Parts of the Middle East will get too hot for humans if we do nothing to stop climate change, according to a new study in Nature Climate Change. The study shows that cities such as Dubai, Doha and Abu Dhabi will experience temperatures beyond the limit of human survival by 2100.

While they may seem extreme the findings neatly illustrate several principles about people and temperature that are relevant to all of us.

When it comes to extreme heat, the air temperature measured by your thermometer isn’t necessarily what’s going to kill you. For human health, a measurement called “wet bulb temperature” is more important. Wet bulb temperature is a measure of temperature and how much moisture is in the air - how “muggy” it feels. This affects how easy it is to lose heat through sweating, which is how we maintain our body temperatures. The wetter the air, the hotter it feels.

The Bureau of Meteorology has a neat chart that shows air temperatures of 30C can feel like 35C at 90% humidity. The Bureau also measures “apparent temperature”, which accounts for the cooling effect of wind. You can find observations for Australian locations here. Wet bulb temperatures should be a serious consideration for people working or playing outside. Sports Medicine Australia recommends cancelling or postponing events when wet bulb temperatures hit 30C.

Researchers now think that people can’t survive wet bulb temperatures 35C and higher for more than six hours. Even healthy people develop hyperthermia (severe heat stress) at these temperatures. If you can’t lose heat and maintain your body temperature, you die.

Nowhere on Earth currently experiences these sorts of temperatures, with the possible exception of, the study notes, “the desert of Northern Afar on the African side of the Red Sea, a region with no permanent human settlements owing to its extreme climate.”

But what if the world warms up about 4C? That’s what the authors of the new study wanted to know. They found out under about 4C of global warming (or unmitigated climate change) that some cities on the Arabian Gulf would experience wet bulb temperatures above 35C occasionally.

The air temperatures are similarly hellish. Kuwait City by the end of the century will experience air temperatures above 60C (although it doesn't get the same extremes of humidity). And you thought 50C was exciting.

What can we take from this?

First, these cities are quite unusual. They are subject to a unique set of circumstances: they’re low-lying, close to water, and the skies are usually cloud free.

Second, the Middle East already struggles with extreme heat. In July this year southern Iraq saw air temperatures above 50C, compounded by high humidity and power blackouts. Quoted in The Guardian, one Middle East resident described summers as they are now:

[Summer] means an intricate hop from air-conditioned site to air-conditioned site – your apartment to your car to the supermarket or the shopping mall or a friend’s similarly temperature-controlled abode.

Finally, temperatures don’t need to get this extreme to kill people. Vulnerable people - older, younger, sick, poor - already die in heatwaves worldwide, even in the UK. We’ve talked about why heatwaves kill people everywhere here. And more will do so thanks to climate change.

Picture from Panoramas/Flickr licensed under CC BY-ND-2.0