Have you ever stepped outside on a hot, humid day and — instantly starting to sweat — told yourself that the temperature must be higher than what the thermometer says? That’s because at higher levels of humidity, sweat evaporates more slowly, making it harder for the human body to cool itself down. The air temperature might only be 32° Celsius (about 90° Fahrenheit), but at a high level of humidity it can feel much hotter than that and the risk of deadly heatstroke rises dramatically. (Source: Mongabay)