Author: O. Watts, Staff Writer | ☀
Abstract – Global climate change is increasingly recognized as a determinant of human health and a source of risk to healthcare systems. Its health consequences extend beyond the direct physiological effects of rising temperatures. Changes in extreme heat, precipitation, drought, wildfire conditions, hydrology, sea level, ecosystems, and the geographic suitability of some disease vectors can alter patterns of illness, injury, mortality, food and water security, population displacement, healthcare utilization, and continuity of care. Importantly, not every weather-related disaster or health outcome can be attributed directly to climate change. Health effects arise through interactions among climatic hazards, population exposure, biological susceptibility, social conditions, infrastructure, public-health capacity, and healthcare access. This review evaluates evidence linking global climate change with major health and healthcare crises, with particular attention to heat-related illness and mortality, wildfire smoke, flooding and waterborne disease, drought and food insecurity, climate-sensitive infectious disease, mental health, displacement, and disruption of healthcare delivery. Historical and contemporary evidence are considered together to identify trends and distinguish well-established causal relationships from emerging associations. The August 2026 Nepal flood disaster is examined as a contemporary example of cascading environmental and healthcare-system disruption while recognizing uncertainty regarding event-specific climate attribution. Collectively, the evidence indicates that climate change functions as a health-risk multiplier: it modifies environmental hazards while interacting with existing disease burden, socioeconomic vulnerability, and health-system capacity. Climate change should therefore be considered not only an environmental concern but an increasingly important challenge for global public health and healthcare-system resilience.
Keywords: climate change, global health, healthcare systems, extreme heat, wildfire smoke, infectious disease,
health-system resilience, environmental health
Introduction
Concerns about the relationship between climate and human health have developed over several decades. Early assessments focused largely on the potential for rising temperatures, changes in infectious-disease distribution, food insecurity, and extreme weather to affect future populations. By 2009, a major Lancet commission concluded that climate change represented a major global health challenge and emphasized that its consequences would be mediated through social, economic, and health-system conditions rather than through climate alone (Costello et al., 2009). A subsequent Lancet commission documented an expanding evidence base linking climate change with heat exposure, air pollution, infectious disease, food production, and other determinants of health (Watts et al., 2015).
More recent discussions have increasingly focused on healthcare delivery itself. Snyder and Arshad-Snyder (2024), for example, framed climate change not only as an environmental and public-health problem but also as a healthcare-management concern. Drawing on earlier Intergovernmental Panel on Climate Change assessments, they described three broad pathways through which climatic change may affect health: direct effects associated with heat and extreme events; indirect effects arising through environmental and ecosystem changes; and effects mediated through social systems, including food insecurity, population displacement, mental-health stressors, and damage to healthcare infrastructure. This tripartite framework remains useful, although contemporary research now provides considerably stronger epidemiologic and health-system evidence for many of these pathways.
The scientific literature has consequently moved beyond asking whether climate change can affect human health. Increasingly, research seeks to quantify how much observed illness or mortality is already attributable to anthropogenic climate change, identify populations at greatest risk, and determine whether healthcare systems are capable of absorbing increasing climatic stress.
Anthropogenic climate change refers to long-term alterations in the Earth’s climate resulting substantially from human activities, particularly greenhouse-gas emissions from fossil-fuel combustion, industrial activity, agriculture, and land-use change. Global warming—the increase in average global surface temperature—is one manifestation of climate change. The broader concept also encompasses changes in precipitation, hydrology, glaciers and ice sheets, sea level, ocean conditions, ecosystems, and some forms of extreme weather.
Current observations provide the environmental context for the health evidence. The World Meteorological Organization (WMO, 2026) reported that 2015–2025 were the 11 warmest years in the instrumental record and that global mean near-surface temperature in 2025 was approximately 1.43°C above the 1850–1900 average. Ocean heat content also reached a new observational record.
