The human body has adapted to survive in extremely hot and harsh environments as a result of its ability to sweat more than that of any other species. It can also adapt to changes in this heat, as long as it remains dry.

But research published in the peer-reviewed journal Nature Climate Change this week looked at what happens when extreme temperature is combined with humidity.

“Future temperature in southwest Asia projected to exceed a threshold for human adaptability” looked at the changes climate change will bring to the region’s average wet bulb temperature. This is the combined measure of temperature and humidity – often casually referred to as mugginess – that is measured by wrapping a bulb thermometer in a moistened cloth.

The researchers from the Massachusetts Institute of Technology and Loyola Marymount University said that when temperatures stay below a wet bulb measure of 35°C, a fit human body can survive the mix of humidity and temperature. But above that even the fittest people struggle to survive.

By this system of measurement, the team equated a 35°C wet bulb reading to the effect a dry temperature of more than 73°C would have on the human body. At that temperature the human body cannot get rid of excess heat by sweating and starts to accumulate heat.

“Beyond this, any exposure for more than six hours would probably be intolerable for even the fittest humans, resulting in hyperthermia.”

This finding was coupled with long-term climate modelling to find which parts of southwest Asia would be worst affected. The area has a perfect mix of extremely high temperatures and low-lying areas, which allows for heat and humidity. The worst affected countries are the Gulf states and parts of Iran, which produce the majority of the world’s fossil fuel oil – a key driver of global warming.

If business as usual continues and serious steps are not taken to curb carbon emissions, the researchers found that by 2070 the usual maximum temperature in Gulf cities would be 45°C. This would regularly drive the wet bulb temperature above 35°C, the researchers said.

Slightly less affected areas include the areas of Saudi Arabia where the Hajj happens – Mecca and Jeddah. Here the wet bulb temperature would rise to 33°C, which would nevertheless make the Hajj dangerous for people with health conditions and those not at the peak of their physical ability.

“One of the rituals of Hajj – the day of Arafah – involves worshipping at the site outside Mecca from sunrise to sunset. In these kinds of conditions, it would be very hard to have outside rituals.”

Without mitigation to lower carbon emission globally, the scientists said large parts of the Gulf would resemble the desert of northern Afar. Sitting across the Red Sea in Ethiopia, the area has the highest average temperature ever recorded and summer temperatures are often higher than 50°C.

The worst affected groups will be those who cannot handle the heat and humidity. The researchers said that in Yemen, where the wet bulb temperature would regularly reach 33°C, “climate change would possibly lead to premature death of the weakest – namely children and the elderly”.

A global climate change meeting at the end of November in Paris – the 21st session of the Conference of the Parties to the United Nations Framework Convention on Climate Change, known as COP 21 – will attempt to stop this from happening. World governments will discuss a text that aims to ensure carbon emissions are lowered globally.