Climate change is no longer a distant ecological threat — it is actively reshaping global health in ways that are becoming increasingly visible and measurable. Over the few decades the planet warms, patterns of disease are shifting; pathogens and the vectors that carry them are expanding into regions previously considered low-risk. These changes are not occurring in isolation or as short-term anomalies. Over recent decades, gradual increases in global temperatures, along with shifting rainfall patterns and more frequent extreme weather events, have altered the environmental conditions that govern disease transmission. Regions that once experienced predictable seasonal risks are now facing longer transmission periods, emerging outbreaks, and unfamiliar health threats. As a result, diseases once limited by climate, geography, or seasonality are beginning to affect new populations, challenging existing surveillance systems and public health preparedness.
Rising temperatures, altered precipitation, and more frequent extreme weather events are driving changes in the ecology of infectious diseases, elevating risks for malaria, dengue, heatstroke, respiratory illnesses, and even mental health conditions. What were once considered stable geographic and seasonal boundaries for many illnesses are now changing, forcing a reassessment of disease risk across regions.
Global health agencies have repeatedly warned that climate change is already influencing disease patterns, with organizations such as the World Health Organization (WHO) identifying it as one of the greatest health threats of the 21st century. [1]
Together, all these global examples point to a clear shift: climate change is no longer shaping disease risk in the distant future but is actively influencing how illnesses emerge and spread today.
This article explores how rising temperatures and environmental instability are changing when, where, and who diseases affect — and why understanding these patterns matters for clinicians, public health professionals, and policymakers navigating a warming world.
In India, the link between climate change and shifting disease patterns is becoming increasingly evident. Rising temperatures, prolonged summers, and changing monsoon behavior directly influence the survival and spread of disease vectors such as mosquitoes. Warmer conditions accelerate mosquito breeding cycles and extend transmission seasons, contributing to the growing burden of dengue and malaria in both urban and semi-urban regions, including areas that previously reported limited cases.
Altered rainfall patterns further compound these risks. Intense monsoon rains and urban flooding create stagnant water sources that favor mosquito breeding, while drought conditions can drive vectors and animal reservoirs closer to human settlements. In India, these altered rainfall patterns have direct public health consequences. Intense monsoon rains frequently overwhelm urban drainage systems, leading to waterlogging in cities and creating ideal breeding conditions for mosquitoes. According to national surveillance data, India has reported a steady rise in dengue cases over the past decade, with major spikes often following years of heavy or erratic monsoon rainfall. Conversely, recurring droughts in several regions reduce natural water availability, forcing vectors and animal reservoirs to move closer to human settlements in search of water. This combination of flooding and water scarcity increases human exposure to disease vectors and heightens the risk of outbreaks, particularly in densely populated and resource-limited settings.
At the same time, recurrent heatwaves across northern and central India have led to a rise in heat-related illnesses, dehydration, and worsening of cardiovascular and respiratory conditions, particularly among the elderly and outdoor workers.
According to assessments by the Intergovernmental Panel on Climate Change (IPCC), rising temperatures, altered rainfall, and extreme weather events are modifying ecological systems in ways that directly affect disease transmission and population health. [2]
Extreme weather events also disrupt public health infrastructure. Floods and cyclones damage sanitation systems, contaminate drinking water, and displace populations, increasing the risk of water-borne and respiratory infections in overcrowded settings. In India, extreme weather events such as floods and cyclones increasingly strain public health infrastructure. Severe flooding and coastal cyclones have repeatedly damaged water supply and sanitation systems, leading to contamination of drinking water and outbreaks of water-borne diseases. Following major flood events in recent years, several states have reported spikes in acute diarrheal illness and respiratory infections, particularly among displaced populations housed in overcrowded relief shelters. These disruptions not only increase immediate disease risk but also weaken routine healthcare delivery, complicating outbreak control and recovery efforts.
These combined biological and social pressures highlight how climate change is reshaping disease risk in India, placing additional strain on already burdened health systems.
Climate change is rapidly altering the geographic distribution and transmission dynamics of vector-borne diseases. Rising temperatures and prolonged warm seasons enhance mosquito survival, accelerate breeding cycles, and shorten pathogen incubation periods, increasing the efficiency of disease transmission. These climatic shifts allow vectors to remain active for longer periods each year and expand into regions that were previously unsuitable for sustained transmission. Changes in rainfall patterns further influence breeding habitats, with increased precipitation creating stagnant water sources and irregular weather extending transmission seasons beyond traditional limits. As a result, vector-borne diseases are increasingly detected outside their historical geographic and seasonal boundaries, complicating surveillance efforts and placing new populations at risk.
