You’ve all heard the term “heat index” to describe the added stress due to high humidities on days that are already hot. But what does this term really mean? Our friends from the NC State Climate Office explain it here in this blog posting. Similar types of indices are used to estimate stress on cattle and other livestock. Heat and humidity are more dangerous as the animals get larger, since large animals have a smaller ratio of surface area and skin that can help the animal cool off compared to their volume or weight.