This year the temps in the Tokyo area set a new record of 105 to 106 degrees (F), with humidity of close to 50%, during exactly the same period that the Olympics are to be held (July 14 to Aug. 9). As the Japanese media pointed out, it was hotter in Tokyo than in Saudi Arabia during this period. These are brutal conditions for someone simply walking down the street, let alone competing in the pinnacle of sport. I know. I live just outside Tokyo.
By allowing the Olympics to be held during the hottest part of the Japanese summer, the IOC has abrogated its responsibility to ensure the safety of the athletes and fans. The 1964 Olympics were held in October for this very reason, and even then the heat and humidity were oppressive (just watch the 1964 Olympic marathon on Youtube).
The rumor mill in Japan says that the 2020 games are being held during the hottest days of summer because the U.S. TV network that has purchased the exclusive rights to broadcast the Games doesn't want them to conflict with the American football season. If that's true, the IOC needs to be reformed.