These environmental changes do not translate directly or uniformly into disease. Instead, climate-related health effects arise through interactions among hazard, exposure, and vulnerability. A hazard is a potentially harmful environmental condition, such as extreme heat or flooding. Exposure refers to contact between populations and that hazard. Vulnerability describes characteristics that increase susceptibility to harm, including age, chronic illness, poverty, inadequate housing, limited mobility, poor infrastructure, or lack of healthcare access.
This distinction is important because a climatic hazard does not inevitably produce a health crisis. A heatwave may be survivable for a population with reliable electricity, air conditioning, strong social networks, and accessible healthcare but deadly for people living in poorly ventilated housing without cooling or medical access. Similarly, heavy rainfall may cause limited disruption in one region but widespread disease and healthcare interruption where drainage, sanitation, transportation, and health infrastructure are fragile.
For this reason, climate change is increasingly described as a risk multiplier: a condition that intensifies or interacts with existing risks rather than acting as the sole cause of a health outcome.
Understanding Attribution and Climate-Sensitive Health Effects
A central challenge in climate-health research is distinguishing among association, contribution, and causation.
Climate attribution is the scientific process of estimating whether, and to what extent, human-caused climate change altered the likelihood or severity of an environmental event or health outcome. Attribution is stronger when researchers can compare observed conditions with a modeled counterfactual world in which anthropogenic climate change had not occurred.
This distinction prevents an important error. A particular hurricane, flood, wildfire, drought, or landslide should not automatically be described as having been “caused by climate change.” Most environmental disasters are multicausal, meaning that several interacting factors contribute to their occurrence and severity. Climate change may alter one or more of those factors without being the sole cause.
Health outcomes require similar caution. A disease is described as climate-sensitive when its incidence, severity, geographic distribution, or transmission is influenced by climatic variables such as temperature, precipitation, humidity, or environmental disturbance. Climate-sensitive does not mean climate-determined. Housing, sanitation, land use, immunity, vaccination, socioeconomic status, healthcare access, public-health interventions, and human behavior may be equally or more important in determining whether illness actually occurs.
The distinction becomes especially important when evaluating infectious disease, disasters, food insecurity, and population movement. By contrast, the evidence allowing direct attribution is stronger for some heat-related health outcomes.
Extreme Heat: From Association to Climate Attribution
Among the health consequences of climate change, the relationship between extreme heat and mortality is particularly well established.
The physiological mechanisms are clear. Human core temperature is maintained within a narrow range through sweating, increased blood flow to the skin, behavioral responses, and other regulatory processes. When ambient temperature and humidity become sufficiently high, these mechanisms may fail. Heat exposure can produce dehydration, electrolyte disturbances, hypotension, acute kidney injury, heat exhaustion, and life-threatening heatstroke.
However, the burden of heat extends well beyond classical heat illness. Elevated temperature increases cardiovascular strain and can exacerbate ischemic heart disease, heart failure, respiratory disease, renal disease, diabetes, and other chronic conditions. Older adults are particularly vulnerable because of reduced thermoregulatory capacity, higher prevalence of chronic illness, social isolation, and medications that may interfere with hydration or heat dissipation.
Snyder and Arshad-Snyder (2024) anticipated these operational implications by identifying heat rash, heat cramps, heat exhaustion, heatstroke, and aggravation of respiratory disease as conditions healthcare systems should expect to encounter with increasing climatic stress. Their discussion was primarily prospective. Subsequent attribution research has strengthened the empirical basis for that concern.
Vicedo-Cabrera et al. (2021) analyzed temperature and mortality data from 732 locations in 43 countries for the period 1991–2018. Using climate models to estimate the additional heat exposure attributable to anthropogenic warming, the investigators concluded that approximately 37% of warm-season heat-related deaths across the study locations were attributable to human-induced climate change. Attributable mortality was identified on every inhabited continent. This study is particularly important because it moves the evidence beyond an association between heat and mortality to an estimate of the health burden already attributable to anthropogenic warming.
