The climate crisis is a health crisis

To date, climate change has been variously framed as an environmental, scientific, economic, or political issue. These framings are valid and important, but one framing that is gaining increasing traction, is climate change as a health issue. The climate crisis is fundamentally a health crisis; one that is already straining health systems globally, shaping patterns of disease, and, concerningly, deepening health inequalities. The World Health Organization (WHO) estimates that climate change will cause approximately 250,000 additional deaths per year between 2030 and 2050. This figure is widely regarded as conservative. Beyond direct morbidity and mortality, climate change is also transforming the social, ecological, infrastructural, and economic determinants of health. From extreme heat and worsening air pollution to infectious diseases, water and food insecurity, displacement, and emerging toxic exposures, the health impacts of climate change are urgent – and paradoxical given the hand we play in causing them. This article unpacks some of the health impacts of climate change.

Extreme weather and heat

Climate change is causing a rise in the incidence and severity of extreme weather events, including floods, wildfires, hurricanes, storms, and droughts. These events cause immediate trauma and mortality, as well as longer-term health consequences. Flooding, for instance, can contaminate water supplies, trigger outbreaks of waterborne disease, and increase rates of skin conditions and rashes. Wildfires produce hazardous particulate matter that can travel thousands of miles, exacerbating respiratory diseases like asthma. The 2019-2020 Australian bushfires were associated with an estimated 400 excess deaths and thousands of hospitalisations due to smoke exposure. Climate-related disasters also damage health infrastructure, disrupting access to care at a time when it is most needed.

Extreme heat is one of the most documented extreme weather events caused by climate change, with health impacts. Over the past two decades, heat-related mortality amongst people aged over 65 has increased by approximately 85% globally. The European heatwave of 2022 alone was associated with an estimated 60,000 excess deaths. Heat stress exacerbates cardiovascular and respiratory disease, increases the risk of kidney injury, drives up cancer and mental health rates, and, importantly for economies, affects labour productivity, particularly for outdoor workers. Urban areas are especially vulnerable due to the “urban heat island” effect, where built environments trap heat and limit cooling. Furthermore, rising temperatures combined with high humidity can push conditions towards lethal “wet-bulb” temperatures (typically around 35°C wet-bulb), at which point the human body can no longer effectively cool itself through sweating. In such conditions, even young and healthy individuals can die within hours, a scenario starkly dramatised in the opening chapter of Kim Stanley Robinson’s The Ministry for the Future and increasingly discussed in climate physiology literature as parts of South Asia and the Middle East approach these thresholds.

Air pollution

Climate change and air pollution share common roots in fossil fuel combustion. Ambient air pollution currently causes approximately 7 million premature deaths annually worldwide. Fine particulate matter (PM2.5), nitrogen oxides, and ozone are linked to cardiovascular disease, lung cancer, stroke, diabetes, adverse pregnancy outcomes, reduced bone density, and cognitive decline. Importantly, air pollution can amplify the health effects of climate change and vice versa. Heat can increase the toxicity of pollutants, while climate-induced stagnation events (a lack of atmospheric mixing and air flow) can trap polluted air over human settlements. 

Expanding infectious diseases

Climate change is also altering the geographic distribution and seasonality of infectious diseases. Warmer temperatures and shifting rainfall patterns expand the habitats of disease vectors such as mosquitoes and ticks. The incidence and geographic range of diseases such as malaria, dengue, chikungunya, Zika, and Lyme disease are already changing. Dengue transmission potential has increased significantly in many regions over the past half-century, placing billions more people at risk. Waterborne diseases are similarly sensitive to climatic shifts. Rising temperatures and extreme rainfall events can increase the proliferation and spread of pathogens such as Vibrio species and cholera. Drought conditions can also compromise sanitation and hygiene, elevating diarrhoeal disease risk.

Climate change may also increase the likelihood of zoonotic spillover events – the transmission of pathogens from animals to humans – by altering habitats and driving wildlife closer to human populations. While the precise origins of COVID-19 remain contested, broader evidence suggests that environmental disruption and biodiversity loss can heighten pandemic risk. As ecosystems destabilise, so too does the delicate balance that has historically limited pathogen emergence.

