Olympics: These cities will be too hot to host by 2050 [Video]

The Paris Olympics opened with rain on its parade, then blistering heat and, finally, a week of pleasant sunshine. As it comes to a close on Sunday, temperatures are expected to again soar up to 95 degrees Fahrenheit, or 35 degrees Celsius.

The only certainty about Summer Olympics weather is that there’s really no certainty at all.

Extreme heat is a growing threat for elite athletes, with cases of heat exhaustion and heatstroke becoming more common as fossil fuel pollution pushes temperatures and humidity levels up. Spectators, especially those those who fly in from cooler climates, are vulnerable to extreme heat, as well.

Most of the world’s cities will be unable to host the Games during summer in the coming decades as they blow past the threshold of safe humid heat, according to a CNN analysis of data from CarbonPlan, a climate science and analytics-focused nonprofit group.

The big picture

Heat stress can …