Temperature
Temperature can be a very dangerous hazard in some biomes and can become lethal in severe cases if not properly regulated. Temperature is calculated based on the biome the player is in, the time of day, direct sunlight, weather, depth/height, items/blocks in the player's hotbar and the surrounding blocks & entities in a 5 block radius of the player. This makes predicting a particular location's temperature fairly difficult but not impossible with experience.
- 43C - Heatstroke III: Brain damage, death imminent!
- 41C - Heatstroke II: Severe fatigue, sanity drops
- 39C - Heatstroke I: Minor fatigue
- 38C - Sweating starts, hydration drops faster
- 37C - Safe
- 35C - Hypothermia I: Slight reduction in speed
- 32C - Hypothermia II: Severe weakness, sanity drops
- 30C - Hypothermia III: Organ failure, death imminent!
Snow biomes or biomes with temperatures below freezing are not somewhere you'd want to stay for long as not only does hypothermia set in quickly but frostbite can result from prolonged exposure to freezing temperatures. Frostbite I causes one's hands to occasionally drop items they are holding and Frostbite II the player's legs are unable to walk/jump making you a sitting duck till you die or are rescued by another player. To stay warm in snow biomes it is best to wear full leather armor, carry buckets of lava in your hot bar and have torches or a flint and steel on hand. Try to stay out of the snow and stay out of icy water at all costs, this will reduce your temperature extremely fast. Although not recommended, if you insist on living in a snow biome it would be wise to invest in a nether rack fireplace or under-floor lava heating in severe cases.
These are not as unforgiving as snow biomes but still pose health risks to the unprepared traveler. This also applies to underground mining near bedrock as geothermal heating coupled with the lava deposits there make for a very hot environment to work in. As long as you have a constant supply of water and aren't wearing iron/gold armor in daylight you should be relatively fine. Thermoregulation of the player's body can normally keep your body temperature at or below 38C as long as you keep your hydration above 75% which is why camel packs come in very handy (more about these in Hydration). Cold water can also be used as an instant reduction in body temperature so it's not a bad idea to carry a few spare bottles.
The temperature meter is not difficult to read and once you know how it works it should be as easy as simply glancing at it. The surrounding air temperature is represented by the 2 black dots (or the height of the thermometer symbol) while the player's body temperature is shown as the white dot and the text value. The white dot will slowly move toward the two black dots, the speed at which depends on the conditions around the player and what they are holding/wearing.
- A Fire Resistance Potion will negate any temperatures above 37C for the duration of the effect making it an almost necessary item for nether travel.
- Fire protection can lower the influence of based on the amount of pieces of armor have the enchantment and the level of effect they have. A full set of max Fire Protection will have an almost similar effect as a Potion of Fire Resistance.
- Due to the high temperatures in the nether it is a good idea to bring a camel pack, plenty of cold water, and possibly some form of fire protection for long trips.
- In cold environments, it's a good idea to carry a bucket of lava in your hotbar.
- Water is usually 10C colder than the biome around it.
- Dry biomes like deserts can get very cold, almost freezing, at night.
- The temperature system was calibrated on plains biomes making them have the perfect temperature to live in.