Climate Change and Human Health: The Full Picture

Climate Change and Human Health: The Full Picture

Editorial advisor: Mr. John Smith, Specialist Environment, PhD in Environmental Engineering.

The World Health Organization describes climate change as one of the greatest threats to human health in the twenty-first century. That assessment is not only about heatwaves. Climate change affects health through heat, air quality, water and food safety, infectious disease, extreme weather injuries, and mental health — and it does so unevenly, hitting hardest those who contributed least to emissions and have fewest resources to cope.

Health is also where climate change becomes personal. A global average temperature is abstract; a child hospitalised during a heatwave, a family displaced by flooding, or a farmer facing crop failure is not. Understanding the health pathways helps explain why health professionals increasingly advocate for climate action as a health intervention, not only an environmental one.

Direct effects: heat and extreme weather

Heat is the most direct health risk. Prolonged heat stresses the cardiovascular system, worsens kidney disease, and can cause heat exhaustion and heatstroke. Older adults, young children, pregnant people, outdoor workers, and people with chronic illness are most vulnerable. Heat also worsens existing conditions: it can trigger asthma attacks, strain hearts, and complicate diabetes management.

Extreme weather causes injuries and deaths directly — drowning in floods, trauma in storms, burns and smoke inhalation in wildfires — and indirectly through disrupted health services, contaminated water, and displacement. After a disaster, health risks continue: waterborne disease from damaged sanitation, respiratory problems from mould in flooded homes, and interrupted treatment for chronic conditions when clinics close or medicines run out.

Air quality: a double burden

Climate change worsens air pollution in several ways. Higher temperatures accelerate the formation of ground-level ozone, a respiratory irritant, especially in cities with traffic and industrial emissions. Wildfire smoke, increasingly common in fire-prone regions, carries fine particles deep into the lungs and can travel hundreds of kilometres, affecting people far from the fire itself. Longer, more intense pollen seasons worsen allergies and asthma.

Many sources of greenhouse gases also emit air pollutants — soot, sulphur dioxide, nitrogen oxides — that directly harm health. Cutting fossil-fuel use therefore brings a health co-benefit: cleaner air. The WHO estimates that air pollution causes millions of premature deaths each year, and climate policies that reduce fossil-fuel combustion can reduce that burden substantially, often quickly, since air quality improves as soon as emissions fall.

Infectious disease and changing ranges

Warming and changing rainfall shift where disease-carrying insects and other vectors can survive. Mosquitoes that transmit dengue, Zika, chikungunya, and malaria are expanding into higher altitudes and latitudes as temperatures rise, and warmer conditions can speed up pathogen development inside the mosquito and lengthen transmission seasons.

Waterborne diseases also respond to climate. Heavy rainfall and flooding can overwhelm sanitation and contaminate drinking water with bacteria and parasites, increasing diarrhoeal disease — already a leading killer of young children in low-income settings. Warmer coastal waters favour Vibrio bacteria, which cause wound infections and seafood-related illness. Tick-borne diseases are expanding in some temperate regions as winters warm and tick habitats shift.

These shifts do not mean every disease will spread everywhere. Public health measures — vector control, clean water, sanitation, vaccination, and surveillance — remain powerful. Climate change makes those measures more necessary and, in some places, harder to sustain, especially where health systems are already stretched.

Food, water, and nutrition

Climate change threatens nutrition through multiple routes. Heat and drought reduce crop yields in many regions, especially for staples such as wheat and maize. Flooding destroys crops and stored food. Higher CO2 levels can reduce the protein, zinc, and iron content of some staple crops, a subtle but widespread nutritional effect. Fisheries are affected as oceans warm and acidify, threatening protein sources for coastal communities.

Water scarcity compounds the problem. When water is scarce, hygiene suffers, diarrhoeal disease rises, and crops fail. When water is contaminated by flooding, the same diseases spread through a different route. For subsistence farmers and low-income urban households, who spend a large share of income on food, price spikes after poor harvests can push families into malnutrition quickly.

Children are especially affected. Undernutrition in early childhood impairs growth and cognitive development with lifelong consequences. Climate-driven food insecurity is therefore not only a present hardship but a future health and economic burden.

Mental health: the quieter toll

The mental health impacts of climate change are increasingly recognised. Direct trauma from disasters can cause post-traumatic stress, anxiety, and depression. Slower stresses — repeated drought, loss of livelihood, displacement, and uncertainty about the future — contribute to chronic anxiety, sometimes called eco-anxiety or climate anxiety, particularly among young people.

Farmers facing repeated crop failure, coastal residents watching their land erode, and displaced families rebuilding lives elsewhere all carry psychological burdens that health systems often overlook. After disasters, mental health needs typically outlast physical reconstruction, yet funding and services often end sooner. Integrating mental health support into disaster response and climate adaptation is now recognised as essential, not optional.

Who is most at risk, and why it matters

Health risks are not distributed equally. Older adults, children, pregnant people, outdoor workers, people with disabilities, and people with chronic illness face higher physiological risk. Low-income communities, informal settlements, and rural areas face higher exposure — to heat without cooling, to flooding without drainage, to disease without clean water — and lower access to health care when harm occurs.

This inequity is central to climate justice. Those least responsible for emissions often face the greatest health risks, and within every country, marginalised groups bear disproportionate burdens. Health adaptation that ignores equity — for example, cooling centres that are inaccessible, or warnings only in a majority language — will fail those who need it most.

Health as a reason for action

Framing climate action through health has practical advantages. Health co-benefits are immediate and local: cleaner air from reduced fossil-fuel use, more physical activity from walking and cycling infrastructure, healthier diets from plant-rich food systems, and cooler cities from green space. These benefits accrue even before global temperature responds, which can take decades.

Health systems themselves must also adapt: heat-action plans in hospitals, climate-resilient clinics that function during floods and power outages, disease surveillance that tracks shifting vector ranges, and supply chains that do not collapse in disasters. The WHO and national health agencies now provide guidance on climate-resilient health systems, recognising that health care cannot treat climate impacts if it is itself vulnerable to them.

Protecting health in a warming world requires both mitigation — cutting emissions to limit future harm — and adaptation — strengthening health systems, housing, water, and food systems for the warming already under way. Neither alone is sufficient.

Sources

• World Health Organization, Climate Change and Health — https://www.who.int/health-topics/climate-change
• World Health Organization, Climate Change Fact Sheet — https://www.who.int/news-room/fact-sheets/detail/climate-change-and-health
• IPCC, Sixth Assessment Report, Working Group II — https://www.ipcc.ch/report/ar6/wg2/
• The Lancet Countdown on Health and Climate Change — https://www.thelancet.com/countdown-health-climate
• US Centers for Disease Control and Prevention, Climate and Health — https://www.cdc.gov/climate-health/