Unless carbon emissions are curtailed, climate change may expose 1.5 billion people in South Asia to potentially lethal heat and humidity in the near future, according to National Geographic.

South Asia, where one-fifth of the world's people live, could face summer heat waves that are impossible to survive without protection, thanks to global warming, new research suggests. Hardest hit regions are in northern India, Bangladesh, and southern Pakistan, home to 1.5 billion people. These are also among the poorest regions in South Asia. Many are dependent on subsistence farming that requires long hours of hard outdoor labor.

"That makes them very vulnerable to these climatic changes,” said MIT professor of environmental engineering Elfatih Eltahir, one of the co-authors.

The study shows that on the current business-as-usual trajectory of carbon emissions these deadly heat waves could hit the region within a few decades with potentially devastating impacts on the fertile Indus and Ganges River Basins that produce much of the region's food supply.

However, cuts in carbon emissions as pledged under the 2015 Paris Climate Agreement dramatically reduces the risk to the region.

“Emission cuts will make a big difference in the lives of the most vulnerable people in the region. This is not an abstract concept,” said Eltahir.

The study, published Wednesday in Science Advances, used state-of-the-art climate models to project potential future heat and humidity in South Asia, already one of the warmest regions of the world. Hot weather's most deadly effects result from a combination of high temperature and high humidity, called a wet-bulb temperature. A temperature of 94 degrees Fahrenheit (34.4 degrees Celsius) and 80% humidity produces a wet-bulb or “feels like” temperature of 129 degrees Fahrenheit (31 degrees Celsius) on the NOAA National Weather Service Heat Index. This is considered extremely dangerous without some way to cool down.