Temperature was introduced in the 0.49 update, and added a system for tracking heat and cold levels of the player. Too high or too low temperature levels may lead to hyperthermia or hypothermia respectively.
Body temperature is measured in heat comfort levels. Too high or too low heat comfort level causes the player to experience negative effects towards a players well being. Several factors decide if the heat comfort rise or drop. Most prominently is the weather on the map. Sun and rain greatly affect the overall temperature on the server, and should be countered with proper clothing or other means of temperature control. Also where on the map a player is located can change temperature, but not is not immediately noticeable. Please note that a players wetness level, and if the clothes are damp, wet or soaked also significantly affects the rise or drop-rate of temperature.
If the heat comfort level reaches beyond a certain point, the player begin to drain energy from the energy reserve the player has. To measure temperature one can use a thermometer, or by looking at the white messages.