Temperatures in Iranian city of Ahvaz hit 129 degrees (54C). The city has a population of more than 1 million. The humidity was high too. The heat index — a measure of how hot it feels factoring in the humidity — exceeded 140F (60C). This combination of heat and humidity was so extreme that it was beyond levels the heat index was designed to compute. Scientists estimate that by 2100 much of the Middle East will be too hot for human survival.