More recent surveillance indicates that the absolute burden remains substantial. The 2025 Lancet Countdown on Health and Climate Change estimated approximately 546,000 heat-related deaths annually under its analytic framework and reported an increase in the heat-related mortality rate compared with the 1990s (Romanello et al., 2025). These estimates should not be interpreted as exact global counts; differences in exposure definitions, statistical models, geographic coverage, and baseline periods produce variation among studies. Their significance lies in the consistency of the overall finding: heat-related mortality is already substantial, and anthropogenic warming has contributed measurably to that burden.
Heat can also create a healthcare crisis without producing a discrete natural disaster. Emergency departments may experience increased presentations for dehydration, cardiovascular disease, renal injury, respiratory exacerbations, and heat illness while healthcare facilities simultaneously face greater cooling demand and potential stress on electrical infrastructure. Healthcare workers, emergency personnel, home-health staff, and patients traveling for care remain exposed to the same environmental hazard.
The health effects of heat are therefore both clinical and systemic.
Wildfire Smoke: A Climate-Sensitive Air-Quality Crisis
Wildfires provide a more complex example of climate-related health risk because fire activity is influenced by numerous climatic and nonclimatic factors. Ignition sources, vegetation, land management, forest ecology, suppression practices, and settlement patterns all affect wildfire occurrence and severity. Climate conditions nevertheless influence fuel dryness, snowmelt, drought, temperature, and the length of fire-conducive seasons in many regions.
The principal health threat from wildfire often extends far beyond the burn area.
Wildfire smoke contains gases and airborne particles, including fine particulate matter, commonly abbreviated PM2.5. The term refers to particles with an aerodynamic diameter of 2.5 micrometers or smaller. Their small size allows them to penetrate deeply into the lungs, and some particles or their constituents may enter the circulation, contributing to inflammatory and cardiopulmonary effects.
A systematic review by Gould et al. (2024) found evidence associating wildfire smoke exposure with all-cause mortality and respiratory hospitalization, while associations with cardiovascular morbidity were less consistent. The review also emphasized methodological challenges in separating wildfire-derived PM2.5 from other air-pollution exposures and in accounting for delayed and nonlinear effects.
The geographic reach of smoke makes wildfire a distinctive healthcare problem. Smoke plumes can travel hundreds or thousands of kilometers, exposing populations that face no danger from flames. Consequently, healthcare systems geographically distant from the originating disaster may experience increases in asthma exacerbations and other respiratory complaints.
Historical comparisons also illustrate why climate change should not be treated as the sole cause of wildfire-related health burdens. Fire existed long before contemporary climate change. The relevant question is whether warming, drought, changing snow patterns, or altered fuel conditions increase the probability, duration, or severity of conditions favorable to fire and therefore increase opportunities for harmful smoke exposure.
The health crisis emerges from the interaction between those climatic conditions, the occurrence of fire, population exposure, air quality, preexisting disease, and healthcare capacity.
Flooding, Extreme Precipitation, and Secondary Health Crises
Floods demonstrate how the greatest health burden from a climatic event may occur after the immediate physical hazard.
Direct effects include drowning, trauma, electrocution, hypothermia, and injuries sustained during evacuation or cleanup. Indirect effects arise when floodwaters contaminate drinking-water systems, overwhelm sewage infrastructure, damage housing, interrupt electricity, destroy medications, obstruct transportation, and displace populations.
Snyder and Arshad-Snyder (2024) similarly emphasized that flooding can create conditions favorable to waterborne disease, expose populations to contaminated water, and damage essential infrastructure. Of particular relevance to healthcare administration, they argued that disruptions to power, water, communications, and transportation may directly compromise a healthcare system’s ability to provide care. Contemporary health-system research has reinforced that observation.
Waterborne disease is one important consequence. Levy et al. (2016), in a systematic review of 141 studies examining diarrheal disease in relation to temperature, rainfall, flooding, and drought, found consistent evidence of increased diarrheal disease following higher temperatures, heavy rainfall, and flooding, although relationships differed by pathogen and location. The analysis demonstrated that climate-health relationships involving infectious disease are contingent on sanitation, water quality, infrastructure, and other local conditions rather than climatic exposure alone.
