Climate change is reshaping global health risks in ways that extend far beyond rising temperatures. As 2024 became Europe’s hottest year on record, southern European destinations experienced 23 “tropical nights”—when temperatures don’t drop below 20°C—nearly three times the historical average of eight such nights.
These sweltering conditions represent more than just discomfort. According to Dr. Madeleine Thomson, Head of Impacts and Adaptation at Wellcome, “Europe is heating up, and we’re not prepared for the toll this will take on our health.” Thomson’s research focuses on climate-sensitive infectious diseases and how communities can better prepare for emerging health threats.
The Science Behind Climate-Sensitive Diseases
Climate-sensitive infectious diseases (CSIDs) are any infectious diseases whose transmission and spread are influenced by changes in climate and weather patterns. These include vector-borne diseases like dengue, Zika, malaria, and Chikungunya, as well as diseases spread through contaminated water or food.
The relationship between climate and disease transmission follows predictable patterns. Temperature drives the rate at which disease vectors like mosquitoes develop and reproduce, while rainfall creates breeding sites. In warmer conditions, adult mosquitoes reproduce more quickly and bite more frequently. Disease-causing pathogens also multiply faster within mosquito vectors, creating higher concentrations of infectious agents in each bite.
Thomson, who spent years conducting field research in Africa and later directed the WHO Collaborating Centre on Malaria Early Warning Systems at Columbia University, explains that “virtually all vector-borne diseases have a climate dimension.”
Geographic Expansion of Health Risks
The geographic boundaries of infectious diseases are shifting as temperatures rise. Areas in the highlands of eastern Africa and Latin America that were previously too cool for dengue or malaria transmission are becoming vulnerable. This creates particular risks because populations in these regions lack immunity to diseases that were historically absent.
Lyme disease provides a striking example of this geographic expansion. The tick-borne illness is moving into northern areas of Canada and even the Arctic, where ticks previously couldn’t survive cold temperatures. Climate and land-use changes may soon enable year-round tick seasons in areas of Scotland and elsewhere.
Even more concerning is the emergence of tropical diseases in temperate regions. When Paris prepared for the 2024 Olympic Games, authorities monitored not just COVID-19 but dengue fever—a disease now considered a potential threat in France due to warming temperatures that support mosquito survival.
Heat as a Direct Health Threat
Rising temperatures pose health risks beyond vector-borne diseases. Extreme heat affects cardiovascular health, pregnancy outcomes, and mental health. During Britain’s 2022 heat wave, an estimated 2,800 additional people aged over 65 died from heat-related causes.
Nighttime temperatures are particularly important for human health because sleep provides essential recovery time. When nighttime temperatures remain above 20°C during tropical nights, this recovery process is disrupted, leading to cascading health effects.
Children face heightened vulnerability because their smaller bodies warm up faster, while pregnant women struggle with temperature regulation during an already physiologically demanding time. Communities with limited healthcare access, inadequate housing, and poor sanitation are especially susceptible to both heat-related illness and infectious disease outbreaks.
Current Adaptation Strategies
Addressing climate health risks requires both technological solutions and practical interventions. Wellcome currently funds 24 research teams across 12 countries to develop digital tools for responding to climate-sensitive infectious diseases. These projects include early warning systems that integrate climate data with health information to predict outbreaks weeks or months in advance.
One example is E-DENGUE in Vietnam, which aims to predict dengue outbreaks up to two months ahead of time, allowing public health officials to concentrate resources and interventions in the most affected areas.
Beyond high-tech solutions, climate adaptation research emphasizes practical urban planning changes. Adding green spaces and waterways to cities can create cooling effects that reduce heat island impacts and protect public health. These interventions are particularly important in urban areas where concrete and asphalt surfaces trap heat.
Building Systemic Preparedness
Thomson advocates for fundamental changes in how health professionals are trained and how health systems prepare for climate-related threats. She argues that incorporating climate and environmental disease drivers into epidemiological training worldwide is essential for effective response.
“If the health sector doesn’t understand the issues, particularly around climate variability and change, then it’s very hard for them to use the information effectively,” she notes. This knowledge gap represents a critical vulnerability as health systems face increasingly complex climate-related challenges.
The challenge extends beyond individual diseases to building adaptive capacity for unknown future threats. Rather than trying to predict exactly which diseases will emerge where and when, Thomson emphasizes preparing systems that can respond rapidly to a broad range of potential health threats.
Unequal Global Impacts
The burden of climate-sensitive diseases falls disproportionately on vulnerable populations. Lower-income countries, particularly those in tropical regions, face higher exposure due to warm, humid climates and the presence of disease-carrying insects, combined with inadequate housing, infrastructure, and healthcare systems.
This creates a double injustice: countries that have contributed least to greenhouse gas emissions often face the greatest health impacts from climate change while having the least capacity to respond effectively. Pakistan exemplifies this pattern, where climate change-linked flooding in 2024 created ideal mosquito breeding conditions, leading to 1.3 million malaria cases compared to 500,000 cases in all of 2021.
Innovation in Disease Control
Research teams are developing innovative approaches to regain control over climate-sensitive diseases. The World Mosquito Program releases mosquitoes infected with Wolbachia, a naturally occurring bacterium that reduces mosquitoes’ ability to transmit viruses like dengue and Zika. However, extreme heat can reduce the effectiveness of this method, highlighting the need for heat-resistant bacterial strains in future programs.
Vaccine development offers additional hope. New dengue vaccines have been approved in several countries, while second-generation malaria vaccines show high efficacy in trials. This summer, Ivory Coast became the first country to roll out the R21/Matrix-M malaria vaccine, representing significant progress in disease prevention.
The Road Ahead
As temperatures continue rising and extreme weather becomes more frequent, the risk of disease outbreaks increases both in regions where diseases are already endemic and in new areas experiencing them for the first time. Professional networks of climate health experts emphasize that preparation requires coordinated action across multiple sectors.
The solution involves both global emissions reduction and local adaptation measures. Cities need rapid infrastructure changes to manage heat, health systems require training in climate-related health risks, and international cooperation must strengthen to support vulnerable communities.
Thomson’s research demonstrates that while the challenges are substantial, effective responses are possible when communities understand the connections between climate and health and act on that knowledge. The question isn’t whether climate change will continue affecting health outcomes—it’s whether societies will build the capacity to respond effectively to these evolving threats.
Current initiatives show promise, from early warning systems that provide months of advance notice for disease outbreaks to urban planning interventions that reduce heat exposure. However, the scale and urgency of climate health risks require sustained commitment to both mitigation and adaptation strategies.
As global health security experts emphasize, the intersection of climate change and health represents one of the defining challenges of this century. The communities and countries that prepare most effectively for climate-driven health risks will be those that integrate climate considerations into health planning, invest in adaptive infrastructure, and build robust early warning and response systems.
The science is clear: climate change is already affecting human health through multiple pathways. The remaining question is how quickly and effectively societies will adapt to protect their populations from these emerging and intensifying threats.