The number of people exposed to dangerously hot temperatures will increase from around 60 million today to two billion by 2100 under current climate policies, a new study has found.
This would represent 22% of the projected end-of-century population living with "dangerous" average temperatures of 29°C or higher.
However, limiting global warming to 1.5°C above pre-industrial levels, rather than a projected 2.7°C, would leave just 5% of the population exposed – saving a sixth of humanity from the extreme temperatures.
The study, led by researchers at the University of Exeter’s Global Systems Institute, highlights the “huge potential” for decisive climate policy to limit the human costs and inequities of climate change.
In “worst-case scenarios” of 3.6°C or even 4.4°C of global warming, it suggests that half of the world’s population could be exposed to dangerous heat.
“The costs of global warming are often expressed in financial terms, but our study highlights the phenomenal human cost of failing to tackle the climate emergency,” said professor Tim Lenton, director of the Global Systems Institute.
“For every 0.1°C of warming above present levels, about 140 million more people will be exposed to dangerous heat. This reveals both the scale of the problem and the importance of decisive action to reduce carbon emissions.
“Limiting global warming to 1.5°C rather than 2.7°C would mean five times fewer people in 2100 being exposed to dangerous heat.”
Human population density has historically peaked in places with an average temperature of about 13°C, with mortality increasing below and above this threshold, according to the study.
Assuming a future population of 9.5 billion people, it suggests that India would have the greatest number of people exposed to dangerous temperatures under 2.7°C of global warming – with more than 600 million.
However, under 1.5°C of global warming, this figure would be about 90 million.
Nigeria would have the second-largest heat-exposed population under 2.7°C of global warming, on more than 300 million, but less than 40 million under 1.5°C of warming.
The research team – which included the Potsdam Institute for Climate Impact Research, the International Institute for Applied Systems Analysis, and the Universities of Washington, North Carolina State, Aarhus and Wageningen – stress that the worst impacts can be avoided by rapid action to cut greenhouse gas emissions.
Speaking about the conception of the study, professor Marten Scheffer, of Wageningen University, said: “We were triggered by the fact that the economic costs of carbon emissions hardly reflect the impact on human wellbeing.
“Our calculations now help bridging this gap, and should stimulate asking new, unorthodox questions about justice.”
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