Floods may also increase healthcare need while simultaneously reducing healthcare capacity. Road closures can prevent patients and employees from reaching hospitals. Power failure can compromise refrigeration and medical equipment. Dialysis, cancer treatment, obstetric services, home oxygen, medication access, and other forms of continuous care may be interrupted even among people who were not physically injured by the disaster. Salas et al. (2024) examined Medicare beneficiaries exposed to 42 major U.S. weather disasters between 2011 and 2016 and identified changes in emergency-department utilization, nonelective hospitalization, and mortality during the weeks after exposure. Importantly, the consequences persisted beyond the immediate disaster period, supporting the argument that conventional measures based solely on deaths occurring during an event may underestimate its healthcare burden.
Nepal, 2026: A Cascading Healthcare Emergency
The devastating Nepal floods of August 2026 provide a contemporary example of these cascading effects.
On August 26, a rapid slope failure involving glacial terrain in Langtang National Park triggered a major debris flow and flooding that traveled approximately 100 kilometers downstream. The U.S. Geological Survey reported that it remained uncertain whether the initiating failure represented a landslide incorporating part of a glacier or a glacial collapse. For that reason, a direct statement that anthropogenic climate change “caused” the event would exceed the available evidence.
The disaster nevertheless demonstrates conditions relevant to climate-health analysis. High-mountain regions are undergoing changes in glaciers, snow, permafrost, precipitation, and hydrology, and those changes can modify the environmental setting in which glacial and slope hazards occur.
The healthcare consequences were substantial. WHO reported widespread damage to homes, roads, bridges, hydropower, water systems, and health infrastructure. Initial assessments found that three health posts were destroyed, one hospital was partially damaged, and access to two additional hospitals was impaired. Approximately 10,000 households required immediate relief. Public-health priorities included traumatic injuries, diarrheal and respiratory disease, unsafe water and food, vector-borne disease, mental-health needs, and continuity of essential healthcare.
The crisis continued after the floodwaters receded. Displacement, crowding, damaged sanitation, and difficult road access led Nepalese authorities and WHO to intensify post-disaster disease surveillance. Routine health services also had to be restored in affected communities.
The Nepal experience illustrates the concept of a cascading disaster—an event in which the initial hazard triggers a sequence of failures across interdependent systems. A flood becomes a transportation emergency, a water and sanitation emergency, a housing crisis, a communicable-disease risk, and ultimately a healthcare-delivery problem.
Drought, Food Insecurity, and Nutritional Health
Drought differs from floods and storms because it often develops gradually, making its health burden more difficult to identify and attribute.
Drought is a prolonged period of abnormally low water availability relative to normal conditions. Meteorological drought involves sustained precipitation deficits, whereas agricultural and hydrological drought may involve soil moisture, river flow, groundwater, or reservoir depletion.
The health pathways are multiple. Salvador et al. (2023) reviewed evidence linking drought with water-, food-, and vector-borne disease, malnutrition, respiratory and cardiovascular disease, mental-health outcomes, and mortality. The authors emphasized that vulnerability differs markedly according to socioeconomic conditions, healthcare access, demographic characteristics, and regional resilience.
Food security provides one of the most important connections. Snyder and Arshad-Snyder (2024) noted that disruption of agricultural systems, fisheries, forests, and transportation can threaten food supply and contribute to malnutrition. More recent scholarship has examined these relationships in greater detail and increasingly portrays climate-related food insecurity as a systems-level problem rather than merely a decline in crop production.
Food security exists when people have reliable physical and economic access to sufficient, safe, and nutritious food. A decline in agricultural production does not automatically cause malnutrition because trade, household income, food assistance, market systems, and dietary substitution can buffer or intensify the effect. Nevertheless, climate-related disruption may place already food-insecure populations at greater risk.
