If global populations continue with a business-as-usual attitude toward greenhouse gas emissions and global warming, a chunk of the population could be in serious peril.

A new study finds that going outdoors could become deadly across areas of India, Pakistan and Bangladesh by the end of the century as climate change causes heat and humidity to spike, making widespread areas uninhabitable. The threat targets up to a third of the people living throughout the Indo-Gangetic Plain, which is home to some 1.5 billion people, according to findings published Wednesday in Science Advances, a peer-reviewed journal.

“The fertile valleys of the Indus and the Ganges, where human population is currently in the hundreds of millions, will likely experience some of the most severe projected hazard from heat waves,” according to the research team.

Researchers based their findings on computer simulations that used global models to project a so-called “wet bulb temperature,” which considers the actual temperature, as well as the humidity and the human body’s ability to cool down through evaporation.

Humidity levels combined with heat play a major role in heat-related heath risks. In cases of high humidity, human sweat doesn’t evaporate, making it difficult for people to regulate and release heat. At a wet bulb temperature above 35 degrees Celsius, or 95 degrees Farehenheit, the human body can’t cool itself enough to survive more than a few hours without protection.

The findings are in keeping with widespread research on climate change that paints the issue as a major threat to mankind. One study found that nearly a third of the world’s population is currently exposed to lethal global warming, while another suggests that thousands will die from climate change-caused air pollution if we can’t curb it.

The threat is already proving deadly, albeit at a lesser rate.

One of the deadliest heatwaves in history swept across South Asia during the summer of 2015, killing an estimated 3,500 people in Pakistan and India.

People in these high-poverty areas are particularly vulnerable because they rely on hours of hard labor in the open sun to fulfill an economic dependence on subsistence farming, according to MIT professor Elfatih Eltahir, who co-authored the report.

“With the disruption to the agricultural production, it doesn’t need to be the heat wave itself that kills people. Production will go down, so potentially everyone will suffer,” Eltahir said.

Luckily, there is still time to change fate.

Scientists say serious mitigation efforts to reduce global carbon emissions have the potential to lessen the growing threat.