Policies currently in place to limit global warming will expose more than a fifth of humanity to extreme and life-threatening heat by the end of the century, researchers warn in a study on Monday.
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The Earth’s surface temperature is on track for a 2.7°C increase by 2100 compared to pre-industrial times, which is expected to push more than 2 billion people – or 22% of the world population by that time – outside the climatic comfort zone that has allowed humanity to develop for millennia, according to this study published in Nature Sustainability.
India (600 million), Nigeria (300 million) or Indonesia (100 million) are the countries with the highest number of people who could face deadly heat in this scenario.
“This represents a profound reshaping of the habitability of the planet’s surface and could potentially lead to a large-scale reorganization of the places where people live,” said lead author Tim Lenton of the UK’s University of Exeter. of the study.
But by limiting warming to 1.5°C, the most ambitious goal of the 2015 Paris agreement, the number of people exposed to these risks would be reduced to less than half a billion people.
The world is already experiencing warming close to 1.2°C as a result of human activity, in particular the use of fossil fuels (coal, oil, gas), with a procession of disasters: heat waves, droughts, forest…
“The costs of climate change are often expressed in financial terms, but our study highlights the phenomenal human cost of failure to tackle the climate emergency,” says Tim Lenton.
“For every 0.1°C warming above current levels, an additional 140 million people will be exposed to dangerous heat,” he said.
The “dangerous heat” threshold was set in the study at 29°C mean annual temperature. Historically, human communities have been densest around average temperatures of 13°C (in temperate zones) and to a lesser extent around 27°C (in more tropical climates).
The risks are accentuated in the regions along the earth’s equator: the climate can be deadly there at lower temperatures than elsewhere because of the humidity, which prevents the human body from cooling itself by perspiration.