The health consequences can include undernutrition, micronutrient deficiencies, impaired childhood development, poorer maternal health, and increased susceptibility to infectious disease. Less visible effects may occur when households respond to higher food prices by purchasing cheaper, less nutritious foods.
Green et al. (2022) demonstrated the interdependence of global food supply, dietary health, sustainability, and vulnerability to climate change, reinforcing the importance of evaluating nutrition within broader food-system dynamics. Drought also affects healthcare delivery directly. Modern health facilities require dependable water for hand hygiene, sterilization, dialysis, laboratory operations, sanitation, cooling systems, food preparation, and infection control. Water scarcity may therefore compromise clinical operations even when patients have not developed a climate-related illness.
Climate-Sensitive Infectious Diseases
The relationship between global climate change and infectious disease is among the most frequently discussed—and most easily oversimplified—areas of climate-health research.
A vector is an organism that carries and transmits a pathogen between hosts. Mosquitoes, ticks, and some other arthropods function as disease vectors. Vector-borne diseases include conditions such as dengue, malaria, chikungunya, Lyme disease, and others transmitted through these organisms.
Snyder and Arshad-Snyder (2024) identified shifting patterns of disease-carrying mosquitoes and ticks and increased waterborne disease as important indirect health consequences of environmental and ecosystem change. That conceptual framing remains consistent with newer evidence, although current research allows substantially more nuanced interpretation.
Vectors are sensitive to environmental conditions because temperature, rainfall, and humidity influence their reproduction, survival, geographic range, biting behavior, and the development of pathogens within them.
De Souza and Weaver (2024) reviewed evidence concerning climate change and vector-borne diseases and concluded that climate can alter vector distributions and transmission potential, but the relationships are complex and sometimes nonlinear. Land use, human mobility, behavior, urbanization, public-health programs, and socioeconomic conditions interact with climate to determine actual disease burden.
For example, warmer temperatures may make a region more suitable for a mosquito species, but this does not guarantee that dengue or malaria will become endemic. Transmission also requires introduction of the pathogen, susceptible human hosts, suitable breeding conditions, and insufficient control to interrupt transmission. Strong surveillance and vector-control programs can prevent or limit outbreaks despite climatic suitability.
Conversely, health systems may confront diseases outside their historically familiar geographic ranges. This creates challenges for clinician recognition, laboratory capacity, surveillance, treatment protocols, and public-health response.
Waterborne and foodborne diseases are also climate-sensitive. Higher temperatures may influence pathogen replication, while heavy rainfall and flooding can introduce sewage or other contaminants into water systems. Warmer coastal waters can increase environmental suitability for some Vibrio species.
Infectious disease therefore provides an example of climate change modifying the ecological opportunity for transmission rather than directly producing infection.
Mental Health and Psychological Effects
Climate-related health crises also include psychological and behavioral consequences.
Research after hurricanes, wildfire, floods, and other disasters has repeatedly documented post-traumatic stress symptoms, anxiety, depression, grief, sleep disturbance, and other forms of psychological distress. The mechanisms include physical danger, bereavement, property loss, displacement, financial strain, disruption of employment, and loss of community.
Snyder and Arshad-Snyder (2024) included mental illness and stress among indirect climate-related consequences mediated through social systems, particularly food insecurity, population displacement, and economic disruption. Since that earlier framing, a growing literature has examined not only acute disasters but slow-onset climate change—environmental changes that develop gradually rather than through a single catastrophic event.
Examples include persistent drought, gradual temperature change, ecosystem degradation, and sea-level rise.
Burrows et al. (2024) systematically reviewed 57 studies examining slow-onset climate processes and mental health. The literature identified associations with depression, anxiety, psychological distress, suicide, grief, and diminished well-being, although results were heterogeneous and causal evidence was less developed than for acute disaster exposure.
This distinction is important. The psychological effects of escaping a wildfire may resemble trauma following other disasters, whereas the mental-health consequences of repeated crop failure or progressive loss of a coastal community may develop over years through financial strain, uncertainty, loss of identity, and deterioration of social networks.
