As the world warms, deaths from extreme heat are expected to rise — but the reasons are more complex, and more human, than climate alone. A new global modelling study, published in The Lancet Planetary Health, has found that an ageing global population is likely to face sharply higher risks from temperature-related mortality, especially under higher global warming scenarios.
But the study also makes a critical distinction: not all temperature-related deaths are caused by climate change — and separating the effects of warming from the effects of demographic change is essential for making sound policy.
What the Study Shows
The researchers modelled temperature-related mortality in 199 countries under three global warming scenarios: 1.5°C, 2°C, and 3°C above pre-industrial levels. They incorporated both projected changes in climate and changes in population age structure out to the year 2100.
Their key finding:
“Most future excess deaths linked to high temperatures will be driven by population ageing, not just climate change alone.”
This is an important clarification. As populations grow older — particularly in Europe, North America, and parts of Asia — more people will fall into high-risk categories for heat-related illness and death. These risks are amplified by rising temperatures, but they are not caused by warming alone.
The Role of Climate Change
Even so, the paper makes clear that climate change substantially increases the burden of heat-related mortality.
- At 1.5°C of warming, the study projects a modest increase in heat-related deaths globally.
- At 2°C, this increase becomes significant, especially in cities and regions with ageing populations and poor infrastructure.
- At 3°C, the combined effect of warming and population ageing leads to “a marked and disproportionate rise in mortality”, particularly in lower-income countries.
The study avoids assigning a precise number of deaths “caused by climate change” — a framing the authors rightly call problematic — but instead shows how climate change makes existing vulnerabilities worse.
Heatwaves that would have once been survivable become deadly. Days once merely hot become extreme. Ageing bodies, often less able to regulate temperature or access cooling, bear the brunt.
Where the Risks Are Highest
The results suggest that Europe will see the greatest absolute number of additional heat-related deaths, due to its rapidly ageing population. But countries in the tropics, such as the Philippines and parts of Africa, face the highest relative increases, as even small temperature shifts push conditions beyond tolerable thresholds.
In Canada and the northern United States — where temperatures are still moderate by global standards — the risk is still real. In particular:
- Urban centres with high concentrations of elderly residents and poor access to cooling may see significant spikes in heat-related mortality, especially under 2°C or higher scenarios.
- The North’s “adaptation gap” — a historical lack of infrastructure to deal with extreme heat — may leave some communities more exposed than they realise.
So What Can Be Done?
The study doesn’t just sound the alarm — it suggests where to focus action:
- Urban cooling strategies such as tree planting, reflective surfaces, and better ventilation in housing for the elderly.
- Targeted heat health warnings, including community-based check-ins for older residents during heatwaves.
- Adaptation planning that takes ageing seriously — integrating it into climate resilience frameworks at every level of government.
Crucially, the authors argue that reducing greenhouse gas emissions remains a direct way to reduce the scale of the future health burden — not just by slowing warming, but by buying time for adaptation.
Nota Bene
It is tempting to ask how many deaths “climate change will cause.” But as this study shows, that’s the wrong question. The better question is: who will be most vulnerable in a warming world, and what can we do now to protect them?
The answer, in part, is clear: as populations age, we must design climate policy that cares for the oldest among us — or risk letting heat do what it does best in silence.
Update
Imperial College London recently published a study on deaths climate change caused in Europe, finding the rate tripled in 2025.
Source
Impact of population aging on future temperature-related mortality at different global warming levels, Nature Communications, 2025-02-27
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