Current policies 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 warned Monday.
The Earth’s surface temperature is on track to rise 2.7 degrees Celsius (4.8 degrees Fahrenheit) above pre-industrial levels by 2100, pushing more than two billion people – 22% of the projected world population – well outside the climatic comfort zone that allowed our species to thrive for millennia, scientists reported In Natural durability.
The countries with the most people facing deadly heat in this scenario are India (600 million), Nigeria (300 million), Indonesia (100 million), as well as the Philippines and Pakistan (80 million each).
“It’s a profound reshaping of the habitability of the planet’s surface, and it could potentially lead to a large-scale reorganization of where people live,” said lead author Tim Lenton, director of the Global Systems Institute at the University of Exeter.
Capping global warming at the Paris climate treaty target of 1.5°C in 2015 would sharply reduce the number of people at risk to less than half a billion, or around 5% of the 9.5 billion of people likely to inhabit the planet in six or seven decades. now, depending on the results.
A warming of just under 1.2°C to date has already amplified the intensity or duration of heat waves, droughts and wildfires beyond what could have happened in the absence of carbon pollution generated by burning fossil fuels and forests.
The past eight years have been the hottest on record.
“The costs of global warming are often expressed in financial terms, but our study highlights the phenomenal human cost of not addressing the climate emergency,” said Lenton.
“For every 0.1°C of warming above current levels, an estimated 140 million additional people will be exposed to dangerous heat.”
The “dangerous heat” threshold used in the new findings is a mean annual temperature (MAT) of 29°C.
Throughout history, human communities have been densest around two distinct MATs – 13°C (in temperate zones) and to a lesser extent 27°C (in more tropical climates).
Global warming is push the thermostat everywherebut the risk of falling into lethal heat is significantly higher in regions already close to the 29°C red line.
Sustained high temperatures at or above this threshold, studies have shown, are strongly linked to higher mortalityreduced labor productivity and agricultural yields, as well as more conflict and infectious diseases.
Just 40 years ago, only 12 million people worldwide were exposed to such extremes.
This number has now quintupled and climb ever steeper in the coming decades, according to the study.
The risk is heightened by regions straddling the equatorwhere human populations are growing fastest: tropical climates can become deadly even at lower temperatures when high humidity prevents the body from cooling itself through sweating.
Extremely humid heat events have doubled since 1979.
The people most exposed to extreme heat mostly live in the poorest countries with the smallest carbon footprints per capita, according to the authors.
According to the World BankIndia emits on average about two tons of CO2 per person each year and Nigerians about half a ton per year, compared to less than seven tons per person in the European Union and 15 in the United States.
Government and corporate carbon-cutting pledges that have yet to materialize would stop global temperature rises to – or even below – 2°C, allowing hundreds of millions to avoid catastrophic heat.
But even worse scenarios than the 2.7C world that would result from current policies also cannot be ruled out, the authors warn.
If past and ongoing emissions trigger the release of natural stores of carbon, such as in permafrost, or warm the atmosphere more than expected, temperatures could soar nearly four degrees above mid-19th century levels, say they stated.