As a result, infections such as dengue, malaria, chikungunya, and Zika are expanding into regions and seasons that were previously considered low-risk. This expansion is occurring not only across geographic boundaries but also across time, with transmission seasons becoming longer and less predictable than in previous decades. Areas that once experienced brief, seasonal outbreaks are now reporting cases over extended periods, challenging existing vector control strategies and disease surveillance systems. For populations in newly affected regions, limited prior exposure and immunity further increase vulnerability, underscoring the need for climate-informed public health planning and early detection measures.
In India, warmer urban environments and irregular monsoon patterns have extended transmission periods beyond traditional post-monsoon months, leading to year-round case detection in some cities. Rapid urbanization, high population density, and challenges in water management further amplify these risks, particularly in metropolitan areas where water storage practices and inadequate drainage create persistent breeding sites. Cities such as Delhi, Bengaluru, and Mumbai have reported dengue and chikungunya cases outside the traditional post-monsoon peak, with surveillance data indicating prolonged or near year-round transmission in some years. Compared to earlier periods when outbreaks were largely seasonal, this shift places sustained pressure on municipal health services and highlights the need for continuous vector surveillance and control rather than time-limited, seasonal responses.
Similar trends are being observed globally, where vector species are moving into higher altitudes and temperate zones, exposing immunologically naïve populations and complicating disease surveillance and control efforts. Regions that historically experienced minimal or no sustained transmission are now reporting sporadic outbreaks and increased vector presence, often without the public health infrastructure or community immunity needed for rapid response. This geographic expansion challenges traditional disease mapping and forecasting models, making it harder to predict outbreak timing and intensity. As vectors adapt to new climates, surveillance systems must also adapt, incorporating climate data and cross-regional monitoring to effectively detect and control emerging transmission zones.
Surveillance data summarized by the World Health Organization (WHO) and the Lancet Countdown on Health and Climate Change show expanding geographic ranges and longer transmission seasons for vector-borne diseases in recent years. [1,3]
Vector-borne diseases such as malaria and dengue are among the most climate-sensitive infections. Rising temperatures not only accelerate the life cycle and biting frequency of Anopheles and Aedes mosquitoes, but also shorten the time required for parasites and viruses to develop inside the vector, increasing transmission efficiency. Warmer conditions also extend breeding seasons and allow these mosquito species to survive in areas that were previously too cool to support sustained transmission, including higher altitudes and some temperate regions. Changes in rainfall patterns further influence mosquito habitats, with increased precipitation and urban water stagnation creating ideal breeding environments. Together, these factors are contributing to longer transmission seasons, shifting disease boundaries, and increased outbreak potential, complicating vector control efforts and challenging existing disease prevention strategies.
Warmer climates extend breeding seasons and allow mosquitoes to survive in regions that were previously too cool, enabling disease spread into higher altitudes and new geographic zones.
Compared to earlier decades, when transmission was largely confined to predictable seasons and endemic regions, recent years have seen longer transmission windows and outbreaks occurring outside traditional geographic and seasonal boundaries. This shift has altered the rhythm of disease occurrence, with cases now appearing earlier in the year and persisting beyond expected peak periods. Health systems that were designed around seasonal preparedness are increasingly required to maintain year-round surveillance and response capacity. As transmission becomes less predictable, early warning systems and vector control strategies must adapt to account for changing climate conditions and evolving disease dynamics.
Annual reports from the Lancet Countdown on Health and Climate Change have consistently documented increasing heat exposure, rising disease vulnerability, and growing strain on health systems compared to previous decades [3]. These reports highlight how climate-related health risks are no longer isolated or episodic but are becoming sustained and cumulative over time. Increasing heat exposure not only raises the risk of heat-related illness but also amplifies the transmission potential of climate-sensitive diseases, placing additional pressure on already stretched healthcare systems. As a result, adapting public health planning to account for long-term climate trends has become increasingly important for reducing future disease burden.
Changes in rainfall patterns further amplify these effects. Increased precipitation and urban water stagnation create ideal breeding environments for Aedes mosquitoes, while irregular monsoons can prolong transmission seasons beyond traditional limits.
In India and other tropical regions, this shift has contributed to prolonged dengue transmission and recurrent outbreaks even in areas with established vector control programs. Factors such as rapid urbanization, population density, and limitations in water and waste management reduce the effectiveness of traditional control measures, allowing transmission to persist despite ongoing interventions. Together, these challenges highlight the need for more adaptive, climate-informed strategies to sustain disease prevention in tropical settings.
