This page talks about the new effect, as of 2.1, of body temperature and its implications.
Description (from Recipaedia)
When you are out in the cold without proper clothes, your body temperature will drop. You view will start to freeze over and you will start losing health. Find a warmer place or get near fire to warm and dry yourself.
Too much warmth will do you no good either, standing too close to a large fire will cause you to overheat.
Sheltered areas are warmer than outside. Plugging all the holes and locking doors will make a shelter warmer still. Even a small hole open to the elements will admit draughts and make a large difference to temperature. Make a fire inside your shelter to make it homely warm and allow you to take your clothes off.
Being wet dramatically increases your susceptability to cold, find a warm place to dry yourself faster.
The best way to deal with cold is to wear multiple layers of thick, dry clothes. You need to cover your entire body, leaving feet or head unclothed will defeat most of the warming effect other clothes have. Clothes made of animal fur are best for keeping cold out.
Warm and Dry
This is a short video about getting cold.
Getting cold can be a major problem in the game. If you get wet, your body temperature will drop fast and you have to dry off before it will begin to warm again.
The best way to get warm and dry is to run to a warmer biome, if you are outside and there is one close enough. The biomes are typically not huge in the standard game so this is a good option.
The best way to stay warm is to be dressed properly. You can dress in layers for best effect. See Clothing for more information. This will not help you if you get wet, however. Any insulation provided by clothing is removed while you are wet. Changing your clothes won't make a difference.
You may be able to dry off and warm up by building a quick shelter and sealing yourself off from the open air. This will not work in the coldest biomes, though.
If you are wet and stuck in the cold or plan to stay in it then you can stay warm by fire.
Warming By Fire
You can set a coal block down and set it on fire with a match. This will give some amount of heat however, in the open outdoors it will only warm about 2 blocks away from it. A bigger fire with 3 blocks will warm an area about 4-5 blocks away. This will let you get warm without being caught on fire.
Realize that it takes a minute to warm the area and more time to warm your body. If you start your fire when you are already freezing, you may not be able to warm up fast enough. Be prepared to start your fire as soon as you start getting too cold.
For the most heat, you need every side and the top of the block burning. Leave open all the blocks around the coal block and the fire block above it - a 3 x 3 x 2 high space with the coal block in the center.
Campfires are very good at heating you up quickly. They are very effective outside, but only last a short time. They are good for emergency heat.
Putting a fire in a sealed area is much more effective. If you dig an emergency pit-shelter, you can dig it out a bit bigger and start a coal block fire. This will dry and warm you quickly.
To best heat any indoor area every opening must be closed off to the outside air. The fire will heat up to 30 blocks away and keep you comfortable to about 20 blocks. 'Comfortable' means you won't get warning messages about the chill. If you are using a cave that's less than 20 blocks deep, you can just place the block at the back of the cave and it will stay cozy inside.
You can design houses to use the full effect of fires even without keeping a fire place in every room. See Heating Your House for more details.
Usually you will not need to worry about staying cool. You will most likely only get over-heated if you stay too close to a fire or stay around magma. When you get overheated, your vision will start to turn black and your character will groan and complain. Once this starts, you need to get away from the heat as fast as possible. This fading will repeat several times until you get away from the heat, or the character passes out and dies.
The only known way to combat heat is to move to a cooler area. Jumping in water will not cool you off any quicker. Get at least 20 blocks away from magma to cool off or seal yourself away from it. If you seal away the heat, you can wait to cool down and then try to break out again and make a run for safety.
Being cold for a long period can cause the flu. See Flu for more details.
- The 'wetness' is related to your body, not your clothes. If you are wet, changing your clothes to 'dry' ones will NOT reduce your wetness or warm you faster.
- Although getting wet will make you get cold faster, it will NOT cool you any faster if you are overheated. Being wet will NOT prevent you from getting overheated.