Such evidence supports recognition of mental health as part of the climate-health burden while also demonstrating the need for caution in attributing individual psychiatric conditions directly to climate change.
Climate-Related Displacement and Continuity of Care
Environmental disasters and gradual environmental deterioration can also contribute to population movement.
Climate-related displacement refers to temporary or permanent movement associated partly with climatic or environmental pressures. Climate change is rarely the sole determinant. Employment, conflict, housing, family relationships, political instability, economic conditions, and established migration networks also influence whether people move.
Snyder and Arshad-Snyder (2024) anticipated population displacement as an important pathway linking climate change with healthcare demand. Their discussion focused partly on the possibility that migration related to extreme weather, sea-level rise, and food shortages could require considerable healthcare planning. Contemporary climate-health scholarship supports the broader concern while emphasizing that migration decisions are typically multicausal.
For healthcare systems, the important issue is not simply why migration occurred but what happens to health during and after displacement.
Patients may lose access to established clinicians, medications, medical records, home medical equipment, rehabilitation, vaccination, dialysis, prenatal care, cancer treatment, and behavioral health services. Temporary shelters can expose displaced populations to overcrowding, inadequate sanitation, and infectious disease.
Climate-related mobility can therefore transform an environmental crisis into a continuity-of-care crisis, particularly for populations with complex chronic illness.
Unequal Health Effects and Climate Vulnerability
One of the clearest themes across the climate-health literature is that climatic hazards do not affect populations equally.
Climate vulnerability refers to the degree to which individuals, communities, or systems are susceptible to and unable to cope with climate-related harm. Vulnerability arises from the interaction of biological, social, economic, and infrastructural factors.
Older adults may have impaired thermoregulation and higher rates of cardiovascular, respiratory, and renal disease. Children have different physiological and developmental vulnerabilities. Pregnant individuals may be susceptible to some heat-related and environmental exposures. Outdoor workers may have limited ability to avoid heat or smoke. People with mobility limitations may face evacuation barriers.
Patients dependent on medical technology represent another particularly vulnerable group. A loss of electricity may threaten a person using a ventilator or oxygen concentrator within hours. Dialysis patients may suffer if transportation, electricity, clean water, or staffing is disrupted. Insulin and other medications may require refrigeration.
Social conditions modify these risks further. Housing quality, neighborhood tree cover, air conditioning, transportation, insurance, income, employment flexibility, and proximity to healthcare all determine the capacity to adapt.
Climate-related health disparities therefore frequently reflect existing social determinants of health—the social and economic conditions in which people live, work, and age—rather than an entirely new form of inequality.
Climate Events as Healthcare-System Crises
A growing body of scholarship has begun examining not only the health effects of climate change but the capacity of healthcare systems to manage them.
This concern was central to Snyder and Arshad-Snyder’s (2024) earlier healthcare-management analysis. They emphasized that failure of critical infrastructure—particularly electricity, water, communications, and transportation—can severely limit the ability of health systems to respond to environmental disasters. They also highlighted hospital evacuation, interruption of care, infrastructure resilience, surveillance, and supply-chain preparedness as areas of concern. Those observations have subsequently gained support from a broader health-systems literature.
Healthcare facilities depend on extensive infrastructure external to clinical care: electricity, water, transportation, telecommunications, information systems, medical gases, refrigeration, food, pharmaceuticals, laboratory services, waste disposal, and supply chains. A structurally intact hospital may therefore become clinically ineffective if one or more supporting systems fails.
Braithwaite et al. (2024) systematically analyzed 129 publications concerning healthcare-system capacity and climate preparedness. Seven recurring areas emerged: workforce, preparedness tools and frameworks, infrastructure and urban planning, communication, surge capacity and increased system burden, service interruption, and financial costs. The authors also identified an important limitation in the literature: evidence was disproportionately concentrated on acute disasters and higher-income countries, leaving substantial uncertainty about healthcare preparedness in many regions likely to face significant climatic risk.
