9.2 A Framework for Understanding Vulnerability

Some populations of concern demonstrate relatively greater vulnerability to the health impacts of climate change. The definitions of the following key concepts are important to understand how some people or communities are disproportionately affected by climate-related health risks (Figure 9.1). Definitions are adapted from the Intergovernmental Panel on Climate Change (IPCC) and the National Research Council (NRC).1,2


Figure 9.1: Determinants of Vulnerability

Figure 9.1: Determinants of Vulnerability
Defining the determinants of vulnerability to health impacts associated with climate change, including exposure, sensitivity, and adaptive capacity. (Figure source: adapted from Turner et al. 2003)22
  • Vulnerability is the tendency or predisposition to be adversely affected by climate-related health effects, and encompasses three elements: exposure, sensitivity or susceptibility to harm, and the capacity to adapt to or to cope with change. Exposure is contact between a person and one or more biological, chemical, or physical stressors, including stressors affected by climate change. Contact may occur in a single instance or repeatedly over time, and may occur in one location or over a wider geographic area. Sensitivity is the degree to which people or communities are affected, either adversely or beneficially, by climate variability and change. Adaptive capacity is the ability of communities, institutions, or people to adjust to potential hazards, to take advantage of opportunities, or to respond to consequences. A related term, resilience, is the ability to prepare and plan for, absorb, recover from, and more successfully adapt to adverse events. People and communities with strong adaptive capacity have greater resilience.
  • Risk is the potential for consequences to develop where something of value (such as human health) is at stake and where the outcome is uncertain. Risk is often represented as the probability of the occurrence of a hazardous event multiplied by the expected severity of the impacts of that event.
  • Stressors are events or trends, whether related to climate change or other factors, that increase vulnerability to health effects.

Figure 9.2: Intersection of Social Determinants of Health and Vulnerability

Figure 9.2: Intersection of Social Determinants of Health and Vulnerability

Social determinants of health interact with the three elements of vulnerability. The left side boxes provide examples of social determinants of health associated with each of the elements of vulnerability. Increased exposure, increased sensitivity and reduced adaptive capacity all affect vulnerability at different points in the causal chain from climate drivers to health outcomes (middle boxes). Adaptive capacity can influence exposure and sensitivity and also can influence the resilience of individuals or populations experiencing health impacts by influencing access to care and preventive services. The right side boxes provide illustrative examples of the implications of social determinants on increased exposure, increased sensitivity, and reduced adaptive capacity.

People or communities can have greater or lesser vulnerability to health risks depending on social, political, and economic factors that are collectively known as social determinants of health.3 Some groups are disproportionately disadvantaged by social determinants of health that limit resources and opportunities for health-promoting behaviors and conditions of daily life, such as living/working circumstances and access to healthcare services.3 In disadvantaged groups, social determinants of health interact with the three elements of vulnerability by contributing to increased exposure, increased sensitivity, and reduced adaptive capacity (Figure 9.2). Health risks and vulnerability may increase in locations or instances where combinations of social determinants of health that amplify health threats occur simultaneously or close in time or space.4,5 For example, people with limited economic resources living in areas with deteriorating infrastructure are more likely to experience disproportionate impacts and are less able to recover following extreme events,6,7 increasing their vulnerability to climate-related health effects. Understanding the role of social determinants of health can help characterize climate change impacts and identify public health interventions or actions to reduce or prevent exposures in populations of concern.4,5,8

Factors that Contribute to Exposure

Exposures to climate-related variability and change are determined by a range of factors that individually and collectively shape the nature and extent of exposures. These factors include:

  • Occupation: Certain occupations have a greater risk of exposure to climate impacts. People working outdoors or performing duties that expose them to extreme weather, such as emergency responders, utility repair crews, farm workers, construction workers, and other outdoor laborers, are at particular risk.9
  • Time spent in risk-prone locations: Where a person lives, goes to school, works, or spends leisure time will contribute to exposure. Locations with greater health threats include urban areas (due to, for example, the “heat island” effect or air quality concerns), areas where airborne allergens and other air pollutants occur at levels that aggravate respiratory illnesses, communities experiencing depleted water supplies or vulnerable energy and transportation infrastructure, coastal and other flood-prone areas, and locations affected by drought and wildfire.10,11,12
  • Responses to extreme events: A person’s ability or, in some cases, their choice whether to evacuate or shelter-in-place in response to an extreme event such as a hurricane, flood, or wildfire affects their exposure to health threats. Low-income populations are generally less likely to evacuate in response to a warning (see Ch. 4: Extreme Events).6
  • Socioeconomic status: Persons living in poverty are more likely to be exposed to extreme heat and air pollution.13,14 Poverty also determines, at least in part, how people perceive the risks to which they are exposed, how they respond to evacuation orders and other emergency warnings, and their ability to evacuate or relocate to a less risk-prone location (see Ch. 8: Mental Health).6
  • Infrastructure condition and access: Older buildings may expose occupants to increased indoor air pollutants and mold, stagnant airflow, or high indoor temperatures (see Ch. 3: Air Quality Impacts). Persons preparing for or responding to flooding, wildfires, or other weather-related emergencies may be hampered by disruption to transportation, utilities, medical, or communication infrastructure. Lack of access to these resources, in either urban or rural settings, can increase a person’s vulnerability (see Ch. 4: Extreme Events).15,16
  • Compromised mobility, cognitive function, and other mental or behavioral factors: These factors can lead to increased exposure to climate-related health impacts if people are not aware of health threats or are unable to take actions to avoid, limit, or respond to risks.17 People with access and functional needs may be particularly at risk if these factors interfere with their ability to access or receive medical care before, during, or after a disaster or emergency.

Characterizing Biological Sensitivity

The sensitivity of human communities and individuals to climate change stressors is determined, at least in part, by biological traits. Among those traits are the overall health status, age, and life stage. From fetus, to infant, to toddler, to child, to adolescent, to adult, to the elderly, persons at every life stage have varying sensitivity to climate change impacts.10,18,19 For instance, the relatively immature immune systems of very young children make them more sensitive to aeroallergen exposure (such as airborne pollens). In addition to life stage, people experiencing long-term chronic medical and/or psychological conditions are more sensitive to climate stressors. Persons with asthma or chronic obstructive pulmonary disease (COPD) are more sensitive to exposures to wildfire smoke and other respiratory irritants. Social and economic factors also affect disparities in the prevalence of chronic medical conditions that aggravate biological sensitivity.20,21

Adaptive Capacity and Response to Climate Change

Many of the same factors that contribute to exposure or sensitivity also influence the ability of both individuals and communities to adapt to climate variability and change. Socioeconomic status, the condition and accessibility of infrastructure, the accessibility of health care, certain demographic characteristics, human and social capital (the skills, knowledge, experience, and social cohesion of a community), and other institutional resources all contribute to the timeliness and effectiveness of adaptive capacity (see Ch. 1: Introduction and Ch. 4: Extreme Events).


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