“Heatstroke will be another major problem, and it’s linked to the humidity, of all things. Air can contain only a certain amount of water vapor, and at some point it hits a ceiling, becoming so saturated that it can’t absorb any more moisture. Why does that matter? Because the human body’s ability to cool off depends on the air’s ability to absorb sweat as it evaporates. If the air can’t absorb your sweat, then it can’t cool you off, no matter how much you perspire. There’s simply nowhere for your perspiration to go.”