Health-system resilience refers to the capacity of a healthcare system to anticipate, absorb, respond to, recover from, and adapt to disruption while continuing to provide essential services.
This concept is broader than disaster preparedness. A resilient hospital requires not only evacuation plans but dependable utilities, supply-chain alternatives, workforce contingency planning, information-system redundancy, communication networks, disease surveillance, transportation planning, and partnerships with public-health and emergency-management agencies.
Climate change creates particular difficulties because multiple components of the system may be affected at the same time. During a heatwave, patient demand may rise while the electrical grid is strained. During a flood, injuries and infectious-disease risks may increase while roads and hospitals are inaccessible. During a wildfire, patients may require respiratory care while healthcare workers themselves are displaced.
The result is a distinctive form of healthcare crisis: demand rises while capacity may simultaneously fall.
Healthcare’s Contribution to Climate-Related Health Risk
The relationship between climate change and healthcare is bidirectional. Health systems treat climate-sensitive illness, but healthcare delivery itself consumes energy and materials and generates greenhouse-gas emissions.
Eckelman et al. (2020) estimated that the U.S. healthcare sector accounted for approximately 8.5% of national greenhouse-gas emissions in 2018. A substantial proportion occurred indirectly through the healthcare supply chain rather than through emissions generated within hospitals themselves.
This distinction introduces the concept of scope 3 emissions, which are greenhouse-gas emissions generated throughout an organization’s value chain—for example, through manufacture and transportation of pharmaceuticals, medical devices, food, equipment, and other purchased goods and services.
Healthcare therefore occupies an unusual position: activities intended to improve health can also contribute indirectly to environmental changes that affect health.
This does not imply that minimizing emissions should supersede patient safety or clinical effectiveness. Infection prevention, reliable supplies, therapeutic effectiveness, cost, and patient outcomes remain fundamental healthcare responsibilities. The issue is better understood as one of environmental stewardship—the responsible management of resources while preserving the quality and safety of care.
Climate Change as a Health-Risk Multiplier
The evidence reviewed here suggests that climate change is best understood not as one additional disease category but as a force capable of interacting with many existing causes of illness.
- Heat interacts with cardiovascular and renal disease.
- Wildfire smoke interacts with asthma and chronic lung disease.
- Heavy rainfall interacts with inadequate sanitation.
- Drought interacts with poverty and food insecurity.
- Changing ecological conditions interact with vector distribution and infectious-disease surveillance.
- Flooding interacts with fragile infrastructure.
- Displacement interacts with interrupted chronic care.
- Extreme weather interacts with healthcare workforce shortages and supply-chain vulnerability.
This systems perspective is consistent with the central premise advanced by Snyder and Arshad-Snyder (2024): the implications of climate change for healthcare cannot be understood only by identifying individual illnesses. They also involve the infrastructure, resources, workforce, management capacity, and social systems required to deliver care.
These interactions explain why climate-related health burden cannot be represented adequately by a single estimate of deaths or hospitalizations.
They also explain the importance of adaptation. Climate adaptation refers to adjustments made in human or natural systems to reduce harm from actual or expected climatic effects. In healthcare, adaptation may include heat-response programs, flood-resistant facilities, disease surveillance, backup power and water systems, supply-chain diversification, emergency staffing plans, and continuity-of-care strategies.
Adaptation differs from mitigation, which refers to efforts to reduce the underlying drivers of climate change, principally greenhouse-gas emissions or enhancement of greenhouse-gas removal.
A related concept, maladaptation, describes an action intended to reduce climatic risk that inadvertently increases vulnerability or creates new harms. For example, a healthcare adaptation strategy that improves short-term resilience but becomes unaffordable, increases inequity, or creates dependence on another fragile infrastructure may shift rather than eliminate risk.
These distinctions matter because responding to climate-related healthcare risk is not simply a matter of implementing more environmental programs. Effective responses must protect patient safety, improve resilience, and account for financial, operational, ethical, and equity consequences.
