An "unprecedented" threat to health. Climate change and the burning of fossil fuels are not only harming the environment, they are also increasingly dangerous – and deadly – for humans, as detailed in a landmark annual report published Wednesday by The Lancet.
– Deadly heat –
This is the major new feature of the 2025 edition of The Lancet Countdown, a report published annually by the medical journal on the health risks of climate change. For the first time, the authors quantify the number of deaths directly caused by heat in recent years.
According to them, an average of 546,000 deaths per year were caused by heat between 2012 and 2021 – mainly in Africa, the Middle East and South Asia – as heatwave episodes accelerate due to global warming.
This figure exceeds by more than half (63%) the level recorded in the 1990s.
This surge is largely linked to the increase in the world's population. But if we take this into account, heat-related mortality nevertheless increases by almost a quarter (+23%).
“Babies under one year old and those over 65 – the most vulnerable age groups – experienced an unprecedented number of heatwave days in 2024,” the researchers point out. For these two categories, the average duration of exposure has more than tripled in twenty years.
Excessive heat can lead to kidney problems, cardiovascular and respiratory diseases, organ failure, and sometimes death.
Its consequences can be more insidious, the report notes. It discourages physical activity and disrupts sleep, two essential components of good physical and mental health.
– Pollution, another killer –
Another major conclusion of the report: the still considerable burden on health of air pollution, both exacerbated by global warming and caused like it by the combustion of fossil fuels – coal, gas… – which reached a new record in 2024.
The authors estimate that air pollution linked to fossil fuels caused more than 2.5 million deaths in 2022. The trend is, however, downward, thanks to the decline in coal use in developed countries.
New to this edition, the authors have quantified the number of deaths specifically caused by pollution linked to forest fires, a phenomenon that is becoming increasingly frequent due to episodes of heat and drought.
"The year 2024 saw a record 154,000 deaths linked to fine particulate pollution from forest fire smoke," the report concludes.
– Natural disasters –
Global warming is intensifying “extreme” weather events: droughts, storms, floods… They caused at least 16,000 deaths in 2024, according to the report.
However, this single figure is far from reflecting the profound effects of these phenomena on human health. They can be disastrous for agricultural production, jeopardizing the food security of many people.
The increasing frequency of droughts and heatwaves threatened the food security of 123.4 million people in 2023, according to the report. And this figure is not exhaustive, as it is based on an analysis of 124 countries, while the world has nearly 200.
– Infectious diseases –
Finally, global warming also facilitates the spread of diseases transmitted by animals, particularly insects that manage to establish themselves in regions previously inhospitable to them.
A striking example is dengue fever, transmitted by the tiger mosquito. This insect, once confined to tropical regions but now widespread in Europe, finds increasingly favorable climatic conditions.
Because of rising temperatures, the global potential for dengue virus transmission has jumped by more than half compared to the 1950s, contributing to the more than seven million cases recorded worldwide in 2024.
And the report cites other insects whose area of establishment continues to expand while they spread very deadly or debilitating diseases: the blood tick, which transmits Crimean-Congo hemorrhagic fever, or the tiny sandfly, which carries leishmaniasis, a parasitic disease.
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