At the same time, malaria risk is increasingly reported from regions that historically experienced limited exposure. These expanding frontiers pose significant public health challenges, as populations in newly affected areas often lack immunity and surveillance systems may be unprepared for early detection and response.
Evidence from 2024–2025 shows dramatic dengue surges in regions experiencing intense heat waves, such as Southeast Asia, where unusually high temperatures corresponded with sharp increases in case numbers and deaths.
Meanwhile, field studies and modeling indicate that malaria’s range may extend into higher altitudes in Africa and beyond, potentially exposing new populations to endemic transmission.
The last 10–15 years have seen consistently higher average temperatures and more frequent heat extremes than the late 20th century, a trend that correlates with shifting disease distribution. Malaria, previously limited to lower altitudes, is now reported in the highlands of East Africa and South America. Likewise, dengue transmission has expanded from tropical/subtropical regions into parts of southern Europe and East Asia, affecting previously unaffected areas.
Climate-disease interactions are evident in India: shifting monsoon and rising urban heat/humidity correlate with longer dengue transmission and recurrent outbreaks in cities previously with seasonal limits. Concurrently, heat-related illnesses have sharply increased during recent heatwaves, with record-breaking temperatures driving up hospital admissions for heatstroke and dehydration, a stark contrast to earlier decades with less frequent extreme heat.
While mosquito-borne diseases often dominate discussions on climate-related health risks, climate change is also driving a broader spectrum of emerging threats involving other vectors and pathogens. Rising temperatures, changing rainfall patterns, and environmental disruption are altering rodent habitats and population dynamics, increasing the risk of zoonotic diseases transmitted through direct contact or contaminated water. In India, heavy rainfall and flooding have been repeatedly associated with outbreaks of leptospirosis, particularly in coastal and flood-prone states such as Kerala, Maharashtra, and parts of Tamil Nadu, where exposure to water contaminated with rodent urine is common [5]. Flood conditions displace rodent populations and bring them into closer proximity with human settlements, increasing opportunities for disease transmission. These patterns underscore how climate-driven ecological changes are expanding zoonotic disease risk beyond traditional mosquito-focused models.
Changes in temperature and humidity are also enabling certain fungal pathogens to survive in new environments, raising concerns about invasive fungal infections, especially among immunocompromised individuals. As climatic conditions become more favorable for fungal growth, these organisms are increasingly encountered in regions where they were previously rare or absent. Higher ambient temperatures and humidity can enhance fungal persistence in the environment and may select for strains capable of surviving at human body temperature, increasing their pathogenic potential. In India, concerns around invasive fungal infections gained prominence following the surge in mucormycosis cases reported during and after the COVID-19 pandemic, with health authorities such as the Indian Council of Medical Research (ICMR) highlighting the role of environmental factors, uncontrolled diabetes, and immunosuppression in disease emergence. This trend underscores the heightened vulnerability of immunocompromised individuals and the challenges posed by delayed diagnosis and limited treatment options.
In addition, climate-driven disruptions to food and water systems increase the risk of water-borne illnesses and antimicrobial resistance, highlighting how environmental change is expanding disease risk well beyond traditional vector-borne models. These disruptions affect both the availability and safety of essential resources. Flooding can contaminate drinking water with pathogens and sewage, while droughts reduce water availability and compromise hygiene practices, increasing susceptibility to gastrointestinal infections. At the same time, climate stress on agriculture and food systems may drive greater reliance on antibiotics in humans and livestock, contributing to the emergence and spread of antimicrobial resistance. Together, these pressures demonstrate how climate change is reshaping disease risk through multiple interconnected pathways, extending its impact far beyond classical models of vector-borne transmission.
The health consequences of climate change extend far beyond rising temperatures and shifting disease vectors. As ecosystems are altered by warming climates, deforestation, and environmental degradation, long-standing balances between humans, animals, and their surroundings are increasingly disrupted. These changes influence how pathogens circulate in nature, how animal reservoirs behave, and how frequently humans come into contact with infectious agents. Environmental disruption linked to climate change, including ecosystem instability and biodiversity loss, has been identified by the UN Environment Programme (UNEP) as a key driver of emerging zoonotic and environmental health threats. [4]
Rodents, Hantaviruses, and Zoonoses
Climate change, particularly milder winters and richer food resources, significantly increases the population of rodent carriers for hantaviruses and increasing exposure in rural and peri-urban regions. Reduced winter mortality and enhanced breeding due to abundant forage lead to a population surge in these rodents. This population boom dramatically raises the environmental concentration of the virus shed in their excretions, heightening the risk of human exposure and subsequent severe illnesses like HPS or HFRS. The danger is most pronounced in rural and peri-urban areas where human and rodent habitats overlap, facilitating the transmission of these zoonoses.