Interpreting the Evidence
The evidence linking climate change and health is substantial, but its strength varies among outcomes.
For extreme heat, attribution research has demonstrated that anthropogenic warming is already responsible for a measurable proportion of heat-related mortality. For wildfire smoke, strong evidence links exposure to respiratory morbidity and mortality, while the degree to which climate change contributes to individual fires varies by region and event.
For infectious disease, climate clearly influences vector and pathogen ecology, but transmission remains highly dependent on nonclimatic factors. For food insecurity, mental health, migration, and disaster-related healthcare disruption, the causal pathways are often longer and include substantial social and economic mediation.
This hierarchy of evidence is important. Scholarly analysis should not treat all climate-health claims as equally certain.
Historical evidence also serves an important role. Studies published a decade or more ago identified many of the pathways now being observed with greater precision. Costello et al. (2009) and Watts et al. (2015), for example, described climate change as a major global health challenge well before the current generation of attribution studies could quantify specific mortality burdens.
The 2024 analysis by Snyder and Arshad-Snyder occupies a useful position within that progression. Drawing heavily on IPCC assessments and healthcare-policy literature, it translated climate science into healthcare-management concerns by emphasizing infrastructure vulnerability, service disruption, food-system effects, migration, and preparedness. More recent studies have increasingly quantified several of those concerns through epidemiologic, attribution, and health-system research.
Thus, the evolution of the literature can be understood as a progression:
plausible health risk → observed association → quantified burden → climate attribution → health-system response.
Not every climate-health pathway has reached the final stages of that progression.
Conclusion
Global climate change is increasingly measurable not only through temperature records, ocean heat, precipitation patterns, glacier loss, or atmospheric greenhouse gases, but also through its consequences for human health and healthcare delivery.
The strength of evidence differs among health outcomes. Heat-related mortality provides one of the clearest examples of direct climate attribution; research indicates that a substantial proportion of observed heat mortality is already attributable to anthropogenic warming. Wildfire smoke has a well-established association with respiratory morbidity and mortality, although individual fires result from climatic and nonclimatic factors. Flooding and extreme precipitation create acute injuries and secondary health crises through water contamination, displacement, disease risk, infrastructure failure, and interruption of care. Climatic conditions modify the ecology of vector-, food-, and waterborne diseases but interact strongly with sanitation, land use, surveillance, socioeconomic conditions, and public-health interventions.
Drought and disruption of food and water systems create additional pathways to malnutrition, disease, and healthcare vulnerability. Both acute disasters and slower environmental changes can affect mental health and population mobility. These effects are disproportionately experienced by populations already vulnerable because of age, chronic illness, poverty, occupation, housing, geography, disability, or limited healthcare access.
The 2026 Nepal disaster illustrates the complexity particularly well. Available evidence does not justify attributing the initiating slope failure directly to anthropogenic climate change. Nevertheless, the resulting destruction demonstrates how an environmental hazard can become a healthcare crisis when transportation, water systems, sanitation, housing, and health facilities fail simultaneously. Such events reveal vulnerabilities that are central to understanding the health consequences of a changing climate.
Healthcare systems themselves are therefore part of the climate-health equation. As Snyder and Arshad-Snyder (2024) argued, climate-sensitive events can challenge the infrastructure required to maintain access, quality, and continuity of care. The contemporary evidence strengthens that concern: healthcare organizations may face increasing health need at the same time that staffing, transportation, electricity, water, communications, facilities, and medical supply chains are impaired.
The accumulated evidence supports a conclusion more nuanced than the assertion that climate change simply “causes” disease. Global climate change alters environmental conditions in ways that increase or redistribute health risks, magnify existing vulnerabilities, and create new challenges for systems responsible for protecting health.
Its significance for healthcare lies in those interactions.
Climate change is therefore best understood as an increasingly important determinant of health, amplifier of existing health disparities, and source of systemic risk to healthcare delivery.
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