate change on child health. Ambul Pediatr. 2003;3:44–52.
7.D'Amato G, Cecchi L. Effects of climate change on environmental factors in respiratory allergic diseases. Clin Exp Allergy. 2008;38:1264–1274.
8.Shea KM, Truckner RT, Weber RW, Peden DB. Climate change and allergic disease. J Allergy Clin Immunol. 2008;122:443–453.
9.Gerba CP, Rose JB, Haas CN. Sensitive populations: who is at the greatest risk? Int J Food Microbiol. 1996;30:113–123.
10.Ochoa TJ, Cleary TG. Epidemiology and spectrum of disease of Escherichia coli O157. Curr Opin Infect Dis. 2003;16:259–263.
11.CDC, 2004. The Impact of Malaria, a Leading Cause of Death Worldwide. Available at Accessed December 17, 2008.
12.Guzmán MG, Kourí G. Dengue: an update. Lancet Infect Dis. 2002;2:33–42.
13.Hajat S, Ebi KL, Kovats RS, et al. The health consequences for flooding in europe and the implications for public health: a review of the evidence. Appl Environ Sci Public Health. 2003;1:13–21.
14.Callaghan WM, Rasmussen SA, Jamieson DJ, et al. Health concerns of women and infants in times of natural disasters: lessons learned from Hurricane Katrina. Matern Child Health J. 2007;11:307–311.
15.Perera FP. Children are likely to suffer most from our fossil fuel addiction. Environ Health Perspect. 2008;116:987–990.
16.Makri A, Stilianakis NI. Vulnerability to air pollution health effects. Int J Hyg Environ Health. 2008;211:326–336.
17.Jamieson DJ, Theiler RN, Rasmussen SA. Emerging infections and pregnancy. Emerg Infect Dis. 2006;12:1638–1643.
18.Semenza JC, Rubin CH, Falter KH, et al. Heat-related deaths during the July 1995 heat wave in Chicago. N Engl J Med. 1996;335:84–90.
19.Medina-Ramon M, Zanobetti A, Cavanagh DP, Schwartz J. Extreme temperatures and mortality: assessing effect modification by personal characteristics and specific cause of death in a multi-city case-only analysis. Environ Health Perspect. 2006;114:1331–1336.
20.Whitman S, Good G, Donoghue ER, Benbow N, Shou W, Mou S. Mortality in Chicago attributed to the July 1995 heat wave. Am J Public Health. 1997;87:1515–1518.
21.Centers for Disease Control and Prevention (CDC). Rapid assessment of the needs and health status of older adults after Hurricane Charley—Charlotte, DeSoto, and Hardee Counties, Florida, August 27–31, 2004. MMWR Morb Mortal Wkly Rep. 2004;53:837–840.
22.Medina-Ramón M, Schwartz J. Who is more vulnerable to die from ozone air pollution? Epidemiology. 2008;19:672–679.
23.Zeka A, Zanobetti A, Schwartz J. Individual-level modifiers of the effects of particulate matter on daily mortality. Am J Epidemiol. 2006;163:849–859.
24.Confalonieri U, Menne B, Akhtar R, et al. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In: Parry ML, Canziani OF, Palutikof JP, van der Linden PJ, Hanson CE, eds. Human health. Climate Change 2007. Impacts, Adaptation and Vulnerability. Cambridge, UK: Cambridge University Press, 2007:391–431.
25.Kalkstein LS. Health and climate change: direct impacts in cities. Lancet. 1993;342:1397–1399.
26.Curriero FC, Heiner KS, Samet JM, Zeger SL, Strug L, Patz JA. Temperature and mortality in 11 cities of the eastern United States. Am J Epidemiol. 2002;155:80–87.
27.Klinenberg E. Heat Wave: A Social Autopsy of Disaster in Chicago. Chicago: University of Chicago Press; 2002:305.
28.O'Neill MS, Jerrett M, Kawachi I, et al. Health, wealth, and air pollution: advancing theory and methods. Environ Health Perspect. 2003;111:1861–1870.
29.Cook JT, Frank DA. Food security, poverty, and human development in the United States. Ann N Y Acad Sci. 2008;1136:193–209.
30.Parry M, Rosenzweig C, Livermore M. Climate change, global food supply and risk of hunger. Philosophical Transactions of the Royal Society B. 2005;360:2125–2138.
31.U.S. Senate Committee on Homeland Security and Governmental Affairs. Hurricane Katrina: A Nation Still Unprepared. Washington DC, 2006: 109th Congress, 2nd Session, S. Rept. U.S. Senate Committee on Homeland Security and Governmental Affairs; 2006:109–322.
32.Louisiana Department of Health and Hospitals. Vital Statistics of All Bodies at St. Gabriel Morgue, February 23, 2006. Available at: Accessed October 12, 2008.
33.Mississippi Department of Health. Mississippi Vital Statistics 2005. Available at: Accessed October 12, 2008.
34.Centers for Disease Control and Prevention (CDC). Morbidity surveillance after Hurricane Katrina—Arkansas, Louisiana, Mississippi, and Texas, September 2005. MMWR Morb Mortal Wkly Rep. 2006;55:727–731.
35.Centers for Disease Control and Prevention (CDC). Mortality associated with Hurricane Katrina—Florida and Alabama, August–October 2005. MMWR Morb Mortal Wkly Rep. 2006;55:239–242.
36.Cefalu WT, Smith SR, Blonde L, Fonseca V. The Hurricane Katrina aftermath and its impact on diabetes care: observations from “ground zero”: lessons in disaster preparedness of people with diabetes. Diabetes Care. 2006;29:158–160.
37.Ford ES, Mokdad AH, Link MW, et al. Chronic disease in health emergencies: in the eye of the hurricane. Prev Chronic Dis. 2006;3:A46.
38.Schwartz J. Who is sensitive to extremes of temperature? A case-only analysis. Epidemiology. 2005;16:67–72.
39.EPA. Excessive heat events guidebook. EPA-430-B-06-005. 2006. Available at: Accessed June 2006.
40.Piacentino JD, Schwartz BS. Occupational risk of lyme disease: an epidemiological review. Occupational and Environmental Medicine. 2002; 59:75–84.
41.Schwartz BS, Goldstein MD. Lyme disease in outdoor workers: risk factors, preventive measures, and tick removal methods. Am J Epidemiol. 1990;131:877–885.
42.Centers for Disease Control and Prevention (CDC). Heat-related deaths among crop workers—United States, 1992–2006. MMWR Morb Mortal Wkly Rep. 2008;57:649–653.

Cited By:

This article has been cited 1 time(s).

Journal of Occupational and Environmental Medicine
Public Health Responses to the Risks of Climate Variability and Change in the United States
Ebi, KL
Journal of Occupational and Environmental Medicine, 51(1): 4-12.
PDF (203) | CrossRef
Back to Top | Article Outline
©2009The American College of Occupational and Environmental Medicine