A research paper released on Monday has raised concerns by unveiling that certain parts of the Persian Gulf would witness extremely hot summers owing to human-caused global warming by the end of the century.

The heat would be to such a level that it would become quite difficult for human survival. As per the report's author, coastal cities from Dubai to Iran's Bandar Abbas could face such summers that would be beyond the human habitability limit. In fact, humidity level would be to such an extent that even the fittest people would not be able to stand for many hours outdoors.

The researchers have even named the Saudi holy city of Mecca to face such extreme summers. Christoph Schaer, a physicist and climate modeler at the Institute for Atmospheric and Climate Science in Zurich, Switzerland, said that effects of global warming on humans would be more severe than previously thought and can take place in this century only.

In the research, scientists have used high-resolution climate models of the Persian Gulf so they could accomplish their goal of knowing what could be the different situations for climate change in the coming decades.

The study, published today in the journal Nature Climate Change, was carried out by Elfatih Eltahir, a professor of civil and environmental engineering at MIT, and Jeremy Pal PhD ’01 at Loyola Marymount University. They conclude that conditions in the Persian Gulf region, including its shallow water and intense sun, make it “a specific regional hotspot where climate change, in absence of significant mitigation, is likely to severely impact human habitability in the future.”

That tipping point involves a measurement called the “wet-bulb temperature” that combines temperature and humidity, reflecting conditions the human body could maintain without artificial cooling. That threshold for survival for more than six unprotected hours is 35 degrees Celsius, or about 95 degrees Fahrenheit, according to recently published research.

It would still be rare, and cities such as Abu Dhabi, Dubai and Doha wouldn't quite be uninhabitable, thanks to air conditioning. But for people living and working outside or those with no air conditioning, it would be intolerable, said Eltahir and Pal. While Mecca won't be quite as hot, the heat will likely still cause many deaths during the annual hajj pilgrimage, Eltahir said.

While the other side of the Arabian Peninsula, adjacent to the Red Sea, would see less extreme heat, the projections show that dangerous extremes are also likely there, reaching wet-bulb temperatures of 32 to 34 C.

Christoph Schaer, a professor of atmospheric and climate science at ETH Zurich who was not involved in this study, provided an independent commentary in the journal, writing that while deadly heat waves have occurred recently in Chicago, Russia, and Europe, in these cases infants and the elderly were most affected.

While many in the Persian Gulf’s wealthier states might be able to adapt to new climate extremes, poorer areas, such as Yemen, might be less able to cope with such extremes, the authors say.

MIT researcher Elfatih Eltahir said that people living in low-lying areas from Iran's southern coast to the great metropolises of Dubai, Abu Dhabi, Doha and Dhahran, Saudia Arabia will be the ones who will face the maximum brunt.

The researchers said, "Our results expose a regional hotspot where climate change, in the absence of significant mitigation, is likely to severely impact human habitability in the future".