Food and water insecurity

Food systems are highly climate-sensitive. Rising temperatures, changing precipitation patterns, and extreme weather events threaten crop yields and nutritional quality. Major staple crops, including wheat, maize, and rice, show declining yield potential in many regions as temperatures exceed optimal thresholds. Elevated atmospheric carbon dioxide concentrations may also reduce the protein and micronutrient content of certain crops, with implications for global nutrition. Undernutrition remains a leading risk factor for child mortality worldwide, and climate-related food insecurity threatens to reverse decades of progress. At the same time, climate stress can increase food prices, contributing to economic instability and dietary shifts towards cheaper, less nutritious options.

Water insecurity is also a concern. Approximately half the global population experiences severe water scarcity for at least part of the year. Climate change intensifies both droughts and floods, affecting reliable access to safe drinking water. Water insecurity increases the burden of a range of health impacts, including diarrhoeal disease and acute kidney disease.

Migration and conflict

Climate change intensifies existing social, economic, and political vulnerabilities. Climate-related displacement is already occurring at scale. In 2022 alone, an estimated 32 million internal displacements were triggered by extreme weather events, many of them climate-related. Displacement disrupts health care continuity, heightens risks of malnutrition, gender-based violence and mental illness, and increases exposure to infectious disease.

Resource scarcity, particularly water and arable land, can exacerbate conflict. While climate change does not directly cause war, it interacts with fragile economic and governance structures to increase instability. From a health perspective, conflict settings are routinely associated with the collapse of health systems, including issues such as the re-emergence of controlled diseases, poor control of chronic illness, and the long-term health effects of prolonged exposure to trauma. 

Mental health

The psychological impacts of climate change are increasingly recognised. Extreme weather events can trigger acute stress reactions, post-traumatic stress disorder (PTSD), anxiety, and depression. Farmers facing prolonged drought, for instance, report elevated suicide rates in some regions. Beyond discrete disasters, a more diffuse phenomenon, often termed “eco-anxiety” or “climate distress”, is emerging, particularly amongst young people. Surveys across multiple countries suggest that a majority of young people feel worried about climate change, with many reporting that it affects their daily functioning and sense of future security. Chronic stress associated with climate instability may also have physiological consequences, contributing to cardiovascular and immune dysfunction.

Emerging and novel risks: cancer and microplastics

Cancer risk is influenced by multiple environmental factors, including air pollution, ultraviolet radiation exposure, and chemical contaminants. Although attributing cancer trends directly to climate change is complex, the cumulative effect of climate-amplified exposures raises concern. Notably, one study across 17 Middle Eastern and North African countries found each 1°C increase in temperature correlated with a rise in cancer cases amongst women from 173 to 280 per 100,000 people, and deaths from 171 to 332 per 100,000.  

Climate change also intersects with other environmental exposures. Microplastics (tiny plastic particles now detected in air, water, food, and human tissues) are an emerging concern. While research is ongoing, early evidence suggests potential links to inflammation, endocrine disruption, and possibly carcinogenesis. Climate change may exacerbate plastic degradation and dispersal through heat and extreme weather events.

Health system mitigation and adaptation 

Health systems themselves are both victims of and contributors to climate change. Globally, the health care sector accounts for approximately 4-5% of total greenhouse gas emissions. Recognising this, many countries and institutions are beginning to integrate climate mitigation and adaptation into health planning.

Mitigation efforts focus on reducing the carbon footprint of care delivery, for example, through energy efficiency, low-carbon procurement and resource use, telemedicine, sustainable transport, and shifts towards prevention-oriented models of care. Adaptation efforts include heat-health action plans, climate-resilient infrastructure, early warning systems for infectious diseases, and disaster-preparedness strategies. Hospitals are investing in flood defences, backup renewable energy systems, supply chain diversification, and community-based care when hospitals are inaccessible. Surveillance systems are being updated to monitor climate-sensitive conditions. Internationally, climate and health are gaining prominence in policy discourse, including at UN climate negotiations and within national adaptation plans. However, funding for health adaptation remains a small fraction of overall climate finance, and implementation gaps persist.

Conclusion: Reframing the crisis

Framing climate change as a health crisis emphasises both its urgency and its stakes for humanity. Health is immediate, personal, and politically resonant. The climate crisis is unfolding in emergency rooms during heatwaves, in clinics managing asthma exacerbations from wildfire smoke, in communities facing malnutrition after crop failure, and in the quiet anxiety of young people contemplating an unstable future. The health framing also presents opportunity. Rapid decarbonisation, resilient infrastructure, equitable food and water systems, and stronger public health capacity would not only help avert climate catastrophe but also reduce existing disease burdens and health inequalities. Climate change is shaping the future of health and health systems, policymakers, and societies must respond at the scale and speed required.

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