Fungal Pathogens on the Rise
Climate change is expanding the environmental niches of fungal pathogens like Aspergillus, posing a growing risk to human health globally. Rising average temperatures allow these molds to proliferate in previously inhospitable regions, increasing the frequency and geographic reach of spore exposure. While the general population may see more superficial infections, the threat is severe for immunocompromised individuals. For them, inhaling Aspergillus spores can lead to life-threatening Invasive Pulmonary Aspergillosis (IPA). This climate-driven expansion broadens the area of risk, necessitating urgent attention, enhanced surveillance, and new public health strategies to mitigate the escalating global burden of these serious mycoses.
Climate change increasingly links to non-communicable or non-infectious conditions and indirect health issues. Poor air quality, worsened by heat and wildfires, causes spikes in asthma and cardiovascular problems. Extreme weather, like floods and droughts, leads to increased psychological stress, anxiety, and post-traumatic symptoms, impacting both physical and mental health. The World Health Organization (WHO) and the UN Environment Programme (UNEP) have highlighted how climate-driven air pollution and extreme heat are worsening cardiovascular, respiratory, and mental health outcomes worldwide [1,4].
Climate change is increasingly influencing the burden of non-communicable diseases (NCDs) through rising temperatures, worsening air quality, and more frequent extreme weather events. Compared to previous decades, when extreme heat events were less frequent and shorter in duration, recent years have seen prolonged heatwaves that place sustained stress on cardiovascular and thermoregulatory systems. This has led to higher rates of heat exhaustion, heatstroke, dehydration, and worsening of pre-existing heart and kidney diseases, particularly among older adults and outdoor workers.
Increased air pollution due to warmer temperatures and stagnant air raises concentrations of particulate matter and ozone. This intensifies health impacts, including more frequent and longer episodes of poor air quality in urban areas, worsening asthma, COPD, and cardiovascular events, and increasing chronic respiratory risk.
The escalating frequency of climate events like floods, cyclones, and droughts has transitioned climate-related stress from an indirect concern to a direct cause of rising psychological distress, anxiety, and post-traumatic symptoms. This trend signifies that climate change is evolving non-communicable disease risk from an occasional environmental stressor into a continuous public health crisis.
The pathways by which climate influences disease are multifaceted:
Thermal suitability: Warming temperatures accelerate pathogen development and replication, as many have narrow optimal temperature bands. Thermal suitability is the specific temperature range required for a vector and its pathogen's survival and efficiency. Sustained rising temperatures shorten the extrinsic incubation period (EIP)—the time a pathogen needs to develop inside the insect vector. A shorter EIP in diseases like dengue and malaria means the vector infects humans sooner and for longer, significantly increasing transmission potential and driving the observed expansion of geographic reach and transmission seasons.
Water Cycle Alteration: Significant alterations to the natural water cycle, primarily driven by climate change and human intervention, profoundly influence public health, particularly through the dual phenomena of flooding and drought.
Flooding: Floods from excessive rainfall create widespread temporary aquatic environments, which are ideal breeding grounds for disease vectors like mosquitoes. The inundation often damages public sanitation infrastructure (sewage, latrines, water treatment), leading to contamination and the spread of waterborne pathogens (Vibrio cholerae, E. coli, Salmonella). This significantly increases the risk of diseases such as cholera, typhoid, and diarrheal illnesses. Population displacement during floods worsens sanitation issues and increases human-vector contact.
Drought: Droughts significantly alter landscapes and disease transmission. As large water bodies shrink, residual pools become nutrient-dense, potentially boosting vector survival and breeding. Water storage by humans during scarcity creates new, protected breeding sites for domestic mosquitoes. Furthermore, reduced clean water access leads to poor hygiene and increased gastrointestinal diseases. The cumulative effect is a shift in vector distribution and density, and heightened human vulnerability due to poor sanitation.
Interconnected Effects: Extreme events upset the ecosystem and human settlements, impacting drinking water, hygiene, and sanitation. They also change disease vector breeding sites, posing a complex public health challenge. Adaptation requires resilient infrastructure and integrated disease surveillance in areas prone to these water cycle disruptions.
