Carbon dioxide emissions continue to increase and the earth is heading for 2.7 degrees of warming by the end of the century. If that happens, about two billion people will end up outside a temperature zone where humans have lived throughout history. The grim conclusion is drawn by British and Chinese scientists.

"I was obviously both shocked and amazed by our results," says Tim Lenton, a professor at the University of Exeter who led the study.

Living in ideal temperature

Just as for animals and plants, according to the researchers, there is a natural niche where people thrive and communities flourish. Most people live where the average temperature is partly around 13 degrees and partly around 27 degrees. But very few have lived in areas where the average temperature has been above 29 degrees. If it gets warmer, it becomes difficult to grow and work, and people live shorter.

"When I was born, there were almost no places on earth with a higher temperature," Tim Lenton told SVT.

Escaping the heat

Tim Lenton believes that some may adapt, but many may be forced to move, both within their own country but also towards colder areas closer to the poles.

"I am sure it will also mean international migration on a large scale.

Reduced emissions relieve

Every tenth of a degree of increase puts another 140 million outside the "comfort zone". If the countries of the world meet the climate goals from Paris and warming stops at 1.5 degrees instead of 2.7, only a fifth as many will be affected.

"It's shocking and I empathize with all the people who will be exposed to a climate no one has experienced. It is a huge humanitarian issue where poor people in the tropics are most vulnerable.