New climate models show that parts of South Asia will become uninhabitable by 2100 if greenhouse gas emissions are not dramatically reduced.

Under a high emissions scenario, where little action is taken to stop climate change, “the heat wave intensity will reach magnitudes that have not been observed before,” Elfatih Eltahir told VOA. Eltahir is a hydro-climatologist at MIT who co-wrote the report published Wednesday in the open-access journal Science Advances.

Ironically, the water that attracted humans to these regions will be what makes the environment intolerable. These won’t be the hottest places in the world, but the heat, humidity, high population density and poverty combined will make them some of the places with the highest risk for deadly heatwaves.

The researchers wanted their analysis to take both heat and humidity into consideration, so that it would be more relevant to human health. They modeled the so-called “wet bulb temperature,” which takes the actual temperature and subtracts the cooling one could hope to achieve though evaporation.

If the wet bulb temperature rises about 35°C (95°F), just below normal human body temperature, a person has no hope of dissipating heat. Under these conditions, even the healthiest individual in the shade, with water, will die after a few hours.

According to the heat index, a heat-humidity metric often used in weather reports, which adds humidity on top of temperature, a wet bulb temperature of 35°C would “feel like” 72°C (161°F).

The models showed that under the high emissions scenario, these temperatures would likely be met sometime during the last three decades of the century in the Ganges River valley, northeastern India, Bangladesh, the eastern coast of India, the Chota Nagpur Plateau, northern Sri Lanka, and the Indus valley of Pakistan.

That doesn’t mean the heat would regularly surpass these temperatures. “If the wet bulb temperature goes above 35 (Celsius), then everybody that’s outside basically dies so it’s a one-off sort of event that’s pretty terrible,” Alexis Berg, a hydro-climatologist at Princeton University, who was not associated with the study, told VOA.

The report did say that under the high emissions scenario, called RCP 8.5, approximately 30 percent of the world’s population would be regularly exposed to extremely dangerous wet bulb temperatures of 31°C (88°F). Under a lower emissions scenario, only 2 percent of the globe would be regularly exposed to those highs.

“RCP 8.5 is a death sentence for a large fraction of the world. It should be avoided at all costs,” said Matthew Huber, a climate scientist at Purdue University. “It does not require impossible effort to avoid RCP 8.5. The choice is very much ours to make.”

He noted that the study, which he was not associated with, is a much more thorough analysis than previous work. He told VOA via email, “This study explores multiple global climate models, multiple climate change trajectories, and also contains a much finer resolved depiction of the underlying physics.”

Everyone with whom VOA spoke emphasized that this future is very avoidable, but Berg also cautions, it could get worse. “Things don’t stop magically in 2100,” he said. “The world keeps warming.”

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