By the end of the century, major cities along the Persian Gulf could be too hot for human survival.

On Monday a scientific study published in the journal Nature Climate Change warned that climate change could make the summer days in the Persian Gulf area too hot for “human habitability.” It would be so hot that even the healthiest of people would only be able to be outdoors for just a few hours. Cities such as Doha, Abu Dhabi, Dubai, and Mecca are at risk if global warming continues at its current rate, according to the Washington Post.

“The threats to human health may be much more severe than previously thought, and may occur in the current century,” Christoph Schaer, a physicist and climate modeler at the Institute for Atmospheric and Climate Science in Zurich, Switzerland, said in a commentary on the study’s conclusions.

The Washington Post reports that the authors of the study are a pair of scientists from Massachusetts Institute of Technology and Loyola Marymount University. Using high-resolution climate models of the Persian Gulf, they were able to view several different scenarios that could affect the area due to climate change over the coming decades. They focused on “wet-bulb temperature,” a key heat measurement that includes evaporation rates and humidity, averaged over several hours to determine when the Persian Gulf would be uninhabitable to humans. They determined that the high temperatures would be so high that the human body would not be able to sweat to ward off the heat.

The scientists predicted that low-lying regions of the Persian Gulf could see temperatures as high as 113 degrees Fahrenheit while other cities including Kuwait City and Al Ain would see temperatures above 140 degrees Fahrenheit. In the summer months, they predict the temperatures rising to as high as 165-170 degrees Fahrenheit, according to the Washington Post and Fox News.

And while some could stave off the heat with air conditioning, the impoverished areas in the Persian Gulf would see disastrous results.

“People who have resources could use air conditioning and avoid the outdoors during heat waves but, in some corners of that region, there are communities and people who don’t have resources to do that,” Elfatih Eltahir, a co-author of the study, told Fox News. “We pointed to some corners of Yemen along the Red Sea that are not as well off as other parts of the Gulf Region.”