Extreme weather events: The increasing frequency and intensity of severe weather phenomena, such as powerful storms, prolonged heatwaves, and catastrophic flooding, pose significant and multifaceted challenges to human society and public health infrastructure. These events place immense, often overwhelming, stress on healthcare systems, leading to emergency room overcrowding, supply chain disruptions for essential medical resources, and physical damage to clinics and hospitals.
Beyond the immediate impact, extreme weather often results in the mass displacement of populations, forcing communities into temporary shelters where sanitation, nutrition, and access to routine medical care are severely compromised. This displacement can exacerbate existing health conditions and lead to the rapid spread of infectious diseases. Furthermore, the disruption of critical public health services, including vaccination campaigns, vector control programs, and chronic disease management, hinders preventive measures and has long-term detrimental effects on community well-being and resilience.
The escalating pace of global climate change is fueling a public health crisis, demanding immediate, climate-informed planning. Nations must integrate granular climate data—on temperature, precipitation, and extreme weather—into public health tools, including disease surveillance and early warning systems. This proactive integration is crucial to anticipate, track, and mitigate the health impacts of climate change effectively.
Health systems in low-resource tropical and subtropical regions face urgent threats. These areas are uniquely vulnerable to climate change due to existing systemic disparities: limited healthcare access, poor sanitation, and constrained adaptive capacity (lack of financial, technological, and human resources). This increases the risk of outbreaks for vector-borne diseases (malaria, dengue), water-borne diseases (cholera), and heat-related illnesses.
Global health security necessitates essential international cooperation and coordinated action, as infectious diseases and their vectors (like mosquitoes and ticks) disregard political borders. Increased global connectivity via travel, trade, and migration rapidly escalates local outbreaks into widespread epidemics or pandemics. A unified global strategy is thus required, including shared surveillance data, joint research for resilient health technologies, and harmonized cross-border response protocols to protect global health in a warming world.
Call for Change “Climate change is already altering the landscape of global disease transmission. From malaria and dengue to fungal threats and zoonotic viruses, the evidence is clear: environmental change is entangled with evolving health risks. Proactive, climate-responsive public health strategies are no longer optional but essential to protect populations, especially the most vulnerable”.
How does climate change affect disease patterns?
Climate change affects disease patterns by altering temperature, rainfall, and ecosystems, which influence the survival, reproduction, and geographic spread of pathogens and disease vectors. These changes allow infections to emerge in new regions and extend transmission seasons.
Why are diseases spreading to new regions?
Diseases are spreading to new regions because warming temperatures, shifting rainfall, and extreme weather events create suitable conditions for vectors and pathogens in areas that were previously inhospitable, exposing populations with little prior immunity.
Are climate-driven disease risks already affecting public health?
Yes. Climate-driven health risks are already evident through rising vector-borne diseases, heat-related illnesses, water-borne infections, and worsening non-communicable and mental health conditions worldwide, including in India.
References
Megersa DM, et al. Effects of Climate Change on Malaria Risk to Human Health, Atmosphere (2025). https://www.mdpi.com/2073-4433/16/1/71
Liu Q, Liu M, Liu J. Climate-Sensitive Infectious Diseases under Global Climate Change, Biomedical and Environmental Sciences (2025). https://www.sciencedirect.com/science/article/pii/S0895398825001503
Wright AKA. Climate Change and Emerging Infectious Diseases: A Global Review, Journal of EHDI (2025). https://www.journalehdi.com/article/climate-change-and-emerging-infectious-diseases-a-global-review-of-shifting-patterns-pathogens-and-16744
Zhang T. Impact of climate change on infectious disease patterns: epidemiological trends and gaps, Frontiers in Climate (2025). https://www.frontiersin.org/journals/climate/articles/10.3389/fclim.2025.1703904/full
Liao H. Climate change, its impact on emerging infectious diseases
(systematic mechanisms), PMC (2024). https://pmc.ncbi.nlm.nih.gov/articles/PMC11138229/
World Health Organization (WHO). Climate change and health.
Intergovernmental Panel on Climate Change (IPCC). Climate Change 2023/2024: Impacts, Adaptation and Vulnerability.
The Lancet Countdown on Health and Climate Change. Annual Report.
United Nations Environment Programme (UNEP). Climate change and environmental health risks.
Integrated Disease Surveillance Programme (IDSP), Ministry of Health and Family Welfare, India. Leptospirosis outbreaks and climate-related risk factors in India.
