TOKYO — Japanese summers are known for their oppressive and sometimes deadly mix of heat and humidity. In late July and early August the past two years, more than 1,000 people, including more than 150 in Tokyo, died of heat-related causes. Tens of thousands were hospitalized.

That kind of heat led Olympic organizers in 1964 to move the Summer Olympics to October. Those Games began on Oct. 10 55 years ago in Tokyo.

Next year, when the Summer Olympics return to Japan’s capital, they will open on July 24 and run until Aug. 9. It will not take an unusual heat wave to turn them into the hottest Olympics in history, endangering athletes, spectators, workers and volunteers. Yet in awarding the 2020 Summer Games to Tokyo in 2013, the International Olympic Committee barely considered the weather.

So why was it so important to stage them in the thick of summer?

“It’s essentially driven by American television,” said Dick Pound, a longtime member of the Olympic committee and former chairman of its television negotiations committee.