Climate Change and Health: What the WHO Figures Show

Climate change is often discussed as an environmental problem. The World Health Organization describes it differently: a threat multiplier that undermines and can reverse decades of health progress, hitting hardest in the places least responsible for it.

This article sets out what the WHO’s own figures say about climate and health — how many people are exposed, how many deaths are attributable, which diseases are moving, and why the people in the worst-affected regions contribute least to the problem.

The headline numbers

From the WHO fact sheet on climate change:

• 3.6 billion people already live in areas highly susceptible to climate change.
• Between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year, from undernutrition, malaria, diarrhoea and heat stress alone.
• In vulnerable regions, the death rate from extreme weather events in the last decade was 15 times higher than in less vulnerable ones.
• Recent research attributes 37% of heat-related deaths to human-induced climate change.
• Heat-related deaths among people over 65 have risen by 70% in two decades.
• Direct damage costs to health are estimated at US$2–4 billion per year by 2030, excluding costs in health-determining sectors such as agriculture, water and sanitation.

That last figure is worth pausing on, because it is the one most likely to be quoted incorrectly. US$2–4 billion sounds modest against the scale of the other numbers, and it is easy to present as the total cost. The WHO is explicit that it excludes agriculture, water and sanitation. The full economic picture is far larger.

How climate change actually damages health

The WHO separates two routes. Direct effects are the injuries and deaths from the hazard itself. Indirect effects arrive through everything that determines whether people stay healthy.

Direct effects

More frequent and intense heatwaves, storms, floods, droughts and wildfires. These kill people in the short term and are the most visible part of the problem.

Indirect effects

This is the larger channel, and it is where climate change does lasting damage:

• Food systems. Climate change affects food availability, quality and diversity, worsening nutrition crises. In 2020, 770 million people faced hunger, predominantly in Africa and Asia. In that same year, 98 million more people experienced food insecurity than the 1981–2010 average.
• Water. 2 billion people lack safe drinking water. Climate stressors heighten waterborne and foodborne disease risk.
• Vector-borne disease. Changes in temperature and precipitation enhance the spread of diseases carried by mosquitoes and other vectors. Deaths from these diseases run at over 700,000 annually, and could rise further without preventive action.
• Foodborne illness. 600 million people suffer foodborne illnesses annually, with children under five bearing 30% of those fatalities.
• Mental health. Climate change produces immediate effects such as anxiety and post-traumatic stress, alongside longer-term disorders driven by displacement and disrupted social cohesion.

What can be attributed to climate change

This is the part most often blurred, so it is worth being precise about what the WHO says.

The Intergovernmental Panel on Climate Change’s Sixth Assessment Report concluded that climate risks are appearing faster and more severely than previously expected, and that adaptation will become harder as warming increases.

On attribution specifically, the WHO notes that while it is unequivocal that climate change affects human health, it remains challenging to accurately estimate the scale of many climate-sensitive risks. Progress has been made: scientific advances increasingly allow researchers to attribute rises in illness and mortality to global warming.

The 37% heat-related death figure is the clearest single attribution in the fact sheet. It is also the most defensible, because heat mortality is well monitored and well studied.

The equity problem

The WHO is unusually direct about this, and it is the section most worth reading.

Low-income countries and small island developing states endure the harshest health impacts despite contributing minimally to global emissions.

And the framing that follows is the one to carry away: the people whose health is being harmed first and worst by the climate crisis are the people who contribute least to its causes, and who are least able to protect themselves against it.

There is a direct financial consequence. Over 930 million people — around 12% of the world’s population — spend at least 10% of their household budget on health care. With the poorest people largely uninsured, health shocks already push around 100 million people into poverty every year, and climate change worsens that trend.

Health systems under strain

Climate change does not only make people ill. It damages the capacity to treat them.

The WHO identifies three ways:

• Increasingly frequent extreme weather events and their disruption of food systems
• Increases in zoonotic, food-, water- and vector-borne diseases
• Damage to health workforce and infrastructure, reducing capacity for universal health coverage

A health system is most likely to fail at the moment it is most needed. Areas with weak health infrastructure — mostly developing countries — are the least able to cope without assistance to prepare and respond.

Why 1.5°C is the line

The WHO’s position is that the world must limit warming to 1.5°C to avert catastrophic health impacts.

It also makes a point that is often lost in the framing of the target. Global heating of even 1.5°C is not considered safe. Every additional tenth of a degree of warming will take a serious toll on people’s lives and health.

1.5°C is presented not as a threshold of safety but as the limit of what can plausibly be avoided.

WHO’s response

The organisation’s work centres on three objectives, plus leadership and evidence work:

1. Actions that reduce emissions and improve health together — supporting a rapid, equitable transition to clean energy, ensuring health is central to climate mitigation, and mobilising the health community to build public support.
2. Building climate-resilient and sustainable health systems — embedding environmental sustainability and climate resilience in universal health coverage and primary health care, and decarbonising health systems that themselves emit heavily.
3. Protecting health from climate impacts — assessing vulnerability, integrating climate risk into surveillance and response for key risks such as extreme heat and infectious disease, and closing the financing gap for adaptation and resilience.
4. Leadership, evidence and capacity building — leading the Alliance for Transformative Action on Climate and Health (ATACH), which WHO set up with partners.

Frequently asked questions

How many people live in areas highly susceptible to climate change?

According to the WHO, 3.6 billion people already live in areas highly susceptible to climate change. This figure is cited in the IPCC’s Sixth Assessment Report.

How many deaths does climate change cause?

The WHO conservatively projects approximately 250,000 additional deaths per year by the 2030s, from climate impacts on diseases such as malaria and coastal flooding. Between 2030 and 2050, roughly 250,000 additional deaths per year are expected from undernutrition, malaria, diarrhoea and heat stress alone.

What share of heat deaths is caused by climate change?

Recent research attributes 37% of heat-related deaths to human-induced climate change. Heat-related deaths among people over 65 have risen by 70% over two decades.

Which countries are worst affected?

Low-income countries and small island developing states endure the harshest health impacts despite contributing minimally to global emissions. In vulnerable regions, the death rate from extreme weather events in the last decade was 15 times higher than in less vulnerable ones.

Can climate change be linked to specific diseases?

Yes, in specific cases with well-established evidence. The clearest attribution in the WHO fact sheet is heat mortality, where 37% of deaths are attributed to human-induced climate change. The WHO notes that estimating the scale of other climate-sensitive risks remains challenging, even though attribution is improving.

How does climate change affect mental health?

The WHO identifies two effects: immediate issues such as anxiety and post-traumatic stress, and long-term disorders driven by displacement and disrupted social cohesion.

Sources

• World Health Organization, “Climate change” fact sheet, 12 October 2023 (page current as of October 2026): who.int
• Intergovernmental Panel on Climate Change, Sixth Assessment Report (AR6), as cited in the WHO fact sheet.
• World Health Organization, “Heat and health” fact sheet, updated 31 July 2026: who.int fact sheet index

This article is general information drawn from published WHO figures. The WHO notes on its own fact sheet that estimating the scale of many climate-sensitive risks remains challenging. Individual health outcomes depend on personal circumstances; for advice about your own health, consult a qualified clinician.